Piezo stack actuator is a linear motor based on electrically controllable deformation of a solid body. The piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in certain crystalline. The piezoelectric effect is a reversible electro-mechanical mechanism:
The reverse piezoelectric is deployed for actuators and is used for static positioning as well as dynamic actuation up to the production of ultrasonic sound waves.
The displacement of a piezo actuator is in first instance proportional to the voltage input. Forces are much higher than that of any other electrical device of comparable size such as a linear voice coil motor. It is extremely important to notice, that the force capability is associated with fairly small stroke.
The generation of strain for actuation requires field strength in the order of 1.000 - 2.000 Volt per mm layer thickness. As generally low voltage is required, many thin piezo layers are stacked to create actuators. This result in a body of piezo material which is furnished with an electrode structure. A design for the electrode structure is the well-known pattern of a MLCC (multi layer ceramics capacitor). Electrodes are insulated against anti-pole electrodes inside the stack. The next figure indicates, that such insulation method result in inhomogeneous field distribution, which cause inhomogeneous field which is associated with mechanical stress concentration (see circle).
The preferred design is presented in the next figure. The internal electrodes of same polarity are connected by external electrodes placed on the face of the actuator. The internal electrodes are insulated from antipode external electrodes with a thin glass layer placed between the faces of the ceramics material and the external electrodes. The insulation alternates for each pole. Thus, each electrode of common polarity are connected by a metallic strip. This result in a perfect internal electric field pattern.
The advanced piezo stack comprises a pile of those piezo layers to increase the displacement performance. The electrodes cover all the layers and are open at side faces of the stack. The layers are contacted with metallic stripes at the side face where antipole electrodes are insulated.
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