JPH09147332A - Biaxial actuator and magnetic head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize the biaxial actuator and to reduce contact wear between a recording medium and a magnetic head and hence to contrive longevity of the magnetic head by performing drive in the orthogonal biaxial directions with one driving part. SOLUTION: The driving part 10 has a structure of a parallel polarization bimorph made by sticking two piezoelectric elements to each other. Then, in a driving circuit 20, when a changeover switches 26 and 27 are changed to contacts A, A, the direction of an electric field of the driving part 10 and the direction of polarization of a piezoelectric plate 11 become opposite to each other, and the piezoelectric plate 11 is expanded in the longitudial direction. On the other hand, the direction of the electric field and the direction of polarization of a piezoelectric plate 12 become opposite to each other, and the piezoelectric plate 12 is contracted in the longitudinal direction. Consequently, the driving part is curved as a whole into a convex shape of the piezoelectric plate 11. On the other hand, the switches 26 and 27 are both changed over to contacts B, B, the driving part 10 is contracted in the longitudinal direction as a whole until contracting force of the individual piezoelectric plates 11 and 12 and resistance force of an intermediate electrode 13 are balanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxial actuator which can be driven in orthogonal biaxial directions, and a magnetic head device which includes the biaxial actuator and exchanges signals with a magnetic recording medium.

[0002]

2. Description of the Related Art For example, a video tape recorder (VT)
A large number of magnetic head devices for recording, reproducing, erasing, etc. are mounted on the rotating drum (R). These magnetic head devices correspond to variable speed reproduction modes such as slow reproduction and reverse reproduction, and different formats such as VH.
Standard mode and triple speed mode and digital
There is one corresponding to the beta cam SP reproduction mode in the beta cam system. These magnetic head devices are equipped with actuators for swinging the magnetic head because it is necessary for the magnetic head to swing and follow the recording tracks of the magnetic tape during variable speed reproduction or the like. As this actuator, the one having a cantilever structure of a bimorph, which is an electromechanical conversion element such as a piezoelectric element, is often used.

[0003]

As described above, a large number of magnetic head devices are mounted on the rotary drum, but not all magnetic head devices are used at the same time during the operation of the VTR. It is often used properly for each mode. However, in each magnetic head device, since the magnetic head is mounted with a predetermined protrusion amount from the outer circumference of the rotating drum, all the magnetic heads are always in contact with the magnetic tape during the operation of the VTR regardless of the exchange of signals. You are doing it. For this reason, the amount of wear of the magnetic head increases and the predetermined amount of protrusion cannot be maintained, so that the contact pressure with the magnetic tape decreases and eventually the contact state with the magnetic tape deteriorates. However,
Since the actuator applied to the magnetic head device is a uniaxial actuator that only swings the magnetic head, there is a problem that it is not possible to avoid the constant contact state between the magnetic head and the magnetic tape.

In view of the above points, the present invention is orthogonal to each other.
An object of the present invention is to provide a biaxial actuator that is driven in the axial direction and a magnetic head device that includes the biaxial actuator.

[0005]

According to the present invention, the above object is to provide, in a biaxial actuator that can be driven in two biaxial directions orthogonal to each other, a first member and an electromechanical conversion element that are joined to each other. A drive unit having a second member, a first drive means for extending one of the first and second members and contracting the other member, and a second drive unit for extending or contracting both the first and second members. Drive means and a drive circuit having a switching means for switching the drive of the first and second drive means.

According to the above construction, the drive section constitutes a so-called bimorph. Therefore, the first and second drive circuits are constructed in accordance with the polarization directions of the first and second members constituting the drive section. By switching the voltage applied from the second driving unit, the driving unit can be swung in one direction and moved back and forth in a direction orthogonal to it.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The embodiments described below are preferred specific examples of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. It is not limited to these forms unless otherwise stated.

FIG. 1 is a perspective view showing a first embodiment of a drive portion which constitutes the biaxial actuator of the present invention.
The drive unit 10 has a so-called parallel polarization bimorph structure in which two plate-shaped electromechanical conversion elements, for example, piezoelectric elements are attached. Two piezoelectric plates 1
Nos. 1 and 12 are bonded to each other with the intermediate electrode 13 interposed therebetween, and surface electrodes 14 and 15 are formed on both surfaces of the bonded electrodes. The piezoelectric plates 11 and 12 are polarized in the thickness direction, and are bonded so that, for example, the intermediate electrode 13 is positive and the surface electrodes 14 and 15 are negative, that is, the respective polarization directions are opposite. There is.

Here, as the material of the piezoelectric plates 11 and 12, a ceramic material such as barium titanate or lead zirconate titanate is used. Further, a polymer material such as poly-vinylidene fluoride can also be used. As a material of the intermediate electrode 13, a metal material having a small expansion coefficient such as titanium alloy or stainless steel is used. The surface electrodes 14 and 15 are made of a piezoelectric plate 11,
A material having a coefficient of linear expansion that is close to or close to that of 12 and has good conductivity and oxidation resistance and easy soldering is preferable. For example, a metal material such as nickel, silver, lead, molybdenum, tin, or the like. Alloy material is used. As a method of forming the surface electrodes 14 and 15, the piezoelectric plates 11 and 1 are used.
There is a method in which a paste of the above material is applied to the surface of No. 2 by a screen printing method or the like and then dried or baked, or a method such as metal spraying, vacuum deposition, sputtering, electroless plating or the like.

FIG. 2 is a circuit diagram showing a first embodiment of a drive circuit constituting the biaxial actuator of the present invention. The drive circuit 20 includes an AC power supply 21 and a DC power supply 22.
It has. At both terminals of the AC power supply 21, two resistors 231, 232 connected in series, and two sets of diodes 241, 242 and zener diodes in which a set of diodes and zener diodes connected in series are further connected in series. 251 and 252 are connected in parallel. One terminal of the AC power supply 21 is connected to the switching contact A of the first changeover switch 26, and the other terminal is connected to the switching contact B of the first changeover switch 26 and one surface electrode 15 of the drive unit 10. Has been done. Resistors 231, 232
Series connection point and diodes 241, 242 and Zener
The series connection point of the diodes 251 and 252 is connected to the switching contact A of the second changeover switch 27.

The negative terminal of the DC power source 22 is grounded, and the positive terminal is connected to the changeover contact B of the second changeover switch 27. The changeover terminal of the first changeover switch 26 is connected to the other surface electrode 14 of the drive unit 10, and the changeover terminal of the second changeover switch 27 is
It is connected to the intermediate electrode 13 of the drive unit 10.

An operation example of such a configuration will be described. First, while switching the first changeover switch 26 to the changeover contact A, the second changeover switch 2
7 is switched to the switching contact A. Then, for example, the potential of the one surface electrode 15 of the driving unit 10 is 0 V,
The intermediate electrode 13 has a potential of 50V, and the other surface electrode 14 of the drive unit 10 has a potential of 100V. Therefore, the direction of the electric field and the direction of polarization of the piezoelectric plate 11 of the drive unit 10 are opposite to each other, so that the piezoelectric plate 11 extends in the longitudinal direction. On the other hand, since the direction of the electric field and the direction of polarization of the piezoelectric plate 12 of the driving unit 10 are positive, the piezoelectric plate 12 contracts in the length direction. Therefore, the entire drive unit 10 is curved so that the piezoelectric plate 11 side is convex. It should be noted that such a driving method is applied to each piezoelectric plate 11,
It is used when it is necessary to cut the reverse electric field because the coercive electric field of 12 is low.

Next, the first changeover switch 26 is changed over to the changeover contact B, and the second changeover switch 27 is changed over to the changeover contact B. Then, for example, the potentials of the surface electrodes 14 and 15 on both sides of the driving unit 10 are 0 V,
The potential of the intermediate electrode 13 of the drive unit 10 becomes 100V. Therefore, since the direction of the electric field and the direction of polarization of the piezoelectric plates 11 and 12 of the drive unit 10 are positive, the piezoelectric plates 11 and 12 contract in the length direction. Therefore, the driving unit 10 as a whole contracts in the lengthwise direction until the force due to the contraction of the piezoelectric plates 11 and 12 and the resistance force of the intermediate electrode 13 are balanced. Each piezoelectric plate 1
If attention is paid to the coercive electric fields of 1 and 12, the driving unit 1 will have a reverse potential.
It is also possible to extend the entire 0 in the length direction. When the entire drive unit 10 is continuously extended in the length direction, the DC power supply 22 may be changed to an AC power supply.

FIG. 3 is a perspective view showing a second embodiment of a drive portion which constitutes the biaxial actuator of the present invention.
The drive unit 30 has a so-called series polarization bimorph structure in which two plate-shaped electromechanical conversion elements, for example, piezoelectric elements are attached. Two piezoelectric plates 3
Nos. 1 and 32 are bonded to each other with the intermediate electrode 33 interposed therebetween, and surface electrodes 34 and 35 are formed on both surfaces of the bonded electrodes. The piezoelectric plates 31 and 32 are polarized in the thickness direction, and are bonded so that, for example, the front surface electrode 34 is positive and the front surface electrode 35 is negative, that is, the respective polarization directions are positive. The materials and forming methods of the piezoelectric plates 31, 32, the intermediate electrode 33, and the surface electrodes 34, 35 are the same as those described above.

FIG. 4 is a circuit diagram showing a second embodiment of the drive circuit constituting the biaxial actuator of the present invention. The drive circuit 40 includes an AC power supply 41 and a DC power supply 42.
It has. One terminal of the AC power supply 41 is grounded,
The other terminal is connected to the intermediate electrode 33 of the drive unit 30. The positive terminal of the DC power supply 42 is connected to the contact of the switch 43, and further connected to the surface electrode 34 of the drive unit 30. The negative terminal of the DC power supply 42 is connected to the terminal of the switch 43 and further connected to the surface electrode 35 of the drive unit 30.

An operation example of such a configuration will be described. First, when the switch 43 is connected to the contact, for example, the potentials of the surface electrodes 34 and 35 on both sides of the drive unit 30 are zero.
V, the potential of the intermediate electrode 33 of the drive unit 30 is 100V. Therefore, the direction of the electric field and the direction of polarization of the piezoelectric plate 31 of the drive unit 30 are opposite to each other, so that the piezoelectric plate 31 extends in the longitudinal direction. On the other hand, since the direction of the electric field and the direction of polarization of the piezoelectric plate 32 of the driving unit 30 are positive, the piezoelectric plate 32 contracts in the length direction. Therefore, as a whole of the driving unit 30, the piezoelectric plate 31
Bend so that the sides are convex. Such a driving method is used when it is necessary to cut the reverse electric field because the coercive electric fields of the piezoelectric plates 31 and 32 are low.

Next, when the switch 43 is disconnected from the contact, for example, the potential of the one surface electrode 34 of the drive section 30 becomes 1
00V, the potential of the other surface electrode 35 of the drive unit 30 is 0V
Becomes Therefore, the direction of the electric field and each piezoelectric plate 3 of the driving unit 30.
Since the polarization directions of 1 and 32 are positive, each piezoelectric plate 3
1, 32 contract in the length direction. Therefore, the drive unit 30 as a whole contracts in the length direction until the force due to the contraction of the piezoelectric plates 31 and 32 and the resistance force of the intermediate electrode 33 are balanced. still,
If the coercive electric field of each piezoelectric plate 31 and 32 is taken into consideration, it is also possible to extend the entire drive unit 30 in the longitudinal direction as a reverse potential. When the entire drive unit 30 is continuously extended in the length direction, the DC power supply 42 may be changed to an AC power supply.

As described above, by switching the first and second changeover switches 26, 27 or the switch 43 of the drive circuit 20 or 40, the drive unit 10 or 3
Since 0 can be swung and expanded and contracted, 2
It can be configured as a shaft actuator. Although the drive circuit 20 or 40 is a modeled circuit, it is not shown in the drawing, but in reality, a circuit for switching the operation mode and controlling the applied voltage is added. It is desirable that this operation mode switching circuit is assembled in consideration of the breakdown voltage.

FIG. 5 is a schematic plan view showing an example of a rotary drum of a VTR equipped with an embodiment of a magnetic head device to which the above-described embodiment of the biaxial actuator is applied. The magnetic head device 50 has a configuration in which a magnetic head 52 is attached to the tip of a trapezoidal bimorph 51 and a conductive holder 53 is attached to the end. Further, the magnetic head 52 has a cantilever structure supported and fixed on the rotary drum 60 via a holder 53 so that the magnetic head 52 is swingably arranged on the circumference of the rotary drum 60. A printed circuit board on which a drive circuit 54 that drives the bimorph 51, a detection circuit 55 that detects the amount of bending displacement of the bimorph 51, and an amplification circuit 56 that amplifies a recording / playback signal are mounted on the rotary drum 60 on the holder 53 side. 57 is fixed.

FIG. 6 is a perspective view showing a detailed example of the magnetic head device 50 described above. In the bimorph 51, two piezoelectric plates 511 and 512 are attached to each other with an intermediate electrode 513 sandwiched therebetween, and surface electrodes 514 and 5 are attached to both surfaces of the attachment.
15 has a structure formed. This bimorph 5
A tip base 521 to which a magnetic head 52 is attached is attached to the tip of 1. Further, the end of the bimorph 51 is sandwiched between the base holder 531 and the pressing holder 532 that constitute the holder 53. The holder 53 and the like configured as described above have an insulating plate sandwiched between the base holder 531 and the rotary drum 60,
It is supported and fixed on the rotary drum 60 by bolts.

Surface electrodes 514 and 515 of the bimorph 51
Is indirectly connected via the base holder 531 and the pressing holder 532, and the intermediate electrode 513 is directly connected to the drive circuit 5
4 is connected. A strain gauge 58, which is attached to substantially the center of the bimorph 51 and whose resistance value changes according to the amount of bending displacement of the bimorph 51, is connected to the detection circuit 55. Then, the magnetic head 52 includes the amplifier circuit 5
6 is connected.

According to the magnetic head device 50 having such a structure, the drive circuit 54 drives the bimorph 51 to bend and the magnetic head 52 moves in the direction of the rotation axis of the rotary drum 60. Magnetic head 5
2 can follow the recording track of the magnetic tape 70 that is obliquely wound around the outer peripheral surface of the rotating drum 60. Further, the driving of the driving circuit 54 causes the bimorph 51 to contract and the magnetic head 52 to move in the direction orthogonal to the rotation axis direction of the rotary drum 60. Therefore, when the magnetic head device 50 is not used, the magnetic head 52 is rotated. The magnetic tape 70 can be separated from the magnetic tape 70 that is obliquely wound around the outer peripheral surface of 60. As a result, excessive wear of the magnetic head 52 can be prevented.

The protrusion amount of the magnetic head 52 from the outer periphery of the rotary drum 60 shown in FIG. 7 can be adjusted by changing the voltage applied to the bimorph 51 by the drive circuit 54. FIG. 8 shows the protrusion change amount (μm) of the magnetic head 52 and the applied voltage (DCV) to the bimorph 51.
It is a figure which shows an example of the relationship of. As is clear from the figure,
It changes in a substantially linear manner, for example, with an applied voltage of 250 V, -13
The protrusion amount is μm. Therefore, it is possible to control the protrusion amount of the magnetic head 52 with high accuracy.

[0024]

As described above, according to the biaxial actuator of the present invention, it is possible to drive in the directions of two axes orthogonal to each other by using only one drive section, so that the biaxial actuator itself can be miniaturized. be able to. Further, according to the magnetic head device of the present invention provided with this biaxial actuator, the protrusion of the magnetic head that is not exchanging signals with the magnetic recording medium can be lowered, so that the contact wear between the magnetic recording medium and the magnetic head. Can be reduced and the life of the magnetic head can be extended.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of a drive unit that constitutes a biaxial actuator of the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a drive circuit constituting the biaxial actuator of the present invention.

FIG. 3 is a perspective view showing a second embodiment of a drive unit that constitutes the biaxial actuator of the present invention.

FIG. 4 is a circuit diagram showing a second embodiment of a drive circuit that constitutes the biaxial actuator of the present invention.

FIG. 5 is a schematic plan view showing an example of a rotary drum of a VTR equipped with an embodiment of a magnetic head device to which an embodiment of a biaxial actuator of the present invention is applied.

6 is a perspective view showing a detailed example of the magnetic head device shown in FIG.

7 is a diagram showing the amount of protrusion of the magnetic head from the outer periphery of the rotary drum shown in FIG.

8 is a protrusion variation amount (μ of the magnetic head shown in FIG.
The figure which shows an example of the relationship of the applied voltage (DCV) to m) and a bimorph.

[Explanation of symbols]

10, 30 Driving unit 11, 12, 31, 32, 511, 512 Piezoelectric plate 13, 33, 513 Intermediate electrode 14, 15, 34, 35, 514, 515 Surface electrode 20, 40 Driving circuit 21, 41 AC power supply 22, 42 DC power supply 231, 232 Resistor 241, 242 Diode 251, 252 Zener diode 26 First changeover switch 27 Second changeover switch 43 Switch 50 Magnetic head device 51 Bimorph 52 Magnetic head 53 Holder 54 Drive circuit 55 Detection circuit 56 Amplification Circuit 57 Printed circuit board 58 Strain gauge 60 Rotating drum 521 Chip base 531 Base holder 532 Holding holder 70 Magnetic tape

Claims (2)

[Claims] 1. A biaxial actuator which can be driven in two orthogonal directions orthogonal to each other, a drive section having a first member and a second member which are electromechanical conversion elements joined to each other, and the first and the second parts. A first drive means for extending one of the two members and a contraction of the other member; a second drive means for extending or contracting both the first and second members; and a first and a second drive means. A biaxial actuator, comprising: a drive circuit having a switching means for switching drive. 2. A magnetic head device for exchanging signals with a magnetic recording medium, comprising: a drive unit having a first member and a second member, which are electromechanical conversion elements joined to each other; and a drive unit at one end of the drive unit. A magnetic head that is attached and exchanges signals with the magnetic recording medium; a first drive unit that extends one of the first and second members and contracts the other; both the first and second members And a drive circuit having a switching means for switching the drive of the first and second drive means.