JPH0430482A - Laminated type piezoelectric actuator - Google Patents

Abstract

PURPOSE:To protect a piezoelectric actuator against mechanical self-damage even if a voltage is applied to it by a method wherein the dimension of the actuator in an axial direction in which a piezoelectric longitudinal effect is induced is 1/3 as large as that in a direction vertical to the axial direction concerned, and a mechanism which gives a compression bias in an axial direction in which a piezoelectric longitudinal effect is induced is provided. CONSTITUTION:Three laminated type piezoelectric actuators 1 of partial electrode structure are stacked up and bonded into an integral structure with bonding agent 2, and the laminated actuators 1 are sandwiched between two brass plates 2a and 2b and tightened up by four bolts 4 and four nuts 5 to be given a compression bias. The actuator 1 is 20 mm square in cross section and 6 mm in thickness. When a direct voltage of 100 V is applied to the single actuator 1 to drive it, a height displacement of 3 mum or so at its maximum is induced at the center of the side face of the actuator 1. The amount of the compression bias is so set as to enable the three-layered actuator to shrink by 9 mum in height as compared with that before it is given a compression bias. By this setup, an actuator of this design can be protected against mechanical damage and produce a large displacement even it is small in volume through the combination of three actuators, and the lower end face of it con be displaced in parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an actuator that utilizes piezoelectric effects.

[Prior Art] FIG. 3 is a perspective view of an example of a conventional laminated piezoelectric actuator having a partial electrode structure, and FIG. 4 shows a cross-sectional structure taken along cut plane A in FIG. 3. In the figure, 31 is piezoelectric ceramics;
32 is a metal internal electrode embedded in a layered manner in ceramics, and 33 is a metal external electrode. Each metal internal electrode 32 is electrically connected in parallel by a pair of metal external electrodes 33 provided on the side surface of the actuator.

When a voltage is applied between the pair of external electrodes, the actuator expands in the height direction due to the piezoelectric longitudinal effect.

[Problems to be Solved by the Invention] By the way, in the internal electrode configuration of such an actuator, as is clear from FIG.
b) is smaller than the cross-sectional area (aXa) of the actuator. Since each internal electrode is electrically connected to the external electrode, the internal electrodes overlap in the upward and downward directions only at the center of the actuator. Therefore, when a voltage is applied to the external electrode pair, the electric field strength is large at the center of the actuator, and is small at the periphery.

As a result, the displacement distribution on the upper and lower end surfaces of the actuator becomes as shown in FIG. That is, FIG. 5 schematically shows the deformation that occurs when the lead wire 54 is taken out from the pair of metal external electrodes 52 and a DC voltage is applied between the electrode terminals 55, using dotted lines. Since piezoelectric strain occurs in proportion to the electric field strength, a large piezoelectric strain occurs in the central region where the electric field strength is high, and piezoelectric strain also decreases in the peripheral region because the electric field strength is low. Therefore, even when a voltage is applied in a free state without mechanical restraint, stress is generated inside the actuator, causing the problem of self-destruction of the actuator.

Further, such non-uniform deformation is also undesirable in practice.

The present invention was made to solve such problems, and an object of the present invention is to provide a piezoelectric actuator that does not mechanically self-destruct even when a voltage is applied.

[Means for Solving the Problems] The present invention provides a laminated piezoelectric actuator with a partial electrode structure, characterized in that the dimension in the axial direction where piezoelectric longitudinal effect strain occurs is one-third or less of the dimension in the vertical direction. , and a laminated piezoelectric actuator having a partial electrode structure, characterized in that it is equipped with a mechanism for applying a compressive bias in the axial direction of generation of piezoelectric longitudinal effect strain, and the dimension of the axial direction of generation of piezoelectric longitudinal effect strain is perpendicular to this. A plurality of laminated piezoelectric actuator elements having a partial electrode structure with a size of one-third or less of the size are stacked and integrated in the direction of the piezoelectric longitudinal effect strain generation axis, and are equipped with a mechanism that applies a compressive bias in the piezoelectric longitudinal effect strain generation axis direction. This is essential for piezoelectric actuators that are characterized by

[Operation] It is known that the amount of displacement generated due to the piezoelectric longitudinal effect of a laminated piezoelectric actuator having a partial electrode structure is about 0.1% of the height dimension.

In the present invention, this height dimension is set to one-third or less of the dimension a in the direction perpendicular to this height dimension. As a result, internal stress is structurally relaxed, and mechanical destruction does not occur even when large-amplitude driving is performed.

In addition, a compression bias mechanism is provided in the direction of the displacement generation axis, and when a voltage is applied with compression bias applied, the actuator deforms to return to its original state without compression bias applied, so the end surfaces of the actuator are parallel to each other. Moving. Furthermore, since the generation of tensile stress can be prevented, the actuator will not be mechanically destroyed.

In addition, for actuators that require large displacements,
The dimension in the axial direction where piezoelectric longitudinal effect strain occurs must be set large, but as mentioned above, in order to prevent self-destruction of the actuator, it is desirable to set the lateral dimension a to at least three times h. Therefore, there is a disadvantage that an actuator for obtaining a large displacement is necessarily large in size.

To solve this problem, as shown in FIG. 6(a), a plurality of laminated piezoelectric actuators 61 having a partial electrode structure that does not cause self-destruction are stacked and bonded together with an adhesive 63, and each external electrode pair 62 There is also a method of connecting the actuators 61 in parallel with lead wires 64 and applying a voltage to the electrode terminals 65 to drive them, but in this case, as schematically shown in FIG. This has the disadvantage that the bonded interface is mechanically destroyed as shown in the figure due to the severe deformation. Even in such a case, if a compression bias mechanism is provided in the direction of the displacement generation axis and a voltage is applied with the compression bias applied, the upper and lower end surfaces of each actuator will be displaced in parallel due to the application of voltage. Mechanical destruction of joint surfaces is prevented.

[Example] Examples of the present invention will be described in detail below.

Example 1 To explain this example with reference to FIGS. 3 and 4, the piezoelectric ceramic 31 contains Pb (Zr, T i )0
3 (PZT) based piezoelectric ceramics were used.

The cross section was a square with one side a, and a = 4.5 mm. The height h was varied within a range of 0.5 to 4.0 mm. For the internal electrode 32, a platinum film with a thickness of about 2 μm was used.

The internal electrode 32 was a square with one side b, and b = 3.5 mm. The interval d between the internal electrodes was approximately 0.1 mm.

The method for manufacturing this actuator will be briefly explained below.

First, a small amount of polyvinyl alcohol and dioctyl heptatalate was added to PZT-based piezoelectric ceramic powder and dispersed in ethyl alcohol to prepare a slurry. This was produced using a thick film manufacturing device based on the doctor blade method until the thickness was approximately 0.
It was processed into a 12 mm thick film. A platinum paste film was printed and coated on one surface of this thick film, and these were stacked and pressed together using a hot press to fix them together. This laminate was first heated at 450°C for 24 hours to thermally decompose the organic substances contained therein. It was then sintered at 1200'C for 1 hour. Silver paste was baked onto the side surface of this sintered body as an external electrode.

The height of the actuator is 0.5゜1.0 respectively.
．． 1.5. 2.0. 10 each of 3.0 mm
(A rigid structure was made, and a DC voltage of 60 V was applied between the pair of external electrodes. In this case, no mechanical damage was observed in any of the actuators. Next, when a voltage of 100 V was applied, = 0.5. 1.0. 1.5m
No mechanical breakdown occurred in the actuator of No. m after 100 hours of voltage application. However, 6 out of 10 actuators with h=2.0 mm were mechanically broken along the internal electrode layer. Furthermore, all actuators with h=3.0 mm were mechanically destroyed.

As is clear from the above examples, in a laminated piezoelectric actuator with a partial electrode structure, if the height dimension and the lateral dimension a satisfy the relationship h/a≦1/3, the mechanical It cannot be destroyed.

Embodiment 2 FIG. 2 is a side view of an example of a laminated piezoelectric actuator having a partial electrode structure with a compression bias pressing mechanism according to the present invention. The laminated piezoelectric actuator 21 with a partial electrode structure is
It is sandwiched between two brass plates 22a and 22b, and compressive bias is applied to the actuator 21 using four bolts 24 and nuts 25.

The dimensions of the piezoelectric actuator 21 are 20 x 20 in cross section.
It had a length of 111 m and a height of 20 mm, and was manufactured in the same manner as in Example 1. 10 in a free state with no mechanical constraints.
When a voltage of 0V is applied, a maximum displacement of about 17 μ is generated in the height direction. The dimensions of the brass plates 22a and 22b are 30
It was set to 30 x 7 mm. The bolt 24 was made of stainless steel with a diameter of 3 mm. The size of the compression bias is 17 u! in the height direction of the actuator! It is adjusted to shrink by n.

When a DC voltage of 100V was applied to the actuator equipped with the above compression bias pressurizing mechanism, the actuator expanded by about 17uIr1, and the two brass plates 22a
, 22b moved upward and downward in parallel.

Further, although a DC voltage was continuously applied for 1000 hours, no phenomenon of mechanical destruction of the actuator was observed.

For comparison, when a DC voltage of 100 V was applied to the laminated piezoelectric actuator with the partial electrode structure used in the example in a free state without mechanical restraint, it was mechanically destroyed in about 10 minutes.

Embodiment 3 FIG. 1 is a side view of another example of a piezoelectric actuator with a compression bias pressurizing mechanism according to the present invention.

Three laminated piezoelectric actuators 1 with a partial electrode structure are stacked and integrated using an adhesive 3, and then bonded to two brass plates 2a.
and 2b, and four bolts 4 and nuts 5 apply compression bias to the actuator.

Each partial electrode structure layered piezoelectric actuator has two sides.
It has a square cross section of 0 mm and a height of 6 mm. When this single actuator is driven by applying a DC voltage of 100 V, a displacement in the height direction of about 3 periods at maximum occurs at the center of the end face of the actuator. The dimensions of brass plates 2a and 2b are 30
The dimensions were 30 x 7 mm. Bolt 4 has a diameter of 3mm
Made of stainless steel. The magnitude of the compressive bias is adjusted so that the height of the three integrated actuators is reduced by approximately 911 In from the state before the compressive bias is applied.

When a DC voltage of 100 V was applied to the actuator equipped with the above compression bias pressurizing mechanism and three actuators were simultaneously driven, the distance between the two brass plates 2a and 2b moved away from each other in parallel for about 8 μs. In this state, a DC voltage of 100 V was continuously applied for more than 1000 hours, but no mechanical damage was observed in the actuator.

[Effects of the Invention] As explained above, according to the present invention, by appropriately setting the dimensions and shape of the actuator, or by applying a compressive bias, it is possible to create a partial electrode structure that does not break mechanically. It becomes possible to provide a laminated piezoelectric actuator. In addition, by combining the two, it is possible to generate a large displacement with a small volume, and in addition,
A piezoelectric actuator is provided that allows the lower end surface to be displaced in parallel.

[Brief explanation of drawings]

1 and 2 are side views of an embodiment of the present invention, FIG. 3 is a diagonal view of an example of a laminated piezoelectric actuator with a partial electrode structure, and FIG. 4 is a cross section taken along plane A in FIG. 3. Figure 5 is an explanatory diagram schematically showing the state when a DC voltage is applied to a laminated piezoelectric actuator with a partial electrode structure, and Figure 6 is an explanatory diagram that schematically shows the state when a DC voltage is applied to a laminated piezoelectric actuator with a partial electrode structure. , is an explanatory diagram schematically showing a state when driven with a DC voltage. "l, 21.51.61...Laminated piezoelectric actuator 2a, 2b, 22a, 22b...Brass plate 3.63...Adhesive 4.24...Bolt 5, 25...Nut 31 ...Piezoelectric ceramics 3?...Metal internal electrodes 33, 52.62...Metal external electrodes 54, 64...Lead wires 55, 65...Electrode terminals

Claims (3)

[Claims] (1) A laminated piezoelectric actuator having a partial electrode structure, characterized in that the dimension in the axial direction where piezoelectric longitudinal effect strain occurs is one-third or less of the dimension in the vertical direction. (2) A laminated piezoelectric actuator with a partial electrode structure, characterized by being equipped with a mechanism for applying a compressive bias in the direction of the axis where piezoelectric longitudinal effect strain occurs. (3) A plurality of laminated piezoelectric actuator elements having a partial electrode structure in which the axial dimension where piezoelectric longitudinal effect strain occurs is one-third or less of the vertical dimension thereof are stacked together in the axial direction where piezoelectric longitudinal effect strain occurs. A laminated piezoelectric actuator characterized by having a mechanism for applying a compressive bias in the direction of the piezoelectric longitudinal effect strain generation axis.