DE2305848B2 - DEVICE FOR RECORDING AND REPLAYING IMAGE INFORMATION - Google Patents

Description

55

The invention relates to a device for recording and reproducing image information on a tape-shaped recording medium, which has a head disk for recording and reading of the information and a control system for synchronizing the image information with a reference signal by controlling the speed of the head disk, which control system includes a first detector for obtaining a first control signal by comparing a first measurement signal with a first component of the reference signal and a second detector for obtaining a second control signal Contains comparison of a second measurement signal with a second component of the reference signal, the Frequency of the second component of the reference signal is significantly greater than that of the first component and wherein the control system further includes a switching unit, with the aid of which a control signal received is a Drive device of the head disk can be supplied and the selectively the second control signal forwards to this drive device as soon as the first control signal falls below a certain limit value.

Such a device is e.g. B. from the journal "Journal of the SMPTE", July 1961, pages 4X9 to 494 known. Such devices are, especially in the professional studio use, can be synchronized very accurately in bezi'g to a reference signal to image information, originating from different sources, to be able to fit together without appreciable transients.

This synchronization takes place by regulating the speed of the top disk. Between this Rotational speed and the time base of the recording medium recorded on the recording medium or from this recording medium There is a clear relationship between the read out signal. This applies to both oblique scanning, at the z. B. a single video head scans an oblique track on the tape, as well as for the Cross scanning, in which several heads scan cross tracks one after the other. Contains in oblique scanning generally one track a raster of the video signal.

In the above known device, the synchronization takes place in two stages, namely through a coarse control and a subsequent fine control. During the coarse control this will be Control signal for the drive device of the head disk essentially through the output signal of the First detector determines a phase comparison between a raster frequency first component of the reference signal and the first measurement signal. This first measurement signal is filtered out by the Raster pulse series of the video signal read out or obtained with the help of a generator that is linked to the Head disk is coupled and provides c in signal, the frequency of which is equal to or proportional to the speed this head disk is.

Through this coarse control, the device is initially roughly synchronized with respect to the reference, after which a switch is made to fine control, during which the control signal for the drive device the head disk is determined by the output signal of the second detector, the one Frequency and phase comparison between a line-frequency second component of the reference signal and the second measurement signal. When playing, this measurement signal is filtered out by the Line pulse train of the read out video signal obtained. Due to the high frequency of the second Detector supplied second component of the reference signal and the second measurement signal can be based on this Way a very precise regulation of the angular position of the top disk can be obtained.

It turns out, however, that the coarse control is already strict for correct synchronization Must meet requirements. If namely ^ h at the point in time at which the switchover from the coarse control on the fine control takes place, the deviation between the reference signal and the signal

Aera of the record carrier, which is provided by the Meli signals, is greater than one line period, ki Ph

jarrestell g p, d

with the fine control no phase comparison between corresponding line pulses e ^; nes grid but is gegeneinanjj _he held a phase comparison between the shifted line pulses. This means that the error that exists when switching is rounded down to a whole multiple of the line period is retained. In order to avoid this error, it must therefore be ensured that the final control error of the large control at the time of switching to the fine control is less than a period of time, which is a very strict requirement

The invention aims to provide a device of the type mentioned, in which the above problem is avoided. The invention is characterized in that d ^; e second component of the reference signal is generated by a variable oscillator, the control input of which is supplied with a control signal which is obtained with the aid of a third detector which compares a third measurement signal with the first component of the reference signal. As a result of the measure according to the invention, it is achieved that the requirements that must be placed on the accuracy of 4 coarse control are considerably less strict than in the case of the known device. When switching from coarse control to fine control, the remaining error can amount to a number of line periods, because such a deviation is detected by the third detector and eliminated by readjusting the oscillation frequency of the variable oscillator. This ensures that the correct line pulses are always finally compared with one another during the fine control, without strict requirements being placed on the coarse control.

Another advantage of the device according to the invention is that the first measurement signal at Playback of the recorded video signal can be supplied by a generator without hesitation can, which is coupled to the head disk and provides a signal, the frequency of which the speed of this Head disk is proportional. This has the advantage that the coarse control of the synchronization process can take place with the belt at a standstill, d. H. without a signal already being read out.

In the known device, this would cause difficulties. There finally a synchronization of the video signal read out from the tape is to be effected with the reference signal, it is for one precise regulation is also required, the measuring signals directly to the signal read out from the tape refer to. A measurement signal taken from a generator coupled to the head disk is necessary not exactly with a measuring signal separated from the read signal, e.g. B. the grid pulse series, to be in sync. So if in the known device the first measurement signal is such a generator would be taken, this means that after switching to the fine control between the first component of the reference signal and the corresponding signal ir. the readout video signal. z. B. the raster pulse series, a deviation of more than one line period can occur, which of, the fine control is not compensated.

In the device according to the invention, the above-mentioned problem need not arise because it it is possible to take the third measurement signal from the video signal read from the tape. Through this wsrd is also a result of a discrepancy between the measurement signal of said generator and the corresponding one Time base of the video signal present on the tape, errors caused by readjustment of the variable oscillator eliminated.

To a phase error brought about by a phase measurement method that is preferably used to compensate is one embodiment of the device according to the invention, characterized in that a delay element is provided via which the first Component of the reference signal or the third measurement signal is fed to the third detector.

Some embodiments of the invention are shown in the drawing and are described below described in more detail. It shows

Fig. 1 the known device, Fig. 2 a first and

3 shows a second embodiment of the device according to the invention, and

FIG. 4 shows a number of voltage forms for explaining FIG. 3.

The known device according to FIG. 1, in which only the parts essential for the synchronization are shown, initially contains a motor M driving the head disk. B. is provided with a hole on the circumference. With the aid of a lamp 2 and a photodetector 3, a measurement signal f _m can then be obtained by means of the disk 1, the frequency of which is a measure of the rotational speed of the top disk. This measurement signal f _m is fed to a first detector D ₁ , which is also fed with the raster frequency reference signal / ,,. This detector D ₁ determines the frequency and phase difference between the said signals and supplies a relevant output signal via a switch S and an amplifier A to a control input of the drive device of the head disk. In the example shown, this control input is formed by the connection points of a coil 5 which is attached to an armature 4. This armature 4 forms, together with the disk 1, an eddy current brake, it being therefore assumed that the motor M normally runs oversynchronously and is regulated down to the correct speed by the eddy current brake. Of course, the excitation of the motor could also be regulated.

With the help of this coarse control, the speed of the backplate is regulated during playback until the screen frequency reference pulse series / _fI and the pulse series f _{m are} synchronized. As soon as the phase difference between these signals has dropped below a certain threshold value, the coarse control is switched off and the fine control is switched on, in that a control command is sent to the switch S via the line c. The switch S then establishes a connection between the output of a second detector D ₂ and the amplifier A. This second detector D ₂ is fed on the one hand a Zeilenfrequen / -Bezugssignal f _n and f on the other hand, the read out from the tape Zcilenimpulsreihe _n, which detector again determines the frequency and phase difference between these signals. In this way, a very precise regulation is obtained because the measuring frequency is now high, namely with 625 lines and 50 Hz screen frequency 15,625

Hz.

When switching from coarse control to fine control, the remaining phase error can still amount to a number of line spacings, which means that the fine control synchronizes the wrong line pulses with one another. This error is avoided in a very simple manner in the device according to the invention according to FIG. 2, corresponding parts being denoted by the same reference numerals and letters. The line frequency reference signal fn is generated in this device by a variable oscillator O , which receives a setting signal from a phase comparison circuit F , which on the one hand the screen frequency reference signal / _H and on the other hand, when playing via the switch P, the read raster pulse series f _r2 and when recording Pulse series f _{m is} supplied. This ensures that a phase difference between this screen frequency reference signal and the screen pulse series of the tape remaining after the fine control has been switched on is eliminated by changing the oscillation frequency of the oscillator O in a compensatory manner. This type of fine control ensures that the detector D ₂ finally compares the correct line pulses with one another.

As shown, the first measurement signal can be formed by the signal f _{m of the photocell 3 both during recording and during playback.} After switching to the fine control, a comparison is made between the read raster pulse series f _r2 and the reference pulse series / _rl during playback. When recording, the measurement signal f _m is naturally fed to the phase comparator F instead of the raster pulse series _{f r2.} The measurement signal f _l2 for the detector D ₂ must then be taken from the head disk. In this case, this measurement signal does not need to be line frequency, but it can be a partial product of the line frequency without hesitation. While this is at the expense of accuracy, this is not so critical when recording.

Instead of taking the control signal for the switch S via the line c from the detector D ₁ , a suitable control signal can also be taken from an additional detector D ₃ , which measures the phase difference between the reference pulse series / _M and the read raster pulse series f _r2.

Fig. 3 shows an embodiment in which the disadvantage of a simple phase measurement process is avoided however, which process usually introduces an error, as shown below with reference to the Fig. 4 is explained.

4a shows the raster frequency reference signal / ,, with a pulse spacing T. A simple phase measuring process then consists in shaping this pulse series into a sawtooth signal, as shown in FIG. 4b. Since the value of this sawtooth-shaped signal is measured at times corresponding to the pulses of the raster pulse series f _{r2 selected} according to FIG. 4c, a signal corresponding to the phase difference can be obtained. In general, with such a system a final control is achieved in which a phase difference is maintained between the two pulse trains because the measured values of the sawtooth voltage are set to a value V ₁ which is between the extreme values of the sawtooth voltage. This means that a constant phase error T _{x is} maintained in the example shown. In the embodiment according to FIG. 3, this phase error is avoided in that the screen frequency reference signal / _{M is} fed to the phase comparison circuit F via a delay element P which introduces a delay T ₂ , whereby the course of this reference signal shown in FIG. 4d is obtained, where the delay T _{2 is} chosen such that T _x + T ₂ = T isl. If the regulation is such that the read out raster pulses come to rest again at times at which the sawtooth voltage (FIG. 4e) has a value V ₁ , as shown in FIG. 4f. it can easily be seen from the figure that the original screen frequency reference pulse series (FIG. 4a) and the read screen pulse series (FIG. 4f) are completely synchronous with one another without a phase error occurring. The only phase difference that can occur between the two pulse series is therefore determined in this system by the quality dot servo control.

The same result can also be achieved in that the read raster pulse series f _{r2 is} delayed. The delay time must then be the same as the nominal delay of the control system mentioned.

The control shown thus results in a very precise synchronism between the reference signals and the video signals read out from the recording medium. It should be noted that the Re The result is by no means even and odd grids, and neither is the phase of the color synchronization signal: (burst) taken into account. For this purpose, additional devices are required for the execution of the Re gel systems are not essential and will not be described in more detail here.

It should also be noted that the signal triggered from the recording medium in general another variable delay line is fed, with the help of which the after the servo control compensates for remaining phase errors

will.

For this purpose 2 sheets of drawings

Claims (4)

Patent claims: 1. Device for recording and reproducing image information on a tape-shaped Recording media with a head disk for recording and reading out the information and a control system for synchronizing the image information with a reference signal by control the speed of the backplate, which Control system a first detector for obtaining a first control signal by comparison a first measurement signal with a first component of the reference signal and a second Detector for obtaining a second control signal * 5 by comparing a second measurement signal with a second component of the reference signal, the frequency of the second component of the reference signal is significantly greater than that of the first component and wherein the control system further contains a switching unit with the aid of which a control signal received from a drive device for the head disk can be supplied and the selectively the second control signal to this Drive device forwards as soon as the first control signal falls below a certain threshold value, characterized in that the second component of the reference signal is generated by a variable oscillator whose A control signal is fed to the control input, which is obtained with the aid of a third detector, which compares a third measurement signal with the first component of the reference signal. 2. Apparatus according to claim 1, characterized in that when playing the first measurement signal is supplied by a generator which is coupled to the head disk and supplies a signal, whose frequency is proportional to the speed of the head disk. 3. Apparatus according to claim 1 or 2, in which 4c the first and second components of the reference signal are a screen frequency and a line frequency signal, respectively are, characterized in that when reproducing the third measurement signal by the from the read image information separated raster pulse series is formed. 4. Device according to one of the preceding claims, characterized in that a Delay element is provided through which the first component of the reference signal or the third Measurement signal is fed to the third detector.