CA1147456A - Automatically compensated movable head servo circuit and method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In an apparatus for automatically maintaining a transducing head assembly on the proper track, which is particularly adapted for a helical scan recording and/or reproducing apparatus capable of providing special motion effects, an automatically compensated movable head servo is disclosed. The apparatus is of the type which utilizes transverse positioning of the transducing head assembly to accurately follow a track during reproducing and, at the completion of the track, to properly position the head in position to either play the next adjacent successive track, replay the same track or play another track so that the appropriate special motion effect is achieved.
Proper tracking is maintained by applying a small oscilla-tory motion to the head to cause it to vibrate laterally of the track, examining the resulting modulation of the reproduced signal's envelope to generate a tracking error correction signal and applying the error correction signal to the head assembly. The reference signal employed in the generation of the tracking error correction signal is automatically phase synchronized in response to the head vibrations to correct errors introduced to the tracking error signal as a result of phase changes intro-duced to the modulation of the reproduced signal's enve-lope by effects other than mistracking by the head.

Description

The present invention generally relates to magnetic recording and reproducing appara-tus, and more specifically to transducing head servo apparat~ls for accurately positioning a head relative a track it scans.
The invention is related to the disclosures of the following applications all assigned to the same assignee as the present invention:
Hathaway et al., Serial No. 274,370, filed March 18, 1977, entitled ''Method and Apparatus for Producing Special Motion Effects in Video Recording and Reproducing Apparatus''.
Ravizza, Serial No. 274,434, filed March 21, 1977, entitled ''Automatic Scan Tracking''.
Ravizza, Serial No. 274,424, filed March 21, 1977, entitled ''Drive Circuitry for Controlling Movable Video Head".
Ravizza, Serial No. 274,421, filed March 21, 1977, entitled ''System for Damping Vibrations in a Deflectable Transducer".
Brown, Serial No. 274,368, filed March 21, 1977, entitled 'Transducer Assembly Vibration Sensor'.

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Mauch, Serial No. 317,223, filed December 1, 1978, entitled -Method and Apparatus for Controlling the Movement of a Recording Medium--.
Ravizza, Serial No. 320,509, filed January 30, 1979, entitled Continuous Slow Motion Automatic Tracking System .
Ravizza, Serial No. 320,326, filed January 6, 1979, entitled -Track Selection Method and Apparatus--.
Ravizza, Serial No. 320,309, filed January 26, 1979, entitled Movable Head Automatic Position Acquisition Circuit .
Ravizza, Serial No. 320,230, filed January 24, 1979, entitled An Automatically Calibrated RF Envelope Detector Circuit .
In the first five above-identified related applications, and, particularly, the Hathaway et al., application, Serial No. 274,370, recording and reproducing apparatus as well as methods are disclosed which represent significant improvements in achieving , ~:

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superior recording and reproducing of video signals whereby special motion effects are obtained. While the apparatus disclosed therein is applicable to various alternative types of equipment and is not limited to recording and reproducing video signals, the apparatus is advantageously adapted for recording and reprodueing video signals on ma~netie tape.
This is because the apparatus can reproduee signals in a manner whereby normal speed reproducing, as well . as special motion effects, such as slow and stop motion and faster than normal motion ean be produced without experiencing a noise band or pieture breakup in mb/4~ ~ 5 ~

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thc video display. There are many di~ferent formats th~t have been developed in magne~ic tape recording and, as described in the above-identi[ied ~lathaway et al appli-cation, the recording format that results Erom transporting tape in a heli~ around a cylindrically shaped drum guide as it is scanned by a transducing head has exhibited many distinct advantaqes in terms of relative simplicity of the tape transport drive and control mechanism, the necessary electronics involved, the number of transducing head~ in the apparatus, and the efficient use of magnetic tape in terms of the quantity of tape that is required to record a given amount of information. By helically wrapping the tape around a drum guide, a single transducing head mounted on a rotating drum guide can be utilized for recording and reproducing infocmation. I~hen a single head is used in a helical scan tape recording apparatus, there are two widely used alternative configurations of guiding (i.e., wrapping) the tape around the cyIindrical arum guide for scanning by the head. They are generally re~
ferred to as the alpha wrap and the omega wrap type of :
. helical scan apparatus. Both wrap configurations involve guiding the tape generally In a helix arouad the drum ~ . :

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guide with the tape exiting the drum sur~ace at a different axially displaced position relative to its entry position. In other words, if the drum is vertically oriented, the tape leaves the drum surface either higher or lower than when it first contacts the surface. The video or other data information signals are recorded along discrete parallel tracks that are positioned at a small angle relative to the ~ength of the tape so that a track length greatly exceeds the width of the tape.
The angular orientation of the recorded tracks are a function of both the speed of the tape being transported around the drum guide as well as the speed of rotation of the scanning head. The resultant angle therefore varies depending upon the relative speeds of the rotating scanning head and the tape being transported.
It should be appreciated that the information signals are recorded on a tape at a predetermined angle ~-that results from precise rotational scanning head and tape transport speeds, and that the subsequent reproducing of the information signal should be performed at these same speeds or the transducing head will not follow the track with precision. If the tape speed is changed during reproducing, i.e., it is reduced or even stopped, the , ~7~

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~7~6 transducing heaci will no longer precisely follow the recorded track and may cross onto an adjacent track.
T~e failure to precisely follow the track in registry during playback results in cross tracking noise and other undesirable signal effects that appear in the represented information, such as the video picture, in the event ~ideo information is being reproduced. While various prior art systems have been proposed to reduce the undesirable effects due to the lack of precise head-to-track registry such systems have not been entirely successful even at speeds that are intended to be identical to those that were used during recording.
Heiical tape recorders that are adapted to create special altered time base reference effects have not been particularly successful to date because of the spurious noise that is generated during playback due to the transducing head crossing from one track to another.
For example, slow motion effects and video recording necessarily require that the data on a track, typically a full video field on each track, be repeated one or more times during playback so that the visual motlon is slowed down. If data is recorded without redundancy, a tcack .; ~
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5iG 7' must he reproducecl one or more times to accomplish this and hence the tape speed must bc slowed. Tile resultant path tllat the transducing head follo~s a:Long the tape during Sucll reprod~lction processes will therefore be substantia~ly differellt than tlle recorded track that was made during the recor(ling process. A more extreme differ-ence is Eound in stop motion or still frame operation, where the tape transport is stopp-_d and the video head `~
scans the same portion of the tape a number of tilnes.
During stop motion operations, the scanning head can cover a portion of thc tapc corresponding to that occupied by ~;
the two or more adjacent tracks of recorded inEormation. To reduce the disturbing effects of noise bars in displayed video still Erames, it has been the practice to adjust the tape position relative to the location of the scanning head so that the head begins and ends each tape scan in the guardbands adjacer,t to the desired track and scans the desired trac~ during the intermediate interval of each tape scan. ~his placcs the visual disturbance noise ?O bars at the top and bottom o~ the displayed video still iranie, leavillg the center of the displayed video relative- -~
ly free of disturbing effects.
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~7456 While techniques have bcen proposed to reduce or ovcrcome thc noise bar that is generated by crossing trac~s, such techniques llave not becn particularly success-ful until the advcnt o~ the apparatus described in the first five above-identified cross referenced applications, ~ ?~3~o particularly, Hathaway et al., Serial No. ~7~. As is comprehensively set forth thcrein, ~he method and apparatus automatically positions a transducing head to accurately follo~ a desired path along a magnetic tape and to rapidly position the ~ransducing head, if necessary, at the begjnning of the path that is desired to be Eollowed next. The next trac~ that is to be followed, whether during reproducing or recording, is a function of the mode of operation that is selected. From the playback of video signals, the various modes may include a slow and still motion effect mode, a speeded up or fast motion effect mode, and a revers~ motion effect mode. Other modes of operation may include skip field recording and compen-sation playback mode as well as a surveillance mode.
In both of the latter modes, the period of time that can be recorded on a given length of tape is greatly increased by s~ipping one or a number of fields during the recording ; ' 4 ~' ~
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operation, such as recordincJ every other ~ield or one of every s;xty fielcls, for example. The apparatus permits the tracks to bc accurately followed evcn Lhou~h the trans port speed of the tape can vary within wide limits. In the event fast motion effects are to be achieved during playback of video signals, the transport spced of the tape must be increascd and, conversely, for slow motion effects the transport speed must be slowed. For the stop motion effèct, one field is typically reproduced many times over and, .
in such modc, the tape is not moving at all, the relative motion between the tape and the transducing head being supplied by the rotation of a rotating drum guide carrying the head. Changing the tape transport speed changes the angle of the path followed by the head along the tape.
Consequently, if the video transducin~ head carried by the rotating drum guide is maintained in a fixed position relative to the drum, it can not exactly follow a pre-viously recorded trac~ when the transport speed of the tape is altered during reprocduction relative to its speed during recording.
The apparatus disclosed in the first five above-identified cross-referencecl applications employs means that move the transducing head transversely relative to the ;
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~47~6 longitudinal direction of the tracks so that the head follows sclectcd tracks along the magnetic tape and, thereafter, selectively alters or changes the positon of thc head after the head completes the scan of a selected track so as to correctly position the head to commence following another track. In the event the head is to follow the next adjacent downstream track, the head would be in the correct position to begin following it at the completion of the scan of a previc.usly selected track. It should be underslood that one complete revollltion of the transducing head causes the head to scan a track at a predetermined angular orientation relative to the length of the tape and, at the end of the revolution, the movement of the tape causes the head to b~ gradually displaced a predetermined lS distance downstream of the tape in position to begin scann-ing the next adjacent track. In this manner, the head, for example, during recording operations, records information along tracks that are parallel to one another and, assuming the transport speed of the tape and the speed ~f rotation of tlle scanning head are maintained constant, the tracks will have a constant spacing relative to adjacent tracks, i.e., the .

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i6 center to center dist~nce between adjacent tracks will be substantially constant in the absence oE geometric errors.
Geometric errors are introduced by temperature or hum;dity induced dimensional changes of the tape, by faulty tension-- 5 ing mechanism in the tape transport that causes stretching of the tape, or by imperfect control of the relative head to tape speed. During normal speed playback operations, i.e., the tape is being moved and the head is being rotated at the same speeds as they were during the recording operation, the scanning head will follow a track during a single revolution and be in position to begin following the next adjacent downstream track during the next revolution. Furthermore, each track will be followed once and produce unaltered time base effects as would be expected, such as normal speed visual effects of recorded video information. In the event it is desired to produce a still frame or stop motion effect, the transport of the tape is stopped - and one recorded track is typically repeated indefinitely.
In this mode of operation, the transducing head will be continuously deflected to follow the track from beginning to end and, at the end, the head will be reset in the direction opposite the direction it has been deflected to : . ~
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;,' D- 2 6fi position it at the be~inning of the same track. The distance that the head is deflected from its normal path as it scans the track, and subsequently reset, is equal to the center to center spacing between adjacent tracXs. Thus, by continuously deflecting the head to follow a track, resetting the head and deflecting the head again to follow the same track, a single field is repe-titively reproduced, thereby permitting a stop motion or still ~rame visual picture to be displayed. This will be more comprehensively described herein with respect to certain figures of the drawings, and is comprehensively described - in the aEorementioned Hathaway et al. application, Serial ~ 7~3 No. G77,U~5.
The apparatus described in the Hathaway et al application represents a significant improvement over other tape recorders in that it is capable of producing speeial motion eEfects, such as slow motion and still frame motion as well as regular motion, all of which can be carried out without the typically experienced disturbing noise bar occurring in the display of the video picture dur~ng playback. Thus, when the apparatus is operating i~ any of its modes, it will reliably operate and produce noise free reproductions of the signal information record-ed on the tape. However, if for any reason the transduc-ing head assembly is changed, thereby changing the naturalresonant frequency tbereof, it may be necessary to read-just the control circuitry for the head assembly following each such change.
Accordingly, it is an objeet of the present invention to provide an improved recording and/or .. . . . .

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method and apparatus that is capable of operating in various signal reproducing modes, inclucling slow/still motion mode, reverse mode, and regular motion mode and which is uniquely -adapted to automatically correct errors introduced to the head tracking error signal by effects other than actual mistrac~ing by a transducing head. ;~
Yet another object of the present invention is to provide a method and circuitry for automatically compensating for any changes in the natural resonant 10 frequency of the transducing head assembly of the ~
improved recording and/or reproducing apparatus described ~ :
hereinbelow.
Other objects and advantages will become. ~ ~:
apparent upon readlng the Eollowing detailed descrip~ion, ;~

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while referring to the attached drawings, in which:
FIG. 1 is an electrical block diagram illustrat-ing automatic track;ng control circuitry in a recording `and reproducing apparatus, as generally disclosed in the aForementioned Hathaway et al cross referenced application, ,3~0 7 Serial No. ~97~

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FIG. 2 is a block diagram of circuitry embodying the improved recording and/or reproducing apparatus, the portions shown in the dotted line box- being adapted for substitution in the circuitry shown within the dotted line box of FIG. l;
FIG. 3 is a more detailed electrical block, diagram of the circuitry shown in FIG. 2;
FIG. 4 is a perspective view of the helical tapa ,~
guide and scanning head assembly portion of an omega wrap helical scan recording and/or reproducing apparatus which is simplified for the sake of clarity;
FIG. 5 is a side elevation of the drum tape guide and scanning head assembly shown in FIG. 1, with portions removed and partially in cross section;
FIG. 6 is an enlarged segment of magnetic tape : -having tracks A-G recorded thereon;
FIG. 7a is a diagram illustrating the voltage amplitude versus time characteristic of a typical RF
envelope and having time exaggerated drop out areas, which diagram may be produced using the drum and head assembly shown in FIGS. 4 and 5 on the magnetic tape shown in FIG. 6;

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.--FIG. 7b is a diagram illustrating a typical voltage waveform that may be produced to provide the desired head deflection of the reproduce heacl shown in FIGS. 4 and 5 when the apparatus is in the slow/still mode and the transport of the tape is stopped;
FIG. 7c is a diagram of the time versus amplitude of the head deflection waveform for the slow/still motion mode and illustrates the operation of circuitry disclosed in the aforementioned Hathaway et al application, Serial 3~o No. G77,01.;
FIG. 7d is a diagram of time versus amplitude of the head deflection waveform Eor a slow motion operation and illustrates the operation of circuitry incorporated in the improved apparatus, when in the slow/still motion .
mode;
FIG. 7e is a diagram of time versus amplitude of the head deflection waveform for a slow motion operation and illustrates the operation of circuitry embodying the the improved apparatus when in the ~5~ of normal speed mode;
FIG. 7f is a diagram of time versus amplitude of the head deflection waveorm during acquisition oE the ~`
proper track and for a subsequent normal speed operation and lllustrates the operation circuitry of the the improv- .
ed apparatus when in the normal speed mode of operation;
FIG. 7g is a diagram of time versus amplitude of the head deflection waveform for a 2 times normal speed operation and illustrates the operation of circuitry ~ .
embodying the improved apparatus when in the 2 times normal ~ ~.
30 speed mode. ~ ~

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:: , ii6 FIG. 8 is a block diagram of the capstan and control track servo circuitry portion oE the improved apparatus FIG. 9 is a diagram illustrating the tape velocity versus time profile that is produced by the capstan and control track servo circuitry shown in FIG.
8;
FIG. 10 is a unitary diagram illustrating orientation of the sheets containing FIGS. lOa and lOb;
FIGS. lOa and lOb together comprise a detailed electrical schematic diagram,illustrating circuitry that may be 'used to carry out the operation of the block diagram oE FIG. 3 as well as certain portions of the block diagram shown in FIG. l;
- 15 FIGS. lOc and lOd illustrate electrical schematic diagrams of modiEications oE the circuitry shown in FIGS.
lOa and lOb that may be used to control still frfame modes durlng which more than one television field is `:~
reproduced to generate still frame displays; ~ ~.
FIG. 11 is a unitary diagram illustrating .~
orientation of the sheets containing FIGS. lla, llb and ~ :
llc;
FIGS. lla, llb and llc together comprise a detailed schematic diagram oE circuitry that can be used to carry out the operation of the capstan servo circuitry portion of bloc~ diagram shown in FIG. 8;
FIG. 12 is an electrical block diagram illustrating -~
the automatic tracking control circuitry in a recording ;~

and/or reproducing apparatus employing the present invention;
FIG. 13 is a schematic block diagram of the automatically compensated movable head servo; ' --19~
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~7~56 FIGS. 14a-14f are timing diagrams illustrating operation of the movable head servo shown in FIG. 13;
FIG, 15 is a frequency spectrum diagram illustrating selection of the dither frequency so as to 5 avoid spectrum overlap; and FIG. 16 is a timing diagram illustrating operation of the track selection logic.
Before describing the method and apparatus that embodies the present invention, the environment in which -the present invention can be utilized will initially be broadly described so as to provide a better understanding of the present invention. While the aforementioned d ~ 3~O
Hathaway et al application, Serial No. C77,~1r, as well

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as Ravizza application, Serial No. GC9,0~7, comprehensively sets forth the background and the environment to which the present invention can be applied, a brief description of the environment will be set forth herein. Also, whila ;
the present invention is particularly adapted for use with helical scan types of video tape recorders for automatically providing continuous adjustment of the position of the trans-ducing head thereof with respect to only head mistracking errors, it should be understood that the present invention is not limited to helical recorders and may be used with quadrature, segmented helical, arcuate and other types of rotary scan video tape recorders. In addition, the present :

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invention is suited for ~se with various tape recording formats charac~eristic of the various rotary scan tape recorders. Furthermore, the present invention is no~
limited to use in rotary scan tape recorders designed for processing video signals. It is contemplated that the present invention will find utility in any application '' where it is desired to record or reproduce, i.e., transfer information with respect to a tape recording medium without the introduction of disturbing transients into the trans-ferred information while the relative head-to-tape speed undergoes changes. ', Turning now to thc drawings, and particularly ' FIGS. 4 and 5, there is shown a helical video scanning head-and cylindrical tape guide drum assembly indicated ,~
generally at 20, with FIG. 5 showing portions broken away.
The head-drum assembly 20 is shown to comprise a rotatable upper drum portion 22 and a stationary lower drum portion 24, the upper drum portion 22 being fixed to a shaft 26 which is rotatably journaled in a bearing 23 that is mounted on the lower drum 24, the shaft 26 be,ing driven by a motor (not shown) operatively connected thereto in a conventional manner. The head-drum asscmbly 20 has a video transducing head 30 carried by the rotatable drum : , ~ . . :
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portion 22 and is shown to be mounted on an elongated movable support element 32 that is in turn mounted at one end in a cantilever type support 34 that is fixed to the upper drum portion 22. The element 32 is preferably of the type that flexes or bends in a direction transversely of the recorded track with the amount and direction of movement heing a funtion of the electrical signals that are applied to it.
- As is best shown in FIG. 4, the head-drum assembly 20 is part of a helical omega wrap video tape recorder which has the magnetic tape 36 advancing toward the lower drum 24 in the direction o~ the arrow 38 as shown. More specifically, the tape is introduced to the drum surface from the lower right as shown in the drawing and is fed around a guide post 40 which brings the tape into contact with the outer surface of the stationary lower drum portion 24 whereupon the tape travels substantially completely around the cylindrical drum tape guide until it passes around a second guide post 42, which changes the direction of the tape as it exits the head-drum assembly 20.

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~7~S6 As is best shown in FIGS. 4 and 6, the con-figuration of the tape path is such that the tape 36 does not contact the guiding drum surface over a full .
360 degree roLation because of the clearance that is required for entrance and exit of the tape. This gap preferably does not exceed a drum angle of more than about 16 degrees which has the effect of creatint~ a drop out interval of information. In the case of recording video in~ormation, the occurrence~ of the drop out is preferably 10 chosen relat~ve to the video information being recorded 50 :
that the in~onnation that is lost does not occur during the active portion oE the video signal and, in the case of ;~ recording and reproducing video signals, so that the start of the scan of a tracl; can be properly field synchronized to the video si~nal.
The transducint3 head 30 is mounted upon the elongated movab~e, pre~erably lexible, element 32 ~ which may comprise an elongated two layer element - (sometimes refelred to as a bimorph) that exhi~its dimensional changes iri the presence of an electri.c~or magnetic field. The deLlectable, movable element~32 is effec~tive to~move the~ transducing head 30 mounted thereto in a~yerticaI direction as shown in ~IG, S in 23~

5~i accordance with the electrical signals that are applied through conductors ~1~ from the automatic head tracking servo circuitry schematically illustrated by a block 46. The head 30 is mounted to e~tend sli.ghtly beyond the outer suLface of the rotatlng drum portion 22, the head extend-ing through an opening ~ in thc outer surEace thereof.
The movable element 32 is adapted _o sweep or bend and displace the transducing head a].ong a path that is trans-versc to the direction of relative motion of the head 30 with respect to the magnetic tape 36, i.e., transverse tothe dircction of the recorded tracks. -If the transport speed of the.magnetic tape 36is changed during the reproàucing of recorded information, relative Lo the speed at ~hich the information was record~d on the tap~, then the angle of the path scanned - by the head 30 relative to the length of thc tape 36 is changed and error correcting sigllals ~ l be produced for the pu-posc of having the transducing head follow the track of recorded information which is at the different ~
20 anyle. Since the movable element 32 is movable in either -~:
direction, the tape can be transported around the tape -2~

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guide drums 22, 24 at ei ~ ~ 7a ~aster or slower speed relative to the recording speed and the movable element can position the head 30 to follow the recorded track for either condition.
Referring to FIG. 6, there is illustrated a segment of magnetic tape 36 having a number of tracks A-G thereon as may-be recorded by the transducing head 30 as the tape is transported about the guide drums 22, 24 shown in FIG. 40 The segment of tape is shown to have an arrow 38 which illustrates the direction of tape movement around the drum and an arrow 50 which shows the direction of the scanning head movement relative to the tape.
Thus, when the upper portion 22 rotates in the direction of the arrow 50 (FIG. 4), the transducing head 30 moves along the tape in the direction of the arrow shown in FIG. 60 With a constant transport speed of the tape 36 and angular velocity of the rotating drum portion 22, tracks A-G will he substantially straight and parallel to one another at an angle 0 (of about 3, for example) relative to the longitudinal direction of the tape~
with each rightward track shown in the drawing-being successi~ely produced during a recording operation.`-5ince track B, for example7 would be recorded immediately after track A was recorded during constant drum and head rotation and tape transport speeds, it should also be appreciated that if these speeds are maintained -~
during the reproducing or playback operation, the transduing head ms~ ~ b ~ ~
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30 would paly back track B during a successive revolution immediately after having reproduced the in~ormation from track A~
If condi-tions were ideal and no tape transport disturbance was introduced, then the trclnsducing head 30 would simply successively follow the adjacent tracks without adjustment, because no error signals would be produced for transversely moving the transducing head 30 relative to the track. Stated in other words, the transducing head is automatically in position t;o begin reprodueing the subseguent track B after completing the reproducing of the information from traek A. It should a~so be appreciated that even if the tape transport speed is varied during reproducing relative to the tape transport speed during recording and the head is transversely moved to maintain aecurate head tracking during reproduetion of the traek, then at the end of the head ! S seanning - of a traek being reproduced/ the head is nevertheless in a posi~ion to begin reproducing the next adjaeent downstream traek, i.e., track B in the event reproduetion of track A was completed. This oecurs even when the tape is stopped or is traveling slower or faster than the transport reeording speed~

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To achieve special motion and other effectsduring reproduction oE the information signals that are recorded on a tape, it is necessary to vary or adjust the transport speed of the tape past ti1e location of the scanning head, i~ence, around the tape guide drums 22, 2-1 in tile illustrated embodiment. To produce a speeded up or fast motion effect, the transport speed is increased during reproduci1lg re].ative to that which was used during the recording process. Similarly, to produce slow motiorl effects, it is necessary to reduce the speed of the transport tape around the tape guide drums during reproducing rela~ive to that which was used during the recording process. In stop motion modes the tape is stopped during reproducing so that the rotating trans ducing head 30 can repetitively reprod~;ce the signals, typically fron a single recorded track.

The apparatus disclosed irl the aforementioned ~7 ~ 3~
Hathaway et al application, Serial No. ~ ,Ol-, can be placed in diferent modes oE operation wherein either `~ 20 forward or reverse motion effects are achieved and the motion can be speeded up or slowed down by~ simply adjusting the transport speed of the tape in such forward or reverse directions to obtain the desired speed of motion upon reproducing the recorded information. Once a motion direction is chosen, the apparatus e~fectively automatically pOSLtiOnS the transducing head to follow a track from beginning to completion and to thereafter adjust the position of the transducing head (if adjustment is needcd) to thc beginning of the proper track. The apparatus automatically provides for transversely moving or resetting the transducinc~ head 30 at the end of the - 10 head scan of a track to a position corresponding to the start of a track other than the next successive adjacent trac~ under certain predetermjned conditions and not transversely moving or resetting the transducing head under other conditions. The decision ~to transversely adjust the positi~n of the transducing hcad depends upon the mode in which t[lC apparatus is operating and whether the amount of transverse movement i9 within the predetermined limits that can be achieved. If the trans- ;~
ducing head 30 is deflected the maximum amQunt in one 20 direction permitted by the movable element 32, ;~
it cannot be moved further in that direction. The total range of movement shall be within the practical limits ;~ determined by the characteristics of the movable element ~ `
32.

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- Wllen thc apparatus i5 il) the slow motion or still frame mode of oper~tion, the transducing head 30 may be requircd to be reset at the completion of the scan by the head of the track bein~ reproduced depending upon S whether the deflec~ion oE tl~e transducing head reaches the predetermined threshold ~imits set for ~he displacement of the element 32 at thc completion oE a track. ~hen the tape 3G is stopped so as to provide still frame or stop ~otion, it is necessary for the transducing head 30 is typically reset at the completion of the scan by the head of the track being reproduced and is thereby be reset to the beginlling oE that trac~ so that its scan can be repeated by the head as many times as is required for the duration of the display of the scene. Thus, the informa-tion recorded in the track is effectively reproduced overand over since the tape 36 is stationary. Since the transducing head 30 is deflected in the reverse direction relative to the direction the tape is transported during a record operation to follow the track during each repeating reproduction, the total deflection-in the reverse direction being equal to the track center to track center spacing, d, of the recorded tracks, the head 30 ~;~
must be reset a correspon;ling distance in the opposite, or forward direction at the completion oC the scan of the track in ordor to be correctly positioned to rescan the same track. Since the angle of the path followed by the head 30 relative to the tape 36 is different when the tape is stopped from the angle of ~ I

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recorded tracks, the head is also gradually being adjusted ~hrough the course of reproducing the information signal on a tr.ack. Thus, as the scanning head 30 moves along the trac~, the error correcting signa's cause it to be moved transversely to maintain head to track registry.
and the head is reseL at thc end of its scan of the.
track essentially one track transvcrse distance, d, in order to he in position for beginning the rescan of the same track.
10To maintain the transducing head 30 in registrat~.on with the track as it follows a track.during a revolution of the rotating drum 22, a servo circuit is used which produces an crror correcting signal that is preferably a ~.
lo~ frequ~ncy or changing DC level and is produced by ~1~ apparatus such as disclose~ in ~he aforementioned Ravizza application, Serial No. ~ . As the head 30 scans a track, the error signal causes the head to be adjusted so as to follow the trac~ regardless of the speed of tape trans-port, provided it is within the limits of movemcnt of the element 32.
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r Referring to FIG. 1, which illustrates a block diagram of circuitry generally embodying the apparatus described in the aforementioned Ravizza and Hathaway et al applications, Serial Nos. 274,434 and 274,370, a dither oscillator 60 applies a sinusoidally varying signal of frequency fd on line 62 that is coupled to a summing circuit 64, where it is added to a DC error correction signal from line 66. The output of the summing circuit 64 is applied on line 68 to a second summing circuit 69 where it is added to the damping signal provided by an electronic damping circuit 71 over line 73, such as disclosed in the aforementioned Ravizza application, Serial No. 274,421 As described in that Ravizza application, extraneous disturbing vibrations in the movable element 32 are detected by the electrically isolated sense strip 83 proximate an edge of the piezoelectric transducer located on one side of the movable element.
The sense strip 83 longitudinally extends along the movable element 32 and is constructed in the manner described in the aforementioned Brown application Serial~No. 274,3680 .The sense strip 83 generates a feedback signal representative of the instantaneou~ deflection velocity of Ihe ~ovabIe element ~ , mg/~- - 31 - ~

and applies the signal to line 77 extending to the input of the elcctronic ~lamping circuit 71.
The elcctronic damping circuit responsively generaLes a damping signal of the proper phase and ampli-tude Eor application to thF movable element to oppose and,thereby dam~en the extraneous distrubing vibrations present therein. The combined error correction signal and damping signal provided by the second summing circuit 69 is coupled by thç line 79 to the input of a drive ampliEier 70 which then provides a signal over ~ line 81 to the pie~oelectric movable element 32 carrying ~he transducing head 30.
The dither drive signal causes the movable element 32 to impart a small peak-~o-peak oscillatory motion (dither) to the head 30 to cause the head to move laterally lS relative to the track alternately between limits as it ~ -scans longitudinally alontl ~he trac~ to reproduce the recorded si~nal. The oscillatory motion imparted to . ~
the head 30 causes an amplitude modulation of the reproduced signal ~hich, when recording video or other high frequency signals, is in the form of an RF envelope o a frequency modulated carrier. The oscillating motion oE tIle movable element 32 produces an amplitude modulation of the RF ;~

, ~ .

s~ ~

envelope. IE the head i5 lccated in the center o~ the track, onl~ evcn harmonic ampli~ude modula~ioll components of the dither signal are produced on the R~ envelope by the action of the movable element 32, because the average head position is at track center and ~he ~P envelope variation caused by dithering appears as a symmetrical function. With the head 30 at track center, the amplitude of the RF produced from the tape is maxi-mum. As the head 30 moves to either side of track center during eacl- hali cycle of the dither signal, the amplitucle of the reproduccd RF envelope decreases.
On the other hand, if the transducing head 30 is located slightly off the center to either side of a tFack, the reproduced RF envelope amplitude variation will not be symmetrical because the head 30 excursions to one sidç of the track will produce a different RF envelope amp1itude change than produced by an excursion towards the opposite side. ~lence, a maximu~-to-r,~inimu~ envelope amplitude variation occurs once for each cycle of the dither signal, or at the dither frequency, Ed, with the order of occurrénce of the maximum and minimum envelope amplitudes ~epending upon the side of the track center to whieh the he,ld 30 is offset. The fundamental of the dither frequency is no longer balanced out, and the reproduced R~ envelope varjations wi]l contain a Eundamental component of ;~
the dither freyuency, with the phase of the fundamental çompo~
nent for an offset to one side of the center of a track .33~

ir . . : ,~ :

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being lB0 dcg2ees different with respect to that for an offset to the other side of the center of the track. Dctection of the order o~ occurrence of the maximum and minimum envelope ampli-tudes, i.e., phase of the envelope amplitude variations, pro-vides information deEinitive of the direction the transducinghead 30 is offset from the center of a track being scanned, and detection of the envelope amplitude variation provides information definitive o the amount of offset.
To obtain the hcad position information, the modulated RF envelope signal reproduced by the head 30 is coupled to detection circuitry through a video preamplifier 72 and is applied to equalization circuitry 74 before it is coupled by a line 75 to an amplitude modulation RF envelope detector circuit 76 that is constructed to recover the dither signal fundamental and its side bands. The output of the envelope detector circuit 76 is then applied to a synchronous amplitude modulation detector 78. The synchronous detector 78 operates on the principle of coherently detecting the amplitude and polarity of an unknown actual phase but known frequency input signal with reference to the phase of a reference signal of the same nominal frequency. ~he reference signal is provided by the dither generator 60 through line 62 whicl is connected to a phase adjust means 85 and, subsequently to the detector 78.
The phase adjust means 85 in the VPR-l video production recorder ~ ;
"' ':

: ,: -. . . .
,, .;.,:. ~: .
...
.

manufactured by ~mpex Corporation is a tnanually-controlled adjustment that is typically set for each head and movable element assembly used in a recorder. The phase of the reEerence signal is adjusted to compensate for phase changes introduced to the dither signal by actors other than the transducing head 30 being located o~f the center of a track being scanned, such as changes in mechanical resonance characteristic of the head and movable element assembly. ~owever, as will be described in detail herein- `
below with reference to FIGS. 12-15, the present invention utilizes an automatically phase compensated reference dither signal to avoid the necessity of having to manually adjust the phase of the dither reference signal for each video record/reproduce apparatus having a positionable head that is controlled in the manner accomplished by the apparatus described herein or in the aforementioned -Ravizza application, Serial No. Gfi~
The synchronous detector 78 provides a rectified output having the amplitude of the unknown recovered dither signal with the rectified output being positive when the reEerence and recovered dither signals are in phase and negative when the two signals are 180 degrees out of phase. Since the signal present at the ~input of the detector from the envelope detector 76 will have a ; 25 component at the fundamental dither frequency, fd, whenever an error occurs in the head track position, - the sync detector 78 will provide on its output line 80 a track error signal representative of the head track ' _ .
:,, . . ~ , :

... ~.. , . .. . . ~

i.~47~L~6 position error. The amplitucle of the error is proportional to the amount that the head 30 is displaced from track center and the polarity of the track error signal is indicative of the dircction of head displacement from the track center. The output line 80 is coupled to circuitry 82 shown in the dotted line box, and the output from that circuitry provides the-error correcting signal on line 66 to the summing circuit 64 as pre-viously described. In the event a reset signal is to be produced for resetting the head 30 to a different track upon completion of the scan of a track, it is accomplished by the circuitry 82.
In the apparatus described in the aforementioned ~lathaway et al. application, the circuitry 82 which generates the pulscs for chan~ing the position of the head 30 relative to its location at the conclusion of scanning a track is in pàrt determined by the mode of operation of the apparatus, i.e., nor~ial reproduction mode, slow motion mode, etc., and, in part, by the circuitry which determines the position of the head 30 with respect to its range of movement. ~s can be seen from FIG. 1, the aforementioned Hathaway et al. application has a mode select switch 84 that is adapted to bring into operatlon an upper slow/still servo amplifier circuit 86 or a lower normal play servo amplifier circuit 88, with the mode being determined by the operator using the recording apparatus. As is evident from the drawing, it is seen that the mode select switch 84 must be changed from one position to the other when changing from normal play to the slow/still mode of operation or from ~he latter to the former. ~hen changing between the normal play and the slow/
still modes by the operation of the switch 84, a disturbing transient interruption occurs in the reproduced Yideo signal because the proper controlling head position error signal is . . .
~ -36-~ ':
,, , .~ , :

.: , , . ~:

5~i temporarily lost. Reacquisition of the eorreet control-ling error signal can take 100 milliseconds or six tele-vision fields. It should be appreciated that this would produce a discontinuous video picture on a monitor.
Referring to ~IG. 2, the circuitry 82 shown in the dotted line box of FIG. 1 is replaced with the universal cireuitry 90 which has input line 80 and output line 66 eorresponding to the input and output lines of the cireuitry -82 in FIG, 1. The circuitry 90 of FIG. 2 effectively earries out both the normal play as well as the slow/still modes of operation with the mode select line 92 controlling the circuitry which replaces the separate circuits 86 and 88 of FIG. 1. The universal circuitry allows the automatie head traeking servo eircuitry to be switched from the slow/still mode to normal play mode without producing servo unlocking and reacquisition transitions, as is experienced by the eircuitry of FIG. 1~ when switching between the slow/still servo ampiifier cireuit 86 and the normal play servo amplifier eircuit 88. The cireuitry of FIG. 2 broadly illustrates that a mode ehange will not cause the switeh-ing out of one eircuit and switching in of another and, ~-thereby, does not result in the loss of and necessitate the reacquisition of the error signal. However, it should be ~. .
appreeiated that different servo response charaeteristics , -37- ~

- : ~ . :

1~47 L~ 5i6 are needed for normal play operations and Eor slow/still operations; and the circuitry 90 shown in FIG. 2 provides the needed difEerent servo response characteristics.
In addition to the universal automatic head tracking servo circuitry, the improved apparatus includes improved circuitry for controlling the movement of the tape around the tape guide drums 22 and 24, herein referr-ed to as the tape transport servo. The improved tape transport servo provides coordinated sequences for chang-.
ing from a slow/still motion mode of operation to the normal speed mode of operation in a manner whereby the automatic tracking servo circuitry can be coordinated to produce the desired stable, noise free video picture on a monitor, for example.
.
The sequence of events that occur during the switching between the slo~/still mode of operation and the ~
normal speed mode enables continuous video reproducing throughout the period of changing velocity because the automatic head tracking servo circuitry operates through~
out the time in which the tape is moved between a stop or 7~i6 slo~ motion and the normal speed motion by the tape transport servo system. As used herein, nor1~al speed is intended to mean the tape speed that is used during recording. ~1hen changing from a stop or slow motion operation to a normal speed operation, the tape i6 is accelerated for a period of about l/2 second until it reaches and is moving at a constant speed that is about 95~ of the normal spced. When the tape 36 is moving at 95~ of the normal speed, the rate at ~hich the tape 36 is transported past the location of the scanning head 30 is 5% less than the normal rate. This decrease in the unlt length of tape transported past the-scanning head location per unit time is referred to as tape slippage. It is during this time that the initial color frame decision is ; 15 made. Color framing is the final step in a video record/
reproduce system servo operation in correctly positioning a head to scan-a s~lected track at the proper head~
to-tape speed relative to a controlling reference, typically studio reference. In the color framing servo operation, -~ 20 the head and tape positioning drives are controlled~so that recorded video fields are reproduced having;a color subcarrier to vertical sync phase relationship whlch corresponds to that of the studio reference. Because the automatic tracking servo circuitry is fully operational 25 during this initial color frame acquisition time, the ;~
video framing information can be evaluated along with the ~ 39~
~ , . , . :

: ~ . , .

reproduced control track data in order to initially determine the color frame. The initial acquisition period varies between about 0.3 and 0.6 second; and, once the initial colcr frame determination has been made, the tape transport servo system switches to accelerate the tape to 100% of normal speed.
It should be understood that a control track 94 (shown in FIG. 6 to be in the longitudina:L direction of the tape 36) provides different color frame information than the actual color frame information obtainable from the video information recorded in the tracks A-G as shown in FIG. 6. ~ecause of machine-to-machine tolerance variations affecting the location of the control track reproduce head 267 (FIG. ~), such as, ~or example, variations in the distance separating the control track and movable video heads and in the mounting oE the video head 30 on the rotating drum portion 22, it is possible that an initial color framing operation performed with respect to a comparison of control track information and ~;
20 studio reference will result in positioning the tape 36 ~-relative to the location of the movable video head 30 wlth the head mispositioned as far as plus or minus one (1) track Erom the proper track for the correct color frame ~`
condition. In other words, instead of the video head 30 of the reproduce video tape recorder being positioned to scan the same track that was previously recorded ~40 .

:
:~ V '' i : ~ :
.. . . .

,: : ~ ,

3~ ~L gL7 ~

simultancously with the detected control track pulse, it is positioned over one of the adjacent ~rac~s because of the aforementioned machine-to-machille tolerance variations although the reproduced control track information indicates that color framing has been achieved. As will be describ-ed in greater detail hereinbelow, the apparatus described herein includes means for automatically verifying that the initial color Erame acquisition is correct and, if color frame acquisition is not verified, for automtically relative positionin~ the video reproduce head 30 and the tape 36 to place the head over the proper track for achieving color frame. Thereafter, the tape transport servo maintains the transport of the tape 36 phase locked to the reproduced control track signals.
The exemplary-embodiment of the apparatus described in the aEorementioned ilathaway et al. applicat-ion, Ser. No. C77, ~1', utilizes level detectors during the slow/still mode of operatlon to determine iE reset pulses are to be applied to'the deflectable piezoelectric ;~
element 32. In this regard, reference is made to FIG. 7a -which illustrates a diagram of the RF envelopes 100 that are produced during successive scanning revolutions, with signal drop out intervals 102 occurring in the RF envelope which corresponds to the interval that the head 30 is --~
25- between the guides 40 and 42 tFIG. 4) where no tape is present during the transducing head's rotation. In FIG.
7a, the drop out intervals 102 are exaggerated to facili-tatç the description. Thus, more speciflcally with -41~

,~. , ~.

respect to FIG. 7a, as the rotating head 30 maXes a revolution, an RF envelopc 100 is reproduced each revolut-ion, with a drop o~t interval 102. When the transducing head 30 is reproducing a track Erom beginning to end, the RF envelope 100 is produced from the left to the right as portrayed in FIG. 7a, with each area 100 representing the signal information that is reproducecl or recorded on a single track and, in the casc of video recording, preferab- -ly represents at least the complete portion of a field of video information displayed on a monitor. In the event the apparatus is operating in the slow/still mode of operation and the tape 36 is stopped so as to be producing a still frame or stop motion video image on a monitor, it is necessary to reset the transducing head 30 at the end of its scan of every track, or a sequence of tracks if a still image monochrome frame or color frame is to be repetitively generated, so that it is in position to - repeatedly reproduce from the same track or sequence o~
tracks. When such is done, it should be appreciated that the automatic head tracking circuitry will follow the track during reproducing and will produce a reset pulse for resetting the transducing head 30 at the completion of its scan of the track or sequence of tracks. A head deflection voltage versus time waveform diagram for still frame opcration in which a single field is repetitively reprQduced to form the displayed still image is shown in ~IG. 7b and includes ramp portions 104 as well as vertical reset portions 106 and generally represents the waveform that is necessary to maintain head tracking ~42~

`':`,',' ~ ~:

~47'~

during reproducing of a track and resetting of the trans-ducing head 30 at the end o its scan of the track. The timing oE the reset is advantageously set in the exemplary embodiment of the aforementioned Hathaway et al. applica-tion to occur during the drop out interval 102 and theamplitude of tne reset pulses effecting the resetting of the head 3b depicted by the reset portion 106 of the head deflection waveEorm in FIG 7b is shown to be that which produces a transverse movement of the head 30 that is equal to the center to center distance d between adjacent tracks, which will often hereafter be referred to as a full one track reset. It is advantageous to time the resetting of the movable he~d 30 with the occurrence of the drop out interval 102 because that interval typically occurs during the vertical blanking period of the video signal, which provides more than sufficient time to reposition the movable head 30 before the video image portion of the recorded video signal is positioned to be reproduced by the head. However, it is not a requirement of the apparatus constructed in accordance with the principles described herein that the resetting of the movable head 30 be timed to occur during a drop out interv.al. ~or example, in video record/reproduce appara~
tus characterized by recording formats without drop ;~
~` 25 out intervals or with the vertical blanking period not .
aligned with the end of the recorded track, or in data recording apparatus for signals other than analog video signals, the resetting of the head position may be : `
~ selected to occur during the intermediate ~ ~

.
~ ~3 portion of a track so that a segment of information is transferred with respect to the recordinq medium by a movable head that scans portions of adjacent tracks and is reset between intermediate locations of the adjacent 5 tracks to rescan the track portions. ~ -Resetting of the movable head 30 is synchronized to occur during the drop out intervals 102 that are located at the ends of the recorded tracks. In this regard, level detectors in the circuitry 90 effective-ly ~onitor the voltage waveform, such as that shown inFIG. 7b, and provide a reset pulse 106 when the voltage near the end of the ramp 104 shown at point 108 exceeds a certain level. As shown in FIGS. 7, the resetting of the movable head 30 begins at the start of the drop out interval 102 and is completed before the end o the drop out interval.
In the apparatus described in the aforementioned Hatha~Yay et al. application, the threshold levels~for determining whether a head position reset should occur are shown in FIG. 7c, together with a representative head ; deElection waveform including the ramp portions 104 and reset portions 106 shown by phantom lines. The logic is - responsive to a processed once arouna drum tach pulse each time the head 30 reaches a point in its rotation-correspond-ing to the point 108 in FIG. 7c to provide a singleamplitude reset pulse (l track forward reset) if the head deflection waveform is at a voltage level corresponding to a head deElection in a direction reverse to the travel of the tape 36 past the scanning head location (labeled reverse) and a double amplitude reset pulse (2 track forward reset) when the voltage exceeds a level correspond-inq to a head deflection in a direction reverse to the travel oE the tape in excess of the spacing between adjacent tracks, for example, as depicted ramp portion 103 When the voltage of the ramp 104 is at a level below that corresponding to a one track reset, no reset pulses are generated and the transducing head 30 will merely follow the next track rather than being reset to rescan the same track. It should also be appreciated that the reset pulses are only produced during the drop out interval and are inhibited when the transducing head 30 is scanning a track and reproducing active video-information. In other words, the level of the voltage of the ramp lOq is detect~
- ed at the decision point lO~ of the ramp 104 ~ust before the drop out interval 102 and, if it is found to be within reset range, an appropriate reset pulse will be generated and applied during the drop out interval Eor deflectlng the movable element 32 the required amount in the direc-tion opposite that it was previously deflected by;the ramp ;
portion 104~of the head deElection voltaqe~wave~Eorm. ;~

7~

To more readily visualize the function of the forward and reverse direction reset pulses, reference is made to FIG. 6, which illustrates a path 110 shown by phantom lines followed by the scanning head 30 relative to the tape 36 during a stop mode of operat:lon. As seen therein, the head starts its scan of the tape 36 at the beginning oE track F and cuts across the trac~ to the end of track E during a single revolution. This occurs if the tape 36 is not moving and the transducing head 30 is not deflected. It should therefore be appreciated, that if the automatic head tracking circuitry is operative to maintain the transducing head 30 so as to follow track F, the head will gradually be deflected ln the reverse direction by a ramp portion of the head deflection wave-form, i.e., in the direction opposite the arrow 38, and ifit were not deflected at the end of the track F, it would be in a position to begin playing the track G. To rescan track F, it is necessary to apply a reset pulse that will move the head 30 in the forward direction, i.e., in the direction of the arrow 38 so as to have the head in position to begin reproducing the beginning of track F. ;
Thus, the reverse and forward terms in FIGS. 7b-7g are in the context of reverse and forward directions of tape -~
movement and the movement of the head is referenced to these same directions.
The circuitry for generating the reset pulses is operable to selectively generate the reset pulses, depending upon the mode of operation of the apparatus. Thus, referr-ing to FIGS. 7d, 7e, 7f, and 79, it is seen that reset pulses '~

r - - - ~ :

4~7'~

will not be produced when the head 30 is deflected in the forward direction by an amount less than a selected distance depending upon the operating mode and a single reset pulse will be produced to reset the head 30 in the .reverse direction when the head is deflected in the Eorward direction by an amount greater than the distance separating adjacent tracks. This appears in all of the diagrams shown in FIGS. 7d, 7e, 7f, and 7g. The reverse direction reset pulses will regularly occur when the tape is moving at a speed between normal speed and twice normal speed.
When the improved apparatus is operating in the slow/still mode, it is desired that reset pulses be generated in the same manner as was performed by the apparatus disclosed in the aforementioned Elathaway et al. application. ~ccordingly, the diagram shown in FIG.
7d illustrates the operation circuitry of the apparatus when it is operating in the slow/still mode;
and it is seen that its characteristics for head deflec-tions in the reverse directions are similar to thoseshown in the diagram of FIG. 7c. Typically, when operating in the slow/still mode, if the waveform 104 at the end of a track scan corresponds to a head deflection from zero to just greater than one traSk center-to-track center spacïng in the reverse direction, then a track reset w:ill occur : whlch will move the transduclng head 30 :

~7~

in the forward direc~ion a distance e~ual to the separa-tion of adjacent track centers. The head deflection waveform 104 of EIG. 7d dcpicts the operating condition wherehy the movable element 3~ is deflected between its æero deflec~ion condition and a deflection condition just grcater than one trac~ center~to-track center spacing in the its f~orward direction.
~ lowever, as can be seen from the head dcflection waveforms 104, 106 and lO~', 106' shown in ~IG. 7e and 113 shown in FIG. 7d, the average level of the head deflection waveform, hcnce, average position of the movable element 32, can vary for the same head tracking condition. For the operating modes illustrated by FIGS. 7d, 7e, 7f and 79, the head position waveform can be any~heLe within a range corresponding to 1 trac~ deflection in the forward direction and 1 trac~ deflection in the forward direction for any instantaneous head tracking condition. Precise head tracking ~ill be ~aintained. A different position within the range only has the effect of altering the average position about which the mov~ble element 32 is deflected.
- FIG. 7d includcs a head deflection waveform 104, 106 shown by phantom lines for a slow motion speed of 1/2 normal speed. As shown therein, this slow motion opera-tion results in the movable head 30 being reset after 25 every other one of its rotations to rescan every other ~-track, hence, field a second time. Between consecutive resets of the movable head 30, the head is deflected to account for the different path angle the head would otherwise follow along the tape 36 and allowed to scan two adjacent tracks during successive rotations oE the head 30.

8~

:

FIGo 7d also includes a head deflection waveform 113, 115 shown by phantom lines for a stop motion or still image operation wherein two adjacent tracks are consecutively scanned to reproduce two consecutive television fields before the movable head 30`is reset or repositioned to rescan the tracks. This is in contrast to the stop motion operation previously described with reference to FIG. 7c, wherein the movable head 30 is controlled to scan a single track repetitively to reproduce a single television field for the generation of the desired still image displaysO As will be described in detail hereinbelow with reference to FIGS. lOa9 lOb9 lOc and lOd, the record/reproduce apparatus includes a transducing head tracking servo that employs circuitry for detecting when the movable head 30 must be repositioned or reset to rescan previously scanned tracks and applying a reset signal to the movable element 32 at the proper time.
This detection and resetting circuitry is arranged to selectively permit still image reproduction from a single repetitively reproduced field, a repetitively reproduced sequence of two fields, i.e., a monochrome frame9 or a , : ' . ': .~

: -' '' mgl~ 48~

.

.
- . : :. : .

repetitively reproduced sequence of four fields, i.e., a color frame. The selective monochrome frame or color franle still image reproduction is achieved by means that prohibits the application of the head repositioning reset signal that normally is applied at the end of the scan of each track when in the still mode until the desired sequence of fields has been reproduced and by means that applies the appro-priate amplitude reset pulsè to reposition the head 30 to the track containing the first field of the sequences upon each completion of the sequence.
The head positioning waveform 113, 115 shown in FIG. 7d illustrates the manner in which the movable head 30 is deflected to repetitively reproduce a sequence of two fields recorded in adjacent tracks so that monochrome frame still image displays can be generated. Generating still image displays from a monochrome frame composed of two conse-cutively reproduced fields has the advantages over the use of a single field of increased vertical resolution of the image (525 line resolution instead of 262-1/2 line resolution) and of avoiding the necessity of introducing a 1/2 line delay in ;

; ~ ' :
' nm/ ~ ~ -48 ``:

: ' ~

alternate reproductions of a single field. Generating still image displays from a color frame composed of four consecu-tively reproduced fields has the further advantage of pro-viding the entire color information content of the displayed image and of avoiding the necessity of separating the lumin-ance and chrominance components of a composite video signal so that the chrominance component can be inverted to provide the proper color subcarrier phase when forming a still image color display from a single field or a monochrome frame.
The aforedescribed operation of the transducing head tracking servo for generating a still color image display from a sequence of fields containing the entire color code sequence is described as arranged to generate the still displays from an NTSC standard color ~elevision signal9 which requires four consecutive fields to color encode the signal. In the PAL and SECAM standardsj color frames are composed of 8 and 4 fields, respectivelyO As described hereinbelow, the head tracking servo can be arranged to reproduce a color frame in each of these standards in the still fra=e mode. For PAL standard color televi~ion :
`
~ `
n=/ Cb -48~ :

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; . .
- . ' . . ` ~: . - . .

signals, the head positioning reset signal is inhibited to permit the reproduction of 8 consecutive fields before a head positioning reset signal is provided to efect the reposition-ing of the head 30 to rescan the 8 consecutive fields. While SECAM standard color television signals have a 12 field color frame sequence, the nature of SECAM signals enables satisfac-tory color displays to be generated from the repetitive repro-duction of 4-consecutive fields. Therefore, the head position-ing reset signal is inhibited to permit the reproduction of 4 consecutive SECAM standard fielcls before a head positioning reset signal is provided to effect the repositioning of the head 30 to rescan the 4 consecutive fieldsO
It should be appreciated that if relative motion is present in the images represented by two or more television fields used to generate monochrome frame or color frame still images, jitter will be present in the repetitively displayed monochrome or color frame. If the jitter is objectionable, the monochrome or color frame display can artificially be generated from a single field or only those flelds wlthout relative motion.

- :

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~ nm/ ~b : -48~

. ~ :, . : . . .: . . .- .

$~-~

Although readily apparent from the above description oE the improved record/reproduce apparatus, it should be emphasized that, when in the monochrome frame or color frame still image mode~ the tape 36 is typically stopped and the head 30 is continuously deflected, for example, as depicated by the ramp portion 113 of the head deflection waveform shown in FIG. 7d, between the applications of appropriately timed consecutive head reset signals, such as, for example, ~e~et step 115 in FI&. 7d. With respect to the particular embodiment of the automatic tracking circuitry shown in FIGS. lOa and lOb, in color frame still image modes9 the variable reference threshold circuitry 126 (FIG.3) employed in conjunction with associated latches and gates to generate the appropriate amplitude head resetting signal is modified to include additional parallel latches and gates as shown in and described hereinbelow with reference to FIG. lOd. Also, as shown in FIG. lOc9 and will be described hereinafter, the ambiguous head track lock circuitry includes means to prop-erly time its operation so that artificial head resetting - signals are properly provided ln accordance with the particu-lar still frame mode.

nm/ f~ 3 -48~-~1 .

7 ~

Wl~en the apL3ratus is switclled from the slow/
still motion modc o operation to normal speed mode of operation, the tape trans~ort servo system accelcrates the tapc 36 up to about 95~ of normal spced. During the tape acceleration intelval, which lasts about 0.6 sec. when the tape 36 is acceler~ted froM s~op, the variable reference threshold circuitry 126 es~ab~ishes the same hcad reset referencc threshold levels as it does for slow/still operat:ing modcs. Upon reaching 95~ of normal speed, the automatic head tracXincJ servo circuitry switches to have the characteristics shown in the diacJr~m FIG. 7e, which is different than the slow/still characteristic shown in FIG.
7d in-that a reset pulse is produced for head deElections in the reverse direction in an amount lcss than one-half the spacing between adjacent track centers. Ilowever, a one track reset pulsc will continue to be produced to move the head 30 in the forward direction whenever the head is deflected in reverse direction by an amount in the range of one-half to just greaLcr than the distance between adjacellt track ccnters. It'is during this time when the tape 36 is being transported at the 953 normal speed, that the initial co~or ~rame determination is made. During this initial detertnination stage, it is desired that the forward reset pulses bc provided only whenever the movable head 30 is de~lected in the reverse direction an amount betwcen one-half and just greater than the distance between adjaccnt track centers so that the head positioning correction waveform will remain more closely centered about the zero voltage level, rather than at an averago nogative value as could be the case with respect to FlG. 7d. By not resetting the head 30 -49- ' ", ' ' ':

.
. . : , ~ , .:: : ~ : ::
' . .,:
,-. . . - . . ' '., ' .. ~ :' . . . - - . .: . . .

when it is ciefleetcd in thc rcv2rse direet:ion by an amount less than one-tlalf the distance scparating adjacent traei;s, tile average value of the head deflcetion waveform will more c]ose]y approach thclt shown in ~IG. 7h, where it is generaliy centered around thc ~ero head deflection mark. Onee the initial eolor [raming determination opera~ion is eomplete and provided that the phasc of the eontrol traek signals are within a predetermincd "window"
when eompared to a refercnee signal, as will be herein-aftcr described, the tape trallC;port servo system switehesfrom the 95% normal specd to lO0~ or normal speed. The tape 36 is quiel;l~ aeeelerated to 100~ of normal speed and the automatie traei;ing eireuitry is thcn s~itched to the normal speecd mode which has the eharaeteristies illustrated in FIG. 7f. Ilowever, before initiating normal reproduetion operations in the normal speed mode, the reprodueeci video signal is c~amined to determine whether the initial monochrome and color frame determination has been eorreetly made. i3ecause thc aforementioncd rnaehine-to-machinc toleranee variations in professional quality video record/reproduec apparatus typieally do not vary outside of a toleranee rallge that would produee more than a plus or minus one (1) traek head positioning error when monoehrome and eolor framing relative to the reeorded control traek signal, the apparatus hereirl described ean take

5 0-.

. : -. . ~- . ,........ . . .. . :~ . , .

~d~

advanta~e oE the inf()rmation content of the rcproduced video signal's tl sync to V sync phase relationship, i.e., monochrome frame information to verify the correctness of the initial monochrome arld color framing. As will be described in furthcr detail hereinbelow, the reproduccd video signal's ll sync to V sync phase relationship is compared to the equivaler~t phase condition of the studio referellce. I tilC monochrollle frame of the reproduced video signal diff~r_ from that of thc studio reference, the automatic trac~ing circuitry responds to a field match signal ~enerator 95 (FIG. ~) to deflect the movable element 32 a distance equal to that separating adjacent trac~ cent:ers and in the proper direction t:o achieve color framin~. FIG. 7f includes a head deflection waveform 106, 109 sho-~:n by phantoDl lines ~or a normal speed mode of operation, including a forward reset portion 106 represcnting a typical one track deflection of the head ~0 for color Eramin~ purposes followcd by a typical head position correction wclveform 109 occurring during normal speed mode operations. Furthermore, as shown in FIG. 7f, the normal speed dynamic ran~c of the automatic tracking circuitry is shown to cxtend from a head deflection in the forward direction just greater than the distance separating adjacenL track centers to a hcad d~flection in the reverse direction of a correspondin~ amount, which means that no reset will occur if the ... . . ..

- - . . . : : :
- : . -:

., ~ . , .

~7~

instantaneo-ls vo]tage ]~ st he~ore thc drop out interval 102 is wi~hin this dynamic {ange. The single track reset pulses (in both directions) are provided to center the transducin~ h~ad 30 if an external disturbance or the like causes the movable elerllent 32 carrying the transducing head 32 to be outside of its normal operating range.
In the two times normal speed mode, the ~ape 36 is transported past the scannin~3 head location at a rate that is two timcs that for the normal speed operating mode. Consequently, as a trac~ is being scanned by the head 30 during this mode, the track is advanced a distance in the forward direction beyond th~ scanning head location correspondiny to the distance separating adjacent track centers. Thcrefore, to maintain head--to-track registra-tion, th2 scannin~ head 30 must be deflected in the forward direction a corresponding distance during the scan of a track. Two times normal speed motion is achieved by reproducing every oth~r recorded field at the normal field rate for video signals, i.e., 60 Hz. By resetting the position of the scanning head 30 in the reverse direction at the ~onclusion oE the scan of a track a distance corresponding to the distance separating adjacent tracks, the scanning head 30 skips the adjacent downstream track ~ ;
:: ; :
,:

~ ~ - ' , - .

~, ':

-;

~7~

that it would normally follow if not reset, which contains the next field of the ~ecorded sequence of video fields, and instead is positioned to reproduce the field recorded in the track that is located two recorded track positions from the track whose scan has just been completed. FIG.7g illustrates the head deflection waveform generated by the circuitry 90 of the apparatus when the tape transport servo system is controlled to transport the tape at two times ~ormal speed. As can be appreciated from the illustrated waveform, when the tape 36 is transported at twice normal speed, the movable head 30 is deflected in the Eorward direction an amount exceeding the distance separating adjacent track centers. When the deElection exceeds that amount, a one (1) track reverse ceset pulse is produced to position that head 30 over a track located two recorded track positions from the track whose scan has just been completed The operational characteristics shown in FIG.
7d, 7e, 7f, and 7g are carried out by the circuitry 90 shown in the block diagram of FIG. 3. The mode control line 92 is connected to logic circuitry indicated general-ly at 111 and has lines 112, 11~, 116 and 118 extending to respective switches 120, 122, 12~ and a variable reference or threshold producing circuit 126. The error detector ;~ -53 ~ ': ' ' ' ' ~; " ' . ~.
... .
. .
.t' .~_ .. .

' ; ~ .

~ 7~

ouLpuL signal ~rom the synchronous detec~or 78 t~IG. 1) is applied via line 80 to the switches 120 and 122, only one of which can be closed at one time by operation of the logic circuitry 111. The switch 120 is connected via line 128, resistor 130 and line 132 to the negative input of an integrator 134, while the switch 122 is connected via line 136, resistor 138 and line 132 to the same integrator input. The values of the resistors 130 and 138 are diffeLent and effectively change the loop gain or compensation of the error signal on line 80 as applied to the input line 132 of the integrator 134 according to which on- of the switches 120 or 122 is closed. When the apparatus is operating in the slow/still mode, switch 120 is closed and switch 122 is open so thac the gain oE the head track positioni.ng servo system is increased so it can' react ~aster, since there is more movement required of ~he movable elemelit 32 carrying the transducing head 30 during the slow/still mode of operation than in most other modes.
~hen the apparatus is placed i.n normal speed mode, switch 122 is closed and switch 120 is open so that the gain is reduced, less movcment for correction being required in - this mode because the transducing head 30 will normally closely follow the track. When the apparatus is in its slow/still mode of operation, switch 124 is also closed :
to connect a DC voltage centering network ~.39 for the ; ~ :

-54~

~'' ' .
..~
-. . :L , ..

7~

integrator. During slow motion modes of operation below one-half normal speed, tilerc is a need rOr the c~ntering networ~ around the integrator 134 to prevent the integra-tor ~rom swinginc~ too far out of its normal operating range and, thereby, require excess time Eor servo acquisi-tion after ti)e apparatus is turned on. During the normal speed mode, the networ~ 139 is unnccessary and therefore switch 124 only brings it into operation during the slo~/still mode oE opcration. Furthermore, when reproduced video is initialy detected during an operating mode signified by a high logic ~ PR signal level on input line 123, the logic circuit 111 functions to close switch 124, to facilitate rapid servo locking.
When the error signal is ap~lied to the input 15 line 132 of the integrator 134, the error signal causes the transducing head 30 to be adjusted so as to follow the track regardless of the speed of tape transport, provided it is within the limits of deflection of the movable element 32. The integrator 134 provides a ramp signal that has a slope which is determined by the speed of transport of the tape 3G and an average DC value that is determined by the DC or low frequency error signal that is derived from thc head trac~ing servo circuitry. Thus, the servo error modulates the average level of the ramp as ~.
the transducing head position error changes and the output of the integrator appears on line 66, which extends to the summing circuit 64 shown in FIG. 1. The reset pulses are summed at the input line 132 of the integrator 134, with : ~ :
`
~ , ,, ... ~.. ...... ... , . : ' 5~ii the reset pulses being dcrived from the processed drum once around tach ~nd sclectively passed by ~ND gatcs 140, 142 and 144. ThC processed once around tach is derived from a tach pu]se gcnerated by a tachometer (not shown) opcratively associated with the rotating drum 22, one tach pulse being providcd Eor each rcvolution of the rotating drum, hence, the scanning head 30. Conventional tachomet-er proccssing circuitry provides the pulsc at the desired system time and of selccted width. The AN~ gate 140 has 10 its output conllected to ~ine 132 via a resistor 146 and A~D yate 142 has its output connected to line 132 via a resistor 1~8 and the output of AND gate 144 is connected to an inverter 150 which in turn is connected to line 132 via a resistor 152. If either of the ~D gates 140 or 142 are activated, then a predeterinined current pulse whose amplitudc is determined by resistors 146, 148 and 152 will appear on line 132 and be applied to the integrator 134 for the purpose of resetting the voltage level at the output thereoE. The actuation of either of the AND gates 20 140 or 142 wlll produce a reset step in the output of the intcgrator 134 oE predetermined value that will correspond to the proper amplitude reset step required to deflect the movable clemcnt 32 a distance in the forward direction corrcsponding to Lhe center to center distance between adjacent tracks, i.e., a one track position deflection distance. If the AND gate 144 is actuated, then by virtue of the invertcr 150, an opposite polarity reset pulse is produced on line 132, as compared to the polarity of the pulse from the ~ND gates 140 and 142, and which opposite polarity effectively cause.s a reset of the movable element ; ~

. ,. , ' '' ~ ' ... . .. . .. ... . ....
_ . ; . ~

32 in the reverse direction as is desired. lf both of the ~ND gates 1~0 and 1~2 are activated simultaneously, ~or example, as occurs during the 95~ normal speed mode when thc head 30 is deflected in the reverse direction a distance gLeater than that corresponding to the track-to-track scparation, a twice amplitude current pulse will appear on line 132 and be applied to the integrator 13 for the purpose of resetting the voltage level at the integrator's output, hence, the position oE the movable head 30, the equivalent of two track positions in the -forward direction.
The output line 66 of the integrator 134 is coupled to one input of each of three level detectors - 156, 15~ and 160, each of which effectively monitors the instantaneous voltage on line 66 to determine if reset pulses are to be genelated. The level detector 156 has its other input coupled to line 162, which is provided with a constant threshold voltage that corresponds to the level for producing the one track forward reset pulse shown in FIGS. 7d, 7e and 7-. Thus, if the instantaneous voltage level on line 66 exceeds the value of the thres-hold voltage on line 162, i.e., the instantaneous level is above the one track reveLse threshold voltage, then ' ' ... .
r ::

-ii6 a forward reset pulse will be generated. The lcvel detector 160 has its other input coupled to line 187, which is provided ~ith a constant threshold voltage that corres-ponds to the level for producinq the one track reverse reset pulse shown in FIG. 79. If the instantaneous voltage level on line 66 is less than the value of the threshold voltage on line 187, i.e., the instantaneous level is below the one track forward threshold voltage, a reverse reset pulse wlll be generated. The level detector 158 has its other input coupled to the variable reference 126 and, as wlll be explaincd further hereinafter, it receives one of alternative reference level signals, the selected alternative being dependent upon the operating mode of the record/reproduce apparatus. In the embodiment of the apparatus shown by FIGS. 10 and 11, the variable reEerence 126 establishes threshold voltage levels used to control the generation of forward head position reset pulses in operating modes below normal speed.-To generate the reset pulses, each of the level detectors 156, 158 and 160 have respective output lines 164, 166 and 168 which are respectively connected to the D
input oE latches 170, 172 and 17~. rrhe Q outputs of the ~:~

' ~.~

~7~

respective latches are connected via lines 176, 178 and lB0 to the AND gates 140, 142 and 11~. A line 182 is connected to the clock inputs, C, of the latches 170, 172 and 174 and to a pulse and clock generator circuit 184.
The generator curcuit 184 also has an output line 186 connected to a second input oE the respective AN~ gates 140, 142 and 144. A pulse derived from the processed once around tach is used by the circuitry 90 to trigger the pulse and clock generator circuitry 184 and to clock the ~ -- 10 latches 170, 172 and 174. In one embodin)ent of the apparatus described herein, the tachometer processing circuit qenerates the processed drum tach pulse about 16 msec. after the occurrence of the once around drum tacho-meter pulse. The once around drum tach pulse occurs at the beginning of the drop out interval io2 (FIG. 7a). The 16 msec. delayed processed drum tach pulse is timed to occur at the following track reset decision time, identified in E`IGS. 7b-e and 7f by the reference number 108. It is this processed drum tach pulse that clocks the latches 170, 172 and 174 to enable them to latch the condition of the outputs of the level detectors 156, 158 and 160, thereby, determining whether a step reset of the movable head 30 is requircd. As will be described in further detail hereinbelow, the actual reset pulse is 2S generated by the pulse and clock generator 184 from .

-'-': - - : . : ; , . ,~ : ' 17~

the processed dru~n tach pulse, but delayed about 0.67 msec so that any step resetting of the movable head 30 occurs during a drop out interval 102. During operation, if the instantaneous voltage on li.ne 66 at the occurrence of the processed once around tach pulse on line 182 exceeds the particular value of the threshold voltage applied at the input of the respcctive level detectors, the output line associated with each Q output of the level detectors whose ~:
threshold voltage is exceeded will be latched to a high logic level by the clocking action of the procesed once around tach si~nal on line 132. For example, if the instantaneous voltage on line 66 exceeds a level corres-ponding to a head deflection in thc reverse direction in excess of the clistance represented by the reference threshold volta~e providecl b}~ the variable reference gencrator 126 (i.e., any reverse deflection of the movable element 30 when in the slow/still operating mode and a reverse deflection, in excess of one-half the distance separating adjacent track centers when in the normal 95%
20. normal speed operatin~ mode), latch 172 is conditioned to enable the associated AND gate 1~2 to provide a single 1 track reset pulse for effecting a for~:ard 1 track step defl~ction of the movable head 30. On the other hand, if the instantaneous voltage on line 66 exceeds a level corresponding to a head deflection in the .

- ' ,.

., : :

4t~

reverse direction in excess of the distance separating adjacent track centers, both latches 170 and 172 are conditioned to enable their respective associated AND
.gates 140 and 1~2 to provide 1 track reset pulses, which are summed at the input line 132 oE the integrator 134, thereby efEecting a Eorward 2 track step deflection oE the movable head 30. In the event the instantaneous voltage on line 66 exceeds a level corresonding to a head deflec-tion in the Eorward direction in excess of the distance separ-.~ djacent track centers, latch 174 is condition-ed to enable the associated AND gate 1~4 and Eollowing inverter 150 to provide a 1 track reset pulse for effect- ~ -ing a reverse direction one track step deflection of the movable head 30.
The line 11~ from the logic 111 con-trols the variable reference circuitry 126 to provide a threshold voltage on line.196 that varies between three levels so as to accomplish selective resetting oE the position of the movable head 30, depending upon the operating mode of the apparatus, as shown in FIGS. 7d, 7e, 7f and 79. As described here;.nbefore, when the apparatus is operating in the slow/still mode, the circuitry 126 provides a threshold voltage such that a forward head :
position reset occurs when the voltage level on line 66 :
exceeds a level corresponding to any head deflection in ~ :

-61~

~ .
' :' .

~7~6 the reverse direction at thc occurrcncc of a processcd drum tach signal on line 182. When the apparatus is switchcd feom the slow/still mode to the 95~ of normal speed mode, thc variab]e reercnce circuitry 126 applies a different threshold to the lcvel detector 158 so that a 1 track forward reset pulse is produced only when the voltage on line 66 at the occurrence of a processed drum tach pulse exceeds a lcvel corresponding to any head deflection in the reverse direction in excess of one-half the distance separating adjacent track centers. Similarly, when the apparatus is switched to the normal speed mode the variable reference circuitry 126 supplies a voltage level to the level detector 153 that disables it so that a pulse cannot be passed by its associated AND gate 142 regardless of the instantaneous level on line 66. The one forward reset pu].se that is generated in the normal speed mode when the instantaneous voltage on line 66 exceeds the level corresponding to a head deflection in the reverse direction exceeding a distance of about 1.1 times the separation of adjacent track centers, is produced by the operation of the level detector 156. As described herein-before, the threshold level for initiating a forward reset ~:
step of the movable element 32 is increased in steps Erom a level corresponding to no head deflection in the forward :~
25 direction to a level corresponding to a head deflection in :;~
excess of the distance separating adjacent track centers as the video record/reproduce apparatus operating mode is -62~
' ' ' ' ' ~:~ ' - ' , ~ '`' ~
, , . . ::
~ ' :

~7~-~5~

changed, for e~ample, from still motion to normal speed forward motion. This keeps the head pos1tioning waveform generated by the integrator 134 at an average level near ~ero deflection so whcn the tape 36 is accelerated to 100% normal speed, the video head 30 wil:L be positïoned to scan the right track for proper monochrome frame and color frame conditions relative to thc studio reference.
With respect to the diagram shown in FIGS. 7d and 7e, where a two trac~ forward head positioning reset pulse indication is shown to be produced when the voltage on line 66 exceeds that corresponding to a reverse head deflection in excess of the distance -separating adjacent track centers, this is accomplished by both level detectors 156 and 158 going high which produces a double amplitude forward reset pulse as previously explained. Both level detectors 156 and 158 cause the enabling of the associated ~ND gates 140 and 142, respectively, because whenever a reverse head deflection exceeds the distance separating adjacent track centers, the voltage on line 66 will exceed both threshold levels established for the level detectors during the operating modes illustrated by FIGS.
~d and 7e.

' , ~ "

'`'"~

.,. ' : .

.i: . . : . , :
- : . ~ ; . , .

~7~

With respect to the two times normal speed mode illustrated by FIG. 79, the level detector 168 functions to cause its associated ~ND gate 1~4 and following inverter 150 to deliver an opposite polarity 1 trac~ reverse reset pulse to the integrator 13~ to effect the resetting of the movable head 30 because, at the end of the head scan of each track, the voltage level on line 66 exceeds the threshold level established for the level detector on line 187.
With respect to the control of the transport of the tape 36 around the tape guide drums 22, 2~ during recording and reproducing operations, reference is made to FIG. 8, which is an electrical block diagram of circuitry of a tape transport servo system that can be used to control the transport of the tape. As previously me.ntion-ed, when the apparatus i9 switched from the slow/still mode of operation to the normal speed mode, the tape transport servo circuitry is made to follow the speed -profile shown in FIG. 9. In video tape record/repro- :~
duce apparatus, the tape 36 is conventionally transported by a capstan 200, which is driven by a motor 202 through a shaft 20~. A capstan tachometer 206 is operably connected to the shaft 204 to provide signals indicative of the rotation of the shaft 20~ and the signals appear on line 208 which is coupled to a frequency discriminator 210, to - :~
variable slow motion control circuitry 2~0 and to a `
phase comparator 212.

:, , The frequency discriminator 210 provides a signal indicative of the velocity at which the capstan 200 - is driven. Its output is connected to a summing circuit 214 via line 216 so that the capstan velocity related signal provided by the frequency discriminator 210 is subtracted from the reference velocity drive signal provided by a velocity reference circuit 250 for correcting - the velocity drive signal provided to the capstan 200.
The output of the summing circuit 214 is connected via a switch means 226 and line 218 to a motor drive amplifier 220 that drives the motor 202 via line 222. The circuitry is controlled by an operator applying, through the opera-tion of appropriate control devices, mode commands to logic circuitry 224, which in turn provides commands to the automatic head tracking circùitry previous-ly discussed as well as to the two position switch means 226 having a movable contact means 228 that can switch between positions 1 as shown or position 2. The commands from the logic circuitry 224 are coupled via control lines 230, these lines also being coupled to control a switch means 232, which has a movable contact means 234 that is capable of being positioned in one of .~ :
three positions. When the apparatus is operated in the ~: :
slow/still mode, to provide slow motion reproductions of ~-25 the recorded video signals re~uiring very low tape trans- . ~
port speeds, typically, less than 1/5 normal speed, a .
variable slow motion control 240, including a tape speed ' :`.: , :~

-control 240' potcntiometer, is adapted to apply a pulse drive signal to the motor drive amplifier 220 via a line 242, contact means 228 of switching means 226 (in position 1), line 218. ~hen in this mode, switch means 232 is in posi.tion 1 and drivc of the capstan motor 202 provided by the motor driv~ ampliier 220 is controlled during the very low tape spceds solely by tne drive signal generated by thc variable slow motion control 240. The variable slow motion control 240 provides the pulse drive signal to drive the capstan motor 20~ until the velocity of the tape 36 reaches about 1/5 normal speed. At this tape speed, velocity control oE the tape drive is switched over to the velocity reerence circuit 250, which responds to the tape - . ' ~:

: ' :
6S~-- --, ~ : : -,: :

~ ~7~6 speed control ~otcntiometer to chancJe the drive sign~ls to motor 202 and selectively vary the speed of the tape 36.
~hc apparatus described herein employs the variable slow motion control circuitry described in the a~oremcntioned 3~, ~lauch application, Seria] No. 47~-ï73-9`;
To swi~ch the velocity control drive from the variable slo~ motion control circuit 240 to the velocity reEerence circuit 250 at the aEorementiol-ed cross-over velocity range, the logic circuitry 224 operates the switch means 226 so that the n~ovahle contact means 228 is eventually placed in position 2 and triggers a velocity reference circuit 250 via a con~mand placed on line 252 extending from the logic circuitry 224. The velocity reference circuit 250 respc,nds to the command placed on-line 252 to generate a voltaye level in accordance withthe position of the operator controlled potentiometer 210' that is coupled by line 25~/ summing circuit 214/ contact means 228 of s~itching means 226 (in position 2) and line ~-218 to the motor drive amplifier 220. E`or the acceleration mode, the logic circuitry 224 provides a command Oll line 252 that triggers the velocity reference circuit 250 to provide a voltage ramp of selected rate and duration, to accelerate the tape 36 to 9S~ normal speed within an interval of O.S sec. When the record/reproduce apparatus is 25 placed in the acceleration mode/ the logic circuit 22~ -issues a command over a control line 230 to cause the movable contact means 228 of the switch means 226 to be ; placed in position 2 so that the voltage ramp signal is cou~led via line 218 to the motor drive amplifier 220 to 30 effect acceleration of the tape 36. ~ ~

_66.j_ ~ ' .. . . . :
..... ,,, . , , ~'~
... .. . .. . . .

~7 ~

The velocity re[eLence circuit 250 provides thc capstan drive velocity se~vo re.ference signal ~or controlled slow motion operating speeds above tile cross over tape velocity of about 1/5 normal speed and for accelerating the tape 36 to 95~ norlllal speed whcn the apparatus is operated to enter a normal speed reproduce mode. During these operating mode conditions, the applicd ramp or volt~e level. velocity servo reEerence drive signal causes the motor to transport the tape 36 at about thc desired speed. The line 208 from the tachometer 206, together with the frequency discriminator 210, line 216, summing circuit 214, contact means 228 and line 218 provide a velocity.lock mode o~ operation, which forces the capstan to follow thc velocity servo reference drive signal provided by the vclocity reLerence CilCUit 250. In this regard, it should be noted that the switch means 232 has the movable contact means 23~ in position 1 during thc velocity lock mode of operation.
~ 7hen accclerating the transport of the tape 36 to enter the 95~ normal speed mode, the capstan 200 accelerat-es the tape 36 to the 95% normal spee~1 level and, upon reaching that speed, switch means 232 is switched by the operation logic circuitry 224 so that the movable contact means 234 is in position 2. This places the capstan velocity servo in a capstan tach phase lock mode oE operation. In this mode, the '~; :
phase comparator 212 compares the phase of the capstan tach signal on line 208 with a tach related servo reEerence signal, which is coupled to line 258 by a variable divider 260. The variable divider 260 is controlled by a control.signal placed on ;~ `
the control line 262 by the logic circuitry 224 together with clock signals on line 264 supplied by clock circuitry 266. The 30 clook signals are in the form of a 64H reference signal provlded ~
by a conventional video reference source commonly found in video ~:

record~reproduce apparatus. The.control signal line 262 sets the 66~-' " ' ' ' ! :
' ~;

::

variable dividcr 260 so that it providcs a divided clock signal to the phase comparator 212 that maintains the specd oL ~he tape 36 at the 95~ normal srced until the initial color frame determination has been completcd, 5 as generally described hereinbefore and will be described in furthcr dctail hcreinbelow.
When the initial color frame determination has bcen complcte~, it i5 then desired to switch from the ~5% normal spccd mode to the normal speed mode, whici lO requires the tape 36 to be accelerclted up to the 100%
normal speed. ~owever, bcforc the final acccleration is perfornied, it is desirable, in addition to making the initial color frame determination, to continue the 5~ slip or slewing until the ph~se of the off tape control track 15 9~ is within a predctermined window ~hen compared with the control track reference signal, i.e., within about plus or minus tcn pcrcent (10~) of the control track servo reference signal. This is desirable in order to insure that when the control of the capstan 200 is switched to the control '~
20 track phase locl: mode frvm the capstan tach phase lock modc that there be a minimum tape velocity disturbance introduced to the tape transport servo. If, for example, the contrvl track loop was enabled when the control track was not-within the phase windo~ with respect to the 25 control track servo refercnce, an undesirable tape speed transition may occur duc to the tape transport servo loop trying to rephase the transport of the tape 36 and the transition may bc drastic enough that the initial color frame condition may be lost.

- -6-7~ - `

~ ' ~

~; : :

7~

A control track hedd 267 o the vidco Lecord/
reproduce apparatus dctect~s thc recordcd control track 94 and cooples it to line 268 cxtending to the input of the color frame detector 280 and control track phase comparator 5 270. The phase comparator 270 serves to compare thc phase of thc reproduced control track signal on line 268 with a 30 ~Iz contro] track servo rc~erence signal on line 272 from the system clock circuitry 266. The phase comparator 270 is a typical circuit cmployed in the control track 10 servo loop of helical scan vidco tape recorders, such as thc VPR-l video production recorder identified herein.
Before the tape 36 is accelerated to 100~ normal speed and the apparatus is switchcd from the capstan tach phase lock mode to thc control track phase loc~ mode, the initial 15 color frame determination is made by the color fra~ne detect circuitry 280 typically included in helical scan video recorders, such as the above-identified VPR-l video production recorder. The color frame detector 280 compares thc 15 ~17. color frame component of the recorded 20 control track 94 rcproduced on line 268 by the control ~ ~ -trac~ head 267 with a color frame reEerence signal provided on line 2g2 by the systern clock circuitry 266. ~hen the signals received by the color frame detector 280 indicate an initial color frame condition, an output signal is 25 provided on line 284 to the logic circuitry 224. Before final acceleration of thc tape 36 to 100~, normal speed, the output of the phase comparator 270 is coupled by line 274 to the input of a ., ~:
'. ' ~:

~- : ' ' ' , . t ~ :
,~ .

:; . , : ~ - : . .. :
- : : . - ~ . ~

~ ~ ~7~

typical control track crror window detector 276, such as also included in the control track sorvo loop of VPR-l type helical scan recorders. The detector 276 is further connected via its output line 27~ to the logic circuitry 224. If the control track error signal provided by the phase comparator 270 is within the error window established by the window detector 276, an enabling signal is issucd over line 278 to the logic circuitry 224.
The logic circuitry 224 responds to the afore-described inputs received from the color frame detector 280 and the control track error window detector 276 by activat-ing the control line 262 to set the variable divider 260 so that capstan tach phaso comparator 212 receives a servo refer-ence input c,orresponding to the tape 36 being transported at 15 100~ norr;lal speed. Following an interval of about 0.5 sec., during which the correctness of the initial color framing is verified as genera~ly described hereinbefore and an appropriate one track head positioning correction is made if the initial color framing was in error, the movable contact means 234 of the switch means 232 is placed in position 3. This places the capstan 200 under servo control of the control track phase comparator 270 by coupling the output line 274 of the comparator to thc summing circuit 214 via switch contact means 234 and - : :
line 244. The capstan motor 202 is now servo controlled by the recorded control track siynal via the motor drive amplifier 202 and its input line 218 extending Erom the summing circuit 214 and the record! reproduce apparatus ready for synchronous reproduction o~ the recorded signals.
-69- ~ , ~ , .

': ' , ~ :

~7~56 Specific circuitry that can be used to carry out the operation of the block dia~ram shown in FIGS. 3 and 8 are illustrated in FIGS. lOa and lOb as well as FIGS. lla, llb and llc. The specific circuitry shown in FIGS. lOa and lOb illustrate the automatic tracking circuitry shown in-the block diagram of FIG. 3, together with portions of the circuitry shown by the block diagram of FIG. lo The circuitry shown in FIGSo lOa and lOb, to the extent that it includes circuitry represented by the prior art block diagram of FIG. 1, is contained in and is also described in catalogs illustrating the detailed construction of the prior art apparatus. In this regard, reference is made to catalogs of the VPR-l Video Production Recorder, catalog Nos. 1809248-01 dated January, 1977 and 1~09276-01 dated February, 1977 prepared by the Audio-Video Systems Division of Ampex Corporation, Redwood City, CaliforniaO In this regard, the circuitry shown in FIGS. lla, llb and llc also incorporate circuitry that e~ists and is illustrated in the above-referenced catalogsO The operation of the circuitry shown in FIGS. lOaJ lOb, lla, llb and llc will not be described in detail since they generally carr~
out the operation pre~iously described wlth respect to ~' ", , , Tnc ~
. .

, .
. : ,. - ~: .
. ~. .

7~

the block diagrams of FIGS. 3 and 8. Moreover, the schematic diagrams contain circuitry ~hose operation is .not directed to the specific invention described herein and perform functions that can best be understood from the overall operation of the video production recordcr, the complcte electrical schematics of which are shown in the aEorementioned catalogs. ~lowever, to the extent that the operation of the block diagrams can be directly correlated to the speeific schematie eireuitry, referenee numbers will be ineluded thereon and certain operations will be hereinafter described.
Turning to the eleetrieal sehematie diagram of FIGS. lOa and lOb, the RF signal from the.equalizer eireuitry 74 is applied via line 75 to an automatieally ealibrat~d RF envelope detector eircuit 76 which also includes an automatic refer~nce level setting feedback loop 299. Envelope detector cireuit 76 ineludes a variable gain amplifier 301 coupled via output pin 8 to an envelope detector 303 ~pin 7) which deteets the amplitude of the RF : :~
~: - ~ :
envelope as modulated by the dither signal. Amplifier 301 -~ ~
: ~ . : ' : :: : . :: : ::

;
: .:

~ `3 4~

and detector 303 herein are integrated circuits having a standard industry designation of MC 1350 and MC 1330 respectively, wherein corresponding pin number connec-tions are identiied in the drawings for reference thereto.
As previously mentioned, the amplitude and polarity of the RF envelope modulation are indicative of the amount and direction respectively of lateral head displacement Erom track center. Therefore, it is necessary that the en-velope detector circuit 76 provide a constant demodulation gain for proper head tracking servo operation. However, detector integrated circuits such as detector 303, exhibit varying sensitivities and DC offset characteristics from chip-to-chip, which inherently causes corresponding variations, and thus ;naccurate measurement of the detected amplitudes. Likewise, different tape formulations, different heads, head and/or tape wear, variations in head-to-tape contact, etc., cause differences in recorded levels between tapes, which also results in inconsistent envelope detector circuit output signals. The feedback loop ~99 thus provides means for automatically compensat-ing for diferences between IC component characteristics, tape R~ level differences, etc., to provide a constant ;~
detector circuit 76 output under all conditions.
-~

-72~

~': ' ':
, -- .: -To this end, a capacitor 305 is coupled between the output of the detector 303 (pin 4) and a junction of switches 307, 309. The other terminals of switches 309, 307 are respectively couplecl to a 5 volt source and to the ?
negative input (pin 2~ of a differential amplifier 311.
The latter's positive input (pin 3) is selectively referenc-ed to a -~2 volt level via a resistor 281 and ~5 volt source. ~n RC network 313 and a diode 315 are coupled across the amplifier 311 negative input (pin 2) and the output (pin 1), with the output coupled in turn to the control input (pin 5) of the variable gain amplifier 301 as well as to a 12 volt source via a zener diode 317.
The switches 307, 309 are controlled via inverters coupled to the time and not time outputs (pins 13 and 4) respectively of a one-shot multivibrator 319. The one-shot generates a pulse which approximately matches the drop out interval 102 (FIG. 7a) of the RF envelope, and is clocked via the drum tachometer signal received from the drum tachometer processing circuitry over line 321, to alternately close switch 307 during the interval of the reproduced RF
envelope 100 and switch 309 during the drop out interval 102 (FIG. 7a).

;

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.

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~ ~7~i6 During each drop out interval, i.e., once or each transducing head rcvolution, the RF envclope ampli-tude is zero, i.e., there is 100% modulation o~ the envelope, whereby during each closure of the switch 309, a reference level charge of +5 volts is set between capacit-or 305 and ground. When switch 307 is closed during the reproduction of the RF envelope, the feedback loop 299 is referenced to +2 volts, thus forcing the reference level setting feedbac~ loop 299 to automatically servo a +3 volt change at the output of detector 303 and thereby provide a constant demodulator gain from the envelope detector circuit 76, regardless of any variations in the tape RF
levels, component chaL-acteristics, etc. The +3 volt change is equivalent to the average amplitude of the RF
lS envelope ~ithout amplitude modula~ion at the output of the envelope detector circuit 76 with the desired average amplitude for an unmodulated R~ envelope at the input 75.
In the apparatus in ~hich the envelope detector circuit 76 is employed, the RF enveIope will be amplitude modulated as a result of the application of the dither signal to the `~
movable element 32. 'tAverage amplitude" and "without amplitude modulation" are~used herein to define an RF
envelope whose amplitude is not modulated, except by the dither signal, if such signal is applied to~the movable element 32.

7~

3~4~S;6 Note that unlike conventional automatic gain control circuits, the reference level setting feedback loop 299 herein tak~s the reference level for the detector circuit gain control from the drop out interval 102 of the input video signal itself.

In other versions oE video record/reproduce systems, the RF envelope may not have the drop out inter-val 102 between the RF envelopes 100 (FIG. 7a). For example, the system may include two transducing heads and may instead generate a continuous RF envelope with no drop out intervals between scans across the tape. In such instances, a drop out interval, wherein the RF envelope is 100~ modulated, i.e., has an amplitude of zero, mày be .
"artificially" generated. By way of example, in FIG. lOa, a diode matrix modulator 323 may be inserted in the continuous RF envelope input on line 75 leading to the envelope detector circuit 76, as depicted in phantom line. The modulator 323 generates a drop out interval in response to the drum tachometer signal on line 321, ~ .
whereby an artificial drop out period is generated identi-cal to the drop out period 102 of previous description.

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The output of the envelope de~ector circuit 76 is, in turn, coupled to an active high pass filter 300 which passes signals above about 175 Hz to the synchronous detector 78, when the active filter is connected in the signal path. A pair of switches 302 and 304 operate to alternatively pass the signal through the filter or bypass the filter as is desired. During initial acquisition of tracking, there may be a 60Hz component present in the signal that is of much higher amplitude than the dither component of about 450 Hz and the closing of the switch 304 for about one second filters the lower frequency comp.onent from the signal until the desired tracking is achieved, at ~hich time switch 304 opens and switch 302 closes to bypass the filter 300. The switches 302 and 304 are controlled to be in opposite states by the level of the tracking delay signal placed on line 325 when an operator activates the automatic head tracking control circuitry and the coupling of the signal through an inverter 327 before applying it to the control input of switch 304.
The signal detected by the envelope detector 76 is applied to the synchronous detector 78 from either switch 302 or 304, and the synchronous detector has at ~
its other input the phase compensated dither signal ~;
received over line 87 from the commutating comb filter 306 of the automatic dither signal reference phase compensat-in~ means of the present invention described in detail hereinbelow. The filter 306 separates and phase compensates the dil:her frequency -components of the signal generated by the sense strip 83 of the bimorph element 30 and coupled to the filter via line 308 that is.connected to a sensing circuit associated with the element 30 and contained within the aforemention-ed electronic dampening circuit 71. The sensing circuitand its operation is coMprehensively described in the aforementioned application o Brown, Ser. No. ~7,~3.

~:' ~14~7~6 ID-26il Referring now to FIG. 12, which illustrates a block diagram of circuitry yenerally employiny the apparatus of this invention, the head tracking position error signal is detected hy -the envelope detector 76 and provided to the synchronous detector 78. The synchronous de-tector 73 also receives a phase compensated reference signal over line 308, which is coupled to its control input. In FIG. 12, like reference numerals identify like components .
described hereinabove. The phase compensated reference si~nal 10 is provided by a commuta-ting comb filter 306 whlch functions to separate the fundamental dither frequency component from all other components established in the movable element 32 by inducing a small oscillatory motion in the element thro~lgn the application of an oscillatory drive signal to the 15 movable element 32. The oscillatory or dither drive is applied to the movable element 32 by the dither oscillator 60. As a result of the oscillatory drive, a vibration is established in the movable element. Only the fundamental frequency component of the vibration is of interest. ~.
20 Therefore, a comb filter 306 is employed to pass the fundamental component ~hile rejecting all other frequencies .
generated by movement of the element. The frequency filtered by the comb filter 306 is processed into a reference signal of the proper phase, irrespe~-tive of 25 any changes in the mass or other characteristics of :~
.the assembly formed of the~elemen-t 32 and t.ransduciny head 30 that efect the response characteristics of the assembly.

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..... . . , , , -This processed reference signal is employed by the synchronous detector 78 for detecting the head position error signal applied to the head position servo circuitry 90 .
The s:ense strip 83 of the movable element 32 is coupled to an input of the electronic damping circuit 71 as explained more fully in the aforementioned Ravizza application Serial No. 274,424. The output signal of the sensing strip 83 is buffered in the damping circuit 71 and, subsequently~ applied to an input of the filter 306 by means of the line 3080 The second output of the .
damping circuit 71 is coupled to one input of the summing circuit 69 as described hereinbefore to provide a damping signal of proper phase and amplitude to the movable element drive amplifier 70 for compensating extraneous disturbing vibrations induced in the movable element.
The dither signal produced by the oscillator 60 (typically 450Hz for 60Hz line standard apparatus and 425Hz for 50Hz line standard apparatus) is applied :
to a second input terminal of the filter 306 by means of the line 62~ and the system clock reference signal REF 2H, is applied to a third input terminal of the filter 306 on a line 404. The output terminal of the filter 306 is ~oupled to the synchronous detector 780 The remaining circuitry of the apparatus illustrated in FIG. 12 functions in the same manner as described hereinabove with reference to FIG~
,~

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The c~mmutating comb fllter 306 is illustrated in more detail in the block diagram oE PIG. 13. The line 62, whicll transmits the dither signal to the filter 306, is coupled to the CLEAR input terminal of a counter 40S; and, the line 404, which transmits t}-e REF 2H clock signal to the filter, is coupled to the CLOCK input terminal of the counter 406. Thc counter 406 is a binary counter havin~
fGur output terminal lines ~0~ coupled to four input terminals of a one-of-ten decoder ~10. The counter 406 and the decoder 410 are illustrated in FIG. 10a (within the :
dashed-line block 306~ with their standard industry designation 74393 and 7445, respectively, along w~.th their connecting pin numbers identified .therein.
The output terminals of the decoder 410 are lS "open" collector terminals of transistors having the emitter terminals thereof coupled to ground potential. Also, `
when an output transistor in the decoder is not selected, a high impedance àppears at the corresponding output terminal.
The decoder 410 output terminals (of ~hich there are ten in this embodiment) are coupled, respectively, to one side of the capacitors Cl through C10. The second side of capacitors Cl ~through C10 are coupled to the input terminal of a buffer amplifier ~12 and to one side of a resistor R10. The second side of the resistor R10 is -77 ~
.'~

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coupled to the line 308. The output terminals of the decoder 410 are eacll cJrounded sequelltially in response to incremental counts of thc counter 406. Thus, each of the capacitors Cl throu~h C10 samples the amplitude of the sensor signal received on the line 308, and the sampled amplitudes are applied to the amplifier 412. The output of the amplifier 412, which is illustrated by the waveform shown in 14C, is applied to the input of a low pass filter 414.
Frequency components other than that of the dither frequcncy are incapable of building up the same charge on the capacitors (Cl through C10~ from cycle ~to cycle.
Thus, any char~e accumulated on the capacitors as a result of frequency components other than the dither frequency . .-will be cancelled out over time. In this manner, the commutating comb filter 306 is designed to have a narrow passhand of less than one hertz centered about ~he dither.frequency and any. frequency component outside that passband will be suppressed. Accordingly, the signal at the.output of the amplifier 412 will have a frequency component equal to the dither frequency only. A general - discussion of the opera-tion of filters, such as the combi- ' nation of counter 406, decoder 410 and capacitors Cl : . through C10, may be had by referencq to an article ::
~ 25 entitled "GET NOTCII q'S IN TIIE ~IUNDREDS" by Mike Kaufman, ' wllich was published in Electronic Design 16, August 2, 1974, at page 94.

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The low pass filter ~1~ smooths out the incre-mcntal steps in the o~tput signal from the amplifier 412, and the outp-lt of thi.s filter i5 applicd to the input of another amplifier ~16. The filter 414 causes an.unwanted phase delay in the signal. Accordingly, the output of the amplifier ~16 is applied to a leacl network 418 to compensate for this phase delay of the signal. :.
The output of the lead networ~ 418 is applied to a level detector amplifier ~20, and the output of this ampli-.'`ier is applied to the input of a limit~r 422 having an output terminal coupled to the synchronous detector 78. The level de-tector amplifier 420 and the limiter 422 operate to shape the phase-corrected and frequency-filtered signal sensed by the sensing strip 83 into a square-wave signal having a frequency and phase ~, corrcsponding to the mechanical vibrations induced in the movable element 32 in response to the applied dither signal. Therefore, the synchronous detector 78 is operated in response to -the actual mechanical vibrations lnduced in the movable element in response to the applied oscillatory dither signal. Accordingly, it may be appreciated tilat any sliyht changes in the phase of the mechanical vibration : .
. of the movable element (as may occur when the element is replaced with another, having a different resonant frequency~ will effective~'y be automatically cancelled out, thereby eliminating any need for an operator con-trolled phase adjustment of the reference signal for the .'~ :

` ' , ' :~,' ~ .. : ' ;; ~

synchronous detector i8 following a subsequen~ replacement of the movable element 32, or a transducer heacl 30 on the elemcnt.
To more fully understand the opcration of the aforedcscribed circuitry, reference is made to the wave-forms illustratcd in FIG.S 14a through l4f. When the system is operating in a slow motion or still frame mode, the oscillatory motion of the movable element 32 corres-ponds to the waveform shown in FIG. 14a. Portion 424, which is at the 6011z standard television vertical fre-quency for a single Eield still motion mode, represents the resetting of the movable element ~2 following the scan of one track to the beginning rescan of the same trac~. `
Portion ~126 of the waveform of FIG. 14a represents the oscillatory motion of the movable element 32 in response to application of -the oscillatory dither signal. The portion 426 only of the waveform 424 is filtered by the comb filter 306 from the other oscillatory motions, such as that represented by the composite waveform 424. It is noted that the dither frequency is preferrably chosen to be bet~een any of -the harmonics of the 60ilz standard television vertical fr~quency so as to avoid spectrum ~;
overlap, which overlap would prevent effective filtering of the dither frcquency from the vertical frequency.
In one embodiment for 60~1z line standard apparatus, the dither frequency was chosen at 450~1z, which is -~~77~

, . . : : , , : :

:: i between thc seventh (42011~ ancl eighth (480Hz~ harmonics of the vertical frequency. Ilowever, the dither frequency need not be at thc precise midpoint between vertic~l frequency harmonics; but may be chosen substanti~lly between such harmonics so long as there is no possibility of spectrum overlap. This may be more fully appreciated by the frequency spectrwll diagram o FIG. 15.
~n~en the apparatus is operating in the normal speed mode, the oscillatory motions of the movable element 32 correspond to the waveform illustrated in FIG. 14b.
Locations 428 in the illustrated wavDform identify the periodicity of the same vertical frequency -to be suppressed by the comb filter 306. Here, as in the waveform of FIG. 14a, it is the dither frequency components of the element oscillatory motions that are to be filtered from ;~
all other oscillatory motion frequency components cf the movable element 32.
It is noted that the waveforms shown in FIGS.
14c through 14f are illustrated on an expanded ~time scale for clarification purposes only, and should not be confused ~ith the periodic relationships of the waveforms shown in E'IGS~ 14a and~14b. The waveform shown in FIG. 14c represents the signal appearing at the output of the buffer ampllfler 412, while that shown in FIG.
; 25 14d represents the signal appearing at the output of the low pass filter 414. Note that -the waveform in FIG. 14d is delayed in phase from that shown in FIG. 14c. This ~7~6 phase delay, as stated above is caused by the low pass fi].ter 414.
The wa~eform shown in FIG. 14c represents the output signal from the amplifier ~20, and is shown to be S back in phase ~ith the signal represented by FIG. ].4c.
The waveform sho~n in FIG. 14f represents the output signal from the limiter 422, which is the wave-shaped and phase-corrected reference signal applied to the si~nchronous detector 78.

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The output of the synchronous detector 78 provides the DC error signal which is applied to an error amplifier servo compensation network 310 shown in ~IGS.
lOa and lOb and the DC error signal appears on line 80 that is applied to switches 120 and 122 as previously mentioned. The circuit 310 includes a disable switeh 312 that is controlled by line 314, which line is also coupled to control another switch 316 in the correction ~;
signal output buffer circuitry 329, which includes the movable element's drive amplifier 70. The line 314 is also eoupled to a switeh 318 assoeiated with the lebel ;
deteetors 156, 157, 158 and 160. The switches 314, 316 and 318 are operative to disable the eireuits with whieh they are associated and such is done when it is not desired that the automatie head traeking eireuitry be operating.
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7~6 For example, when the tape is being shuttled at a very fast rate, a low logic level WIND DISABLE signal is placed on line 432 as a result of an operator initiated shuttle command being provided to the record~reproduce apparatus.
During such operations, it is essentially impossible for the automatic head tracking circuitry to lock onto a track. Therefore, it is desired that the automatic head tracking circuitry be disabled and line 314 is controlled through the logic circuitry shown in FIGS. lOa and lOb when the o~erating condition of the video record/reproduce apparatus, as determined by the operator. ~hen the operator terminates the shuttle, the WIND DISABLE signal goes to a high logic signal level and the disable signal is-removed from the switches. The input signals on lines 283, 285 and 287 to the circuitry shown in FIGS lOa and lOb also, dictate that the switches to be set to disable the automatic tracking circuitry. The line 283 receives a logic level state signal indicative of whether the operator ~-has initiated operation of the automatic head tracking circuit. The lines 285 and 287 receive logic level state -signals according to whether the record/reproduce~apparatus is in a capstan tach phase lock operating mode or a ~: ~
slow/still or acceleration operating mode, respectivelyO '~
; These logic level state signals are received from the :
portion of the capstan servo circuitry shown in FIGS. lla, llb and llc.

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The circuitry for providing reset pulses to the AND gates 140, 142 and 144, as well as the color frame verification circuitry 340 described in further detail hereinbelow, includes line 182 which extends to the clock input of the latches 170, 172 and 174, to the color ~rame veriEication circuitry 340 and to the pulse and clock generator circuitry 184. The generator circuitry 184 produces the reset pulses on line 186 that extend to and are passed by any of the gates 140, 142 and 144 that are ena~led by their associated latch. The pulse and clock ~enèrator circuitry 184 includes a two stage flip-flop ci.cuit 324 that has its clock input coupled to the not true ~ -~
output of a one-shot 331 that serves to delay the genera-tion of the reset pulses so that they coincide with the occurrence of the drop out lnterval 102 (FIG. 7a). More specifically, the one-shot 331 receives the processed drum tach signal coupled to its clock input by line 182 at a time before the occurrence of the drop out interval 102 of about 0.67 msec., which, as described hereinbefore, is at the reset decision time identified in FIGS. 7 by the reference number 108. The timing circuit oÇ the one-shot 331 is set by the adjustment of the reset potentiometer 333 to have a period that produces a 0.67 msec. negative pulse :: .

~7~S6 at its not true outL-ut. T~e po~itive goin~ trailing edge of the negative pulse is col~pled to the clock input of the first stage oE the flip-flop circuit 324, which responsively conditions the second stage so th~t, upon the occurrence oE the next reference 2H pulse received over linc 322 from the studio re~erence source, the flip-flop circuiL removes an inhibitinq signal placed on the clear input, CLR, of a counter 326. In addition, the flip-flop circui~ 324 switches ~lle opposite phased signal levels placed on lines 186. Following the removal of the inhibitin~ signal from its clear input, CLR, the counter 326 counts the 2H pulses received over line 322 until it reaches its terrninal count, which takes a time of 5;2 microseconds. At this time, the count provides a signal to the flip-flop circuit 324 that clears it, which returns the flip-flop circuit to its state that provided an inhibiting signal to the counter by switching signal levels on lines 186 back to the levels that existed prior to thc receipt o~ the processed drum tach signal. This ~
20 switching of the siqnal levels on lines 186 serves to ~ ;
generate the reset pulses that are coupled to the AND ~ ;
gates 140, 142 and 144 each time a processed drum tach occurs. A reset pulse is passed by an AND gate to the integrator 134 for resetting the voltage level on its ~;25 output line 66 whenever the AND gate (or ~ND gates if a two track Eorward reset is called for) is enabled by its associated latch.

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The three threshold reference levels for the level detector 158 that are produced by the variable reference circuit 126 are shown in ~IG. lOa as being produced by the operation of open collector gates 328 and 330, which are in turn controlled by the control lines 118a and 118b from logic gates 332. The logic gatcs control thc open collector gates 323 ancl 330 in accordance with the conditions of the slow/still, 95% norma~ speed and normal speed operating mode related input signals applied to the logic gates, which appear on mode control lines 285 and 287 and at the output of the inverter 450, as shown in FIGS. lOa and lOb. -Each of the gates 328 and 330 is of the type which effectively apply a low logic signal level at its output when it receives an enabling high logic signal level at its input and, depending on which, or if both of the gates are enabled, results in a different voltagc being applied on linc 19~ which extends to the-level detector 158. ~lore particularly, when gate 330 receives a high logic signal level at its input (caused by a SLOW/STILL low logic signal level on mode control line 287 during the velocity ramp and !~
slow/still operating modes), then line 196 i5 esscntially .~
grounded (low logic signal level) to set the threshold reference level for the level de~ector 158 at a point corresponding to no head deflection in the reverse direction in the velocity ramp and slow/still modes of operation. ~ `~
If gate 328 rcceives a high logic signal level at its ~ -input ~caused by an AST tach low logic signal level on mode control line 285 during the 95% normal speed mode and r ~7~sS~i the absence of 100~ ~ach pulse at the input of the inverter 450 during the 1003 normal speed mode, i.e., during the entire capstan tach phase lock mode), then its output i5 essentially grounded and resistors 33~ and 336 comprise a S voltage divider network which applies an intermediate voltage on line 196. ~his sets the threshold reference level for the level detector i53 for the 95~ normal speed operating mode i.e., at a point corresponding to a head deflection in the reverse direction of just greater than (about 10% more than) one-half the separation of adjacent track centers. If neither of gates 328 and 330 receives a high logic signal level at their respective inputs (when in operatiny modes other than slo~/still and 95% normal), then a high voltage (high loyic signal level) appears on 15 line 196. The high voltage on line 196 disables the variable reference level detector 158. With the level detector 158 disabled, only the fixed threshold reference levles associated-with the level detectors 156 and 160 control the repositioning of the movable head in the normal speed mode. From the foregoing, it can be seen that the open collector gates function together with the source of fixed threshold reference levels to selectively cause the generation head positioning reset pulses in accordance with the operating mode of the apparatus. ;~

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, The output of the integrator 134 appears on line 66 wllich extend~ to the level detectors 156, 157, 158 and 16û for monitoring and, through gain adjustinq switch 337, through an ~C and DC correction adder circuit 338 and 5 finally to the output buEfer circuit 329 for app]ication to the second summing circuit 69 and eventually the movable element 32 (~IG. 12). The added AC error correc-tion signal is derived from the output of the error amplifier network 310 prescnt on line 80a. The error 10 correction signal provided by the error amplifier network 310 contains AC and low rate, or DC components. Line 80a extends to a band selective filter (not shown) such that the comb filter employed in the apparatus described in the .~ above-identi~ied ~avizza, et al application Ser. No.
~ Y~
15 66~ 7-, to obtain the AC error component from the compo- ?
site error signal. The AC error signal provided by the eomb ~ilter is coupled to the adder circuit 338 via input line 80b. The AC and DC head position error signals are summed together by the adder circuit 338 and the summed 20 head position error signal is coupled by line 66a to the ~`

first summing circuit 6~ for combining with the dither signal provided by the dither oscilllator 60. The output of the first summing circuit 64 is coupled by the buffer eircuit 329 to line 68 that extends to the second summing circuit 69, which adds the dampening signal provided by the electronic dampening circult 71 (FIG. 12) to form a eomposite head position error correction signal for driving the movable element 32 via the drive amplifier 70.

-a .... ' . ~, _... , ' . . , . , ; , ' ' ', ' .~' .

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A color frame verification circuit 340 shown in FIG. lOa verifies whether a correct initial color frame determination was made and, in the event the movable head 30 is scanning the wrong track for proper color framing, effectively causes it to be deflccted to the proper track before initiating normal reproduction operations in the '' normal speed mode. The color fra~e verification circuit 340 is enabled during the 100~ normal speed operating mode just prior to synchronous reproduction operations by the 100% TACH signal provided by the logic circuitry 22~ shown in FIGS. llb and llc. This occurs at the time that the control of the transport servo is switched from the capstan tach servo phase lock mode to the control track servo phase lock mode.
A signal entitled "Field Mismatch", which is coupled to one of two inverting input terminals of an AND
gate 441, is derived by the field match generator 95 (FIG.
2) of the apparatus from the video transducing head output and not from the control track read head. The field mismatch signal is derived from a comparison between the video tracks being reproduced by the apparatus and re'ference signals provided by a user of the apparatus, such as conventional studio~reference signals. Circuitry ' for deriving the field ml~smatch signal is typically found in helical scan video record/reproduce apparatus, such as the -82~-.

i6 aforementioned VPR-l video production recorder. As previously explained, if a wrong initial color frame determination has been made, the movable element 32 will be in an erroneous deflected position for proper color frame conditions. The 5 color frame verification circuit takes advantage of the condition that, iE a wrong initial color frame determination has been made, the incorrect monochrome field will be reproduced. Rriefly, however, a monochrome field mismatch is determined by applying the studio reference vertical 10 siqnal to the data (D) input of a first flip-flop, and the studio reference hori~ontal signal to the clock ~C) input terminal of the same flip-flop. Likewise, the vertical and horizontal signals reproduced by the transducing head 30 of the apparatus are applied to the data (D) and clock 15 (C) input terminals of another flip-flop. The true (Q) output terminals of these two flip-flops are coupled to two input terminals of an EXCLVSIVE OR gate, and the output of this gate comprises the field mismatch signal -referred to herein. The output of the EXCLUSIVE OR gate 20 is in opposite states for monochrome field match and mismatch conditions. In the apparatus herein, a low logic level at the input of the AND gate 441 signifies that an erroneous monochrome field match exists, hence, the ;
initial color frame determination was erroneous and a high ~i 25 logic level that a monochrome field match exists, hence, a u correct determination was made.

, .: ,. : ..

L~!~7 P~ ~ 6 When a Eield mismatch occurs, circuitry 340 applies a reset step to the movable element output bufEer circuit 329 to move the transducing head to the proper track. Alternatively, the capstan drive could be pulsed to move the tape 36 so as to position the head 30 adjacent the proper track as is the practice in the prior art.
However, it is virtually impossible in commercially practical tape record/reproduce apparatus to accelerate and decelerate the tape 36 in the short time alotted (about 0.5 msec.) to reposition thc tape within the drop out period and, therefore, it is common to experience . disturbances in the dsplay of prior art record/reproduce - apparatus when the tape is slewed to correct a field mismatch..
The output terminal of the gate 441 is coupled to-the data (D) input terminal oE a flip-flop 442 and to the inverting clear (CLR) input terminal of this same flip-flop. The true (Q) output terminal of the flip-flop 442 is coupled to the data (D) input terminal of a flip-flop 444. The true (Q) output terminal of the flip-flop 444 is coupled back to the second inverting input terminal of the AND gate 441, thereby forming a latch that compris-es gate 441 and the flip-flops 442 and 444.
A signal entitled "Video Record", which is at a .
low level when the apparatus is in a record mode of operation and at a high level during a reproduce mode of operation, is applied to an input terminal of a one-shot 446. The true (Q) output terminal of the flip-flop 446 is coupled to one of two inverting input terminals of a NOR
gate 4~8. Another input signal entitled "100% TACEI"

.... . . .

~7~

502 ~IG. 16) provided by the tape transport scrvo of the apparatus when switched to the 100% normal speed in the capstan tach lock mode, is coupled to an input terminal of an inverter 450. The output of the inverter 450 is 5 coupled to one of two inverting input terminais of the AND
gate 332, and to the second inverting in~ut terminal of the NOR gate 448.
The output terminal of the NOR gate 448 is coupled to the positive trigger input terminal of a one-shot 452. The 10 output terminal of the one-shot 452 is coupled to the clock (C) input terminal of the flip-flop 442 and to the inverting clear (CLR) input terminal of the flip-flop 444. Accordingly, a trailing positive edge transition 503a (FIG. 16) at the con-clusion of the 100~ TACH signal 502 will trigger the one-shot 15 452 by means of the inverter 450 and the NOR gate 448.
Assume for the present discussion that the ~'~
flip-Çlops 442 and 444 are reset, and that a field mis-match has been detected by the field match generator 95.
The output of the AND gate 441 will be at a high level, .
20 and the triggering oE the one-shot 452 will clock the fiip-flop 442 into a set state to enable the AND gate 456 to respond to the receipt of an inverted processed drum .
; tach at the output of the inverter 454.

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The processed drum tach signals 510 (FIG.16), which are supplied on the line 182, are applied to the input terminal of an inverter 454 and the output of this inverter is coupled to the clock (C) input terminal of the flip-flop 444 and into one of two inverting input terminals of an AND gate 456. The not true output terminal of the flip-flop 442 is coupled to the second inverting input terminal of AND gate 456. The output terminal of the AND
gate 456 is coupled to one of two input terminals of each ~-10 of NAND gates 458 and 460. When the flip-flop 442 is in a set state, as described above, the processed drum tach . ;
signal is inverted by the inverter 454 and gated through the AND qate 456 to input terminals of the NAND gates 458 and 460. On the positive-going trailing edge of this tach 15 signal, the flip-flop 444 is set which disables the ~ :~
AND gat~ 456. Consequently only one setting pulse is :applied to the NAND gates 458 and 460 in response to the single negative transition o the field mismatch signal.
~:~ The ouput of the 1evel detector 157 ~FIG. 10b), indicating the position of the; movable transducing head, (that is whether or not the head is deflected in either :
the forward or reYerse direction a distance corresponding to the separation of adjacent track centers after the initial color frame determination is complete), is .
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~ 85~

: ~: ,: :

provided on line 159; and this line is coupled to the second input terminal o~ thc NAND gate ~58 (FIG. lOa) and to the input terminal of an inverter ~62. The output terminal of the inverter 462 is coupled to the second input terminal of the N?~ND gate l60. The output terminal of the NAND ~atc ~S~ is coupled to the inverting set (S) input terminal oE the latch 170. 5imilarly, the output terminal of the NAND gate 460 is coupled to the inverting set (S) input terminal of the latch 174. The single setting pulse, generated from the processed drum tach signal and provided by NAND gate 458 or 460 for displacing the head onc track, if one of these NAND gates is enabled by the signal level appearing on the line 159, as will be furthcr described below. -Yollo~ing the generation of a reset pulse for effecting the repositioning oE the movable head 30, a field reference pulse, designated FIELD ~EF, gencrated by a conventional tachometer processing circuitry, is provid-ed on line ~64 and is coup]ed to the clear input terminal of the latches 170, 172 and 174. The field reference pulse is derived from the once around drum tachometer pulse and is timed to occur about 1/120 of a second follow-ing the tachometer pulse. Upon the occurrence of the field reference pulse, each of the latches is placed in its clear state, thereby, removin~ the enabling input from the associated AND gates 140, 142 and 144. Furthermore, in the modified form oE the automatic head tracking servo circuitry described in detail hereinafter with reference _ - to FIGS. lOc and lOd, the field reference pulse is coupled to also clear the additional latches provided for NTSC, PAL and SECAM color Erame still motion modes of operation.
-86~

~ ;-z ~ . . , . . , . . :

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: ~ : : ~ ::
.~: . . :. : :' i. :

s~

To more fully understand the operation of the aforedescribed circuitry 340, reference i~ made to FIG.
16, wherein a timing diagram illustrating operation of the track selection logic is illustrated. Waveform 500 illustrates the same tape velocity versus time profile shown in FIG. 9 and described hereinahove. Waveform 502 illustrates the 100~ TAC~I signal applied to the input terminal of the inverter 450. Portion 503 of the waveform 502 is approximately a 0.6 second window produced by a one-shot 371 included in the logic circuitry 224 illus-trated in FIG. llb, which is triggered in response to the CApst~n 200 reachln- lO~t nor~al tPeed.

-86~

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i6 Waveform 504 is a diagram of the changing track reset conditions during the transitory period of speed changing as illustrated by the waveform 500. The time periods 504a, 504b and 504c correspond to the three different modes of operation illustrated in PIGS. 7d, 7e and 7f, respectively, and described hereinabove. During the time period corresponding to the portion 503 oE the waveform 502, a track reset window is opened to plus or minus one track reset range so that if the movable head 30 is mispositioned after the inïtial color frame determina-tion in the reverse ~or forward) direction by one trac~
position, it will not be reset forward due to the threshold level provided to the level detector 158 as the automatic head tracking servo circuitry operates to correct the mispositioned 15 head 30. ~:;
Waveform 506 illustrates the signal at the true (Q) output terminal of the one-shot 452 during this transitory time period. The leading edge 507 of the pulse portion of the waveform 506 is timed to trailing edge 20 503a of the pulse portion 503 of the waveform 502.
Waveform 506' is the waveform 506 shown in expanded time scale for clarification purposes only.
Waveform 510 illustrates the processed drum tach signal applied at the input te mlinal of the inverter 454 -87~

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5, . .: , ,, , ~ ,~

and waveform 512 illustrates an crroneous monochrome ~ield mismatch, hence, erroneous initial color frame determination, and the following high levcl of the same signal illustrates a corrected monochrome field mismatch. Edge 513 is the result of correcting the monochrome field mismatch error that was represcnted by the low-level signal state at the input of the AND gate 441. The edge 513 coincides with the vertical sync of the reproduced signal (not shown), which is approximately 0.5 msec after the occurrence of edge 511b of the procesed drum tach pulse 511 that initia-tes the one trac~ head positioning step for co~recting the Eield misinatch Waveform 514 illustrates the signal appearing at the true (Q) output terminal of the flip-flop 442 as a result of the prescnce of a field mismatch when the apparatus is switched to the normal speed mode. When the waveform 512 is at a low levcl and waveform 506 ma~es a transition to a high level (i.e., at leading edge 507), the flip-flop 442 sets at leading edge 515. Waveform 516 illustrates the signal apearing at the output of the AN~
gate 456 in response to the above-described signals. In response to leading edge 515 of the pulse signal 514,the AND gate 456 is enabled to pass a setting pulse 517 to enable the setting of latch 170 or 174 as determined by the state of the forward/ reverse signal supplied on the line 159 by the level detector 157 as a result of the `
voltage level on line 66 at the output of the integrator 134. That is, if the transducing head 30 is mispositioned at the conclusion of the initial color frame determination in the reverse direction by one track position, the level detector 157 of -~8-, ~

, ~ ., . . - -:: .

s,~

the color frame verification circuitry 340 detccts an erroneous initial color frame determination and effects a one track ~orward field mismatch correcting reset movement of the movable element 32. Conversely, if the transducing S head 30 is mispositioned in the forward direction by one track position, it is d~tected by the level detector 157 and circuitry 390 effects a one track reverse field mismatch correcting reset movement of the element.
Accordingly, if the transducing head 30 is detected as being on th~ wrong track after the initial color frame determination, that is a field mismatch condition, the appropriate one of the N~ND gates 458 or 460 is enabled by the signal level placed on the line 159 by the level detector 157, and the enabled NAND gate passes the setting pulse 517 to the set (S) terminal of the appropriate one of the latches 170 or 174, if a setting pulse 517 is provided by the AND gate 456. By setting one of the -latches 170 or 174, the associated AND gate 140 or 144 is enabled and as described hereinbefore, this places a reset pulse on line 186 to be coupled to the integrator 134 for !' ~:
resetting the head 30 the necessary one track forward or reverse direction as required to obtain proper color frame field match. The direction of the reset is deter~
- ~ mined by the position of the head 30 at the occurrence of the leading edge 517a of the setting puIse 517.

r -~

Should the initial color frame determination be correct, the res-llting high level of the field mismatch signal 512 at the input of the ~ND gate 441 disables the color frame verification circuit 840 and the ~ND gate 456 5 does not provide a sctting p~llse 517 to the latches.
llence, the head 30 is allowed to rcmain in the same position after the initial color frame determination as it was at the determination.
During the time frame encompassed by pulse 10 portion of the waveform 506 (time duration of the one-shot 452) numerous processed drum tach pulses (waveform 510) occur. As briefly discussed above, only a single reset step should be applied to the movable element 32 to correct for a single detected one trac~ mispositioning of 15 the head 30. To this end, the flip-flop 444 operate`s to lock out the additional processed drum tach pulses during the color frame correction period as described above.
Waveform 518 illustrates the true (Q) output signal of the flip-flop 444 which is applied to the input of the ANV
20 gate 441. The pulse 517 coincides with the processed drum tach pulse 511. The proces~sed drum tach pulse 511 is expandccl in time for sake of clarification of the description.
The leading edge 520 of the waveform 518 provided at the output of the flip-flop . , : : . :. .-:: .

444 coincidcs with the trailing edge 511b of the tach pulse 511. This resets the latch comprising the AND gate 441 and Elip-flops 442 and 444, which disables the AND
gate 456, thereby inhibiting any additional setting pulses ~waveform 516) being applied to the NAND gate 458 or 460.
The trailing edge 521 of the waveform 518 coincides with the trailing edge 508 of the waveforln 506 as a result of the one-shot 452 being timed out. This defines a color frame correction head track adjustment window of about 0.25 second, after which no further reset pulses are applied to the integrator 134 by the color frame verifica-tion circuit 340. This condition remains until another :
color frame correction is required.

: `

.

s~

Changes in the head to track positioning errorexceeding the bandwidth of the automatic head tracking servo circuitry will not, of course, be processed and, hence, not corrected. Operating characteristics of the particular video record/reproduce apparatus, for which the automatic head tracking servo illustrated by FIGS. 10a and 10b is designed, dictated that a servo bandwidth of 30 ~z was preferred. However, some operating conditions of the video record/reproduce apparatus can result in the head 30 being mispositioned so that the resulting track positioning error signal is at a rate that exceeds the 30 H~ servo bandwidth. For example, when the video record/reproduce apparatus is in the still Erame operating mode, the automatic head tracking servo may initially provide a head positioning signal on line 66 ~FIG. 3) that causes the head 30 to be mispositioned so that at the start of the scan of the tape 36 the head starts its scan over one track, crosses the guard band between adjacent tracks and ends its scan over an adjacent track. Under these circum-stances, the track crossing of the head 30 produces a 60 Hz error signal and the head tracking servo will be unable to respond to correct the head's misposition. Instead the head tracking servo would act as if the head 30 is correct-ly positioned and, thereby, issue an output signal that leaves the head 30 mispositioned. As a-result of such - ;
cross-tracking, the resulting RF envelope reproduced by the transducing head 30 shrinks in amplitude to a minimum amplitude when the head crosses the center of the guard band. Because of limited bandwidth of the servo circuit, ~ `
a transient reset E)ulse is produced by the integrator 13 in the head positioning signal on line 66.

` -92-:! ' `~ ' : : :~ , ,: - : : ~ :

7~

This transient reset pulse typically is of insufficient amplitude to trigger the reset of the movable element 32.
Accordingly, the servo system is in an ambiguous state of scanning portions of two adjacent tracks as a result of not .resetting the position of the movable element 32 for a rescan of the first of the two adjacent tracks. The scanning path 105 followed by the head 30 along the tape 36 under such circumstances is depicted in phantom line in FIG

6.
A disturbance in the head positioning servo circuitry or in the deflection of the movable element can also lead to permanent head mispositioning. If the distur-bance is synchronous with the timing of alternate resets of -~the head position during a still ~rame mode so that such resets are not performed, the head positioning servo circuit will allow the head to scan two adjacent tracks in succession and then issue a two track Eorward reset step to the movable element 32. .The two track forward reset step is issued because after the scan of the second of the two consecutively scanned tracks, the head positioning signal provided on line 66 by the integrator 134 is in excess of both the O and 2 track forward reset threshold levels of the level detectors 158 and 156 (FIG. 3). Consequently, as previou.~ly described, a two.times amplitude reset ~93 .~ :
. .:

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: : .
: :,, . ~

pulse is provided to the intcgrator 134. As long as the synchronous disturbance persists, the movable element 32 will be controlled by ~he automatic head positioning servo to repetitively scan two adjacent tracks. If the image information contained in the two video fields reproduced Erom the two tracks contains relative movement, a horizontal jitter will appear in the displayed signal. The head positioning signal provided by the integrator 134 under such condition is depicted in the connected phantom lines 103 and 104 in FIG. 7c.
Ambiguous track lock resolving circuitry 342 (portions in both FIGS. lOa and lOb) prohibits the servo system of the apparatus from locking in the aforementioned ambiguous states when the video record/reproduce apparatus lS is operating in a still frame mode. The circuitry 342 is disposed for detecting such a reset failure at the end of a scan of a single track when the apparatus is in the still frame mode of operation. One-shot 343, having an input terminal coupled to receive a signal on input line 339 derived ;
from the reproduced control track pulses 94 detects the absence of tape motion such as occurs during the still frame mode of operation. The output of one-shot 343 is coupled to one of two input terminals oE a NAND gate 345, and the output terminal of this NAND gate is coupled to the set input terminal of the latch 172.
j ~
- - - .

.

' ' - .. . .: 1 ~ , : . -. : .

~ ~7~S~
The not tru~ ou~put terminal of the latch 172 is coupled to one oE two input terminals of the AND gate 142, and the second input terminal of this AND gate is coupled to receive, over one of the lines 186, the reset pulse ~rom the not true output terminal of the flip-flop circuit 324 located within the pulse and clock generator circuit 184. In the still frame operating mode, the output terminal of the gate 142 should produce a reset pulse for stepping the movable element 32 every head revolution. In addition, the output of the AND
gate 142 is coupled to the negative trigger input terminal of a one-shot 347, and the true output terminal of this one-shot is coupled to one of two input terminals of a NAND gate 349. The positive trigger input terminal of the one-shot 347 is coupled to +5 volts, and the one-shot time duration is determined by the time constant of the associated resistor/capacitor network coupled to pins 14 and 15 of this one-shot. The not true -output terminal of the one-shot 347 is coupled to a set input terminal of another one-shot 351.
The embodiment shown in FIGS. lOa and lOb is arranged for controlling the tracking position of the scanning head 30 ; when NTSC standard television signals are recorded and reproduced by the apparatus described herein. ~odifications of the automatic head tracking servo shown in FIGS. lOa and lOb for controlling the scanning head's tracking position when other television signal standards, such as PAL and SECA~, are recorded and reproduced by the apparatus described herein are shown in ~IGS.
lOc and IOd. For NTSC tolevision signals, one-shot 347 is set for a timing of approximately 25 msecs., and the one-shot 351 is set for a timing of 160 msecs. Thus, the resulting 25 msec. pulse provided by the one-shot 347 is greater than the interval between consecutive reset pulses provided to the AND gate 142, and less than the time required between two consecutive reset pulsès. As descrlbed hereinbefore, a ~ ~95~
: , ; : :;

reset pulse is provided by the pulse and clock generator circult 324 for each revolution of the head 30, hence, at a frequency of a 60 Hz. Consequently, if a reset pulse is not provided at the output of the AND qate 142, the one-shot 347 will time out and, thereby, set the one-shot 351 and condition the NAND gate 349. The setting of the one-shot 351 corres-ponds to the time required for approximately ten consecutive reset pulses. Conditioning of the NAND gate 349 in response~
to setting of the one-shot 351 will condition the NAND gate 345, which wlll hold the latch 172 in a set state for the approximately ten reset pulse time period. Accordingly, ten consecutive reset pulses will be provided at the output terminal of the AND gate 142, at the proper times for such reset pulses, to thereby reset the output of the integrator 134 an amount equivalent to a forward 1 track deflection of the ~.ovable head 30 and force the servo system out of the ambiguous state. -, :~ ' , ' ~; ~ :
' ' - ~ .
' '~ ;'`':;

- . . . . :

- . - , ~ ::- . :. ~ .

7~

The modifications to the automatic head tracking servo circuitry shown in ~IGS. lOa and lOb to condition the circuitry for still mode operations during which multiple fields are reprocluced from a plurality of tracks and to condition the ambiguous track lock resolving circuitry 342 for proper operatio-~ with a signal standards other than NTSC, as briefly discussed hereinabove, are illustrated in FIGS. lOc and lOd. The illustrated modifications permit operations with PAL and SECA~i'television signals. Ths line 182, which transmits the processed drum tach signal, is coupled to the clock input terminal of an 8-bit divider circuit 380 formed of three flip-flops 381, 38~ and 383 coupled in a conventional cascaded manner. Also, -the line 182 is coupled to a position 1 contact terminal of a switch 384. The output terminals of the flip-flops 381, 382 and 383 are coupled to position 2, 3 and 4 contact terminals of the switch 384~ T4e operating terminal of the switch 384 is coupled to junction 183 along line lg2, which extends to the reset enabling latches associated with the integrator 134, flip-flop circuit 32~ and color frame verification circuitry 340 (FIG. lOa). The "Field .~'.ismatch" signal, as discussed above, is applied to the inverting clear input terminals of the flip-flops 381, 382 and 383 to inhibit operation of the divider 380 until a field match condition exists. Changing the position of the movable con-tact of the switch 384 results in changing the number of processed drum tach pulses required to be received over line 182 before a reset pulse is pro-vided to the AND gate circuitry connected to line 132. This ; permits thc frequency of the reset signal provided to the integrator 134 to be selectively varied for different still frame modes.

' ' ' '-97-4 ~::

:: . . ~ :

': ': .: ' : ~ : : ' :

Switch 384 is mechallically coupled to switches 386 ancl 387, having operating terminals thereoE cou~led to the ~5 volt supply. Positions l-q of the swltchcs 384, 386 and 387 correspond to one another so that when switch 384 is in position 1, switches 386 and 387 are also in position 1. The position 1 contact terminal of the switch 386 is coupled to pin 15 of the oneshot 347 througll resistor R20, and position 1 of the s~itch 387 is coupled to pin 7 of the oneshot 351 through resistor R22. The values for the resistors R20 and R22 are the same as that discussed above to provide a 25 msec. time duration for oneshot 347 and a 160 msec. time dnration for oneshot 351. With the movable contacts of switches 386 and 387 in position 1, the ambig-uous track lock resolving circuitry is arranged for opera-tion in the still frame mode wherein a single field is repetitively reproduced to generate a still display.
The three contact terminals (positions 2; 3 and 4) of switch 386 are coupled through resistors R24, R26 and R28, respectively, to pin 15 of the oneshot 347. Positions 2, 3 and 4 of the switch 387 are similarly coupled through resistors R30, R32 and R34 to pin 7 of the oneshot 351.
The values for the resistors R26, R28 and R30 are selected to provide time durations of 50 msec., 100 msec. or 200 msec., respectively, of the oneshot 347. Simllarly, the values for the resistors R30, R32 and R34 are selected to ;~
provide time durations of 320 msec., 640 msec. or 1280 msec., respectively, of the oneshot 351.
With the movable contact of the switches 386 and 387 respectively in one of the positions 2, 3 and 4, the am~iguous track lock resolving circuitry 342 is arranged for operation in one of the still frame modes, wherein a .... ... .
. . .

: - .:

~7~5~

two (for monochrome frame), four (for NTSC or SECAM color frame) or eight (for PAI. color frame) field sequence, respectively, is repetitively reproduced to generate a still display.
The values of the capacitors bridging the pins 15 and 1~ of the oneshot 3~7 and pins 7 and 6 of the oneshot 351 remain unchanged in `this embodiment. ~owever, the eapacitors could also be switehed while maintaining the value o~ the resistors constant, or both the capacitors and resistors could be conjointly changed, to change the time eonstants of the oneshot circui-ts as recluired for the desired still frame operating mode.
When switches 38~, 386 and 387 are in positions 2, 3 or 4, the processed drum tach pulses are divided by two, four or eight, respectively. Accordingly, the position of the transducing head 30 will be reset after scanning the seeond, fourth or eighth consecutive field of the reeorded information as selected by the mechanically coupled switches 38~, 386 and 387. However, the amplitude of the reset signal applied to the movable element 32 is correspondingly selected by the threshold circuitry operated in conjunction with the associated latches and gates as shown in FIG. lOd and described in greater detail hereinbelow. Because the movable contact of the switch 384 is ganged to operate with those of switches 386 and 387, the proper divided proeess drum taeh signal is provided in the seleeted still frame mode for effeetincJ issuanee of the correcting head position reset signal to the movable element 32. ~ ~

; .
-. - . . I :
,.................................................. ~ I
. . . ` I ', , . , ::
.. . . . ~ .

,, . . , , Thus, it may be appreciated that when the apparatus is operating in the still frame mode, an operator places the switches 384, 386 and 387 in position 1 Eor scanning a single field between resets of the transducins head 30. If, however, it is desired to scan two consecutive Eields between resets of the head, such as for a complete monochrome frame, the operator places these switches in position 2. Position 3 of these switches will cause the transducing head 30 to scan four consecutive Eields between resets which will produce a complete NTSC color frame, or a jitter-free color frame Eor SECA~ television signals. The position 4 of these switches will cause the apparatus to produce a complete color frame from PAL television signals, when such signals are recorded on the tape.

' ~ -1 00-': ' ' , ~ :
:: :

.-;~
`~`'.'' ' ~7~i6 Thc modified c.ircuitry for generating the appro-priate reset pulsc of current that is coupled by linc 132 (FIG. 3) to cause the integrator 134 to effcct a correspondin~ly appropriate reset of the head position for the various single and m~lltiple field still mode opcrations is shown in FIG.
lOd. In the same manncr as described hreillbefore, the vari-able threshold reference source 126 establishes head reset determing threshold voltage levels for the level dctector 158 and associated .~ D gate 142 that generates, in response to the head deflection signal lcvel on line 66, the appro-priate forward head position reset current pulse placed on line.132 for operating modes below normal speed. Also, the level detectors 156 and 160 receive the Eixed threshold voltage leve]s 1 track reverse and 1 track forward, respect-ively, for effecting the appropriate reset of the mo~/able head 30 as described hereinbefore. For still mode operations, wherein a single television field is repetitively repro-duced Erom the tape 30, the level detec~or 158 receives a thresllold voltzge.from the.reference source 126 corres?onding to any head deflection in the reversc direction. At the -occurrence Oc each processed drum tach pulse, the movable element 32 carrying head 30 will be in a deflected condition -correspondi.n~ to reverse directioll head deflecti.on at the conclusion of the scan of the track by the head. Therefore, the level detector 158 enables the latch 172 which, when clocked places an enabling signal on one of the inputs of the associated ~ND gate 1~2, which passes the following ; reset pulse coupled to its other input by line 186 that .
extends from the fl.ip-flop circuit 324 (PIG. lOa) of the -101~-: :~
' ! , ~: . ...... . . ~ . . ` . `

- , - : : ` : ~ : "

pulse and clock generator 184 (PIG. 3~. The sin~le reset pulse pased by the ~ND c~ate 1~2 is eonverted by the resistor -1~8 to a puls~ of eurrent on line 132 at the eonclusion of eaeh revolution, hence, scan of a track, by the head 30, or at a frequency of 60 Hz in a 60 Elz field rate standard and at a frequeney of 50 Elz in a 50 Hz field rate standard.
T.his effeets a 1 track fon~ard reset of the head so that it . -101~
, , . "

~:~7~

rescans the track during its next rcvolution. ~s long as the record/reproduce apparatlls is in the single field, still motion mode, the head 30 is repetitively reset by reset pulses of current generated by the AND gate 142 and asso-ciated resistor 148, whereby a single television field is repetitively reproduced from a repetitively scanned track.
For monochrome frame (composed of two interlaced odd and even television fields), still motion operating modes, level detectors 156 and 158, together with associated latches 170 and-172, AND gates 140 and 142 and cùrrent forming resistors 146 and 148, f~mction to provide a two track fon~ard reset current pulse over line 132 to the inte-grator 134, ~hich responsively causes the repositionins of the movable head 30 after every two revolutions of the head to the track containing the first field of the repe-titively reproduced two field sequence. ~his is accomplished ~;
by placing the movable contact of the switch 384 at the output oE the eight bit divider circuit 380 (FIG. lOc~ in position 2. With the switch 384 so positioned, the eight bit dividcr circuit 380 provides frequency divided processed drum tach pulse and reset pulse on lines 182 and 186, respectively, at the completion of every second revolution of the track scanning head 30, or at a frequency of 30 E3~ in a 60 Elz field rate standard and at a frequency of 25 EEz in a 60 }3z field rate standard.
Since the reset current pulses will be pro~ided to the integrator 134 after every two revolutions of the head 30, the integrator will provide a head deflection ramp -102~-~ ~

.:

signal, lasting for two head revolutions bet~een consecutive reset eurrent pulses, that deflects the movable element 32 a distance in the reverse direction eorresponding to the distance separating thrce adjacent traek centers.
Therefore, upon the oecurre.nce of the :~', ::

-102~
, ..
,:

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.... .. . . . .

frequency divided processcd drum tach pulse on line 182, both level detectors 156 and 158 are cond;tioned by the signal level on line 66 exceeding the threshold levels established Eor the latches, as described hereinbefore, to provide signals on lines 164 and 166, respectively, coupled to the D input of the latches 170 and 172 that enable the following associated ~ND gates 140 and 142 to p~ss frequency divided reset pulses when received over line 186.
As ~escribed hereinbeEore with reference to FIG. 3, the two reset pulses passed by the ~ND gates 140 and 1~2 are con-verted to corresponding current pulses by the resistors 146 and 1~8 and added tosether to produce a two track forward reset current signal on line 132. The two track fonward reset signal causes the head deflection sisnal on line 66 to be reset and, thereby effect a two tracX fon~ard deflection of the movable ele~lent 32 after each reproduction of a two field sequence. In this manner, a monochrome frame still image is provided by the record/reproduce apparatus for all televlsio~ sign~l st~ndards.

.

-10~
`', :; ' "

: . : . . . .' . : .:

s For color frame still ~notion operating n~ocles with NTSC and SEC~M standard sic;nals, four consecutive television fields are repcti~ively reproduccd in sequence to ~orm the still motion color image. In these modes, a level detector 550, toge~her with associated latch 552, AND
gate 554 and resistor 556 connected to the output of the AND gate 55~, function together to provide an additional two trac~ forward reset current pulse over line 132 to the - integrator 134. The impccianee value of resistor 556 is selected to be one-half the value of the resistors 146 and 148 ~resistors 146 and 148 being of ecIual value) so that a single reset pulse passed by ~ND gate 554 will be con-vcrted to a two track forward reset current pulse on line 132. In these still frame modes, AND c;ates 140 and 142 together also cause a two track for~iard reset current -- - pulse to be provlded over linc 132, ~hieh is added to the additional two trae~ forward reset current pulse to form a four trac~ forward reset current signal for effecting a repositioning of the head 30 after four revolutions.
The integrator 13~ responds to the four track for~:ard reset current signal on line 132 to cause the reposition~
ing of the movable head 30 to the track containing the first - .
field of a repetitively reproduced four field sequence after every four revolutions of thc head. This is ac-complished by placing the movable contact of the switch 38~ at the output of the eight bit divider circuit 380 (FIG. lOc) in positlon 3. ~ith the switch 384 so positioned, the eight bit divider eireuit 380 provides frecluency dividccl processed drum tach pulses and reset pulses on line 132 and 186, ... .. . . . .
. .
.. ,,, '' , ::

respectively, at the completion of evcry fourth revolution of the track scanning head 30, or at a frequency of lS ~Iz in a 60 ~Iz field rate standard and at a frequency of 12.5 ~z in a 50 ~Iz field rate standard.
Since the reset current pulses will be provided to the integrator 134 after every Eour revolutions of the head 30, the inte~rator will provide a head deflection ramp si~nal, lasting for four head revolutions betwecn consecutive reset current pulses, that deflects the movable element 32 a distance in the reverse direction corresponding to the distance separating four adjacent track centers.

-104~-.

... .. . .
:r - - - , . . .. . .~
' .

Therefore, upon the occurrcnce of the frequency divicled processed drum tach pulse on line 182, all level detectors 156, 158 and 550 are conditioned by the signal level on line 66 excecding the threshold levels established for the latches to provide slgnals to the D input of the latches 170, 172 and 552, respcctively, that enable the following associated A~D gates 140, 142 and 554 to pass frequenc~
divided reset pulses when received over line 186. For all color frame still motion modes, regardless of the television signal standard, a fixed head reset de-terming threshold voltage level is provided on line 558 extending to one of the inputs of the level detector 550 corresponding to a head deflection in the reverse direction equal to the distance separating the centers of four adjacent tracks.
As described hereinabove, the three reset pulses ;~
passed by the AND gates 140, 142 and 554 and converted by resistors 146, 148 and 556 to the appropriate pulse c~rrent levels are added together on line 132 to produce a four track forward reset siqnal at the input of the integrator 134.
The four track forward reset current signal causes the head deflection signal on line 66 to be reset and, thereby, - effect a four track forward deflection of the movable element 32 after each reproduction of a four field sequence. In this manner, either an NTSC or SECA~I color (depending on the siqnals being reproduced) still motion image is provided .
by the record~reproduce apparatus. ~ ;

-105-- "

::. ~ - , : . :: : :

For P~L standard color frame (composed of eight consecutive televisioll fields) still motion operating modes, a level detector 560, together with associated latch 562, AND gate 564 and current forming resistor 566 connected to the output of ~ND gate 564 function together to provide an additional four tr.ack fo~ard reset current pulse over line ].32 to the integrator 134. To form the four track forward resct current pulse from a single reset pulse passed by ~ND gate 564, the impedance value of the current forming resistor 566 is selected to be one-quarter the value of resistors 146 and 148. In this s~ill frame mode, AND gates 140, 142 and 554 also cause a four track forward reset current pulse to be provided over line 132, which is added to the additional four track forward reset current pu].se to form an eight track forward reset current signal for effecting a respositioning of the head 30 after eight rcvolutions. The integrator 134 responds to the . :
eight track forward reset current singal on line 132 to cause the repositioning of the movable head 30 to the track con- ~ .
taini.ng the first field of a repetitively reproduced eight ~ :
field PAL color frame sequence after every eight revolutions of the head. This is accomplished by placing the movable contact of the switch 384 at the output of the eight bit ~ ;
divider circuit 380 tFIG. lOc) in position 4. With the :
: 25 switch 384 so positioned, the eight bit divider circuit 380 .
.~ provides frequency divided processed drum tach pulses and ~: reset pulses on lines 182 and 186, respectively, at the ,, ~ completion of every eighth:revolution of the track scanning ~:
head 30, or at a frequency of 6.25 ~Iz in a S0 Hz field rate . 30 P~L standard. . .
-106~

-,.. :.~..

t~56 Since tho reset current pulses will bo provided to the inte~rator 134 after every eight revolutions of the head 30, the integrator will provide a head deflection ramp signal, lasting for eight head revolutions between consecutive reset current`pulses, that deflects the movable element 32 a distance in the reverse direction corresonding to the distance separating eight adjacent track cen-ters.

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., : .

~s~

Therefore, upon the occurrence of the frequency divided processed drum tach pulse on line 182, all le~el detectors 156, 158, S50 and 560 are conditioned by the signal level on line 66 yo provide signals to the D input of the latches 170, 172, 552 and 562 respectively, that enable the following assocaited AND gates 1~0, 1~2, 55~ and 556 to pass frequency divid~d reset current pulses when received over line 186.
For the P~L color frame sitll motion mode, a fixed eight -track reverse reference threshold voltage level is provided over a line 572 ex-tending to one of the inputs of the level detector 560. As described hereinabove, the four reset pulses passed by the AND gates 140, 142, 554 and 56~ and converted by resistors 196, 1~8, 556 and 566 to the appropriate current pulse levels, are added togehter on line 132 to produce an eight track forward reset signal at the input of the integrator 134. The eight track forward reset signal causes the head deflection slgnal on line 66 to be reset and, thereby, effect an eight track forward deflection of the movable element 32 after each reproduction of an eight field PAL color frame sequence. In this manner, a PAL color frame still image is provided by the record/
reproduce apparatus. It should be appreciated -tha-t when the record/reproduce apparatus is not operated to repro-duce multiple field still mo-tion displays, the variable thres-hold reference source 126 is set to place disabiling signals on lines 558 and 572 extendirlg to one of the inputs of the level detectors 550 and 560, respectively. As described hereinbefore with respect to the function of level detector 154 ~
..
, , ' ' ~ ~'' '' ' - . :

. ` , : ' : ': ': ' ~: ' : ' .

in the other operating modes of the record/reprocluce apparatus, this prevents the level detectors 550 and 560 fro~. enabling their associated AND gates to pass reset pulses to the line 132 (PIG. 3~ that controls the resetting of the integrator 134.

lQ7 s The modificd por~lon of the automatic heacl tracking servo circuitry shown in FIG. lOd coopcrates with the modified portion of the scrvo circuitry shown in F~G. lOc to provide the required reset pulse signal for the various still frame operating modes described hereinabove to prevent the servo system oE the apparatus from locking in the ambiguous states described hereinabove. In this respect, line 574 extends from the NAND gate 345 (~IG. lOa), which provides the aforedescribed latch hold signal lasting for a period of ten reset pulses. The unmodified head tracking servo circuitry shown in FIGS. lOa and lOb is arranged to provide a latch hold signal only to the set terminal of the latch 172 because the servo circuitry is arranged to produce still ~otion displays from a single repetitively reproduced field and this requires o~ly a one track forward reset of the head 30. In a monochrome frame still motion mode, a 2 track forward reset signal is required because two consecutive fields are repetitively reproduced. To provide a 2 -track forward reset signal for the ten-reset-pulse period, a switch 576 is closed when operating in thc monochrome frame s~ill motion mode so that the set terminal of the latch 170 also receives the latch hold signal placed on line 574. Since both latches 170 and 172 are placed in the set state for the ten-reset-pulse period, their associated AN~ gates 140 and 142, respectively, are enabled for the same period, which, as described herein~
before, results in the generation of a 2 track forward reset current signal on the line 132 extending -to the input of the integrator 13 : ~:

., .~ .

. . : . . .
.. . . .

In either an NTSC standard or SlC~M standard color frame still motion operation, a 4 track forward reset curren~ signal is required because four consecutive fields are repetitively reproduced. To provide a ~ track fon~ard reset current signal for the ten-res~t-pulse period, both switches 576 and 578 are closed when operating in all color frame still motion modes so that the set terminals of the latches 170 and 552 also rcceive the latch hold s;gnal placed on line 574. Since the three latches 170, 172 and 552 are placed in the set state for the`ten-reset-pulse period, their assoc ated AND gates 140, 142 and 554, respectively, are enabled for the same period, which, as described hereinbefore, results in the generation of a 4 track fon~ard reset current signal on line 132.
In the P~L color frame still motion mode, an 8 track forward reset current signal is required for the ten-reset-pulse period because eight consecutive fields are repetitively reproduced. To effect the generation of an

8 track forward reset current signal for the ten-reset-pulse period, a switch 580 is also closed so that the set terminal of the latch 562 also receives the latch hold signal placed on line 574. Since all of the latches are placed in the set state for ten-reset-pulse period, their associated A~D gates are enabled for the same period, which, as described hereinbefore, resutls in the generation of an 8 track forward reset current signal on line 132.

109t , ' ,. ~.

, `

q~ :

The excmplari e~.bodiment of the automatic head tracking servo circuitr~ shown in FIGS. lOa and lOb have provisions for performing other special functions in accordance with certain input signals received. For e~ample, because the head positioning error signal typically is a low rate error signal in normal speed operating modes, it is advan-tageous to sample the sync}lronous detector output signal on line 80 during the intermediate portion of the scan of a track by the rotatins head 30. For this purpose, a normally open s~itch 122 (FIG. lOb) is interposed in the line 80 of tlle head position error feedback path extending between the output oE the synchronous dctector 78 and the input of the integrator 134. During normal speed modes, the AUTO TP.~ signal on input line 283 enables an NAND gate 429 to pass a DC G~TE signal provided on input line 430. ~:~
- The DC GATE signal is derived from the 60 llz drum tach signal and is delayed to occur interm~diate of consecutive drum tach signals. The DC GATE signal is passed by the ~ :
NAND gate as a low level pulse signal lasting for about 4 MSEC. If the.automatic head tracking circuit shown in ~
FIGS. lOa and lOb is switched on, the following low level - ~ :
. AND gate 431 issues a high level. pulse corresponding in ~ :
duration to the DC Gf~TE signal to enable thc switch 122 . . to pass the low. rate head positioning error signal to the integrator 134, which responds by adjusting the DC level of -the head position servo correctio~ signal provided on ~ -line 68 extending to the second summing circuit 69 (FIG. 12).
~.
The automatic head tracking servo circuit also :
; includes means to disable it in the event the drum portion 22 of the tape guide drum assembly 20 (FIG. 9), hence, -109~

- , . . - . .:
;~
. - ., . . .. , . . . : . . . : . ~ . :

~7~

movable hcad 30 is not rotating. If the drum portion 22 is not rotatin~, a low logic signal level is placed on input line ~3~ (FIG. lOb) that is processed by the logic circuitry 111 of the automatic head tracking servo circuit to provide disabling signals that open switches 312 and 316.
Frequently, a recorded tape will be played back on different record/reproduce apparatus. In many instances, the recording apparatus an~ reproducing apparatus will be charactcrized by diEferential geometric head-to-tape tracking trajectory variations that lead to interchanqc errors.
Because such geometric variations are random in na-ture, severe mistracking conditions can occur during reproduction operations. To facilitate the control of the movable head 30 so that the tracks of such recordinss can be precisely follo~ed, a switching means 433 is included in the dither oscillator 50 that is controllable by an operator to double the amplitude oE the dither signal provided to the movable element 32 via the line 62. The twice amplitude dither signal is selected by an operator causing, through suitable control device, a high logic level AST RANGE signal to be placed on input line 435. Applying a twice amplitude dither signal to the movable element 32 has the efEect of increasing the servo capture gain of the head tracking servo circuit, thereby extending the servo capture range.
As previously described herein, the movable element 32 has a limited range over which it can be deflected. For record/reproduce apparatus previously constructed for commercial applications, this range has been selected to be a distance ; ~ ~ :
corresponding to + 1.5 times the distance separating adjacent -losd~
':

, ~
.
'~ . -- - ; ~

track centers To facilitate trac~ing of the recorded information without the introduction oE undcsirable disturbillg effccts in the reproduced signals ~:hcn the apparatus is operated in the a~oredescribed e~tended range, the apparatus includes an automatic tape slew drive conmand signal gen-erator 436, which is responsive to thc combined DC error plus head deflection signal present Oll linc 66a to generatc one or ~ore trac~ sle~ tape drive co~mands on the appropriate one of the o-ltput lines 437 and 438. These lines extend to thc capstan motor drivc amplifier 220 for coupling the tape sle~ commands thereto. Because of the severc mistracking conditions encountered in t}ie extended range operating mode, the movable ele~ent 32 frequently is displaced to~ards one of its limits. To maintain the movable element ~ithin its deflection range in such mode of operation, the generator 436 is arranged to provide a slew command to the capstan motor drive amplifier 220 whenever the deflection of the movable element 32 exceeds ~ 15~ of the distance separating adjacent track centers. In this manner, the movable element 32 is maintained ~ithin its deflection range limits~ In the event the movable element 32 exceeds the 15% deflection limit-in the for~ard deflcction direction, the head deflection threshold referencc level associated with the tape slew reverse control is exceeded and SLF.Il R~V commands are provided by the generator 436 over output line 438 to slo~ down, or reverse the direction of the transport of the tape 36, whichever is needed. SLE~
Fh'D commands are provided by the generator 436 over line 437 when the movable element 32 exceeds the 15% deflection limit -in the reverse deflcction direction.

~ ~ ?
:.:
-1oge~ ' , , ; : ,, .: ~ : ~ .: . :

-: ~ ~ , : : ~ .. -Turning now to FIGS. lla, llb and llc, there is shown one embodiment of specific circuitry that can be used to carry out the opcration of a portion of the ~rans-port servo illustrated by the block di2~ram of FIG. 8.
The portions of the tape transport servo sllown in the block diagram of FIG. 8 not included in FIGS. lla, llb and llc are those previously identified, namely, the control trac~ phase comparator 270, control trac~ error window detector 276 and color framc detector 280, as being in-cluded in typical helical scan video rccord/reproduce apparatus that provide signals used by the tape transport servo to carry out its operations. Furthermore, the trans-port servo is arranged to control the transport of the tape 30 so that the record/reproduce appratus can be oper-ated to record and reproduce television signals of both 50 Hz and 60 f~z line standards. The 50/60 ~z signal level placed on the input line 338 sets the transport servo in the operating condition necessary for the television signal standard of concern. The specific circuitry shown in FIGS. lla, llb and llc is arranged to control the transport of the tape when recording or reproducing NTSC television signals for PAL and SECAM television signals, certain timing provided by the transport servo circuitry sho~m in FIGS. lla, llb and llc is preferably changed to account ~ ~;
for differences in the timing associated with such signals, which changes will be readily apparent from the following description of the transport servo and, hence, need not be descri~ed in detail herein.
, .

' ~ , ~
.. . -~ : -^ :
- - - - - . . . :

: :: :: -:. : - .- :-: ~

~47~

The recorcl/r~produce apparatus, for which the transport servo illustrated by FIGS. lla, llb and llc is constructed, has several operatinq modes that can be selected throuqh the operation of operator controls, with each operating mode requiring a different response from the illustrated transport servo. In slow/still operating modes, an operator initiated slow/still mode command (SLOW) is placed on input line 353 (FIG. lla) and is coupled thereby to condition the logic circuitry 224 (FIG. 8) so that the transport servo provides the required control of the transport of the tape 30. At tape transport speeds less than 95% normal speed, the transport servo provides velocity control of the transport of the tape 30.

'~

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,- ; .
:, ,~ , :

s.~

With reference to FIG. lla, velocity control of the tape transport at less than normal spceds during slow/
still operating modes is provided by t~le variable slow motion control circuitry 2~tO. The control circui.try gene-ates 5. the variable capstan drive for driving the capstan motor 202 (FIG. 8) within a speed range from a very slow speed up to a maximum of about 95~ of normal speed. The operation of the entire circuitry 240 i~ described in detail in the afore-~ ~7,~Z3 1 mentioned application of Mauch, Serial No. ~7-~,7~. The variable width pulses generated by the variable slow motion control circuitry 2~0 for driving -the capstan motor 202 in velocity control servo modes of operation at speeds below the cross-over velocity of about 1/5 normal speed are pro-vi.ded on line 242 in response to the pulse reference signal received over input line 355, whi.ch is a level and gain adjusted signal corresponding to the setting of the potentiometer 240' (FIG. 8). At tape transport speeds :
below the cross-over velocity, a velocity drive control circuit 356, which is coupled to examine the output of the fre~uency discriminator circuit 210, issues a command over one of the control lines 230a that causes switch means 226 ~
to co~nect the pu].se drive outpu-t line 242 of the variable ~:
slow motion control circuitry 240 to the motor drive amplifier 220 (FIG. 8) via line 218 and disconnects the capstan and control track phase comparators 212 and 270 from the capstan motor drive circuitry. This circuit condition corresponds to the block diagram illustration of FIG. 8 :~:

.. ... ~ . : . -.~ , , . - - ,, . ~ - . .

~4~56 with the movahle contact means 228 of the switch means 226 in position 1.
The tachometer input appears on line 208 in the upper left'corner of PIG. lla and is coupled for processing by tachometer input processing circuitry 352, the processed capstan tachometer signal being coupled to the input of the velocity loop frequency discriminator 210, The velocity loop frequency discriminator is operatively connected to a velocity loop error amplifier 354 and the velocity drive switch control circuit 3~6 to provide velocity control over the transpo~ of the tape 36. When the potentiometer 240' (FIG. 8) of the variable slow motion control circuitry is adjusted to cause the capstan 200 (FIG. 8) to be driven to '-transport the tape 36 at speeds within the range of about 1/6 to 1/3 normal speed, the velocity drive switch control circuit 356 responds to the velocity related signal level provided by the frequency disc~iminator 210 and a following inte-grating circuit 357 by issuing commands over control ine .
230a that toggles the switch means 226 respectively between its two conditions. As described in detail in the afore-mentioned Mauch application, Ser. No. -37~ 3, toggling .
switch means 226 a~ternately couples to the capstan motor drive amplifier 220 (FIG. 8) via,line 218 the puise drive .

signal present at line 242 of the variable slow motion circuitry 240 and the analog drive signal present on line 2i7, which is generated by the frequency discriminator 210 and associated circuitry in response to the tape velocity ' .. .
, ~ ' .

7~

related signal in ~he form of proc~ssed capstan tachometer signals and a vclocity reference signal generatcd by the vclocity reference circuitry 250. ~ tape speeds in e~cess of 1/3 normal specd the switch me~ns 226 is maintained in a condition to couple the ~rive si~nal generated by the cooperative action of the velocity reference circuit 250 and the frequency discriminator 210. In these higher slow motion operating modes the tape transport specd is con-trollcd by the potenti.ometer 240 (FIG. 8) whicll i.s con-nected to provide the slow speed control signal on input line 363. A command placed on con~nand linc 252a by the logic circuitry 224 enabl.es a switch means 362 to permit the slow speed control signal to be coupled to establish a voltage level at the input of an integrating circuit 15359 of the velocity reference circuit 250 that corrcsponds to the setting of the potentiometer 290 . The output signal provided by the velocity reference circuit is coupled to one input of a summin~ junction formed by a sun~ing amplifier 361 for subtraction with the velocity feedbac~ signal generated by the frequency discriminator 210 and coupled to another input of the summing amplifier 361. ~ny difference bet~een the signals represents a tape velocity error and is coupled as a velocity error signal to the output line 217 of the velocity loop error amplifier 35~ for application to the capstan motor drive amplifier 220 (FIG. 8) via s~itch means 226 and line 218.
~ he transport servo also provides velocity control over the transport of the -tape.30 whenever the rccord/
reproduce apparatus is operated to accelerate the tape to enter a normal reproduce mode of operation. A normal speed reproduce mode of operation is initiated by the `~ .

. . ` , ' ,, , - , . ~ .
.
. . . ~ : , . ~ :
~ . . , . :

7~5~

oper~tor ac~ivatin~ contrOls t~-~at p]aces a PL~Y modc command si~nal on linc 364, whic~ callscs thc loqic circ~litry 324 to place t~l~ con~land on the command line 252h that results in thc generatio,~ of a volta~e step on line 363. Thc inte(Jrating circuit 359 responds to the voltage st~p by gcncratin~ on its output line 254 a ramp signal of a fi~ed, selccted interval for application to the summing amplifier 361. As descrihcd hereinbcfore, the output of thc summin~ amplifier is coupled to drive the capstan motor 202 and, ~ihen the sul~ing amplifier 361 receives a ramp signal from the intecJratin~ circuii, the capstan motor 202 is caused to accelerate according to the slope of the ramp si~nal.
The tachometer referencc divider 260 is shown in FIG. lla and is controlled by control line 262 which has a lo~l logic level when the tape 30 is transported at the 95%
of norm~l tape speed and a higll logic level when it is transported at lO0~ of normal tape speed, with the line 252 extcndin~ from logic circuitry shown in FIG. llc. The transport servo is placed in the capstan tach phase lock modc by an operator initiated PLAY modc command coupled to input line 364. Initially, the transport servo logic circuitry places the transport servo in the aforcdescribed acccleration mode of operation for a predeterlllined acceleration interval o~ about 0.5 sec., if the tape 30 is - stopped at the time the PLAY modc command is received and a correspondingly shorter time if the tape is already in motion when the PLAY command is received. The interval is , set to provide sufficient time for the servo to establish the desircd veloc:ity controlled servo lock condition.
-114~- -... , ' - ~' - .
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,s . .. :. ~:, :

: ~ :. :: ` `.` . - : : . `` `

~7~6 A one-shot 365 providcs a settling dclay oE about 0.3 sec.
after control of the transport servo is switched to the capstan tach phase comparator 212. Upon initiation of the 0.3 sec.
settling dclay interval, the logic circuitry issues a conunand over one of the control lines 230b to close the switch 232a (FIG. llc) and, thereby, allow the capstan phase comparator 212 to be coupled to control the capstan drive. In addi-tion, the logic circuitry places a low logic level on line 262, which causes the variable dividcr 260 to generatc a 95Do normal speed mode servo reference signal from the 6~1 clock on input line 26~, which reference signal is coupled by line 258 to the input of the capstan tachometer . .
servo loop phase comparator 21 (FIG. llc). ~ny phase error between the capstan tach signal received Otl input line 208 and the 95D~ normal speed ~ode servo reference signal is detected by the phase comparator 212, which responsively provi~es a proportionate voltage level signal on the input line 369 of a tachometer loc~ error amplifier 360 shown in FIG. llc.

,,,~ ,, ., ' . '`~ ' ` ' . , ~

.. . . .

7~

The output of the tachometer ]oop error amplifier 360 is coupled by the closed switcll 232b (~hich corresponds to the movable contact means 23~ of the s~itching means 232 shown in FIG. 8 being in position 2) to line 2~1 that.
extends to the summing junction 2l~1 and, as described here-inbefore, eventually to the cal?stan drive ampliEier via line 218 for driving the capstan 200 undcr the desi.red capstan tach phase lock conditions.
Servo control of the transport of the tape 30 is switched from 94% normal speed capstan tach phase lock mode to the 100~ normal s~eed capstan tach phase lock mode ~hen the initial color framing is co~plete, i.e., the correct field sequence for proper color frame conditions is rep3:0duced, and the detected control trAck error is within the afore-descri~ed + 10~ window dcfined by the control track servo reference siqnal, so that thc initial color ~ran~e condition will not be lost when servo control is switched. The :
logic circuit portion 374 (FIG. llb) primarily coordinates the acquisition of the correct field for reproduction operations and controls the switching of the -transport ~:
~. .
servo system from the caps-tan tach phase lock mode to the :
control track phase lock mode. When the initial color -frame opcration performed with respect to the reproduced :
control track signal is complete, the color frame detector 25 280 (FIG. 8) provides a high logic siqnal level, designated ~ .`
CT COLOR FI~IE, at its output on line 28~1a (FIG. llb), -115- `,- .`

: ' ' - ~.

~ ~.;, .

.. ~.. .. , .: . ,. , .. ., ' ,. .:

~7~5~i which extends to a pair of cascaded D latches 373 included in the portion 37~ of the logic circuitry. Also, a studio reference signal, designa-te~ CT R~F, is coupled by the line 28~b to the clock input of th~ first of the cascaded D latches 373. The CT R~F signal is a 30~1z-logic level changing signal having a low-to-high logic signal level transition displaeed in time relative to the oeeurrence of the 30~lz st~dio control track reference by an amount equal to 1/60 sec. This signal serves to clock the level of the CT COLOR FRA~IE signal present on line 284a to the second of the caseaded D latehes. ~hen the control traek error signal present on line 274 at the output of the eon-trol traek phase eomparator 270 is within the aforedeseribed - 10~ error window, the control track error window deetector -eireuit 276 (~IG, 8~ generates a high logie signal level, designated CT WINDOI~T, on line 278 extending to the eloek input of the second of the caseaded D latehes 373~ If this oeeurs following the establishment of the proper eolor rame reproduetion eonditions, the low-to-high signal level transition of the CT ~INDOW signal elocks the proper eom-plemen-tary logie signal levels at the output of D lateh eireuitry 373. These signals eondition the following logie eireuitry to eause a high logie signal level to be plaeed on line 262, whieh sets the variable divider 260 to generate a 100% normal speed mode eontrol traek servo referenee ` signal. This servo referenee signal is eoupled to line 258 , , , - . '.~'; -. ' ~, .~ , , . :
. ~ ,~_ . ., , '.

that extends to the input of the capstan tachometer servo loop phase comparator 212. Because at this ti~e the tape 30 is being transported at a speed corresponding to 95% of the normal speed, the capstan tach phase comparator 212 generates an error signal that is processed by the tachometer lock error amplifier 360 to provide a corresponding capstan motor drive signal for accelerating the transport of the tape 36 to the normal speed characteristic of normal motion reproduction operations. After a settling interval of about 0.6 sec. determined by the active interval determining time constant of the one-shot 371, the logic circuitry 224 generates a CT SERVO command over control line 230c (FIG~ . llc) that closes switch 232b while simultaneously opening the switch 232a by terminating the switch closure command on line 230b. Placing switches 232a and 232b in the afore-described states corresponds to the movable contact means 234 of the switching means 232 shown in FlGo 8 being in position 3. Opening the switch 232a removes the capstan tach phase comparator 212 from tape transport servo loop.
The closed switch 232b couples the control track error signal generated by the control track phase comparator 270 on the line 274 to the summing junction 214 and, as described hereinbeEore, eventually to the capstan motor drive ampliEier 220 (FIG. 8)- for providing the drive to the capstan 200 ; under the desired control track phase lock conditions.

~ mg/~ 117 ~

.

~7~6 As previously discussed herein, the control o~
the tape transport servo is coordinated with thc control of the automatic head trac~ing servo circuitry sho~n in ~IGS. lOa and lOb. This coordination is accomplished primarily by the portion 370 of th~ loqic circuitry shown in FIGS. llb and llc, which couplcs the appropriate coordinating control siqnals to the automatic head tracking servo circuitry over lines 372a, 372b, 372c and 372d.
~lhen the apparatus is operatincJ in the slow/still mode, the logic circuitry portion 370 places a low logic signal level on line 372a that enables the automatic head tracking servo circuitry to control the position of the movable head during slow/still modes of operation. ~hen the apparatus is operating in the capstan tach phase lock mode during both the 95~ and 100~ normal speed modes, the logic circuitry portion 370 places a low logic signal level on line 372b a~ter the control of the transport servo is s~itched to the capstan tach phase lock mode. This signal is designated AST TACH and is coupled by line 372b to condition the automa-tic head tracking servo circuitry to control the position of the movable head during capstan tach phase lock mode tha-t occurs during the 95~ and 100 normal speed operating modes. When the transport servo is commanded to accelerate the tape 36 to a speed corres ponding to 100~ normal speed, the logic circuitry portion 370 places a low logic level pulse 503 (~IG. 16) on line 372c, which has a duration of about 0.6 sec. This signal, -.

~ 118- ~ ~

,, , 1' , , . ~ :
.

.

design~ted 100~ TACII, is coupled to the automatic head tracking servo to condition it for controlling the position oE the movable head at thc completion of the initial capstan tach phase lock mode portion of the 100% normal speed mode. As described hereinbefore, the presence of the lO0~ TACH pulse signal at the input of the inverter 450 (FIG. lOa) disables the level detector 158 by con-ditioning the associated open collector gates of the variable reference threshold level source 126 to place a high voltage level on line 196. Consequently, only the level detectors associated with 1 TRX REV and 1 TRK FWD threshold - levels are enabled to control the position of the movable head 30 during the 100~ normal speed mode. Furthermore, the trailing edge 503a (FIG. 16~ of thc 100~ TACH pulse enaole~i ~he color frame verification circuitry 340 to respond to the ~IELD MIS~ATCII signal present at the one of the inputs of the AND gate 441 to reposition the movable head 30 a distance in the appropriatedirection corresponding to the distance separating adjacent track centers in the event a field mismatch is detected at the time control of the transport servo is sw~tched to the control track ;~
phase comparato~ 270 (FIG. 8)~
. Synchronous reproduction of the recorded sign~ls uncler automatic head tracking servo conditions is commenccd in resporlse to the provision of the AUTO TRK . ;~
. signal on line 372d àt the conclusion of the 100% TACE~ .

,~
:

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., , . , ~:

- - . , . ~ . .

7~5~

signal if an ACT ~UTOTR~ enabling mode command si~nal is received on input line 358 as a result of an operator initi<lted control switch. Thc ~UTO TI~K signal occurs simultalleously with the preserlce of t~le CT SE~VO signal on the control line, which as described hereinabove, inserts the control track phase comparatox 270 in the transport servo for controlling the transport of the tape.
The ~UTO TRK signal is couple~ to mode control line 285 of thc! automatic head trac~ing servo to condition it for controlling the moval;le head during the normal speed mode as previously described herein.
The exemplary embodime2lt of the transport servo shown in FIGS. lla, llb and llc have provisions for performillg other special functions in accordance ~ith certain input signals received. For e~le, the logic circuitry 224 includ~s means to inhibit sequencing of transport servo if certain operating conditions are not satisfied. If the drum portion 22 is not rotating, hence, record and reproduce operatiolls not being carried out, a DRUM OFF high logic signal level is provided by the apparatus on input line 368 (FIG. lla) that inhibits the logic circuitry sequence. Similarly, in the event re produce~ video is not present, the apparatus inhibits the logic circuitry sequence by removing an enabling high logic level P~F PR signal from the input line 375 (FIG. llb).
If the video signal is being reproduced from a tape that does not include a recorded control track sign~l (or the control track signal is momentarily lost), the logic circuitry sequence is interrupted at (or returned to) the 95% normal speed mode condition and servo control of the ``
transport of the tape 30 is retained by the capstan tach .
,, :

~47~16 phase comparator 212 as a result of the r~moval of the high logic level CT ~R signal from input line 376 (FIG. llb).
Automatic resumption of the transport servo sequencing occurs if the switch 293 (FIG. llb) has its movable contact in the AUTO position. If the s~-itch 293 is in the ~1~N posi-tion, resequencing of the transport servo is initiated by causing one of mode commands to be placed on an input line to the transport servo.
The transport servo is also arranged to permit control of the transport of the tape 30 with respect to a remotely occurring event, such as the recording on a remotely loca-t~d record/reproduce apparatus of the video signal reproduced by the record/reproduce apparatus con-trolled by the illustrated transport servo. Program editins is an example of this. In such operations, the transport of tape 30 must be carefull} controlled rela-tive to the transport of the remotely located tape so that the reproduction of -the video signal from the tape 30 is . initiated at the desired instant. To release tlle transport servo to rer~ote control, an operator initiated low logic siqnal level, designated TSO mode command, is placed on the input line 377 (FIG. llb). The logic circuitry responds io the TSO mode command~signal by placing the transport servo in the velocity servo mode and enabling the tape ;
speed override circuitr~ 378 (FIG. llc) to couple on ~;~ external velocity reference signal to the input of the , s~lmming amplifier 361~(~IG.~lla) for comparison with the velocity feedbac~ signal gcnerated by the frequency discriminator 210. Thusly, the tape 30 is transported at 30~ ~ a speed determined by the external velocity xeferencc `~

~7456 siynal present at the input line 379 of thc tape speed override circuitry 378.
Reverse tape drivo operations are controlled by the transport servo by cou~ling operator initiated mode command signals, designated REV JOG ENABLE and REV JOG S~ITC~i, to the input lines 290 and 291, re-spectively. The generation of these two signals is initiated by adjusting the potentiometer 240' (FIG. 8) to provide reverse velocity drive. Signal processing circuitry, like that provided for processing the ~ULSE RE~
and SLOI~ SPEED CONTROL signals, generates the REV JOG
EN~LE and the ~EV JOG SWITCH signals. The REV JOG SWITCH
mode command signal is coupled to place the capstan motor 202 in the reverse drive operating condition, as long as the reverse tape velocity is less than about 1/3 normal tape speed. The REV JOG ~ABLE mode con~mand signal condi- -tions the variable slo~ motion control circuitry 240 -to provide reverse tape motion velocity control in the same manner as described hereinbefore with respect to forw~rd tape motion velocity control at reverse ~ape speeds less than about 1/3 normal tape speed.

: - , : - ~

: ~ : , :, ~ 122~

, From the foregoing description, it should be appreciated that a method and apparatus has been described which is particularly adapted for use w:ith a signal record/
reproduce apparatus of the type which has a transducing head that is movable to automatically follow a track during the transfer of information with respect to the record medium and which can then move the transducing head to the appro-priate track depending upon a mode of operation of the apparatus. By uniquely controlling the interaction of the transport servo system that controls record medium movement as well as the automatic tracking circuitry that controls transducing head movement, non-disruptive, noise free transfers of information, such as a video image can be maintained, even though significantly different circuit operations occur.
The resul~ing advantages are most evident in the absence of disturbing eEfects in the transferred information during the mode transitions, which are an important operationai con-sideration in commercial broadcasting of television informa- ; :~
tion where such problems are avoided wherever possible. In 20 addition, by employing processed signals generated by the ;~
; dither motion of the movable element itself as reference ::
;~ signals for the automatic head tracking circuitry, any ;~ changes in the natural resonant frequency of the transducing head assembly are automati~cally compensated. An~exemplary advantage of this arrangemeDt is that fewer manual adjust~
ments a~e required following replacement of the transducing head assembly.

It should be understood that altllough prcferred embodiments of the prcsent invention have been illustrated and described, various modifications thereof will become apparent to those skilled in the art; and, accordingly, the scope of the present invention should be defined.only by the appended claims and equivalents thereof.
Various features of the invention are set forth in the following claims.

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Claims (8)

WHAT IS CLAIMED IS:

1. In a recording and/or reproducing apparatus having transducing means operatively supported for transferring information with respect to tracks along a record medium the transducing means mounted on movable means for displacing the transducing means in opposite directions in response to signal being applied thereto the combination comprising:
means for generating an oscillatory signal coupled to effect oscillatory motion of said movable means;
signal generating means responsive to the oscillatory motion of said movable means for generating a signal representative of the motion of said movable means;
means responsive to a signal representative of the position of said transducing means relative to the tracks along the record medium and a reference signal for controlling the position of the movable means; and means responsive to said signal representative of the motion of said movable means for producing the reference signal.

2. A circuit as in Claim 1 further characterized by said signal representative of the motion of the movable means is an oscillatory signal and said means for producing the reference signal includes means for filtering a selected frequency component from said oscillatory signal representative of the motion of the movable means for generation of said reference signal.

3. A circuit as in Claim 2 further characterized by said means for producing the reference signal includes wave-shaping means coupled to an output of said means for filtering for forming said reference signal from the filtered frequency component.

9. A circuit as in Claim 2 further characterized by said means for filtering comprising a commutating capacitor filter operative in response to reference timing signals.

5. A circuit as in Claim 1 wherein said signal representative of the position of the transducing means is an AC signal of a frequency corresponding to that of the oscillatory signal applied to the movable means, said reference signal producing means provides an AC signal of a frequency corresponding to that of the oscillatory signal applied to the movable means, and said transducer position controlling means includes a synchronous detector responsive to the AC signals.

6. A circuit as in Claim 5 wherein the signal representative of the motion of the movable means is an oscillatory signal, and said means for producing the reference signal includes a controllable filter means coupled to receive the signal representative of the motion of said movable means and the oscillatory signal generated by the signal generating means and responsive to pass a selected frequency component of the oscillatory signal representative of the motion of the movable means.

7. In a recording and/or reproducing apparatus having transducing means operatively supported for transferring information with respect to tracks along a record medium, the transducing means mounted on movable means for displacing the transducing means in opposite directions generally transverse to the direction of said tracks in response to signals being applied thereto, a method of controlling the position of the movable means, said method comprising the steps of:
oscillating the movable means to displace the transducing means in opposite directions generally transverse to the direction of the track followed by the transducing means, sensing the oscillatory movement of said movable means;
sensing the position of the transducing means relative to the tracks along the record medium; and adjusting the position of the transducing means relative to the tracks along the record medium in response to a comparison of the sensed oscillatory movement of the movable means and the sensed position of the transducing means.

8. A method as in Claim 7 wherein the said step of sensing the oscillatory movement of the movable means includes sensing a selected frequency component of said oscillatory movement of said movable means.