Design considerations for complementary inchworm actuators

An inchworm actuator is described, which uses complementary configurations for the two clamping sections. In one configuration, clamping and release are achieved using high and low voltages, respectively, while for the other, clamping and release are achieved using low and high voltages, respectively. The resulting inchworm actuator can be driven by a two-channel controller with the two clamps sharing the first channel and the extender piezoelectric actuator using the second channel. The paper also describes a diode-shunted delay circuit that causes unclamping to occur more slowly than clamping. It is shown that by using the delay circuit in series with each clamp, the overall force drive capability of the actuator is increased. The paper presents simulated and experimental results of clamp force versus time during the switching transient. An analysis of a generalized delay circuit having both resistive and reactive elements shows that a purely resistive design provides the better tradeoff between increased force drive capability and power loss in the delay circuit.

I. Introduction

INCHWORM¹

Inchworm is a registered trademark of Burleigh Instruments, Inc.

actuators are devices that achieve long-range motion by rapidly repeating a clamp-extend-clamp cycle [1]. They typically use two piezoelectric actuators for two clamp sections and a third one for the extender section [2]. Magnetostrictive [3], electrostrictive [4], or electrostatic [5] actuation has also been proposed for the clamp or extender sections. In the coarse positioning mode, the clamp and extender sections are activated in the required sequence by a three-channel controller. A fine positioning mode can also be realized by activating the extender section under continuous feedback control while one clamp is on and the other is released [2]. The specific form and timing of the waveforms for each actuator can influence the inchworm performance [6]–[8].