JP6708542B2 - Piezoelectric actuator - Google Patents

Description

The present invention relates to a piezoelectric actuator having a metal cap that expands and contracts when a voltage is applied.

Conventionally, there is known a laminated piezoelectric actuator in which a plurality of piezoelectric elements in which internal electrodes and piezoelectric layers are alternately laminated are connected. Multilayer piezoelectric actuators are used for mass flow controllers, positioning stages, etc.In order to maintain moisture resistance and durability, the piezoelectric actuator body with multiple stacked piezoelectric elements is covered with a metal cap. Composed.

Patent Document 1 discloses a piezoelectric actuator in which a metal case having a simple structure can be used by covering the entire laminated piezoelectric element with ceramics and applying pressure to the piezoelectric element with the ceramics.

Patent Document 2 describes a piezoelectric actuator having a compact structure in which the transmission body that transmits the displacement of the piezoelectric actuator main body has a small diameter portion so that the cap does not have a large diameter while having a bellows portion.

JP, 11-284241, A JP, 2005-060982, A

In any of Patent Documents 1 and 2, a bellows structure is used on a part of the side surface of the cap, or a diaphragm structure is used at the tip of the cap to configure a piezoelectric actuator that can expand and contract along the displacement direction of the laminated piezoelectric element. is doing. An external force may be applied to the piezoelectric actuator in a direction perpendicular to the displacement direction. At this time, if the proof stress of the cap is weak, the cap may be deformed and eventually the internal piezoelectric element may be destroyed. However, neither of Patent Documents 1 and 2 pays attention to the proof stress against an external force in the direction perpendicular to the displacement direction.

The present invention has been made in view of such circumstances, and a piezoelectric actuator capable of expanding and contracting along the displacement direction while maintaining a high yield strength and reducing deformation against an external force in a direction perpendicular to the displacement direction. The purpose is to provide.

(1) In order to achieve the above object, a piezoelectric actuator of the present invention is a piezoelectric actuator that is displaced by application of a voltage, wherein a plurality of piezoelectric elements are connected in series and one end is fixed, and A transmission body that is provided at an end portion on the displacement side of the piezoelectric actuator main body and that transmits the displacement of the piezoelectric actuator main body, and the piezoelectric actuator main body and the transmission body are accommodated, and are formed to be expandable and contractable along the displacement direction. A cap made of metal having a stretchable portion on its side surface, and a cross-sectional shape of the stretchable portion along the displacement direction has a first convex toward the accommodated actuator body side and the piezoelectric actuator body side. Is a wave-shaped curve in which the second convexes directed to the opposite side are alternately continuous, and the vertical distance to the apex of the first convex when the apex of the second convex is a reference is 0.3 mm. Is not less than 3.0 mm, the distance between the vertices of the adjacent second protrusions is not less than 1.0 mm and not more than 3.0 mm, and the point connecting the second protrusion and the first protrusion of the curve. The inclination of the tangent with respect to the displacement direction is 0.31 or more and 9.43 or less.

This makes it possible to expand and contract along the displacement direction, while maintaining high yield strength against external force in the direction perpendicular to the displacement direction and reducing deformation. Further, even if the piezoelectric actuator is downsized, the range of motion is widened and it is possible to follow the expansion and contraction of the laminated piezoelectric element inside. As a result, durability is improved.

(2) Further, the piezoelectric actuator of the present invention is characterized in that the wavy curve representing the cross-sectional shape of the expandable portion is a sine wave shape. As a result, it is possible to secure a high elasticity and a high yield strength against an external force in a direction perpendicular to the displacement direction. Also, the cap is easy to manufacture.

(3) Further, the piezoelectric actuator of the present invention is characterized in that the expandable portion is provided within a range of ⅔ from the tip of the cap. Thereby, the proof stress can be further improved against the external force in the direction perpendicular to the displacement direction.

(4) Further, the piezoelectric actuator of the present invention is characterized in that the cap has a diaphragm portion which can be deformed in an uneven manner at a closed portion at a tip thereof. As a result, even when the piezoelectric actuator is downsized, the range of motion is widened and it is possible to follow the expansion and contraction of the laminated piezoelectric element inside.

According to the present invention, it is possible to expand and contract along the displacement direction, while maintaining a high yield strength against an external force in a direction perpendicular to the displacement direction and reducing deformation. Further, even if the piezoelectric actuator is downsized, the range of motion is widened and it is possible to follow the expansion and contraction of the laminated piezoelectric element inside. As a result, durability is improved.

It is a sectional side view which shows the piezoelectric actuator of this invention. (A) is a schematic diagram of a Wave structure. (B) is a schematic diagram of a bellows structure. (A), (b) is a side sectional view showing a cap in which the expandable portion has a Wave structure. 3A and 3B are side cross-sectional views showing a cap having a bellows structure as an expandable portion. 4A and 4B are side cross-sectional views showing a cap in which the position of the expandable portion of the cap shown in FIG. 3 is changed. 7 is a table showing the proof stress against external stress in a direction perpendicular to the displacement direction of a cap having an expandable portion having a Wave structure and a cap having an expandable portion having a bellows structure. 7 is a table showing the proof stress against external stress in the direction perpendicular to the displacement direction when the position of the expansion/contraction part is changed in the cap having the expansion/contraction part of the Wave structure.

Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same constituent elements in each drawing, and duplicate description will be omitted.

(Structure of piezoelectric actuator)
FIG. 1 is a side sectional view showing an example of the piezoelectric actuator of the present invention. The piezoelectric actuator 100 expands and contracts when a voltage is applied, and its tip is displaced according to the voltage, and is used for a positioning device, a mass flow controller, or the like. As shown in FIG. 1, the piezoelectric actuator 100 includes a piezoelectric actuator body 105, a cap 160, and a seat 140.

The piezoelectric actuator main body 105 is configured such that a plurality of piezoelectric elements 110 are stacked in the series direction and expand and contract on a straight line (multiple connection). The piezoelectric element 110 is formed by alternately stacking piezoelectric layers and internal electrodes. The internal electrodes of the piezoelectric element 110 are alternately connected to the pair of external electrodes 115. The external electrodes 115 of the plurality of piezoelectric elements 110 are connected by lead wires 120, respectively. By applying a voltage to the pair of lead wires 120, the piezoelectric actuator body 105 contracts when one voltage is applied, and expands when the other voltage is applied.

The piezoelectric actuator main body 105 is made up of a plurality of piezoelectric elements 110, which are connected in series in the expansion and contraction direction at the end faces thereof to form a multiple connection. By arranging the piezoelectric elements 110 in multiple rows, a large displacement can be efficiently obtained. In the example shown in FIG. 1, the piezoelectric actuator main body 105 is formed by connecting six piezoelectric elements 110 in series. In this way, the displacement amount in the case where the piezoelectric elements 110 are arranged in six rows can be obtained from the piezoelectric actuator main body 105. The piezoelectric actuator main body 105 preferably has a structure of about 6 stations in consideration of the ease of manufacture and the amount of displacement, but may be composed of one piezoelectric element 110.

A transmission body 130 including a transmission body projection 132 and a shim plate 131 is provided at the tip of the piezoelectric actuator body 105 (the tip on the side opposite to the side fixed to the seat 140). The transmitter 130 transmits the displacement of the piezoelectric actuator main body 105 to the outside. The transmission body protrusion 132 and the shim plate 131 are preferably made of SUS, but may be made of ceramic. In FIG. 1, the transmitter protrusion 132 is formed in a hemispherical shape, but may be in the shape of, for example, a semi-ellipsoid or a truncated cone as long as the displacement of the piezoelectric actuator main body 105 can be transmitted to the outside. Further, the transmission body 130 may be configured by only the transmission body protrusion 132 without using the shim plate 131.

The cap 160 is made of a metal such as SUS or titanium, and has a cylindrical shape with a bottomed opening. Then, on the bottom side, a protrusion 162 for transmitting displacement is provided as the tip of the piezoelectric actuator 100. Although the protrusion 162 is formed in a hemispherical shape in FIG. 1, the protrusion 162 is not limited to a hemispherical shape and may be formed according to the shape of the transmitter protrusion 132. The cap 160 accommodates the piezoelectric actuator main body 105 inside, and transfers the displacement of the piezoelectric actuator main body 105 to the outside by the protrusion 162 of the bottom portion contacting the transfer body protrusion 132 of the tip of the piezoelectric actuator main body 105. The opening of the cap 160 is fixed to the seat 140, and the lead wire 120 connected to the external electrode 115 of the piezoelectric element 110 is taken out through the seat 140 to seal the inside of the cap 160.

A stretchable portion 170 is provided on a part of the tubular portion of the cap 160. Thereby, when the piezoelectric actuator main body 105 is displaced, the cap 160 can follow and be displaced. A diaphragm portion that can be deformed into concaves and convexes may be provided at the closed portion at the tip of the cap 160. As a result, even if the piezoelectric actuator 100 is downsized, the range of motion is widened and it is possible to follow the expansion and contraction of the internal piezoelectric actuator body 105. The thickness of the cap 160 varies depending on the material used, but when the material is SUS, for example, it is preferably 0.15 mm or more and 0.2 mm or less.

The seat 140 supports the piezoelectric actuator body 105, and the cap 160 is fixed thereto. For example, in a positioner or the like, the piezoelectric actuator body 105 is housed in a state in which a preload is applied between the tip of the cap 160 and the seat 140.

(Structure of the elastic part)
The expansion/contraction part 170 has a Wave structure. In this specification, the Wave structure means that the cross section of the expansion/contraction part 170 when the cap 160 is cut along a plane including the central axis parallel to the displacement direction is a smooth curve, and the tangent line at each point on the curve is displaced. A structure that does not form a straight line perpendicular to the direction. However, the end points of the curve are excluded. In addition, in the present specification, the bellows structure means that the cross section of the expandable portion 170 when the cap 160 is cut along a plane including the central axis parallel to the displacement direction is a continuous curve, and is a point other than the end points on the curve. , A structure having a point where the tangent line is a straight line perpendicular to the displacement direction or a point where the tangent line cannot be drawn. FIG. 2A is a schematic diagram of an example of a Wave structure, and FIG. 2B is a schematic diagram of an example of a bellows structure.

Since the expansion/contraction part 170 is configured by the Wave structure, the expansion/contraction part 170 has high proof stress against an external force in a direction perpendicular to the displacement direction. As a result, the cap 160 can maintain a high yield strength and reduce deformation against an external force in a direction perpendicular to the displacement direction. Therefore, it is possible to reduce the damage of the piezoelectric actuator body 105 due to the external force. It is considered that this is because the curve of the cross section of the Wave structure is smooth and does not have a tangent line in the direction perpendicular to the displacement direction. If there is a point where a tangent line cannot be drawn on the curve of the cross section, that point becomes an angle, so when an external force in the direction perpendicular to the displacement direction is applied to the piezoelectric actuator 100, stress concentrates at that point and the point deforms. It is considered that it becomes a section of and is deformed more greatly. Further, if there is a point on the curve of the cross section where a tangent line perpendicular to the displacement direction exists, when an external force in the direction perpendicular to the displacement direction is applied to the piezoelectric actuator 100, the material in the vicinity of that point exerts a resistance force against the external force. Since it rarely exhibits, it is considered that the stress concentrates on the other parts, resulting in larger deformation.

It is preferable that the elastic portion 170 is provided within a range of 2/3 from the tip of the cap 160. Thereby, the proof stress can be further improved against the external force in the direction perpendicular to the displacement direction.

As shown in FIG. 2( a ), the cross section of the Wave structure has a wavy shape in which the first convex toward the housed actuator body and the second convex toward the opposite side of the actuator body are alternately continuous. Is the curve of. The first protrusion and the second protrusion may have different sizes, but they have the same size in consideration of the balance of the proof stress against the external force in the direction perpendicular to the displacement direction of the cap 160 and the miniaturization of the cap 160. Is preferred.

As shown in FIG. 2A, the first convex apex (protruding to the actuator body side of the cap 160) based on the second convex apex (the apex of the mountain protruding to the exposed side of the cap 160) is used as a reference. The vertical distance to the displacement direction up to the apex of the crest) is referred to as the mountain valley depth, and the distance between the apexes of the adjacent second protrusions is referred to as the pitch. In addition, the inclination of the tangent line at one of the displacement directions at the inflection point (either outside or inside of the cap 160, which is taken outside in the figure) that connects the second convex and the first convex of the curve is taken. It is simply a tilt. Note that the slope takes an absolute value when it becomes negative.

The mountain valley depth is 0.3 mm or more and 3.0 mm or less. When the valley depth is less than 0.3 mm, the amount of displacement is small and the durability is low. When it exceeds 3.0 mm, the element size cannot help being reduced because of interference with the internal element, and the generated force becomes small. The pitch is 1.0 mm or more and 3.0 mm or less. This is because the cap 160 having a pitch of less than 1.0 mm is difficult to manufacture. Further, when it exceeds 3.0 mm, the displacement amount becomes small and the durability may be lowered. Note that low durability means that the possibility of cracking at the tip of the cap increases. The slope is 0.31 or more and 9.43 or less. This is because if the inclination is too small, the displacement amount becomes small, and if it is too large, the proof stress becomes low with respect to the external force in the direction perpendicular to the displacement direction. By setting each variable in such a range, the piezoelectric actuator 100 can expand and contract along the displacement direction, while maintaining high proof stress against external force in the direction perpendicular to the displacement direction and reducing deformation. Further, even if the piezoelectric actuator is downsized, the range of motion is widened and it is possible to follow the expansion and contraction of the laminated piezoelectric element inside. As a result, durability is improved.

The wave-shaped curve representing the cross-sectional shape of the expandable portion 170 is preferably sinusoidal. As a result, it is possible to secure a high elasticity and a high yield strength against an external force in a direction perpendicular to the displacement direction. Also, the cap is easy to manufacture. When the waveform of the wave shape representing the cross-sectional shape is a sine wave shape, if the slope is k, the valley depth is A, the pitch is p, and the pi is π, then the slope k is k=A×π/p. Can be calculated.

Further, the wavy curve representing the cross-sectional shape of the stretchable portion 170 preferably has a curvature at the apex of 2 or more and 5 or less. By having the curvature at the apex in such a range, it is possible to secure high elasticity and high yield strength against an external force in a direction perpendicular to the displacement direction.

(Piezoelectric actuator manufacturing method)
Next, a method of manufacturing the piezoelectric actuator 100 configured as described above will be described. First, the piezoelectric actuator body 105, the cap 160, and the seat 140 are prepared. In the piezoelectric actuator main body 105, first, a predetermined number of piezoelectric elements 110 are bonded at the end faces in the stacking direction and connected in series (multi-connection), the lead wires 120 are connected to the external electrodes 115, and polarization processing is performed. Then, the transmission body 130 including the transmission body projection 132 and the shim plate 131 is provided at one end to manufacture. The cap 160 is made of one metal plate such as SUS having a predetermined thickness, and the expandable portion 170 having a Wave structure in the above numerical range.

Next, the piezoelectric actuator body 105 is inserted into the cap 160. Finally, the cap 160 and the seat 140 are fixed, and the hole through which the lead wire 120 passes is sealed. In this way, it is possible to easily manufacture the piezoelectric actuator 100 capable of expanding and contracting along the displacement direction, yet maintaining high proof stress against external force in the direction perpendicular to the displacement direction and reducing deformation.

(Example)
3A and 3B are side cross-sectional views showing the caps 3a and 3b in which the expandable portion has the Wave structure. 4A and 4B are side cross-sectional views showing caps 4a and 4b in which the expandable portion has a bellows structure. 5(a) and 5(b) are side sectional views showing caps 5a and 5b in which the position of the expansion/contraction part of the cap shown in FIG. 3 is changed. A simulation was performed to calculate the proof stress against the external stress in the direction perpendicular to the displacement direction of the cap of the piezoelectric actuator having the expandable portion having the Wave structure and the cap of the piezoelectric actuator having the expandable portion having the bellows structure. The simulation was performed using the finite element method.

It is assumed that the cap is made of SUS316L having a thickness of 0.15 mm, has a diameter (outer diameter) of 8 mm, a total length of 40 mm, and has an expandable portion formed of a Wave structure or a bellows structure in a predetermined position on the side surface within a range of 20 mm. The yield strength was calculated. The Wave structure was formed so that the side wall had a sinusoidal cross section, and the bellows structure was formed so that the peaks and valleys of the side wall had a curvature of 4. 3(a), (b), 4(a), (b) and 5(a), (b) are schematic diagrams, and the depth of the valleys, the pitch, the number of the valleys, the displacement of the side surface. The inclination with respect to the direction, the curvature of the peaks and valleys, the thickness of the material, etc. do not accurately represent the conditions of the simulated cap.

FIG. 6 is a table showing the proof stress against the external stress in the direction perpendicular to the displacement direction of the cap having the expandable portion having the Wave structure and the cap having the expandable portion having the bellows structure. The models having the same numbers in the example and the comparative example have the same ridge depth and pitch. According to this, when the expansion and contraction portions have the same ridge and valley depth and pitch, the piezoelectric actuator having the expansion and contraction portion having the Wave structure has a direction perpendicular to the displacement direction more than the piezoelectric actuator having the expansion and contraction portion having the bellows structure. It can be seen that it has a small deformation with respect to external force and has a high yield strength. The configuration such as the depth and pitch of the ridges and valleys of the expansion and contraction portion is determined by the design of the entire piezoelectric actuator such as the piezoelectric actuator body provided inside the cap.

FIG. 7 is a table showing the proof stress against external stress in the direction perpendicular to the displacement direction when the position of the expansion/contraction part is changed in the cap having the expansion/contraction part of the Wave structure. According to this, even in the Wave structure having the same ridge/valley depth and pitch, in the piezoelectric actuator in which the position of the expansion/contraction part is provided within the range of ⅔ from the tip of the cap, the expansion/contraction part has the end of the cap. It can be seen from Table 1 that the piezoelectric actuator, which is not provided within the range of ⅔, has a smaller deformation with respect to the external force in the direction perpendicular to the displacement direction and has a higher yield strength.

As described above, the piezoelectric actuator of the present invention is capable of expanding and contracting along the displacement direction, while maintaining high yield strength against external force in the direction perpendicular to the displacement direction and reducing deformation. Further, even if the piezoelectric actuator is downsized, the range of motion is widened and it is possible to follow the expansion and contraction of the laminated piezoelectric element inside. As a result, durability is improved.

100 piezoelectric actuator 105 piezoelectric actuator main body 110 piezoelectric element 115 external electrode 120 lead wire 130 transmitter 131 shim plate 132 transmitter protrusion 140 seat 160, 3a, 3b, 4a, 4b, 5a, 5b cap 162 protrusion 170 expansion part

Claims (4)

A piezoelectric actuator that is displaced by applying a voltage,
A piezoelectric actuator body in which a plurality of piezoelectric elements are connected in series and one end of which is fixed,
A transmission body that is provided at an end portion on the displacement side of the piezoelectric actuator body and that transmits the displacement of the piezoelectric actuator body;
A metal cap that houses the piezoelectric actuator body and the transmission body, and has a stretchable portion on a side surface that is stretchable and formed along the displacement direction,
A cross-sectional shape of the expandable portion along the displacement direction is a wave in which a first convex toward the housed piezoelectric actuator main body and a second convex toward the opposite side of the actuator main body are alternately continuous. Is a curve of shape,
The vertical distance to the apex of the first convex when the apex of the second convex is a reference is 0.3 mm or more and 3.0 mm or less,
The distance between the vertices of the adjacent second convexes is 1.0 mm or more and 3.0 mm or less,
A piezoelectric actuator, wherein an inclination of a tangent line at a point connecting the second protrusion and the first protrusion of the curve with respect to the displacement direction is 0.31 or more and 9.43 or less. The piezoelectric actuator according to claim 1, wherein the wavy curve representing the cross-sectional shape of the expandable portion is a sine wave. The piezoelectric actuator according to claim 1 or 2, wherein the expandable portion is provided within a range of 2/3 from the tip of the cap. The piezoelectric actuator according to any one of claims 1 to 3, wherein the cap has a diaphragm portion that can be deformed irregularly at a closed portion of a tip thereof.

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