GB1579854A

GB1579854A - Method and apparatus for producing time base altered effects in data recording and reproducing apparatus

Info

Publication number: GB1579854A
Application number: GB1050577A
Authority: GB
Original assignee: Ampex Corp
Current assignee: Ampex Corp
Priority date: 1976-03-19
Filing date: 1977-03-11
Publication date: 1980-11-26
Also published as: AT385382B; CA1252205A; JPH0534723B2; JPS6348081B2; FR2345035B1; FR2345035A1; NL7702995A; DE2711703A1; DE2711703C2; JPH03162709A; ATA188177A; JPS52117106A; IT1073210B

Description

(54) METHOD AND APPARATUS FOR PRODUCING TIME BASE ALTERED EFFECTS IN DATA RECORDING AND REPRODUCING APPARATUS (71) We, AMPEX CORPORATION, a Corporation organized and existing under the laws of the State of California, United States of America, of 401 Broadway, Redwood City, State of California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention generally relates to the playback of data, particularly television signals, recorded in oblique tracks on an elongate record medium, such as a magnetic tape, and is intended to facilitate the production of the effect of an altered time base in the played back signals.

The invention is particularly (although not exclusively) intended for application to helically scanning machines. In such a machine when it is used for recording signals are recorded in tracks which extend obliquely across a tape at an angle which is determined by the rate of rotation of the scanning head and (to a lesser but still significant extent) by the rate of lengthwise movement of the tape. If the tape's speed is changed for playback, a pick-up head will not follow the recorded track precisely and may even cross onto an adjacent track.

The noise that is produced when a head crosses from one track to another is troublesome and attempts to subdue it have not been particularly successful. In consequence, the simulation of changed motion, such as slow motion, stop and fast motion effects have heretofore not been successfully produced by helical-scan machines.

According to the invention, there is provided a method of recording or playing back a signal in which method a transducing head disposed on a carrier and an elongate record medium are moved such that the head is caused to scan the medium along each of a succession of parallel tracks, each of which extend in a direction which is obliquely across the medium and the head is, during its scanning along each track, progressively displaced relative to the carrier in a sense which is transverse to the said direction of the track.

It is normally intended that the lengthwise velocity (which may be zero) of the medium is such that an action which the signal represents appears to occur at a changed rate when played back.

The invention is particularly intended for a machine in which the medium is an elongate tape which is disposed in a helical path and the carrier is a cylindrical drum which rotates about its axis to effect the scanning of the tape by the head. The invention also subsists in a helically-scanning recording or playback machine which is capable of recording a signal in, or playing back a signal recorded in, a succession of discrete parallel tracks each extending obliquely across a magnetic tape and which comprises a transducing head for scanning the tape, a rotary carrier, a guide for constraining the tape to follow a helical path around the carrier, and a mount which carries the head and is borne by the carrier and which is deflectable relative to the carrier to permit displacement of the head to and fro in a direction transverse to the tracks in accordance with applied control signals, means being provided to apply to the mount control signals for displacing the head in respective opposite senses during the scanning of the tape and between scannings respectively.

Reference will now be made to the accompanying drawings, in which: FIG. 1 is a schematic illustration of a helical scanning drum simplified for the sake of clarity; FIG. 2 is a part-sectional view of the scanning drum shown in FIG. 1, with portions removed; FIG. 3 shows an enlarged segment of magnetic tape having tracks A-F recorded thereon; FIG. 4 is a further simplified view of an omega wrap helical recording apparatus; FIG. Sa is a displacement pattern for a transducing head when the apparatus is operating in a skip field mode; FIGS. Sb-Sd are displacement patterns for a transducing head when the apparatus is operating in a slow motion mode; FIG. Se is a displacement pattern of a transducing head when the apparatus is operating in a still frame or stop motion mode; FIG. Sf is a displacement pattern for a transducing head when the apparatus is operating in a surveillance mode; FIGS. Sg and Sh are displacement patterns for a transducing head when the apparatus is operating in fast motion modes; FIGS. Si and Sj are displacement patterns for transducing heads when the apparatus is operating in slow motion and normal speed, respectively, with the tape being transported in the reverse direction; FIG. 6 is a schematic block diagram illustrating the electrical circuitry associated with the apparatus embodying the present invention; FIG. 7a is a voltage output wave form produced by the circuitry shown in FIG. 6 for producing the displacement pattern for the half speed slow motion operation shown in FIG. Sb; FIG. 7b is a voltage output wave form of the circuitry shown in FIG. 6 for producing the displacement pattern for the slow motion reverse direction operation shown in FIG. Si; and, FIG. 8 represents electrical schematic diagrams of one form of circuitry that can be used to implement the block diagram of FIG. 6.

Broadly stated, the present invention is directed to a method and apparatus for successfully achieving altered time base reference effects in the art of recording and reproducing information signals on a medium. While it is suited for use in many different kinds of signal recording applications, the present invention is particularly useful in creating altered or special motion effects from video signals.

While a variety of video recording formats exist and may be adapted to the present invention the invention is particularly intended for use with helical tape recording apparatus to achieve special motion effects such as slow motion, fast motion and stop motion, with the slow and fast motion being carried out in both the forward and reverse directions. Thus, it is contemplated that the present invention can be used with quadrature, segmented helical and arcuate types of video tape recorders, in addition to the various helical tape recording formats.

While the present invention will be specifically described in connection with an omega wrap helical video tape recording apparatus, it is equally applicable to an alpha wrap helical tape recording apparatus. Additionally, while the present invention will be described in conjunction with a 360" omega wrap apparatus (it being understood that the tape does not contact the drum a full 360" because of tape entrance and exit dimensional requirements), the present invention is also applicable to helical video tape recorders which utilize less than 360" wrap, e.g., a 1800 wrap tape path apparatus having more than one head. It should also be understood that the present invention is applicable to arrangements where the scanning head can move in either rotational direction and the tape can be introduced either above or below the exit path and moved around the scanning drum in either direction. The relationships of head rotation, tape transport direction and manner of tape guiding, i.e., introducing the tape above or below the path of its exit, can represent up to eight different configurational relationships of which only one will be specifically described herein as shown by the direction of the arrows in FIG. 1 of the drawings.

Broadly stated, the present invention is directed to a method and apparatus for accurately positioning a transducing head to follow a track and to rapidly position the transducing head, if necessary, at the beginning of the track that is desired to be followed next. The next track that is to be followed is a function of the mode of operation that is selected. In the playback of video signals, the various modes may include slow motion effects, speeded up or fast motion effects, as well as stop motion or still frame effects. Moreover, other modes of operation may include skip field recording and compensating playback, as well as a surveillance mode which greatly increases the period of time that can be recorded on a given length of tape (at the expense of continuity of motion), it effectively skipping a great number of fields, such as recording one of every sixty fields, for example. The apparatus permits the tracks to be accurately followed, even though the transport speed of the tape can vary within wide limits. In the event fast motion effects are to be achieved, during the playback of video signals, the transport speed of the tape must be increased and, conversely, for slow motion effects, the transport speed must be slowed down. A stop motion effect requires that the same fields be reproduced many times and in such condition the tape is not moving at all, the relative motion between the tape and the transducing head being supplied by the rotation of the scanning drum carrying the same. Since changing the tape transport speed changes the headto-track angle as well, it is apparent that the video transducing head that is carried by the scanning drum would not exactly follow the track when the transport speed of the tape is altered, in the event the transducing head is maintained in a fixed position.

The present invention comprises means for moving the transducing head transversely relative to the longitudinal direction of the tracks of the information and thereafter selectively alters or changes the position of the head so as to correctly position the head to commence following another track, the track being a track other than the next adjacent successive downstream track if the position of the head is in fact changed. It should be understood that during recording, one complete revolution of the scanning drum causes the transducing head to record a track at a predetermined angular orientation relative to the length of the tape and at the end of the sweep, the movement of the tape causes the recording head to be gradually displaced a predetermined distance downstream in position to begin recording the next adjacent successive track. In this manner, the tracks are recorded parallel to another and, assuming the transport speed of the tape is maintained constant as is the speed of rotation of the scanning drum carrying the record transducing head, the tracks will have a constant spacing relative to adjacent tracks, i.e. the center to center distance between adjacent tracks will be substantially constant in the absence of geometric errors that can be introduced due to stretching, or other temperature or humidity induced dimensional changes of the tape or by faulty tensioning mechanisms in the tape transport or the like.

Turning now to the drawings and particularly FIGS. 1 and 2, there is shown a helical video head scanning drum, indicated generally at 10, with portions broken away in FIG. 2. The scanning drum is shown to comprise a rotatable upper drum portion 12 and a stationary lower drum portion 14, the upper drum 12 being fixed to a shaft 16 which is rotatably journaled in a bearing 18 that is mounted on the lower drum 14, the shaft being driven by a motor (not shown) operatively connected thereto in a conventional manner. The scanning drum 10 has a video transducing head 20 carried by the rotational drum portion 12 and is shown to be mounted on an elongated movable support element 22 that is in turn mounted at one end in a cantilever type support 24 that is fixed to the upper drum portion 12. The element 22 is preferably of the type that flexes or bends in a direction transversely of the recorded track during playback with the amount and direction of movement being a function of electrical signals being applied thereto, all of which will be described in detail hereinafter.

As best shown in FIG. 1, the scanning drum 10 is part of a helical omega wrap video tape recorder which has the magnetic tape 26 advancing toward the drum in the direction of the arrow 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 28 which brings the tape into contact with the outer surface of the stationary lower portion 14 whereupon the tape travels substantially completely around the drum until it passes around a second guide 30 which changes direction of the tape as it exits the scanning drum after it has been either recorded or played back.

As is best shown in FIGS. 1 and 4, the omega wrap video tape recorder is of a configuration such that the tape being introduced is in a noninterfering relationship with the exiting tape in the sense that they do not require being crossed over one another as in the alpha wrap format and, for this reason, the lower portion of the exiting tape can overlap the upper portion of the tape being introduced so as to provide a small unrecorded band that can be used for audio and control signals and the like. The overlapping segment A is shown in the lower portion of the tape illustrated in FIG. 4.

As is best shown in FIGS. 1 and 3, the configuration is such that the tape does not contact the scan drum surface over a full 360 because of the clearance that is required for entrance and exit of the tape. However, this gap preferably does not exceed a drum angle of more than 16 which has the effect of creating a dropout of information. The drop out is preferably chosen so that the line interval that is lost does not occur during an active video line and the start of a scan of a track is field synchronized. As will be more fully explained hereafter, the dropout in the omega wrap configuration can be used to advantage.

As previously mentioned, the transducing head 20 is mounted upon the elongated movable, preferably flexible element 22 which may comprise an elongated two layer or bimorphous element which supports the transducer. It preferably comprises a thin leaf bimorphous or two layer element which exhibits dimensional changes in the presence of the electric or magnetic field and may be constructed of two layers of material suitably bonded together, at least one layer of which is piezoelectric, electrostrictive or magnetostrictive, although a bimorpher or bimorph cell comprised of two piezoelectric layers with their axis of polarity oriented in such a way that application of a field causes the deflector to flex or bend is preferred. In this regard, reference is made to our copending applications Nos. 10260/77 and 10036/77 respectively (Serial Nos. 1579853 and 1579852), which are directed to a deflecting element and mounting structure of this type. Another configuration that is electromechanically driven for moving the head transversely of the tracks in a manner that achieves the same result as the deflectable bimorph is also disclosed in Application No. 10036/77 (Serial No. 1579852).

The deflectable element 22 is effective to move the transducing head 20 mounted thereto in a vertical direction as shown in FIG. 2 in accordance with the electric signals that are applied thereto through conductors 32 from circuitry schematically illustrated by block 34. The head 20 is mounted so as to extend slightly beyond the outer surface of the rotating drum portion 12, the head extending through an opening 36 in the outer surface thereof.

By using the thin leaf piezoelectric bending element to suspend the transducing head for controlled positioning with respect to the magnetic tape, it is cantilevered from the support 24 that is attached to the rotating drum portion 12 for controlled positioning with respect to the magnetic tape. Thus, the deflectable element 22 is adapted to sweep or bend and displace the transducing head in response to applied electric field signals. The cantilevered deflectable element 22 is arranged with the direction of bending motion of its free end carrying the transducing head along a path that is transverse to the direction of relative motion of the head with respect to the magnetic tape, i.e. the direction of the recorder tracks. Preferably, the thin leaf piezoelectric deflectable element extends from the rotating drum normal to a plane tangent to the recording surface at the point of head-to-record surface interface and substantially parallel to the direction of relative head-to-record surface motion. The transducing head 20 is mounted on the outer free end of the piezoelectric deflectable element 22 for operative engagement with the magnetic tape such that its transducing gap is oriented to have the gap length in a direction of width dimension of the deflectable element and its gap width in the direction of the thickness dimension of the deflectable element, hence in a direction transverse to the direction of relative motion between the head and the tape.

In order to respond rapidly to positioning commands and follow changes in the command signals, a low mass thin leaf piezoelectric element construction is preferred. Moreover, the thickness of the deflectable element relative to its width should be such that virtually no deflection or movement of the transducuing head can occur in a direction other than transverse relative to the track length. Thus, by applying appropriate signals to alter the position of the transducing head during operation of the apparatus, it should be understood that the head can be moved from side to side relative to the track being followed and if an appropriate error correcting signal is obtained, the head can be moved so as to accurately follow the track during playback. In this regard, the aforementioned copending applications describe two apparatus for generating error correcting signals for application to the drive circuitry for the deflectable element to cause it to move the transducing head into an accurate tracking position. The apparatus provided by either of these auto tracking head applications effectively produce error correcting signals that are applied to the deflectable element 22 which moves the transducing head into coincidence with the track from the start to finish thereof which occurs during one complete revolution of the scanning head 10.

If the transport speed of the magnetic tape is changed relative to the speed in which the information was recorded, then the effective angle of the helix is changed and error correcting signals will be produced for the purpose of having the transducing head follow the track at the different angle. Since the deflectable element is movable in either direction, the tape can be transported around the scanning head at either a faster or slower speed relative to the record speed and the element can position the head to follow the track being reproduced for either condition.

In accordance with an aspect of the present invention and referring to FIG. 3, a segment of tape 26 having a number of tracks A through F thereon is shown together with arrows 40 and 42 which illustrate the direction of tape motion around the scanning drum 10 and the direction of head scan relative to the tape itself, respectively. The orientation of the tracks and the arrows shown in FIG. 3 coincide with what is produced by the movements of the scanning drum 10 and tape 26 shown in FIG. 1 (see arrows 44 and 46). With a constant transport speed and angular velocity of the scanning drum portion 12, tracks A through F will be substantially straight and parallel to one another at angle 8 (of about 3 , for example) relative to the longitudinal direction of the tape, with the rightward tracks shown in the drawing being subsequently produced during the recording operation.

Since track B, for example, would be recorded immediately after track A was recorded during constant scanner rotation and tape transport speeds, it should also be appreciated that if these speeds are maintained during the reproducing or playback operation, the transducing head 20 would playback track B during a successive revolution immediately after having reproduced the information from track A.

If conditions were ideal and no distortion was introduced, then the transducing head 20 would simply follow the successive adjacent tracks without adjustment, since no error signals would be produced for transversely moving the transducing head 20 relative to the track. Stated in other words, the transducing head is automatically in position to begin reproducing the subsequent track B after completing the reproducing of the information from track A. It should also be appreciated that even if the tape transport speed is varied relative to the transport speed during record, and the angle of the track is thereby changed relative to the transducing head, if it is transversely moved to maintain accurate tracking through playback of the track, at the end of the track being played, it is nevertheless in a position to begin reproducing the next adjacent downstream track, i.e., track B in the event A was completed. This occurs even when the tape is stopped or is traveling slower or faster than the transport recording speed.

To achieve special motion and other effects during reproduction of the information signals that are recorded on a video tape or other medium, it is necessary to vary or adjust the transport speed of the tape around the scanning drum. To produce a speeded up or fast motion effect, the transport speed is increased relative to that which was used during recording. Similarly, to produce slow motion effects, it is necessary to reduce the speed of the transport tape around the scanning drum relative to that which was used during the recording process. Stop motion requires that the tape be stopped so that the transducing head on the scanning drum can repetitively reproduce the information signal from a single track.

In accordance with the present invention, the apparatus can be placed in different modes of operation wherein either forward or reverse motion effects are achieved and the motion can be speeded up or slowed by simply adjusting the transport speed of the tape in such forward or reverse directions to obtain the desired speed of motion during playback. Once the direction is chosen, the apparatus is effective to automatically position the transducing head to follow a track from begining to completion and thereafter adjust the position of the transducing head (if adjustment is needed) to the beginning of the proper track.

Broadly stated, the present invention provides for resetting or transversely moving the transducing head at the end of a track to a position corresponding to the start of a track other than the next successive adjacent track under certain predetermined conditions and not resetting or adjusting the transducing head under other predetermined conditions. The decision to transversely move or adjust the transducing head depends upon the mode in which the apparatus is operating and whether the amount of transverse movement is within the predetermined limits that can be achieved. In other words, if the transducing head is deflected its maximum amount in one direction it will not be moved further in that direction. The total range of movement should be within practical limits determined by the characteristics of the element 22.

The manner in which the transducing head is controlled during the various modes of operation will now be described in connection with FIG. 5 with particular attention being initially given to FIG. 5e which is directed to the still frame or stop action mode of operation.

The stop motion or still frame mode of operation requires that the transducing head be reset at the completion of the track being reproduced and be reset to the beginning of the track so that it can be repeated as many times as is required for the duration of the stop motion.

Thus, the track is effectively replayed over and over since the tape is stationary. Since the reproducing head follows the track during repeating playback, it must be reset by a distance that is equal to the track to track spacing d of the recorded tracks in order to be correctly positioned to replay the track. Since the angle of the track (i.e.

the scan of the tape by the head) is also different when the tape is stopped from the angle that was made during recording, the head is also gradually being adjusted through the course of reproducing the information signal on the track. Thus as the scanning head moves along the track, the error correcting signals cause the trans ducing head to be moved transversely to follow the track and it must be reset essentially one track transverse distance d in order to be in position for beginning the replay of the same track. With the format illustrated in FIG. 1 and using the tape segment shown in FIG. 3, wherein the track width is about 5.6 mils (5.6/1000 of an inch) and the center-to-center spacing distance d between adjacent tracks is about 8.7 mils. The deflectable element 22 shown in FIG. 2 is adapted to move about 8.7 mils in either direction and these design limits are shown in the displacement pattern versus time diagrams of FIGS. 5a through 5j. Moreover, the rotating portion of the scanning drum is rotated at a constant velocity of 60 revolutions per second so that the time for playing each of the tracks is relatively constant at about 16.7 milliseconds in duration. In all of the patterns shown in FIGS. Sa-Sj, the 0 position on the ordinate is intended to be representative of the unbiased or home position of the transducing head which preferably occurs when no voltage is applied to the deflectable or movable element 22.

Referring specifically to the still frame or stop motion displacement pattern for positioning the transducing head shown in FIG. 5e, it is shown that each successive play of track A, for example, has an inclined portion labeled play which is followed by a reset portion that is represented by a substantially vertical line with the vertical distance of the reset approximately 8.7 mils, which is the center-to-center track spacing d between adjacent tracks. Thus, as the transducing head begins reproducing at the start of a track it must be positioned approximately 4.35 mils upwardly relative to the home or 0 position and through the course of the playback of the track, it gradually moves downwardly to its lowermost position indicated to be about 4.35 mils below the center line or 0 home position of the transducing head. At the end of the track, the transducing head must be reset or transversely moved to be in posi tion to start playback of the same track again and a suitable control signal is ap plied to cause the deflectable element 22 to move the transducing head upwardly a total of 8.7 mils which will accurately position it to begin replaying the same track again. The repetition occurs for as long as the still frame is to be maintained.

The resetting of the transducing head is produced by a pulse being generated which has an amplitude that is proportional to and determines the 8.7 mils of deflection. The pulse will be automatically produced unless it is inhibited with the inhibiting being a function of the position of the transducing head near the end of a playback i.e. at or near the lower point of the play portion of the pattern shown in FIG. 5e. If the position of the transducing head is detected to be below the home or 0 position at the end of the scan of a track, then a reset pulse will be pro duced and the head will be reset in the illustrated manner. However, if the position of the transducing head is above the home or 0 position at the completion of scanning a track, then the reset pulse will be inhibited and the next track will be begun. In the absence of the application of any control signals that would reposition the transducing head, it would be in posi tion to begin tracking the next adjacent track at the completion of the foregoing track as has been previously described.

Thus, the absence of a reset pulse causes the transducing head to advance from track A to track B, for example, the condition arising due to producing an inhibiting signal that inhibits the reset pulse. The manner in which the signals are produced and inhibited will be more fully described with respect to the description of the operation of the circuitry shown in the block diagram of FIG. 6.

Turning now to a general description of the displacement patterns that are followed during slow motion effects reference is made to FIGS. 5b, Sc and 5d which re spectively illustrate the displacement pat terns for slow motion effects where the tape is transported at 1/2 (FIG. 5b), 1/5 (FIG. 5c) and 1/10 (FIG. 5d) of the speed during recording. It should be understood that the patterns are intended to illustrate the number of repetitions or replays that occur for each track and this number is a function of the transport speed relative to the speed during the recording process.

Thus, if the transport speed of the tape around the drum is reduced to 1/2 of the speed during recording, it is then necessary that each track be played twice since the scanning drum continues to operate at the same r has the transducing head deflected downwardly about 4.35 mils until it reaches the completion of the track whereupon it is reset a total of about 8.7 mils upwardly in position to replay track A a second time.

Near the completion of the second playback of track A, the transducing head approaches the home or 0 deflection position which is detected and the reset is inhibited so that the track B can be scanned.

Similarly, the transducing head is deflected downwardly about 4.35 mils as was the case with respect to track A and the pattern is repeated from track to track as is shown.

In the event the transport speed is slowed further, such as 1/5 the record speed shown in FIG. Sc or 1/10 the record speed as is illustrated in FIG. 5d, the tracks will be replayed 5 or 10 times, respectively, as shown in the drawings. With respect to the displacement pattern in FIG. 5c, the head begins in its home position on the first play of track A and is deflected downwardly until it reaches the end of the track whereupon it is reset to play at the track again, requiring about 8.7 mils displacement. It follows the track a successive number of times, the lower displacement of each successive play gradually approaching the home position since the track is physically moving around the scanning drum during the successive plays and therefore moves gradually upwardly along the helical path of the tape. During the last play of track A, the position of the transducing head near the end of the play is above the 0 or home position which is detected and results in beginning the first play of the next track B. In a similar man- ner, the slower movement of the tape around the scanning drum shown in FIG.

5d results in track A being replayed a total of ten times before the transducing head is at or above its home position near the completion of the final play which is detected and permits the head to begin playing track B.

From the three foregoing described speeds of tape transport that results in the slow motion play, it should be understood that a track will be replayed as many times as is required to result in the transducing head being at or above the home or 0 position at the completion of the playback of the track being repeated, no matter how many times this occurs. When this condition is detected, the reset is inhibited and the transducing head starts the playback of the next adjacent successive track. The amount of movement during each reset is constant at the approximately 8.7 mils for the apparatus described herein, the distance being equal to the track to track spacing d.

In accordance with another aspect of the present invention, other special motion effects in addition to the slow and stop motion that has been described are capable of being achieved, particularly reverse motion at normal and slower speeds. Referring to Fig. 5j, a displacement pattern is shown for the transducing head and illustrates the movement of the head during reverse direction tape transport at normal playback speed. Unlike the other pattern shown in FIG. 5, track A is shown to the right with the tracks B, C and D being successively leftward which is opposite the direction of the other figures. This denotes the reverse direction as is desired, it being understood that the scanning head follows each track in the same direction as was followed with respect to slow motion and stop motion, i.e., the direction of scan is from the top to the bottom of the angled portion of the pattern of FIG. 5j, followed by a reset movement to position the transducing head for playback of the next desired track. While the scanning head moves in the same direction relative to the tracks during playback of the tracks, the tracks must be played in reverse sequential order relative to the order during forward direction playing. The displacement pattern shown in FIG. 5j is for regular speed in the sense that the tape is transported around the scanning drum at the same velocity as was used during recording, but in the opposite direction. As is shown by the displacement pattern in FIG. 5j, the resetting of the transducing head is greater than has been heretofore described, in effect moving two 8.7 mil distances for a total of 17.4 mils, with the greater movement being necessary to traverse a total of two center-to-center spacings d to correctly position the tape on the upstream or prior track. This can be readily visualized if it is recalled that to replay a track during slow motion or stop motion effects, it was necessary to displace the transducing head a single center-to-center distance of about 8.7 mils in order to reposition it for repeating playback of the same track. In the event a track prior to the track being played is to be played, still another track to track distance would be required to position it at the beginning of the prior track. Thus, a total of two multiples of center-to-center spacing d are required to reproduce the information signal in a reverse direction at normal speed.

To achieve slow motion in the reverse direction, it is necessary to reduce the tape transport speed in the reverse direction and repeat the playback of the tracks one or more times, depending upon the reverse transport tape speed. Thus, referring to FIG. 5i, a reverse direction half speed displacement pattern is illustrated wherein each of the tracks is repeated once before the next preceding track is played. Thus, after track C, for example, is played the first time, the transducing head is reset a distance of one center-to-center spacing d, i.e. 8.7 mils, and track C is played a second time until the downward deflection of the transducing head is detected at the lower extreme of the second play which causes a "double" magnitude reset signal to be produced and the transducing head is deflected about 17.4 mils upwardly which positions it at the start of track B. The lower extent of the first play of track B is at a downward deflection of about 4.35 mils which is not a sufficient deflection to cause generation of a double magnitude reset pulse so that only an 8.7 mil deflection is produced which causes the track B to be played a second time. In this manner, the slow motion effect in the reverse direction is achieved. When the position of the transducing head at the end of a track is sufficiently displaced relative to the home position, then a signal that deflects two center-to-center track spacings or about 17.4 mils is produced.

The manner in which the circuitry associated with the present invention operates to produce the displacement patterns that have been discussed above will be described in connection with the schematic block diagram of FIG. 6. As previously alluded to, an error correcting signal that is preferably a low frequency or changing D.C. level is produced by apparatus such as the sensing heads disclosed in the aforementioned application No. 10260/77 (Serial No.

1579853) or the dither apparatus disclosed in the aforementioned application No.

10036/77 (Serial No. 1579852) both of which are assigned to the same assignee as the present invention, with the error signal being applied to an integrator 50 through input line 52. During the scanning of a track, the error signal causes the transducing head to be adjusted so as to follow the track regardless of the speed of tape transport, provided that it is within the limits of deflection of the element 22. The integrator provides a ramp signal, the slope of which is. determined by the D.C. or low frequency error signal that is derived from the head positioner servo circuitry. Thus, the servo error modules the slope of the ramp as the transducing head position error changes, and the output of the integrator appears on line 54 which extends to summation circuits that drive the transducing head movable element 22. In addition to the low frequency or changing D.C. level error signals, a dither signal and high frequency error signals may be added to the composite control signal that is used to drive the positioner in addition to the reset pulse which effectively produces the reset portion in the displacement patterns of FIG. 5 as previously discussed. A pulse generator 56 produces the reset pulse which has a magnitude that is proportional to a desired one track deflection that is to be achieved by the element 22. In other words, the size of the reset pulse determines the amount of deflection needed to reset the transducing head a distance equal to the center-tocenter distance d, i.e., the 8.7 mils in the illustrated embodiment, or a reset pulse that will produce 17.4 mils of displacement which represents two multiples of the center-to-center spacing d. The pulse generator 56 is adapted to produce the pulses an output line 58 when the tape is transported in either of the reverse and forward directions and pulse generator 60 provides an output pulse on line 62 of the same magnitude as that produced by generator 56 under certain conditions which only occur when the tape is transported in the reverse direction. If pulses appear on both outputs, an adder 64 will provide an output pulse that is the sum of the two pulses and thus provide a pulse that will produce a reset of two centerto-center spacings. The reset pulses appear on line 66 which extends to the input of integrator 50.

A forward mode tape level detector 68 monitors the indicator output and is adapted to provide an inhibit output signal on line 70 for inhibiting the pulse generator from producing a pulse on output 58 when the ramp signal is below a set level at the end of a scan. Similarly, the reverse mode level detector 72 monitors the ramp voltage from the integrator 50 and produces an inhibit signal on line 74 until the ramp signal reaches a predetermined level that is slightly more than one track higher than the level of detector 68. In the reverse mode, the inhibit signal inhibits an output on line 62 so that only a single track spacing reset magnitude pulse will be produced by the pulse generator 56 which is triggered in response to receiving an advanced end of scan command on line 76 derived from a tachometer generator mounted for rotation with the rotatable drum 12 of the scanning drum. The tachometer may be of conventional design for providing a tachometer pulse once for each revolution of the rotatable drum 12. For convenience, the tachometer is mounted to the rotatable drum 12 so that it occurs just before the dropout. Tachometer processing circuits conventional to helical recording devices are employed to provide from the scanner tach pulse circuit timing pulses to the helical recording device used to control operative functions. For the purpose of triggering pulse generator 56 to provide the reset pulse to integrator 50, the advanced end of scan command is generated from the scanner tach pulse provided just prior to the end of the scan of a previous track. The previous track related tach pulse is processed by a conventional counter included in the tachometer processing circuits to be present on line 76 just prior to the end of the scan of the current track.

The circuit is operable to provide a wave form at the output of the integrator for the various modes of operation which is generally the reciprocal or mirror image of the displacement patterns of FIG. 5 for the various modes. As an example, the half speed slow motion in the forward direction having the displacement pattern shown in FIG. 5b results from the integrator output wave form shown in FIG. 7a. By comparing the wave forms of FIGS. Sb and 7a, it is apparent that the shape is merely inverted. Thus, in FIG. 7a, the integrator 50 provides an output wave form that rises during the playback of a track, with the slope of the damp portion of the wave form being a function of the D.C. error input applied on line 52 that is derived from error detecting circuitry. With the voltage ramp rising during the playing of a track, the end of scan trigger pulse from the conventional trigger pulse generating circuitry (not shown but previously described) triggers the pulse generator 56 and it will provide an output pulse at the end of playing a track which will be applied through the adder 64 and line 66 to the input of the integrator 50. Since the output pulse from the pulse generator it has the effect of resetting the output 56 is a very short duration positive pulse, voltage to a level which produces the desired displacement of the transducing head in position to play the track a second time.

As the integrator output increases during the second playback of track A, the end of scan trigger circuitry will provide the trigger pulse to the pulse generator 56 at the appropriate time near the completion of the second play. However, the forward level detector 68 continually monitors the instantaneous voltage at the output of the integrator 50 and provides an inhibiting signal on line 70 which inhibits the pulse generator 56 whenever the instantaneous voltage is less than about zero. Thus, as the second playback of track A is approaching completion and the end of scan trigger pulse is applied to trigger the generator, the detector will detect that the output voltage is less than 0 as shown in FIG. 7a and the detector will generate an inhibit signal on line 70. The pulse generator will thereby be inhibited which results in the integrator 50 not being reset and continues onward in effect following track B through the first playback. Since the voltage of the integrator output near the end of the first play is positive, the forward level detector 68 does not inhibit the generator and a reset pulse is produced.

When the tape is transported in the reverse direction for the purpose of providing backward or reverse motion effects during playback, it is necessary for the transducing head to be reset to play a preceding in time track as previously mentioned. In the event that slow motion reverse direction playback is to be performed, at half speed, for example the circuit of FIG. 6 will produce a voltage output wave form shown in FIG. 7b. A comparison of the wave form of FIG. 7b with the displacement pattern of FIG. Si shows a mirror image or inverted pattern as was the case with respect to those shown in FIGS.

5b and 7a. As the tape is following track A through the first play, the instantaneous voltage near the end of the scan is above 0 as shown in FIG. 7b and pulse generator 56 will therefore poduce a reset pulse which will have the effect of resetting the transducing head one center-to-center spacing distance of 8.7 mils. The transducing head will then follow track A through a second scan or playback and the voltage of the ramp will approach the higher level V2, which higher voltage is detected by the reverse level detector 72. When the end of scan triggr pulse is produced, the pulse generators 56 and 60 will both be operable, because level detector 72 will not provide an inhibit on line 74. The output pulses of the pulse generators 56 and 60 are added together by the adder circuit 64 and a pulse having a double magnitude appears on line 66 which is applied to the input of integrator 50, resetting the same so that the transducing head is moved a distance equal to two center-to-center track spacings or about 17.4 mils in the illustrated embodiment. In this manner the tracks are played back in reverse time or sequence order, but are also replayed once to achieve the slow motion effect.

A specific schematic circuit diagram that can be used to carry out the operation of the circuit shown in the block diagram in FIG. 6 is shown in FIG. 8 to comprise the integrator 50 with input line 52 receiving the low frequency or D.C. error signal from a synchronous detector circuit associated with error detecting circuitry which does not form a part of the present invention. The error signal is applied through an analog switch 80 which may be a CMOS device that is close circuited when a posi tive voltage (operator mode control command) is present on line 82 and open circuited when it is not. Its function is to disable the special effects circuitry during normal play. The integrator 50 comprises an operaitonal amplifier 81 having the industry standard number in parenthesis and pin numbers adjacent thereto with a feedback capacitor 84 with its output connected to line 54. The forward level detector 68 is coupled to the output line 54 through line 86 and resistor 88 and comprises an operational amplifier that is set to monitor the instantaneous voltage and provide a high output level on line 70 whenever the instantaneous voltage is about equal or greater than 0. Similarly, reverse level detector 72 also comprises an operational amplifier which also monitors the instantaneous output voltage through line 86 and a resistor 90 and it compares the output voltage with a voltage present on pin l which is adjustably controlled by a potentiometer 92 which is set at a higher level, such as about 3 volts for example.

When the instantaneous output voltage approaches the preset limit, then the output voltage of the operational amplifier appearing on line 72 goes high.

The pulse generators 56 and 60 comprise monostable multivibrators or "one shots" which are actuated or fired when both inputs B are high and inputs A receive a negative-going transition. When each of the pulse generators is fired, a positivegoing pulse is produced on their respective Q outputs which is applied to the input of integrator 50 through line 66, adder 64 and respective lines 58 and 62. The Q output from each generator extends to other circuitry and is used for time base error correction. Line 76 is connected to input A of both pulse generators and is low when the advanced end of scan trigger pulse is present. Pulse generator 56 is connected to the forward limit detector 68 by line 70 connected to the B input. Since the generator 56 is fire on a negative-going transition on line 76 when the input B is at a logic high level, whenever the level detector 68 detects a voltage below about 0, the pulse generator 56 will be inhibited.

Similarly, line 74 which interconnects the output of reverse level detector 72 with the B input of pulse generator 60 is low whenever the voltage being monitored is less than the preset value of about 3 volts for example. Thus, pulse generator 60 will always be inhibited except when the voltage ramp approaches the higher level which represents the limit of transducing deflection in that direction. When this occurs both pulse generators fire producing the pulse of double magnitude for resetting the transducing head a total of 2 tracks. For example, for half-speed reverse slow motion, the pulse generator 56 will be fired after every track is played and pulse generator 60 will be fired at the end of every second playback of a track.

Zener diodes 94 and 96 are provided to translate the voltage range of the outputs of the level detectors 68 and 70 to a range that is compatible with the pulse generators 56 and 60. Diodes 98 are provided to maintain a self centering feedback voltage to the input of the integrator to facilitate rapid lockup when a signal is resumed subsequently of a period where no signal was applied to the input. It should also be appreciated that the voltage of the output on line 54 extends to other summing circuits to which other signal components are added for application to the circuitry which drives the movable element 22. The output voltage is proportional to the deflection that is ultimately produced by the element.

In accordance with yet another aspect of the present invention, speeded up or fast motion effects can be achieved with the present invention. It should be understood that the circuitry specifically illustrated in FIGS. 6 and 8 will not accomplish fast motion operation because the ramp voltage from the integrator is inverted relative to that which is required. However, similar circuitry with appropriate level detectors and switching circuitry for connecting the same while the apparatus is operating in the fast forward mode (while simultaneously deactivating the circuitry of FIG. 6) while not shown, is within the scope of the present invention. Fast motion effects would be achieved by advancing the transducing head one or more directions while the tape is being transported at a speed that is faster than the transport speed during recording. Referring to FIGS. 5g and 5h, displacement patterns for fast motion where the tape is transported two and three times, respectively, are illustrated, with repositioning of the transducing head at the completion of every track. With respect to the two times fast motion, it is seen that every second track is skipped during playback with the transducing head being moved about 8.7 mils or one track to track spacing. It should be appreciated that the displacement of the transducing head will be in the opposite direction that occurred during slow rnotion or still frame modes of operation. With respect to the three times fast motion shown in FIG. 5h, it is necessary to have the trasnducing head skip two tracks so that every third track is replayed during operation at this speed, a repositioning distance of 17.4 mils is produced. It should also be appreciated that the three tirnes fast motion shown in FIG. 5 has a total displacement of two center-to-center spacings, a displacement of about 17.4 mils, and that faster motion would require still additional deflection which must be compatible with the design and operation of the movable element 22 in terms of speed and total range of movement.

With respect to yet another aspect of the present invention, the apparatus is adapted to operate in a surveillance mode as well as a skip frame mode of operation.

Referring to FIG. 5f which illustrates the displacement pattern for the transducing head when the apparatus is operating in a surveillance mode, the information is recorded at a significantly lower transport speed than during normal recording. Thus, the displacement pattern shown in FIG. 5f is produced when the head 20 follows a track that was recorded at 1/60 of the normal speed and the switching circuitry was adapted to record every sixtieth frame. Thus, the video recorder scanner is triggered to record only one scan per second and disregard the next 59 scans which results in a synchronized recorded format with helix angles approximating a stop motion playback track. The recording of every sixtieth frame merely represents a specific example, it being understood that a greater or lesser number of frames than the 59 described could be skipped. In other words, the longitudinal tape transport speed during recording does not change the static or stop motion generated helix very much.

During normal speed playback, an error in tracking occurs just as occurs in stop motion mode of operation for signals that were recorded at the normal transport speed. The tracking pattern shown in FIG.

5f will result in the transducing head accurately following the track during replay and repositioning the transducing head at the beginning of the next track by moving it downwardly as shown. The surveillance mode of operation permits a television field of information to be recorded each second which provides a good record in terms of a sequence of informaion fields that can approximate motion with an extraordinary savings in magnetic tape. Moreover, the quality of the reproduced signal is unimpaired by mistracking and crossover during playback.

With respect to the skip field mode of operation, and particularly a skip 1 field system having a displacement pattern of operation as shown in FIG. 5a, every other field is recorded and the other field is disregarded. The record and playback tape speeds are about 1/2 the normal transport speed when no fields are skipped. Since the record and playback speeds are identical (at the lesser speed) to angle of the tracks will be substanially identical during playback as during record so that no appreciable transverse movement of the transducing head is required during playing of a track and this is reflected by the horizontal lines during playing as shown in the drawing. However, during playback, the continual 60 Hertz information rate is required, which necessitates repeating each track twice. Thus, track A is replayed once by moving the transducing head at the completion of the first play of track A a distance of about 4.35 mils which places it in the correct position to repeat the playback of the track A. At the completion of the second play, it is necessary to advance the transducing head by moving it transversely downwardly for the first play of track B. It should be understood that the repositioning of the transducing head after each track is played requires a deflection of only 1/2 that required with respect to the 8.7 mils shown in the other displacement pattern for 1 center-to-center distance for the reason that the tape is moving only 1/2 of the speed during recording compared to the recording speed of the tracks that were described with respect to the other modes of operation. By utilizing the repositioning of the transducing head after playback of every track, the sigle head can achieve the same result as two heads have produced in similar skip field operation on prior art apparatus. It should also be appreciated that while the skip one field system displacement pattern is shown, the invention can be used to skip more than one field (each field occupying one track). Thus, every nth field may be recorded on a track, the intermediate fields disregarded, the tape driven at 1/n the normal transport speed during recording and playback and the transducing incrementally adjusted in a manner similar to that shown for the n equal 2 case described above. If every rjh field is recorded, it is necessary to playback each field n times or stated in other words, playback each track and repeat it n-l times.

From the foregoing description, it should be understood that the embodiment represents a closed loop system in the sense that the error correcting signals that are used to maintain the transducing head on track during playback of a track receives continuously updated information from the error detecting circuitry. Because of the closed loop operation, the transducing head will accurately follow the track regardless of the transport speed or direction that is used. Since the circuitry is adapted to automatically make the decision when to have the transducing head advance to the next adjacent successive track during forward motion or the preceding-in-time track during reverse transport motion of the tape, conventional "infinitely adjustable" capstan drive circuitry can be used. Since the operator may wish to vary the slow motion speed for viewing an instant replay of a sporting contest, event, for example, a potentiometer controller such as a "joy stick controller" may be used to control the capstan drive which transport the tape.

Furthermore, the automatic decisionmaking feature of the error detecting circuitry permits the operator to advance the tape at abritary rates, including in a fieldby-field step fashion with long intervals of stop motion, by manually turning the reels.

This provides the operator with a valuable tool for tape editing purposes.

While the disclosed embodiment describes the closed loop system, it should be understood that an open loop apparatus is within the scope of the present invention and may be used. In such an open loop system, the integrator 50 would not receive the low frequency or D.C. error signal from the error detecting circuitry, but would typically employ an adjustable D.C.

source that would be connected to the input of the integrator and adjusted to provide a voltage wave form that is related to the desired predetermined tracking or special motion effect. Such an open loop system would require that the tape speed be very carefully controlled so that the tape would run at the precise speed expected by the programming apparatus generating the voltage wave form for producing the appropriate displacement patterns similar to those shown in FIG. 5.

The careful precise controlling of the transport speed may impose a limitation on such a system from a practical standpoint.

From the foregoing description, it should be understood that a method and apparatus is described for achieving altered time base reference effects in the art of recording and reproducing information signals on a medium. In this regard, the invention is particularly well suited for creating special motion and other effects in the field of video recording without detracting from the quality of the signal being reproduced from the recording medium. Furthermore the invention is especially suited for use in helical wrap video tape recorders for the reason that special motion effects, such as slow motion, still frarne or stop motion and fast motion effects can be achieved without impairing the video signal that is derived from the magnetic tape. The sy

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tape, conventional "infinitely adjustable" capstan drive circuitry can be used. Since the operator may wish to vary the slow motion speed for viewing an instant replay of a sporting contest, event, for example, a potentiometer controller such as a "joy stick controller" may be used to control the capstan drive which transport the tape. Furthermore, the automatic decisionmaking feature of the error detecting circuitry permits the operator to advance the tape at abritary rates, including in a fieldby-field step fashion with long intervals of stop motion, by manually turning the reels. This provides the operator with a valuable tool for tape editing purposes. While the disclosed embodiment describes the closed loop system, it should be understood that an open loop apparatus is within the scope of the present invention and may be used. In such an open loop system, the integrator 50 would not receive the low frequency or D.C. error signal from the error detecting circuitry, but would typically employ an adjustable D.C. source that would be connected to the input of the integrator and adjusted to provide a voltage wave form that is related to the desired predetermined tracking or special motion effect. Such an open loop system would require that the tape speed be very carefully controlled so that the tape would run at the precise speed expected by the programming apparatus generating the voltage wave form for producing the appropriate displacement patterns similar to those shown in FIG. 5. The careful precise controlling of the transport speed may impose a limitation on such a system from a practical standpoint. From the foregoing description, it should be understood that a method and apparatus is described for achieving altered time base reference effects in the art of recording and reproducing information signals on a medium. In this regard, the invention is particularly well suited for creating special motion and other effects in the field of video recording without detracting from the quality of the signal being reproduced from the recording medium. Furthermore the invention is especially suited for use in helical wrap video tape recorders for the reason that special motion effects, such as slow motion, still frarne or stop motion and fast motion effects can be achieved without impairing the video signal that is derived from the magnetic tape. The system accurately follows the track during playback and automatically detects the position of the playback head near the completion of a track and decides whether to move the transducing head to a track other than the next adjacent successive track or not. Since the invention automaticaly makes the decision near the completion of playback of a track, the tape being transported in the slow motion mode can be moved at virtually any speed, thereby permitting the infinitely adjustable slow motion playback. The fast motion effect is limited only by the range of deflection of the transducing head, with the embodiment described and shown in the drawings permitting two or three times the "normal motion speed". WHAT WE CLAIM IS: -

1. A method of recording or playing back a signal in which method a transducing head disposed on a carrier and an elongate record medium are moved such that the head is caused to scan the medium along each of a succession of parallel tracks, each of which extends in a direction which is obliquely across the medium and the head is, during its scanning along each track, progressively displaced relative to the carrier in a sense which is transverse to the said direction of the track.

2. A method according to claim 1, in which the head is, during an interval between its scanning of one of the said tracks and its scanning of another of the said tracks, displaced relative to the carrier in a sense opposite the aforementioned sense.

3. A method according to claim 2 in which the head is displaced during each interval between consecutive scannings by a similar distance so as to reposition the head for each scanning.

4. A method according to claim 3 in which the said distance corresponds to the spacing of adjacent tracks.

5. A method according to claim 4 in which the displacement of the head has limits equally spaced one to each side of a datum and the displacement in the said interval moves the head from one limit to the other if the head reaches the said one limit.

6. A method according to claim 5 in which the separation of the limits corresponds to twice the spacing of the centres of adjacent tracks.

7. A method according to claim 5 or claim 6 in which the pick-up head is displaced during the said interval by half the distance between the limits if it does not reach either limit.

8. A method of playing back a recorded signal comprising a method according to claim 1 in which the head is a pick-up head.

9. A method according to claim 8, in which the pick-up head is, during an interval between its scanning of one of the tracks and its scanning of either the same track again or another of the said tracks, displaced relative to the carrier in a sense opposite the aforementioned sense.

10. A method according to claim 9, in

which the lengthwise velocity (which may be zero) of the medium is such that an action which the recorded signal represents appears to occur at a changed rate when reproduced from the played back signal.

11. A method according to claim 10 in which the pick-up head is displaced during each interval between consecutive scannings of a track or tracks by a similar distance so as to reposition the pick-up head for each scanning.

12. A method according to claim 11 in which the said distance corresponds to the spacing of adjacent tracks.

13. A method according to claim 11 or 12 in which the lengthwise velocity of the medium is such as to cause the pick-up head to scan a track more than once and the pick-up head is repositioned progressively differently at the beginning of each scan of the same track.

14. A method according to claim 11 in which the displacement of the pick-up head has limits equally spaced one to each side of a datum and the displacement in the said interval moves the pick-up head from one limit to the other if the pick-up head reaches the said one limit.

15. A method according to claim 14 in which the separation of the limits corresponds to twice the spacing of the centres of adjacent tracks.

16. A method according to claim 14 or claim 15 in which the pick-up head is displaced during the said interval by half the distance between the limits if it does not reach either limit.

17. A method according to any of claims 14 to 16 in which the lengthwise velocity of the medium is such as to produce a reversal of the said rate.

18. A method according to any of claims 14 to 16 in which the lengthwise velocity of the medium and the displacements during the said intervals are such as to cause the pick-up head to scan intermittent tracks and thereby produce the effect of an acceleration of the said action.

19. A method of recording and playback comprisng recording a signal in a succesion of oblique tracks on the said elongate record medium, the signal being composed of a succession of fields of which only every n h field is recorded and in which each track is played back n times according to the method according to claim 13, where n is an integer greater than 1.

20. A method according to any of claims 10 to 18 in which the lengthwise velocity is varied.

21. A method according to any foregoing claim in which the medium is an elongate tape which is disposed in a helical path and the carrier is a cylindrical drum which rotates about its axis to effect the scanning of the tape by the head.

22. A recording or playback machine which is capable of performing the method according to any one of the foregoing claims.

23. A helically-scanning recording or playback machine which is capable of recording a signal in, or playing back a signal recorded in, a succession of discrete parallel tracks each extending obliquely across a magnetic tape and which comprises a transducing head for scanning the tape, a rotary carrier, a guide for constraining the tape to follow a helical path around the carrier, and a mount which carries the head and is borne by the carrier and which is deflectable relative to the carrier to permit displacement of the head to and fro in a direction transverse to the tracks in accordance with applied control signals, means being provided to apply to the mount control signals for displacing the head in respective opposite senses during the scanning of the tape and between scannings respectively.

24. A machine according to claim 23, further comprising a servomechanism which monitors deviation of the head from a datum extending along a track and develops an error signal which denotes the deviation and is applied to the mount to correct that deviation, means for generating a control signal which produces on its application to the mount a displacement in said direction and means for inhibiting the application of the positioning signal for predetermined ranges of value of the error signal.