JPS60219618A - Tracking control system - Google Patents

Abstract

PURPOSE:To realize various circuits of the titled system by means of the software of a microcomputer without deteriorating the tracking accuracy by varying the attenuation of an attenuation means in response to the amplitude of a signal in a delay means and using an output of the attenuation means so as to drive an electromechanical transducing element. CONSTITUTION:An output of a sample and hold circuit A24 is a value corresponding to an output of a 1-frame delay circuit 14, inputted to a variable attenuator 28, where said output is attenuated. An output of the variable attenuator 28 is inputted to a comparator circuit 12, where it is compared with a tracking signal and added with the output value of a sample and hold circuit C26, the result is inputted to a drive circuit 17, the output of which drives the electromechanical transducing element 18 so as to provide a displacement to a reproducing head 20. Thus, the tracking accuracy is improved and various circuits such as a minute correction circuit, the 1-frame delay circuit, an amplitude measuring circuit, a preset waveform generating circuit, a timing control circuit and a switching circuit are realized easily by using the software of the microcomputer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to a recording and reproducing device 9, for example, a device for recording and reproducing video signals and information signals such as VTRs and video discs, and is capable of reproducing recorded information. Method for improving tracking performance when recording % Formula % Conventional configuration and its problems In recent years, magnetic recording and reproducing devices such as VTRK have made remarkable progress, and recording density has been improved and tracks have become narrower. In particular, as the track becomes narrower, the following problems arise. That is, a problem arises in that the track locus recorded on the magnetic tape using the rotating head is not perfectly straight but curved. This is due to mechanical errors and disturbances, and in particular, when the recording device and the reproducing device are different, the track curvature that occurs will be different.
Even if the tape format is the same, compatibility becomes difficult.

For this reason, formats that have been proposed in recent years record a pilot signal for tracking control on the tape using the same magnetic head, superimposing it on the video signal to be recorded, and use that pilot signal during playback. It performs tracking control.

By using the pilot signal, it is possible to perform more advanced tracking, that is, to follow track bending, compared to conventional control signals used in the VH8 system and the like.

First, a method of creating a tracking error signal using a pilot signal will be explained. Various methods have been proposed for creating a tracking error signal using pilot signals, ranging from those using one type of pilot signal to those using four types of pilot signals, but the tracking error signal obtained by each method is the same. Therefore, the present invention can be applied to various methods for generating tracking error signals. Here, a four-frequency pilot signal method using four types of pilot signals will be explained as an example.

In FIG. 1, A1. B1. A2. B2...
are each recording track recorded on the magnetic tape by the A head and the B head. Arrow a indicates the scanning direction of the rotary head. In each recording track, f,
Each pilot signal indicated by ~f4 is sequentially recorded for each field. The recording order of pilot signals is fl,
f2. f3. It circulates in the order of f4, and fl is recorded after f4. Further, within each one field period, the type of pilot signal is fixed and recorded. The frequency of the pilot signal is set to a value shown in Table 1, for example. Note that in Table 1, fH indicates the frequency of the horizontal synchronization signal in the video signal, and 6.5fH in Table 1 indicates a frequency that is 6.6 times the frequency of the horizontal synchronization signal.

The frequency difference of the pilot signal between each recording track is the first
As shown in the figure, the frequency is fH or 3fH.

When the head scans the At(i=1.2...) track, the frequency difference between the pilot signal of the scanning track and the pilot signal recorded on the adjacent track on the right on the paper is always fH. The one on the left side is always 3f H. When the head scans a Bi (i=1.2...) track, the relationship is opposite to the above, and the frequency of the pilot signal between the scanning track and the adjacent track on the right side is The difference is always 3fH and that on the left is always fH.

Since the pilot signal is a relatively low frequency signal around 100 KHz, the pilot signal recorded on the adjacent track can be reproduced as a crosstalk signal without the head scanning over the adjacent track. for example,
The pilot signal obtained when the head scans the A2 track just on track for reproduction is f 3 - f
It is a composite signal of 2 * f 4, and its level is f3
is the largest, followed by f2. f4 is played back at the same level. When the head slightly deviates from track A2 toward track B2 and performs reproduction scanning, the level of the obtained reproduction pilot signal decreases in the order of f 3 * f 4 * f 2. Conversely, when the head shifts toward track B1 and scans, the obtained pilot signal is f3. f2. It becomes smaller in the order of f4. Therefore, the difference signals fH and 3fH between the pilot signal on the main scanning track and each pilot signal recorded on both adjacent tracks are separated and extracted.
By comparing the reproduction levels of both signals, the amount and direction of deviation of the head from the main scanning track can be determined.

FIG. 2 is a block diagram of a reproducing circuit for obtaining a tracking error signal. In FIG. 2, a signal in which a video signal and a pilot signal are combined is input from terminal 1. A low-pass filter 2 extracts only the pilot signal from the combined reproduced signal. The pilot signal obtained at this time is a composite signal of the main scanning track and the pilot signals recorded on both adjacent tracks.

3 is a balanced modulation circuit which multiplies the above-mentioned composite pilot signal by the reference signal supplied from terminal 4; The reference signal supplied from terminal 4 supplies a signal of the same frequency as the pilot signal recorded on the main scanning track.

For example, in FIG. 1, when the head performs reproduction scanning on track A2, the input signal to the balanced modulation circuit 3 is f 2 ,
The signals inputted from terminal 4 are f3 and f3. Therefore, the output signal of the balanced modulation circuit 3 is f2°f3. Signals having the sum and difference frequencies of each signal of f4 and the signal of f3 are output.

6 is a tuned amplifier circuit tuned to the fH signal, and 7 is a s
This is a tuned amplifier circuit that tunes to the fH signal.

6.8 is an amplitude detection rectifier circuit, and e is a level comparison circuit.

Therefore, each pilot signal taken out as a crosstalk signal from both adjacent tracks is taken out as a difference signal with the pilot signal recorded on the main scanning track, and then the level comparison circuit 9 compares the level. A signal corresponding to the difference is taken out at terminal 1°. As for the signal obtained at the terminal 16, when the reproduction level of fH is higher than the reproduction level of 3fH, a potential of ■ corresponding to the level differential pressure is taken out, and in the opposite case, a potential of ○ is taken out. Terminal 1
Since the signal outputted as 0 includes information on the amount and direction of the head's track deviation, it can be used as a tracking error signal. However, a tracking error signal that is actually suitable for practical use requires further processing. This is because, as is clear from Figure 1, the Ai track and the Bi track
) rack, the relationship between the head displacement direction and the multiplication output (fH or 3fH) obtained at that time is opposite to each other. Therefore, analog inverting circuit 1
1 and switch 12 to invert the signal at terminal 10 in an analog manner when the head scans the Al track and when the head scans the Bi) rack. That is, the terminal 14 is connected to the terminal 1o through the switch 12 during Ai) rack scanning, and is connected to the output of the analog inversion circuit 11 during Bi) rank scanning. As a result, the output signal of the terminal 14 is always at the potential ■ when the head deviates to the right from the track to be scanned, and always at the potential θ when the head deviates to the left, regardless of the rack (At, Bi). . Therefore, if the tracking error signal obtained at the terminal 14 is used to control the amount of displacement of the capstan motor and the magnetic head, the head can always scan on the main scanning track on trunk. The above is an overview of the method for obtaining a tracking error signal using four types of pilot signals.

FIG. 3 is a block diagram of a conventional tracking control method, and the conventional example will be explained based on this.

The tracking error signal obtained from the tracking error detection circuit 10 is input to the capstan control circuit 11 and used as a phase control signal for tape feeding, and is also input to the 1 comparison circuit 12. The comparison circuit 12 compares the output value of the DA converter 15 and the tracking error.

Reference numeral 13 denotes a slight correction circuit, which slightly corrects the output value of the one-frame delay circuit 14 according to the output of the comparison circuit 12.

The 1 frame delay circuit 14 outputs the output of the slight correction circuit 13 by 1 frame.
This is to delay the frame period. The output of the one-frame delay circuit 14 is input directly to the DA converter 16, or after adding the output of the preset waveform generator 19, the output is input to the DA converter 16. The timing control circuit 22 selects which signal to input to the DA converter 15.
This is done by The output of the DA converter 16 is input to the comparison circuit 12 and sample hold circuit 16. The sample hold circuit 16 is driven by a timing control circuit 22, and includes a preset waveform generator 19 and a one frame delay circuit 1.
The output value of the DA converter 16 is sampled and held in synchronization with the addition value of each signal with 4 is input to the DA converter 16. That is, the output of the sample hold circuit 16 is
This is the sum of the output value of the one-frame delay circuit 14 and the output value of the preset waveform generation circuit 19. The output of the sample and hold circuit 16 passes through a drive circuit 17 and drives an electro-mechanical conversion element 18 . As an electro-mechanical conversion element,
For example, there are piezoelectric elements. This electro-mechanical conversion element 1
Since the reproducing head 20 is mounted on the reproducing head 8, the displacement of the reproducing head 20 can be electrically controlled.

Next, the operating principle will be explained. Comparison circuit 12. Minor correction circuit 13, 17 frame delay circuit 14. The DA converter 16 constitutes an AD converter.

That is, at each instant, the AD converter is configured by comparing and correcting the input tracking error and the tracking error one frame before. Therefore, one frame of tracking error is accumulated in the one frame delay circuit 14. That is, 1
The frame delay circuit 14 stores track bending information.

Next, the preset waveform generation circuit 19 will be explained. The preset waveform is used to absorb changes that cannot be tracked by the above-described slight correction of the tracking error. In other words, tracking at any playback speed can be converted so that the same tracking error is obtained when playing back at the same speed as during normal recording. It has a sawtooth waveform. For example, if the playback speed is six times the recording speed, the sawtooth amplitude will correspond to four tracks. That is, if the electro-mechanical conversion element 18 is driven using this preset waveform, tape phase control using the capstan can be realized using only the preset waveform, provided there is no track curvature. In practice, since the electro-mechanical conversion element 18 is driven by adding the tracking error to the preset waveform, it is possible to follow track curvature and to reproduce at any reproduction speed.

Now, the problems with this conventional example are as follows. That is, the minimum resolution of the tracking error AD conversion section is limited by the preset waveform generation circuit 19. For example, if the number of bits of the DA converter 16 is 8, there are only 256 output values, and if the maximum displacement amount by the preset waveform generation circuit 19 is 16 tracks, the minimum resolution of the AD converter is 1/16). As a result, performance is limited. Moreover, if the actual track curvature is not very large, the DA converter 16 will only use a part of the width regarding the track curvature. That is, there is a problem in that the larger the maximum displacement amount by the preset waveform generation circuit 19, the more the tracking performance (accuracy) decreases. The maximum displacement is
Since it is proportional to the value of how much the speed differs from the standard and single speed (for example, when playing at 8x speed, there will be 7 tracks), if the variable range of playback speed is wide, the tracking accuracy will decrease. It turns out.

One possible solution to this problem is to increase the number of bits in the DA converter 16, but increasing the number of bits not only increases the circuit scale of the DA converter itself, but also increases the number of bits in the 1-frame delay circuit 14. The circuit scale of the preset waveform generation circuit 190 also increases. For example, even if it is realized by software such as a microcomputer,
It is clear that this would result in a significant increase in memory and is not practical in either case.

OBJECTS OF THE INVENTION The present invention overcomes the problems of the prior art.
This method provides a method that does not reduce tracking accuracy even if the maximum displacement is increased without increasing the number of bits of the A converter. Moreover, it can be realized with a simple configuration and can be easily implemented using microcomputer software. This provides a method that can be used to achieve this goal.

Structure of the Invention The present invention is a tracking control method in which a signal from a tracking error detection circuit is processed to drive an electro-mechanical conversion element, and the electro-mechanical conversion element displaces a reproduction head to perform tracking. (ii) means for comparing the tracking error with a value one frame before, which will be described later; means for slightly modifying the value before the frame using the comparison value; means for delaying the slightly modified signal by one frame; and one frame delay means. means for detecting the amplitude of the signal within the frame, means for generating a preset waveform according to the playback speed, means for varying the degree of attenuation based on the amplitude value obtained by the amplitude detecting means, and the one-frame delay The output of the means is input to the attenuation degree variable means, the output value of the attenuation degree variable means is inputted to the comparison stage, and compared with the tracking error, and a value obtained by adding the output from the preset waveform generation means. The electro-mechanical conversion means is driven by the control device to perform tracking control, and the correction amount of the minute correction section is changed depending on the amplitude value of the tracking error, so that the correction amount can be optimized.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described based on the drawings. In FIG. 4, a signal obtained by a reproducing head 2o mounted on an electro-mechanical conversion element 18 is amplified by an amplifier 21 and then input to a tracking error detection circuit 1o. The tracking error detection circuit 10 extracts a pilot signal from the input signal, converts it into a tracking error signal, and outputs the signal. A tracking error signal output from the tracking error detection circuit 10 is input to a capstan control circuit 11 and used for tape feeding phase control, and is also input to a comparison circuit 12.

Comparison circuit 12 compares the output of variable attenuator 28 and the tracking error signal, and inputs the result to minute correction circuit 13 . The slight modification circuit 13 slightly modifies the output value of the 1-frame delay circuit 14 based on the output value of the comparison circuit 12, and applies the modified value to the 1-frame delay circuit 14.
Enter. The output of the one-frame delay circuit 14 is input again to the minute correction circuit 13, and is also input to the DA converter 16 through the switching circuit 3o. Sara KDA converter 16
The output is input to the sample hold circuit A21. The sampling timing of this sample hold circuit A24 is determined by the timing control circuit 23, and the switching circuit 30 is set to 1.
It is synchronized with the timing connected to the frame delay circuit 14. That is, the output of the sample hold circuit A24 is a value trap corresponding to the output of the one frame delay circuit 14.

The output of the sample hold circuit A24 is the variable attenuator 28.
input and attenuated. The output of the variable attenuator 28 is input to the comparator circuit 12, where it is compared with the tracking error signal, added to the output value of the sample and hold circuit C26, and input to the drive circuit 17. Drive circuit 1
The output of 7 drives the electro-mechanical transducer 18 to give displacement to the reproducing head 2 degrees. On the other hand, the amplitude measuring circuit 27 measures the amplitude value of the signal in the one frame delay circuit 14, and the measurement result is sent to the D through the switching circuit 30.
Output to A converter 16. The output of the DA converter 16 is input to a sample and hold circuit B26, and the timing control circuit 23 causes the switching circuit 3o to switch to the amplitude measuring circuit 27.
When connected to the output of the DA converter 16, the output value of the DA converter 16 is sampled and held. That is, the output of the sample and hold circuit B25 has a value corresponding to the output of the amplitude measurement circuit 27. The output of the sample and hold circuit B25 is input to the variable attenuator 28, and the attenuation rate of the variable attenuator 28 is controlled. The output of the preset waveform generation circuit 19 is input to the DA converter 16 through the switching circuit 30. D.A.
Since the output of the converter 16 is connected to the sample and hold circuit 026, the output of the DA converter 16 is sampled and held by the timing control circuit 23 when the switching circuit 30 is connected to the output of the preset waveform generation circuit 19. That is, the output of the sample hold circuit C26 is
The value corresponds to the output of the preset waveform generation circuit 19. The output of the sample and hold circuit C26 is added to the output value of the variable attenuator 28, and then inputted to the drive circuit 17, which drives the electro-mechanical conversion element 18 and drives the playback head 2o.
Displace.

In FIG. 4, comparison circuit 12. Minor correction circuit 13.1
Frame delay circuit 14. DA converter 16° sample hold circuit A24. The variable attenuator 28 constitutes a kind of AD converter, and the one frame delay circuit 14 stores track bending information for one frame. In other words, since the track curvature has a high correlation for each frame, if the value of the previous frame is slightly corrected, the track curvature information will eventually be accumulated in the 1-frame delay circuit 14 with the precision of the quantization error. be done. That is, the output of the variable attenuator 28 has a value obtained by improving the accuracy of the minimum resolution of the DA converter 16 by the attenuation rate of the variable attenuator 28. For example, even if the minimum resolution of the DA converter 16 is 20 mV, if the attenuation rate of the variable attenuator 28 is 1/100, then the variable attenuator 2
The resolution at the output of 8 can be improved to 2 mV. Particularly when the amplitude of the track bending information is small and only a narrow range of values is used in the DA converter 15, by increasing the attenuation rate of the variable attenuator 28, the resolution can be improved for the same tracking error amplitude. has improved. The output of the variable attenuator 28 is added to the output of the preset waveform generator 19 to drive the electro-mechanical transducer 18 and control the displacement of the reproducing head 2o, resulting in improved tracking accuracy. Become.

Therefore, if the amplitude of the tracking error is large, the amplitude measurement circuit 27 issues a command to lower the attenuation rate, and if the amplitude is small, it only needs to issue a command to increase the attenuation rate, and the amplitude measurement circuit 27 issues an appropriate resolution according to the amplitude of the tracking error. Obtainable.

Further, in this embodiment, since the AD converter is constructed as a loop including the variable attenuator 28, the variable attenuator used does not need to have linearity, and implementation is easy.

Furthermore, in the present invention, the minute correction circuit, one-frame delay circuit, amplitude measurement circuit, preset waveform generation circuit, timing control circuit, and internal switching circuit can be extremely easily realized using microcomputer software, and in particular, , corresponding to the amplitude measurement circuit, the software can be easily realized by simply determining the maximum value and the minimum value and calculating the difference between them. Therefore, it is clear that the embodiments of the present invention are not limited to this example.

Effects of the Invention The present invention has the effect that tracking accuracy can be improved according to track curvature in tracking control that requires a wide operation amount, and in a variable attenuator,
There is no need to have linearity (implementation is easy).

[Brief explanation of the drawing]

Fig. 1 is a recording magnetization trajectory diagram showing the principle of a 4-frequency pilot signal, Fig. 2 is a block diagram showing a tracking error detection method for a 4-frequency pilot signal, and Fig. 3 is a block diagram showing the configuration of a conventional example. , FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. 10... Tracking error detection circuit, 12.
...Comparison circuit, 13...Minor correction circuit,
14...1 frame delay circuit, 16...
DA converter, 16°24.25.26... Sample hold circuit, 17... Drive circuit, 1
8... Electro-mechanical conversion element, 19... Preset waveform generation circuit, 20... Playback head,
22, 23...timing control circuit, 27...
...Amplitude measurement circuit, 28...Variable attenuator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (2)

[Claims] (1) A tracking control pilot signal recorded together with an information signal on a recording medium is reproduced by a reproducing head mounted on an electro-mechanical conversion element to obtain a tracking error signal'. A means for comparing the signal with a tracking error signal before a certain period of time, a means for slightly modifying the tracking error signal before the certain period of time based on the comparison result, and a means for delaying the slightly corrected value for the certain period of time. According to the output value of the delay output stage, the electric current is
A tracking control method for driving a mechanical transducer, the method comprising: means for detecting the amplitude of a signal within the means for delaying the fixed period; and attenuation means between the output of the delay means and the comparison means; A tracking control system characterized in that the amount of attenuation of the means is varied according to the amplitude of the signal within the delay means, and the electro-mechanical conversion element is driven by the output value of the attenuation means. (2) means for generating a preset signal for driving the electro-mechanical transducer so that the reproducing head can be scanned roughly along the recording trajectory at a given reproduction speed; a manner in which the preset signal generating means is output; 2. The tracking control system according to claim 1, further comprising means for adding the outputs of the attenuating means, and an electro-mechanical conversion element is driven by the output of the adding means.