JPH04367288A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To protect a piezoelectric actuator and a driving device for the actuator from an overcurrent. CONSTITUTION:A piezoelectric actuator of a structure, wherein a plurality of pieces of electrostrictive effect elements 1a to 1e of a laminated ceramic capacitor structure are bonded together in such a way that they are stacked and are electrically connected in parallel to each other, is constituted by a method wherein a protective circuit (a fuse) 3 is connected in series to a lead wire 2a connected in parallel to the elements 1a to 1e. When a working voltage is applied in error, the elements 1a to 1e can be protected from breakdown in the case a driving device for the actuator is made to drive exceeding a resonance frequency or the like.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator, and more particularly to the structure of a piezoelectric actuator having a protection circuit.

0002

2. Description of the Related Art Piezoelectric actuators using electrostrictive elements that convert electrical energy into mechanical energy are currently used in industrial fields such as mass flow controllers, X-Y table drives, and injection molding machines. FIG. 3 is a longitudinal cross-sectional view of a conventional piezoelectric actuator. A plurality of ceramic capacitor-type electrostrictive effect elements each having lead wires attached to both ends ( For example, 5 pieces) The surfaces perpendicular to the displacement or force generation axis of the electrostrictive effect elements are glued together with a metal plate in between, and electrically connected in parallel with lead wires, and the electrostrictive effect that remains without being glued This is a piezoelectric actuator in which metal fittings are glued to the plane perpendicular to the displacement or force generation axis of the element for attachment to equipment.

0003

[Problems to be Solved by the Invention] In the conventional piezoelectric actuator described above, the lead wires led out from each of the stacked ceramic capacitor type electrostrictive effect elements electrically connect the ceramic capacitor type electrostrictive effect elements to each other. After connecting in parallel, the electrostrictive element is directly output to the outside, so if the drive voltage is applied incorrectly or excessively, or if the electrostrictive element is driven beyond its resonant frequency, the electrostrictive element will be damaged. There was a problem.

[0004] The purpose of the present invention is to solve the problem when excessive driving voltage is applied by mistake, when the electrostrictive element is driven beyond the resonant frequency, or when the insulation between the layers of the electrostrictive element is broken. It is an object of the present invention to provide a piezoelectric actuator that can protect an electrostrictive element even when the electrostrictive element is protected.

[0005]

[Means for Solving the Problems] The piezoelectric actuator of the present invention is a ceramic capacitor type electrostrictive element in which piezoelectric ceramic members and internal electrode conductors are alternately laminated, and each internal electrode is alternately connected to two external electrodes. A piezoelectric actuator is a piezoelectric actuator in which a plurality of piezoelectric actuators are stacked and bonded together and an electrostrictive element is electrically connected in parallel, and a protection circuit is electrically connected to the electrostrictive element.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a longitudinal section of a piezoelectric actuator according to an embodiment of the present invention. 1a to 1e, piezoelectric ceramic members and internal electrode conductor layers are alternately laminated, and a pair of external electrode conductors 7a,
7f, a pair of lead wires 2a and 2b electrically connect the external electrode conductors 7a to 7e and 7f to 7i of the electrostrictive elements 1a to 1e in parallel, respectively; , 2c are lead wires connecting one of the above-mentioned pair of lead wires and the electrostrictive effect element to the fuse 3, which is electrically connected in series;
Reference character e is a lead wire led out to the outside for connection to a power source when power is supplied to the piezoelectric actuator described above. 4
a to 4d are metal plates, and 5a and 5b are metal plates (for example, screws) to facilitate attachment of the electrostrictive element to the equipment.
It is a processed metal fitting.

Next, a method for assembling the piezoelectric actuator of the present invention will be explained. First, the surfaces perpendicular to the displacement or force generation axis of the electrostrictive elements 1a and 1b are bonded to each other via the metal plate 4a, and then the symmetric surfaces of the bonded surfaces of the electrostrictive effect element 1b and the electrostrictive The effect element 1c is bonded to a surface perpendicular to the axis of displacement or force generation via a metal plate 4b. Similarly, electrostrictive elements 1d and 1e are bonded via metal plates 4c and 4d. Next, a metal fitting 5 is partially processed on the target surface of the bonded surfaces of the electrostrictive elements 1a and 1e for attachment to the equipment.
Glue a and 5b. Next, the lead wires 2a, 2 are connected to the external electrode conductors 7a to 7e, 7f to 7i of the electrostrictive elements 1a to 1e.
b are connected by soldering so that the electrostrictive effect elements 1a to 1e are electrically connected in parallel. Furthermore, lead wire 2
A and a fuse 3 for protecting the electrostrictive effect element are electrically connected in series with the electrostrictive effect element through a lead wire 2c by soldering, and a lead wire 2d for supplying power from the outside,
2e is soldered and connected to the fuse 3 and lead wire 2b, respectively, to complete the assembly.

Next, its operation will be explained. The ceramic capacitor type electrostrictive effect element used in this example has a capacitance of 0.5μ.
F, insulation resistance 1MΩ, withstand voltage 200V, maximum working voltage 1
It has a characteristic value of 50V. This has a fusing current of 0.
If a fuse with a characteristic value of 3A is used, the current flowing through the electrostrictive element will rapidly increase if the power supply is connected incorrectly or the electrostrictive element is driven beyond its resonant frequency. The fuse is blown to prevent overcurrent from flowing to the electrostrictive element.

FIG. 2 is a longitudinal sectional view of another embodiment of the invention. External electrode conductor 7 of each of the electrostrictive elements 1a to 1e
After connecting the fuse 3 to each of a to 7e, the lead wires 2a, 2b, 2d, and 2e are connected by soldering so that the electrostrictive elements 1a to 1d are electrically connected in parallel. In this embodiment, a fuse is connected to each of the electrostrictive elements bonded one on top of the other, so even if the insulation between the layers of some electrostrictive elements breaks down, only that part of the fuse is blown. The electrostrictive element has the advantage that it operates normally and rarely causes any defects in the operation of the device in which it is incorporated.

0010

As explained above, the present invention has the following effects by electrically connecting the electrostrictive element and the protection circuit in series. (1) Even if the insulation between the layers of the electrostrictive element suddenly breaks down when a voltage is applied, the protection circuit (fuse) is blown to prevent damage caused by overcurrent on the power supply side. (2) Even if the operating voltage is incorrectly applied, the protection circuit (fuse) is blown to protect the electrostrictive element. (3) Even when the electrostrictive element is driven beyond its resonant frequency, the protection circuit (fuse) is blown to protect the electrostrictive element.

Although a fuse is used in the protection circuit in this embodiment, it goes without saying that the same effect can be obtained even if the fuse is replaced with a component having a similar function.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a piezoelectric actuator according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a piezoelectric actuator according to another embodiment of the present invention.

FIG. 3 is a longitudinal cross-sectional view of an example of a conventional piezoelectric actuator enclosed in a metal case.

[Explanation of symbols]

1a to 1e Electrostrictive effect element 2a-2e Lead wire 3 Fuse 4a-4d　　　Metal plate 5a, 5d Metal fittings 7a-7j External electrode conductor

Claims (3)

[Claims] [Claim 1] A plurality of ceramic capacitor-type electrostrictive elements in which piezoelectric ceramic members and internal electrode conductors are alternately laminated and each internal electrode is alternately connected to two external electrodes are stacked and bonded, and electrically A piezoelectric actuator comprising electrostrictive elements connected in parallel, the piezoelectric actuator comprising a protection circuit electrically connected to the electrostrictive elements. 2. The piezoelectric actuator according to claim 1, wherein the protection circuit is connected in series to each of the stacked electrostrictive elements. 3. The piezoelectric actuator according to claim 1, wherein the protection circuit is connected in series to a lead wire to which electrostrictive elements are connected in parallel.