CA1128201A - Open loop servo-system for accurate tracking in a video signal reproducing apparatus - Google Patents
Open loop servo-system for accurate tracking in a video signal reproducing apparatusInfo
- Publication number
- CA1128201A CA1128201A CA291,970A CA291970A CA1128201A CA 1128201 A CA1128201 A CA 1128201A CA 291970 A CA291970 A CA 291970A CA 1128201 A CA1128201 A CA 1128201A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- transducer
- record medium
- output
- speed
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/584—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes
- G11B5/588—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes by controlling the position of the rotating heads
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/584—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes
- G11B5/588—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes by controlling the position of the rotating heads
- G11B5/592—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on tapes by controlling the position of the rotating heads using bimorph elements supporting the heads
Landscapes
- Adjustment Of The Magnetic Head Position Track Following On Tapes (AREA)
Abstract
ABSTRACT
In a VTR having a rotary transducer for scanning paral-lel tracks on a record medium in which signal information is recorded and being displaced at a skew angle with respect to the direction of travel of the record medium, an electro-mechanical adjustable transducer support, preferably of a piezo-ceramic material supports the transducer for displacement transversely with respect to the parallel tracks in response to a drive signal, and an open loop servo circuit is provided for generating the drive signal to align the scanning path of the transducer with one of the parallel tracks. The open loop servo system includes a first detecting device for detecting the position of the beginning of one of the parallel tracks, a second detecting device for detecting the rotational position of the rotary transducer, a device for generating an output speed signal corresponding to the speed of the record medium, and a signal processing device receiving the outputs of the first and second detecting devices and the speed signal generating device for generating a first component signal which corresponds to the deviation between the beginning of the transducer scanning path and a recorded track and is a function of the relative speed between the rotary transducer and the record medium. The open loop servo system further includes a sawtooth waveform generating device responsive to an output from the second detecting device, and an amplitude adjusting device supplied with the output of the sawtooth waveform generating device and being responsive to the output of the speed signal generating device for generating a second component signal, with the first and second component signals being added for producing the drive signal by which the transducer is transversely displaced with respect to a parallel record track.
In a VTR having a rotary transducer for scanning paral-lel tracks on a record medium in which signal information is recorded and being displaced at a skew angle with respect to the direction of travel of the record medium, an electro-mechanical adjustable transducer support, preferably of a piezo-ceramic material supports the transducer for displacement transversely with respect to the parallel tracks in response to a drive signal, and an open loop servo circuit is provided for generating the drive signal to align the scanning path of the transducer with one of the parallel tracks. The open loop servo system includes a first detecting device for detecting the position of the beginning of one of the parallel tracks, a second detecting device for detecting the rotational position of the rotary transducer, a device for generating an output speed signal corresponding to the speed of the record medium, and a signal processing device receiving the outputs of the first and second detecting devices and the speed signal generating device for generating a first component signal which corresponds to the deviation between the beginning of the transducer scanning path and a recorded track and is a function of the relative speed between the rotary transducer and the record medium. The open loop servo system further includes a sawtooth waveform generating device responsive to an output from the second detecting device, and an amplitude adjusting device supplied with the output of the sawtooth waveform generating device and being responsive to the output of the speed signal generating device for generating a second component signal, with the first and second component signals being added for producing the drive signal by which the transducer is transversely displaced with respect to a parallel record track.
Description
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BACKGROUND OF THE INVENTION
This invention generally relates to a tracking-error correcting apparatus for use in an apparatus of the kype where-in signal information is recorded in parallel skewed tracks on a record medium and has particular application to a video tape recorder tVTR) in which stop-motion, slow-motion or fast-motion pictures as well as normal~motion pictures can be reproduced.
In a conventional VTR, a rotary transducer head as-sembly is provided with one or more magnetic transducers which scan successive parallel tracks on a magnetic record tape so as to record and/or reproduce video signals in such tracks.
In general, while the one or more transducers rotate across the tape, the tape itself is transported in the longitudinal direction thereof. A typical ~TR includes one, and preferably two, record andjor playback transducers mounted on a suitable rotary assembly so as to rotatably scan a magnetic tape which is helically wrapped about at least a portion of a guide drum forming a part of the transducer assembly. During recording, a tracking servo system controls the rotation of the trans-ducers with respect to the tape movement, and control pulse signals are recorded on a marginal portion of the tape. During reproduction, the same or a similar servo control system is used to synchronize the movement of the tape to the rotation of the transducers in accordance with the recorded control pulse signals. Consequently, an accurate video picture can be displayed in response to the reproduced video signal. This accuracy is, in large part, due to the $act that the servo control system tends to control the relative movement and position between the rotary transducers and the tape such that each ~2~
transducer scans substantially the same track during reproduc-tion operation as was scanned during the recording opera~ion, Therefore, during normal tape speed (normal mode), the servo system serves to insure that the scanning path o~ the heads substantially coincides with the previously recorded tracks.
Recently, many VTR systems have been provided with various reproducing operations, such as "stop or still-motion", "slow-motion" and "quick or fast-motion". In these various reproducing modes, the tape speed differs from the speed during the recording mode. Consequently, the scanning path is different from the recorded track during these different reproducing modes. That is, the scanning path is inclined, or angularly disposed, with respect to the recorded track.
Thus, in various modes other than "normal operation", guard band noise and cross-talk with result due to tracking errors or scanning deviation. Generally, upon leaving the pre-recorded track, the transducer starts scanning a guard band disposed in-between recorded tracks. Accordingly, the output signal of the transducer will be reduced and contain a noise component. On the other hand, as the transducer starts scanning the next recorded track, the transducer picks up signals frsm two adjacent tracks resulting in cross-talk.
This tracking error due to the variation in the tape speed results in a deterioration of the reproduced pictures.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to pxovide a video recording and reproducing apparatus of the type employing a rotary transducer for reproducing signal information recorded in a plurality of parallel skewed ~, '1~28Z~L
tracks on a record medium, which apparatus automatically causes the rotary transducer to trac]c the recorded tracks on the record medium regardless of the speed o~ the record medium.
It is another object of the invention to provide a video tape recorder having various modes such as stop-motion, slow-motion, and fast-motion as well as normal operation which produces a good quality picture in all modes of operation.
It is a further object of the instant invention to provide an improved video tape recorder of the type employing a rotary transducer head assembly wherein the transverse postion of the transducer with respect to a recorded track is automatically varied as a function of tape speed.
According to an aspect of the invention, in an apparatus of the type in which signal information is recorded in a plurality of parallel tracks on a record medium, with the parallel tracks being disposed at a skew angle with respect to the direction of travel of the record medium, and in which a rotary transducer for scanning the parallel tracks is supported by an electro-mechanical adjustable trans-ducer support operative to displace the transducer trans-versely with respect to the parallel tracks in response to a drive signal, an open loop servo system is provided for generating the drive signal to align the scanning path of the transducer with one of the parallel tracks~ The open loop sexvo system comprises first detecting means for detecting the position of the heginning of one of the parallel tracks along the direction of the travel of the record medium and providing a first output, second detecting means for detecting the rotational position of the rotary ~rans-ducer and providing a second output, means for genexating . ,~,,.,~ .
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an output signal corresponding to the speed of the record medium, and signal processing means receiving as inputs the outputs of the first and second detecting means and the speed signal generating means for generating the drive signal.
In a preferred embodiment, the open loop servo system further comprises sawtooth waveform generating means responsive to the second detec-ting means for producing a sawtooth waveform signal having a fixed period which is sub-stantially equal to the time required for the rotary trans-ducer to traverse its scanning path on the record medium, amplitude adjusting means connected to receive the output ~f the sawtooth waveform generating means and responsive to the output of the speed signal means for changing the slope of the sawtooth waveform signal as a function of the speed of the record medium, and adding means for adding the outputs of the signal processing means and the amplitude adjusting means for generating the drive signal.
More particularly there is provided: in an apparatus of the type wherein signal information is recorded in a plurality of parallel t.racks on a record medium, said parallel tracks being disposed at a skew angle with respect to the direction of travel of said record medium, said apparatus having a rotary transducer for scanning said parallel tracks and an electro-mechanical adjustable trans-ducer support provided to support said transducer in scanning relation to said record medium, said transducer support being operative to displace said transducer transversely with ~z~
respect to said parallel tracks in response to a drive signal, the improvement comprising an open loop servo system for generating said drive signal to align the scanning path of said transducer with one of said parallel trac~s, said open loop servo system comprising first detec~ing means or detecting the position of the beginning of one o said parall~l tracks in the direction of travel of said record ~edium and providing a first output, second detecting means for detecting the rotational position of said rotary transducer and providing a sscond output, speed signal generating means for generating an output signal corresponding to the speed of said record medium, and signal processing means receiving as inputs the outputs of said first and second detecting means and said speed signal generating means for generating said drive signal.
There is also provided:
In an apparatus of the type wherein signal informa-tion is recorded in a plurality of parallel tracXs on a record medium, said parallel tracks being skewed with respect to the direction of travel of said record medium, said apparatus having a rotary ~ransducer for scanning said parallel tracks and an electro-mechanical adjustable transducer support provided to sup-port said transducer in scanning relation to said record medium, said transducer support being operative to displace said trans-ducer transversely with respect to said parallal trac~s in re-sponse to a drive signal, the improvement comprising an open loop servo system for senerating said drive signal to align the scanning path of said transducer with one or said parallel tracks, said open 100D servo system co~?rising detectins ~eans for ae-tecting the rotational position of said rotary transducer, s~eed 30 signal generating means for generating an output signal corres-ponding to the speed of said record medium, sawtooth waveform generating means responsive to said detecting means for producing a sawtooth waveform signal having a fixed period which is substan--5a-tially equal to the time required for said rotary transducer to traverse its scanning path on said record medium, and amplitude adjusting means connected to receive the outputs of said sawtooth waveform generating means and said speed signal generat,ing means for changing the slope of said sawtooth waveform signal as a function of the speed of said record medium.
The above, and other objects, features and advantages of the invention will be apparent in the following detailed description of an illustrative embodiment of the invention which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The manner in which the foregoing o~jects and other advantages of the invention are attained will be better ~mder-stood from the following detailed description of a preferred embodiment with reference to the accompanying drawings, in which:
Figs. lA and lB are top and side schematic views, res-pectively, illustrating a rotary transducer head assembly and the manner in which a tape record medium is helically wrapped around a guide drum;
Figs. 2A, 2B and 2C collectively are plan views of a tape record medium diagramatically illustrating the parallel skew-ed record tracks produced by the assembly shown in Figs. lA and lB
and an example of the resulting mis-tracking of the rotary trans-ducer due to a variation in the speed of the tape record medium;
Figs. 3A, 3B and 3C are schematic diagrams which collec-tively illustrate the basic structure and principles of operation of the electro-mechanical adjustable transducer support used in the preferred embodiment of the present invention;
Figs. 4A and 4B are top and side schematic view, respectively, showing the structure of the electro-mechanical adjustable transducer support;
Fiy. 5 is a block diagram of the open loop servo control ,,~ 6 -circuit according to the invention;
Fig. 6 is a top vlew similar to Fig. lA illustra~ing the positions of the magnetic head for detecting recorded control pulses and the pick-up head for detecting the relative position of the rotary transducer; and Fig. 7A is a plan view of a tape record medium diagramatically illustrating the geometric and dimensional relations between the parallel skewed record tracks, a displaced scanning path of a rotary transducer and recorded control pulses, and Figs. 7~, 7C
and 7D are pulse diagrams related to the plan view of Fig. 7A.
DETAILED DESCRIPTION OF TH~ PREFERRFD EMBODIMENT
The following detailed description, given by way of example, will best be understood in conjunction with the accompanying drawings. For the purpose o~ simplification and to facilitate an understanding of the present invention, the following description relates to the environment of a video signal recorder and, more particularly, to a VTR. However, the problems to which the present invention is addressed, and the solution to those problems, as disclosed herein, are not limited solely to video signal recording apparatus. Hence, it should be understood that this description also is applicable to other types of analog signal recording devices, to digital sign~l recording devices and to other rotary head scanning apparatus which can be used for recording, reproducing, or other purposes.
Turning now to ~ig. lA, there is schematically illustra~ed ~lZ~
a top vlew of a typical rotary head scanning device, such as used in a VTR. As is conventional, this device is formed wi~h two magnetic record/playback transducers la, lb which are adapted for rotation about a central axls. A guide drum 2 is adapted to receive a record medium, such as tape 3, wrapped helically thereabout for at least 18Q. Transducers la and lb may be mounted on diametrically opposed arms which are rotated so as to scan successive, parallel, skewed tracks across tape 3. Thus, transducers la and lb rotate in the clockwise dlrection as indicated by the arrow while tape 3 is advanced to the right and counter-clockwise about the guide drum so as ~o record signal information thereon.
Alternatively, and as shown in Fig. lB, guide drum 2 may be formed of two drums 2a, 2b disposed in face-to-face con-figuration and spaced so as to define a scanning gap therebetween.
Tape 3 is helically wrapped about a portion of the surface of guide drum 2 so that the record tracks recorded by transducers la, lb are skewed relative to the longitudinal direction of the tape. When two transducers are used, it will be appreciated that alternate tracks are recorded thereby, ~hat ~irst transducer la records one track,then transducer lb records the next adjacent track, then transducer la records the following track, and so on. In the alternative structure of Fig. lB, transducers la and lb are mounted on one of drums 2a, 2b, this , drum being rotated relative to the other drum such that the heads , ~ ' l~Z~ZY~
traverse the aformentioned scanning paths.
During a signal recording operation and during a "normal" signal reproducing operation, the relative speed of tap~ 3 with respect to transducers la and lb is the same.
Suitable servo control circuitry (not shown) generall~ is provi~ed to account for relatively small changes in tap~-drive and head-drive motor speeds, tape shrinkage, tape stretching, differences from one apparatus to another, and the like. To this effect, a head-position generator is provided to generate pulses when transducers la, lb rotate into predetermined position, such as when transducer la first contacts tape 3, that is, when trans-ducer la commences its scanning path. Typically, the head-position generator is formed o magnetic elements 4a, 4b which are secured to the shaft which rotates transducers la, lb. ~le-ments 4a, 4b rotate with transducers la, lb and pass a fixedly disposed magnetic pick-up sensor 5 which generates a position detecting pulse as a function of the rotational position of elements 4a, 4b. In a typical video recording apparatus, each transducer records a complete field in a respective record track, and the transducers are rotated at a speed of 30 rps.
Consequently, the position detecting pulses generated by pick-up sensor 5 have a frequency of 30 x 2 Hz or 60 Hz.
Desirably, the video signal recording/reproducing apparatus exhibits both a normal reproducing mode and a "non-normal" reproducing mode. In the former, the record medium is advanced at the same speed during the reproducing operation as during the recording operation. However, in the latter, _g_ ~ ' ~2~
although transducers la, lb are rotatecl at the same rate as during the recording mode, the speed of the record med1um is changed. Thus, in a non-normal reproducing mGde, ~he relative speed of movement between the record medium and the transducers differs from that during the recording mode.
Typical examples o~ such non-normal reproducing modes are the "stop-motion" mode wherein the record medium is stopped completely so that the same record track is scanned repetitively by the transducers; the "slow-motion" mode wherein the record medium is advanced at a fraction of its normal speed such that the transducers scan substantially the same track a multiple number of times; and the "quick or fast-motion" mode wherein the record medium is advanced at a much faster speed than during recording. A common problem in each of these non-normal reproducing modes is that the scanning path traversed by the transducers no longer coincides with the previously recorded record track.
- This, of course, is due to the change in the relative speed of movement of the record medium with respect to the scanning transducers during such non-normal reproducing mode as compared to the normal recording speed. Because o~ such deviation, the transducers are not aligned correct-ly with the record track and, therefore, may pick up noise from the guard bands separating successive record tracks or crosstalk from adjacent tracks. Although this problem is associated with all of the non-normal reproducing modes, as aforesaid, it can be best appreciated by considering the "stop-motion" mode~
~1 Turning to Fig. 2A, there is shown the plurality of parallel tracks T which are recorded on tape 3 during a recording operation. Since tape 3 is advanced in the direction indicated by arrow A, and since the scanning heads, such as head la, scan across the surface of tape 3 in the direction indicated by arrow B, parallel tracks T are formed which are skewed relative to the longitudinal axis of the tape. During the normal reproducing operation, tape 3 once again is moved in the direction of arrow A at the same speed as during the recording operation. Also, transducers la, lb are moved in the direction B, at the same speed as during the recording mode. Hence, the scanning path ofl for example, transducer la during normal reproducing mode is the same as the scanning path of that transducer during the recording mode. Consequently, the scanning path or transducer la coincides with track T, whereby the previously recorded video signals are reproduced accurately.
Let it now be assumed that in the "stop-motion"
reproducing mode, tape 3 is stopped such that transducer la first contacts the tape at a location coincident with the beginning of a recorded track, as shown in Fig. 2B. Since tape 3 is stopped, the scanning path traversed by transducer la no longer coincides with the parallel tracks 7 as shown.
Accordingly, in the assumption represented in Fig. 2B, the scanning path Pl is inclined, or angularly disposed with respect to the record tracks T such that only the beginning and terminal portions of the scanning path Pl coincide with the beginning and terminal portions of the adjacent recorded tracks T. If tape 3 is stopped such that the central portion of the scanning path, shown as P2 in Fig. 2C, coincides with the central portion of a recorded track T, the deviation between the scanning pa~h and recorded track is as represented in that figure. Although transducers la, lb traverse the respective scanning paths Pl and P2 depend~
ing upon the particular position at which tape 3 is stopped, as shown in Figs. 2B and 2C, respectively, the signal reproduced by the transducers may not be accurate reproduc-tions of the recorded signals because of the illustrated deviations between the scanning path and the recorded tracks. Thus, when one of the transducers deviates to one or the other side of the recorded track which is to be scanned, noise or cross-talk signals from~*he guard band or an adjacent track are picked up and distort the repro-duced signals. The purpose of the present invention is to minimize these deviations automatically. By mou~ting transducers la and lb on adjustable support members, the position of each transducer relative to a recorded track T can be changed while the transducer scans the tape such that the scanning path thereof coincides with the recorded track.
In a preferred embodiment, each adjustable head support assembl~ is formed o~ a piezoelectric member which is responsive to a drive voltage applied thereto so as to bend or deflect in a direction perpendicular to the longitudinal axis thereof. An example of a head support assem~ly con-structed of piezoelectric members is described in U~S. Patent No. 3,787,616.
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A head support assembly which can be used with the present invention is shown schematically in Figs. 3A 3C.
This assembly is formed of a pair of lea me~ber~ 7 and 9, each being constructed o~ piezo-ceramic material in which the directions of polarization thereof are represented by arrows c and d, respectively. The opposite surfaces of piezo-ceramic leaf member 7 are plated with electrodes 6a and 6b, respectively; and the opposite surfaces of piezo-ceramic member 9 likewise are plated with electrodes 8a and 8b, respectively. If piezo-ceramic members 7 and 9 overlie each other such that electrodes 6b and 8a are in contact, and if a varia~le drive voltage is applied across the respective members, as shown in Fig. 8B, then piezo-ceramic member 7 tends to expand in its lengthwise direction while piezo-; ceramic member 9 tends to compress. As a result of these oppositely-acting forces, the head support assembly bends, or deflects, by ~n amount which is a function of the strength of the electric field applied across each member. If the polarity of the electric field is reversed, the direction in which the assembly bends, or deflects, correspondingly is reversed.
If the direction of polarization of the piezo-ceramic members is made opposite to each other, that is, if electrode 6a of member 7 now contacts electrode 8a of member 9, the manner in which voltage is applied to the assembly to effect a displacement thereo~ is as shown in Fig. 3C.
Hence, a voltage need not be applied to the electrodes in common contact with each other.
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Instead, a bias voltage is applied to electrode 8b and if a varia~le voltage is applied to electrode 6b, ~he illustrated assembly will bend in a down~ard direction if the variable drive vcltage is less than the bias voltage, and will bend in an upward direction if the variable drive voltage exceeds the bias voltage.
For convenience, it is assumed that the bias voltage has a mag-nitude Vo/2 while the drive voltage is variable between 0 and VO -A practical embodiment of a transducer support assembly formed of the leaf members in Figs. 3A - 3C is il~ustrated in Figs. 4A and 4B, which are top and side views, respectively.
A mounting base 10 receives the piezo-ceramic members which may be secured thereto by a suitable adhesive or plastic molding 11.
~The leaf members extend outwardly from base 10, and magnetic transducer la (or lb) is mounted on the free end thereof. Mounting base 10 may be secured to the rotary arms of the rotating head assembly or, alternatively, may be secured to the bottom surface of guide drum 2a (Fig. lB). In either event, the leaf members extend in a direction outward from the rotary axis o~ the heads.
Preferably, damping or resilient members 13a and 13b such as butyl gum, soft plastic or the like are provided to prevent damp free or resonant oscillation of the leaf members which may be caused by the forces exerted in response to the bending voltages applied to the respective elec~rodes. For example, - 14 ~
, .
these forces may bend the leaf members from a startin~ posi~ion to an ending position as the head mounted thereon tra~erses its scanning path, and then return the leaf members ~o their starting position in preparation for another scan. The damping members are intended to damp such oscil~ation of the leaf members caused by this bending. Accordingly, damping members 13a and 13b are attached to tabs 12a and 12b, respectively, these tabs extending from damping member mounting plate 14 which, as shown, extends outwardly from mounting base 10. Desirable damping action is achieved when damping members 13a and 13b are pressed between the sides of the leaf members and tabs 12a and 12b with suitable force to prevent oscillation in the direction,as sho~n by arrow e but not ; to prevent deflection of the leaf members in the direction as shown by arrow f in response to the voltage applied thereto.
As also shown, contactin~ leads are secured to the respective electrodes of the leaf members for receiving the deflecting voltage. If necessary, a stopper means (not shown) may be inserted in-bet~een the leaf members and the mountin~ plate 14 in order to damp or limit any excess deflection due to a high voltage applied across the electrodes. It should be noted that the shape of the leaf members 7 and 9 as shown in Fig. 4A is not rectangular but is instead triangular, magnetic transducer la (or lb) being attached at the apex. By selecting such a shape, the fundamental resonant frequency of the piezoelectric material can be chosen to be suitably high.
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During the recording operation, transducers la ana lb remain in a normal, undeflected position. Hence~ while recording, a deflecting or drive voltage is not applied ~o the pair of leaf members. However, during a non-normal reproducing mode, it is preferred that a drive voltage be applied. For example, if the scanning path relative to a record track corresponds to scanning path Pl (Fig. 2B), the drive voltage should increase from a zero level at the start of the scanning path to maximum level at the end of the scanning path. If the scanning path P2 (Fig. 2C), then the drive voltage should increase from a minimum level at the start of the scanning path to a zero level at the mid-point thereof and then increase to a maximum level at the end of the scanning path. A suitable drive voltage for deflecting the head support assembly to correct the scanning path deviations shown in Figs. 2B - 2C may have a ramp or sawtooth waveform. For the particular deviation and for the pie20-ceramic leaf assembly shown in Fig. 3C, a ramp wave-form applied as the variable drive voltage V should have a mid-point amplitude equal to the bias voltage (Vo/2).
Apparatus for generating a suitable drive voltage for application to the piezo-ceramic leaf assembly for correcting deviations in the scanning path relative to a recorded track during the reproducing mode is shown in Fig.
5. In this apparatus, magnetic head 21 is a separate, fixed head for the control track ~1 .
of the tape 3 by which the beginning Or the record~d ~racks can be detected, and pick-up head 5 is the pulse generator by w~lch an accurate position of the rotary transducers la and lb can be detected. The head 21 is dlsposed at the outside of ~ne tape drum 2,as sho~n in Fig. 6,to detect the recorded control ~ulses CTL as represented in Fig. 7A. On thé other hand, the pick-up head 5 is disposed in such a manner that magnetic element 4b (or 4a) passes the location of the pick-up head 5 to cause a position detecting pulse PG identifying the position of the rotation to be generated. The rotary transducer lb (or la) starts scanning tape 3 at a time after the position detecting pulse PG is generated, this time being a function of longitudinal tape speed and the fi~ed phase angle ~ between the magnetic element 4b (or 4a~ and the rotary transducer lb (or la).
When the initial points of the scanning track Pl and a recorded track T are coincident with each other (Fig. 2B)~ a control pulse signal CTL will be reproduced through head 21 at a time coincident with the beginning of scan of one o~ the rotary transducers.
On the other hand, when the initial points of the scanning track P2 and a recorded track T are not coincident with each other (Fig. 2C), a control pulse signal CTL will be reproduced at a time before the beginning of scan of one of the rotary transduc~rs.
- In Fig. 7B, control track pulses from the head 21 are shown where the relationship or timing between the starting point of each recorded track T and the recorded control pulse CTL is predetermined. As shown in Fig. 7A, if there is an initial mis-tracking or tracking deviation, shown by the dotted line P, this deviation can be detected by a pulse PG which indicates the rotary transducer position, as shown in Fig. 7D. According to the embodiment shown, the pulse PG is advanced by the time T of the timing shown in Fig. 7C, which corresponds to the starting position of the mis-track P.
Thus, through amplifiers 22 and 23, a reproduced control pulse signal CTL (Fig. 7B) and a pulse PG detecting the position of the rotary transducer are respectively supplied to a phase comparator 24 where the phase difference t (Fig. 7D) is detected. This phase difference t can then be used to develop a signal proportional to a distance com-ponent of the initial tracking deviation. This distance component is a function of the relative speed v between the transducer and the tape, or v-t~ The relative speed v, however, is the sum of the tangential speed of the trans-ducer and the tape speed. Since the tangential speed of the transducer is constant, this can be represented by a fixed bias voltage. The tape speed, however, is variable depending on the mode of operation. A voltage proportional to tape speed may be produced by the simplified circuit 27 shown in Fig. 5. In this circuit, the tape speed is con-trolled by a DC motor 25. The speed of the DC motor 25 is in turn controlled by a potentiometer 26 controlling the voltage supplied to the motor 25.
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The output of the phase comparator 24 corresponding to the phase difference t and a voltage from the wiper arm of the potentiometer 26 corresponding to the speed o motor 25 are respectively supplied to a variable gain amplifier 28 where an output corresponding to v t is obtained, it being understood that a fixed bias voltage corresponding to the tangential speed of the transducer is also applied to the variable gain amplifier 28. Amplifier 28 thus performs the function of a multiplier to produce a signal which is proportional to the product of the relative speed v between the transducer and the tape and the phase difference or time t.
The output of the amplifier 28 is supplied to pro-cessor 30 together with the output of amplifier 29. The amplifier 29 is similar to variable gain amplifier 2~ and generates an output corresponding to v- T where the phase difference T iS a constant value as defined hereinbefore.
Thus, both the phase difference ~ and the tangential speed of the transducer may bP represented as fixed bias voltages, and for the sake of simplification, these bias voltages may be combined as a single bias voltage for amplifer 29. The output of amplifier 29 corresponding to v T iS proportional to another distance component of the initial tracking deviation.
At processor 30, the computation Q - ~-t- v T = d is carried out, where Q is the distance between recorded tracks, that isl the pitch and is a constant value, and d is the initial tracking 9~28;î~Q~
deviation. The processor 30 ma~ be composed of' sum and difference networks. More specifically, the outputs of amplifiers 28 and 29 are first summed and the resulting output is then subtracted from a fixed voltage representing the distance Q.
In order to compensate for the initial track error or deviation d, an initial deviation for transducer la or lb should be given via ~he piezoelectric members so that the beglnning point of the scann`ing track P will be coincident with that of the recorded track T. The direction of head deviation due to flexure of~the piezoelectric members will be roughly at right angles with respect to the track direction. Therefore, it is necessary to compute D = d sin~, where D is the right angle resolved tracking error and 9 is the skew angle of the track P. This is accomplished by means of a resolver 31 which is connected to the output of processor 30. Resolvers which produce outputs proportion~
to the sine or cosine of a resolving angle multiplied times an input variable are well known in the art. However, since the angle ~ and hence sin~ are predetermined fixed constants, the resolver 31 can be simply implemented by means of an attenuator which multiplies the output of processor 30 by a value proportional to sina. The output of resolver 31 is supplied as one input to adder 32.
On the o~ther hand, the pulse PG from amplifier 23 is also supplied to multivibrator 33 to shi~t the pulse timlng corresponding to the fixed phase an~le T. Thus, the shifted - 20 - ~
~3 :
~12~
pulse corresponding to the he~inn~n~ Point of the scannin~ txack P will trigger sawtooth waveorm sign~l genexator 34~ ~rom which a fixed period sawtooth waveform signal iS o~tained~ The period of the sawtooth waveform signal is substantially equal ~o the time required for the transducer to tra~erse its scanning path.
The output of sawtooth waveform signal generator 34 is supplied to a gain and polarity control circuit 35 where the sawtooth wave-form signal will ~e controlled or limited in accordance with the voltage derived from circuit 27, this voltage being proportional to tape speed. With a decreased tape speed relative to the normal speed, the angle ~ of the scanning track P will be increased with respect to the recorded tracks, whereas an increased tape speed relati~e to t~e normal speed will result in a decrease in the angle ~ with respect to the recorded tracks. To adjust the angle ~ or to scan the recorded track precisely, a slope-controlled saw-tooth waveform signal is required during scanning. The circuit 35 provides this control by controlling the maximum amplitude and polarity of the sawtooth waveform signal. More specifically, if the output voltage from circuit 27 corresponds to normal tape 2Q speed, the outp~t signal ~rom circuit 35 is reduced to zero. On the other hand, if the output voltage from circuit 27 corresponds to a non-normal tape speed as is required for "stop-motion", "slow-motion" or l'fast-motion" modes of operation, the output sawtooth waveform signal will-have a maximum amplitude determined by the difference in tape speed from normal speed and a polarity determined by whether the tape speed is greater than or less than the normal speed. The output of circuit 35 is supplied to the second input of adder 32 which produces at its output the com-posite drive signal for the electro-mechanical adjustable trans-ducer support.
By means of the circuit shown in Fig. 5~ identi~icationof the beginn~n~ point ~or scannin~, and adjusting for mistracking ,~
1.~ ~-.! ;2 1 8;i~Q~l during scanning~ due to ~riable t~pe s~peeds, axe both ~ccom-plished. The output o~ t~e adder 32 is applied to the electro-mechanical transducers 7 and 9 through a driving circuit (not shown).
The tracking-error correcting system accordiny to this invention has been descr~ed ~or particular use in correcting tracking errors which occur during the non-normal reproducing modes. Thus, e~en though the xecord medium moves at a relatively slower rate during the "slow-motion" reproducing mode and at a relatively faster rate during t~e "fast-motlon" reproducin~ mode, tracking errors~which arise during these reproducing modes can be corrected b~ t~is invention. Essentially, during the "slow-motion"
or "~ast~motion" modes~ the drive signal produced ~y the circuitry shown in Fig. 5, for the purpose of adjusting the beginning point ;;
for scannin~ and the scanning path traversed by the head so as to precisely track the recorded track, is not a constant level.
Rat~er~ this dri~e signal is changed and controlled periodically as a function of the speed of the record medium. According to this inYent;on, ~is-tracking can be automatically compensated not ~ ;
2Q only in the case of normal reproducing mode but also in the cases of the various non-normal reproducing modes. In addition, a de-sired speed mode of operation can be carried out without any deterioration of reproduced signal quality. ~he means used to accomplish this is an open loop servo system which is both simple and accurate. Finally, it is not necessary to detect or use the envelope of the output 5 ignal ~rom the rotary transducer itself in a closed loop servo system to accompllsh the automatic tracking.
This is of practical ~mportance because it means that a conven-tional video integrated circuit (IC) can be used without modifi-3Q cation.
HaYing described a specific embodiment of the invention~ith reference to the accompanying drawings, it is to be under-.,,~
'l~Z8Z~
stood that the invention is not limited to that precise embodi-ment, and that vario.us changes and modifications may be efecked therein by one skilled in the art without departing rom the scope or spirit of the invention as defined in khe appended claims.
lQ
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BACKGROUND OF THE INVENTION
This invention generally relates to a tracking-error correcting apparatus for use in an apparatus of the kype where-in signal information is recorded in parallel skewed tracks on a record medium and has particular application to a video tape recorder tVTR) in which stop-motion, slow-motion or fast-motion pictures as well as normal~motion pictures can be reproduced.
In a conventional VTR, a rotary transducer head as-sembly is provided with one or more magnetic transducers which scan successive parallel tracks on a magnetic record tape so as to record and/or reproduce video signals in such tracks.
In general, while the one or more transducers rotate across the tape, the tape itself is transported in the longitudinal direction thereof. A typical ~TR includes one, and preferably two, record andjor playback transducers mounted on a suitable rotary assembly so as to rotatably scan a magnetic tape which is helically wrapped about at least a portion of a guide drum forming a part of the transducer assembly. During recording, a tracking servo system controls the rotation of the trans-ducers with respect to the tape movement, and control pulse signals are recorded on a marginal portion of the tape. During reproduction, the same or a similar servo control system is used to synchronize the movement of the tape to the rotation of the transducers in accordance with the recorded control pulse signals. Consequently, an accurate video picture can be displayed in response to the reproduced video signal. This accuracy is, in large part, due to the $act that the servo control system tends to control the relative movement and position between the rotary transducers and the tape such that each ~2~
transducer scans substantially the same track during reproduc-tion operation as was scanned during the recording opera~ion, Therefore, during normal tape speed (normal mode), the servo system serves to insure that the scanning path o~ the heads substantially coincides with the previously recorded tracks.
Recently, many VTR systems have been provided with various reproducing operations, such as "stop or still-motion", "slow-motion" and "quick or fast-motion". In these various reproducing modes, the tape speed differs from the speed during the recording mode. Consequently, the scanning path is different from the recorded track during these different reproducing modes. That is, the scanning path is inclined, or angularly disposed, with respect to the recorded track.
Thus, in various modes other than "normal operation", guard band noise and cross-talk with result due to tracking errors or scanning deviation. Generally, upon leaving the pre-recorded track, the transducer starts scanning a guard band disposed in-between recorded tracks. Accordingly, the output signal of the transducer will be reduced and contain a noise component. On the other hand, as the transducer starts scanning the next recorded track, the transducer picks up signals frsm two adjacent tracks resulting in cross-talk.
This tracking error due to the variation in the tape speed results in a deterioration of the reproduced pictures.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to pxovide a video recording and reproducing apparatus of the type employing a rotary transducer for reproducing signal information recorded in a plurality of parallel skewed ~, '1~28Z~L
tracks on a record medium, which apparatus automatically causes the rotary transducer to trac]c the recorded tracks on the record medium regardless of the speed o~ the record medium.
It is another object of the invention to provide a video tape recorder having various modes such as stop-motion, slow-motion, and fast-motion as well as normal operation which produces a good quality picture in all modes of operation.
It is a further object of the instant invention to provide an improved video tape recorder of the type employing a rotary transducer head assembly wherein the transverse postion of the transducer with respect to a recorded track is automatically varied as a function of tape speed.
According to an aspect of the invention, in an apparatus of the type in which signal information is recorded in a plurality of parallel tracks on a record medium, with the parallel tracks being disposed at a skew angle with respect to the direction of travel of the record medium, and in which a rotary transducer for scanning the parallel tracks is supported by an electro-mechanical adjustable trans-ducer support operative to displace the transducer trans-versely with respect to the parallel tracks in response to a drive signal, an open loop servo system is provided for generating the drive signal to align the scanning path of the transducer with one of the parallel tracks~ The open loop sexvo system comprises first detecting means for detecting the position of the heginning of one of the parallel tracks along the direction of the travel of the record medium and providing a first output, second detecting means for detecting the rotational position of the rotary ~rans-ducer and providing a second output, means for genexating . ,~,,.,~ .
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an output signal corresponding to the speed of the record medium, and signal processing means receiving as inputs the outputs of the first and second detecting means and the speed signal generating means for generating the drive signal.
In a preferred embodiment, the open loop servo system further comprises sawtooth waveform generating means responsive to the second detec-ting means for producing a sawtooth waveform signal having a fixed period which is sub-stantially equal to the time required for the rotary trans-ducer to traverse its scanning path on the record medium, amplitude adjusting means connected to receive the output ~f the sawtooth waveform generating means and responsive to the output of the speed signal means for changing the slope of the sawtooth waveform signal as a function of the speed of the record medium, and adding means for adding the outputs of the signal processing means and the amplitude adjusting means for generating the drive signal.
More particularly there is provided: in an apparatus of the type wherein signal information is recorded in a plurality of parallel t.racks on a record medium, said parallel tracks being disposed at a skew angle with respect to the direction of travel of said record medium, said apparatus having a rotary transducer for scanning said parallel tracks and an electro-mechanical adjustable trans-ducer support provided to support said transducer in scanning relation to said record medium, said transducer support being operative to displace said transducer transversely with ~z~
respect to said parallel tracks in response to a drive signal, the improvement comprising an open loop servo system for generating said drive signal to align the scanning path of said transducer with one of said parallel trac~s, said open loop servo system comprising first detec~ing means or detecting the position of the beginning of one o said parall~l tracks in the direction of travel of said record ~edium and providing a first output, second detecting means for detecting the rotational position of said rotary transducer and providing a sscond output, speed signal generating means for generating an output signal corresponding to the speed of said record medium, and signal processing means receiving as inputs the outputs of said first and second detecting means and said speed signal generating means for generating said drive signal.
There is also provided:
In an apparatus of the type wherein signal informa-tion is recorded in a plurality of parallel tracXs on a record medium, said parallel tracks being skewed with respect to the direction of travel of said record medium, said apparatus having a rotary ~ransducer for scanning said parallel tracks and an electro-mechanical adjustable transducer support provided to sup-port said transducer in scanning relation to said record medium, said transducer support being operative to displace said trans-ducer transversely with respect to said parallal trac~s in re-sponse to a drive signal, the improvement comprising an open loop servo system for senerating said drive signal to align the scanning path of said transducer with one or said parallel tracks, said open 100D servo system co~?rising detectins ~eans for ae-tecting the rotational position of said rotary transducer, s~eed 30 signal generating means for generating an output signal corres-ponding to the speed of said record medium, sawtooth waveform generating means responsive to said detecting means for producing a sawtooth waveform signal having a fixed period which is substan--5a-tially equal to the time required for said rotary transducer to traverse its scanning path on said record medium, and amplitude adjusting means connected to receive the outputs of said sawtooth waveform generating means and said speed signal generat,ing means for changing the slope of said sawtooth waveform signal as a function of the speed of said record medium.
The above, and other objects, features and advantages of the invention will be apparent in the following detailed description of an illustrative embodiment of the invention which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The manner in which the foregoing o~jects and other advantages of the invention are attained will be better ~mder-stood from the following detailed description of a preferred embodiment with reference to the accompanying drawings, in which:
Figs. lA and lB are top and side schematic views, res-pectively, illustrating a rotary transducer head assembly and the manner in which a tape record medium is helically wrapped around a guide drum;
Figs. 2A, 2B and 2C collectively are plan views of a tape record medium diagramatically illustrating the parallel skew-ed record tracks produced by the assembly shown in Figs. lA and lB
and an example of the resulting mis-tracking of the rotary trans-ducer due to a variation in the speed of the tape record medium;
Figs. 3A, 3B and 3C are schematic diagrams which collec-tively illustrate the basic structure and principles of operation of the electro-mechanical adjustable transducer support used in the preferred embodiment of the present invention;
Figs. 4A and 4B are top and side schematic view, respectively, showing the structure of the electro-mechanical adjustable transducer support;
Fiy. 5 is a block diagram of the open loop servo control ,,~ 6 -circuit according to the invention;
Fig. 6 is a top vlew similar to Fig. lA illustra~ing the positions of the magnetic head for detecting recorded control pulses and the pick-up head for detecting the relative position of the rotary transducer; and Fig. 7A is a plan view of a tape record medium diagramatically illustrating the geometric and dimensional relations between the parallel skewed record tracks, a displaced scanning path of a rotary transducer and recorded control pulses, and Figs. 7~, 7C
and 7D are pulse diagrams related to the plan view of Fig. 7A.
DETAILED DESCRIPTION OF TH~ PREFERRFD EMBODIMENT
The following detailed description, given by way of example, will best be understood in conjunction with the accompanying drawings. For the purpose o~ simplification and to facilitate an understanding of the present invention, the following description relates to the environment of a video signal recorder and, more particularly, to a VTR. However, the problems to which the present invention is addressed, and the solution to those problems, as disclosed herein, are not limited solely to video signal recording apparatus. Hence, it should be understood that this description also is applicable to other types of analog signal recording devices, to digital sign~l recording devices and to other rotary head scanning apparatus which can be used for recording, reproducing, or other purposes.
Turning now to ~ig. lA, there is schematically illustra~ed ~lZ~
a top vlew of a typical rotary head scanning device, such as used in a VTR. As is conventional, this device is formed wi~h two magnetic record/playback transducers la, lb which are adapted for rotation about a central axls. A guide drum 2 is adapted to receive a record medium, such as tape 3, wrapped helically thereabout for at least 18Q. Transducers la and lb may be mounted on diametrically opposed arms which are rotated so as to scan successive, parallel, skewed tracks across tape 3. Thus, transducers la and lb rotate in the clockwise dlrection as indicated by the arrow while tape 3 is advanced to the right and counter-clockwise about the guide drum so as ~o record signal information thereon.
Alternatively, and as shown in Fig. lB, guide drum 2 may be formed of two drums 2a, 2b disposed in face-to-face con-figuration and spaced so as to define a scanning gap therebetween.
Tape 3 is helically wrapped about a portion of the surface of guide drum 2 so that the record tracks recorded by transducers la, lb are skewed relative to the longitudinal direction of the tape. When two transducers are used, it will be appreciated that alternate tracks are recorded thereby, ~hat ~irst transducer la records one track,then transducer lb records the next adjacent track, then transducer la records the following track, and so on. In the alternative structure of Fig. lB, transducers la and lb are mounted on one of drums 2a, 2b, this , drum being rotated relative to the other drum such that the heads , ~ ' l~Z~ZY~
traverse the aformentioned scanning paths.
During a signal recording operation and during a "normal" signal reproducing operation, the relative speed of tap~ 3 with respect to transducers la and lb is the same.
Suitable servo control circuitry (not shown) generall~ is provi~ed to account for relatively small changes in tap~-drive and head-drive motor speeds, tape shrinkage, tape stretching, differences from one apparatus to another, and the like. To this effect, a head-position generator is provided to generate pulses when transducers la, lb rotate into predetermined position, such as when transducer la first contacts tape 3, that is, when trans-ducer la commences its scanning path. Typically, the head-position generator is formed o magnetic elements 4a, 4b which are secured to the shaft which rotates transducers la, lb. ~le-ments 4a, 4b rotate with transducers la, lb and pass a fixedly disposed magnetic pick-up sensor 5 which generates a position detecting pulse as a function of the rotational position of elements 4a, 4b. In a typical video recording apparatus, each transducer records a complete field in a respective record track, and the transducers are rotated at a speed of 30 rps.
Consequently, the position detecting pulses generated by pick-up sensor 5 have a frequency of 30 x 2 Hz or 60 Hz.
Desirably, the video signal recording/reproducing apparatus exhibits both a normal reproducing mode and a "non-normal" reproducing mode. In the former, the record medium is advanced at the same speed during the reproducing operation as during the recording operation. However, in the latter, _g_ ~ ' ~2~
although transducers la, lb are rotatecl at the same rate as during the recording mode, the speed of the record med1um is changed. Thus, in a non-normal reproducing mGde, ~he relative speed of movement between the record medium and the transducers differs from that during the recording mode.
Typical examples o~ such non-normal reproducing modes are the "stop-motion" mode wherein the record medium is stopped completely so that the same record track is scanned repetitively by the transducers; the "slow-motion" mode wherein the record medium is advanced at a fraction of its normal speed such that the transducers scan substantially the same track a multiple number of times; and the "quick or fast-motion" mode wherein the record medium is advanced at a much faster speed than during recording. A common problem in each of these non-normal reproducing modes is that the scanning path traversed by the transducers no longer coincides with the previously recorded record track.
- This, of course, is due to the change in the relative speed of movement of the record medium with respect to the scanning transducers during such non-normal reproducing mode as compared to the normal recording speed. Because o~ such deviation, the transducers are not aligned correct-ly with the record track and, therefore, may pick up noise from the guard bands separating successive record tracks or crosstalk from adjacent tracks. Although this problem is associated with all of the non-normal reproducing modes, as aforesaid, it can be best appreciated by considering the "stop-motion" mode~
~1 Turning to Fig. 2A, there is shown the plurality of parallel tracks T which are recorded on tape 3 during a recording operation. Since tape 3 is advanced in the direction indicated by arrow A, and since the scanning heads, such as head la, scan across the surface of tape 3 in the direction indicated by arrow B, parallel tracks T are formed which are skewed relative to the longitudinal axis of the tape. During the normal reproducing operation, tape 3 once again is moved in the direction of arrow A at the same speed as during the recording operation. Also, transducers la, lb are moved in the direction B, at the same speed as during the recording mode. Hence, the scanning path ofl for example, transducer la during normal reproducing mode is the same as the scanning path of that transducer during the recording mode. Consequently, the scanning path or transducer la coincides with track T, whereby the previously recorded video signals are reproduced accurately.
Let it now be assumed that in the "stop-motion"
reproducing mode, tape 3 is stopped such that transducer la first contacts the tape at a location coincident with the beginning of a recorded track, as shown in Fig. 2B. Since tape 3 is stopped, the scanning path traversed by transducer la no longer coincides with the parallel tracks 7 as shown.
Accordingly, in the assumption represented in Fig. 2B, the scanning path Pl is inclined, or angularly disposed with respect to the record tracks T such that only the beginning and terminal portions of the scanning path Pl coincide with the beginning and terminal portions of the adjacent recorded tracks T. If tape 3 is stopped such that the central portion of the scanning path, shown as P2 in Fig. 2C, coincides with the central portion of a recorded track T, the deviation between the scanning pa~h and recorded track is as represented in that figure. Although transducers la, lb traverse the respective scanning paths Pl and P2 depend~
ing upon the particular position at which tape 3 is stopped, as shown in Figs. 2B and 2C, respectively, the signal reproduced by the transducers may not be accurate reproduc-tions of the recorded signals because of the illustrated deviations between the scanning path and the recorded tracks. Thus, when one of the transducers deviates to one or the other side of the recorded track which is to be scanned, noise or cross-talk signals from~*he guard band or an adjacent track are picked up and distort the repro-duced signals. The purpose of the present invention is to minimize these deviations automatically. By mou~ting transducers la and lb on adjustable support members, the position of each transducer relative to a recorded track T can be changed while the transducer scans the tape such that the scanning path thereof coincides with the recorded track.
In a preferred embodiment, each adjustable head support assembl~ is formed o~ a piezoelectric member which is responsive to a drive voltage applied thereto so as to bend or deflect in a direction perpendicular to the longitudinal axis thereof. An example of a head support assem~ly con-structed of piezoelectric members is described in U~S. Patent No. 3,787,616.
, ~
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A head support assembly which can be used with the present invention is shown schematically in Figs. 3A 3C.
This assembly is formed of a pair of lea me~ber~ 7 and 9, each being constructed o~ piezo-ceramic material in which the directions of polarization thereof are represented by arrows c and d, respectively. The opposite surfaces of piezo-ceramic leaf member 7 are plated with electrodes 6a and 6b, respectively; and the opposite surfaces of piezo-ceramic member 9 likewise are plated with electrodes 8a and 8b, respectively. If piezo-ceramic members 7 and 9 overlie each other such that electrodes 6b and 8a are in contact, and if a varia~le drive voltage is applied across the respective members, as shown in Fig. 8B, then piezo-ceramic member 7 tends to expand in its lengthwise direction while piezo-; ceramic member 9 tends to compress. As a result of these oppositely-acting forces, the head support assembly bends, or deflects, by ~n amount which is a function of the strength of the electric field applied across each member. If the polarity of the electric field is reversed, the direction in which the assembly bends, or deflects, correspondingly is reversed.
If the direction of polarization of the piezo-ceramic members is made opposite to each other, that is, if electrode 6a of member 7 now contacts electrode 8a of member 9, the manner in which voltage is applied to the assembly to effect a displacement thereo~ is as shown in Fig. 3C.
Hence, a voltage need not be applied to the electrodes in common contact with each other.
,~
.,~. .
Instead, a bias voltage is applied to electrode 8b and if a varia~le voltage is applied to electrode 6b, ~he illustrated assembly will bend in a down~ard direction if the variable drive vcltage is less than the bias voltage, and will bend in an upward direction if the variable drive voltage exceeds the bias voltage.
For convenience, it is assumed that the bias voltage has a mag-nitude Vo/2 while the drive voltage is variable between 0 and VO -A practical embodiment of a transducer support assembly formed of the leaf members in Figs. 3A - 3C is il~ustrated in Figs. 4A and 4B, which are top and side views, respectively.
A mounting base 10 receives the piezo-ceramic members which may be secured thereto by a suitable adhesive or plastic molding 11.
~The leaf members extend outwardly from base 10, and magnetic transducer la (or lb) is mounted on the free end thereof. Mounting base 10 may be secured to the rotary arms of the rotating head assembly or, alternatively, may be secured to the bottom surface of guide drum 2a (Fig. lB). In either event, the leaf members extend in a direction outward from the rotary axis o~ the heads.
Preferably, damping or resilient members 13a and 13b such as butyl gum, soft plastic or the like are provided to prevent damp free or resonant oscillation of the leaf members which may be caused by the forces exerted in response to the bending voltages applied to the respective elec~rodes. For example, - 14 ~
, .
these forces may bend the leaf members from a startin~ posi~ion to an ending position as the head mounted thereon tra~erses its scanning path, and then return the leaf members ~o their starting position in preparation for another scan. The damping members are intended to damp such oscil~ation of the leaf members caused by this bending. Accordingly, damping members 13a and 13b are attached to tabs 12a and 12b, respectively, these tabs extending from damping member mounting plate 14 which, as shown, extends outwardly from mounting base 10. Desirable damping action is achieved when damping members 13a and 13b are pressed between the sides of the leaf members and tabs 12a and 12b with suitable force to prevent oscillation in the direction,as sho~n by arrow e but not ; to prevent deflection of the leaf members in the direction as shown by arrow f in response to the voltage applied thereto.
As also shown, contactin~ leads are secured to the respective electrodes of the leaf members for receiving the deflecting voltage. If necessary, a stopper means (not shown) may be inserted in-bet~een the leaf members and the mountin~ plate 14 in order to damp or limit any excess deflection due to a high voltage applied across the electrodes. It should be noted that the shape of the leaf members 7 and 9 as shown in Fig. 4A is not rectangular but is instead triangular, magnetic transducer la (or lb) being attached at the apex. By selecting such a shape, the fundamental resonant frequency of the piezoelectric material can be chosen to be suitably high.
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During the recording operation, transducers la ana lb remain in a normal, undeflected position. Hence~ while recording, a deflecting or drive voltage is not applied ~o the pair of leaf members. However, during a non-normal reproducing mode, it is preferred that a drive voltage be applied. For example, if the scanning path relative to a record track corresponds to scanning path Pl (Fig. 2B), the drive voltage should increase from a zero level at the start of the scanning path to maximum level at the end of the scanning path. If the scanning path P2 (Fig. 2C), then the drive voltage should increase from a minimum level at the start of the scanning path to a zero level at the mid-point thereof and then increase to a maximum level at the end of the scanning path. A suitable drive voltage for deflecting the head support assembly to correct the scanning path deviations shown in Figs. 2B - 2C may have a ramp or sawtooth waveform. For the particular deviation and for the pie20-ceramic leaf assembly shown in Fig. 3C, a ramp wave-form applied as the variable drive voltage V should have a mid-point amplitude equal to the bias voltage (Vo/2).
Apparatus for generating a suitable drive voltage for application to the piezo-ceramic leaf assembly for correcting deviations in the scanning path relative to a recorded track during the reproducing mode is shown in Fig.
5. In this apparatus, magnetic head 21 is a separate, fixed head for the control track ~1 .
of the tape 3 by which the beginning Or the record~d ~racks can be detected, and pick-up head 5 is the pulse generator by w~lch an accurate position of the rotary transducers la and lb can be detected. The head 21 is dlsposed at the outside of ~ne tape drum 2,as sho~n in Fig. 6,to detect the recorded control ~ulses CTL as represented in Fig. 7A. On thé other hand, the pick-up head 5 is disposed in such a manner that magnetic element 4b (or 4a) passes the location of the pick-up head 5 to cause a position detecting pulse PG identifying the position of the rotation to be generated. The rotary transducer lb (or la) starts scanning tape 3 at a time after the position detecting pulse PG is generated, this time being a function of longitudinal tape speed and the fi~ed phase angle ~ between the magnetic element 4b (or 4a~ and the rotary transducer lb (or la).
When the initial points of the scanning track Pl and a recorded track T are coincident with each other (Fig. 2B)~ a control pulse signal CTL will be reproduced through head 21 at a time coincident with the beginning of scan of one o~ the rotary transducers.
On the other hand, when the initial points of the scanning track P2 and a recorded track T are not coincident with each other (Fig. 2C), a control pulse signal CTL will be reproduced at a time before the beginning of scan of one of the rotary transduc~rs.
- In Fig. 7B, control track pulses from the head 21 are shown where the relationship or timing between the starting point of each recorded track T and the recorded control pulse CTL is predetermined. As shown in Fig. 7A, if there is an initial mis-tracking or tracking deviation, shown by the dotted line P, this deviation can be detected by a pulse PG which indicates the rotary transducer position, as shown in Fig. 7D. According to the embodiment shown, the pulse PG is advanced by the time T of the timing shown in Fig. 7C, which corresponds to the starting position of the mis-track P.
Thus, through amplifiers 22 and 23, a reproduced control pulse signal CTL (Fig. 7B) and a pulse PG detecting the position of the rotary transducer are respectively supplied to a phase comparator 24 where the phase difference t (Fig. 7D) is detected. This phase difference t can then be used to develop a signal proportional to a distance com-ponent of the initial tracking deviation. This distance component is a function of the relative speed v between the transducer and the tape, or v-t~ The relative speed v, however, is the sum of the tangential speed of the trans-ducer and the tape speed. Since the tangential speed of the transducer is constant, this can be represented by a fixed bias voltage. The tape speed, however, is variable depending on the mode of operation. A voltage proportional to tape speed may be produced by the simplified circuit 27 shown in Fig. 5. In this circuit, the tape speed is con-trolled by a DC motor 25. The speed of the DC motor 25 is in turn controlled by a potentiometer 26 controlling the voltage supplied to the motor 25.
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The output of the phase comparator 24 corresponding to the phase difference t and a voltage from the wiper arm of the potentiometer 26 corresponding to the speed o motor 25 are respectively supplied to a variable gain amplifier 28 where an output corresponding to v t is obtained, it being understood that a fixed bias voltage corresponding to the tangential speed of the transducer is also applied to the variable gain amplifier 28. Amplifier 28 thus performs the function of a multiplier to produce a signal which is proportional to the product of the relative speed v between the transducer and the tape and the phase difference or time t.
The output of the amplifier 28 is supplied to pro-cessor 30 together with the output of amplifier 29. The amplifier 29 is similar to variable gain amplifier 2~ and generates an output corresponding to v- T where the phase difference T iS a constant value as defined hereinbefore.
Thus, both the phase difference ~ and the tangential speed of the transducer may bP represented as fixed bias voltages, and for the sake of simplification, these bias voltages may be combined as a single bias voltage for amplifer 29. The output of amplifier 29 corresponding to v T iS proportional to another distance component of the initial tracking deviation.
At processor 30, the computation Q - ~-t- v T = d is carried out, where Q is the distance between recorded tracks, that isl the pitch and is a constant value, and d is the initial tracking 9~28;î~Q~
deviation. The processor 30 ma~ be composed of' sum and difference networks. More specifically, the outputs of amplifiers 28 and 29 are first summed and the resulting output is then subtracted from a fixed voltage representing the distance Q.
In order to compensate for the initial track error or deviation d, an initial deviation for transducer la or lb should be given via ~he piezoelectric members so that the beglnning point of the scann`ing track P will be coincident with that of the recorded track T. The direction of head deviation due to flexure of~the piezoelectric members will be roughly at right angles with respect to the track direction. Therefore, it is necessary to compute D = d sin~, where D is the right angle resolved tracking error and 9 is the skew angle of the track P. This is accomplished by means of a resolver 31 which is connected to the output of processor 30. Resolvers which produce outputs proportion~
to the sine or cosine of a resolving angle multiplied times an input variable are well known in the art. However, since the angle ~ and hence sin~ are predetermined fixed constants, the resolver 31 can be simply implemented by means of an attenuator which multiplies the output of processor 30 by a value proportional to sina. The output of resolver 31 is supplied as one input to adder 32.
On the o~ther hand, the pulse PG from amplifier 23 is also supplied to multivibrator 33 to shi~t the pulse timlng corresponding to the fixed phase an~le T. Thus, the shifted - 20 - ~
~3 :
~12~
pulse corresponding to the he~inn~n~ Point of the scannin~ txack P will trigger sawtooth waveorm sign~l genexator 34~ ~rom which a fixed period sawtooth waveform signal iS o~tained~ The period of the sawtooth waveform signal is substantially equal ~o the time required for the transducer to tra~erse its scanning path.
The output of sawtooth waveform signal generator 34 is supplied to a gain and polarity control circuit 35 where the sawtooth wave-form signal will ~e controlled or limited in accordance with the voltage derived from circuit 27, this voltage being proportional to tape speed. With a decreased tape speed relative to the normal speed, the angle ~ of the scanning track P will be increased with respect to the recorded tracks, whereas an increased tape speed relati~e to t~e normal speed will result in a decrease in the angle ~ with respect to the recorded tracks. To adjust the angle ~ or to scan the recorded track precisely, a slope-controlled saw-tooth waveform signal is required during scanning. The circuit 35 provides this control by controlling the maximum amplitude and polarity of the sawtooth waveform signal. More specifically, if the output voltage from circuit 27 corresponds to normal tape 2Q speed, the outp~t signal ~rom circuit 35 is reduced to zero. On the other hand, if the output voltage from circuit 27 corresponds to a non-normal tape speed as is required for "stop-motion", "slow-motion" or l'fast-motion" modes of operation, the output sawtooth waveform signal will-have a maximum amplitude determined by the difference in tape speed from normal speed and a polarity determined by whether the tape speed is greater than or less than the normal speed. The output of circuit 35 is supplied to the second input of adder 32 which produces at its output the com-posite drive signal for the electro-mechanical adjustable trans-ducer support.
By means of the circuit shown in Fig. 5~ identi~icationof the beginn~n~ point ~or scannin~, and adjusting for mistracking ,~
1.~ ~-.! ;2 1 8;i~Q~l during scanning~ due to ~riable t~pe s~peeds, axe both ~ccom-plished. The output o~ t~e adder 32 is applied to the electro-mechanical transducers 7 and 9 through a driving circuit (not shown).
The tracking-error correcting system accordiny to this invention has been descr~ed ~or particular use in correcting tracking errors which occur during the non-normal reproducing modes. Thus, e~en though the xecord medium moves at a relatively slower rate during the "slow-motion" reproducing mode and at a relatively faster rate during t~e "fast-motlon" reproducin~ mode, tracking errors~which arise during these reproducing modes can be corrected b~ t~is invention. Essentially, during the "slow-motion"
or "~ast~motion" modes~ the drive signal produced ~y the circuitry shown in Fig. 5, for the purpose of adjusting the beginning point ;;
for scannin~ and the scanning path traversed by the head so as to precisely track the recorded track, is not a constant level.
Rat~er~ this dri~e signal is changed and controlled periodically as a function of the speed of the record medium. According to this inYent;on, ~is-tracking can be automatically compensated not ~ ;
2Q only in the case of normal reproducing mode but also in the cases of the various non-normal reproducing modes. In addition, a de-sired speed mode of operation can be carried out without any deterioration of reproduced signal quality. ~he means used to accomplish this is an open loop servo system which is both simple and accurate. Finally, it is not necessary to detect or use the envelope of the output 5 ignal ~rom the rotary transducer itself in a closed loop servo system to accompllsh the automatic tracking.
This is of practical ~mportance because it means that a conven-tional video integrated circuit (IC) can be used without modifi-3Q cation.
HaYing described a specific embodiment of the invention~ith reference to the accompanying drawings, it is to be under-.,,~
'l~Z8Z~
stood that the invention is not limited to that precise embodi-ment, and that vario.us changes and modifications may be efecked therein by one skilled in the art without departing rom the scope or spirit of the invention as defined in khe appended claims.
lQ
`. ~
Claims (7)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an apparatus of the type wherein signal in-formation is recorded in a plurality of parallel tracks on a record medium, said parallel tracks being disposed at a skew angle with respect to the direction of travel of said record medium, said apparatus having a rotary transducer for scanning said parallel tracks and an electro-mechanical adjustable transducer support provided to support said transducer in scanning relation to said record medium, said transducer support being operative to displace said transducer transversely with respect to said parallel tracks in response to a drive signal, the improvement comprising an open loop servo system for generating said drive signal to align the scanning path of said transducer with one of said parallel tracks, said open loop servo system comprising first detecting means for detecting the position of the beginning of one of said parallel tracks in the direction of travel of said record medium and providing a first output, second detecting means for detecting the rotational position of said rotary transducer and providing a second output, speed signal generating means for generating an output signal corresponding to the speed of said record medium, and signal processing means receiving as inputs the outputs of said first and second detecting means and said speed signal generating means for generating said drive signal.
2. The apparatus of claim 1, said signal processing means including phase detecting means for producing an output error signal corresponding to a phase difference between the outputs of said first and second detecting means and multiply-ing means connected to receive the outputs of said phase de-tecting means and said speed signal generating means.
3. The apparatus of claim 2, said multiplying means comprising a first multiplier connected to receive as inputs the outputs of said phase detecting means and said speed signal generating means for producing a first distance signal propor-tional to the product of said output error signal and the speed of said record medium, a difference circuit connected to receive the output of said first multiplier and providing a track error deviation signal proportional to the difference between the dis-tance between adjacent ones of said parallel tracks, along the direction of travel of said record medium, and said first distance signal, and an angle resolving circuit connected to receive the output of said difference circuit to produce a signal proportional to the product of said track error deviation signal and the sine of the skew angle of said parallel tracks.
4. The apparatus of claim 3, wherein said second detecting means produces an output at a predetermined fixed phase in advance of the scanning track of said rotary transducer, said multiplying means further includes a second multiplier connected to receive, as inputs, the output of said speed signal generating means and a fixed bias corresponding to said predetermined fixed phase for producing a second distance signal proportional to said fixed bias and the speed of said record medium, the output of said second multiplier is connected to an input of said difference cir-cuit and said track error deviation signal is proportional to the difference of said distance between adjacent ones of said parallel tracks and the sum of said first and second distance signals.
5. The apparatus of claim 1, wherein said open loop servo system further comprises sawtooth waveform generating means responsive to the output from said second detecting means for producing an output sawtooth waveform signal having a fixed period which is substantially equal to the time required for said rotary transducer to traverse its scanning path on said record medium, amplitude adjusting means connected to receive the out-puts of said sawtooth waveform generating means and said speed signal generating means for changing the slope of said sawtooth waveform signal as a function of the speed of said record medium and adding means for adding the outputs of said signal processing means and said amplitude adjusting means for generating said drive signal.
6. The apparatus of claim 5, wherein said second detecting means produces an output at a predetermined fixed phase in advance of the scanning track of said rotary transducer, and further comprising delay pulse generating means connected between said second detecting means and said sawtooth waveform generating means and being responsive to the output from said second detect-ing means for producing trigger pulses for said sawtooth waveform generating means, said trigger pulses being delayed by a time period corresponding to said predetermined fixed phase.
7. In an apparatus of the type wherein signal informa-tion is recorded in a plurality of parallel tracks on a record medium, said parallel tracks being skewed with respect to the direction of travel of said record medium, said apparatus having a rotary transducer for scanning said parallel tracks and an electro-mechanical adjustable transducer support provided to sup-port said transducer in scanning relation to said record medium, said transducer support being operative to displace said trans ducer transversely with respect to said parallel tracks in re-sponse to a drive signal, the improvement comprising an open loop servo system for generating said drive signal to align the scanning path of said transducer with one of said parallel tracks, said open loop servo system comprising detecting means for de-tecting the rotational position of said rotary transducer, speed signal generating means for generating an output signal corres-ponding to the speed of said record medium, sawtooth waveform generating means responsive to said detecting means for producing a sawtooth waveform signal having a fixed period which is substan-tially equal to the time required for said rotary transducer to traverse its scanning path on said record medium, and amplitude adjusting means connected to receive the outputs of said sawtooth waveform generating means and said speed signal generating means for changing the slope of said sawtooth waveform signal as a function of the speed of said record medium.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP51145113A JPS6031009B2 (en) | 1976-12-02 | 1976-12-02 | automatic tracking device |
| JP145113/76 | 1976-12-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128201A true CA1128201A (en) | 1982-07-20 |
Family
ID=15377679
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA291,970A Expired CA1128201A (en) | 1976-12-02 | 1977-11-29 | Open loop servo-system for accurate tracking in a video signal reproducing apparatus |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4167762A (en) |
| JP (1) | JPS6031009B2 (en) |
| AT (1) | AT378880B (en) |
| CA (1) | CA1128201A (en) |
| DE (1) | DE2753786A1 (en) |
| FR (1) | FR2373119A1 (en) |
| GB (1) | GB1592377A (en) |
| NL (1) | NL7713358A (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54117627A (en) * | 1978-03-06 | 1979-09-12 | Sony Corp | Video signal reproducing device |
| US4318142A (en) * | 1978-03-23 | 1982-03-02 | Ampex Corporation | Automatically compensated movable head servo circuit and method |
| JPS54132120A (en) * | 1978-04-06 | 1979-10-13 | Sony Corp | Reproduction device of video signal |
| JPS5539478A (en) * | 1978-09-14 | 1980-03-19 | Sony Corp | Regenerator of video signal |
| JPS5563187A (en) * | 1978-11-07 | 1980-05-13 | Nec Corp | Special reproduction device |
| AU539426B2 (en) * | 1979-03-15 | 1984-09-27 | Sony Corporation | Automatic head height control apparatus |
| DE3021480C2 (en) * | 1979-06-04 | 1985-07-11 | Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka | Tracking system for video recording and playback devices |
| US4327434A (en) * | 1980-01-28 | 1982-04-27 | Rca Corporation | Video disc stylus position sensor system |
| US4313189A (en) * | 1979-12-20 | 1982-01-26 | Rca Corporation | Stylus position sensor for video disc player apparatus |
| JPS56101621A (en) * | 1980-01-17 | 1981-08-14 | Victor Co Of Japan Ltd | Tracking system of magnetic reproducing device |
| JPS56127925A (en) * | 1980-03-13 | 1981-10-07 | Sony Corp | Tracking device of magnetic head |
| JPS58172078A (en) * | 1982-04-02 | 1983-10-08 | Sony Corp | Reproducing device |
| FR2566952B1 (en) * | 1984-06-28 | 1989-03-31 | Enertec | TRACK TRACKING ALIGNMENT FOR ROTATING MAGNETIC HEAD |
| US4766450A (en) * | 1987-07-17 | 1988-08-23 | Xerox Corporation | Charging deposition control in electrographic thin film writting head |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3355547A (en) * | 1962-10-20 | 1967-11-28 | Matsushita Electric Industrial Co Ltd | Open loop servo system for magnetic tape recording and reproducing apparatus |
| US3293359A (en) * | 1962-12-01 | 1966-12-20 | Matsushita Electric Industrial Co Ltd | Magnetic recording and reproducing devices |
| US3358080A (en) * | 1964-04-20 | 1967-12-12 | Ampex | Control system for wideband recording and reproducing systems |
| DE2216077C3 (en) * | 1972-04-01 | 1978-04-20 | Loewe Opta Gmbh, 1000 Berlin | Automatic track scan control circuit for video magnetic tape recorder and player |
| JPS5650329B2 (en) * | 1972-05-22 | 1981-11-28 | ||
| US3787616A (en) * | 1972-06-05 | 1974-01-22 | Newell Ind | Time base error correction system and method |
| JPS4986014U (en) * | 1972-11-11 | 1974-07-25 | ||
| JPS5633772B2 (en) * | 1972-12-20 | 1981-08-06 | ||
| DE2530482C2 (en) * | 1974-07-15 | 1984-11-15 | N.V. Philips' Gloeilampenfabrieken, Eindhoven | Servo system for a video recorder |
| JPS598891B2 (en) * | 1974-11-26 | 1984-02-28 | ソニー株式会社 | Rotating magnetic head device |
| JPS6059787B2 (en) * | 1975-10-14 | 1985-12-26 | ソニー株式会社 | Video signal reproducing device |
| IT1073210B (en) * | 1976-03-19 | 1985-04-13 | Ampex Corp Soc | SYSTEM FOR PRODUCING SPECIAL MOVEMENT EFFECTS IN VIDEO RECORDING AND PLAYBACK DEVICES |
| JPS5326107A (en) * | 1976-08-24 | 1978-03-10 | Sony Corp | Tracking correcting apparatus |
| JPS6032258B2 (en) * | 1976-09-13 | 1985-07-26 | ソニー株式会社 | Automatic tracking control device |
| GB1560023A (en) * | 1976-10-05 | 1980-01-30 | Sony Corp | Automatic magnetic-head scan tracking arrangements |
-
1976
- 1976-12-02 JP JP51145113A patent/JPS6031009B2/en not_active Expired
-
1977
- 1977-11-29 CA CA291,970A patent/CA1128201A/en not_active Expired
- 1977-12-01 US US05/856,845 patent/US4167762A/en not_active Expired - Lifetime
- 1977-12-01 GB GB50200/77A patent/GB1592377A/en not_active Expired
- 1977-12-02 FR FR7736399A patent/FR2373119A1/en active Granted
- 1977-12-02 AT AT0866977A patent/AT378880B/en not_active IP Right Cessation
- 1977-12-02 NL NL7713358A patent/NL7713358A/en not_active Application Discontinuation
- 1977-12-02 DE DE19772753786 patent/DE2753786A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2753786C2 (en) | 1988-04-28 |
| DE2753786A1 (en) | 1978-06-08 |
| US4167762A (en) | 1979-09-11 |
| GB1592377A (en) | 1981-07-08 |
| FR2373119B1 (en) | 1985-05-17 |
| AT378880B (en) | 1985-10-10 |
| FR2373119A1 (en) | 1978-06-30 |
| ATA866977A (en) | 1985-02-15 |
| JPS5369617A (en) | 1978-06-21 |
| NL7713358A (en) | 1978-06-06 |
| JPS6031009B2 (en) | 1985-07-19 |
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