JPH0132755Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric bimorph element that prevents deformation over time when the piezoelectric bimorph element is driven.

In general, a bimorph element among piezoelectric displacement elements is an element that uses transverse effect displacement, and operates by using the elongation and contraction displacements of two elements as strain displacements. Since the amount of deflection can be large compared to the applied voltage, it is applied to various devices.

Conventionally, a common drawback of this type of piezoelectric displacement element is that the displacement is highly hysterical and the amount of displacement is unstable over time. In other words, in order to obtain huge displacement, a material must have a large piezoelectric d-constant as a characteristic value, but piezoelectric ceramics based on zircon/lead titanate with a large piezoelectric d-constant generally have a low Curie point and spontaneous polarization. This is because the instability of Furthermore, in a piezoelectric bimorph that maintains a voltage applied state under certain conditions, the amount of deflection may gradually increase. Furthermore, changes in the piezoelectric constant due to temperature changes and temporal fluctuations in the power supply voltage also cause changes in the displacement of the piezoelectric bimorph element. Therefore, in bimorph devices that need to maintain a constant amount of displacement over a long period of time, complicated methods such as detecting deviations in displacement, feeding back the detected deviations, and controlling applied voltage to correct deviations in displacement are required. Control systems have become essential.

In view of this, in order to constantly correct the amount of displacement over time of the piezoelectric bimorph element, the present invention divides the bimorph drive electrode and provides a contact point protruding from each electrode to create a time contact that causes a deflection amount exceeding a set value. The main purpose of this invention is to propose a piezoelectric bimorph element that eliminates the need for special applied voltage control or control based on the temporal displacement of applied voltage by configuring the drive of the bimorph to be stopped depending on the distance between .

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a perspective view showing an example of the bimorph device of the present invention. 1 and 2 indicate piezoelectric bimorphs,
This has an elastic metal plate 3 interposed in the middle. Incidentally, the polarization direction of the bimorph elements 1 and 2 is set in the thickness direction, as shown in FIG. The bimorph element 1 is provided with first and second electrodes 1a and 1b, respectively, which divide approximately the middle position. Note that the electrodes of the bimorph element 2 are provided over the entire surface. The electrodes 1a of the bimorph element 1 and the electrodes of the bimorph element 2 are connected in common, and power is applied between them and the leads from the elastic metal plate 3. Further, one end of the first electrode 1a and the second electrode 1b is connected to the electrode 1a, 1b, respectively.
A first conductor 4a and a second conductor 4b are provided, which are fixed to each other and whose free ends are in contact with opposing conductors. It is preferable to use elastic conductors such as phosphor bronze for the first and second conductors 4a and 4b. As shown in FIG. 2, the bimorph element configured in this way is made to elongate on the piezoelectric ceramic plate 1 by applying a negative voltage to the piezoelectric ceramic plate 1 side and a positive voltage to the elastic metal plate 3 side. At the same time, a shrinkage stress is generated in the piezoelectric ceramic plate 2,
Therefore, a bending deformation occurs with the elastic metal plate 3 located at the center serving as a neutral line. Note that the direction of the deformation is the direction shown by arrow X. This displacement increases or decreases in proportion to the applied voltage. In this case, when the applied voltage is increased, the displacement of the bimorph element gradually increases, but when a certain displacement is reached, the contact between the first and second conductors 4a and 4b is broken, as shown in FIG. As a result, the piezoelectric change in the piezoelectric ceramic plate 1 located at the second electrode 1b disappears, and the electric charge at the electrode 1b starts spontaneous discharge, and the voltage between the electrode 1b and the internal electrode gradually decreases, which The stress caused by elongation is alleviated. Therefore, the amount of deflection of the bimorph element gradually returns, and the first and second conductors 4a and 4b come into contact again. For this reason, electrode 1b is again
Electric charge is accumulated in the piezoelectric layer to generate piezoelectric displacement, and thus the bimorph element of the present invention can limit the amount of deflection within a certain displacement value range. Therefore, even if the applied voltage varies, the amount of displacement is always kept constant. Moreover, the displacement of the bimorph element itself over time is also controlled by the first and second conductors 4a,
It becomes possible to maintain a constant amount of deflection depending on the contact distance of 4b.

FIG. 3 is a diagram showing another example of the present invention. In this example, the electrodes of the first piezoelectric ceramic plate 9 are divided into many parts, and each has contacts 9a, 9b, 9c,
9d is provided. The other structure is almost the same as the example shown in FIG. Therefore, by applying a predetermined voltage, a certain piezoelectric displacement is generated,
Therefore, the contact points 9a, 9b, 9c, and 9d are spaced apart and maintain a constant displacement.

As described above, according to the present invention, in a piezoelectric bimorph element consisting of first and second piezoelectric ceramics polarized in the thickness direction, the electrode of the first piezoelectric ceramic is divided into a plurality of parts, and the plurality of electrodes are divided into a plurality of parts. The piezoelectric ceramics are electrically connected to each other through contacts, and a voltage is applied in a direction that extends in the length direction to the first piezoelectric ceramic and causes the second piezoelectric ceramic to contract in the length direction, respectively, so as to cause flexural deformation. As a result, the temporal hysteresis, which is a common drawback of piezoelectric bimorph elements, can be improved, and the bimorph element of the present invention can accurately maintain the set displacement amount even when the power supply voltage fluctuates. can. Therefore, the present invention is extremely suitable when applied to a device that needs to maintain a constant amount of displacement over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a piezoelectric bimorph element showing an example of the present invention. FIG. 2 is a diagram for explaining the operation of the bimorph device according to the present invention, and FIG. 3 is a diagram showing another example of the present invention. DESCRIPTION OF SYMBOLS 1... First piezoelectric ceramic plate, 2... Second piezoelectric ceramic plate, 3... Elastic metal plate, 4a, 4b... Electrical contacts.

Claims (1)

[Scope of utility model registration request] In a piezoelectric bimorph element made of first and second piezoelectric ceramics polarized in the thickness direction, the electrode of the first piezoelectric ceramic is divided into a plurality of parts, and the plurality of electrodes are electrically coupled through contacts, and the 1. A piezoelectric bimorph element, characterized in that a voltage is applied to a first piezoelectric ceramic in a direction that causes contraction in the length direction, thereby causing bending deformation.