Piezo Actuators: Types and Applications
A piezoelectric actuator converts an electrical signal into a precisely controlled physical displacement (stroke). If displacement is prevented, a useable force (blocking force) will develop. The precise movement control afforded by piezoelectric actuators is used to finely adjust machining tools, lenses, mirrors, or other equipment. Piezoelectric actuators are also used to control hydraulic valves, act as small-volume pumps or special-purpose motors, and in other applications requiring movement or force.
Types of Piezoelectric Actuators
Two different types of piezo actuators are stack actuators and stripe actuators.
Stack Actuator: Stack actuators offer low stroke and a high blocking force. Based upon the user’s requirements stack actuators can be either discrete or co-fired.
Discrete stacks (high-voltage stack actuators) are composite structures made by stacking separately finished piezoelectric ceramic discs or rings and metal electrode foils with an adhesive. Operating voltages ranging from 500 V thru 1,000 V are typical.
Co-fired multilayer stack actuators, also called “monolithic stacks”, involve no adhesive, but rather a high temperature sintering of the complete ceramic and electrode pile. Operating voltages of a co-fired stack are up to 200 V. Rectangular cross sections are typical due to the ease of cutting processes in production.
Both the discrete and co-fired stacks can be insulated with a coating material — a bare stack — or encased in stainless steel when protection from mechanical stress and environmental extremes are needed.
Stripe Actuator: A Stripe actuator, also called a bending actuator, is designed to produce a relatively large mechanical deflection in response to an electrical signal. This deflection offers a large stroke and avery limited blocking force when compared to a stack actuator.
In a stripe actuator, thin two layers of piezoelectric ceramic are bonded together, usually with the direction of polarization coinciding, and are electrically connected in parallel. When electrical input is applied, once ceramic layer expands and the other contracts causing the actuator to flex.
Piezoelectric Actuator Applications
Given its simple design, minimal moving parts, no requirement for lubrication to operate and the high reliability characteristics, the piezoelectric actuator is used in a variety of industrial, automotive, medical, aviation, aerospace and consumer electronics applications. Piezo actuators are found in precision knitting machinery and braille machines. The silent drive characteristics make piezo actuators an excellent auto focusing mechanism in microphone-equipped video cameras and mobile phones. Finally, since piezo actuators require no lubrication to operate, they are used in cryogenicand vacuum environments.
Using a stack actuator, extremely fine, virtually infinite resolution is possible with very high voltages corresponding to minute movements of expansion. A piezo actuator can operate billions of times without wear or deterioration. Its response speed is exceptional and it is limited only by the inertia of the object being moved and the output capability of the electronic driver. When operating in an energized state, a piezo actuator consumes virtually no power and generates very little heat.
For more information about piezoelectric actuators and piezoelectric ceramic actuators, please download our reports: Piezo-Mechanics: An Introduction and Lowvoltage co-fired multilayer stacks, rings and chips for actuation.