JPH0258384A - Laminated type piezoelectric element - Google Patents

Abstract

PURPOSE:To radiate heat generated by high speed driving to the outside so as to restrain the temperature rise of an element, and to decrease the lowering of displacement amounts attendant upon the temperature rise of the element by jutting out an internal electrode layer from the periphery of a piezoelectric material layer so as to put it in structure that an element itself has a radiation plate. CONSTITUTION:Cylindrical internal electrode layers 2A and 28 which are made in diameters larger than that of a piezoelectric material layer 1 so that they may jut out from the periphery of the piezoelectric material layer 1 are laminated alternately so as to constitute a laminated type piezoelectric element. External electrode layers 3A and 3B are connected to the internal electrode layers 2A and 2B, respectively, on alternate layers through holes which are opened alternately right and left in the internal electrode layers 2A and 2B. Voltage is applied to between the internal electrode layers 2A and 2B through the external electrode layers 3A and 3B. By making the internal electrode layers 2A and 2B of metallic foils, the heat generated in the piezoelectric material layer is transmitted efficiently to the internal electrode layer, and further by jutting out this internal electrode layer from the periphery of the piezoelectric material layer, it is made to effect the role of a radiation plate so as fo radiate the heat positively to the outside.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a laminated piezoelectric element used as an actuator.

[Conventional technology]

With the rapid development of mechatronic equipment, actuators used in this field are attracting attention. Currently, the majority of actuators are driven by electromagnetic force, which not only consumes a large amount of power but also generates heat and electromagnetic noise.Therefore, there is a desire to develop actuators that can replace this. On the other hand, actuators that utilize the piezoelectric effect of a solid state not only can overcome the drawbacks of actuators that are essentially electromagnetic, but also have the advantage of being small, lightweight, and resistant to vibrations and shocks. This piezoelectric actuator consists of a large number of piezoelectric plates stacked in layers. There is a stacked piezoelectric element driven by longitudinal effect. This multilayer piezoelectric element directly utilizes the piezoelectric longitudinal effect, so it has excellent features such as fast response speed and large generated force, and can be used for high-speed processing such as engraving. Proposed. FIG. 3 shows a conventional general configuration of such a laminated piezoelectric element. In FIG. 3, 11 is a piezoelectric material layer made of piezoelectric ceramics, 12A and 12B are internal electrode layers, and 13A and 13B are external electrode layers. In such a laminated piezoelectric element, the external electrode jiJ13A, 1
Internal electrode layer 12A of each piezoelectric material Jill through 3B
, 12B, each piezoelectric material layer 11 expands and contracts due to the piezoelectric longitudinal effect, and the laminated piezoelectric element is displaced in the sewing direction as a sum total.

[Problem to be solved by the invention]

By the way, in a laminated piezoelectric element having such a configuration, in order to increase the amount of displacement as much as possible, a ceramic material having a large dielectric constant, which is a parameter directly related to the amount of displacement when voltage is applied, is selected. As a result, ceramic materials are used that have a low temperature at which they no longer exhibit piezoelectricity, the so-called Curie temperature. On the other hand, if the dielectric constant is large, heat will be generated when driven at high speed, but piezoelectric ceramics generally have a soft crystal lattice, so they have poor thermal conductivity, and the generated heat is accumulated internally, causing a rise in the temperature of the element itself. easy. However, since the laminated piezoelectric element is constructed using a ceramic material with a low Curie temperature as described above, there is a problem in that an increase in the temperature of the element leads to a decrease in displacement. Figure 4 shows this situation. When the multilayer piezoelectric element shown in Figure 3 is driven at a frequency of, for example, 50 seconds, the element temperature rises in just about 20 seconds, and the amount of displacement returns to its initial value. This shows a significant decrease from X0. It is an object of the present invention to provide a multilayer piezoelectric element that suppresses the temperature rise of the multilayer piezoelectric element and provides a stable displacement amount even when driven at high speed.

[Means to solve the problem]

In order to achieve the above object, the present invention has piezoelectric material layers and internal electrode layers stacked alternately, and a voltage is applied between the internal electrode layers via an external electrode layer to cause the piezoelectric material layers to expand and contract. In the laminated piezoelectric element, the internal electrode layer is formed of metal foil, and the internal electrode layer is made to protrude from the outer peripheral surface of the piezoelectric material layer.

[For use]

By forming the internal electrode layer with metal foil, the heat generated in the piezoelectric material layer is efficiently transferred to the internal electrode layer, and by making the internal electrode layer protrude from the outer peripheral surface of the piezoelectric material layer, it can function as a heat sink. This allows heat to be actively dissipated to the outside.

【Example】

FIG. 1 is a schematic sectional view showing an embodiment of the invention. In FIG. 1, 1 is a disc-shaped piezoelectric material layer made of piezoelectric ceramics, and 2A and 2B are made of metal foil, which are formed to have a larger diameter than the piezoelectric material layer 1 so as to protrude from the outer peripheral surface of the piezoelectric material N1. These disc-shaped internal electrode layers are stacked alternately as shown in the figure to constitute a stacked piezoelectric element. 3A and 3B are external electrode layers, and internal electrodes N2A, 2
Every other layer is connected to the internal electrode layers 2A and 2B through holes formed alternately on the left and right sides of B. An external electrode layer 3A is provided between the internal electrode layers 2A and 2B. A voltage is applied through 3B. Such a laminated piezoelectric element is formed as follows. First, a raw material powder of lead zirconate titanate piezoelectric ceramics having a Curie temperature of around 130°C and a displacement of 0.1% at room temperature with respect to an electric field strength of 1 kV/mm is mixed with a binder such as polyvinyl alcohol. This is then dried by a spray drying method to obtain a powder for pressing having a particle size of about 100 μm. Therefore, press molding is performed using this press powder to obtain a piezoelectric ceramic molded body having a diameter of 40 m and a thickness of 2 mm. This molded body is fired at a temperature of 1200° C. for 2 hours, and then polished to obtain a piezoelectric ceramic plate having a diameter of 30 mm and a thickness of 1 cylinder. Therefore, silver electrode paste is applied to both the front and back surfaces of the piezoelectric ceramic plate and baked to form the piezoelectric material layer 1. Next, the internal electrode layers 2A and 2B are made with a diameter of 50 mm and a thickness of 0.
．． Disks of metal foil with holes of 2 mm in diameter are prepared and laminated alternately with piezoelectric ceramic plates. At this time, the holes made in the metal foil for passing the external electrode layers 3A and 3B are aligned in opposite directions every other layer. Finally, external electrode layer 3
Connect the metal foils every other layer using conductors A and 3B. The laminated piezoelectric element configured in this way has a piezoelectric material layer 1
When a voltage of 1 kV is applied to a stack of 100 sheets, a displacement of about 100 μm occurs. Here, set the voltage to 5
FIG. 2 shows the relationship between temperature change and displacement of the element with respect to time when a 0 Hz sine wave is used. According to FIG. 2, it can be seen that due to the heat dissipation effect of the internal electrodes N2A and 2B, the temperature rise of the element is suppressed and the fluctuation in the amount of displacement is reduced.

【Effect of the invention】

According to this invention, the internal electrode layer is formed of gold gI4 foil, and the internal electrode layer is made to protrude from the outer peripheral surface of the piezoelectric material layer so that the element itself has a heat dissipation plate. It is possible to easily dissipate heat generated by high-speed driving of the piezoelectric element to the outside, thereby suppressing a rise in the temperature of the element, and reducing a decrease in the amount of displacement due to a rise in the temperature of the element.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention, FIG. 2 is a diagram illustrating the relationship between time, temperature, and displacement in the laminated piezoelectric element shown in FIG. 1, and FIG. 3 is a conventional example. FIG. 4 is a diagram illustrating the relationship between time, temperature, and displacement in a conventional example. ■... Piezoelectric material layer, 2A, 2B... Internal electrode layer, 3
A, 3B...external electrode layer. Figure 1 Figure 3eT11 (excerpt) Gin (excerpt) Figure 2

Claims (1)

[Claims] 1) In a laminated piezoelectric element in which piezoelectric material layers and internal electrode layers are alternately laminated, and the piezoelectric material layers expand and contract by applying a voltage between the internal electrode layers via an external electrode layer, the internal electrode layers What is claimed is: 1. A laminated piezoelectric element characterized in that the internal electrode layer is made of metal foil and that the internal electrode layer protrudes from the outer peripheral surface of the piezoelectric material layer.