JPS6256566B2 - - Google Patents

Description

[Detailed Description of the Invention] Recent video recording and playback devices (VTRs) are capable of not only normal playback, which plays back at the same tape speed V _T as during recording, but also still playback, which plays back with the tape stopped and is slower than V _T . It is now possible to perform playback at various tape speeds, such as slow motion playback performed at tape speed and quick motion playback performed at a speed faster than V _T .

By the way, during normal playback, the tape speed is the same as during recording, so tape 1 in the playback head
The inclination angle θ _P of the scanning trajectory above is the arrow (2) in Figure 1.
As shown by , the inclination angle θ _T of the recording track T is equal to the angle of inclination, and the reproducing head correctly scans the recording track.

However, the playback speed is the recording tape speed V _T
If the moving direction of the tape 1 is the direction of arrow 5 in the figure, the scanning direction of the playback head on the tape 1 will be the direction of arrow 3 if the tape speed is faster than V _T . If it is slow, it becomes as shown by arrow 4, and its inclination angle is different from the inclination angle θ _T of the recording track T, as shown by θ _S and θ _f , respectively.

Therefore, in this case, the playback head will scan across multiple recording tracks,
There is a drawback that the reproduced image becomes unsightly due to the influence of guard band noise and the like.

Therefore, the reproducing rotary head is mounted on an electrically controllable movable element such as a bimorph plate.
A method has been devised to ensure that the reproducing rotary head always scans the recording track T correctly.

First, I will explain about the bimorph plate.As shown in FIG. 2, this plate has metal electrodes 6 on both sides.
A plate 6 made of a piezoelectric element on which a and 6b are attached by plating etc., and metal electrodes 7a and 7b on both sides similarly.
It is formed by bonding a plate 7 made of a piezoelectric element to which a metal electrode 6b is adhered, and a surface to which a metal electrode 7a is adhered, for example.

Here, the polarization directions of the plates 6 and 7 made of piezoelectric elements are aligned in the thickness direction, but if an electric field is applied in the same direction as the polarization direction, the plates 6 and 7 will become polarized due to the piezoelectric effect. The plates 6 and 7 change to extend in the longitudinal direction, and when an electric field is applied in the opposite direction to the polarization direction, the plates 6 and 7 change to shrink in the longitudinal direction. Therefore, for example, the plates 6 and 7 are pasted together so that their polarization directions are the same as shown in the figure, and each electrode is connected to the power source B as shown in FIG. An electric field is applied to the plate 7 in the direction from the electrode 6a to the electrode 6b, and an electric field is applied to the plate 7 in the direction from the electrode 6a to the electrode 6b.
If an electric field is applied in the direction from b to electrode 7a, the bimorph plate will be distorted as shown, and the displacement will depend on the magnitude of the voltage. Furthermore, if the direction of the electric field is reversed, the direction of displacement of the bimorph plate will also be reversed.

Therefore, one end of such a bimorph plate should be connected to the third
As shown in Figures A and B, by fixing the bimorph plate to the substrate 8 with adhesive 9, attaching the magnetic head 10 to the other end of the bimorph plate, and applying a voltage to the electrodes of the bimorph plate as described above, the magnetic head 10 can be As shown by the arrow in FIG. 3A, it is displaced in a direction intersecting the scanning direction.

In a VTR, the bimorph plate to which the magnetic head is attached is fixed to a rotating body, such as an upper drum, with the head 10 facing outward, and the head 10 is displaced in the direction of its rotation axis.

Therefore, depending on the amount of deviation between the scanning direction shown by arrow 2 in Figure 1 during normal playback and the scanning direction shown by arrow 3 or 4 in the same figure when playing at other tape speeds, By supplying a voltage, in this case a sawtooth wave voltage, to the bimorph plate, the rotating magnetic head will correctly scan one recording track T, resulting in a noise-free reproduced image. .

By the way, this electromechanical conversion element such as a bimorph has a hysteresis characteristic in its conversion characteristics. Therefore, even when the above correction operation is completed and the correction voltage is no longer supplied to the bimorph plate, the bimorph plate does not completely return to its original state, but remains in its original state with residual distortion. It will stop in a more biased state. This residual distortion becomes large when the amount of deflection of the bimorph plate (the amount of deflection of the head) is large, so there is a risk of large residual distortion after slow motion playback, still playback, or quick motion playback. .

However, when recording is subsequently performed after playback has been completed and the above-mentioned correction operation has been completed, if there is residual distortion as described above, the scanning position of the magnetic head on the tape may not match the intended recording track position. As a result, the intervals between the recording tracks become misaligned, resulting in the inconvenience that the recording tracks overlap with the previous recording track.

For this reason, conventionally, the head mounted on the bimorph board is used only for reproduction, and the rotary head for recording is provided separately. Therefore, the number of heads increased accordingly, making the VCR expensive.

In view of the above-mentioned points, the present invention provides a magnetic recording and reproducing device that can detect the height position of a magnetic head with respect to a reference plane and control the height position to bring it to a predetermined position. This is what I am trying to do.

Hereinafter, an example of the magnetic recording/reproducing apparatus according to the present invention will be explained using a VTR for video signals as an example with reference to FIG. 4 and subsequent figures.

FIG. 4 shows the structure of an example of a rotary drum device for a VTR, which is an example of the device of the present invention.

In the figure, 11 is a fixed lower drum, 12 is a rotating upper drum, and 13 is a rotating shaft.

A bimorph plate 14 is provided on the lower surface of the rotating upper drum 12.
is attached by attaching its one end side to this lower surface, and this bimorph plate 1
The other end of 4 is a free end, and a magnetic head 15 is attached to this free end. In addition, the rotating upper drum 1
A recess 16 is formed on the lower surface of the bimorph plate 14 at the other end where the head is attached to the bimorph plate 14.
The other end of the bimorph plate 14 is a free end.

In the present invention, optical detection means for detecting the height position of the head 15 from the reference plane is provided.

In this example, the reference plane is the chassis 17, and the light emitting element 18 is provided near the magnetic head 15 of the bimorph plate 14, while the light emitting element 18 is placed above and below the position of the light emitting element 18 at a certain height position Ho of the head 15. Slits 19 and 20 are provided at positions equidistant from each other, and light transmitted through the slits 19 and 20 is received by light emitting elements 21 and 22.

In this example, when the position of the head 15 is Ho, the detection outputs of the light-receiving elements 21 and 22 are equal, and when it deviates from Ho, the outputs of the light-emitting elements 21 and 22 change depending on the direction of the deviation. It will be something that increases or decreases differentially.

Therefore, the height position of the head 15 can be controlled as shown in FIG.

That is, the output of the light receiving element 21 is transmitted to the reproducing amplifier 3.
0 to one input terminal of the differential amplifier 32, and the output of the light receiving element 22 is supplied to the other input terminal of the differential amplifier 32 through a reproducing amplifier 31 and an inverter 33. Therefore,
The output of this differential amplifier 32 is located at the head 15.
When the position is at the height Ho, the signal is zero, and when the height deviates from the position Ho, a signal with a polarity corresponding to the direction of the deviation and a level corresponding to the amount of deviation is obtained. The output of this differential amplifier 32 is supplied to a control circuit 34, and the output of this control circuit 34 is supplied to the bimorph board 14 through a drive circuit 35, so that the height position of the head 15 is controlled to be Ho. It is something that

As described above, according to the present invention, the height position of the movable element, for example, the magnetic head provided on the bimorph plate, from the reference plane is detected, and the detected output is used to move the rotating magnetic head to a desired height. Since the head mounted on the bimorph board can be used not only for reproduction but also for recording, even if the bimorph board has hysteresis, recording can be performed without any problem.

Therefore, the magnetic head mounted on the movable element can be used for both recording and reproduction.

Since the height position detecting means is an optical means, leakage magnetic flux does not affect the magnetic recording head, unlike when magnetic means is used to detect the height position, for example. In addition, in the case of magnetic detection means, the detectors must be placed extremely close to each other, and output fluctuations due to installation errors are large, making adjustment difficult, whereas in the case of optical detection means, the This makes it easier to attach and adjust the detector to the drum.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the relationship between the tape speed and the scanning locus of the rotating head on the tape, Figures 2 and 3 are diagrams for explaining the bimorph plate, and Figure 4 is a diagram for explaining the magnetic field according to the present invention. FIG. 5 is a diagram illustrating an example of a main part of a recording/reproducing apparatus, and is a system diagram of an example of a height position control circuit. 11 is a fixed lower drum, 12 is a rotating upper drum,
14 is a bimorph plate, 15 is a magnetic head for video signals, 17 is a chassis, 18 is a light emitting element, 19, 2
0 is a slit, and 21 and 22 are light receiving elements.

Claims (1)

[Claims] 1. A magnetic head attached to an electrically controllable movable element on a rotating drum, one of a light receiving element and a light emitting element being attached to the movable element, and the other being attached to the movable element through a slit. and a control signal forming means for forming a control signal according to the output from the light receiver of the optical detecting means. A magnetic recording/reproducing device in which the magnetic head is maintained at a predetermined height by controlling a movable element.