JP4991047B2 - Actuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an actuator and, for example, relates to an actuator used for a precision positioning device such as an optical device, a drive element for vibration prevention, a drive element for fuel injection of an automobile engine, and the like.
[0002]
[Prior art]
Conventionally, a piezoelectric body has an inverse piezoelectric effect that expands and contracts when a voltage is applied. However, since the amount of expansion / contraction of each piezoelectric material is very small, a multilayer piezoelectric actuator formed by laminating a plurality of piezoelectric materials has been manufactured. In this laminated piezoelectric actuator, a voltage is applied to a piezoelectric body to extend it by several to several tens of μm and serve as a driving force source for the actuator.
[0003]
By the way, conventionally, in order to cut off from the outside air, improve moisture resistance, and prevent entry of foreign matters such as oil and fuel, an actuator is configured by housing a multilayer piezoelectric element in a metal case. The displacement of the piezoelectric element is transmitted to the metal case, and the metal case itself is displaced.
[0004]
As such an actuator, one disclosed in JP-A-6-283778 is known. In the actuator disclosed in this publication, the laminated piezoelectric element is sealed in a metal case, so that it can be shut off from the outside air, improved in moisture resistance, and prevented from entering oil or fuel.
[0005]
Further, according to this publication, by providing a load application holding means between the multilayer piezoelectric element and the inner wall of the bellows (diaphragm), a preload opposite to the displacement direction is applied to the multilayer piezoelectric element. The multilayer piezoelectric element can be mounted without using any adhesive, and has a structure in which troubles such as corrosion due to outgassing of the adhesive do not occur.
[0006]
That is, in the actuator disclosed in this publication, a bellows (diaphragm) applies a preload to the multilayer piezoelectric element and transmits a displacement amount.
[0007]
[Problems to be solved by the invention]
However, in the actuator disclosed in the above-mentioned JP-A-6-283778, a preload is applied to the laminated piezoelectric element by the bellows, and the displacement is transmitted by the deformation of the bellows. When the piezoelectric element is displaced at a high speed for a long period of time, the bellows deteriorates with time, and it becomes impossible to apply a preload, resulting in a problem that the actuator does not function.
[0008]
Further, in such an actuator, when the load applied to the multilayer piezoelectric element is removed or when a temperature change occurs, a dimensional change (dimensional contraction) occurs in the multilayer piezoelectric element in the metal case. There is a problem that the preload applied at the time of assembly cannot be applied as designed, the laminated piezoelectric element becomes free in the metal case, and moves freely in the metal case.
[0009]
In addition, when the laminated piezoelectric element moves in the metal case in a load-free state and is set in an inclined state, a piece-by-piece state occurs, and driving is performed by applying a load or voltage in this state. In this case, there is a problem that bending stress is applied to the multilayer piezoelectric element, and the multilayer piezoelectric element is damaged when this is continued for a long time.
[0010]
That is, according to the present inventors, as shown in the dimensional change of the multilayer piezoelectric element at the time of load application and load removal in FIG. 4, the multilayer piezoelectric element is laminated as the applied load increases. It was confirmed that when the load was removed, the dimension in the stacking direction contracted without returning to the original dimension (0 point).
[0011]
In recent years, actuators have been used under various wide temperatures such as a low temperature of 0 ° C. or lower and a high temperature of about 200 ° C. for the purpose of use. Under such a use environment, it was confirmed that the dimension in the stacking direction contracted as the temperature increased, as shown in the relationship between the ambient temperature and the dimensional change of the stacked piezoelectric element shown in FIG.
[0012]
This phenomenon is that a piezoelectric ceramic used for a laminated piezoelectric element is elongated by applying a polarization treatment to generate a reverse piezoelectric effect when a voltage is applied. This is because, as the temperature rises, as the temperature approaches the Curie temperature of the material, the domain that has been oriented in one direction due to the polarization treatment returns to the unpolarized state.
[0013]
From these phenomena, in the actuator disclosed in the above-mentioned JP-A-6-283778, when the load applied to the multilayer piezoelectric element is removed or when a temperature change occurs, the multilayer piezoelectric element in the metal case is removed. Since the element undergoes dimensional change (dimension shrinkage), the preload applied during assembly is not applied, and there is a problem that the multilayer piezoelectric element is free in the metal case.
[0014]
In the present invention, the multilayer piezoelectric element is sealed in a metal case to cut off from the outside air, improve moisture resistance, prevent intrusion of oil and fuel, and even when a load change or temperature change occurs. An object of the present invention is to provide an actuator that can be driven for a long period of time while a preload is always applied in the stacking direction of the stacked piezoelectric elements.
[0015]
[Means for Solving the Problems]
The actuator of the present invention is in a metal case composed of a case main body having a cylindrical cross section, a base member fitted into the lower end of the case main body, and an upper end sealing member disposed on the upper surface of the case main body. An actuator that hermetically accommodates a multilayer piezoelectric element formed by alternately laminating piezoelectric bodies and internal electrodes, and expands and contracts the metal case by expanding and contracting the multilayer piezoelectric element. A load-applying ring that fits the inner periphery of the case main body and that accommodates and fixes the multi-layer piezoelectric element and applies a load in the expansion and contraction direction of the multi-layer piezoelectric element; and a lower surface of the load applying ring. contact, and has been preloaded application unit composed of a spring member for pressing the multilayer piezoelectric element downwardly is provided adjacent to the該予load application part, the displacement Den said fixed to the laminated piezoelectric element Provided an easily deformable portion that expands and contracts by the member, and the case body, and the load applying ring, said base member, and said upper sealing member and made of the same material and welded by laser welding It is characterized by that.
[0016]
In such an actuator, when the multilayer piezoelectric element is driven, the easily deformable portion of the metal case is displaced by the displacement transmitting member, and the preload application portion that applies a load in the expansion and contraction direction of the multilayer piezoelectric element is not displaced. Even if the laminated piezoelectric element is driven, the preload application section does not deform, and the preload application section does not deteriorate due to long-term driving, so that even when a load change or temperature change occurs, the laminate is always stacked. The displacement can be transmitted in a state where a preload is applied in the stacking direction of the piezoelectric elements.
[0017]
In the actuator of the present invention, it is desirable that the easily deformable portion is configured by forming a metal case in a bellows shape. Thereby, a metal case can be produced at low cost by plastic working such as drawing, and the easily deformable portion of the metal case can be easily deformed.
[0018]
Furthermore, in the actuator of the present invention, it is desirable that the spring constant of the easily deformable portion of the metal case is 30 to 100 kgf / mm. As a result, the amount of displacement generated by the multilayer piezoelectric element can be transmitted without lowering, and the impact caused by the reaction force received from the easily deformable portion when the multilayer piezoelectric element is displaced can be reduced. It can be improved.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the actuator of the present invention is configured by housing a laminated piezoelectric element 2 in a metal case 1. As shown in FIG. 2, the multilayer piezoelectric element 2 includes an element body 9 formed by alternately laminating piezoelectric bodies 5 and internal electrodes 7, and a pair of external bodies formed on the outer surface of the element body 9. The electrode 11 is constituted.
[0020]
Insulators 13 are formed every other layer at the end of the internal electrode 2, and the end of the internal electrode 7 where the insulator 13 is not formed is connected to the same external electrode 11.
[0021]
As the piezoelectric body 5, for example, lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material mainly composed of barium titanate BaTiO ₃ is used. It is not limited, and any ceramics having piezoelectricity may be used.
[0022]
As the piezoelectric body 5 material, those piezoelectric strain constant d ₃₃ is high is preferable. The thickness of the piezoelectric body 5, that is, the distance between the internal electrodes 7, is preferably 0.05 to 0.25 mm from the viewpoint of downsizing and applying a high electric field.
[0023]
The internal electrode 7 is exposed on all side surfaces of the element body 9, and grooves are formed on every two side surfaces of the element body 9 every other layer of the end portion of the piezoelectric body 5 including the end portions of the internal electrode 2. An insulator 13 such as glass, epoxy resin, polyimide resin, polyamideimide resin, or silicone rubber is filled. The insulator 13 is preferably made of a material having a low Young's modulus, such as silicone rubber.
[0024]
Thus, the internal electrodes 7 are alternately insulated every other layer, and the other end surface of the non-insulated internal electrodes 7 is electrically conductive with the conductive heat-resistant adhesive previously applied to the side surface of the element body 9. The external electrode 11 can be formed by applying and thermosetting a thermosetting conductive adhesive with the members in close contact.
[0025]
Inactive portions 14 for mechanically holding the element body 9 and transmitting the generated force to the outside are laminated and bonded to both end surfaces of the element body 9 in the stacking direction.
[0026]
The metal case 1 includes a case main body 1a having a cylindrical cross section, a base member 1b fitted into the lower end of the case main body 1a, and an upper end sealing member 1c disposed on the upper surface of the case main body 1a. Are stacked in an airtight manner.
[0027]
The laminated piezoelectric element 2 is fixed to the base member 1b, and a pair of hermetic lead pins 15 is provided on the base member 1b. One end of these hermetic lead pins 15 is fixed to the base member 1b. The laminated piezoelectric elements 2 are connected to the external electrodes 11 respectively.
[0028]
In the actuator of the present invention, as shown in FIG. 1, the laminated piezoelectric element 2 is accommodated and fixed in the metal case 1, and a load is applied to the laminated piezoelectric element 2 in the expansion / contraction direction (piezoelectric lamination direction). The preload application unit 17 is provided, and an easily deformable unit 21 that is provided above the preload application unit 17 and is stretched and deformed by the displacement transmission member 19 fixed to the multilayer piezoelectric element 2 is provided.
[0029]
That is, the preload applying portion 17, a load applying ring 23 fitted to the inner periphery of the case body 1a, a spring member for pressing contact with the lower surface of the load applying ring 23, the multilayer piezoelectric element 2 downwards consists 25. as a load applying ring 23 a reaction force by the spring member 25, the multi-layer piezoelectric element 2 is pressed against the base member 1b side.
[0030]
Deformable portion 21, the upper end has a displacement transmission member 19 made contact with the pin on the upper end sealing member 1c, the lower end is inserted through the load applying ring 23, in contact with the upper surface of the multilayer piezoelectric element 2 ing. Moreover, the case main body 1a in the easily deformable member 21 is formed in a bellows shape. Accordingly, the case body 1a can be manufactured at low cost by plastic processing such as drawing, and the easily deformable portion 21 of the case body 1a can be easily deformed.
[0031]
The easily deformable portion 21 is obtained by plastic processing such as drawing of a metal cylinder such as SUS304 or SUS401L having a thickness of 0.1 to 0.4 mm. In the present invention, the entire case body 1a is made of the above material.
[0032]
Moreover, the spring constant of the easily deformable portion 21 of the metal case 1 is 30 to 100 kgf / mm. As can be understood from the relationship between the spring constant shown in FIG. 3 and the displacement amount of the multilayer piezoelectric element, the spring constant of the easily deformable portion 21 increases as the spring constant of the spring member 25 for applying a preload increases. Since the displacement amount of the multilayer piezoelectric element is reduced, it is desirable that the displacement be 30 to 100 kgf / mm in order to transmit the displacement of the multilayer piezoelectric element 2 without reducing it.
[0033]
Further, when the multilayer piezoelectric element 2 is displaced, an impact due to the reaction force of the easily deformable portion 21 is applied to the multilayer piezoelectric element 2, and this impact is repeatedly applied particularly in continuous driving by applying a voltage pulse. In order to improve the durability of the multilayer piezoelectric element 2, the spring constant is particularly preferably 30 to 60 kgf / mm. When the spring constant of the easily deformable portion 21 becomes larger than that of the spring member 25, the displacement generated by the multilayer piezoelectric element 2 is constrained by the easily deformable portion 21 and the displacement is reduced. Is preferably smaller than that of the spring member 25.
[0034]
Furthermore, a metal load application ring 23 such as SUS is welded to the preload application unit 17 by a method such as laser welding, and lamination is performed by pressing a spring member 25 such as a coil spring or a disc spring with the load application ring 25. Since a load is applied to the piezoelectric element 2, the spring constant of the spring member 25 is 30 to 30 mm so that the displacement of the multilayer piezoelectric element 2 does not decrease, as does the spring constant of the easily deformable portion 21. 100 kgf / mm is desirable.
[0035]
The case body 1a, the load application ring 23, the base member 1b, and the upper end sealing member 1c used for sealing the multilayer piezoelectric element 2 are welded by laser welding or the like. At this time, when each member is made of a different material, since the welded portion is cracked during the cooling after welding due to the influence of the difference in linear expansion of each member, it becomes difficult to hermetically seal. It is desirable to do.
[0036]
The piezoelectric actuator of the present invention is manufactured as follows. First, a multilayer piezoelectric element is prepared by preparing a slurry in which a calcined powder of piezoelectric ceramic such as lead zirconate titanate Pb (Zr, Ti) O ₃ , a binder made of an organic polymer, and a plasticizer are mixed. Then, a ceramic green sheet having a thickness of 50 to 250 μm is produced by a slip casting method.
[0037]
A conductive paste mainly composed of silver-palladium serving as the internal electrode 7 is printed on one side of the green sheet to a thickness of 1 to 10 μm by screen printing. After the conductive paste is dried, a predetermined number of green sheets coated with the conductive paste are stacked, and the green sheets are not coated with the conductive paste at both ends in the stacking direction of the laminate. Are laminated.
[0038]
Next, pressure is applied while heating the laminated body at 50 to 200 ° C. to integrate the laminated body. After the integrated laminate is cut to a predetermined size, the binder is removed at 400 to 800 ° C. for 5 to 40 hours, and the main firing is performed at 900 to 1200 ° C. for 2 to 5 hours. A laminated sintered body to be the main body 9 is obtained. The end of the internal electrode 7 is exposed on the side surface of the element body 9.
[0039]
Thereafter, on the two side surfaces of the element body 9, the depth is 50 to 500 μm every other layer and the width 50 in the stacking direction so that the two side surfaces alternate with the end portions of the piezoelectric body 5 including the end portions of the internal electrodes 7. A groove of ˜300 μm is formed, and the groove 3 is filled with an insulator 3 such as silicone rubber.
[0040]
Thereafter, the internal electrodes 7 are alternately insulated on the side surfaces of the element body 9 every other layer, and an external electrode paste is applied to the side surfaces of the element body 9 and dried to form the external electrodes 11. Silicone rubber is coated on the outer peripheral surface of the piezoelectric element 2 by a method such as dipping. Then, a final laminated piezoelectric element 2 is obtained by applying a polarization voltage of 0.1 to 3 kV to the external electrode 11 and subjecting the entire laminated piezoelectric element 2 to polarization treatment.
[0041]
After the laminated piezoelectric element 2 thus obtained is fixed to the base member 1b using an adhesive, the external electrode 11 of the laminated piezoelectric element 2 and the hermetic lead pin 15 are connected by soldering or the like. Next, a case main body 1a in which a spring member 25 such as a disc spring is set on the convex displacement transmission member 19 and placed on the upper end of the multilayer piezoelectric element 2, and the load application ring 23 is welded by a method such as laser welding. In a state where a preload of 50 to 150 kgf is applied with a press machine for pressurization, the lower end portion of the case main body 1a and the base member 1b are welded by a method such as laser welding. Thereafter, the upper end sealing member 1c is placed on the upper surface of the case main body 1a, and a load of 5 to 20 kgf is applied by a press machine so that the displacement transmitting member 19 contacts the upper end sealing member 1c. The actuator of the present invention can be manufactured by welding.
[0042]
【Example】
A slurry is prepared by mixing a calcined powder of piezoelectric ceramic such as lead zirconate titanate Pb (Zr, Ti) O ₃ , a binder made of an organic polymer, and a plasticizer, and a thickness of 150 μm is obtained by a slip casting method. A ceramic green sheet was prepared.
[0043]
A conductive paste mainly composed of silver-palladium serving as the internal electrode 7 was printed on one side of the green sheet by a screen printing method to a thickness of 5 μm, and the conductive paste was dried, and then the conductive paste was applied. 400 green sheets were laminated, and 10 green sheets to which no conductive paste was applied were laminated at both ends in the lamination direction of the laminate.
[0044]
Next, the laminated body subjected to pressure while heating at 100 ° C., and integrally laminate was cut into a size of 10 mm × 10 mm, subjected to binder removal over 10 hours at 800 ° C., 1100 ° C. The main body was fired for 2 hours to obtain a laminated sintered body to be the element body 9.
[0045]
After that, on the two side surfaces of the element body 9, grooves having a depth of 100 μm every other layer and a width of 50 μm in the stacking direction so as to alternate between the two side surfaces at the end portions of the piezoelectric body 5 including the end portions of the internal electrodes 7. And filled with the insulator 13. Thereafter, the other end face of the internal electrode 7 that is not insulated is heated at 200 ° C. in a state in which a silver foil of a conductive member having a thickness of 0.5 mm is in close contact with the conductive heat-resistant adhesive previously applied, The external electrode 11 is formed by heat-curing, and thereafter, the outer peripheral surface of the multilayer piezoelectric element is coated with silicone rubber by a dipping method, and then a polarization voltage of 1 kV is applied to polarize the entire element. A laminated piezoelectric element 2 was produced.
[0046]
The laminated piezoelectric element and the base member 1b made of SUS304 were bonded with an epoxy resin, and the hermetic lead pin 15 and the external electrode 11 were connected with solder. Next, 3 disc springs of JISH4 arranged in series so that the spring constant of the load application unit is 50 kgf / mm are alternately stacked and set in 4 parallel, and this is placed on the displacement transmission member 19 and then laminated. Placed on top of the piezoelectric element 2.
[0047]
Case body made by drawing a SUS304 cylinder with a thickness of 0.15 mm, forming the easily deformable portion 21 so that the spring constant becomes 30 kgf / mm, and laser welding the load application ring 23 made of SUS304. 1a was applied, a pressurizing press preload of 50 kgf was applied, and welding was performed with a laser welder.
[0048]
Thereafter, the upper end sealing member 1c is placed on the case main body 1a, a load of 5 kgf is applied by a pressurizing press so that the displacement transmission member 19 contacts the upper end sealing member 1c, laser welding is performed, and the multilayer piezoelectric element Was hermetically sealed to produce an actuator of the present invention.
[0049]
For comparison, the multilayer piezoelectric element 2 is housed in a metal case having a bellows portion with a spring constant of 30 kgf, and a preload is applied using the bellows portion. An actuator was manufactured. When welding the upper end sealing member, laser welding was performed by applying a load of 5 kgf.
[0050]
First, in order to compare these displacement characteristics, the voltage / displacement characteristics were measured at an applied voltage of 0 to 200 V. As a result, it was found that both actuators generated a displacement of 40 μm and there was no difference in the displacement characteristics. It was.
[0051]
Next, in order to compare the durability, an endurance test was performed in which a DC electric field of 0 V to +200 V was applied at a frequency of 50 Hz under an atmospheric temperature of 100 ° C. and a humidity of 90%. As a result, it was confirmed that the product of the present invention was driven without problems even at 1 × 10 ⁹ times with a displacement of 40 μm. In addition, as a result of observing the appearance of the metal case after the endurance test, it was confirmed that there was no occurrence of cracks or the like due to long-term driving, and that there was no deterioration in both the easy driving part and the preload application part.
[0052]
Further, the actuator for comparison could not be driven 1 × 10 ⁷ times. As a result of disassembling the laminated piezoelectric actuator and observing the sealed laminated piezoelectric element, it was confirmed that a crack was generated near the inactive portion and a short circuit was established between the two electrodes starting from this portion. The crack in the vicinity of the inactive portion occurred because the multilayer piezoelectric element was brought into contact with each other in the metal case due to a dimensional change of the multilayer piezoelectric element as the temperature rose, and bending stress was generated.
[0053]
Further, in the actuator disclosed in Japanese Patent Application Laid-Open No. 6-283778, in order to check whether the easy driving unit 21 is deteriorated due to long-term driving, the bellows is not generated even if a dimensional change occurs. A preload of 50 kgf was applied using the part, laser welding was performed, and a comparative actuator was produced. This actuator was subjected to an endurance test in which a DC electric field of 0 V to +200 V was applied at a frequency of 50 Hz under an atmospheric temperature of 100 ° C. and a humidity of 90%.
[0054]
As a result, although it was confirmed that the displacement was 40 μm and it was driven without any problem even 1 × 10 ⁹ times, the appearance of the bellows portion was observed, and as a result, it was confirmed that a crack was generated. This is presumably because the deterioration of the bellows portion due to long-term driving was promoted because a preload of 50 kgf was applied using the bellows portion. From this result, the product according to the present invention is provided with a preload applying part and an easily deformable part separately provided in the metal case, so that the metal case is not deteriorated even in long-term driving and is excellent in durability. I understand.
[0055]
【Effect of the invention】
As described above in detail, in the actuator of the present invention, the metal case is provided with a preload application unit that applies a load to the multilayer piezoelectric element in the expansion and contraction direction, and adjacent to the preload application unit. Because the easily deformable part that expands and contracts by the displacement transmission member fixed to the metal is provided, the easily deformable part of the metal case is displaced, and the preload application part that applies a load in the expansion and contraction direction of the multilayer piezoelectric element is not displaced. Since the preload application section does not deform even when the laminated piezoelectric element is driven, the preload application section does not deteriorate due to long-term driving, and this ensures that even when a load change or temperature change occurs. Displacement can be transmitted in a state where a preload is applied in the stacking direction of the stacked piezoelectric element.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an actuator of the present invention.
FIG. 2 is a perspective view showing an example of a laminated piezoelectric element.
FIG. 3 is a graph showing a relationship between a spring constant and a displacement amount of a multilayer piezoelectric element.
FIG. 4 is a graph showing a dimensional change of the multilayer piezoelectric element during load application and load removal.
FIG. 5 is a graph showing the relationship between the ambient temperature and the dimensional change of the multilayer piezoelectric element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Metal case 2 ... Laminated piezoelectric element 5 ... Piezoelectric body 7 ... Internal electrode 11 ... External electrode 17 ... Preload application part 19 ... Displacement transmission member 21 ...・ Easy deformation part

Claims (3)

A piezoelectric body and an internal electrode are disposed in a metal case composed of a case main body having a cylindrical cross section, a base member fitted into the lower end of the case main body, and an upper end sealing member disposed on the upper surface of the case main body. Is an actuator that hermetically accommodates a laminated piezoelectric element formed by alternately stacking and expanding and contracting the laminated piezoelectric element, and extends and contracts the metal case. A load application ring that fits the inner periphery of the case body, and abuts against the lower surface of the load application ring, a preload applying portion, which is composed of a spring member for pressing the piezoelectric element downwardly is provided adjacent to the該予load application part, easy to stretch deformed by the displacement transmitting member fixed to the laminated piezoelectric element Actuators provided and shape portion, and said case body, said load applying ring, said base member, and said upper sealing member and made of a same material, characterized by being welded by laser welding . The deformable portion is an actuator according to claim 1, wherein, characterized in that it is constructed by forming the metal case like bellows. Claim 1 or 2 binary actuator, wherein the spring constant of the deformable portion of the metal case is 30~100kgf / mm.

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