JPH04109558U - Laminated piezoelectric actuator - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent cracks from occurring and improve durability and reliability by making the amount of displacement in the piezoelectric plate of a laminated piezoelectric actuator uniform at all locations. [Structure] Piezoelectric plate 1 whose thickness gradually decreases from the center to the outer periphery
A piezoelectric element pellet 18 has an internal electrode layer formed by printing and baking silver paste 12 so that the thickness including the piezoelectric plate 11 is uniform on the top and bottom surfaces of the piezoelectric element pellet 18, and an internal electrode layer provided with a terminal for external extraction. A large number of electrode plates 13 are alternately stacked.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention provides a piezoelectric element pellet with an internal electrode layer formed on the laminated surface of the piezoelectric plate. The present invention relates to a stacked piezoelectric actuator of a type in which a plurality of piezoelectric actuators are stacked with a plurality of electrode plates interposed therebetween.

0002

[Conventional technology]

For example, in Japanese Patent Application Laid-open No. 60-121784, there is a gap between the piezoelectric plate and the internal electrode plate. A product configured to bond the two with a conductive metal paste interposed between them. Layered piezoelectric actuators have been proposed. This conventional technology will be explained based on FIG. do. FIG. 7 is a side view showing the overall configuration of a conventional laminated piezoelectric actuator B. In the figure, 1 is a piezoelectric plate with a thickness of about 0.5 mm, and 2 is a conductive plate printed on the laminated surface of the piezoelectric plate. paste, such as silver paste. 3 has a terminal 4 for external extraction It is an internal electrode plate, and 6a is a lead connected to the positive electrode, and 6b is a lead connected to the negative electrode. It is a line. The piezoelectric plate 1 and the internal electrode plate 3 are arranged alternately when the silver paste 2 has adhesive ability. These piezoelectric plates 1 and internal electrode plates 3 are connected by the adhesive action of silver paste 2. After drying, it is heat-treated and molded into one piece. In addition, the terminal of the internal electrode plate 3 4 is set at a position shifted by 180 degrees from the terminal 4 of the adjacent internal electrode plate 3. The terminal 4 of the internal electrode plate 3 is bent in the axial direction and connected to the end of the adjacent internal electrode plate 3. It interferes with the child 4 and is electrically connected by spot welding at the interference point. in this way A shaft of a laminated piezoelectric actuator B in which a plurality of piezoelectric plates 1 and internal electrode plates 3 are laminated. A lead wire 6a connected to the positive electrode of the power source is connected to the first set of terminals 4 connected in the direction. The second set of terminals 4 installed and 180° shifted from the first set of terminals 4 has a A lead wire 6b connected to the negative electrode is attached.

0003

[Problem that the idea aims to solve]

By the way, the laminated type structure described in the above-mentioned Japanese Patent Application Laid-Open No. 60-121784 When a piezoelectric actuator is driven, the temperature of the piezoelectric plate itself increases due to the heat generated by the drive. do. However, since the outer periphery of the actuator is in contact with the atmosphere, it Good heat dissipation. Therefore, a temperature difference occurs between the center part and the outer peripheral part of the piezoelectric plate. In general, the displacement of piezoelectric materials increases as the temperature rises, so the amount of heat dissipated is small. The center part of the piezoelectric plate, which is at a high temperature, has a larger displacement than the outer peripheral part. This kind of condition If the actuator continues to be driven at There is a problem in that the piezoelectric plate becomes uniform and a crack occurs in the center of the piezoelectric plate.

0004 This invention aims to reduce the amount of displacement due to the influence of temperature on the piezoelectric plate by changing the thickness of the piezoelectric plate. The durability and reliability of the laminated piezoelectric actuator can be improved by offsetting the The purpose is to raise

[0005]

[Means to solve the problem]

The laminated piezoelectric actuator of the present invention that achieves the above object has a structure that On the laminated surface of the piezoelectric plate whose thickness gradually decreases, the thickness including the piezoelectric plate is made uniform. A piezoelectric element pellet with a conductive internal electrode layer and an end for external extraction. It is characterized in that a plurality of internal electrode plates with electrodes are alternately stacked.

[0006]

[Effect]

According to the structure of the laminated piezoelectric actuator according to the present invention, the piezoelectric actuator with a small amount of heat radiation The center part of the plate has a higher temperature than the outer peripheral part, so the displacement becomes larger. However, pressure When the same voltage is applied to the entire electric plate, the thicker the piezoelectric plate, the more electric current per unit thickness. Since the pressure is lower, by making the center of the piezoelectric plate thicker than the outer circumference, The displacement of the outer peripheral portion can be made smaller than the displacement of the outer peripheral portion. Therefore, the total displacement due to temperature and thickness can be calculated as can be made the same at the outer periphery, making the displacement of the piezoelectric plate uniform during continuous operation. This prevents the piezoelectric plate from cracking due to stress concentration.

[0007]

【Example】 Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 shows the configuration of an embodiment of the laminated piezoelectric actuator A of the present invention. be. In the figure, 11 is a piezoelectric plate, 12 is a silver paste, 13 is an internal electrode plate, 14 is a terminal of the internal electrode plate 13, 15 is an insulating plate, and 16a is a lead wire connected to the positive electrode. , 16b is a lead wire connected to the negative electrode, and 17a is a lead wire connected to the positive electrode side. 17b shows the lead plate connected to the lead wire on the negative electrode side. .

[0008] Next, the manufacturing process of this laminated piezoelectric actuator A will be explained. Each piezoelectric plate 11 to be laminated is first made of a piezoelectric material containing Pb, Zr, and Ti as main components. were mixed and formed into a disk shape using a press machine. Next, this press-formed product It was fired at a firing temperature of 1300°C and then ground to the dimensions shown below.

First, as shown in FIG. 2, the diameter t ₁ of the piezoelectric plate 11 was set to 20 mm, and the thickness t ₂ of the outer periphery of the piezoelectric plate was set to 0.5 mm. Next, the thickness _t3 of the center portion of the piezoelectric plate was set as follows because it is necessary to offset the amount of displacement due to the influence of temperature with the amount of displacement due to thickness. In general, the amount of heat dissipated from the center of a stacked piezoelectric actuator is smaller than the amount of heat dissipated from the piezoelectric plates at both ends in the axial direction, so the piezoelectric plate at the center has a higher temperature than the piezoelectric plates at both ends. It is known that when viewed as a single piezoelectric plate, the radial center part of the piezoelectric plate is always higher in temperature than the outer peripheral part, and that there is a substantially constant temperature difference regardless of the stacking position. When actually measured, there was a temperature difference of about 7° C. between the center and the outer circumference of the piezoelectric plate, regardless of the lamination position. Therefore, in a piezoelectric plate (uniform thickness) having the same dimension as the thickness t ₂ of the outer peripheral part of the piezoelectric plate of this example, that is, a thickness of 0.5 mm, how much the displacement increases when the temperature rises by 7°C is as follows. An internal electrode plate was attached to the piezoelectric plate, and a voltage of 800V was applied to investigate. The results are shown in FIG. This figure shows that when the temperature increases by 7°C, the displacement increases at a rate of approximately 2.8%. The relationship between temperature and displacement was also investigated in the same manner when the piezoelectric plate was made even thicker. As a result, it was found that there is a similar trend between temperature and displacement.

Based on these results, FIG. 6 shows the relationship between the thickness and displacement of the piezoelectric plate when the temperature of the piezoelectric plate is 20° C. and 27° C. From this figure, it can be seen that when the temperature of the piezoelectric plate is constant, the displacement decreases as the thickness of the piezoelectric plate increases. This is due to the fact that the thicker the piezoelectric plate, the smaller the voltage per unit thickness. Therefore, in the case of this example, since the thickness _t2 of the outer peripheral part was initially set to 0.5 mm, the displacement amount when the piezoelectric plate was 0.5 mm thick and the temperature was 20 degrees Celsius was calculated as shown in FIG. Reading from the graph shows that it is 35 μm. That is, the total amount of displacement due to the influence of temperature and the amount of displacement due to thickness of the outer peripheral portion of the piezoelectric plate is 35 μm. On the other hand, based on the fact that there is a temperature difference of 7°C between the center and the outer periphery of the piezoelectric plate, we can read from the graph at 27°C how thick the piezoelectric plate is when it is displaced by 35 μm at 27°C. It can be seen that the thickness is 0.55 mm. That is, in order to make the sum of the amount of displacement due to the influence of temperature and the amount of displacement due to thickness at the center of the piezoelectric plate the same as that at the outer periphery, the thickness should be set to 0. This means that 55mm would be fine. From the above, in order to offset the amount of displacement due to the influence of temperature with the amount of displacement due to thickness, the thickness _t3 of the center portion of the piezoelectric plate of this example was set to 0.55 mm.

Next, as shown in FIG. 3, a silver paste 12 is applied to the laminated surface of the piezoelectric plate 11 so that the diameter t ₄ is 18 mm and the thickness t ₅ is 0.56 mm at all locations including the piezoelectric plate 11. was printed and baked to obtain a piezoelectric element pellet 18. Fifty layers of the piezoelectric element pellets 18 and internal electrode plates 13 were alternately stacked, and insulating plates 15 were installed at both ends in the axial direction. As shown in FIG. 4, the internal electrode plate 13 has a diameter of 18 mm and includes a terminal 14 that protrudes from the outer circumference of the piezoelectric element pellet 18 after lamination, and this terminal is connected to the terminal 14 of the adjacent internal electrode plate 13. are stacked on the piezoelectric element pellet 18 so that they are oriented 180 degrees apart. Thereafter, the terminals 14 protruding every other layer from each side surface are bent in the axial direction of the piezoelectric element pellet 18 and spot welded to the flat lead plates 17a and 17b, respectively. Then, a lead wire 16a connected to the positive electrode of the power source is attached to the first lead plate 17a joined to the first set of terminals 14, and a second lead 16a is attached to the first lead plate 17a, which is shifted by 180 degrees from the first lead plate. A lead wire 16b connected to the negative electrode is attached to the plate 17b.

[0012] The laminated piezoelectric actuator A thus completed was pulse-driven at an applied voltage of -20 to 600V. As a result, while a conventional laminated piezoelectric actuator with a piezoelectric plate having a uniform thickness cracked after 1×10 ⁶ cycles, this example showed no abnormality even after being driven 1×10 ⁸ times. I was not able to admit. Also, if there is a temperature difference between the center and the outer periphery of the piezoelectric plate that is greater than this example, the thickness should be made thicker taking into account the amount of displacement due to the influence of temperature, and conversely, if the temperature difference is small, the thickness should be increased. It goes without saying that the same effect can be obtained by making it thinner.

[0013] As explained above, according to the laminated piezoelectric actuator of the present invention, the influence of temperature The amount of displacement due to sound can be offset by the amount of displacement due to thickness, and the amount of displacement within the piezoelectric plate is reduced. This makes it possible to prevent cracks from occurring in the center of the piezoelectric plate.

[0014]

[Effect of the idea]

According to the laminated piezoelectric actuator of the present invention, during continuous operation, the piezoelectric plate By offsetting the amount of displacement due to temperature with the amount of displacement due to the thickness of the piezoelectric plate, the total Displacement can be made uniform at all locations. Therefore, the crack in the center of the piezoelectric plate The occurrence of racks is eliminated, and durability and reliability can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a laminated piezoelectric actuator of the present invention.

FIG. 2 is a side view of a piezoelectric plate used in the present invention.

FIG. 3 is a cross-sectional view of a piezoelectric element pellet used in the present invention.

FIG. 4 is a perspective view of an internal electrode plate used in the present invention.

FIG. 5 is an explanatory diagram showing the relationship between temperature and displacement when a voltage of 800 V is applied to a piezoelectric plate with a thickness of 0.5 mm.

FIG. 6 is an explanatory diagram showing the relationship between thickness and displacement at piezoelectric plate temperatures of 20° C. and 27° C.

FIG. 7 is a side view showing the overall configuration of a conventional laminated piezoelectric actuator.

[Explanation of symbols]

11... Piezoelectric plate 12... Silver paste (internal electrode layer) 13... Internal electrode plate 14... Terminal 15... Insulating board 16a... Lead wire 16b... Lead wire 17a... Lead plate 17b... Lead plate 18... Piezoelectric element pellet

Claims (1)

[Scope of utility model registration request] 1. A conductive internal electrode layer is provided on the laminated surface of a piezoelectric plate made of a piezoelectric material and whose thickness gradually decreases from the center to the outer periphery so that the thickness including the piezoelectric plate is uniform. A multilayer piezoelectric actuator characterized in that a plurality of piezoelectric element pellets and internal electrode plates each having a terminal for external extraction are alternately stacked.