JPH0677291B2 - Magnetic reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a helical scan type video tape recorder (hereinafter referred to as “VTR”), and more particularly to an automatic tracking control device for a playback head.

[Prior Art] FIG. 4 is a block circuit diagram showing a reproducing system of a conventional magnetic reproducing apparatus disclosed in, for example, JP-A-55-32241.
In the figure, (1) is a piezoelectric element which is an electro-mechanical conversion element, (2) is a magnetic head bonded to the piezoelectric element (1),
(3) is a drive circuit for wobbling the piezoelectric element (1), and the drive circuit (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. Reference numeral (6) is a phase shifter, which acts to match the wobbling drive signal with the phase of the actual wobbling operation of the piezoelectric element (1). (7) is a multiplier or a synchronous detection circuit (hereinafter referred to as "synchronous detection circuit"), which is composed of an inverting amplifier (17), a non-inverted amplifier (18), a waveform shaping circuit (19) and an analog switch (20). Phase shifter (6)
From the band pass filter (4) is multiplied or synchronously detected. (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 copper diagram (W) shows the movement of the piezoelectric element (1), and the motion diagram (B) shows the waveform of the output signal of the bandpass filter (4) when the magnetic head (2) is displaced to the A position. 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 diagram (C) is 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 (registered trademark) system and β system, which are VCRs for consumer use using the current 1 / 2-inch tape. is there. 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 operation principle of a general wobbling method will be briefly described below.

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.

FIG. 8 shows general frequency characteristics of the piezoelectric element (1).
The wobbling frequency is selected in a band where the drive voltage and the minute vibration of the voltage element are out of phase, that is, in a band lower than the primary resonance frequency due to mechanical factors of the piezoelectric element (1). One of the main reasons for this is that since there are large variations in the product of piezoelectric elements, there may be variations in multiple mechanical resonance frequencies. Therefore, because the wobbling frequency cannot be selected higher than the primary resonance frequency, this band It is selected.

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 calculated by the phase shifter (6). After the phase adjustment, it is 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 positive, and the inverting amplifier (17) when the wobbling waveform W is negative.
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.

Generally, a video tape recorder (hereinafter referred to as "VTR") equipped with a movable head actuator is not only used for dynamic tracking to follow the track bend during normal playback, but also for special playback (high-speed playback). , Slow playback, still, etc.) are often used. Assuming a VTR that uses a guard bandless recording method that uses azimuth loss as the VTR recording method, when the track pitch is α, the movement amount x that the actuator must drive during special playback is n times faster. It is given by the following equation.

x = (n−1) × α Now, let us consider the VHS system which is one of the consumer 1/2 inch VTR systems as an example of this embodiment. Assuming that the track pitch α in the 2-hour mode of the VHS system is 58 μm and the forward / reverse 5 × speed reproduction is assumed, the head movement amount that the actuator should drive is in the forward 5 × speed …… 58 × (5-1) = 322 (μm) Reverse speed at 5 times speed: 58 × (−5-1) = − 348 (μm), which shows that at least the drive range of P-P 700 μm is required for the actuator.

Considering the case where the actuator is assumed to be a bimorph which is a piezoelectric element as in the conventional case, the bimorph is known as an element having a large amplitude amount for a driving voltage among piezoelectric elements. And the displacement amount ξ of bimoflu is given by the following equation.

Where ξ: displacement, V: applied voltage, d31: voltage constant l: effective length, t: thickness per voltage body Sk: electrode coefficient (0.94 to 0.95) R: loss factor (0.9) where piezoelectric constant d31 is applied It is a function of voltage and has a relationship of d31 → high when V → high. Sk, k is a constant determined by the shape of the bimorph electrode.

The displacement amount ξ of the bimorph is determined by various factors in this way.However, when it is used as an actuator for a VTR, it should have a large amplitude and a low mechanical resonance gain. , The piezoelectric constant d31 of which is large is selected. However, it is the effective length l of the bimorph that is the square term that mainly affects the displacement ξ, and l
The longer the is, the larger the displacement ξ can be taken.

Considering the application to the VHS system, the diameter of the drum on which the actuator is mounted is fixed, so the effective length l of the bimorph is also limited. For example, when a bimorph shape is set as shown in FIG. 9, it is a well-known fact that the movable range of 700 μm is generally not taken. Therefore, various measures are taken to increase the effective length of the bimorph within the limited drum diameter. For example, there is the ring-shaped bimorph of FIG. 10 shown in JP-A-55-22285, and the example of FIG. 11 shown in JP-B-63-41130. However, even if the effective length is lengthened in this way and the displacement amount ξ is obtained, there are the following problems.

FIG. 12 is a diagram showing the relationship between the effective length of the bimorph and the inclination of the magnetic head. Displacement ξ, effective length l and head inclination θ
The relationship with and is given by the following equation.

Fig. 13 shows the required moving distance ξ for VHS reverse 5x speed playback.
The relationship between the effective length of the bimorph and the head slope in the case of = 348 μm is shown. Since the head tilt leads to image quality deterioration, the tilt angle is generally limited to less than 1 °. In this case, the effective length is 40 for the head inclination to be less than 1 °.
It must be more than (mm). In the case of the VHS system, the drum diameter is 62φ, and it is possible to obtain an effective length of 40 (mm) or more by various methods such as making the shape of the bimorph a ring, but it is effective depending on the drum size. Since the length cannot be set indefinitely, the head inclination is close to 1 °, and deterioration of image quality cannot be avoided.

In addition, a bimorph requires a large voltage (100 to several hundreds of volts) to drive, hysteresis occurs, mechanical strength is not sufficient, and there is a danger of breaking if the magnetic head is changed with a large amplitude. There are problems such as changes over time and high prices, so there are still many problems for commercialization in consumer VTRs.

[Problems to be Solved by the Invention] A magnetic reproducing device equipped with a conventional automatic tracking device uses a piezoelectric element that requires high voltage driving for an actuator, and has a frequency lower than the primary resonance of the piezoelectric element, that is, a phase. Since the wobbling frequency was selected in the band where the amount of rotation was zero, the wobbling frequency could not be set high (480H
(about z), the servo band is limited so that highly accurate tracking is impossible, and a high voltage is required for driving the piezoelectric element itself. There is hysteresis, there is a change over time. When shaken with a large amplitude, a head tilt occurs. The mechanical strength is not sufficient and the magnetic head may be destroyed if it is displaced with a large amplitude. There were problems such as high prices.

The present invention has been made to solve the above-mentioned problems, and it is possible to perform highly accurate automatic tracking during normal reproduction without using a piezoelectric element and to perform special reproduction (high-speed reproduction, slow reproduction, still reproduction). The objective is to obtain a multi-functional, high-performance and inexpensive magnetic reproducing device capable of automatic tracking without causing noise bars.

[Means for Solving the Problems] A magnetic reproducing apparatus according to the present invention includes an electromagnetically driven actuator that is mounted on a rotating drum and moves a magnetic head in a direction perpendicular to a longitudinal direction of a recording track on a recording medium. Driving means for slightly vibrating the actuator with a signal of a constant frequency, means for extracting a minute vibration signal component from the reproduction envelope signal from the magnetic head, and phase matching of this extracted signal component with the minute vibration drive signal supplied to the actuator Means, means for obtaining a phase error signal between the recording track and the magnetic head by smoothing by synchronous detection or multiplication of both signals having the same phase, and a magnetic head for the recording track by negatively feeding back this position error signal to an actuator. And a means for correcting the relative position error of
The frequency of the microvibration drive signal is set between the primary resonance frequency and the secondary resonance frequency of the actuator.

[Operation] In the magnetic reproducing apparatus of the present invention, since the actuator is an electromagnetic drive type actuator, the wobbling frequency can be increased, the servo band can be increased, and the head tilt can be generated even during special reproduction. It is possible to drive large amplitude with low driving voltage.

[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 an embodiment of the present invention.
(10) is an electromagnetic drive type actuator which is an electro-mechanical conversion element, and (5) is a region in which the phase of the actuator (1) is rotated 180 ° in the flat and the primary resonance frequency and 2
An oscillator (11) for generating a sine wave signal having a frequency f ₀ set between the next resonance frequencies, and a reaction amplifier (11) for inverting the phase of the constant frequency signal from the oscillator (5) by 180 °. The other components are the same as those in the conventional example shown in FIG.

FIG. 2 is a schematic vertical sectional view of an electromagnetic drive type actuator (10), (21a) and (21b) are permanent magnets, (22a) and (22b).
Is a disk-shaped yoke, (23) is a cylindrical yoke, (24) is a center pole, (25a) and (25b) are gimbal springs, (26) is a bobbin, (27) is a coil, and (26) and (27). The moving coil (28) is composed of a gimbal spring (25a), (25
When the upper and lower ends are held by b) and a drive current is applied to the coil (27), the moving coil (28) is displaced in the axial direction. (29) is a head support member, and the magnetic head (2) is fixed to the open end thereof. If the actuator is configured in this way, the drive voltage is only a few V, there is no hysteresis, no head tilt occurs, and the characteristics are stable, so high reliability is maintained, durability is good, and cost is low. There are advantages.

However, such an electromagnetically driven actuator generally has a drawback that the mechanical resonance point is low. FIG. 3 shows the frequency characteristics of the electromagnetic drive type actuator. As can be seen from the figure, the primary resonance frequency is 300 Hz and the secondary resonance frequency is 7 KHz, which is lower than that of the bimorph. Here, like the conventional bimorph, 1
Consider the case where the wobbling frequency is selected in a band lower than the next resonance. For example, when the wobbling frequency is set to 60 Hz, the servo band is several Hz, and it is impossible to follow the track bending pattern (30 Hz, 60 Hz, 120 Hz, etc.).

Therefore, consider the case where the wobbling frequency is selected in the band between the primary resonance frequency, which is the region in which the actuator phase is rotated 180 ° around the flat, and the secondary resonance frequency. For example, in the case of this embodiment, assuming that the wobbling frequency is 720 Hz, the servo band extends to around 60 Hz, and the track bending pattern can be followed. However, since the actuator rotates the phase by 180 °, the phase of the wobbling frequency component of the reproduction envelope is rotated by 180 ° as compared with the conventional example.
Therefore, in this embodiment, this problem is solved by inserting an inverting amplifier (11) that inverts the phase of the wobbling signal from the oscillator (5) by 180 °. Needless to say, the same effect can be obtained by inserting the inverting amplifier (11) between the bandpass filter (4) and the synchronous detection circuit (7).

The other tracking servo methods and configurations are the same as those of the conventional example, and therefore description thereof is omitted.

Although the tracking error signal is created using the synchronous detection circuit in the above embodiment, it may be multiplied by a multiplier.

In the above embodiment, the VHS system, which is one of the consumer 1/2 inch VTR systems, is shown. However, in addition to this, the consumer 1/2 inch VTR S-VHS system, β system, EDβ The same effect can be obtained even when applied to a system or the like.

[Effects of the Invention] As described above, according to the present invention, the wobbling frequency can be set to a high frequency between the primary resonance frequency and the secondary resonance frequency by using the electromagnetic drive type actuator. , The phase of the wobbling drive signal and the phase of the wobbling signal extracted from the reproduction envelope signal are made to match, and tracking control is performed by the phase error signal between the track and the magnetic head obtained from both signals having the same phase. In addition, highly accurate tracking is possible, the image quality is improved, and a magnetic reproducing device that does not generate a noise bar even during special reproduction is obtained.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a schematic vertical sectional view of an electromagnetic drive type actuator of this embodiment, FIG. 3 is a frequency characteristic diagram of the electromagnetic drive type actuator, and FIG. FIG. 5 is a block circuit diagram of a tracking control system of a conventional magnetic reproducing apparatus, FIG. 5 is a diagram showing an amplitude change of a reproduction signal envelope from a magnetic head with respect to a track shift, FIG. 6 is a wobbling drive signal, and FIG. A waveform diagram showing the relationship between the phase and amplitude of the wobbling signal extracted from the reproduction envelope signal at the track shift position,
FIG. 7 is a waveform diagram of the synchronous phase detection output signal at each track shift position in FIG. 5, and FIG. 8 is a schematic diagram showing general frequency characteristics of a conventional bimorph, FIG. 9, FIG. 10, and FIG. Figure is a plan view showing the drum arrangement of a conventional bimorph, Fig. 12 is a diagram showing the relationship between the displacement amount and effective length of the bimorph and the head inclination, and Fig. 13 is a diagram showing the relationship between the effective length of the bimorph and the head inclination. Is. (2) ... magnetic head, (3) ... drive circuit, (4) ...
… Band pass filter, (5) …… Oscillator, (6) ……
Phase shifter, (7) ... Multiplier or synchronous detection circuit, (8)
…… Low pass filter, (9) …… Adder, (10) ……
Electromagnetic drive type actuator, (11) …… Inverting amplifier. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An electromagnetically driven actuator mounted on a rotary drum for moving a magnetic head in a direction perpendicular to a longitudinal direction of a recording track on a recording medium, and a drive for slightly vibrating the actuator with a signal of a constant frequency. Means, means for extracting the minute vibration signal component from the reproduction envelope signal from the magnetic head, and means for matching the phase of the extracted signal component with the minute vibration drive signal supplied to the actuator Means for obtaining a position error signal between the recording track and the magnetic head by synchronously detecting or multiplying both signals and smoothing; and a relative position of the magnetic head with respect to the recording track by negatively feeding back the position error signal to the actuator. A means for correcting an error, the frequency of the microvibration drive signal being Magnetic reproducing apparatus comprising set between the primary resonance frequency and the secondary resonant frequency of the motor.