JPH048867B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to, for example, a so-called helical scanning type VTR that forms a recording track that is inclined with respect to the longitudinal direction of a magnetic tape, or a recording track that is concentric or spiral with respect to a disk. The present invention relates to an actuator for driving and controlling a head, etc. of an information recording/reproducing apparatus formed optically.

A magnetic head is attached to the tip of a bimorph element (a type of piezoelectric element) in one of the conventional actuators of this type, and by applying a predetermined voltage to the bimorph element based on tracking information, the center of the gap of the magnetic head is adjusted. Some control the head position so that the position always coincides with the center position of the track. Since the mechanical strength of the bimorph element itself is relatively weak, the bimorph element described above is susceptible to external forces such as force generated when the tip of the magnetic head comes into contact with the recording surface of a magnetic tape or magnetic disk, when applied to the magnetic head. , the magnetic head may deviate greatly from the predetermined position and move to another position due to the external force. In such a case, in order to return the magnetic head to its optimal operating position, it is necessary to apply a large voltage to the bimorph element for correcting the amount of deviation. Therefore, it is necessary to sufficiently increase the dynamic range of the amplifier for supplying the above applied voltage, which is disadvantageous in terms of cost.
Further, the amount of deviation gives an offset to the tracking servo system. Therefore, in order to absorb the above offset, the servo gain of the tracking servo system must be extremely large, which also poses a problem in terms of ensuring the stability of the servo system.

A bimorph element has a structure in which two sheets of thin ceramic are glued together, or a piezoelectric element and a non-piezoelectric element such as a metal plate or polymer film are glued together. Therefore, in order to move the magnetic head significantly in position, it is necessary to make the bimorph element sufficiently long. Long ceramics have weak strength, so thick materials must be used. However, thick bimorph elements do not operate satisfactorily unless the driving voltage is increased.

As described above, there is a correlation between the thickness of the bimorph element, the length of the element, the driving voltage, and the amount of deformation (the amount of movement), making it difficult to design a driving element suitable for the device.

The present invention was made based on these circumstances, and its purpose is to provide a device with sufficiently high mechanical strength that can stably hold the driven object, such as a magnetic head, even if an external force is applied to the driven object, such as a magnetic head. To provide an actuator that can be used as a head actuator of a small portable magnetic recording device, etc., which can be formed compactly as a whole without increasing the length of a driving element, has a simple configuration, and is easy to assemble and wire. There is a particular thing.

In order to achieve the above object, the present invention is characterized by the following configuration. That is, in the present invention, a frame body including two legs facing each other in parallel at a predetermined distance is formed of a member with high mechanical strength, and an object to be driven is placed in the center between the two legs of the frame body. First and second laminated piezoelectric elements are inserted between one side of the driven object and the inner side of the one leg, and between the other side of the driven object and the inner side of the other leg, respectively. By applying a control voltage of a predetermined polarity according to drive control information to these first and second laminated piezoelectric elements, the object to be driven is controlled to be driven to a predetermined position. 1. As the second laminated piezoelectric element, a plurality of piezoelectric elements are laminated with their polarization directions alternately different by 180 degrees. Thus, in the present invention, the driving object is controlled by utilizing the longitudinal vibration in the thickness direction of the piezoelectric element without using an element with a bimorph structure, thereby preventing the structural weakness of the bimorph element and the elongation of the element. With,
The present invention is characterized by simplifying the structure of the electrodes inserted between the individual piezoelectric elements, simplifying the assembly, and simplifying the wiring.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing the structure of a mechanical section of an embodiment of the present invention, in which reference numeral 11 denotes a rotating magnetic disk;
12 is a recording track formed on the magnetic disk; 13 is a step motor for moving the head; 14 is a ball screw provided on the shaft of the motor; 15 is a recording track formed on the magnetic disk;
The head holder moves in steps in the radial direction of the head.

FIG. 2 is a perspective view showing a specific structure of the head holder 15 shown in FIG. 1. In FIG. 2, 20 is an H formed of a member having sufficient mechanical strength.
The frame body 20 has a magnetic head 22 having a gap G between the opposing legs 21a and 21b, and first and second laminated piezoelectric elements 23 on both sides.
It is inserted while being held between a and 23b. A positive or negative potential control voltage amplified by voltage amplifiers 24 and 25 is applied to the laminated piezoelectric elements 23a and 23b in Tables 1 and 2. Note that frame body 2
between the two legs 21a, 21b of 0 and the first and second laminated pressure elements 23a, 23b, and the magnetic head 22.
Both side surfaces and the first and second laminated piezoelectric elements 23a, 2
3b is bonded with adhesive or the like.

FIG. 3 shows the first and second laminated piezoelectric elements 23a, 2.
FIG. 3b is a diagram showing a detailed configuration of FIG. However, FIG. 3 shows only the first laminated piezoelectric element 23a. In the figure, 31, 32, 33, 34, 35, 36
is a single piezoelectric element, which is laminated with the polarization directions alternately different by 180° as shown by the arrows in the figure. Between each of the piezoelectric elements 31 to 36 and 31
and 36 have electrode layers 41, 42, 43,
44, 45, 46, and 47 are provided. Odd numbered electrode layers 41, 43, 4 among the above electrode layers
5 and 47 are commonly connected and connected to the output terminal of the voltage amplifier 24, and the even numbered electrode layers 42 and 4
4 and 46 are commonly connected and grounded. Thus, each of the piezoelectric elements 31 to 36 has a voltage amplifier 2.
Control voltages corresponding to the tracking information voltage amplified in step 4 are applied in parallel. As a result, each piezoelectric element 31 to 36 expands in the direction of arrow I in FIG. 3 if the control voltage is at a positive potential, and in the direction of the arrow I in FIG. 3 if the control voltage is at a negative potential. compresses and applies a biasing force to the head 22. Note that the first and second piezoelectric elements 23a and 2 are arranged so that the directions in which the biasing force acts on the head 22 are the same in the first and second laminated piezoelectric elements 23a and 23b.
3b is controlled so that when one expands, the other compresses.

That is, in FIG. 2, the laminated piezoelectric element 23
When a voltage with a potential that causes the element 23a to expand in the thickness direction is applied from the voltage amplifier 24 to a, a voltage of a potential that causes the element 23b to be compressed in the thickness direction is applied to the laminated piezoelectric element 23b from the voltage amplifier 25. A voltage is applied. As a result, 23a, 2
3b, the head 22 moves in the direction A shown in the figure.

FIG. 4 is a diagram showing tracking information detection means. In FIG. 4, 51 and 52 are a pair of heads for detecting tracking information. The detection heads 51 and 52 are positioned so that when the head 22 is in the optimum tracking state, the respective gap centers of the heads 51 and 52 coincide with both ends of the track 12, and the detection heads 51 and 52 are integrally tracked together with the head 22. 12 in the width direction. The tracking information detection head 5
Each output of 1 and 52 is an envelope detector 53 and 5.
4, each signal is subjected to envelope detection and then supplied to a differential amplifier 55. Differential amplifier 5
The output of 5 is given to the voltage amplifiers 24 and 25 as tracking information.

Since this device is configured as described above, when a tracking error occurs in the head 22, a difference occurs between the outputs of the detection heads 51 and 52, and tracking information corresponding to the difference is sent out from the differential amplifier 55. Ru. This tracking information is transmitted to voltage amplifier 2.
4 and 25, and is applied to the laminated piezoelectric elements 23a and 23b as a positive or negative potential control voltage. Therefore, the laminated piezoelectric elements 23a, 23b
As shown in FIG. 2, a driving force is applied to the head 22 in the direction A or B, and tracking control is performed so that the center position of the head 22 coincides with the center position of the track 12.

Now, suppose that some external force is applied to the head 22. However, the head 22 is sandwiched on both sides by laminated piezoelectric elements 23a, 23b, and the outer sides of both piezoelectric elements 23a, 23b are held by the legs 21a, 21b of the frame 20, which is formed of a member with high mechanical strength. Since it is firmly held, there is no risk that the position of the head 22 will be significantly displaced by the external force. Therefore, a large voltage is applied to the piezoelectric element 23 for correcting the amount of deviation as in the conventional case.
There is no need to make the dynamic range of the amplifiers 24 and 25 particularly large in order to increase the dynamic range of the amplifiers 24 and 25. Furthermore, since there is no need to ensure servo gain for offset absorption, stability of the servo system can be achieved. On the other hand, as shown in FIG.
3a and 23b, the head 22 can be held evenly on both sides without any special adjusting means.
It has the advantage that perpendicularity and parallelism can be easily obtained and assembly is easy.

In addition, the first and second laminated piezoelectric elements 23a and 23b
As shown in FIGS. 2 and 3, since it utilizes the longitudinal vibration in the thickness direction of the piezoelectric element, there is no structural weakness of the bimorph element, and there is no risk of it becoming too long. Furthermore, as shown in Fig. 3, since the individual piezoelectric nests 31 to 36 are laminated with their polarization directions alternately different by 180°, the electrode layers interposed between each piezoelectric element can be made into a single layer. It can be shared by two piezoelectric elements adjacent to each other on both sides. As a result, the structure of each electrode layer is simplified and the wiring is also simplified, compared to a structure in which the polarization direction is uniform and the layers are stacked as shown in FIG. In addition, in Figure 5,
61 to 66 are respective piezoelectric element bodies, 71a, 71b to
75a and 75b are electrode layers disposed on both sides of each piezoelectric element body 61-65, and 81-86 are insulating layers.
According to this embodiment, each pair of electrode layers 71a,
As a result of each of 71b to 75a and 75b being unified, insulating layers 81 to 86 can also be omitted, and it is sufficient to connect every other electrode in common.

FIG. 6 is a perspective view showing another embodiment of the invention. In FIG. 6, 91 is a step motor;
2 is a pole screw, 93 is a U-shaped frame, 94 is a magnetic head disposed between two legs 93a, 93b of the frame, and 95a, 95b are first and second laminated piezoelectric elements. In this embodiment, the gap position of the head 94 is different from that in FIG. 2 by 90 degrees. Even with such a configuration, it goes without saying that the same effects as in the embodiment described above can be achieved.

Note that the present invention is not limited to the embodiments described above. For example, in the above embodiment, the present invention is used as a head actuator for a magnetic disk device, but it can also be used as a head actuator for a helical scanning VTR. However, in this case, the ball screw 14 shown in FIGS. 2 and 6 is not necessary, and the shaft of the frame provided at the ball screw insertion site may be mounted parallel to the shaft of the rotating cylinder. Furthermore, it can be used as an optical head actuator or focusing actuator for an optical disk device.

As explained above, according to the present invention, the object to be driven, which is placed between the two legs of the frame made of a member with high mechanical strength, is held from both sides by the first and second laminated piezoelectric elements. By applying a control voltage of a predetermined polarity to each piezoelectric element according to the drive control information, the object to be driven is controlled to a predetermined position, and the longitudinal vibration in the thickness direction of the piezoelectric element is suppressed. Since the mechanical strength of the driving element is sufficiently large, it is possible to stably hold the driven object even if an external force is applied to the driven object, and the driving element does not become long and the entire structure is maintained. Can be formed compactly. Further, according to the present invention, as the first and second laminated piezoelectric elements, a plurality of single piezoelectric elements are alternately polarized by 180 degrees.
Since different layers are used, the electrode structure inserted between each piezoelectric element can be simplified, and the structure is simple and assembly and wiring are easy.For example, it is suitable for small portable magnetic recording devices. It is possible to provide an actuator suitable for use as a head actuator or the like.

[Brief explanation of drawings]

1 to 4 are views showing one embodiment of the present invention, in which FIG. 1 is a cross-sectional view showing the structure of the mechanism part, FIG. 2 is a perspective view showing the specific structure of the head holder, and FIG.
The figure shows the detailed structure of the first and second laminated piezoelectric elements, FIG. 4 shows the tracking information detection means, and FIG. 5 shows the laminated piezoelectric element shown for explaining the operation of the same embodiment. FIG. 6 is a perspective view of a head holder showing another embodiment of the present invention. 11... Rotating magnetic disk, 12... Recording track, 13, 91... Step motor for head feeding, 14, 92... Ball screw, 15... Head holder, 20, 93... Frame, 21a, 21b,
93a, 93b... Bipod, 22, 94... Magnetic head, 23a, 23b, 95a, 95b... Laminated piezoelectric element, 24, 25... Voltage amplifier, 31-3
6... Single piezoelectric element, 41-47... Electrode layer, 5
1, 52... Playback head for tracking information detection, 53, 54... Envelope detector, 55...
...Differential amplifier.

Claims (1)

[Scope of Claims] 1. A frame body formed of a member with high mechanical strength and having two legs facing each other in parallel at a predetermined distance, and a driven object disposed at the center between the two legs of this frame body. a first laminated piezoelectric element inserted between one side of the driven object and the inner side of the one leg; and a first laminated piezoelectric element inserted between the other side of the driven object and the inner side of the other leg. a second laminated piezoelectric element inserted between;
An actuator comprising a control means for applying a control voltage of a predetermined polarity according to drive control information to the first and second laminated piezoelectric elements to drive and control the driven object to a predetermined position. 2. The actuator according to claim 1, wherein the first and second laminated piezoelectric elements are each a plurality of piezoelectric elements laminated with their polarization directions alternately different by 180°. 3. The actuator according to claim 1 or 2, wherein the first and second laminated piezoelectric elements are controlled so that when one expands, the other is compressed. 4. The actuator according to claim 1, wherein the driven object is a magnetic head. 5. The actuator according to claim 1, wherein the driven object is an optical head.