JPS6212565B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides, for example, a helical scan type
In a VTR, the scanning position of a rotary head relative to a video track is servo-controlled over the entire length of the video track during playback, and the object is to particularly improve the response characteristics of the servo control.

First, let us explain the outline of this invention.

In FIG. 1A, 1 indicates a reproducing head and 9 indicates a magnetic track. It is assumed that the track widths of head 1 and track 9 are both equal in Tw, and that a video signal is recorded on track 9 at a constant level after being converted to an FM signal. Then, assuming that the distance between the centers of head 1 and track 9 is x, the relationship between this distance x and the reproduction level E of head 1 is as shown in characteristic 8 in FIG. 1B.

Therefore, the playback level E of head 1 is
It shows the size of the tracking deviation of
Correct tracking can be achieved by shifting the head 1 in the track width direction based on this level E.

However, in characteristic 8 in Figure 1B, level E changes in the same way whether head 1 shifts in the positive direction (to the right in the diagram) or in the negative direction (to the left in the diagram). , the direction of displacement of the head 1 cannot be detected, and therefore even if the head 1 is to be displaced in the track width direction, it cannot be determined in which direction the head 1 should be displaced.

Therefore, in the present invention, first, as shown in FIG. 2 (the curve 1C indicates the scanning locus of the center of the head 1), the track 9 is scanned while the head 1 is vibrated (wobbled) in the track width direction. Note that the frequency of this vibration is ω, and the amplitude is Δw.
shall be. Further, the amplitude Δw is, for example, 10% of the track width Tw.

Therefore, if we take the distance between the center of vibration of head 1 and the center of track 9, that is, the average center distance, as shown in FIG. When the track 9 is being scanned while being the center of vibration, the reproduction level E changes as shown in FIG. 3B.

Also, as shown in FIG. 4A, head 1 is =
When scanning is performed with a shift in the positive direction by _{x 1} (0<x ₁ Δw), the reproduction level E changes as shown in FIG. 4B.

Furthermore, as shown in FIGS. 5A and 6A,
As the deviation of the head 1 increases, the reproduction level E changes as shown in FIGS. 5B and 6B.

On the other hand, as shown in FIG. 7A, head 1 is =
In the case of a negative shift of −x ₂ , the playback level E changes as shown in FIG. 7B.

Therefore, when the change ΔE (envelope) of the reproduction level E is extracted and this is synchronously detected with a signal of frequency ω, the detection output Eω has a characteristic as shown in FIG. 8 with respect to the average center spacing. . That is, in the case of =0 (FIG. 3), the change ΔE in the reproduction level E does not include a component of the frequency ω, so that Eω=0.

Further, in the case of =x ₁ (FIG. 4), the change ΔE in the reproduction level E includes a component of the frequency ω, and the level of this component increases as the interval increases.

Furthermore, in the case of = _x2 (FIG. 5), the change ΔE in the reproduction level E is only the frequency ω component, and the level of this component does not change even if the interval changes.

In the case of = _x3 (FIG. 6), the change ΔE in the reproduction level E includes a component of the frequency ω, but it becomes smaller as the interval becomes larger.

Therefore, first, in the case of >0, the characteristics are as shown in the right half of FIG.

On the other hand, the phase of the vibration of head 1 is the same in Fig. 5A and Fig. 7A, but in Fig. 5B and Fig. 7B.
The phase of the change ΔE in level E is reversed. Therefore, when <0, the synchronous detection output Eω is at the same level as when >0, but the polarity is reversed.

Therefore, the relationship between the synchronous detection output Eω and the interval is as shown in FIG.

Therefore, the direction of deviation of the head 1 is controlled based on the polarity of the detected output Eω, and the detected output Eω is controlled based on the polarity of the detected output Eω.
By controlling the amount of deviation of head 1 based on the level of ω, tracking servo of head 1 can be performed over the entire length of track 9.

In order to vibrate the head 1 as shown in FIG. 2, it may be configured as shown in FIGS. 9 and 10, for example. That is, in these figures, reference numeral 11 indicates a substantially band-shaped electrostrictive element, one end 11A of which is attached to a head substrate 13 with, for example, adhesive 12, and the head 1 is attached to the other end 11B with, for example, adhesive. At the same time, a damper material 14 is installed between the element 11 and the substrate 13.
is provided. In this case, the direction of polarization of the element 11 is selected so that when a voltage is supplied to the element 11, the head 1 is shifted in the track width direction as shown by the arrow 15 in accordance with the polarity and level of the voltage.

Therefore, if an alternating voltage with a frequency ω is supplied to the element 11, the end 11B of the element 11 will vibrate at the frequency ω in the direction of the arrow 15 with the end 11A as a fulcrum, so that the head 1 will move as shown in FIG. The track 9 is scanned while vibrating at the frequency ω.

At this time, if the voltage Eω is supplied to the element 11, the head 1 will automatically track the track 9.

However, in the configuration shown in FIGS. 9 and 10, the mechanical resonance frequency of the element 11 is 1 kHz or less, depending on the size of the element 11. Therefore, when the element 11 is made to vibrate, the frequency ω of the vibration must be several hundred Hz, which is sufficiently lower than this resonant frequency.
For this reason, the response of the tracking servo becomes slow.

Of course, if the element 11 is made smaller, its resonant frequency becomes higher, and therefore the vibration frequency ω can be increased, so that the response of the tracking servo can be made faster. However, in that case, the end portion 11B of the element 11
Since the amount of deviation of the head 1 becomes small, when the head 1 deviates significantly from the track 9, it becomes impossible to bring the head 1 into alignment with the track 9.

In view of these points, it is an object of the present invention to provide a servo device whose tracking servo has a quick response and a wide response range.

Let's explain one example below.

In this invention, the electrostrictive element 11 is configured as shown in FIGS. 11 and 12, for example. That is, in these figures, reference numerals 111 and 112 indicate, for example, piezoelectric bending bimorph plates, which are formed approximately in a band shape, with the thickness direction 15 being the polarization direction, and the polarization directions being opposite to each other. They are bonded to each other with a cyanoacrylate monomer adhesive, for example, with a thin plate 113 of the same shape sandwiched between them so as to serve as an electrode and reinforcement. Then, electrodes 115A and 115B are formed on the surface of the bimorph plate 111 opposite to the thin plate 113 by plating, for example. In this case, the electrodes 115A and 115B are formed by being divided in the length direction of the element 11;
A is, for example, 2/2 from one end 11A of the element 11.
The electrode 115B is formed over a region of 3.
It is formed over the remaining ⅓ region from the other end 11B of the element 11 and not in contact with the electrode 115A.

Moreover, electrodes 116A and 116B are provided on the surface of the bimorph plate 112 opposite to the thin plate 113.
15A and 115B are similarly formed.
Then, a pair of terminals 1 are connected to the electrodes 115A and 116A.
17A is connected, and a pair of terminals 117B are also connected to electrodes 115B and 116B.

A pair of such electrostrictive elements 11 is prepared, and each element 11, 11 is arranged as shown in FIGS. 9 and 10, for example.
As explained in the figure, the head substrates 13, 13
The magnetic heads 1A and 1B are also attached to the elements 11 and 11, respectively. In this case, the end 11A of the element 11 on the electrode 115A side is the substrate 13 side, and the end 11B on the electrode 115B side is the head 1A, 1B side.

For example, as shown in Fig. 13, the VTR
is configured. That is, the substrates 13,
13 is attached to a tape guide drum (not shown) and rotated at the frame frequency. A magnetic tape 2 is wound obliquely around the rotating peripheral surfaces of the heads 1A and 1B over an angular range of over 180 degrees, and is run at a constant speed. On this tape 2, the video signal is the FM signal Sf at a constant level, and one field is one.
They are recorded sequentially as diagonal magnetic tracks 9 of the book.

Therefore, the heads 1A and 1B alternately reproduce the FM signal Sf from the tape 2 one field at a time. The reproduced FM signal Sf is then supplied to the switch circuit 4 through the reproduction amplifiers 3A and 3B, and the switch circuit 4 is supplied to the heads 1A and 1.
The switch circuit 4 is switched in synchronization with the rotation of the switch B, and the FM signal Sf is continuously taken out from the switch circuit 4.

This FM signal Sf is then supplied to an FM demodulation circuit 6 through a limiter 5 to demodulate a video signal, and this signal is taken out to a terminal 7.

Further, the tracking servo circuit 20 is configured as follows. That is, an oscillation signal So having a predetermined frequency ω is formed in the oscillation circuit 21, and this signal So is further transmitted to the terminal 1 through the amplifier 22.
17B to electrodes 115B and 116B of elements 11 and 11 supporting heads 1A and 1B, respectively. Therefore, since the bimorph plates 11, 11 vibrate in the direction of the arrow 15 due to the signal So, the heads 1A, 1B vibrate as shown in FIG.
The track 9 of the video signal is scanned in a meandering manner with a period of 1/ω of the signal So.

In this way, heads 1A and 1B scan track 9 in a meandering manner, so that the reproduced
The level E of the FM signal Sf changes as shown in FIG. 8 with respect to the distance between the center of vibration of the heads 1A, 1B and the center of the track 9, that is, the average center distance.

Therefore, the FM signal Sf from the switch circuit 4 is
FIG. 3B is supplied to the envelope detection circuit 23.
~As shown in FIG. 7B, a detection signal Sd indicating the level E of the FM signal Sf is generated, and this signal Sd is supplied to the synchronous detection circuit (phase comparison circuit) 24, and
The signal So is supplied from the oscillation circuit 21 to the detection circuit 24, and the signal E〓 having the characteristics shown in FIG. 8 is taken out from the detection circuit 24. , 1B are supplied to the electrodes 115A, 116A of the elements 11, 11 supporting the elements 11, 1B.

According to such a configuration, the polarity and level of the signal E change as shown in FIG. 8 with respect to the average center distance between the heads 1A, 1B and the track 9, and 11 is deflected in the direction of arrow 15 or in the opposite direction depending on the polarity of the signal E≦ supplied thereto, and the amount of deflection corresponds to the level of the signal E≦. Therefore,
Heads 1A and 1B are shifted in the direction of arrow 15 or the opposite direction in accordance with the polarity of signal E〓, and the amount of deviation corresponds to the level of signal E〓, so that the scanning of heads 1A and 1B is The position will be =0 on average.

Thus, according to the present invention, tracking servo is performed for the heads 1A and 1B on the track 9. In this case, according to the present invention, the response of the servo control can be made faster and the response range can be widened. That is, the electrodes of the electrostrictive element 11 are
Since it is divided into two into relatively large electrodes 115A, 116A and small electrodes 115B, 116B, and an alternating signal So for vibration of the heads 1A, 1B is supplied to the electrodes 115b, 116B, the element 11
Only the portion sandwiched between the electrodes 115B and 116B bends and vibrates in response to the signal So, and therefore, the substantial vibrating portion becomes smaller, and its resonant frequency becomes higher. For example, element 1
The thickness of 1 is 0.6 mm, the width is 5 mm, electrode 115A, 1
When the length of 16A is 13 mm and the length of electrodes 115B and 116B is 7 mm, the electrode 115 of element 11
The resonance frequency of the part sandwiched by B and 116B is 5k
Hz or higher. If the resonant frequency is increased in this manner, the frequency ω of the signal So can be increased, thereby making it possible to speed up the response of the tracking servo.

In this case, since the vibration part of the element 11 caused by the signal So becomes small, its amplitude also becomes small, and therefore the amplitude Δw of the vibration of the heads 1A and 1B
However, this amplitude Δw is originally only about 10% of the track width Tw, so there is no problem.

In addition, the tracking error detection signal, that is, the signal E
Since the element 11 is supplied to the track 9A, the element 11 will be deflected greatly in response to the signal E. Therefore, the deviation of the heads 1A and 1B with respect to the signal E can be large, so that the heads 1A and 1B are connected to the track 9. Even if the track position deviates significantly from the track position, it can be corrected to the correct track position.

Thus, according to the present invention, tracking servo control with quick response can be performed, and the response range can be widened.

In addition, when the directions of polarization of the bimorph plates 111 and 112 are made the same, they may be connected as shown in FIG. 14. Furthermore, when the outputs of the amplifiers 22 and 25 are single outputs, for example, the electrode 115
The outputs of amplifiers 25 and 22 are supplied to electrodes 116A and 115B, and amplifier 2 is supplied to electrodes 116A and 116B.
It is sufficient to supply a DC bias equal to the DC level of the outputs No. 5 and 22.

Furthermore, when the tape 2 is run at a speed different from that during recording to perform still playback or slow motion playback, the scanning loci of the heads 1A and 1B shift at a certain rate with respect to the track 9; , the voltage that corrects this deviation is the signal E〓
It is sufficient to supply it to the electrodes 115A and 115B in a superimposed manner.

[Brief explanation of the drawing]

1 to 10 are diagrams for explaining this invention, FIGS. 11 and 12 are a plan view and side view of an example of the essential parts of this invention, and FIG. 13 is a system diagram of an example of this invention. , FIG. 14 is a diagram showing another example of the present invention. 11 is an electrostrictive element, 115A to 116B are electrodes,
20 is a servo circuit.

Claims (1)

[Claims] 1. An electro-mechanical conversion means is constructed by arranging first and second electrodes in the length direction of a common piezoelectric element material, and the end of the electro-mechanical conversion means on the first electrode side is part is attached to the head board,
A magnetic head is provided at the end on the second electrode side, and an alternating voltage of a predetermined frequency is supplied to the second electrode to vibrate the magnetic head in the width direction of the magnetic track. The reproduced signal and the alternating voltage are phase-compared, and the voltage obtained by this phase comparison is supplied to the first electrode as a voltage indicating a tracking error of the magnetic head with respect to the magnetic track. A tracking servo device for performing tracking servo of the magnetic head.