JPS6132728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking correction device for a rotating magnetic head for automatically correcting the tracking position of the magnetic head in a rotating magnetic head type video tape recorder (hereinafter referred to as VTR). .

In recent years, in order to increase the recording density of VTRs, the pitch of recording tracks on magnetic tapes has been reduced. When recording tracks with such narrow pitches, compatibility between multiple VTRs of the same system becomes a serious problem. This poor compatibility is mainly caused by the poor linearity of the recording track, and in general household VTRs, there is a maximum deviation from the straight line of about 20 μm that cannot be corrected even by the tracking volume. In order to reduce the variation in the amount of deviation between VTRs, it is possible to improve the machining and assembly accuracy of the mechanical parts of the rotary head device, but rotary head devices are currently possible (mass production). It is manufactured with the highest mechanical precision (including possible), and achieving even higher precision would significantly increase manufacturing costs, reduce productivity, and make the product price extremely high. Put it away.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the prior art, and is capable of significantly correcting the deviation of the magnetic head from the storage track without increasing the mechanical precision of the rotating magnetic head device. The object of the present invention is to provide a tracking correction device for a rotating magnetic head.

Preferred embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

First, FIG. 1 is a schematic perspective view of a rotary magnetic head device 1 to which the present invention is applied, and FIG. 2 is a plan view of a rotary disk 2 of the rotary magnetic head device 1. In these FIGS. 1 and 2, the upper drum 3
The upper and lower drums 4 are fixed to the chassis of the VTR (not shown), and the rotary disk 2 placed between the upper and lower drums 3 and 4 is rotated in the direction of arrow A by a motor 5. Rotationally driven. The magnetic tape 6 is attached to these upper and lower drums 3 and 4.
It travels in the direction of arrow B while being wrapped diagonally within an angular range of about 180°. This magnetic tape 6
In order to keep the traveling position constant, guide poles 7, 8, etc. are arranged at predetermined positions around the rotating magnetic head device 1, and the circumferential surface of the lower drum 4 is approximately
In the range of 180°, there is a stepped portion 9 for guiding the magnetic tape 6.
is formed, and the press pin 1 provided on the upper drum 3
Due to the elastic force in the direction of arrow C, the end of the magnetic tape 6 slides into contact with the stepped portion 9 and is positioned.
Here, the elastic force of the pressing pin 10 is so slight that the thin magnetic tape 6 does not bend.

Next, near the periphery of the rotating disk 2, there are
Two magnetic heads _11A with an angular difference of 180°,
11 _B is installed. Here, magnetic head 1
1, as shown in FIG. 3, one end of an electromechanical transducer, such as a bimorph plate 14, is adhesively fixed to a head base 13 so that the other end is movable in the direction of arrow D, and a head chip 12 is attached to the other end. It is constructed by gluing and fixing. Here, the displacement direction D is equal to the gap direction of the head chip 12 of the magnetic head 11. The bimorph plate 14 is made of piezoelectric material.
It is constructed by using two plates such as PZT (a solid solution of PbZrO ₃ and PbTiO ₃ ) with electrodes adhered to both sides and bonding them together so that their polarization directions are opposite to each other. Lead wires 15 and 16 are connected to both outer electrodes of this bimorph plate 14, respectively, and a voltage is applied between the two electrodes via a drive circuit 17 as shown in FIG. The amount and direction of displacement of the head chip 12 fixed to the other end of the bimorph plate 14 in the direction of arrow D are determined according to the direction of the bimorph plate 14.

Next, the magnetic heads 11 _A and 11 _B move the magnetic tape 6
Theoretically, the trajectory when tracking the magnetic tape is a straight line as shown by the dashed-dotted line in FIG. The actually recorded recording track T is as shown by the solid line in FIG. FIG. 5 shows a track pattern on the magnetic tape 6 in which a plurality of tracks are formed by the VTR shown in FIG. 4, which tends to form recording tracks in a non-linear manner. In this case, a magnetic tape having a track pattern as shown in FIG. 5 recorded by a VTR with tracking characteristics as shown by the solid line in FIG. When playing back on a VTR with a tracking characteristic that performs head tracing, there is a large discrepancy between the recorded track and the magnetic head, and the envelope of the playback signal for one track (one vertical period) becomes as shown in Figure 6, resulting in a significant drop in image quality. As mentioned above, this causes severe deterioration. Here, the displacement direction D of the head chip 12 of the magnetic head 11 is the gap direction, which is substantially perpendicular to the tracking direction E on the magnetic tape 6. Therefore, the bimorph plate 1 is moved in the direction of correcting the above tracking characteristics.
4, ideal tracking characteristics as shown by the dashed line in FIG. 4 can be obtained.

By the way, the curves of the recording track T, such as the solid lines in FIGS. 4 and 5, have tracking characteristics such that at least the rotation period of the rotary disk 2 is one period, or the tracking characteristics of each magnetic head _11A , _11B . If it is equal, 1/2 of the above rotation period is 1
It can be expressed as a periodic function such that it is a period. This periodic function can be expanded into a Fourier series, and if the frequency of the reference period (for example, the rotational frequency of the rotating disk 2) is set to ₀ , the frequency of each term in the Fourier series becomes n ₀ (where n is a natural number). Therefore, a voltage waveform equal to the curve of the recording track T is created using an oscillator with a frequency of _n0 , and this is applied to the bimorph plate 14 (provided that the direction of displacement is opposite to the direction of displacement of the magnetic head). ), tracking correction can be performed.

That is, in this embodiment, a tracking correction circuit 20 as shown in FIG. 7 is configured. In this tracking correction circuit 20, the rotation detector 2
1 detects the rotation of the rotary disk 2 and outputs a pulse indicating the switching point of each of the magnetic heads 11 _A and 11 _B. The oscillation frequency is ₀ , ₂₀ ,...
The rotation detection pulse is sent as a trigger pulse to each of the oscillators 22 ₁ , . . . , 22n of n ₀ . Each of these oscillators 22 ₁ ,……,
In order to make the oscillation output of 22n each term of the Fourier series of a desired periodic function with a period of _1/0 , it is necessary to adjust the phase and coefficient (maximum amplitude). For this purpose, phase shifters 23 _{1 ,} 23 n and gain control circuits 24 ₁ , 24 n are connected as adjustment means to each oscillator 22 1 , 22 n, respectively. The phase of the oscillation output is changed by the phase shifter 23 ₁ ,
......, 23n, the coefficient is the gain control circuit 24
₁ , . . . , 24n, each can be adjusted. In this way, the outputs whose phases and coefficients have been adjusted are mixed in the mixer 25 with a period of 1/1
The desired voltage waveform of ₀ is output. This output is applied to the bimorph plate 14 via the bimorph drive circuit 17 to displace the head chip 12. Here, if the tracking characteristic of the rotating magnetic head device itself is as shown by the solid line in FIG.
If they are displaced as indicated by the broken line in the figure, the tracking deviations will be canceled and an ideal straight line trajectory will be drawn as indicated by the dashed line in FIG.

Next, each phase shifter 2 of the tracking correction circuit 20
3 ₁ ,……, 23n and gain control circuit 24
₁ , ......, 24n can be adjusted in various ways, but for example, a magnetic tape on which a recording track is formed in a straight line is prepared as a reference tape, and this magnetic tape is used as a VTR before tracking correction adjustment.
While reproducing the signal, each phase shifter 23 ₁ , . . .
..., 23n and gain control circuit 24 ₁ , ......
..., 24n should be adjusted. In addition, after recording signals using an unadjusted VTR, the recording track on the magnetic tape is analyzed to determine the periodic function.
This may be expanded into a Fourier series to calculate the phase and coefficient of each term.

By the way, if the continuity of the re-output signals obtained from the two magnetic heads _11A and _11B is poor, that is, the end of the waveform of one channel A does not match the front end of the waveform of the other channel B. Even if the magnetic head 11 is not in contact with the magnetic tape 6
Sufficient correction can be made by resetting to the initial position. At this time, the bimorph plate 14
The voltage waveform applied to is, for example, as shown in FIG. 8a. This deterioration in the continuity of the reproduced signal is caused by
This may occur due to poor mechanical precision of the rotating magnetic head device 1, but when the running speed of the magnetic tape 6 is changed, for example, during still playback, slow-motion playback, or high-speed playback, the difference between channel A and channel B may occur. A discontinuity occurs with As shown in FIG. 9, when considering the case where tracking by the magnetic head 11 is started from a point s on the recording track T, if the tape running speed in the direction of arrow B is different, the point e at which tracking ends is: This is because they are different, for example, e ₁ , e ₂ , and e ₃ . In FIG. 9, the trajectory when the recording track T is normally tracked is a straight line se ₁ , and the straight lines se ₂ and se ₃ also follow the magnetic head 11.
By displacing the head tip 12 in the direction of arrow D, it is necessary to correct it so that it overlaps the straight line _se1 . Although such dynamic correction can also be performed by the tracking correction circuit 20, it is practically preferable to perform it using a sawtooth wave generation circuit 26 as shown in FIG. The output from this sawtooth wave generating circuit 26 is transmitted to a phase shifter 27 which is an adjusting means.
and the mixer 2 via the gain control circuit 28.
You can send it to 5. Here, if the waveform to be applied to the bimorph plate 14 is a waveform as shown in FIG.
The waveform shown in FIG. _8B is created, and the waveform shown in FIG.

In addition, to express any function with a period of _1/0 as a Fourier series, ₀ , 2 ₀ , ......, n
n of ₀ is necessary to infinity, but in real VTR
In this case, the ₂₀ and ₄₀ components are extremely large, and if these ₂₀ and ₄₀ components are corrected, almost linear tracking characteristics can be obtained, and sufficient compatibility for practical use can be obtained. Therefore, the oscillator 22 ₁ ,...
..., 22n can improve compatibility, which is the intended purpose. One of the reasons for this is considered to be that the positions of the guide poles 7 and 8 become nodes of the standing wave, and ₂₀ is emphasized, and the position of the press pin 10 becomes a node, which emphasizes ₄₀ .

As is clear from the above description, the tracking correction device for a rotating magnetic head according to the present invention includes an electro-mechanical conversion means, such as the bimorph plate 14, which supports the head chip of the rotating magnetic head so as to be displaceable in the gap direction, and the above-mentioned bimorph plate 14. A plurality of periodic signal output means, for example, an oscillator 22, each outputting a plurality of periodic signals in accordance with the rotation of the rotating magnetic head.
₁ , ......, 22n, and a plurality of adjusting means, such as phase shifters 23 ₁ , ......, 23, that adjust the phase and maximum amplitude of these periodic signals, respectively.
n, and gain control circuit 24 ₁ ,……, 24
The apparatus is characterized in that it includes a mixing means, for example a mixer 25, for mixing the outputs from these adjusting means, and the output signal from the mixing means is applied to the electro-mechanical conversion means. Therefore, deviations from the tracking straight line can be corrected with high precision without increasing the mechanical precision of the rotating magnetic head device itself, and multiple units can be used at a relatively low cost.
This makes it possible to increase compatibility between VTRs.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be easily applied to, for example, not only 2-head type VTRs but also 1-head type and 1.5-head type VTRs. Moreover, each oscillator 22 ₁ ,...
......, 22n, instead of using one high frequency oscillator and dividing this oscillation output with multiple frequency dividers etc., ₀ , 2 ₀ , ......, n ₀
It is also possible to obtain a signal such as

[Brief explanation of the drawing]

The figures are all for explaining one embodiment of the present invention, and FIG. 1 is a perspective view schematically showing a rotating magnetic head device, FIG. 2 is a plan view of the rotating disk 2 shown in FIG. 1, and FIG. Figure 3 is a perspective view of the magnetic head 11 in Figure 2, and Figures 4 and 5 are the same.
A plan view showing the shape of the recording track T on the magnetic tape 6 before tracking correction of the VTR, FIG. 6 a waveform diagram showing the envelope of the reproduced signal, and FIG. 7 a block circuit diagram showing the tracking correction circuit 20.
8a, b, and c are waveform diagrams for explaining an example of the voltage signal applied to the bimorph plate 14, and FIG. 9 is a plan view showing the locus of the magnetic head at different tape running speeds. 2... Rotating disk, 6... Magnetic tape, 11
...Magnetic head, 14...Bimorph plate, 20...
... Tracking correction circuit, 22 ... Oscillator, 23
... Phase shifter, 24 ... Gain control circuit, 25 ... Mixer.

Claims (1)

[Scope of Claims] 1. Electromechanical conversion means for supporting the head tip of a rotating magnetic head so that it can be displaced in the gear direction, rotational position detection means for detecting rotation of the rotating magnetic head, and output pulses from this detection means. A plurality of periodic signal output means each outputting a plurality of periodic signals based on a position, a plurality of adjustment means each adjusting the phase and maximum amplitude of these periodic signals, and outputs from these adjustment means. A tracking correction device for a rotating magnetic head, comprising a mixing means for mixing, and configured to apply an output signal from the mixing means to the electro-mechanical conversion means.