Piezoelectric motor

A piezoelectric motor or piezo motor is a type of electric motor based upon the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors make use of the converse piezoelectric effect whereby the material produces acoustic or ultrasonic vibrations in order to produce a linear or rotary motion. In one mechanism, the elongation in a single plane is used to make a series of stretches and position holds, similar to the way a caterpillar moves.

Motors are made in both linear and rotary types.

One drive technique is to use piezoelectric ceramics to push a stator. These piezoelectric motors use three groups of crystals: two of which are Locking and one Motive, permanently connected to either the motor's casing or stator (not both) and sandwiched between the other two, which 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 employs the use of surface acoustic waves (SAW) to generate linear or rotational motion.

A second drive technique is illustrated by the Squiggle motor, in which piezoelectric elements are bonded orthogonally to a nut and their ultrasonic vibrations rotate and translate 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 being applied to a Normally Locked motor, the spindle or carriage (for rotary or linear types, respectively) will not move under external force. For a Normally Free motor, the spindle or carriage will move freely under external force. However, if both locking groups are powered at rest, a Normally Free motor will resist external force without providing any motive force.

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