JPS6131379Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is a magnetic recorder (VTR) using a Hercal scan method that uses a rotating magnetic head to sequentially record and reproduce image signals as recording trajectories inclined with respect to the longitudinal direction of a magnetic tape. This tracking device is constructed so that good reproduced images can be obtained not only during normal reproduction at normal tape speeds but also as still images or double-speed images.

Generally, in a VTR, the rotating magnetic head during reproduction does not necessarily match the recording trajectory on the magnetic tape.

This may be due to dimensional changes in the magnetic tape,
There are changes in the mechanical dimensions of the VTR and dimensional differences between the recording device and the playback device, which deteriorate the quality of the playback signal.

For example, if the playback scanning locus is 3 for track 2 recorded on magnetic tape 1 as shown in Figure 1, the envelope of the frequency-modulated playback output signal will deviate from the track as shown in Figure 2. As the output signal level decreases, the image quality deteriorates.

In order to prevent this, a method is used to keep track of the relative positions of the magnetic head and the track of the magnetic tape so that there is no deviation at all times.

For example, an electromechanical transducer can be made using a material with a very large piezoelectric effect, such as barium titanate porcelain, and used as a support arm for the magnetic head to position the magnetic head. Common. As an electro-mechanical transducer, we utilize the characteristic of piezoelectric elements that when an electric field is applied in the direction, the shape extends in the direction of the electric field and contracts in the direction perpendicular to it, to form electrodes as shown in Figure 3. They are made into a so-called bimorph by gluing them together on oppositely polarized surfaces, with one side fixed and the other free to attach a magnetic head.

In this manner, the magnetic head is positioned by applying voltage to the bimorph electrodes.

That is, in FIG. 3a, both sides of the piezoelectric element plate 4 are made conductors to form electrodes 5, and the two plates are glued together to form a bimorph structure, one end of which is fixed with a fixture 6 and a magnetic head 7 is provided at the other end. It is provided so as to be in contact with the magnetic tape 8. By applying potentials of opposite polarity to terminals 10 and 11 with respect to terminal 9, the bimorph is deformed as shown in Figure b, and the position of magnetic head 7 is moved perpendicular to the direction of rotation of the magnetic head. Therefore, the purpose of the track deviation in FIG. 1 is achieved by moving the magnetic head in the directions of arrows A and B.

An example of a specific configuration for automatically tracking this is shown in FIG. In FIG. 4, the output signal of the oscillator 12 (typically several hundred
Hz) is added as a search signal to the bimorph 15 from the bimorph drive circuit 14 via the adder 13,
The magnetic head 7 is caused to vibrate mechanically. If the magnetic head deviates from the recording track of the video signal on the magnetic tape, an amplitude fluctuation occurs at the same frequency as the frequency supplied to the envelope of the output signal of the magnetic head. etc., and the synchronous detection circuit 17
The error signal detected by and smoothed by the smoothing circuit 18 is applied to the adder 13 to drive the bimorph to displace and track the position of the magnetic head. Note that 19 is a phase shifter for matching the phase of the signal waveform input to the synchronous detector 17. FIG. 5 shows the waveform. In Fig. 5A, when the oscillator output waveform a is applied to the bimorph as a search signal and mechanical vibration is applied to the magnetic head, a waveform b is obtained as the magnetic head output, and this is filtered by a bandpass filter or the like to reduce the amplitude due to the mechanical vibration. Separate only the fluctuation component to obtain c.
By synchronously detecting this with the a waveform, it becomes the d waveform, which is then smoothed to obtain the error signal e. This is added to the a waveform via an adder, and the f waveform is supplied to the bimorph to correct the trajectory of the magnetic head. If there is no track deviation, even if waveform a is supplied to the bimorph as shown in Figure 5b, the magnetic head output signal will only have a fluctuating component of twice the frequency as shown in b, and therefore this component A signal c is obtained by separating the , which is synchronously detected to obtain a signal d. This d is a complete alternating current component, so even if it is smoothed, it becomes e without an error signal. Therefore, the signal f applied to the bimorph is only the search signal. The above method is also used when the position of the reproducing head does not deviate too much from the locus of the recording track.

However, such recording/playback devices do not always play back the tape at almost the same speed as the recorded state, and may perform so-called double-speed playback where the tape speed is faster than the normal state, slow playback where the tape speed is slowed down, or still playback where the tape is stopped. In this case, since the playback head scans with a trajectory that is significantly deviated from the recording track, it is necessary to increase the amplitude of the search signal applied to the bimorph to increase the vibration. It takes time to correct the playback scanning locus, and the quality of the upper part of the playback image is likely to deteriorate. FIG. 6 is a diagram showing the relationship between the recording track of the azimuth high-density recording and reproducing system using two rotary heads and the basic scanning locus of the magnetic head. In this figure, tracks 21A and 21B are recorded in azimuth on a magnetic tape 20 in order at a specific azimuth angle, and when the tape speed is normal, magnetic heads A and B scan each track. A playback signal is obtained, but for example, in the case of so-called still playback in which the tape stops, the playback head scanning locus will be as shown in 22. In order to reproduce this so that a good image is obtained, for example, the A head must: The starting head position remains the same, but as it scans, it is necessary to pull the playback head back in the direction of the arrow 23, and at the B head, at the starting point, it is shifted by one track pitch in the direction shown by the arrow 24 and gradually moved back to the original position. An operation is required to return it to its position. For example, when the tape speed is three times the normal speed, that is, when playing at triple speed, the head scanning trajectory becomes as shown at 25, and as shown in the figure, it is necessary to move the head by two track pitches in the direction shown by the arrow 26 at the end. FIG. 7A shows an example of the basic movement amount of the magnetic head during still playback B at 1/4 slow speed playback and C at 3x speed playback. As shown in this figure, the magnetic head is not always located within the recording track at the start and end points during re-output. For this reason, response speed becomes a problem when tracking only with search signals,
Generally, in the case of such bimorphs, the frequency of the search signal is on the order of several hundred Hz, so the track deviation until complete tracking is related to the amount of movement of the magnetic head, but may occur over several tens of horizontal periods. . Furthermore, in the case of slow playback, a case may be considered in which tracking is performed on a track different from the desired recording track. That is, there is a possibility of tracking the recording track closest to the starting point.

FIG. 8 shows a block diagram as an example of the present invention. In this figure, elements 7 to 18 operate essentially the same as those in Figure 4, so their explanation will be omitted. A vertical synchronizing pulse separated from the reproduced video signal or a pulse signal synchronized therewith, or a control pulse or a pulse signal synchronized therewith is supplied to the terminal 30, and based on this signal, the optimum signal is determined for each mode. For example, the waveform shown in FIG. 7 is generated by the waveform generator 31.
The waveform is shaped in advance by the selector switch 32, and is changed according to each mode.
is supplied to the bimorph 15 via the bimorph drive circuit 14 along with the search signal and the detection error signal. By doing this, even with the waveform created in advance, the reproduction scanning locus is brought close to the recording track, and the slight remaining track deviation is corrected by the search signal.

As described above, according to the present invention, the reproduction scanning locus is brought to a point close to the recording track using the preset signal waveform, so there is little track deviation at the starting point of the reproduction head, and therefore complete tracking is achieved. It takes less time to do so, and can prevent deterioration in image quality.

Also, increasing the amplitude of the search signal will affect the running of the magnetic tape, making it more likely that wows and flutters will appear in the audio. However, by doing this, the amplitude of the search signal can be reduced, so wows and flutters will not occur in the audio. It becomes difficult.

Furthermore, in the case of slow playback, especially in the case of azimuth recording, it is necessary to track and scan a fixed recording track in order to make the image move smoothly.
If the search is performed completely freely, the recording track closest to the magnetic head is often scanned at the starting point, which may result in a slow slow playback image lacking in smoothness, but in this invention, the recording track is scanned in the specified order. Scanning can be performed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the recording track on the magnetic tape and the scanning locus of the reproducing head, Fig. 2 is a diagram showing the envelope characteristics of the output of the reproducing head, and Fig. 3 is a diagram showing the magnetic head moving means used in the present invention. 4 is a block diagram showing the basic configuration of the present invention, FIG. 5 is a waveform diagram explaining the same operation, and FIG. 6 is a diagram showing the scanning locus of the playback head during still playback and double speed playback. FIG. 7 is a diagram showing the amount of movement of the playback head during still playback, 1/4 slow playback, and triple speed playback, and FIG. 8 is a block diagram showing an embodiment of the present invention. 7... Magnetic head, 12... Oscillator, 13...
Adder, 14... Bimorph drive circuit, 15...
Bimorph (electro-mechanical converter), 16... Bandpass filter, 17... Synchronous detection circuit, 18...
... Smoothing circuit, 19 ... Phase shifter, 31 ... Waveform generator, 32 ... Changeover switch.

Claims (1)

[Scope of utility model registration request] Prepare multiple signal waveforms set in advance based on the vertical synchronization signal according to the tape running speed, select the signal waveform according to the tape running speed, and combine the selected signal waveform with a constant frequency. and a search signal to an electro-mechanical converter,
Move the position of the magnetic head attached to this,
A tracking control device characterized in that an envelope fluctuation of a magnetic head output signal caused by the search signal is detected and negatively fed back to the electro-mechanical converter as an error signal.