Piezoelectric motor

A piezoelectric motor or piezo motor is a type of electric motor based on the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors use the converse piezoelectric effect of piezoelectric sensors, in which deformation or vibration of the piezoelectric material produces an electric charge. An electrical circuit makes acoustic or ultrasonic vibrations in the piezoelectric material, which produce linear or rotary motion. In one mechanism, the elongation in a single plane makes a series of stretches and position holds, analogous to the way a caterpillar moves. A piezoelectric motor or piezo motor is a type of electric motor based on the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors use the converse piezoelectric effect of piezoelectric sensors, in which deformation or vibration of the piezoelectric material produces an electric charge. An electrical circuit makes acoustic or ultrasonic vibrations in the piezoelectric material, which produce linear or rotary motion. In one mechanism, the elongation in a single plane makes a series of stretches and position holds, analogous to the way a caterpillar moves. One drive technique uses piezoelectric ceramics to push a stator. These piezoelectric motors use three groups of crystals—two locking, and one motive that permanently connects to either the motor's casing or stator (not both). The motive group, sandwiched between the other two, provides the motion. These piezoelectric motors are fundamentally stepping motors, with each step comprising either two or three actions, based on the locking type. These motors are also known as inchworm motors. Another mechanism uses surface acoustic waves (SAW) to generate linear or rotational motion. A second drive type, the squiggle motor, uses piezoelectric elements bonded orthogonally to a nut. Their ultrasonic vibrations rotate a central lead screw. This is a direct drive mechanism. The non-powered behaviour of the first type of piezoelectric motor is one of two options: normally locked or normally free. When no power is applied to a normally locked motor, the spindle or carriage (for rotary or linear types, respectively) does not move under external force. A normally free motor's spindle or carriage does move freely under external force. However, if both locking groups are powered at rest, a normally free motor resists external force without providing any motive force. A combination of mechanical latches and crystals can do the same thing, but would restrict the maximum stepping rate of the motor. The non-power behaviour of the second type of motor is locked, as the drive screw is locked by the threads on the nut. Thus it holds its position with the power off.