Design, Modeling, and Performance of a High Force Piezoelectric Inchworm Motor

Abstract

A linear inchworm motor was developed for structural shape control applications. One motivation for this development was the desire for higher speed alternatives to shape memory alloy based devices. Features of the subject device include compactness (60 x 40 x 20 mm), large displacement range (6 mm), and large holding force capability (200 N). There are three active piezoelectric elements within the inchworm: two "clamps" and one "pusher." Large displacements are achieved by repetitively advancing and clamping the pushing element. Although each pusher step is small, on the order of 10 microns, if the step rate is high enough, substantial speeds may be obtained (8 mm/s). In the past, inchworm devices have been used primarily for precision positioning. The development of a robust clamping mechanism is essential to the attainment of high force capability, and considerable design effort focused on improving this mechanism. To guide the design, a lumped parameter model of the inchworm was developed. This model included the dynamics of the moving shaft and the frictional clamping devices, and used a variable friction coefficient. It enabled the simulation of the time response of the actuator under typical loading conditions. The effects of the step drive frequency, the pre-load applied on the clamps, and the phase shifts of the clamp signals to the main pusher signal were investigated. Using this tool, the frequency bandwidth, the optimal pre-load and phase shifts which result in maximum speed were explored. Measured rates of motion agreed well with predictions, but the measured dynamic force was lower than expected.

Piezoelectric Motor Using In-Plane Orthogonal Resonance Modes of an Octagonal Plate

“…Because the generated movement at the contact point is in the tangential direction, these motors should be considered as inertia-drive types. There are also piezo-walk-drive motors that are operated at resonance [61,62].…”

A brief review of actuation at the micro-scale using electrostatics, electromagnetics and piezoelectric ultrasonics

“…A large number of piezoelectric motors are designed to operate at resonance frequencies to take advantage of the amplified stator motion; they are commonly referred to as ultrasonic motors because the resonance frequencies are typically in the ultrasonic range. There are non-resonant designs such as inchworm motors [31,32], however their very-hightorque-at-low-speed characteristics [56] makes them better for high holding force applications such as precision platform positioning than for the propulsion of microrobots. We will thus focus upon ultrasonic motors.…”

Investigation of active materials as driving elements of a hydraulic hybrid actuator

“…The concept of frequency rectification involves conversion of the bi-directional strain of a smart element into a continuous uni-directional output, providing larger stroke at a lower bandwidth. Examples of frequency rectification in actuators are inchworm motors, rotary piezostack motors, and ultrasonic motors, although these actuators are not ideal for a smart rotor application [24][25][26]. These actuators experience rapid wearing due to their use of friction to generate motion.…”