JPS6136287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic tracking device for a magnetic recording/reproducing apparatus that automatically corrects deviation or displacement of a magnetic head from a recording track on a magnetic tape.

In magnetic recording and reproducing devices such as video tape recorders (hereinafter referred to as VTRs), in order to obtain good reproduction signals, it is necessary to accurately scan the recording tracks of the magnetic tape with a reproducing magnetic head. For this reason, it has been conventionally practiced to use an automatic tracking device that automatically returns the magnetic head to the center position of the recording track when the reproducing magnetic head deviates from the recording track.

By the way, with a VTR that records and plays back video signals for one screen (one frame = two fields) in time-divided manner using multiple magnetic heads, it is necessary to switch the magnetic heads, so it is difficult to realize an automatic tracking device. Have difficulty. That is, the tracking correlation between different heads and tracks is generally low, and in this case, a head position detection signal for controlling the magnetic head is obtained only intermittently.
Further, the transient of the detection signal generated when switching the heads induces unnecessary movement in the magnetic head, making it impractical for practical use. In particular, when a plurality of recording tracks are provided at different positions in the width direction on a magnetic tape, or when tracking control is performed only on a specific recording track, the above-mentioned drawback becomes noticeable.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks and provide an automatic tracking device for a magnetic recording/reproducing apparatus that can perform good automatic tracking even in a VTR or the like that uses a plurality of magnetic heads for recording and reproducing.

That is, the present invention includes an electro-mechanical transducer that supports a magnetic head for magnetic recording and reproducing, a circuit that generates a sine wave signal of a reference frequency c, and an electro-mechanical transducer that generates a sine wave signal of a reference frequency c in accordance with the signal of the frequency c of this circuit. a drive circuit that drives the conversion element to vibrate the magnetic head in the width direction of the recording track; a circuit that performs envelope detection of the reproduced signal from the magnetic head to detect only the signal caused by the vibration; A filter circuit that converts the signal of frequency c synchronized with the vibration of the electro-mechanical conversion element, a multiplication circuit that multiplies the signal of frequency c from this filter circuit by the signal that detected the vibration, and the output of this multiplication circuit. and a filter circuit that removes the frequency 2c component of the magnetic head and extracts a signal corresponding to the displacement of the magnetic head in the recording track width direction, and the displacement detection signal from the filter circuit is used to transmit the electric-mechanical signal through the drive circuit. In an automatic tracking device for a magnetic recording/reproducing apparatus that moves a conversion element to correct the magnetic head to the center position of a recording track, the reference frequency c is synchronized with the switching period of the magnetic head, and the main part of the magnetic recording/reproducing signal is Using a main magnetic head that handles the magnetic head and an auxiliary magnetic head that handles other parts, the main magnetic head is vibrated at the reference frequency c, and during the operation time of the auxiliary magnetic head, the auxiliary magnetic head is vibrated at the same time as the one immediately before the auxiliary magnetic head starts operating. It is characterized by the addition of a function to hold the reproduction envelope signal of the main magnetic head.

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram schematically showing an embodiment of the present invention, and the rotary head device includes a main magnetic head 2 and an auxiliary magnetic head 3 on a rotary disk 1. A 1.5 head type rotating head device is used. This 1.5
Since head-type rotary head devices are already known, their outline will be briefly explained. That is,
A 1.5-head type rotary head device has a magnetic tape wound diagonally (in a spiral) around a cylindrical guide drum over an angle range of approximately 330 degrees, and a rotary disk 1 placed horizontally within the guide drum. A main magnetic head 2 and an auxiliary magnetic head 3 are attached at a predetermined angle near the outer periphery of the guide drum, and the tips of the magnetic heads 2 and 3 are made to protrude through slits cut horizontally in the guide drum to attach the magnetic tape. configured to make contact. During recording or reproduction, the motor 5 rotates the rotary disk 1 at a predetermined speed, the magnetic heads 2 and 3 scan the surface of the magnetic tape diagonally, and the magnetic tape runs while being wound around the outer periphery of the guide drum. do. The auxiliary magnetic head 3 is responsible for recording and reproducing a part of the video signal near the vertical synchronizing signal, and the main magnetic head 2 is responsible for recording and reproducing the other main portion of the video signal.

In the 1.5 head rotary head device of this embodiment, the main magnetic head 2 is mounted on the rotary disk 1 via a bimorph 4 which is an electro-mechanical conversion element. This bimorph 4
In this method, two piezoelectric material plates are pasted on both sides of a conductive metal plate with a thickness of approximately 10 μm, and the polarization directions (thickness direction) of these piezoelectric material plates are opposite to each other. A conductive metal film such as silver is deposited on each surface as an electrode. Terminals a and b are connected to these electrodes, respectively. Examples of the above piezoelectric materials include
A solid solution of PbZrO ₃ and PbTiO ₃ is used.
One end of the bimorph 4 is fixed onto the rotary disk 1 via a support stand, and the main magnetic head 2 is attached to the movable part at the other end. Here, if voltage is applied to terminals a and b of the electrodes on both sides of the bimorph 4, the bimorph 4 will bend according to the direction and strength of the electric field between the two electrodes, and the other movable end will be displaced in the thickness direction. The main magnetic head 2 is also displaced in the same direction. The direction of this displacement is perpendicular to the rotational movement direction of the main magnetic head 2 (the scanning direction of the main magnetic head 2 on the magnetic tape).

Next, a servo system for keeping the rotational speed of the rotary disk 1 constant will be explained. First, the rotation of the rotary disk 1 is detected by the rotation detector 6. This rotation detector 6 includes, for example, a rotating magnet provided on the rotating shaft 7 of the rotating disk drive motor 5.
By detecting this rotating magnet with a magnetic head, a pulse is generated when the magnetic head 2 or 3 is at a predetermined rotational position. This rotation detection pulse is sent to the servo circuit 8. The servo circuit 8 compares the number of rotations obtained by detecting the rotation with a preset number of rotations, and sends an electric signal corresponding to the amount of error to the motor drive amplifier 9 at the next stage. The motor drive amplifier 9 controls the number of revolutions of the motor 5 to a preset number of revolutions by controlling the electric power etc. supplied to the motor 5. Incidentally, a rotation control pulse generator is provided inside the servo circuit 8, and controls the rotation speed of the rotary disk 1 (for example,
A reference pulse output having a frequency c (this is taken as a reference frequency, for example 720 Hz) which is an integral multiple of 60 c/s) is generated, and a part of this reference pulse output is taken out from the output terminal d of the servo circuit 8.

Further, the rotation detection pulse is also sent to the synchronization pulse generation circuit 10.
From 0, a pulse for switching between the main magnetic head 2 and the auxiliary magnetic head 3 is obtained. Note that during recording, an external synchronization pulse (horizontal synchronization pulse of a video signal) is input to the servo circuit 8 and the synchronization pulse generation circuit 10.

Next, the reproduced video signals from the magnetic heads 2 and 3 are amplified by RF amplifiers 11 and 12, respectively, and then sent to a switching circuit 13. This switching circuit 9 is connected to the synchronous pulse generating circuit 1.
Switching is controlled by output pulses starting from 0, and signals from the magnetic heads 2 and 3 are sent out alternately. The reproduced video signal obtained from the switching circuit 13 is demodulated by the FM demodulator 14 to become a normal AM video signal, which is taken out from the video signal output terminal c.

A portion of the reproduced video signal from the switching circuit 13 is sent to an envelope detector 16. This envelope detector 16 extracts an envelope signal of the FM carrier wave of the reproduced video signal. This envelope signal is gate-controlled by a gate circuit 17 at the next stage. This gate circuit 17 is supplied with pulses from the synchronizing pulse generating circuit 10 as a control signal, and operates in synchronization with the switching circuit 13 to control the reproduced video signal from the main magnetic head 2. Only the envelope signal is sent to the next hold circuit 18. The hold circuit 18 is connected to the main magnetic head 2.
This circuit holds the voltage value of the envelope signal immediately before switching from the magnetic head to the auxiliary magnetic head 3. The output signal from the hold circuit 18 is passed through a high-pass filter (hereinafter referred to as a high-pass filter) 19, in which frequency components around the rotational speed of the rotating head 1 are removed. e.

On the other hand, the pulse output of the reference frequency c obtained from the output terminal d of the servo circuit 8 is sent to a low-pass filter (hereinafter referred to as a low-pass filter) 21. This low-pass filter 21 is a second-order or third-order CR active filter, and the pulse of frequency c passes through this low-pass filter 21, thereby becoming a substantially sinusoidal wave of frequency c. This sine wave output is passed through the summing amplifier 22,
The signal is sent to the low-pass filter 23. The characteristics of the low-pass filter 23 are configured to have electrical secondary resonance system characteristics corresponding to the response characteristics of the mechanical vibration system of the bimorph 4 in which the main magnetic head 2 is provided. The output of the low-pass filter 23 is sent to the other input terminal of the multiplication circuit 20 via a high-pass filter 24 having characteristics similar to those of the high-pass filter 19. This multiplier circuit 20 is a type of balanced modulator that multiplies the respective output signals from the high-pass filters 19 and 24. Two outputs of opposite polarity from this multiplier circuit 20 are sent to two twin T-type filters 27 and 28, respectively. These twin T-type filters 27 and 28 have their null points set at 2c, and remove the frequency component of 2c. These twin T type filters 2
The outputs of 7 and 28 are operational amplifiers (operational amplifiers) 2
9 and 30, phase compensation and voltage slope limitation are performed. Further, the voltage is shifted by the breakdown voltage of the Zener diode 31 and the forward voltage of the diode 32, and after being adjusted to the DC level, one input terminal g of the high voltage differential amplifier 33 for driving the bimorph 4 is applied. Sent. The other input terminal h of the high-voltage differential amplifier 33 is fed with a sine wave signal having a reference frequency c from the summing amplifier 22. Two output terminals of this high voltage differential amplifier 22 are connected to terminals a and b of the electrodes of the bimorph 4, respectively.

By the way, the synchronization pulse from the synchronization pulse generation circuit 10 is also supplied to the program pulse generation circuit 25. This program pulse generating circuit 25 is for compensating for signal fluctuations due to rise characteristics etc. when switching the magnetic heads 2 and 3.
It is connected to the. When the above compensation is not required, switch 26 is turned off.

Next, the operation will be explained.

The reproduced signals obtained from the magnetic heads 2 and 3 are FM
The modulated video signal from the switching circuit 13 appears, for example, as shown in FIG. 2A. In FIG. 2A, the period between times t ₁ and t ₃ corresponds to the period of one revolution (for example, 1/60 seconds) of the rotating disk 1, and the period between times t ₁ and t ₂ is reproduced by the auxiliary magnetic head 3. The period between times t ₂ and t ₃ is the portion reproduced by the main magnetic head 2 . The envelope signal obtained by envelope detection of this signal is shown in FIG. 2B, and transients appear at head switching points such as times t ₁ , t ₂ , and t ₃ . This envelope signal is sent to gate circuit 17 and hold circuit 18. Here, the control terminal of the gate circuit 17 is connected to a pulse signal (C
Since the gate circuit 17 operates in synchronization with the switching circuit 13, the period during which the auxiliary magnetic head 3 is in the reproducing operation (times t ₁ and t ₂
The signal is temporarily cut off during the interval (between times t ₂ and t ₃ ), and the signal is sent to the next hold circuit 18 during the interval during which the main magnetic head 2 is in playback operation (between times t 2 and t 3 ). The hold circuit 18 is a circuit that holds the final value of the input/output signal, that is, the value of the reproduced signal from the main magnetic head 2 at time _t1 , until the next input signal arrives (time _t2 ). Therefore, the envelope signal passing through the gate circuit 17 and the hold circuit 18 has a waveform with suppressed transients as shown in FIG. 2D. Therefore, control disturbances caused by transients when switching magnetic heads can be reduced. By the way, in FIGS. 2A and 2B, the amplitude at time t ₁ and the amplitude at time t ₂ are made different for the sake of explanation, and this makes the residual transient at time t ₂ in FIG. Although it is depicted as occurring, if the automatic tracking device of this embodiment is operating effectively in closed loop control, the amplitudes at times t ₁ and t ₂ will be approximately equal, so the above residual amount can be ignored. It can be as small as

Here, the long-period waves appearing in the envelope signal between times t ₂ and t ₃ in FIG. 2B and D are caused by the main magnetic head 2 being displaced from the recording track. The amplitude is maximum when the head 2 scans the center position of the recording track, and the amplitude becomes smaller as the amount of displacement from the center position increases. In addition, the short-period wave riding on this long-period wave causes the signal of the reference frequency c obtained from the summing amplifier 22 to vibrate the bimorph 4 via the high-voltage differential amplifier 33, and the main magnetic head 2 to the recording track. This is caused by vibration in the width direction. In this case, it must be noted that depending on the direction of displacement of the main magnetic head 2, the phases of the short-period waves of the obtained reproduced envelope signal become opposite to each other.

That is, FIGS. 3A, B, and C show the relationship between the scanning locus R of the main magnetic head 2 and the recording track T, and in FIG. 3A, the vibration center of the main magnetic head 2 is the center of the recording track T. When passing through the position, Figure 3B
3C shows the case where the center of vibration is displaced in the direction of arrow _Z1 , and FIG. 3C shows the case where the center of vibration is displaced in the direction of arrow _Z2 . In FIG. 3, arrow Y indicates the scanning direction of the main magnetic head 2, and arrows Z ₁ and Z ₂ indicate the vibration direction or displacement direction of the main magnetic head 2, respectively. What the main magnetic head 2 actually reproduces is only the shaded area of the recording track T, and the shape of the envelope signal of the reproduced signal approximately corresponds to the shape of the shaded area in the figure.
In FIGS. 3B and 3C, envelope signals having mutually opposite phases (phase difference of 180°) are obtained at frequency c. Therefore, for example, the main magnetic head 2
passes from the position in Figure 3B to the position in Figure 3A,
The envelope signal of the reproduced signal when displaced to the position shown in FIG. 3C is as shown in FIG. 4A. That is, the portion T _B shown on the time axis (horizontal axis) of FIG. 4A is at the position in FIG. 3B, the portion T _A is at the position in FIG _. correspond to the respective positions. By passing the signal in the vicinity of the reference frequency c through the high-pass filter 19 of the signal shown in FIG. 4A, only a short-period signal due to bimorph vibration as shown in FIG. 4B is obtained. The signal shown in FIG. 4B is supplied to one input terminal e of the multiplication circuit 20. The other input terminal of this multiplier circuit 20 is supplied with a sine wave signal having a reference frequency c.

By the way, when the bimorph 4 is vibrated with a sine wave signal of the reference frequency c from the summing amplifier 22, the bimorph 4 vibrates with a delay of a predetermined phase amount due to the mechanical vibration characteristics of the bimorph 4. Therefore, the signal from the summing amplifier 22 is electrically delayed by the predetermined phase amount by the low-pass filter 23, and is further passed through the high-pass filter 24 to generate a signal synchronized with the mechanical vibration of the bimorph 4 (FIG. 4C). ), then the multiplication circuit 2
0 to the other input terminal.

In the multiplier circuit 20, these signals of FIG. 4B and C
A signal as shown in FIG. 4D is obtained by multiplying the signal by the signal . That is, in the portion T _B , the signal B and the signal C are in phase, so the product signal D appears on the positive side, whereas in the portion T _C , the signal B and the signal C are in opposite phase, so the product signal D appears. appears on the negative side. As is clear from the figure, the period of these product signals D is 1/2c. In part T _A , signal B
The period of is 1/2c, and the positive and negative signals are distributed at almost the same rate during this one period. Therefore, the product signal D of this signal B and the signal C with a period of 1/c has positive and negative values near the zero level. will be distributed in the same proportion.

From the multiplication circuit 20, the signal D and the signal D
and a signal with opposite polarity (positive, negative) is obtained. These signals are passed through twin T filters 27 and 2, respectively.
8, the frequency 2c component is removed and the operational amplifier 2
9 and 30 perform differential addition, loop phase compensation and amplification, and a signal as shown in FIG. 4E is obtained. This signal E is further adjusted in DC level by a Zener diode 31 and a diode 32, and then supplied to one input terminal g of a high voltage differential amplifier 33 for driving the bimorph. At this time, the bimorph 4 is driven in a direction opposite to the direction of displacement, and the main magnetic head 2 returns to the center position of the recording track T. Note that FIG. 2E shows the displacement control signal supplied to the terminal g when the reproduction signal of FIG. 2A is obtained. In this way, a control loop for detecting the deviation (displacement) between the main magnetic head 2 and the recording track T and dynamically correcting it is completed. When this control loop is operating normally, the obtained reproduction signal is as shown in FIG. 5A, and the bimorph drive control signal for displacement correction (one input terminal g of the high voltage differential amplifier The supplied signal) is as shown in FIG. 5B. by the way,
At the head switching time _t2 , the reproduction signal such as the rise characteristic may fluctuate as shown by the thick solid line in FIG. What is necessary is to supply the summing amplifier 22 with a signal having a waveform that corrects the above fluctuation amount.

As is clear from the above explanation, the displacement of the main magnetic head 2 is detected by the frequency c component of the envelope signal, and since this c component is due to the mechanical vibration of the bimorph 4, it is not a noise in the video signal. It is possible to perform reliable displacement detection with few malfunctions. Further, the transient of the envelope signal at the time of head switching is reduced by passing through the gate circuit 17 and the hold circuit 18, and is reduced to almost zero during normal operation. Furthermore, by the program pulse generator 25,
It is also possible to compensate for fluctuations in the reproduced signal due to the rise characteristics at the time of head switching. Therefore, even in the case of a VTR in which a video signal for one screen is recorded and reproduced using a plurality of magnetic heads, good automatic tracking control can be performed.

The present invention is not limited to the above-mentioned embodiments, but can be applied to various magnetic recording and reproducing apparatuses, such as a two-head type VTR in which two magnetic heads are arranged at an angle of 180 degrees to each other on a rotating disk. Applicable. In addition to bimorphs, various electromechanical transducers such as monomorphs can be used.

[Brief explanation of the drawing]

1 is a block circuit diagram schematically showing an embodiment of an automatic tracking device for a magnetic recording/reproducing apparatus according to the present invention, 2A to 2E are time charts for explaining the operation of the circuit in FIG. 1, and 3. 4A to 4E are time charts for explaining the operation of the multiplier circuit 20 in FIG. 1, and FIG. A and B are time charts for explaining the operation of the circuit of FIG. 1 when the control operation is performed normally. DESCRIPTION OF SYMBOLS 1...Rotating disk, 2...Main magnetic head, 3...Auxiliary magnetic head, 4...Bimorph, 8...Servo circuit, 10...Synchronizing pulse generation circuit, 13...Switching circuit, 17...Gate circuit, 18...Hold circuit, 20... Multiplier circuit, 21...low pass filter,
22...Summing amplifier, 33...High voltage differential amplifier, 2
3...Low pass filter.

Claims (1)

[Scope of Claims] 1. An electromechanical transducer that supports a magnetic head for magnetic recording and reproducing, a circuit that generates a sine wave signal with a reference frequency c, and an electromechanical transducer that generates a sine wave signal with a reference frequency c, A drive circuit that drives a mechanical transducer to vibrate the magnetic head in the width direction of the recording track, a circuit that performs envelope detection of the reproduced signal from the magnetic head to detect only the signal caused by the vibration, and a circuit that detects only the signal caused by the vibration. a filter circuit that converts the signal of frequency c synchronized with the vibration of the electro-mechanical conversion element; a multiplication circuit that multiplies the signal of frequency c from this filter circuit by the signal that detected the vibration; and an output of this multiplication circuit. and a filter circuit that removes the frequency 2c component of the magnetic head and extracts a signal corresponding to the displacement of the magnetic head in the recording track width direction, and the displacement detection signal from the filter circuit is used to transmit the electric-mechanical signal through the drive circuit. In an automatic tracking device for a magnetic recording/reproducing apparatus which moves a conversion element to correct the magnetic head to the center position of a recording track, the reference frequency c is synchronized with the switching cycle of the magnetic head, and the main part of the magnetic recording/reproducing signal is The main magnetic head is controlled at the reference frequency c using a main magnetic head that handles the magnetic head and an auxiliary magnetic head that handles other parts.
An automatic tracking device for a magnetic recording and reproducing apparatus, characterized in that the automatic tracking device for a magnetic recording and reproducing apparatus is further added with a function of vibrating the main magnetic head and holding the reproduction envelope signal of the main magnetic head immediately before the start of operation of the auxiliary magnetic head during the operation time of the auxiliary magnetic head. .