JPS63268279A - Piezo-electric bimorph element - Google Patents

Abstract

PURPOSE:To manufacture a piezo-electric actuator in high reliability due to easy manufacture eliminating the bonding process by a method wherein the polarization levels of two phases are differentiated to make the piezo-electric constant different by two ceramics bordered on a central line having respectively different dielectric constant ratios due to the difference in the dielectric constant of the two ceramic layers. CONSTITUTION:One composition of piezo-electric ceramics is selected from a part high in dielectric constant and high in electromechanical bonding coefficient as well as another part of the same level of dielectric constant or exceeding the same but of a low electromechanical bonding coefficient. A compound laminated layer ceramics sheet can be manufactured by laminating two component sheets of this powder thermal pressure-fixed in specified thickness and size as well as stamping in rectangular shape and firing for several hours. Electrodes are formed on both surfaces of this compound laminated sheet by firing-finish silver paste, etc., and then the space between electrodes is impressed with DC current at specified temperature to be polarization-processed. The piezo-electric ceramics layers 1.2 of different dielectric constant are mutually bonded to form electrodes 3 on upper and lower surfaces as a fundamental structure with one end thereof fixed by fixtures 4, 4 for application. Thus, respective electrodes 3 connected to lead terminals 5 are impressed with specified voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Overview of the Technical Field The present invention relates to a piezoelectric bimorph element that utilizes strain generated by the inverse piezoelectric effect of a piezoelectric material.

In actuators that utilize piezoelectricity, since the amount of strain generated by the piezoelectric material is absolutely small, the piezoelectric material itself is rarely used as is.

Currently, there are two types of piezoelectric actuators commonly used: a laminated piezoelectric actuator and a bimorph piezoelectric actuator.
Piezoelectric ceramic materials with large piezoelectric constants are often used. The former uses the longitudinal effect (expansion and contraction in the same direction as the polarization direction), and the unit is a ceramic plate with electrodes on both sides and polarized in the thickness direction, and multiple pieces are stacked in the thickness direction, and each unit element is When electrically connected in parallel and a voltage is applied, the strain generated by each unit element is added in the thickness direction, so the amount of strain generated by the longitudinal effect of a single piezoelectric ceramic rod is It is possible to obtain a strain that is twice as large as the number of laminated layers.

On the other hand, piezoelectric bimorphs are based on the lateral effect (
It uses two rectangular piezoelectric ceramic plates with electrodes formed on both sides and polarized in the thickness direction as the intermediate electrode layer, and a conductive thin shim plate sandwiched between them. Two pieces of piezoelectric ceramic are pasted together, one end is fixed, and a voltage is applied to one of the two piezoelectric ceramics in the same direction as the polarization to cause it to shrink in the length direction, and a voltage is applied to the other in the opposite direction to the polarization. This creates an elongation strain in the length direction, causing the free end to bend significantly.

This structure is equipped with a displacement expansion mechanism,
A relatively large distortion can be generated.

A laminated piezoelectric actuator has a small amount of displacement but can generate a large force. Furthermore, although the bimorph actuator has a large amount of displacement, the force that it can generate due to its structure is small. Each is used according to its characteristics.

<Problems with the Prior Art> Incidentally, this type of piezoelectric bimorph actuator is basically constructed by bonding two piezoelectric ceramic plates, so that the middle part of the bonding process increases the cost.

■Performance variations occur due to variations in adhesion. ■There is a risk of cracks in the ceramic during the bonding process, and there are drawbacks such as low reliability.

<Object of the present invention> In view of the above, the present invention provides that when electrodes are formed on both sides of a single fired body and polarization treatment is performed, the electric field is There is a difference in strength, so that the electric field strength applied to one ceramic layer with a high dielectric constant is insufficient to sufficiently polarize that part, and a sufficient polarization electric field is applied only to the other ceramic layer with a low dielectric constant. As a result, the structure has a difference in piezoelectric strain constant without creating a large difference in the degree of polarization, and when a voltage is applied between the electrodes, the difference in piezoelectric strain constant is converted into a dielectric constant. Due to the difference in electric field strength, one side generates distortion while the other does not, so when one end is fixed, the other free end can be bent significantly, making it easy to manufacture. The main purpose is to propose a low-cost and highly reliable piezoelectric bimorph element.

Embodiment of the present invention> An embodiment of the present invention will be described in detail below with reference to the drawings.

It is known that the properties of piezoelectric ceramics can be adjusted over a wide range by changing the compound structure. Figures 1, 3 and 2 show Pb(Mn,...), which is an example of PZT-based piezoelectric ceramics, which is a typical piezoelectric ceramic.

Nb2. , )03P b Z r O3P b T
It is a ternary map showing the relationship between the composition, dielectric constant, and electromechanical coupling coefficient of a ternary piezoelectric ceramic with + Ov j of 1%. A composition with a large dielectric constant and electromechanical coefficient exists on a line where the composition of PbZ'0. This is a large portion.Moreover, even if it deviates from this line in any direction, the dielectric constant and electromechanical engagement coefficient become smaller, and the piezoelectric d constant also becomes smaller.

Therefore, one composition is selected from a part with a high dielectric constant and a high electromechanical coupling coefficient, and a part with a permittivity of the pond at the same level or higher and a low electromechanical coupling coefficient, and an organic binder is added to this powder. 2, which was mixed and processed in a specified manner to form a slurry, and then made into a sheet using a doctor blade method, etc.
Two sheets of the composition are laminated to a certain thickness and size by thermo-compression bonding and punched into a rectangular shape, treated for several hours at about 600℃, the temperature at which binders decompose, and then at a temperature of around 1200℃ for several hours. A composite laminated ceramic plate is obtained by firing.

The important point is that there is no difference in the shrinkage rate during the firing process of the sheet made of powder of two compositions, and to adjust this, it is necessary to control the density of the green sheet with some additives and sheet manufacturing conditions. There is.

This composite laminate is polarized by forming electrodes on both sides of the plate by baking, vapor deposition, sputtering, etc. with silver paste, and then applying a DC voltage between the electrodes at a constant temperature.

For convenience, the above manufacturing processes are summarized as follows: ■Powder production (weighing, calcination, pulverization), ■Sheet formation, ■Thermocompression bonding, ■Punching, ■Binder treatment, ■Sintering, ■Electrode formation, ■Polarization. Become.

FIG. 3 is a diagram showing the basic structure of the present invention. 1.degree.2 indicates piezoelectric ceramic layers having different dielectric constants, which are bonded to each other. Electrodes 3 are formed on the upper and lower surfaces, and the ends thereof are fixed by fixtures 4, 4, when used. A lead terminal 5 is connected to each electrode 3, and a constant voltage is applied thereto.

The meaning of the electric field strength applied to the layers made of ceramics of these two compositions will be explained using FIG. 4. When a voltage V is applied between both electrodes, the electric flux density remains unchanged between the electrodes, so equation (1) holds true.

D=εIE,=ε2E2...(1) (However, ε
1. ε2 is the dielectric constant of the two ceramic layers, E, , E2
is the electric field strength).For the relationship with the applied voltage ■, formula (2) holds true.

V=EIL1+E2t2...(2) (However, L
l and I2 are the thicknesses of the two ceramic layers) Therefore, according to equations (1) and (2), 1) El=V/ll+(ε1/ε2)t.

E2;=V/(ε1/ε2)J+t,...(3
)t+=t2, E,=V/l・1/1+(ε 1/ε2)E 2=
V /l・1/(ε2/ε1)+1...(3') Formula (
According to 3'), if the ratio of ε2/ε1 is 2, E, /E
It can be seen that the ratio of 2 is also 2. Therefore, by selecting a predetermined ratio of the dielectric constants of both ceramics, it is possible to set polarization conditions such that an electric field sufficient for polarization is applied to one ceramic and an electric field insufficient for polarization is applied to the other. Therefore, a composite ceramic plate polarized at a predetermined temperature and voltage can be composed of a piezoelectric portion and a non-piezoelectric portion with the boundary layer as a boundary.

Therefore, the constituting ceramic has two phases with dielectric constants ε1 and ε2. The Young's modulus is assumed to be equal to Y, , r-, and the shape of the rectangular plate fixed at one end is 5×W×2t, and when a voltage ■ is applied between both electrodes, the deflection δ of the free end is determined.

As ε2〈ε1, the energy U1 stored on the side ε is,
U, = 1/2E, ・D, ・W (l t=172・WI
27t・ε1/(1+ε1/ε2)2・V2 The mechanical energy Um stored in the ceramic on the ε1 side is as follows: U = 3/4, 2・Ul = 374, 2・1/2W (1/l・ε1/(1+
ε1/ε2)2・V2 The energy source that causes the rectangular plate to warp is Um. If the radius of curvature when warping is occurring is R, then the elastic energy Um' of warping is: Um' = (l Y Iz/2 R2Um' is Um itself, and ffYIz/2R2=374 is 3.2・W , 17/21
ε+7(1+ε1/ε2)2・■2 The relationship between the displacement δ at the tip of the bimorph and the curvature R can be determined from a simple geometrical consideration in Figure 5 as follows: δ=Rcosθ=R(1cosθ) Medium R(1(1−θ2) /21+...))=Rθ2
/'2=R/2・I22/2R=ρ2/2R Therefore, δ=3/4JT−a2/(1+ε1/ε2)・d31V
/12 Now, ε1=ε. ×3000, ε2−ε, X 60
00, d31=250×10-12m/■, (1=5
0 mm, t=0.25 mm, and V=100V, a displacement of δ=0.35 mm will be obtained.

Therefore, when a DC voltage is applied between both electrodes of a piezoelectric bimorph structured as shown in Figure 3 in the same direction as the polarization, shrinkage distortion occurs in both layers in the length direction, but one is large and the other is As a result, the free end is pulled in the direction of the larger strain and bends.Even when a voltage is applied in the opposite direction, the free end bends in the opposite direction due to the difference in the amount of strain in elongation.

Therefore, the movement of this free end can be applied to a piezoelectric actuator as a force/displacement generation source, just as in conventional piezoelectric bimorphs.

Note that the field to which the present invention is applied is the piezoelectric fan.
Coin processing in vending machines, etc., as well as piezoelectric pumps, piezoelectric relays, etc.

<Configuration and effects of the present invention> As described above, according to the present invention, 21
When performing polarization treatment by forming electrodes on both sides of a composite ceramic plate, which is made by mixing the raw material powder of a single piezoelectric ceramic with an organic binder to form a sheet, and firing the laminated body by thermocompression bonding, Since the dielectric constant ratio of the two ceramic layers with the neutral line as the boundary is determined by the difference in the dielectric constant of each layer, a difference in the degree of polarization of the two phases is created and a difference is created in the piezoelectric strain constant. A piezoelectric actuator can be constructed by forming electrodes and polarizing both sides of the same sintered body, so it is easy to manufacture and inexpensive, and there is no bonding process, making it highly reliable. have

In other words, although the piezoelectric actuator according to the present invention can generate displacement or force that is less than half the performance of conventional piezoelectric bimorphs, it has low cost and high reliability due to its simple manufacturing and structure. This has advantageous advantages and thus makes it possible to provide a piezoelectric actuator that is simple to manufacture, reliable and has the advantage of low cost.

[Brief explanation of drawings]

Figures 1 and 2 show PZT, which is an example of piezoelectric ceramics.
A ternary map showing the relationship between the system pressure main piezoelectric ceramic composite composition, dielectric constant, and electromechanical coupling coefficient. Fig. 3 is a configuration diagram showing an example of a bimorph element constructed by the method of the present invention. FIG. 5 is a diagram used to explain the electric field strength, and FIG. 5 is a diagram used to explain the warpage of the bimorph of the present invention.

Claims (1)

[Claims] Electrodes are formed on both sides of a composite ceramic plate, which is made by mixing raw material powders of piezoelectric ceramics with two compositions with different dielectric constants with an organic binder and forming them into sheets, and then firing the laminated body by thermocompression bonding. Electrodes are formed on both sides of the composite ceramic plate. When doing this, the dielectric constant ratio of the two ceramic layers with the neutral line as the boundary is determined by the difference in the dielectric constants to create a difference in the degree of polarization of the two phases, thereby creating a difference in the piezoelectric strain constant. A piezoelectric bimorph element characterized by: