JP2663700B2 - Piezoelectric actuator with displacement transmission mechanism - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator, and more particularly, to a structure of a displacement transmitting mechanism in a piezoelectric actuator with a displacement transmitting mechanism.

[Conventional technology]

2. Description of the Related Art Piezoelectric actuators generate minute displacement using an electrostrictive effect element (hereinafter referred to as an element) that converts electric energy into mechanical energy by an electrostrictive effect. Operates at high speeds such as mass flow controllers, XY tables of exposure equipment, or fields that require precise control of the movement of minute positions, such as plastic injection molding machines, or printer heads. Used in areas where it is necessary to:

This element basically has a structure in which electrodes are formed on two opposing surfaces of a solid having a large electrostrictive effect, such as lead zirconate titanate ceramics, and a potential difference between the electrodes. Displacement is generated by using the strain of a solid that occurs when applied, but as an actual element structure, an electrostrictive material is thinned so that a large displacement can be obtained at a low voltage. A so-called laminated structure in which thin layers of materials and internal electrodes are alternately laminated is widely used.

 FIG. 6 shows the structure of the above-mentioned stacked element.

FIG. 6 is a diagram showing a cross section taken along a plane parallel to the element stacking direction.

In FIG. 6, the element 1 includes a ceramic portion in which internal electrodes are provided at regular intervals, and a ceramic portion not including the internal electrodes.

The portion of the ceramic having an internal electrode therein is usually called an active layer 2, and when a voltage is applied between the internal electrodes, an electrostrictive effect is generated in the ceramic and contributes to the operation as an element.

In this active layer 2, internal electrodes 4a and 4b are formed at regular intervals inside a ceramic 3 exhibiting an electrostrictive effect, and alternately, external electrodes 5a provided on side surfaces of the element are provided.
The internal electrodes are connected alternately to a and 5b so that adjacent internal electrodes serve as opposing electrodes with a ceramic layer interposed therebetween.

The distance between the internal electrodes can be reduced to a minimum of about 10 μm by the ordinary multilayer ceramic capacitor technology.

On the other hand, a portion having no internal electrode therein is usually referred to as a protective layer 6, and is a portion which does not exhibit an electrostrictive effect and does not contribute to the operation as an element because of no internal electrode. This is necessary in order to prevent the components of the ceramics 3 of the active layer 2 from fluctuating due to the high-temperature heat treatment in the above.

When the structure of the device is formed as the above-described stacked type, the active layer 2
Since the distance between the internal electrodes can be shortened, a high electric field can be applied to the electrostrictive effect material even at a low voltage, and an element that generates a large displacement at a low voltage can be realized.

By the way, in order to transmit the displacement generated in the element as described above to the outside and operate this element as a piezoelectric actuator, it is necessary to fix the element to which the displacement is to be transmitted and the element. In general, a method of connecting using an adhesive has been used.

Moreover, in this case, as described above, the adhesive has a high rigidity after curing (having a high Young's modulus) so as not to absorb the displacement generated in the element for the purpose of accurately controlling the minute displacement. ) A thermosetting resin is used, and a metal to which displacement is to be transmitted is often a metal having high rigidity and easy processing.

[Problems to be solved by the invention]

As described above, in a conventional piezoelectric actuator, in actual use, as schematically shown in FIG.
A metal object (hereinafter referred to as a metal member) 7 to which displacement is to be transmitted is bonded to the element 1 using a highly rigid thermosetting resin adhesive 8 so that the displacement generated in the element 1 is reduced. Often communicated to the outside.

In this case, the metal member 7 as the element 1 is 150 to 200 ° C.
And then cooled to room temperature and bonded.

At this time, since the coefficient of linear thermal expansion of the metal member 7 is larger than the coefficient of linear thermal expansion of the element 1, the amount of shrinkage during cooling in the above bonding step is smaller in the metal member 7 than in the element 1. growing.

For this reason, a compressive stress as shown by an arrow A in FIG. Further, as a result of the action of the above-described compressive stress, a tensile stress as shown by an arrow B in the drawing acts on the side surface of the protective layer 6.

As a result, the protective layer 6 is deformed as shown by a broken line in the figure, and cracks may occur in the protective layer 6 or breakage may occur at the interface between the protective layer 6 and the active layer 2. .

That is, in the conventional piezoelectric actuator, since the element to which displacement is to be transmitted and the element are bonded using a highly rigid thermosetting adhesive, a crack is easily generated in the protective layer. There was a drawback that breakage easily occurred between the active layer and the active layer.

[Means for solving the problem]

The piezoelectric actuator with a displacement transmitting mechanism according to the first aspect of the present invention is a plurality of rigid spheres arranged on both end surfaces in the expansion and contraction direction of the element so as to be in contact with the end surfaces, so that the respective end surfaces do not overlap. And a mechanism for transmitting the displacement of the element to the outside by a rigid body attached so as to sandwich the sphere between the end face and the sphere, the contact surface with the sphere being smooth. Features.

According to a second aspect of the present invention, in the displacement voltage mechanism according to the first aspect, a shape of the rigid body sandwiching the sphere between the element and the end face of the element is opposite to a side in contact with the sphere. Has a hemispherical shape.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing the structure of the first embodiment of the present invention.

As shown in FIG. 1, the piezoelectric actuator with a displacement transmission mechanism according to the present embodiment includes an element 1 and two displacement transmission mechanisms 9, and the displacement transmission mechanism 9 extends and contracts in the direction in which the element 1 expands and contracts (arrows in FIG. (Indicated by).

FIG. 2 is a longitudinal sectional view showing the structure of the piezoelectric actuator with a displacement transmitting mechanism according to the present embodiment.

In FIG. 2, the element 1 has the following configuration.

In the active layer 2, a ceramic 3 having a thickness of 100 μm mainly composed of lead zirconate titanate, platinum having a thickness of 5 μm,
Alternatively, 64 internal electrodes 4a and 4b made of an alloy of silver and palladium are alternately laminated.

Of these, the internal electrodes exposed on the side surfaces of the element 1 are:
On one pair of opposing side surfaces, every other layer is insulated from the external electrodes 5a and 5b by the insulating glass 10.

The remaining internal electrodes of the non-insulated layer are connected to external electrodes 5a or 5b mainly composed of silver, and a voltage is externally applied through a lead wire 11 soldered to the external electrodes.

Note that the connection relationship between the external electrodes 5a and 5b and the internal electrodes 4a and 4b is such that adjacent internal electrodes are opposed to each other with ceramics interposed therebetween.

On the upper and lower sides of the above-mentioned active layer 2, the same thickness as that of the active layer, made of a ceramic mainly composed of lead zirconate titanate, is used.
A 1.2 mm protective layer 6 is laminated.

Next, the displacement transmission mechanism 9 is shown in FIG.
As shown in an exploded perspective view in FIG. 3, the assembly is performed as follows.

First, the frame 12 is adhered to the side surface of the protective layer 6 with an adhesive 13, and the balls 14 are buried on the end surface of the protective layer 6 so that the balls 14 do not overlap each other.

Next, the end face plate 15 is inserted into the positioning groove 16 provided in the frame 12, and the positioning protrusion 17 of the end face plate 15 is used.
Are fitted together, and further pressed down from above with a stopper 18 to fix the end face plate 15 so as not to come off the frame 12.

In the thus obtained piezoelectric actuator with a displacement transmitting mechanism according to the present embodiment, when transmitting the displacement to the outside, it is necessary to adhere the end face of the protective layer made of ceramics to the object to which the displacement is to be transmitted. No, displacement transmission is spherical
Since the processing is performed through the step 14, no compressive stress is generated on the protective layer in a plane parallel to the end face of the element.

Therefore, cracks generated in the ceramic due to a difference in linear thermal expansion coefficient between the ceramic to be transferred and the ceramic, and breakage at the interface between the protective layer and the active layer can be suppressed.

FIG. 4 shows the result of comparing the defective rate when a pulse-like voltage is repeatedly applied using the present embodiment and a conventional piezoelectric actuator in which a metal member is directly bonded to an end face of an element. is there.

The contents of the defect include cracks generated in the ceramics of the protective layer 6 and breaks generated at the interface between the protective layer 6 and the active layer 2.

The shape of the element used was 10 mm × 10 mm × 20 mm, and the number of samples subjected to the test was 100 each.

In addition, as a pulse-like voltage waveform, the frequency is 30 Hz,
A rectangular wave having a voltage of 150 V was used.

The determination of a defect was made by observation with an optical microscope and the naked eye.

As is apparent from FIG. 4, there is already a difference between the two in the initial state before the voltage is applied, and the defect transmission rate of the conventional piezoelectric actuator is 7%. No failure was observed in the piezoelectric actuator with a mechanism.

In addition, as the number approaches 10 to 100 million times, the failure rate of the conventional piezoelectric actuator increases remarkably, reaching 45%, and about half of the failures. In the actuator, the defect rate was as low as 4% even after 100 million pulse voltage application.

 Next, a second embodiment of the present invention will be described.

FIG. 4 is a longitudinal sectional view showing the structure of the second embodiment of the present invention.

In this embodiment, the first embodiment shown in FIG. 1, FIG. 2 and FIG.
Of the displacement transmitting mechanism 9 in the embodiment of the present invention,
As shown in FIG. 4, the shape of 15 has a hemispherical surface on the side not in contact with the sphere.

This embodiment includes the effect of the first embodiment, and also has the effect that the displacement can be transmitted in a direction having an arbitrary angle from the expansion and contraction direction of the element 1.

〔The invention's effect〕

As described above, according to the first aspect of the present invention, a sphere is arranged on both end faces of the element of the piezoelectric actuator in the direction of expansion and contraction so as to be in contact with the end face, and the sphere is sandwiched between the end face of the element and the sphere. A mechanism for transmitting the displacement generated in the element to the outside by the attached rigid body is provided, so that no compressive stress is generated in the ceramic of the protective layer of the element in the plane direction parallel to the end face. This has the effect of preventing cracks in the ceramics of the layer and breaking at the interface between the protective layer and the active layer.

Further, according to the second aspect of the present invention, by making the shape of the end face plate of the displacement transmission mechanism into a hemispherical shape,
It is possible to transmit the displacement in a direction having an arbitrary angle from the expansion and contraction direction of the element.

This means that in a machine that incorporates a piezoelectric actuator with a displacement transmission mechanism, the installation direction is not limited to one direction, and the degree of freedom in assembling into the machine is greatly increased compared to conventional piezoelectric actuators. It is very effective in increasing the mounting density of machines.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the structure of a first embodiment of the present invention,
FIG. 2 is a longitudinal sectional view showing the structure of the first embodiment of the present invention, FIG. 3 is an exploded perspective view of the displacement transmitting mechanism in the first embodiment of the present invention, and FIG. FIG. 5 is a diagram showing the relationship between the number of times of pulse application and the defect rate when a pulse-like voltage is applied to the first embodiment of the present invention and the conventional piezoelectric actuator.
FIG. 6 is a longitudinal sectional view showing the structure of the second embodiment of the present invention, FIG. 6 is a longitudinal sectional view showing the structure of the element of the piezoelectric actuator, and FIG. FIG. 4 is a diagram for explaining the occurrence of cracks and the occurrence of breakage at the interface between the protective layer and the active layer. 1 ... element, 2 ... active layer, 3 ... ceramics, 4a, 4
b: internal electrode, 5a, 5b: external electrode, 6: protective layer, 7
... metal members, 8, 13 ... adhesive, 9 ... displacement transmission mechanism,
10 ... insulating glass, 11 ... lead wire, 12 ... frame, 14 ...
Sphere, 15 ... end face plate, 16 ... groove, 17 ... convex part, 18 ...
… Clasp.

Claims (2)

(57) [Claims] A plurality of rigid spheres disposed on both end faces in the direction of expansion and contraction of the element so as to be in contact with the end faces, wherein the spheres fill each end face so as not to overlap with each other; A piezoelectric actuator with a displacement transmission mechanism, further comprising a mechanism for transmitting the displacement of the element to the outside by a rigid body attached to the sphere so as to sandwich the sphere therebetween and having a smooth contact surface with the sphere. 2. The displacement transmitting mechanism according to claim 1, wherein a shape of the rigid body sandwiching the sphere between the element and an end surface of the rigid body is a hemispherical shape on a side opposite to a side in contact with the sphere. Piezoelectric actuator with displacement transmission mechanism.