JPH0527168B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a head position control circuit for a rotary head suitable for reproducing recorded signals in a variable speed reproduction mode in a helical scan type magnetic recording and reproducing apparatus such as a video tape recorder. [Background of the Invention] In a helical scan type magnetic recording/reproducing apparatus, it is essential to perform tracking control so that the rotating head correctly traces the inclined recording track on the magnetic tape during reproduction. As is well known, such tracking control uses control signals for tracking control recorded on the magnetic tape in the standard playback mode in which the magnetic tape is played back by running at the same speed as the running speed at the time of recording. This can be done by a tracking servo that controls the rotational phase of the rotary head. However, in a variable speed playback mode in which the magnetic tape is played back by running (or stopping) at a speed different from that during recording, such as slow motion playback, quick playback, and still playback in a video tape recorder, the tracking servo is As a result, it is no longer possible to perform sufficient tracking control. Recently, therefore, the rotating head is attached to an electro-mechanical transducer (for example, a bimorph plate), and tracking control signals obtained by detecting the momentary tracking state of the rotating head are used.
An auto-tracking device has been proposed which corrects the tracking deviation of the rotary head by controlling the electro-mechanical transducer described above and can obtain a reproduced image free of noise bands even in variable speed reproduction mode. First, an example of such a conventional auto-tracking device will be explained with reference to FIGS. 1 to 4. FIG. 1 is a block diagram schematically showing a video tape recorder using the above-mentioned auto-tracking device. In the figure, 1 and 2 are rotary heads attached to the movable parts of bimorph plates 3 and 4, respectively. As is well known, these rotating heads rotate together with the rotating drum 11, alternately scan the magnetic tape 10 that is running while being wrapped around the rotating drum 11 in a range of approximately 180 degrees, and scan the magnetic tape 10 over the magnetic tape 10. The FM video signal recorded on the tilt recording track is played back. The reproduced FM video signal is amplified by an amplifier 5, and then demodulated by a demodulator 16.
It is output from the output terminal 17. Reference numeral 6 denotes an automatic tracking circuit, and this circuit 6 receives reproduced FM video signals from the rotary heads 1 and 2 and a well-known head switching signal (hereinafter referred to as TSW signal).
Based on the signal from the generator 14, a phase correction signal is generated so that the level of the FM video signal is maximized. Reference numeral 7 denotes an applied signal generation circuit, into which the phase correction signal generated by the automatic tracking circuit 6 is inputted, as well as a signal from the HSW signal generator 14 and capstan rotation speed information (hereinafter referred to as a CFG signal). A signal from a generator 15 (referred to as "1") is also input. The output from the applied signal generation circuit 7 is amplified by amplifiers 8 and 9, and then applied to the bimorph plates 3 and 4 to control their positional displacement and to perform tracking control of the rotary heads 1 and 2. It's getting old. Note that 12 is a drum motor, and 13 is a capstan motor. Next, the operating principles and configurations of the automatic tracking circuit 6 and the applied signal generation circuit 7 will be explained in more detail. FIG. 2 is a block diagram showing a specific example of the configuration of the automatic tracking circuit 6 shown in FIG.
9 is an input terminal for the HSW signal, 20 is an input terminal for the CFG signal, and parts corresponding to those in FIG. 1 are given the same reference numerals. Reference numeral 6 shows an automatic tracking circuit as a whole, and the automatic tracking circuit 6 includes an envelope detection circuit 21, a sample hold circuit 22, an analog-digital converter (hereinafter referred to as an A/D converter) 23, and a shift register. 24, 25, a shift pulse generating circuit 26, and a displacement direction determining circuit 27. In Fig. 2, playback input from terminal 18
As is well known, the FM video signal is produced by alternating playback output from two rotating heads using the HSW shown in Figure 3a.
It is obtained by switching depending on the signal.
The reproduced FM video signal is input to the circuit 21 and subjected to envelope detection. The envelope detection output (hereinafter referred to as the reproduced envelope signal) is shown in FIG. 3b. In the figure, A _o , A _o+1 , ... are reproduced envelope signals obtained from one rotary head A, and B _o , B _o+1 , ... are reproduced envelope signals obtained from the other rotary head B. It shows.
The sample and hold circuit 22 creates a sampling pulse 28 shown in FIG.
The reproduced envelope signals output from 1 are sequentially sampled and held. As is clear from FIG. 3, this sample and hold operation is performed near the center of the reproduction scanning period of each rotary head A, B. The output of the sample and hold circuit 22 is then
The signal is input to the D converter 23 and converted into a digital signal. The operating principle of this digital conversion is as follows: First, the sampling pulse 28 and the sample hold circuit 22
(the output obtained by sampling and holding the envelope of the reproduced FM video signal) is the A/D converter 23
Based on these inputs, the A/D
As shown in FIG. 3d, the converter 23 rises in synchronization with the falling edge of the sampling pulse 28, and has a time width proportional to the output voltage of the sample and hold circuit 22. )29 is output. The conversion pulse 29
indicates the operating period of the A/D converter 23, and since the A/D converter 23 counts the reference clock during the operating period, the output of the sample and hold circuit 22 is converted into a digital signal. converted. The digital signal is output from the shift pulse generating circuit 26 as shown in FIG.
Using shift pulses 30 having the required number of bits (6 bits in the illustrated example), the data is sequentially shifted from the most significant digit and output from the A/D converter 23.
The output from the A/D converter 23 is sequentially shifted and stored in the shift register 24 and then in the shift register 25 each time the output is obtained, that is, each time the digital conversion operation is completed. It is output from the register 25. That is, the digital signal A′ _o corresponding to the reproduced envelope signal A _o is now output from the A/D converter 23.
When the digital signal A'o is output, the digital signal _A'o is stored in the shift register 24. Next, when the A/D converter 23 outputs a digital signal B' _o corresponding to the reproduced envelope signal B o, this digital signal B' _o is newly stored in the shift register 24, and the digital signal B' _o corresponding to the reproduced envelope signal B o is newly stored in the shift register 24. digital signal
A′ _o is shifted into the shift register 25 and stored. Further, when the A/D converter 23 outputs the digital signal A′ _o+1 corresponding to the next reproduced envelope signal A o+ ₁ , the digital signal A′ _o+1
is stored in the shift register 24, the digital signal _B'o is shifted to the shift register 25, and the digital signal _A'o is output from the shift register 25. Similar operations are repeated sequentially thereafter. The digital signal output from the A/D converter 23 (sample hold value by the sample hold circuit 22) and the output of the shift register 25 are used in a displacement direction determining circuit that determines the displacement direction of each rotary head A, B. 27, and their sizes are compared. On the other hand, the applied signal generating circuit 7 supplies a tracking control signal to the bimorph plates 3 and 4 during each alternate non-reproduction scanning period of each rotary head A and B, and tracks each rotary head A and B by a predetermined step. The displacement direction is determined by the displacement direction determining circuit 27.
determined by. That is, if the reproduced envelope signal A _o+1 shown in FIG. 3b is obtained during a certain reproduction scanning period of the rotating head, its sample hold value (output A' _o+1 of the A/D converter 23) is
is the reproduced envelope signal one rotation period before that
It is compared with the output A'o of the shift register ₂₅ , which is a sample-and-hold value of _Ao , and based on the comparison result, the displacement direction determining circuit 27 is necessary to obtain the best tracking state. Determine the direction of the displacement step of rotating head A during the next non-reproducing scan period. A truth table for such displacement direction determination is shown below as Table 1.

[Purpose of the invention]

An object of the present invention is to provide a magnetic recording and reproducing apparatus which eliminates the drawbacks of the prior art described above, reduces the amount of displacement per step for correcting the phase of the head position, and increases the track width of the rotary head, thereby allowing precise tracking. head position control circuit. [Summary of the Invention] In order to achieve this object, in the present invention, a direction correction circuit that outputs a tracking correction direction signal of a head position control circuit that controls the head position of a rotary head is adapted to control the rotation of a recording track of a rotary head. A first storage means (corresponding embodiment code 24,
25), a second storage means (corresponding embodiment numerals 35 and 36) for sequentially storing the sample and hold values and sequentially outputting them after two rotation scanning periods of the rotary head; and an output of the first storage means. first displacement direction determining means (corresponding embodiment code) for determining the displacement direction of the rotary head based on the comparison result between 37), and a step of determining the displacement direction of the rotary head based on the comparison result between the output of the second storage means and the sample hold value and the displacement direction of the rotary head when the sample hold value was obtained. When the outputs of the first and second displacement direction determining means match, the output of the second displacement direction determining means (corresponding embodiment code 38) is selected, and when they do not match, the output of the second displacement direction determining means is selected. Judgment circuit for selecting and outputting the output of the displacement direction determining means of No. 1 (corresponding embodiment code 39)
and . [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 5 is a block diagram schematically showing an embodiment of the head position control circuit according to the present invention, in which 3 and 4 are bimorph plates, 7 is an applied signal generation circuit, 8 and 9 are amplifiers, and 18 is a bimorph plate. Input terminal for playback FM video signal, 19 is input terminal for HSW signal, 20
is a CFG signal input terminal, 21 is an envelope detection circuit, 22 is a sample hold circuit, 23 is an A/D converter, 24 and 25 are shift registers, 2
Reference numeral 6 denotes a shift pulse generation circuit, which corresponds to the parts with the same symbols in the conventional example shown in FIG. 35 and 36 are shift registers,
37 is a first displacement direction determining circuit, 38 is a second displacement direction determining circuit, and 39 is a determination circuit. In this embodiment, in addition to the two shift registers 24 and 25 that were also provided in the conventional example,
In addition, by providing two shift registers 35 and 36, a value (digital signal) obtained by sampling and holding the reproduced envelope signal of one rotation scan period before each rotation head is stored, and a value (digital signal) obtained by sampling and holding the reproduced envelope signal one rotation scan period before each rotation head is stored. The sample hold value of is also stored. That is, when the A/D converter 23 outputs the digital signal _A'o-1 of one rotating head A (the sample-and-hold value by the sample-and-hold circuit 22), the digital signal A'o _-1 becomes , are stored in the shift register 24.
Next, the A/D converter 23 connects the other rotary head B.
When the digital signal B'o _-1 is output, the digital signal B'o _-1 is newly stored in the shift register 24, and the previously stored digital signal A'o _-1 is stored in the shift register 25. shifted and stored. When the next digital signal _A'o is output from the A/D converter 23, the digital signal _A'o
is stored in the shift register 24, and the digital signals B' _o-1 and A' _o-1 are shifted and stored in the shift registers 25 and 35, respectively, and at the same time,
A digital signal A'o _-1 is output from the shift register 25. Next, when the digital signal _B'o is output from the A/D converter 23, the digital signal _B'o is stored in the shift register 24, and
Digital signals _A'o , B'o _-1 , A'o _-1 are shifted and stored in shift registers 25, 35, and 36, respectively, and at the same time, digital signal B'o _-1 is output from shift register 25. . Then, when the next digital signal A'o ₊₁ is output from the A/D converter 23, this digital signal A'o ₊₁ is stored in the shift register 24, and the digital signals _B'o , A ′ _o and B′ _o-1 are respectively shift register 2
5, 35, and 36 and stored, and at the same time, digital signals _A'o and A'o _-1 are outputted from the shift registers 25 and 36, respectively. Similar operations are repeated sequentially thereafter. Output of A/D converter 23 and shift register 25
The output of the A/D converter 23 and the output of the shift register 36 are input to first and second displacement direction determining circuits 37 and 38, respectively.
A comparison is made between the sizes of each. The first displacement direction determination circuit 37 compares the magnitudes of the outputs of the A/D converter 23 and the shift register 25 and the previous step displacement direction (the displacement direction in which the output of the A/D converter 23 was obtained). ) is stored in the judgment circuit 3.
A first phase correction signal is output based on the output of 9. Similarly, the second displacement direction determining circuit 38
is the A/D converter 23 and the shift register 36
A second phase correction signal is output based on the output of the determination circuit 39 and the output of the determination circuit 39. In other words, now,
When the digital signal A'o ₊₁ is output from the A/D converter 23, the first displacement direction determining circuit 37 outputs the digital signal A'o+1 and the digital signal A'o ₊₁ output from the shift register 25 at this time. The current step displacement direction is determined based on the comparison result and the above-mentioned step displacement direction ₍ the displacement direction in which A' _o+1 was obtained). is output as the first phase correction signal. Similarly,
The second displacement direction determining circuit 38 is connected to the A/D converter 2
The digital signal A'o ₊₁ outputted from the shift register 36 is compared in magnitude with the digital signal A'o _-1 outputted from the shift register 36 at this time, and based on the comparison result and the previous step displacement direction. , determines the current step displacement direction, and outputs this as a second phase correction signal. The first and second phase correction signals are input to a determination circuit 39, and the circuit 39 determines which of the first and second phase correction signals should be output to the applied signal generation circuit 7. 3,
It is determined whether the current phase correction signal should be actually applied to 4. Here, the determination operation of the determination circuit 39 is performed by comparing the first phase correction signal with the previous phase correction signal actually output to the applied signal generation circuit 7. That is, now, based on the comparison result between the digital signals A'o ₊₁ and _A'o , the current step displacement direction by the first phase correction signal determined to obtain the best tracking state of the rotary head A is determined. , does not match the step displacement direction of the previous actual phase correction signal that led to obtaining the digital signal A'o ₊₁ , that is, the first displacement direction determination circuit 37 determines that the current step displacement direction is different from the previous one. If it is determined that the rotation is reversed, the determination circuit 39 outputs the first phase correction signal to the applied signal generation circuit 7. On the contrary, if the current step displacement direction by the first phase correction signal matches the step displacement direction of the previous actual phase correction signal, that is, the first displacement direction determination circuit 37 determines the current step displacement direction. If it is determined that the displacement direction is also the same as the previous one, the determination circuit 39 outputs the second phase correction signal to the applied signal generation circuit 7 instead of the first phase correction signal. Therefore, depending on the decision of the first displacement direction determining circuit 37 as to whether or not the current step displacement direction is to be reversed to the previous step displacement direction, the first and second phase correction signals are respectively changed to the bimorph direction. This is the current phase correction signal that is actually applied to plate 3 or 4, but here, the second
As mentioned above, the phase correction signal of
Since it is based on the comparison result between A'o ₊₁ and the digital signal A'o _-1 two rotational scanning periods before, the accuracy of the magnitude comparison is improved. In other words, if the displacement amount of one step for correcting the phase of the head position is Δl, then the phase difference in the recording track width direction of the same rotary head with two rotational scanning periods different from each other is 2·Δl.
Or, since it is 0, it is easier to compare the magnitude compared to the case of comparing the phase differences of the same rotating heads that differ by one rotation scanning period as in the prior art described above. Therefore, the displacement amount Δl of one step can be set small. Note that the above digital signals (for example, A′ _o-1 , A′ _o , A′ _o+1 ) output from the A/D converter 23 are as follows:
Since all were obtained using the same sample and hold circuit 22, there is no error due to sample and hold. Furthermore, although the above explanation has mainly been about one rotary head A, the same applies to the other rotary head B. Next, a more specific configuration and operation of the embodiment shown in FIG. 5 will be explained with reference to FIG. 6. FIG. 6 is a block diagram showing a specific configuration example of the first and second displacement direction determining circuits 37, 38 and determination circuit 39 in FIG. 5. The components corresponding to those in FIG. A reference numeral is given and the explanation thereof will be omitted. In the figure, 40 and 41 are magnitude comparison circuits, 42 to 44 are exclusive OR circuits, and 45 to 4 are exclusive OR circuits.
7 is an inverter, 48 to 50 are NAND gates,
51 to 54 are latch circuits. Now, when the digital signal A'o ₊₁ of one rotary head A is output from the A/D converter 23, the digital signals A'o _and A' are output from the shift registers 25 and 36, respectively, as described above. _o-1 is output.
The digital signals A'o ₊₁ and _A'o are input to the magnitude comparison circuit 40, and the digital signals A'o ₊₁ and A'o _-1 are input to the magnitude comparison circuit 41, starting from the most significant digit.
A size comparison is made. Next, the comparison results of these magnitude comparison circuits 40 and 41 are the previous actual phase correction signal held by the latch circuit 54 (the phase correction that was applied to the applied signal generation circuit 7 to obtain A′ _o+1). signal) to exclusive OR circuits 42 and 43, respectively, and the output signals of the circuits 42 and 43 are inverted by inverters 45 and 46, respectively. In this way, the first phase correction signal that determines the current displacement direction based on the comparison result of the digital signals A′ _{o+1 and} A′ _o is held in the latch circuit 51, and A second phase correction signal that determines the current displacement direction based on the comparison result of A'o _-1 is held in the latch circuit 52. The first phase correction signal that is the output of the latch circuit 51 is then input to the exclusive OR circuit 44 together with the previous actual phase correction signal that is the output of the latch circuit 54, and these two signals do not match. In this case, the output of the circuit 44 becomes a high level, the NAND gate 48 is opened, and the first phase correction signal, which is the output of the latch circuit 51, is input to the applied signal generation circuit 7 and becomes the current actual phase correction signal. Become. At this time, since the inverter 47 is involved,
NAND gate 49 is closed. On the contrary,
When the first phase correction signal input to the exclusive OR circuit 44 and the previous actual phase correction signal output from the latch circuit 54 match, the circuit 4
The output of inverter 47 becomes low level and
, the NAND gate 49 is opened (the NAND gate 48 is closed), and the second phase correction signal, which is the output of the latch circuit 52, is input to the applied signal generation circuit 7 and becomes the current actual phase correction signal. . In this manner, by using the exclusive OR circuit 44, it is possible to easily determine which of the first and second phase correction signals should be input to the applied signal generation circuit 7. It goes without saying that the above description also applies to the other rotary head B. [Effects of the Invention] As explained above, according to the present invention, when comparing the sample-and-hold values obtained by sampling and holding the reproduced envelope signals of each rotating head,
In addition to comparing the sample-and-hold values of the same rotating head with one rotation scanning period different, the sample-and-hold values of the same rotating head with two rotation scanning periods different are also compared, and tracking control is performed based on these comparison results, so the head position can be adjusted. The amount of displacement in one step for correcting the phase of the magnetic head can be made smaller than that of the conventional technology, which enables precise tracking. A head position control circuit can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an outline of a video tape recorder using a conventional auto-tracking device, FIG. 2 is a block diagram showing a specific example of the configuration of the above-mentioned auto-tracking device, and FIG. FIG. 4 is a timing chart for explaining the operation of the conventional auto-tracking device, FIG. 4 is a tape pattern diagram for explaining the operation of the conventional auto-tracking device, and FIG. 5 is a head position control according to the present invention. FIG. 6 is a block diagram schematically showing an embodiment of the circuit. FIG. 6 is a block diagram showing a specific example of the configuration of the embodiment of the present invention. 3, 4...Electro-mechanical conversion element (bimorph plate),
7... Applied signal generation circuit, 22... Sample hold circuit, 23... A/D converter, 24, 25, 35,
36... Shift register, 26... Shift pulse generation circuit, 37... First displacement direction determining circuit, 38... Second displacement direction determining circuit, 39... Determination circuit, 40,
41... Size comparison circuit, 42-44... Exclusive OR circuit, 51-54... Latch.

Claims (1)

[Scope of Claims] 1. In a head position control circuit of a magnetic recording/reproducing device that controls an electro-mechanical conversion element to perform a tracking operation on a rotary head, the head position control circuit includes a phase correction circuit that outputs a tracking correction amount signal and a tracking correction direction signal. and a direction correction circuit, the direction correction circuit sample-holding a level of the reproduced output signal for each rotational scan of the recording track of the rotary head;
a first storage means that sequentially stores the sample hold values and sequentially outputs them after one rotational scanning period of the rotary head; a second storage means that sequentially stores the sample hold values and sequentially outputs them after two rotational scanning periods of the rotary head; a first displacement direction for determining a displacement direction of the rotary head based on a comparison result between the output of the first storage means and the sample hold value and a displacement direction of the rotary head when the sample hold value was obtained; a determining means; a first unit for determining a displacement direction of the rotary head based on a comparison result between the output of the second storage means and the sample hold value and a displacement direction of the rotary head when the sample hold value was obtained; When the outputs of the first and second displacement direction determining means match, the output of the second displacement direction determining means is selected, and when they do not match, the output of the first displacement direction determining means is selected. 1. A head position control circuit for a magnetic recording and reproducing device, comprising: a determination circuit that selects and outputs a head position control circuit for a magnetic recording/reproducing apparatus.