JP2001078471A - Piezoelectric transducer element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the drive efficiency of a piezoelectric transducer element by eliminating element sections which do not contribute to the drive of the element by forming the element in a nearly solid columnar body. SOLUTION: First and second electrodes 11a and 12a are respectively formed on the surfaces of sheet-like first and second piezoelectric elements 11 and 12. The first and second piezoelectric elements 11 and 12 are laminated upon another, by facing the electrode nonforming surface of the element 11 opposite to the electrode forming surface of the element 12, and a nearly solid columnar body is formed by winding the laminate, so that spaces are hardly left in the central part. Then a piezoelectric transducer element 10 is obtained by baking the columnar body and polarizing the electrodes 11a and 12a by supplying a voltage across the electrodes 11a and 12a. Since spaces which do not contribute to the drive of the element 10 scarcely exist in the central part, the drive efficiency of the element 10 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transducer, and more particularly to a structure of a piezoelectric transducer formed by winding a sheet-shaped piezoelectric material into a solid columnar body.

[0002]

2. Description of the Related Art An actuator using a piezoelectric conversion element has a high conversion efficiency for converting supplied electric energy into driving force, is small in size and light in weight, generates a large driving force, and easily controls the driving force. As a result, it has been used for driving and positioning of driven members of cameras, measuring instruments, and other precision machines.

Some of the piezoelectric transducers, which are driving sources used in such actuators, include a plurality of unitary piezoelectric elements stacked. This is because the displacement in the thickness direction generated in the unit piezoelectric element is taken out as large as possible.

[0004] Piezoelectric transducers composed of a plurality of unitary piezoelectric elements laminated require the complicated steps of providing electrodes on the surface of each unit element, laminating and bonding, and connecting the electrodes of each layer. It is expensive because it is manufactured after passing through.

[0005] For this reason, there has been proposed a piezoelectric conversion element formed by winding a laminate in which two thin plate-shaped piezoelectric elements each having electrodes formed on the surface thereof are stacked in a hollow cylindrical shape.

FIG. 13 is a perspective view showing an example of a piezoelectric transducer formed by laminating such two thin plate-shaped piezoelectric elements into a cylindrical shape. FIGS. FIG. 15 is a plan view for explaining a state of an end face in a cylindrical axis direction of a piezoelectric transducer formed in a cylindrical shape.

The manufacturing process of the piezoelectric transducer will be described. First, as shown in FIG. 14A, a first piezoelectric element 101 and a second piezoelectric element 102 made of a piezoelectric ceramic formed in a thin plate shape are prepared. Here, the length in the winding direction of the second piezoelectric element 102 is set to the first piezoelectric element 101.
Longer than the dimension d.

A first electrode 103 is formed on the front surface of the first piezoelectric element 101, and the back surface is a surface on which no electrode is formed. Further, a second electrode 104 is formed on the front surface of the second piezoelectric element 102, and the back surface is an electrode non-formed surface (see FIG. 14A).

Next, as shown in FIG.
Of the piezoelectric element 101 on which the electrode is not formed and the second piezoelectric element 10
The two electrodes are stacked so that the electrode forming surfaces face each other, and the stacked body is wound using a work winding shaft made of cellulose or the like to form a cylindrical body as shown in FIG.
Thereafter, the piezoelectric element is fired at a predetermined temperature and further subjected to a polarization treatment to fire and complete the piezoelectric transducer. Since the work take-up shaft is burned off by firing, a cylindrical space remains in the innermost part of the cylindrical body.

By making the length of the first piezoelectric element 101 in the winding direction shorter than the length of the second piezoelectric element 102 in the winding direction, the first piezoelectric element
And the ends of the second electrodes 104 are shifted, and the lead wires 103a and 104a can be easily connected to those electrodes.

[0011]

In the cylindrical piezoelectric transducer having the above-described structure, as shown in FIG. 15, a cylindrical space remains in the innermost portion of the cylindrical body due to its structure. The second piezoelectric element 102 includes a first electrode 103 and a second electrode 104.
A portion X that is not sandwiched is generated. This portion does not cause expansion and contraction displacement even when a voltage is applied between the first electrode 103 and the second electrode 104 of the piezoelectric transducer, and the expansion and contraction displacement of the element portion in contact with the outside and where expansion and contraction occurs. As a result, the expansion / contraction performance of the entire piezoelectric conversion element is reduced.

This problem can be solved by forming electrodes on both surfaces of the piezoelectric element 102 located on the innermost side of the cylindrical body. However, there is a disadvantage that the number of manufacturing steps increases accordingly. I do.

When the diameter of the inner space portion is larger than the outer diameter of the cylindrical body, that is, when the thickness of the cylindrical body is smaller than the outer diameter of the cylindrical body, the piezoelectric transducer is axially moved in the axial direction. However, there is an inconvenience that the strength against buckling fracture and compression fracture when a load of 1) is applied is insufficient.

Further, since the electrodes provided on the surface of the piezoelectric element do not cause the expansion and contraction displacement, they act to inhibit the expansion and contraction displacement of the piezoelectric element. The thinner the thickness of the piezoelectric element, the higher the electric field strength can be obtained at a lower voltage, which is advantageous in forming a drive circuit.However, the thickness of the piezoelectric element is thinner than the thickness of the electrodes formed on its surface. In this case, the expansion and contraction displacement of the piezoelectric element is hindered by the electrode, resulting in a reduction in the expansion and contraction displacement performance of the entire piezoelectric conversion element. An object of the present invention is to solve the above problems.

[0015]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. According to the first aspect of the present invention, a sheet-like piezoelectric element made of a ceramic-based piezoelectric material having electrodes formed on its surface is wound up, A piezoelectric conversion element formed in a columnar body.

The sheet-like piezoelectric element comprises a sheet-like first piezoelectric element made of a ceramic-based piezoelectric material having a first electrode formed on the surface thereof and a ceramic-based piezoelectric material having a second electrode formed on the surface thereof. A second piezoelectric element in the form of a sheet, and laminating the laminated body such that the electrode-free surface of the first piezoelectric element and the electrode-formed surface of the second piezoelectric element face each other, It is good to form in a columnar body.

Further, the sheet-shaped piezoelectric element comprises a sheet-shaped piezoelectric element made of a ceramic piezoelectric material having a first electrode and a second electrode formed on both surfaces, respectively.
The laminate may be folded into two at a substantially central portion of the length in the winding direction and wound up around the folded portion to form a solid columnar body.

The ratio of the diameter of the space portion slightly remaining at the center of the solid pillar to the outer diameter of the solid pillar is preferably 0.15 or less.

It is preferable that the ratio of the thickness of the electrode formed on the surface to the thickness of the sheet-like piezoelectric element is 0.1 or less.

[0020]

Embodiments of the present invention will be described below.

[First Embodiment] FIG. 1 is a perspective view showing the structure of a piezoelectric transducer according to a first embodiment, and FIG. 2 is a cross-sectional view thereof. For convenience of explanation, the thickness of the piezoelectric element is enlarged. Is shown.

The piezoelectric transducer 10 of the first embodiment is
Sheet-shaped first and second piezoelectric elements 11 and 1 made of a piezoelectric ceramic-based piezoelectric material formed in a thin plate shape
A first electrode 11a and a second electrode 12a
Are formed, and the electrode non-formed surface of the first piezoelectric element 11 and the electrode formed surface of the second piezoelectric element 12 are laminated so as to face each other. It is formed in.

The manufacturing process of the piezoelectric transducer 10 will be described.
First, as a material of the first piezoelectric element 11 and the second piezoelectric element 12, a piezoelectric ceramic mainly composed of PZT (PbZrO ₃ .PbTiO ₃ ) is used. This ceramic powder is mixed with a solvent, a dispersant, a binder, a plasticizer and the like, formed into a uniform plane using a blade or the like, and stretched to a certain thickness, for example, a thickness of 20 to 100 μm. When the solvent is evaporated and dried, a flexible sheet called a green sheet can be obtained.

Next, a paste-like electrode material, for example, platinum (Pt) -based, silver-palladium (Ag-P) is formed on the surface of the green sheet (piezoelectric element) by screen printing or the like.
d) An electrode material obtained by converting the system electrode material into a paste with an appropriate resin binder is printed to a thickness of 3 to 7 μm (after firing, the resin binder volatilizes to about 1 to 3 μm) to form an electrode. I do.

The green sheet having the electrode formed on the surface is cut into a predetermined size, and the first piezoelectric element 11 having the first electrode 11a formed on the surface and the first piezoelectric element 11 having the second electrode 12a formed on the surface. Then, two piezoelectric elements 12 are formed.

The electrode-free surface of the first piezoelectric element 11 and the second
The piezoelectric element 12 is laminated with the surfaces on which the second electrodes 12a are formed facing each other, and the end of the laminated body is folded back small as shown in FIG. It is wound up so that it does not remain and formed into a substantially solid columnar body.

FIG. 4 is a cross-sectional view showing an example of a hoisting device suitable for winding the above-mentioned laminated body.
There is provided a structure in which a roller 17 which is pressed by a suitable urging means such as a spring toward the circular arc surface 16a is arranged on a base 16 having 6a.

As shown in FIG. 4, the folded portion 13 formed at the end of the laminate composed of the first piezoelectric element 11 and the second piezoelectric element 12 is connected to the arcuate surface 16a of the base 16, the roller 17 and When the roller 17 is rotated in the direction of the arrow w and the roller 17 presses the laminate against the arcuate surface 16a, the laminate is wound up with little space left in the center thereof. The inner diameter of the folded portion 13 is equal to or less than the thickness of the laminate, and is as small as possible.

Instead of forming the folded portion 13 at the end of the laminate, a work take-up shaft made of a material such as cellulose or synthetic resin, which is burned off when the laminate is fired, is connected to the end of the laminate. It can also be attached or pressed into contact with and wound up. In this case, the diameter of the working winding shaft is made as small as possible.

Next, the rolled-up laminate is fired under a predetermined temperature condition, and the first electrode 11a and the second electrode 12a are fired.
Are connected to lead wires 11b and 12b, respectively, and are polarized by applying a predetermined high DC voltage.
Is completed.

As shown in FIG. 5, for example, as shown in FIG. 5, the temperature is gradually increased up to 500 ° C. in about 5 hours, and after baking at 500 ° C. for a certain time, 9 hours after the beginning, it is gradually increased to 1200 ° C. To increase the temperature. In addition, 120
After baking at 0 ° C. for about 0.3 hours, it is cooled to room temperature over about 6 hours.

The direction of polarization is the thickness direction of the sheet-like piezoelectric element.
A voltage of 1.5 kV / mm is applied between the first electrode a and the second electrode 12a for 20 minutes for polarization. By polarizing the piezoelectric element, displacement of the piezoelectric conversion element 10 in the cylindrical axial direction can be generated.

FIG. 6 shows the diameter D of the space portion (remaining space portion) remaining in the center portion of the piezoelectric transducer and not involved in expansion and contraction, that is, the ratio D () between the diameter of the non-stretchable portion and the outer diameter of the piezoelectric transducer. FIG. 6 is a diagram showing an experimental result obtained by examining a relationship between%) and a displacement d (μm). The experiment was performed by applying a constant voltage between the electrodes of the piezoelectric transducer.

As is clear from the experimental results, the smaller the ratio D between the diameter of the non-stretchable portion remaining in the central portion and the outer diameter of the piezoelectric transducer, that is, the smaller the ratio of the outer diameter of the piezoelectric transducer to the center of the piezoelectric transducer. It can be seen that a larger displacement d is obtained as the remaining space is smaller, and that the conversion efficiency indicating the magnitude of the generated displacement with respect to the applied voltage is better.

[Second Embodiment] FIG. 7 is a perspective view showing the structure of a piezoelectric conversion element according to a second embodiment, and FIG. 8 is a cross-sectional view thereof. For convenience of explanation, the thickness of the piezoelectric element is enlarged. Although a small space is provided between the laminates, the laminates are actually in close contact with each other.

The piezoelectric transducer 20 of the second embodiment is
A first electrode 21a and a second electrode 21b are respectively formed on the front and back surfaces of a single sheet-shaped piezoelectric element 21 made of a piezoelectric ceramics-based piezoelectric material formed in a thin plate shape. And is wound up so that almost no space remains in the center portion around the folded portion 23 to form a substantially solid columnar body.

Therefore, the first portion of the piezoelectric element 21
The electrode 21a and the first electrode 21 of the folded piezoelectric element 21
a and oppose each other, and similarly, the second electrode 21b also opposes and contacts each other.

Since the material of the piezoelectric element 21 and the formation of the green sheet and the formation of the electrode material and the electrode are the same as those of the first embodiment, the description is omitted here.

The first electrode 21a and the second electrode 21
The green sheet on which b is formed is cut into a predetermined size, and the piezoelectric element 21 is formed.

The piezoelectric element 21 is folded and laminated at a substantially central portion in the longitudinal direction, and wound up so as to leave almost no space in the central portion with the folded portion 23 as a center, thereby forming a substantially solid columnar body. For the hoisting operation, a hoisting device 15 as shown in FIG. 4 can be used as in the case of the first embodiment.

Next, the rolled-up laminate is fired under a predetermined temperature condition, and the first electrode 21a and the second electrode 21b are fired.
Are connected to lead wires 22a and 22b, respectively, and a predetermined DC high voltage is applied to polarize them.
Is completed.

In the piezoelectric transducer 20 according to the second embodiment, since there is no portion not involved in expansion and contraction at the center portion, even if a residual space portion occurs at the center portion during winding, the magnitude of the displacement generated with respect to the applied voltage is large. Although it does not affect the conversion efficiency, which is a measure of mechanical strength, a solid columnar structure having no residual space at the center is preferred from the viewpoint of mechanical strength.

FIG. 9 is a diagram showing the results of an experiment in which mechanical strength was tested by pressing the piezoelectric transducer 20 of the second embodiment in the radial direction. The abscissa represents the central portion with respect to the outer diameter of the piezoelectric transducer. And the vertical axis represents the pressing force T.
(Newton). The thickness of the piezoelectric element used in the experiment was about 40 μm, and the thickness of the electrode was about 3 μm.

As is clear from this figure, if the diameter of the unwound space at the center is smaller than 0.15 times the outer diameter of the piezoelectric transducer, mechanical strength equivalent to that of the solid columnar structure can be obtained. It is understood that it is possible.

FIG. 10 is a diagram showing the results of an experiment in which the effect of the thickness of the material of the piezoelectric transducer on the amount of displacement was examined. The horizontal axis represents the ratio of the thickness of the electrode to the thickness of the piezoelectric element, ie, electrode thickness / electrode thickness. The piezoelectric element thickness G (%) is shown, and the vertical axis shows the displacement d (μm). The voltage applied to the piezoelectric transducer was adjusted so that the electric field strength was constant in the piezoelectric transducer.

As is apparent from this figure, when the thickness of the electrode is 10% or less of the thickness of the piezoelectric element, no displacement is hindered by the electrode, and a large displacement can be obtained.

Next, the structure of an actuator using the above-described piezoelectric transducer will be described with reference to FIGS. In the following description, an actuator using the piezoelectric transducer 10 of the first embodiment will be described, but the same applies to a case where the piezoelectric transducer 20 of the second embodiment is used.

FIG. 11 is a sectional view showing the structure of the actuator. In FIG. 11, 31 is a base, 32, 33, 3
Reference numeral 4 denotes a support block, and reference numeral 35 denotes a drive shaft. The drive shaft 35 is supported by the support block 33 so as to be displaceable in the axial direction (the direction of the arrow a and the direction opposite thereto) by the axial displacement generated in the piezoelectric transducer 10. It is movably supported by a block 34.

Reference numeral 10 denotes a solid columnar piezoelectric transducer.
One end of the piezoelectric transducer 10 is adhesively fixed to the support block 32, and the other end is adhesively fixed to one end of the drive shaft 35.

Reference numeral 40 denotes a drive pulse generating circuit for generating a sawtooth pulse having a gentle rising portion and a rapid falling portion, or a rapid rising portion and a gentle falling portion. The drive pulse generation circuit 40 supplies a drive pulse between the electrodes 11 a and 12 a of the piezoelectric conversion element 10 to drive the piezoelectric conversion element 10.

Numeral 36 denotes a slider, and the slider 36 and the drive shaft 35 are frictionally coupled by an appropriate frictional force. FIG.
FIG. 9 is a cross-sectional view showing a configuration of a frictional coupling portion between the slider and the drive shaft 35. A drive shaft 35 penetrates the slider 36, and an opening 36a is formed in a lower portion of the slider 36 through which the drive shaft 35 penetrates. Are formed, and the lower half of the drive shaft 35 is exposed. A pad 37 which is in contact with the lower half of the drive shaft 35 is inserted into the opening 36a, and the pad 37 is pushed up by a leaf spring 38, and the drive shaft 35, the slider 36 and the pad 37 are connected to the leaf spring 38. They are pressed against each other by the urging force F, and are frictionally coupled by an appropriate frictional force. Also,
It is assumed that a driven member such as a table (not shown) is connected to the slider 36.

The operation will be described. When the first electrode 11a and the second electrode 12a of the piezoelectric conversion element 10 are connected to the drive pulse generation circuit 40 and a sawtooth wave drive pulse of several tens of kHz is applied between the first electrode 11a and the second electrode 12a, Since the expansion and contraction displacement occurs in the conversion element 10 in the axial direction, reciprocating vibrations having different speeds in the axial direction occur in the drive shaft 35 coupled to the piezoelectric conversion element 10. As a result, the slider 36 frictionally coupled to the drive shaft 35 moves in the direction of slow vibration due to the asymmetry of the reciprocating vibration of the drive shaft while sliding on the drive shaft 35, thereby moving a driven member such as a table coupled to the slider. Can be moved.

[0053]

As described above, the piezoelectric transducer of the present invention is formed by winding up a sheet-like piezoelectric element made of a ceramic-based piezoelectric material having electrodes formed on the surface thereof. It is rolled up so that almost no space remains, and is formed into a substantially solid columnar body.

By forming the piezoelectric conversion element in a substantially solid columnar shape, there is almost no space portion that does not contribute to expansion and contraction displacement at the center portion, so that the expansion and contraction displacement performance of the entire piezoelectric conversion element can be improved.

Furthermore, by forming the piezoelectric conversion element in a substantially solid columnar body, a remarkable operational effect can be obtained, for example, the strength against buckling breakage and compression breakage due to an externally applied load can be increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the appearance of a piezoelectric conversion element according to a first embodiment.

FIG. 2 is a sectional view of the piezoelectric conversion element according to the first embodiment.

FIG. 3 is a perspective view illustrating a folded portion formed at an end of the piezoelectric element laminate.

FIG. 4 is a cross-sectional view illustrating an example of a hoisting device that winds a laminate.

FIG. 5 is a diagram showing an example of firing temperature conditions for a piezoelectric conversion element.

FIG. 6 is a diagram showing the relationship between the ratio of the diameter of the non-stretchable portion at the center of the piezoelectric transducer to the outer diameter of the piezoelectric transducer and the amount of displacement.

FIG. 7 is an exemplary perspective view showing the appearance of a piezoelectric transducer according to a second embodiment;

FIG. 8 is a sectional view of a piezoelectric transducer according to a second embodiment.

FIG. 9 is a diagram showing an experimental result regarding mechanical strength of a piezoelectric transducer.

FIG. 10 is a view showing experimental results regarding the thickness and displacement of the material of the piezoelectric transducer.

FIG. 11 is a sectional view showing a configuration of an actuator using a piezoelectric transducer.

FIG. 12 is a cross-sectional view illustrating a configuration of a frictional coupling portion between a slider of an actuator and a drive shaft.

FIG. 13 is a perspective view showing an example of a conventional piezoelectric transducer formed by laminating two thin plate-shaped piezoelectric elements into a cylindrical shape.

FIG. 14 is a view for explaining an electrode forming surface and a laminated state of the conventional piezoelectric transducer shown in FIG.

FIG. 15 is a plan view illustrating an end face of the conventional piezoelectric transducer shown in FIG. 13 in a cylindrical axis direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Piezoelectric conversion element 11 1st piezoelectric element 12 2nd piezoelectric element 11a 1st electrode 12a 2nd electrode 13 Folding part 15 Hoisting device 16 units 16a Arc surface 17 Roller 20 Piezoelectric conversion element 21 Piezoelectric element 21a First electrode 21b The second electrode 23 folded part

Claims (5)

[Claims] 1. A piezoelectric conversion element wherein a sheet-like piezoelectric element made of a ceramic-based piezoelectric material having electrodes formed on its surface is wound up and formed into a solid columnar body. 2. The sheet-like piezoelectric element has a first surface on its surface.
A first piezoelectric element in the form of a sheet made of a ceramic piezoelectric material having electrodes formed thereon, and a second piezoelectric element in the form of a sheet made of a ceramic piezoelectric material having a second electrode formed on the surface thereof have a first shape. Of the piezoelectric element having no electrode and the second
2. The piezoelectric conversion element according to claim 1, wherein the laminated body is wound up and formed into a solid columnar body so that the electrode forming surface of the piezoelectric element faces the electrode. 3. The sheet-shaped piezoelectric element comprises a sheet-shaped piezoelectric element made of a ceramic-based piezoelectric material having a first electrode and a second electrode formed on both surfaces thereof, and has a length in a winding direction. 2. The piezoelectric conversion element according to claim 1, wherein the laminated body folded in two substantially at the center is wound up around the folded portion to form a solid columnar body. 4. The ratio of the diameter of the space portion slightly remaining at the center of the solid columnar body to the outer diameter of the solid columnar body is 0.15.
The piezoelectric conversion element according to claim 1, wherein: 5. The piezoelectric device according to claim 1, wherein the ratio of the thickness of the electrode formed on the surface to the thickness of the sheet-shaped piezoelectric element is 0.1 or less. Conversion element.