Evolving Design Challenges with Piezoelectric Motion Devices (Part 1 of 3)
Read next: Evolving Design Challenges (Part 2 of 3)
In the world of Motion, Piezoelectricity is a characteristic of certain solid materials whereby electric charge accumulates internally and is released when the material is stressed—was discovered by Jaques and Pierre Curie in 1880. The reverse effect, whereby piezo materials will exhibit a deformation resulting from an applied charge, was deduced by Gabriel Lippman in 1881 and successively demonstrated by the Curies.
The initial effective motors using the reverse piezoelectric effect were created by the mid-1960s at the Kiev Polytechnic Institute. The technology has continued to evolve, and today a range of linear and rotary motion devices are available offering precise motion control down to nanometer precision. However, they are typically high-cost devices and are primarily used in specific premium market applications such as optics, semiconductor, and photonics.
Leveraging continued research evolving the founding work at the Kiev Polytechnic Institute, new methods for configuring & controlling Piezoceramic materials, along with new techniques to establish motion devices, have been identified. These developments have led to a portfolio of patents that have in turn enabled the design of a range of linear and rotary motion devices with numerous useful technical benefits. These can be used by the medical device and instrument designer and be comparable in cost to typical good-quality dc and stepper motor solutions.
These motor designs use a patented configuration of a single monolithic piezoceramic drive element and a novel excitation method, which only requires one connection to simultaneously excite the piezoceramic to oscillate along and perpendicular to its axis. A high-frequency ac signal is applied to achieve resonance in the piezoceramic. The simultaneous excitation results in an elliptical motion being established on a drive tooth on the side of the element. A short pulse of around 30 microseconds results in the piezoceramic being excited into resonance and undertaking a single elliptical rotation at the drive tooth tip.
The revolving drive tooth can be applied to a linear or rotating element to create motion. The technology uses simple electronics and, depending upon the specifications, the applied voltage to the piezoceramic resonator is between 50 V and 80 V, which is lower than typical existing piezo motors.
The motor is structured with a simple piezo motor driver. Driver boards have a 5 V or 12 V supply, a three-wire connection to the motor and a three-pin connection for control. One control pin is ground and the other two establish motor movement in each direction when a transistor-transistor logic (TTL) high signal is applied. A continuous high will lead to the motor running in continuous mode in the direction selected. The motor motion can be controlled in open loop with pulse width modulation of the voltage applied to the control pins.
The motors can achieve very precise position control. A single incremental step on linear motors is under 50 nanometers. The rotary motors achieve rotary increments down to 10 microradians, which is more than 600,000 steps per revolution. For precise positioning, such as in optics and laser assemblies for mirror and lens control, this avoids the complexity and expense of gearing systems.