Editing Piezoelectricity (section)

===Piezoelectric motors===
[[File:Slip-stick actuator operation.svg|thumb|A stick-slip actuator]]
{{Main|Piezoelectric motor}}
Types of piezoelectric motor include:
* The [[ultrasonic motor]] used for [[auto-focus]] in [[single lens reflex|reflex cameras]]
* [[Inchworm motor]]s for linear motion
* Rectangular four-quadrant motors with high power density (2.5&nbsp;[[watt|W]]/cm<sup>3</sup>) and speed ranging from 10&nbsp;nm/s to 800&nbsp;mm/s.
* Stepping piezo motor, using [[stick-slip]] effect.

Aside from the stepping stick-slip motor, all these motors work on the same principle. Driven by dual orthogonal vibration modes with a [[phase (waves)|phase]] difference of 90°, the contact point between two surfaces vibrates in an [[ellipse|elliptical]] path, producing a [[friction]]al force between the surfaces. Usually, one surface is fixed, causing the other to move. In most piezoelectric motors, the piezoelectric crystal is excited by a [[sine wave]] signal at the resonant frequency of the motor. Using the resonance effect, a much lower voltage can be used to produce a high vibration amplitude.

A stick-slip motor works using the inertia of a mass and the friction of a clamp. Such motors can be very small. Some are used for camera sensor displacement, thus allowing an anti-shake function.