Piezoelectric linear actuators use the piezoelectric effect to convert electrical current into motion in a crystal. There are two types: stepping and continuous acting. Layering crystals can result in larger movements, and reversing polarity can cause the actuator to move in the opposite direction.
Some crystalline structures give an electric charge when stressed or twisted, which is known as the piezoelectric effect. This is used in many electronic circuits. A piezoelectric linear actuator uses this effect in reverse, as an electric current causes motion in the crystal. These actuators are often found in microelectronic motors, or very small ones, and where small straight-line movements are required, such as microswitches.
There are two main types of piezoelectric actuators, stepping and continuous acting, which differ in the action that results from electrical input. A stepped piezoelectric crystal displaces a measurable amount with each electrical actuation. This is the type of motion normally associated with a piezoelectric linear actuator, moving back and forth in a linear or rectilinear motion.
Many piezoelectric crystals also have resonant frequencies, where an electrical input of a specific voltage will cause the crystal to resonate or vibrate at a specific rate. Resonant frequency effects can be used for continuous actuators, where each vibration causes a small movement. By taking advantage of resonance, small movements can be combined into one movement that appears continuous.
A piezoelectric linear actuator uses a friction pad on a crystal surface that can be positioned adjacent to a rod, wheel, or other device that needs to be moved. As the crystal moves, the friction pad transfers that motion to the device. After the electrical input is cut off, the crystal returns to its original shape and the friction pad moves away from the device until the next activation.
Layering or stacking of single crystals can result in larger movements. Electrical connections are made to each crystal in the stack, and when triggered, the combined motion is approximately the sum of each crystal in the stack. Placing the crystals facing each other along the length of the actuator can create longer linear motion. The electrical input alternates with the crystals on each side of the piezoelectric linear actuator rod, which causes it to move further than a single input.
The movement of the crystal structure depends not only on the electric charge, but on the polarity or direction of the flow of electrons. Reversing electrical polarity can cause crystals to move or warp in the opposite direction. This effect is used to move a piezoelectric linear actuator in the opposite direction or back and forth by repeatedly changing the polarity.
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