Amplified Piezoelectric Actuator
Encyclopedia
Amplified piezoelectric actuators are specific actuators using piezoelectric materials as active material, and having a specific design to overcome traditional limitations of classical direct piezoelectric actuator, the limited stroke. As classical piezoelectric materials have a strain of 0.1%, it is practically impossible to reach significant stroke without displacement amplification (1 mm displacement would required 1 meter of piezoelectric material). The solution to reach middle range stroke is to use an amplification system.
. A small deformation of the great axis creates a large displacement of the small axis. The amplification ratio can typically reach 20 times, that means such actuators can reach strokes of 1 mm.
The goal of the elliptic shell is not only to amplify the displacement. It has also to apply the correct pre-stress to the piezoelectric material in order to allow dynamic and precise motion. The other advantage is that this kind of flextentional actuator is very reliable.
Displacement amplification can also be accomplished by using rigid struts connected by flexure bearings
. This separation allows inverted geometries, allowing either contraction or expansion of the output even if the dominant motion of the piezo is expansion. Actuators of this type can have a stroke of 2 mm.
for example studied and tested its own actuators for cryogenic applications. Other organisations like ESA or ISRO are also studying such solutions. The space industry's interest in amplified piezoelectric actuators is due to the high power density of these actuators, high positioning accuracy, high reliability, and low power losses when used in quasi-static operation.
Amplified piezoelectric actuators have no sliding parts due to the flexural hinges and do not require lubrication. Lubrication-free performance is important for cryogenic applications, where traditional lubricants may freeze, and for vacuum applications, where lubricants could outgas or trap atmospheric gasses.
Piezoelectric actuators can also be made with nonmagnetic materials, which allows their use in nonmagnetic environments such as an MRI machine
.
Controlling helicopter rotor blades using active flaps has been investigated for some time without being put into production. The most commonly used technology is the amplified piezoelectric actuator.
Single-cell actuator
The principle is based on the deformation of an elliptic shell to amplify the ceramic strain. The ceramic stack is aligned with the great axis of the ellipseEllipse
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
. A small deformation of the great axis creates a large displacement of the small axis. The amplification ratio can typically reach 20 times, that means such actuators can reach strokes of 1 mm.
The goal of the elliptic shell is not only to amplify the displacement. It has also to apply the correct pre-stress to the piezoelectric material in order to allow dynamic and precise motion. The other advantage is that this kind of flextentional actuator is very reliable.
Displacement amplification can also be accomplished by using rigid struts connected by flexure bearings
Flexure bearing
A flexure bearing is a bearing which allows motion by bending a load element.A typical flexure bearing is just one part, joining two other parts. For example, a hinge may be made by attaching a long strip of a flexible element to a door and to the door frame...
. This separation allows inverted geometries, allowing either contraction or expansion of the output even if the dominant motion of the piezo is expansion. Actuators of this type can have a stroke of 2 mm.
Multi-cell actuator
In diamond shaped amplifiers, using 4 piezo crystals instad of one increases control of movement, particularly in changing temperatures. More movers result in more force at similar displacement.Lever arm amplification
Another method of amplifying the piezo stroke is to use a lever arm. The lever arm can be a primary or a secondary amplification mechanism, and can be used to generate displacements of up to times 10.Applications
Piezoelectric actuators, and especially amplified piezoelectric actuators, have been historically studied and used in aerospace applications. NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
for example studied and tested its own actuators for cryogenic applications. Other organisations like ESA or ISRO are also studying such solutions. The space industry's interest in amplified piezoelectric actuators is due to the high power density of these actuators, high positioning accuracy, high reliability, and low power losses when used in quasi-static operation.
Amplified piezoelectric actuators have no sliding parts due to the flexural hinges and do not require lubrication. Lubrication-free performance is important for cryogenic applications, where traditional lubricants may freeze, and for vacuum applications, where lubricants could outgas or trap atmospheric gasses.
Piezoelectric actuators can also be made with nonmagnetic materials, which allows their use in nonmagnetic environments such as an MRI machine
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
.
Controlling helicopter rotor blades using active flaps has been investigated for some time without being put into production. The most commonly used technology is the amplified piezoelectric actuator.
External links
- Amplified Piezoelectric Actuators European Space Agency, Published March 1998.