What is a Piezoelectric Motor?
The word piezo comes from the Greek word “piezein”, which means to squeeze or press. The piezoelectrical effect is best described as the ability of some materials, (e.g. piezoceramics, piezoelement) to generate an electrical charge in response to a mechanical force (e.g. being squeezed or pressed). The piezoelectric effect is reversible, in that materials exhibiting the effect can also exhibit the reverse effect “the inverse piezoelectric effect”. Thus they change shape or size when excited by an electric charge and the inverse piezoelectric effect is the basis for the design of piezoelectric motors (piezo motors).
Although, the inverse piezoelectric effect has been well known and studied for some years, it is only recently that commercial motorized devices incorporating piezo technology have begun to find practical applications in everyday gadgets (e.g. focusing mechanism of certain digital cameras, industrial valves, toys etc.).
This situation is now changing rapidly as an increasing number of companies search for alternatives to conventional electromagnetic motors to solve modern day problems associated with growing demand for better performance, increased energy efficiency, miniaturization, and green technology. In a growing number of instances companies are finding that piezo motor technology offers the only efficient and cost-effective answers to these problems.
Piezo motors can be designed in either linear or rotary form and applied to host of applications as both single and complex multi-axis system that enable very precise, repeatable and reliable motion control. The small size of the piezo motor means they can be used in a variety of locations where other solutions may have limitations. In addition, because piezo motors are not magnetic that can often be used in applications that require the generation of strong magnetic fields environments, such as medical MRI machines.
Precision positioning and motion control applications have advanced significantly from the use of piezoelectric equipment because they enable accurate movements down to the nanometer level. In environments with little room for error, having an accurate and repeatable positioning system in place can be the deciding factor between other alternative solutions.
There are numerous reasons why a piezo motor is a great fit for many motion control system designs. To start off with, they are by nature energy-efficient since electricity only needs to be used when movement is required. With no electric current sent to a piezo motor system, the device maintains its position and can stay locked in place due to the science behind the piezo effect.
Motion of a piezo motor is controlled by a train of electrical pulses typically supplied by a digitally controlled AC voltage source applied directly to the piezo element. For the duration of each pulse the excitation AC voltage is applied to the piezo element at its ultrasonic resonant frequency causing it to vibrate (and change shape). The speed of the motor is altered by varying either the repetition rate of the pulses comprising the duration of each individual pulse (i.e. Pulse Width Modulation “PWM”). Digital control can enable any movement from a single nanometer step to continuous motion to be set up accurately and repeatably.