JPH0679401B2 - Magnetic reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic reproducing apparatus, and more specifically, in a helical scan type VTR equipped with a movable magnetic head and a fixed magnetic head, the movable magnetic head and the fixed magnetic head during reproduction. Both of the magnetic heads are associated with a magnetic reproducing device capable of tracking control.

[Prior Art] FIG. 4 is a block circuit diagram showing a reproducing system of a conventional magnetic reproducing apparatus disclosed in, for example, Japanese Patent Laid-Open No. 55-32241. In FIG. 4, (1) shows an electro-mechanical conversion element. Is a piezoelectric element, (2) is a magnetic head bonded to the piezoelectric element (1),
(3) is a drive circuit for wobbling the piezoelectric element (1), and (4) is a bandpass filter for extracting the wobbling frequency contained in the reproduction signal from the magnetic head (2). (5) is an oscillator, which generates a signal having a wobbling frequency. (6) is a phase shifter, which has a wobbling drive signal and
It acts to match the phase of the wobbling operation of the actual piezoelectric element (1). (7) is a multiplier or a synchronous detection circuit (hereinafter referred to as "synchronous detection circuit"), which is an inverting amplifier (1
7), forward amplifier (18), waveform shaping circuit (19) and analog switch (20), multiply or synchronize the signal from phase shifter (6) with the signal from bandpass filter (4). To detect. (8) is a low-pass filter which limits the band of the output signal of the multiplier (7). (9) is an adder.

FIG. 5 is a diagram showing changes in the amplitude of the reproduction envelope signal from the magnetic head (2) with respect to the amount of track deviation. In the figure, A is a position displaced to the left of the track center,
B represents a track center, and C represents a position displaced to the right from the track center.

Fig. 6 shows the reproduction signal of the magnetic head (2) at the track shift positions A, B, and C after passing through the bandpass filter (4), with the vertical axis representing the amplitude and the horizontal axis representing the time. Is. The figure (W) shows the movement of the piezoelectric element (1), and the figure (B) shows the waveform of the output signal of the band pass filter (4) when the magnetic head (2) is displaced to the position A. Figure (B) shows the waveform of the output signal of the bandpass filter (4) when the magnetic head (2) is in the B position, and Figure (C) shows the bandpass when the magnetic head (2) is displaced to the C position. The waveform of the output signal of the filter (4) is shown.

7 (A), (B) and (C) are shown in FIG. 6 (A),
Similar to (B) and (C), the waveforms of the output signals after synchronous detection at the respective track positions A, B and C of the magnetic head (2) are shown.

Next, the operation will be described.

Generally, in a helical scan magnetic reproducing device,
Many methods have been proposed for detecting the relative displacement between the rotary magnetic head and the recording track for tracking control. For example, several low frequencies outside the band of the video signal are recorded so that different frequencies are adjacent to each other over several tracks, and the relative positional deviation amount is determined by the difference in the crosstalk level of the left and right tracks during playback. How to detect,
There is a method of detecting the relative displacement by making a minute vibration (hereinafter referred to as "wow ring") of the rotating magnetic head at a constant frequency (hereinafter referred to as "wow ring frequency") in a direction perpendicular to the scanning direction of the rotating magnetic head. is there. Of these, the former requires recording a control signal for control at the time of recording, which cannot be realized by the VHS system and β system, which are the current consumer VTRs using 1/2 inch tapes. However, the latter does not require recording of control signals, so it can also be applied to existing consumer VTRs. Since this wobbling method has been conventionally proposed,
The operating principle of a general wobbling method will be briefly described.

Generally, the amplitude of the reproduction envelope signal reproduced from the magnetic head (2) changes as shown in FIG. 5 with respect to the amount of relative positional deviation with respect to the magnetic head (2) with respect to the recording track. Here, when the piezoelectric element (1) is driven by the drive circuit (3) by the sine wave signal generated by the oscillator circuit (5), the magnetic head (2) for the recording track vibrates minutely in a sine wave, and at this time When the band pass filter (4) that allows only the wobbling frequency of the reproduction envelope of the magnetic head (2) to be passed through is passed through, as shown in FIG. 6 (A), (B), or (C), corresponding to the track shift amount. The signal is obtained.

When the wobbling frequency selected in this way is used for wobbling at, for example, point A in FIG. 5 (when it is displaced to the left with respect to the track center), the output of the bandpass filter (4) is the magnetic head (2). A signal having a phase inverted with respect to the wobbling waveform (shown in FIG. 6 (W)) is obtained as shown in FIG. 6 (A). In the case of the reverse C point, the signal having the same phase as shown in FIG. 6 (C) is obtained. Is obtained. In the case of the point B which is the track center, a signal having a frequency twice the wobbling frequency is obtained, but the signal amplitude is attenuated because the frequency is outside the pass band of the band pass filter (4), and the signal is attenuated as shown in FIG. ) The signal is as shown in.

Next, when the waveform W representing the movement of the magnetic head (2) in FIG. 6 and the waveforms A to C that have passed through the band pass filter (4) are synchronously detected by the synchronous detection circuit (7), For each of the relative displacement points A, B, C, see FIG. 7 (A),
Waveform signals as shown in (B) and (C) are obtained. At this time, a waveform W representing the movement of the magnetic head (2),
Since the phase of the sine wave generated by the oscillator (5) does not necessarily match due to the phase rotation due to mechanical resonance or the like of the piezoelectric element (1), this phase shift amount is used as the phase shifter (6). The phase is adjusted by and then input to the synchronous detection circuit (7). The synchronous detection circuit (7) pushes the analog switch (20) to the non-inverting amplifier (18) side when the wobbling waveform W is negative, and the inverting amplifier (17) when the wobbling waveform W is positive.
It is realized by making it move to the side.

Finally, the output signal of the synchronous detection circuit (7) is smoothed by a low-pass filter (8) to obtain a signal (hereinafter referred to as "tracking error") corresponding to the relative positional deviation amount of the magnetic head (2) with respect to the recording track. A signal ") is obtained, and this signal is fed back to the piezoelectric element (1) that moves the magnetic head in the direction in which the amount of relative positional deviation converges, thereby forming a tracking control system.

A drive circuit (3) for driving the piezoelectric element (1)
As a result, a wobbling signal for slightly vibrating the piezoelectric element (1) and a feedback signal corresponding to the relative positional deviation amount are added and input.

[Problems to be Solved by the Invention] Since the conventional magnetic reproducing apparatus is configured as described above, for example, a magnetic head displaceable in a direction perpendicular to the scanning direction and an impossible magnetic head are mixed. In the case of a magnetic reproducing apparatus having a large rotating magnetic head, when a displaceable magnetic head follows a low-frequency track deviation, another immovable magnetic head causes a track deviation. It was However, it is difficult to make all of the rotating magnetic heads movable heads in terms of cost and dimensional restrictions built in the rotating drum.

Also, in order to displace the magnetic head, in order for the actuator to follow all track deviations,
The low-frequency gain of the tracking control system must be set to a sufficiently large value.If the gain is forcibly increased, the above-mentioned machine will be used when an electromagnetic drive type actuator whose mechanical resonance frequency is relatively lower than that of a piezoelectric element is used. Due to the influence of the phase around the resonance, the phase margin of the control system decreases and there are problems such as oscillation.

Further, in the conventionally used bimorph, the magnetic head is tilted with respect to the tape as compared with the drive displacement amount, so that it is difficult to perform a large amplitude operation during high speed special reproduction.

The present invention has been made to solve the above-mentioned problems, and even in the case of having a rotating magnetic head in which displaceable magnetic head and impossible magnetic head are mixed,
When the movable head is tracking, all the other fixed heads will not cause low frequency track shift except for track bending, and the low frequency gain of the tracking control system will be expanded to reduce the deviation from the track offset. The purpose is to obtain a magnetic reproducing device that can be used.

[Means for Solving the Problem] A magnetic reproducing apparatus according to the present invention detects an tracking error signal from an actuator that displaces a magnetic head, minutely vibrates the actuator, and reproduce envelope information at this time. A means for feeding back the tracking error signal to the actuator by extracting a relatively high frequency component including a track bend up to the servo band frequency of the tracking error signal, and a relatively low frequency including a track shift component from the direct current of the tracking error signal. Means for extracting the component and adding it to the phase control signal of the capstan motor whose phase is controlled by the control signal written in the linear track on the magnetic tape.

[Operation] In the control system according to the present invention, the tracking error signal is frequency-divided by the filter, the high frequency component is fed to the actuator, and the low frequency component is fed back to the phase control system of the capstan motor. The tracking control of the fixed magnetic head can be performed by the feedback to the motor, and the tracking control of the movable magnetic head can be performed by the feedback of the actuator.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram of this embodiment, and the same reference numerals as those in FIG. 4 denote the same parts. (20) is a rotating drum,
(21) is a movable magnetic head, (22) is a fixed magnetic head,
(23) is an electromagnetic drive type actuator, (24) is a slip ring that supplies a drive current to the rotating part, (25) is a head amplifier, (26) is an auto gain control circuit (hereinafter,
The so-called "AGC circuit") ensures that the reproduction envelope amplitude, which is the output from the head amplifier (25), is always constant even with variations in the electromagnetic system. (27) is a rotation phase signal output from a rotary encoder that detects the rotation phase of the rotary drum (28), and (28) is a phase locked loop circuit (hereinafter, referred to as "PLL circuit"), which is an output of the rotary encoder ( It oscillates a signal whose frequency is phase-locked to 27). (29) is a bandpass filter, which passes only the wobbling oscillation frequency in order to shape the rectangular wave from the PLL circuit (28) into a sine wave. (30) and (31) are monostable multivibrator circuits (hereinafter referred to as "mono-multi circuits") that shift the phase of the output pulse of the PLL circuit (28). (32) is a lag lead type low-pass filter showing a phase delay-advance characteristic, (33) is a lag type low-pass filter having only a phase delay characteristic, (34) is a control head, and is written on the linear track of the magnetic tape (40). Read the embedded control signal. (35) is a capstan phase control circuit (hereinafter referred to as “capstan APC”).
("Auto phase lock circuit") synchronizes the phase of the capstan motor (37) with the signal from the control head (34). (36) is a drive circuit for driving the capstan motor (37), (37) is a capstan motor, (38) is a magnetic tape, and (39) is an adder.

FIG. 2 is a diagram showing how the magnetic heads (20) and (21) trace a track on the magnetic tape (38). FIG. 2 (a) shows an electromagnetically driven actuator ( The trace positions of the fixed head (22) and the movable head (21) when the high frequency component in the tracking error signal is fed back are shown only in (23).
Fixed head (2) when the low frequency component in the tracking error signal is fed back to the capstan motor (37).
2) and the trace position of the movable head (21) are shown.

FIG. 3 is an open loop characteristic of the control system of this embodiment,
FIG. 3 is a diagram showing frequency characteristics of an electromagnetic drive type actuator and a capstan motor. In FIG. 3 (a), a characteristic A is an open loop characteristic of a loop fed back to the capstan motor (37) in this control system. The characteristic B
Shows the open loop characteristic of the loop feeding back to the electromagnetic drive type actuator (23), and the frequency d is the spring resonance frequency of the electromagnetic drive type actuator (23).

FIG. 3B is a diagram showing the drive current-displacement characteristic of the electromagnetic drive type actuator (23), and the frequency e is the mechanical resonance frequency of the electromagnetic drive type actuator (23).

Further, FIG. 3 (c) shows the drive current of the Kitapstan motor--
In the figure showing the rotation phase characteristic, the frequency is the corner frequency of the DC motor.

The operation of this embodiment will be described below.

In FIG. 1, a signal (27) corresponding to the rotation phase of the rotary drum (20) is passed through a PLL circuit (28) so that the rotary drum (2) has a high frequency necessary for wobbling.
It is possible to obtain a wobbling signal synchronized with the rotation of (0). This is because the jitter component generated when wobbling the reproducing magnetic head (21) is synchronized with the rotation of the rotating drum (20), so when reproducing a helical scan system video signal, etc. Since the resulting jitter is fixed, it is difficult for the human eye to detect it. In this way, the reproduction signal obtained by wobbling the movable magnetic head (21) is amplified by the head amplifier (25) to obtain a reproduction envelope signal. At this time, the bandpass filter (4) and the synchronous detection circuit (7) are passed through the AGC circuit (26) so that the amplitude of the reproduction envelope signal is always constant with respect to variations in the electromagnetic system, as in the case of the conventional example. ) And a smoothing circuit (8), a tracking error signal is obtained. This tracking error signal is normally fed back to the electromagnetic drive type actuator (23) in the direction in which the positional deviation is reduced. Will not do. That is, the movable head (21) is controlled so as to be on-track to the recording track, while the fixed head (22) is moved to the movable head (2).
Since 1) moves in the direction perpendicular to the scanning direction, a head step with respect to the movable head (21) is generated, and on-track does not occur. However, as in this embodiment, when a low-pass filter (33) is used to extract from the DC component in the tracking error signal to a relatively low frequency component and added to the phase control loop of the capstan motor (37),
A capstan motor can be used to compensate for DC-like track deviations.

That is, the capstan phase control system uses magnetic tape (3
8) The phase is locked with respect to the control signal written in the upper linear track. Here, by correcting the rotational phase of the capstan motor (37) in accordance with the amount of track deviation of the fixed magnetic head (22) within the range where the capstan phase control system is locked, The capstan phase control system absorbs the track shift. Then, the amount of relative displacement including components such as track bending excluding the DC component is calculated by the electromagnetic drive type actuator (2
When the feedback back is applied to 3), the head step difference as shown in FIG. 2 (a) does not occur, and the fixed head (22) can be made on-track as shown in FIG. 2 (b). Furthermore, since the movable head (21) is controlled so that the movable head (21) is always on-track even when a track deviation including a relatively high frequency component such as a track bend is detected, the fixed head (22) is Although it is not possible to follow the track deviation of high frequency components such as bending, there is no direct track deviation. In this case, since the movable head (21) is mounted in, for example, an electromagnetically driven actuator having a movable portion supported by a spring, the fixed head (22) is not controlled, that is, when the driving current is zero.
It must be adjusted so that the head level difference between and is small. However, when the head step difference is adjusted, a direct current may be constantly supplied to the movable head (21) to electrically adjust the head step difference.

Since the movable head (21) also follows the track bend, it is possible to use a magnetic head having the same width as the recording track pitch. If this movable magnetic head (21) is used for video signals, the azimuth effect can be obtained. It is possible to improve the image quality by reducing the amount of low frequency crosstalk.

If the fixed head (22) is a magnetic head wider than the recording track pitch, there will be no direct track deviation, so that even a slight track bend can be sufficiently reproduced. It can also be used for audio.

When the movable part of the electromagnetic drive type actuator is of a type that is supported by a spring, the displacement amount with respect to the drive current has the characteristic shown in FIG. 3 (b), and up to a frequency slightly lower than the spring resonance frequency e. Servo band can be taken. This is because there is no phase rotation of the actuator up to near the spring resonance frequency e, so that a phase margin can be secured. Apart from this, there is also a method in which phase advance compensation is performed and the servo band is set between the spring resonance frequency d and the mechanical resonance frequency e. The drive current-rotational phase characteristics of the capstan motor (37) are as shown in Fig. 3 (c), and the response speed of the capstan motor (37) is higher than that of the electromagnetic drive type actuator (23). Therefore, the characteristic of the entire tracking control system is a characteristic obtained by combining the characteristic C and the characteristic D. However, since the characteristic of the capstan motor (37) includes a perfect integrator between the rotational speed and the rotational phase in the transfer function of the capstan motor, the characteristic becomes larger as the frequency becomes lower (Fig. 3). (C) Shown),
Since it has the effect of sufficiently ensuring the low-frequency gain of the characteristics of the entire tracking control system, it is possible to sufficiently ensure the synthesis of the entire control system with respect to low-frequency disturbance.

As described above, by using both the capstan motor (37) and the electromagnetic drive type actuator (23), the control band can be extended while ensuring the low-frequency gain of the entire tracking control system.

Also, in the case of special playback mode such as double speed, triple speed,
In addition (9), the wave height of 3 corresponding to the special playback mode
When the angular waveform signals are added, even in the special reproduction mode, the tracking control system operates so as to correct the deviation between the movement of the movable head due to the added triangular wave and the actual track, so that the track deviation occurs. In the analog type helical scan VTR, there is no noise bar on the TV screen, so noiseless special playback is possible.

[Effects of the Invention] As described above, according to the present invention, the low frequency component of the tracking error signal obtained by wobbling the actuator in the rotary drum is applied to the capstan phase control system, and the high frequency component is applied to the capstan phase control system. Since the actuators are fed back to the actuators, the tracking of the fixed head in the rotary drum can be obtained and the control band can be extended while securing the low range gain of the tracking control system. Further, since the movable head width is the same as the track pitch, there is an effect that the crosstalk amount can be reduced.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing a scanning position of a magnetic head in this embodiment.
FIG. 3 is a diagram showing the open loop characteristic of the control system of this embodiment, the characteristic of the electromagnetic drive type actuator and the frequency characteristic of the capstan motor, and FIG. 4 is a block circuit diagram of the tracking control system of the conventional magnetic reproducing apparatus. 5 shows changes in the amplitude of the reproduction signal envelope from the magnetic head with respect to the track deviation, and FIG. 6 shows the wobbling drive signal and the wobbling signal extracted from the reproduction envelope signal at each track deviation position in FIG. FIG. 7 is a waveform diagram showing the relationship between the phase and the amplitude, and FIG. 7 is a waveform diagram of the synchronous detection output signal at each track shift position in FIG. (3), (36) ... drive circuit, (4), (29) ... bandpass filter, (7) ... synchronous detection circuit, (8),
(32), (33) …… Low-pass filter, (9), (39)
...... Adder, (22) …… Fixed magnetic head, (20) …… Rotary drum, (21) …… Movable magnetic head, (23) …… Electromagnetic drive type actuator, (26) …… Auto gain control circuit , (28) …… Faise lock droop circuit,
(30), (31) ... monostable multivibrator circuit,
(34) …… Control head, (35) …… Capstan motor phase control circuit, (37) …… Capstan motor, (38) …… Magnetic tape. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An actuator mounted on a rotary drum for displacing a movable magnetic head in a direction perpendicular to a scanning direction on a magnetic tape of the magnetic head, and a fixed magnetic head mounted on the rotary drum. Means for generating a wobbling drive signal in synchronism with the rotational movement of the rotary drum and applying it to the actuator, and detecting a tracking error signal for a recording track of the movable head from the reproduction envelope signal of the movable head and the wobbling drive signal. Means, a feedback circuit for extracting a high frequency component of the tracking signal and adding it to the wobbling drive signal with a polarity at which the tracking error converges, and a low frequency component including a DC component of the tracking error signal. Key to drive the above magnetic tape. Magnetic reproducing apparatus having a feedback circuit to the phase control signal Pusutanmota tracking error of the stationary magnetic head for adding a polar converged.