However, piezoelectric motors are able to generate larger forces and resist higher loads before being backdriven. From a high-level control perspective, these piezoelectric motors behave much like piezoelectric stick-slip actuators. Other piezoelectric motors use various forms of “inchworm” strategies in which multiple piezoelectric actuators are successively stretched and relaxed in a sequence that results in a net stepping behavior. However, they can be easily backdriven when powered off by overcoming the static friction. Piezoelectric stick-slip actuators behave much like admittance-type actuators during normal operation, in that they are very precise and they maintain their position when not commanded to move. By taking multiple successive steps, large net motions are possible. The result is an actuator that is similar in behavior to a stepper motor with extremely small steps, but with a stochastic step size. When the piezoelectric element is rapidly retracted, the inertia of the distal element causes slipping relative to the piezoelectric element, resulting in a net displacement of the distal element. Piezoelectric stick-slip actuators utilize a piezoelectric element that stretches when a voltage is applied (e.g., by 1 µm), with a distal element that is moved by the piezoelectric element through static friction. However, standard piezoelectric actuators are typically not capable of large motions. In addition, motions can be commanded at high bandwidth. These actuators are capable of extremely precise motions, typically measured in nanometers. Piezoelectric actuators exhibit a strain (i.e., they stretch) when a voltage is applied. Iulian Iordachita, in Handbook of Robotic and Image-Guided Surgery, 2020 36.5.1.2 Piezoelectric actuation The capacitance is a function of the excitation voltage frequency. Resonance is the frequency at which the actuators respond with maximum output amplitude. For piezoelectric actuators, it is the force needed to elongate the device by a certain amount, normally specified in terms of Newtons per micrometer. Stiffness is a term used to describe the force needed to achieve a certain deformation of a structure. Other factors to consider are stiffness, resonant frequency, and capacitance. The critical specifications for piezoelectric actuators are displacement, force, and operating voltage of the actuator. The effect of amplification is not only larger displacement, but it can also result in slower response times. In addition, piezoelectric actuators can be either direct or amplified. They are especially useful for controlling vibration, positioning applications, and quick switching. Ultrasonic actuators are specifically designed to produce strokes of several micrometers at ultrasonic (>20 kHz) frequencies. Other less common configurations include block, disk, bender, and bimorph styles. Ring actuators are disk actuators with a center bore, making the actuator axis accessible for optical, mechanical, or electrical purposes. A disk actuator is a device in the shape of a planar disk. Tube actuators are monolithic devices that contract laterally and longitudinally when a voltage is applied between the inner and outer electrodes. Piezoelectric stack or multilayer actuators are manufactured by stacking up piezoelectric disks or plates, the axis of the stack being the axis of linear motion that occurs when a voltage is applied. There are many applications where a piezoelectric actuator may be used, such as ultra-precise positioning and in the generation and handling of high forces or pressures in static or dynamic situations.Īctuator configuration can vary greatly, depending on application. Piezoelectric actuators are devices that produce a small displacement with a high force capability when voltage is applied. Peng Zhang, in Advanced Industrial Control Technology, 2010 (1) Piezoelectric actuators
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