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Principle, structure and characteristics of PZT piezoelectric ceramic actuator

Views:6     Author:Site Editor     Publish Time: 2019-09-12      Origin:Site

A piezoelectric ceramic actuator is a device that utilizes the inverse piezoelectric effect of a piezoelectric ceramic to apply an electric field in an appropriate direction of the piezoelectric ceramic to generate a corresponding displacement and force. When a voltage is applied to the polarized piezoelectric ceramic, it is elongated in the polarization direction (longitudinal effect) and shortened in the vertical polarization direction (lateral effect). The piezoelectric ceramic actuator has a laminated type utilizing piezoelectric longitudinal effects and a double diaphragm curved type utilizing piezoelectric transverse effects.

Since the piezoelectric actuator is a device for displacement control and power source, the material used must be able to generate large strain and stress under a small electric field, and the efficiency of converting electrical energy into mechanical energy is high, so the most important thing is to use piezo round disc transducer. A soft material with a large constant d, such an increasing electric field (about 1 M V/m), produces a large strain (Δl/l about 10 -2 ) and a stress (about 9.8 MPa). On the other hand, the response variable is large, and the requirements for dielectric strength and mechanical strength are also high. At present, the materials used in piezoelectric ceramic actuators are mainly piezoelectric ceramic materials based on lead zirconate titanate (PZT).

3.1 Laminated piezoelectric ceramic driver

Although the piezoelectric ceramics driver has the above-mentioned excellent performance, it is difficult to set the control loop because the driving voltage is as high as 1 kV or more. If multiple layers are stacked in parallel, the distance between the internal electrodes can be as short as about 10 μm. The driving voltage can be reduced to less than 100V. For the deformation caused by the piezoelectric longitudinal effect, piezo ceramic has a deformation of about 0.3 μm, and a multilayer laminate can be deformed by several tens of micrometers.

3.2 double diaphragm type piezoelectric ceramic driver

The laminated type is superior in response characteristics and generating force, and PZT material piezo ceramic disc has a disadvantage in that the displacement amount is small. Therefore, in order to obtain a displacement of several hundred micrometers, it is necessary to use a double diaphragm bending type. The double diaphragm bending type is to press two piezoelectric ceramics together. When one piece is stretched, the other piece is shortened, and the deformation is proportional to the applied electric field. The double diaphragm bending type is divided into two types: series and parallel. the main features of the two are compared. It can be seen from the table that the parallel piezoelectric double diaphragm bending type has a large displacement amount for the same voltage.

3.3 piezoelectric ceramic driver performance superiority

1) Using a thick film lamination technique, a solid piezoelectric disc crystal that is integrally sintered is obtained without a binder.
2) By introducing the IC process and the insulation technology, the internal electrodes are in line with the component cross-section, and the stress distribution is uniform, thereby increasing the damage limit.
3) The piezoelectric ceramic layer is thinned, and the electrode pitch can be reduced to about 10 μm, enabling low-voltage driving.
4) The introduction of HIP technology (isostatic hot pressing sintering technology) can achieve high density, and the mechanical strength is increased by about 30% compared with ordinary sintered bodies.
5) Voltage drive, no electromagnetic noise.
6) The change of displacement over time, small drift, and good temperature stability) It can be mass produced and the cost is low for piezoelectric ceramic driver application

4.1 Mechanical applications

A practical printhead for an impact dot matrix printer has been obtained which is a combination of a laminated piezoelectric actuator and a displacement amplifying mechanism. This printer head has a power supply voltage of 90 V, a displacement magnification of about 30 times, and a terminal displacement of about 600 μm. It can achieve high-speed printing performance of 100 words/s or more, and has low power consumption and low heat generation.In addition, it is also used in ultra-precision positioning devices for semiconductor manufacturing and ultra-precision machining. The displacement is mostly in the sub-micron range. In consideration of hysteresis and linearity, attention must be paid to closed loop control.

4.2 Application in power

Applications in power units such as piezoelectric fans, piezoelectric valves, piezoelectric pumps, and ultrasonic motors are mainly due to the low power consumption and precise control of piezoelectric actuators. The displacement of these devices must be several hundred micrometers, and the double diaphragm bending type is often used, and the piezoelectric valve used for flow control is close to practical.

4.3 Optical applications

At present, the application of piezoelectric ceramic actuators in new fields such as optical communication systems, such as the determination of the tiny position of the laser mirror, the fiber optic docking coupler, and the fiber polarization controller, are being widely carried out.

4.4 Application in sensors

Compared with a general pressure sensor, a laminated piezoelectric actuator can obtain a large output voltage with a small pressure, and thus can be used as a highly sensitive pressure sensor and an acceleration sensor.

At present, some piezoelectric ceramic actuators have entered the practical stage, and some are in the research stage. In all fields of science and technology, their applications will become more and more extensive. The practical and commercialization of piezoelectric actuators will lead to more rapid development in the control of ultra-precision micro-displacement and various power sources.

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