piezoelectric actuator

Abstract

The piezoelectric actuator disclosed herein comprises: a piezoelectric element having a longitudinal direction; a housing having a cover, a bottom, and a cylindrical portion, and housing the piezoelectric element therein; and a strain gauge located in the cylindrical portion. The cylindrical portion has a plurality of curved portions in the longitudinal direction that bend due to the expansion and contraction of the piezoelectric element. The strain gauge is located in the curved portions.

Description

Technical Field

[0001] This disclosure relates to a piezoelectric actuator. Background Technology

[0002] As a piezoelectric actuator used in mass flow controllers, precision positioning devices for XY stages, etc., a stacked piezoelectric element disclosed in Japanese Patent Application Publication No. 63-66980 (hereinafter referred to as Patent Document 1) is known. The stacked piezoelectric element includes a piezoelectric element and a housing that houses the piezoelectric element. A strain gauge is attached to the surface of the housing, thereby enabling the displacement of the stacked piezoelectric element to be detected. Summary of the Invention

[0003] The piezoelectric actuator disclosed herein is characterized by comprising: a piezoelectric element having a long side direction; a housing having a cover, a bottom, and a cylindrical portion, and housing the piezoelectric element therein; and a strain gauge located in the cylindrical portion, the cylindrical portion having a plurality of curved portions in the long side direction that bend due to the expansion and contraction of the piezoelectric element, the strain gauge being located in the curved portions. Attached Figure Description

[0004] Figure 1 This is a schematic perspective view showing an example of a piezoelectric actuator.

[0005] Figure 2 yes Figure 1 A schematic longitudinal sectional view of an example of a piezoelectric actuator is shown.

[0006] Figure 3 This is a schematic longitudinal sectional view of another example of a piezoelectric actuator.

[0007] Figure 4 This is an enlarged cross-sectional view of the main part of another example of a piezoelectric actuator.

[0008] Figure 5 This is an enlarged cross-sectional view of the main part of another example of a piezoelectric actuator.

[0009] Figure 6 This is an enlarged cross-sectional view of the main part of another example of a piezoelectric actuator.

[0010] Figure 7 This is an enlarged cross-sectional view of the main part of another example of a piezoelectric actuator.

[0011] Figure 8 This is an enlarged cross-sectional view of another example of a piezoelectric actuator.

[0012] Figure 9 This is a schematic perspective view showing another example of a piezoelectric actuator.

[0013] Figure 10This is a schematic longitudinal sectional view showing another example of a piezoelectric actuator. Detailed Implementation

[0014] Hereinafter, embodiments of the piezoelectric actuator of this disclosure will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiments shown below.

[0015] Figure 1 The piezoelectric actuator 10 shown includes a piezoelectric element 1 and a housing 2 that houses the piezoelectric element 1 and includes a bottom 21, a cylindrical portion 22 and a cover portion 23.

[0016] like Figure 2 As shown, the piezoelectric element 1 constituting the piezoelectric actuator 10 is, for example, a piezoelectric element having a laminated body. This laminated body has an active portion formed by alternating layers of piezoelectric body layers and internal electrode layers, and an inactive portion including piezoelectric body layers at both ends in the lamination direction of the active portion. Here, the active portion is the part where the piezoelectric body layer elongates or contracts in the lamination direction during actuation, and the inactive portion is the part where the piezoelectric body layer does not elongate or contract in the lamination direction during actuation.

[0017] The laminate constituting the piezoelectric element 1 is, for example, formed as a cuboid with a length of 4mm to 7mm, a width of 4mm to 7mm, and a height of 20mm to 50mm. It should be noted that the laminate can also be, for example, a hexagonal prism or an octagonal prism.

[0018] The piezoelectric layer constituting the laminate is composed of a piezoelectric ceramic having piezoelectric properties, and the average particle size of the piezoelectric ceramic is set to, for example, 1.6 μm to 2.8 μm. As the piezoelectric ceramic, perovskite oxides composed of lead zirconate titanate (PbZrO3-PbTiO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), etc., can be used.

[0019] Furthermore, the internal electrode layers constituting the laminate are primarily composed of metals such as silver, silver-palladium, silver-platinum, and copper. For example, positive and negative electrodes are alternately arranged along the lamination direction. A positive electrode is led out from one side of the laminate, and a negative electrode is led out from the other side. According to this structure, in the active part, a driving voltage can be applied to the piezoelectric layer sandwiched between adjacent internal electrode layers in the lamination direction.

[0020] It should be noted that the laminate may also include layers used to mitigate stress, metal layers that do not function as internal electrode layers, etc.

[0021] Furthermore, external electrodes are respectively provided on a pair of opposing sides of the laminate containing the positive or negative electrode (or ground electrode) of the internal electrode layer, and are electrically connected to the internal electrode layer. The external electrodes are, for example, metallization layers containing silver and glass.

[0022] On the other hand, on the opposite side of the laminate, the positive and negative (or ground) electrodes of the internal electrode layer are exposed, and a coating layer containing an insulator is provided on this side as needed. By providing the coating layer, surface discharge between the electrodes that occurs when a high voltage is applied during driving can be prevented. Ceramic materials can be used as the insulator for this coating layer. In particular, materials that can follow the driving deformation (expansion) of the laminate when driving the piezoelectric actuator and can deform according to stress can be used to eliminate the possibility of surface discharge caused by coating peeling. Specifically, partially stabilized zirconium oxide and Ln can be used as examples, which can deform by undergoing a local phase transition and volume change when stress is generated. 1- X Si X AlO 3+0.5X (Ln represents at least one selected from Sn, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), x = 0.01 to 0.3, etc., or piezoelectric materials such as barium titanate and lead zirconate titanate, where the interionic distance within the crystal lattice changes to mitigate the resulting stress. This coating is formed, for example, by applying it to the side of a laminate through dipping or screen printing after it has been made into an ink-like form, followed by sintering.

[0023] The housing 2 constituting the piezoelectric actuator 10 includes a bottom 21, a cylindrical portion 22, and a cover portion 23. Furthermore, the housing 2 houses the piezoelectric element 1 inside, with the lower end face of the piezoelectric element 1 abutting against the upper surface of the bottom 21 and the upper end face of the piezoelectric element 1 abutting against the lower surface of the cover portion 23.

[0024] The bottom 21, the cylindrical portion 22, and the cover portion 23 can be metal bodies such as SUS304 or SUS316L. Alternatively, the bottom 21, the cylindrical portion 22, and the cover portion 23 can be formed integrally, or they can be formed by joining the separate components using known techniques such as welding or bonding.

[0025] The cylindrical portion 22 is a cylindrical body extending vertically and open at both ends. The cylindrical portion 22 has a curved portion 221 that bends due to the expansion and contraction of the piezoelectric element 1. Due to the expansion and contraction of the piezoelectric element 1, the curved portion 221 bends in a manner extending along its long side, thereby allowing it to expand and contract as a whole as the housing 2. For example, after the curved portion 221 is manufactured into a seamless tube according to a predetermined shape, it is formed into a corrugated (snake-belly) shape through rolling, hydrostatic pressing, or other processes. The cylindrical portion 22 has a predetermined spring constant so that it can follow the expansion and contraction of the piezoelectric element 1 when a voltage is applied, and its spring constant is adjusted by its thickness, groove shape, and number of grooves. For example, the thickness of the cylindrical portion 22 is, for example, 0.1 to 0.5 mm. In addition to the curved portion 221, the cylindrical portion 22 may also have a straight portion. Furthermore, multiple curved portions 221 exist in the long side direction. This allows for the dispersion of stress generated in the curved portion 221 during the expansion and contraction of the housing 2. Therefore, the possibility of stress concentration and breakage in the bending section 221 can be reduced.

[0026] The outer diameter of the cover portion 23 is formed to be the same as the inner diameter of the end side opening of the cylindrical portion 22. The cover portion 23 is inserted into the end side opening of the cylindrical portion 22, and its side (outer periphery) is joined to the inner wall near the end side opening (near the upper end) of the cylindrical portion 22 by means of welding, for example. At this time, the joint between the cylindrical portion 22 and the bottom 21 is referred to as the welded part.

[0027] The bottom 21 has, for example, a base plate and an annular protrusion erected on the base plate. The base plate is circular, and in the example shown in the attached figure, the periphery is thinner than other parts. It should be noted that two through holes are formed in the bottom 21 for inserting the pins 33. The gaps between the through holes are filled with, for example, soft glass 34, thereby fixing the pins 33 in place. A lead 31 is connected to the front end of the pin 33, and the lead 31 is mounted to the external electrodes of the piezoelectric element 1 via solder 32, thereby applying a driving voltage to the piezoelectric element 1.

[0028] The strain gauge 4 is a component for detecting the displacement of the housing 2. The strain gauge 4 is, for example, a plate-shaped component with metal wires inside. The strain gauge 4 has a shape along its long side, for example, a length of 0.1 mm to 50 mm and a width of 2 mm to 120 mm. The strain gauge 4 can also be, for example, a circular plate with a diameter of 2 to 8 mm. The strain gauge 4 is attached to the housing 2, which is the object to be measured, using, for example, a resin-based adhesive material. As the housing 2 expands and contracts, the metal wires inside the strain gauge 4 expand and contract, thereby changing the resistance value of the metal wires. By measuring this change in resistance, the strain of the housing 2 can be measured. The strain gauge 4 is attached to the cylindrical portion 22 within the housing 2.

[0029] like Figure 1As shown, in the piezoelectric actuator 10 according to this disclosure, the strain gauge 4 is located in the bend 221. Since the cylindrical portion 221 has a bend 221, adhesive can easily accumulate in the bend 221. Therefore, the adhesive strength between the strain gauge 4 and the housing 2 can be improved. As a result, the possibility of the strain gauge 4 peeling off from the housing 2 can be reduced.

[0030] In addition, such as Figure 2 As shown, the strain gauge 4 can also be located on the outside of the housing 2. When the strain gauge 4 is installed inside the housing 2, the adhesive used to attach the strain gauge 4 to the housing 2 may react with oxygen, potentially generating moisture that could cause a short circuit in the piezoelectric element 1. In contrast, by placing the strain gauge 4 on the outside of the housing 2, the possibility of moisture generating a short circuit can be reduced. As a result, the durability of the piezoelectric element 1 can be improved.

[0031] It should be noted that the strain gauge 4 does not need to be integrally mounted on the bending section 221, such as Figure 2 As shown, the curved portion 221 can also be provided to a straight portion.

[0032] In addition, such as Figure 3 As shown, the strain gauge 4 can also be located inside the housing 2. When the strain gauge 4 is located outside the housing 2, there is a concern that the adhesive of the strain gauge 4 may oxidize due to the external environment, leading to a decrease in adhesion. In contrast, by placing the strain gauge 4 inside the housing 2, the influence of the external environment can be reduced. As a result, the decrease in adhesion can be suppressed.

[0033] With the strain gauge 4 located inside the housing 2, the lead wire 41 can also be inserted through the through hole in the bottom 21 through which the pin 33 is inserted. In this case, even if the number of strain gauges 4 is increased, it is not necessary to increase the number of through holes in the bottom 21, so that the strain gauge 4 can be energized without reducing the strength of the bottom 21.

[0034] In addition, such as Figure 4 As shown, the cylindrical portion 22 can also be serpentine in shape, with the strain gauge 4 located in the serpentine portion of the cylindrical portion 22. Here, serpentine refers to a repeating shape with multiple protrusions or concave sections, but it can also have a straight section. Alternatively, serpentine can also be a shape with multiple grooves provided in the circumferential direction. By making the cylindrical portion 22 serpentine, the stress generated in the bending portion 221 can be dispersed. Therefore, the stress applied to the bending portion 221 when driving the piezoelectric actuator 10 can be reduced. As a result, the durability of the piezoelectric actuator 10 can be improved.

[0035] In particular, in recent years, there has been a demand for the use of piezoelectric actuators 10 in high-temperature environments. Therefore, it is possible that the stretching behavior of the serpentine portion may change locally due to metal fatigue during long-term use. By placing the strain gauge 4 on the serpentine portion, it is possible to detect these local changes in stretching behavior. As a result, the durability of the piezoelectric actuator 10 can be improved.

[0036] In addition, such as Figure 4 As shown, the strain gauge 4 can also be located on the convex surface of the bend 221. The curvature of the strain gauge 4 increases when the housing 2 extends and decreases when the housing 2 contracts. That is, the behavior of the strain gauge 4 bending itself due to the expansion and contraction of the housing 2 is shown. Therefore, local stress measurement of the convex portion is possible.

[0037] In addition, Figures 4-8 For ease of understanding, only a portion of the strain gauge 4 and the cylindrical part 22 are described, and other components such as the lead wire 41 and adhesive are omitted.

[0038] In addition, such as Figure 5 As shown, the strain gauge 4 can also be located on the concave surface of the bend 221. In this case, compared to the case where it is located on the convex surface of the bend 221, the outer or inner diameter of the housing 2 can be reduced. Therefore, a smaller piezoelectric actuator 10 can be achieved. In particular, when the strain gauge 4 is provided inside the housing 2, the strain gauge 4 is located on the concave surface of the bend 221, thereby reducing the possibility of a short circuit due to contact between the piezoelectric element 1 and the strain gauge 4.

[0039] Furthermore, because the strain gauge 4 is sandwiched between the convex surfaces within the housing 2, it is not easily detached from the housing 2. Additionally, in the event that the housing 2 is subjected to extreme compression due to external stress, the strain gauge 4 is held in place by the convex surfaces, thereby enabling strain detection and thus preventing damage to the housing 2 beforehand. Furthermore, the strain gauge 4 can also be positioned closer to the concave side than the top of the convex surface in a direction perpendicular to the long side of the piezoelectric element 1.

[0040] In addition, such as Figure 6 As shown, the strain gauge 4 can also be located within the curved portion 221, extending from the convex to the concave surface. In this case, the strain gauge 4 can detect the displacement of half a cycle of the convex-concave shape. Therefore, by multiplying the detected displacement value by twice the number of convex surfaces, the overall displacement of the housing 2 can be calculated. That is, the overall displacement of the housing 2 can be determined without increasing the bonding area between the housing 2 and the strain gauge 4, thus reducing the stress between the housing 2 and the strain gauge 4 and decreasing the possibility of the strain gauge 4 peeling off from the housing 2.

[0041] In addition, such as Figure 7As shown, the strain gauge 4 can also be positioned from the convex portion to the convex portion. Thus, the strain gauge 4 itself becomes spring-shaped, capable of expanding and contracting like the component. Therefore, the strain gauge 4 is less likely to peel off from the housing. Simultaneously, because the strain gauge 4 deforms locally at the convex, concave, and convex portions, the stress generated at the joint between the strain gauge 4 and the housing 2 can be dispersed. As a result, the possibility of the strain gauge 4 peeling off from the housing 2 can be reduced. Furthermore, shear stress generated at the inflection points between the convex and concave portions can be detected, thus improving detection sensitivity.

[0042] Similarly, strain gauge 4 can also be positioned within the range from the concave portion to the concave portion. In this case, the same effect as described above can be obtained.

[0043] In addition, such as Figure 8 As shown, the strain gauge 4 can also be located symmetrically around the piezoelectric element 1. The portion of the bend 221 where the strain gauge 4 is located tends to concentrate stress, but even if the deformation of the housing 2 is hindered, the housing 2 as a whole can still be symmetrically displaced, thus dispersing the stress generated in the housing 2. As a result, the durability of the piezoelectric actuator 10 can be improved.

[0044] In addition, such as Figure 9 As shown, the strain gauge 4 can also be a plate-shaped component with its long side aligned with the circumferential direction of the housing 2. This allows for the detection of torsional stress caused by the expansion and contraction of the piezoelectric element 1.

[0045] Alternatively, strain gauge 4 can be placed near the weld. This allows for the detection of deformation near the weld, where deformation would not otherwise be desired. Specifically, for example... Figure 9 As shown, the strain gauge 4 can also be located at the position closest to the weld in one of the multiple bends 221.

[0046] In addition, by attaching multiple strain gauges 4, local time-dependent changes in the housing 2 can be detected, thereby suppressing damage to the piezoelectric actuator 10.

[0047] In addition, such as Figure 10 As shown, a strain gauge 4 can also be provided on the surface of the housing 2, and a second strain gauge 5 can be provided on the side of the piezoelectric element 1. This allows for the detection of deformation of the housing 2 and the detection of changes in the piezoelectric element 1 over time. Therefore, for example, if the piezoelectric element 1 does not deform but only the housing 2 deforms, if the housing 2 deforms due to the deformation of the piezoelectric element, or if either the strain gauge 4 provided on the piezoelectric element 1 or the second strain gauge 5 provided on the housing 2 peels off, the deformation of the housing 2 can be detected immediately.

[0048] In particular, in the case where, as an example, the piezoelectric element 2 does not deform and only the housing 2 deforms, and a part of the housing 2 cracks or breaks due to metal fatigue caused by stress concentration, by placing the strain gauge 4 on the housing 2 and the second strain gauge 5 on the piezoelectric element 1, it is possible to detect the abnormality of the housing 2 before the housing 2 cracks or breaks, thereby suppressing the damage to the actuator 10.

[0049] Explanation of reference numerals in the attached figures:

[0050] 10... Piezoelectric actuator;

[0051] 1...piezoelectric elements;

[0052] 2...shell;

[0053] 21...bottom;

[0054] 22...Tubular part;

[0055] 221...bend;

[0056] 23... lid part;

[0057] 31...lead wire;

[0058] 32... Solder;

[0059] 33... pins;

[0060] 34... Soft glass;

[0061] 4...Strain gauge;

[0062] 41...lead wire;

[0063] 5...Second strain gauge.

Claims

1. A piezoelectric actuator, wherein, The piezoelectric actuator includes: A piezoelectric element having its long side along its direction; A housing having a cover, a bottom and a cylindrical portion, and housing the piezoelectric element inside; as well as The strain gauge is located in the cylindrical section. The cylindrical portion has multiple curved sections along its long side that are bent due to the expansion and contraction of the piezoelectric element. The strain gauge is arranged along the convex surface in the curved portion in the long side direction.

2. A piezoelectric actuator, wherein, The piezoelectric actuator includes: A piezoelectric element having its long side along its direction; A housing having a cover, a bottom and a cylindrical portion, and housing the piezoelectric element inside; as well as The strain gauge is located in the cylindrical section. The cylindrical portion has multiple curved sections along its long side that are bent due to the expansion and contraction of the piezoelectric element. The strain gauge is arranged along the concave surface in the curved portion in the long side direction.

3. A piezoelectric actuator, wherein, The piezoelectric actuator includes: A piezoelectric element having its long side along its direction; A housing having a cover, a bottom and a cylindrical portion, and housing the piezoelectric element inside; as well as The strain gauge is located in the cylindrical section. The cylindrical portion has multiple curved sections along its long side that are bent due to the expansion and contraction of the piezoelectric element. The strain gauge is arranged along the long side of the curved portion from the convex surface to the concave surface.

4. A piezoelectric actuator, wherein, The piezoelectric actuator includes: A piezoelectric element having its long side along its direction; A housing having a cover, a bottom and a cylindrical portion, and housing the piezoelectric element inside; as well as The strain gauge is located in the cylindrical section. The cylindrical portion has multiple curved sections along its long side that are bent due to the expansion and contraction of the piezoelectric element. The strain gauge is arranged circumferentially on the concave surface of the curved portion of the housing.

5. The piezoelectric actuator according to any one of claims 1 to 4, wherein, The strain gauge is located inside the housing.

6. The piezoelectric actuator according to any one of claims 1 to 4, wherein, The strain gauge is located on the outside of the housing.

7. The piezoelectric actuator according to any one of claims 1 to 4, wherein, The cylindrical portion is shaped like a snake's belly. The strain gauge is located in the serpentine section of the cylindrical portion.

8. The piezoelectric actuator according to any one of claims 1 to 4, wherein, Multiple strain gauges are arranged symmetrically around the piezoelectric element.

9. The piezoelectric actuator according to any one of claims 1 to 4, wherein, The piezoelectric actuator also has a second strain gauge. The second strain gauge is disposed on the surface of the piezoelectric element.

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