JPH03159278A - Laminated type displacement element - Google Patents

Abstract

PURPOSE:To obtain a laminated displacement element which is excellent in insulating property and very rarely dielectrically broken down by a method wherein a thin plate formed of electromechanical conversion material and an inner electrode formed of conductive material are constituted in a specific form. CONSTITUTION:Thin plates 1 formed of electromechanical conversion material are formed nearly the same in planar outline and contact area, and each of the plates 1 is so constituted so to satisfy a formula I. In the formula I, S denotes the cross-sectional area of the plate 1 vertical to a laminating direction, S0 represents the cross-sectional area of the processing affected layer formed in the plate 1 vertical to a laminating direction, rho is the resistivity of the electromechanical conversion material of the plate 1, and rho0 denotes the resistivity of the processing affected layer. Inner electrodes 2a and 2b are formed on all the surfaces of each of the plates 1, the plates 1 provided with inner electrodes 2a and 2b are laminated, pressure-joined together, and cut into a laminated body as prescribed in shape and size, and the laminated body is burned for a few hours at a prescribed temperature into a laminated body 5. By this setup, a laminated type displacement element of this design can be remarkably improved in insulation resistance, protected against dielectric breakdown even if it operates in an ambient atmosphere of high temperature, and improved in reliability.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an actuator for an industrial robot.

This relates to electromechanical transducers used in ultrasonic motors, etc., and in particular improves laminated displacement elements that increase the amount of displacement by laminating multiple thin plates made of electromechanical transducer material via internal electrodes. It is related to.

However, S: cross-sectional area of the thin plate in the plane perpendicular to the lamination direction So: cross-sectional area of the processed damaged layer in the thin plate in the plane perpendicular to the lamination direction ρ: specific resistivity of the electromechanical transducer material forming the Fii plate [conventional [Technology] Conventionally, laminated piezoelectric elements used for displacement elements used in X-Y stage positioning mechanisms and brakes, etc., are made by providing electrodes on a thin plate made of piezoelectric ceramic material processed into a predetermined shape. After polarization, a method of bonding with an organic adhesive directly or via a thin metal is used. However, when stacking layers using adhesive as described above, depending on the usage conditions, the adhesive layer may absorb displacement due to vibration of the piezoelectric element, or the adhesive may deteriorate due to high temperature environment or long-term use. There are drawbacks.

For this reason, recently, multilayer piezoelectric elements having a multilayer chip capacitor structure have been put into practical use. That is, 1. For example, as described in Japanese Patent Publication No. 59-32040, a paste-like piezoelectric ceramic material made by adding a binder to raw material powder and kneading is formed into a thin plate of a predetermined thickness, and one side of this thin plate or Internal electrodes are formed by coating both sides with a conductive material such as silver-palladium. A predetermined number of the above thin plates are laminated and crimped.

Further, after being processed into a predetermined shape, the laminate is made into a ceramic by firing, and external electrodes are formed on both sides of the laminate. The laminated piezoelectric element with the above structure has excellent adhesion between the thin plate made of piezoelectric ceramic material and the internal electrode, and has stable thermal properties, so it can be used satisfactorily even in high-temperature environments, and can be used for long periods of time. It has the advantage of extremely little deterioration over time.

FIG. 4 shows an example of the structure of the laminated piezoelectric element.

This is the so-called alternating electrode type. In FIG. 4, 1 is a thin plate made of piezoelectric ceramic material,
Positive and negative internal electrodes 2a and 2b are alternately sandwiched and stacked to form a stacked body 5. The internal electrodes 2a, 2b are each formed so that one end edge protrudes or is exposed to the outside, and are connected to external electrodes 3a, 3b each extending in the stacking direction, and the lead wire 6 is connected thereto.

With the above configuration, when positive and negative voltages are applied to the external electrodes 3a and 3b, an electric field is generated between the internal electrodes 2a and 2b, and the thin plate 1 is extended in the thickness direction due to the longitudinal effect of the piezoelectric ceramic material, causing displacement. .

Next, the one shown in FIG. 5 is an example of another laminated piezoelectric element, which is a so-called full electrode type with improved piezoelectric displacement efficiency (see, for example, Japanese Patent Application Laid-Open No. 58196068, etc.). In FIG. 5, the same parts are indicated by the same reference numerals as in FIG. 4, but the internal electrodes 2a, 2b are formed so as to cover the entire surface of the thin plate 1, and the required number of internal electrodes are laminated in the same manner as described above. Next, on one side of the laminate 5 formed as described above, the edges of the internal electrodes 2a, 2b are lined with (
For example, a coating 4 made of an insulating material is provided only on the internal electrode 2b, and an external electrode 3a made of a conductive material is applied over the coating 4. On the other hand, on the other side of the laminate 5, an internal electrode (for example 2a
) is provided with a coating 4 in the same manner as described above, and an external electrode 3b is applied thereon. The effect of the above configuration is similar to that shown in FIG. 4 above.

Note that in the element having the above configuration, the internal electrode 2a.

In order to prevent short circuits between the laminates 5 and 2b, measures have been taken to provide a coating (not shown) made of a resin material or a highly insulating elastic body 9, such as silicone rubber, on the side surface of the laminate 5 (for example, as disclosed in Japanese Patent Application Laid-Open No. 59-218784).

[Problem to be solved by the invention]

Although it is possible to prevent contamination from the outside of the laminate 5 or the adhesion and intrusion of non-insulating substances that affect the insulation properties by providing the coating with the above-mentioned structure,
The insulation resistance of the thin plates 1 constituting the laminate 5 cannot be improved.

Generally, the laminate 5 is formed by cutting a laminate block with a cross section of, for example, about 50 mm x 50 mm using a band saw or the like, and then processing such as polishing to form the laminate 5 having a cross section of, for example, about 5 mm x 5 mm. A process-affected layer is formed on the processed surface by the band saw or polishing process.

Since the specific resistivity of this process-affected layer is extremely low compared to the specific resistivity of the electromechanical conversion material constituting the thin plate 1, it is possible to significantly reduce the insulation resistance between the internal electrodes 2a and 2b. Become. Therefore, the internal electrodes 2a, 2b
The high voltage generated when the voltage applied between them fluctuates in a pulse-like manner causes a large current to flow instantaneously, causing an avalanche phenomenon.

There is a problem that dielectric breakdown occurs. Furthermore, the electromechanical transducer material constituting the thin plate 1 has a property that its specific resistivity decreases as the temperature increases;
There is also the problem that as the temperature of the operating atmosphere increases, the possibility of causing dielectric breakdown further increases.

The present invention solves the problems existing in the above-mentioned prior art and provides a laminated displacement element with excellent insulation properties, which has an extremely high insulation resistance value and an extremely low risk of causing dielectric breakdown. purpose.

[Means to solve the problem]

In order to achieve the above object, one aspect of the present invention is as follows.

A laminate is formed by alternately laminating a plurality of thin plates made of an electromechanical transducer material and internal electrodes made of a conductive material formed on the planar contour and contact area of the path, and the inner electrode is formed on the side surface of this laminate. In a laminated displacement element provided with a pair of external electrodes to be connected to electrodes every other layer.

However, S: cross-sectional area of the thin plate in a plane perpendicular to the lamination direction So: cross-sectional area of a processed damaged layer in the thin plate in a plane perpendicular to the lamination direction ρ: specific resistivity ρ0 of the electromechanical conversion material forming the thin plate. It is configured to have the specific resistivity of the process-affected layer. A technical method was adopted.

The reasons for the numerical limitations are described below.

FIGS. 6(a) and 6(b) are perspective views schematically showing thin plates forming a laminate. In both figures, the cross-sectional area of the thin plate l in the plane perpendicular to the lamination direction is S.

The thickness is t. In Figure 6(b), la
is a process-affected layer, which is formed at the periphery of Iil. The specific resistivity of the electromechanical conversion material forming the thin gold plate 1 is ρ, and the specific resistivity of the processed damaged layer 1a is ρ. Then, the sixth
The electrical resistance R1°R2 of the thin plate 1 in the cases shown in FIGS. (a) and (b) is expressed as follows.

ρ t R,= Accordingly, the above required specifications can be satisfied. On the other hand, RI/
If Rt exceeds 40, although it has a predetermined insulation resistance value at room temperature, the insulation resistance value decreases in a temperature range of 150° C., which is disadvantageous because dielectric breakdown may occur.

becomes.

Next, the Curie temperature of common electromechanical conversion materials is 15
Although the specific resistivity tends to decrease as the temperature rises around 0°C, it is necessary to have a predetermined insulation resistance value at least at the above 150°C. On the other hand, the insulation resistance value conventionally required for piezoelectric elements is
50 MΩ or more is required at looV. Said (1
), if R, /R, is l, then the work-affected layer 1a (
(see FIG. 6(b)) does not exist at all.

Although this is an ideal state, even if some work-affected layer 1a is present, it is sufficient to have an insulation resistance value that satisfies the above specifications. In the present invention, R, /Rz≦40 [Example] Figures 1(a) to 1c) are perspective views showing examples of the present invention, and the same parts are shown in Figures 4 and 5 above. First, in FIG. 1(a), which is indicated by the same reference numeral ``,'' for example, P b (Z r + T t ) Os powder is mixed with PVB as an organic Pygoo and BPBG as a plasticizer.

Trichlene was added as an organic solvent and mixed.

This mixed material is coated with a doctor blade method to a thickness of approximately 100 mm.
It is formed into a sheet-like thin plate 1 of μm. Next, platinum conductive paste or silver palladium paste for forming internal electrodes 2a, 2b is screen printed over the entire surface of this thin plate 1. For example, 100 sheets of the thin plates 1 having the internal electrodes 2a and 2b formed as described above are alternately laminated and crimped, and then cut into a predetermined size and shape 9 of, for example, 5 mm x 5 mm to form a laminate. After firing for ~5 hours to form a laminate 5, coatings 7a and 7b made of an insulating material are applied to adjacent sides of the laminate 5, and internal electrodes 2a and 2b are coated on adjacent sides of the laminate 5.
provided so as to cross the In FIG. 1(b), 8a,
Reference numeral 8b indicates a groove, and the covering 7a,
Internal electrode 2a of 7b.

It is engraved at the position corresponding to 2b. In FIG. 1(c), external electrodes 3a, 3b are placed on coatings 7a, 7b.

By providing the grooves 8a, 8b so as to cross them, the external electrodes 3a, 3b and the internal electrodes 2a, 2b can be connected to each other in a corresponding manner. When the insulation resistance was measured in this state, it was 1.5×10@Ω. In this case, the laminate 5
There is a process-altered layer. On the other hand, the insulation resistance of the laminate 5, which was mirror-polished on all four sides to remove most of the damaged layer, was 2.1×10 10 Ω. Note that the measurement voltage was 100V in all cases.

Next, chemical etching with a hydrochloric acid solution was applied to the side surface of the laminate 5 where the process-affected layer was present, and the insulation resistance was successively measured. FIG. 2 is a diagram showing the relationship between machining allowance and insulation resistance. As is clear from FIG. 2, the insulation resistance increases as the machining allowance increases, and is saturated at a machining allowance of approximately 13 μm. Therefore, the thickness of the process-affected layer is estimated to be 13 μm. In this case, the cross-sectional area of the damaged layer in a plane perpendicular to the stacking direction is 0.013X5X4=0.013X5X4 from FIG. 6(b).
26mm”, so in the above equation (1), R+=2.1x
lO"Ω, Rt = 1.5X10"Ω.

By substituting So = 0.26 mm'' and S = 25 mm'', we obtain ρ ζ], 3X10'. That is, the specific resistivity of the process-altered ρO layer differs by four orders of magnitude from the specific resistivity of the electromechanical conversion material. Therefore, the insulation resistance of the entire element is significantly reduced.

Figure 3 is a diagram showing the relationship between temperature and insulation resistance, and the numbers in the figure are the machining allowances (unit: μm) for the process-affected layer.Curve a is for the case where no process-affected layer exists. It is. Both were determined using the same laminate as the object in FIG. 2 above. As is clear from Figure 3, the temperature is 150
In order to ensure insulation resistance of 50MΩ or more at ℃,
The processing allowance must be 2 μm or more. Note that since the insulation resistance corresponding to curve a at 150° C. is 500 MΩ, R and /R in the above equation (1) are approximately 10.

In other words, even if some process-affected layers remain, R+/R
As long as the zO value can be maintained at 10 or less, an insulation resistance of 50 MΩ or more can be ensured even in an atmosphere at a temperature of 150°C. The above relationship is Rl / Rt at room temperature
It becomes ζ40. Note that since it is easy and reliable to measure R, /R, at room temperature, R, /R, = 40.
It is preferable to set the upper limit to . Therefore, the above formula (]) is.

S ρ0 In this embodiment, an example in which chemical etching was used as a means for removing the process-affected layer was shown.

Other etching and polishing such as ion etching,
It is also possible to use a process-affected layer removing means such as polishing or annealing, or a processing means that does not easily generate a process-affected layer.

In this embodiment, an example of the full-surface electrode type with the configuration shown in FIG. 1 has been described, but the alternate electrode type shown in FIG. 4 and the full-surface electrode type with the configuration shown in FIG. 5 are also described. is also naturally applicable. In addition, the planar projection shape of the thin plate and the internal electrodes may be a square, a circle, an ellipse, or other geometric shapes other than a rectangle. Alternatively, in order to obtain a larger displacement, it is also possible to use a plurality of the elements bonded together with a heat-resistant adhesive. In the above embodiment, an example was described in which screen printing was used as a means of forming the internal electrodes and external electrodes, but the same effect can be obtained by other methods such as plating, vapor deposition, and coating. It is.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above,
The absolute total resistance value of the laminated displacement element, which has been insufficient in the past, can be significantly improved.

Even when the temperature of the operating atmosphere is high, dielectric breakdown can be prevented and the reliability can be improved.

[Brief explanation of the drawing]

FIGS. 1(a) to C) are perspective views showing embodiments of the present invention, FIG. 2 is a diagram showing the relationship between processing allowance and insulation resistance,
Figure 3 is a diagram showing the relationship between temperature and insulation resistance, Figures 4 and 5 are diagrams each schematically showing an example of a conventional laminated displacement element, and Figures 6 (a) and (b) are respectively FIG. 2 is a perspective view schematically showing thin plates forming a laminate. 1: thin plate, 5: laminate.

Claims (1)

[Claims] (1) A laminate is formed by alternately stacking a plurality of thin plates made of an electromechanical transducer material and internal electrodes made of a conductive material, which are formed to have approximately the same planar contour and contact area, and the side surfaces of this laminate are In the laminated displacement element having a pair of external electrodes to be connected to the internal electrodes every other layer, the thin plates are 1+S_0/S(ρ/ρ_0-1)≦40, where S: a plane perpendicular to the stacking direction. Cross-sectional area of the thin plate S_0: Cross-sectional area of the process-affected layer in the thin plate in the plane perpendicular to the lamination direction ρ: Specific resistivity of the electromechanical conversion material forming the thin plate ρ_0: Specific resistivity of the process-affected layer A laminated displacement element characterized by comprising: