JPS5817536A - magnetic recording/playback head - Google Patents

Abstract

PURPOSE:To prevent a shift in the position of a head for automatic scanning tracking due to fluctuations of ambient temperature, by using a material which has a coefficient of thermal expansion nearly equal to that of a piezoelectric ceramic plate for a holder for holding a bimorph plate base end part. CONSTITUTION:The base end part of a bimorph plate 2 is fixed to a holder 10 through a thin adhesive layer 3. The bimorph plate 2 is constituted by sticking piezoelectric ceramic plates 2a and 2b with a metallic plate 2c as an intermediate electrode between. The holder 10 uses a material which has a coefficient of thermal expansion nearly equal to those of the piezoelectric ceramic plates 2a and 2b. According to fluctuations of ambient temperature, the holder 10 expands and contracts as shown by an arrow, but the free ends of the bimorph plates having a little variation. therefore, even if the ambient temperature fluctuates, there is no expansion and contraction difference generated between the holder 1 and bimorph plates 2, so a head chip 4 is held at a stable position.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic recording and reproduction, particularly to automatic scanning and tracking using a bimorph plate as an electro-mechanical transducer.

An automatic scanning and tracking head that uses a bimorph plate as an electro-mechanical transducer is incorporated into a magnetic recording/reproducing device, especially a rotary helical scan type video tape recorder (hereinafter referred to as ■l), and is used to record data from a VTR. It is controlled by the signal to accurately follow the tracks recorded on the magnetic tape.

As shown in FIG. 1, in a conventional automatic scanning tracking head, the base end of a bimorph plate 2 is fixed to a holder 1 in the form of two cantilevers via a thin adhesive layer 3, and the tip of the bimorph plate 2 is fixed to a holder 1 through a thin adhesive layer 3. It has a structure in which a head chip 4 is attached to the part. The holder 1 is attached to a rotating body 6 with screws 5.

The bimorph plate 2 that supports the head chip 4 with the structure described above is made of a ferroelectric material. Two piezoelectric ceramic plates 2a, 2 made of lead zirconate titanate, for example.
b and a metal plate 2c serving as an intermediate electrode.

These two piezoelectric ceramic plates 2a and 2b mutually expand and contract in response to control signals from the VTR, so that the bimorph plate 2 is displaced. The expansion and contraction of the piezoelectric ceramic plates 2a and 2b at this time is very small, but since they have a so-called bimetal structure, at the free end of the bimorph plate 2, the piezoelectric ceramic plate 2a.

The change due to expansion and contraction of 2b is magnified approximately 100 times.

However, due to the difference in thermal expansion coefficient between the holder 1 and the bimorph plate 2, as the holder 1 expands and contracts, the piezoelectric ceramic plate 2a bonded to the holder 1 also expands and contracts, which causes the bimorph plate 2 to expand and contract. All indicate that the free end is changeable. This phenomenon is not a problem when the control voltage is applied to the bimorph plate 2, that is, in the automatic scanning truck or king mode, but when the control voltage is not applied to the bimorph plate 2, and the automatic scanning truck or king head This becomes a problem when it is necessary to keep the object in a fixed position.

For example, if you use an automatic scanning tracking head for playback only,
When another magnetic head (not shown here) is used exclusively for recording, the automatic scanning tracking mode is turned off in the 2 editing mode, that is, no voltage is applied to the bimorph plate 2.

Due to changes in ambient temperature, the position of the automatic scanning and tracking head changes, and its relative position to the recording head differs from the initial set value. As a result, the video track pitch changes at the joint portion in program editing [7] There is a risk that the image may be distorted during playback. For conventional automatic scanning and tracking, the holder 1 is made of metal, and the bimorph plate 2 is fixed via an adhesive layer 3, and the coefficient of thermal expansion of the metal is one order of magnitude larger than that of the piezoelectric ceramic plate. Therefore, when the ambient temperature rises, the holder 1 extends in the direction of the arrow as shown in FIG. 2, and the tip of the bimorph plate 2 is displaced downward.

As a result, the position of the automatic scanning and tracking head changes, resulting in the drawback that normal editing operations cannot be performed as described above.

Also, the automatic scanning tracking mode is completely turned off.

When playing back simultaneously, the position of the automatic scanning tracking head changes depending on the surrounding temperature, and the relative position to the recording head differs from the initial fixed value, so it is necessary to maintain a high-quality and stable replay image. The disadvantage was that it was not possible.

In order to solve these drawbacks, the present invention provides a holder for holding the base end of the bimorph plate.

That is, by using piezoelectric ceramic, a material with a coefficient of thermal expansion almost equal to that of the plate, it is possible to completely prevent the position of the automatic scanning and tracking head from changing due to changes in ambient temperature.

The present invention will be described below with reference to all embodiments shown in FIG.

Explain in detail. In the support structure according to the present invention, the l fiVr of the bimorph plate 2 is fixed to the holder 10 via three thin adhesive layers, and the holder 10 is attached to the rotating body 6 with screws 5, as in the conventional structure described above. It is being

Then, the bimorph plate 2 is made of zirconium titanate [IPb(
Piezoelectric ceramic plate 2a, 2 such as ZrTt)O
bd: It is constructed by bonding together with an adhesive or the like via a metal plate 2c which is an intermediate electrode.

However, the material of the holder 10 is the conventionally used general metal or 9 synthetic resin (for example), but the bimorph plate 21 is made of a material with almost the same coefficient of thermal expansion as the piezoelectric zeramic plates 2a and 2b used (for example, A major feature is that it uses all of the aluminum (alumina).

This effect will be explained below. Due to the rise in ambient temperature, the holder 10 is stretched in the direction of the arrow (·ζ).

Since this proportion is approximately equal to the bimorph plate, the changes at the free end of the bimorph plate are much smaller than in conventional automatic scanning tracking heads.

Also, when the ambient temperature becomes low, the same result becomes Cτ, only the direction of the arrow is reversed.

Therefore, even if the ambient temperature changes, no difference in expansion or contraction occurs between the holder 1 and the bimorph plate 2.

The position of the head chip 4 can be kept stable.

For the above reasons, an automatic scanning truck according to the present invention is provided.

If you use the king head, it will automatically scan when the king mode is off, even if the ambient temperature changes.

Changes in the position of the automatic scanning and tracking head can be kept to a minimum, and the relative position to the recording head can therefore be kept constant, allowing normal editing work and ensuring that the relative position to the recording head is correctly installed at the beginning. In other words, it is possible to maintain high quality and stable simultaneous playback image quality. As the material for the holder according to the present invention, since the coefficient of thermal expansion of the piezoelectric ceramic plate is approximately 8×10 - /C, ceramics of the same type as the piezoelectric ceramic plate, titanium, etc. are suitable.

As explained above, according to the present invention, even if the ambient temperature changes when the automatic scanning tracking mode is off, the change in the position of the tip of the movable part of the bimorph plate can be suppressed to a small extent. The relative position between the print head and the recording head can be kept constant.

Therefore, normal editing work can be performed, and high quality and stable simultaneously reproduced images can always be obtained regardless of the application of the control voltage to the bimorph plate.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a conventional automatic scanning tracker head, Fig. 2 is a cross-sectional view exaggerating changes in the automatic scanning tracker and king head when the temperature rises, and Fig. 3 is an embodiment according to the present invention. Give an example. 1.10: Holder, 2: Bimorph plate, 2a, 2b: Piezoelectric ceramic plate, 2c: Intermediate electrode, 3: Adhesive layer.

Claims (1)

[Claims] In a magnetic recording/reproducing head in which a magnetic head is attached to the distal end of a plate-shaped electro-mechanical transducer, and the entire proximal end of the element is supported and fixed to a holder, the holder is substantially equal to the electro-mechanical transducer. A magnetic recording/reproducing head characterized by being made of a material having a coefficient of thermal expansion.