Complementary Inchworm actuator for high-force high-precision applications

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 voltage respectively while for the other clamping and release are achieved using low and high voltage 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. In the coarse positioning mode the direction of motion is determined by whether the extender voltage pulse overlaps the leading or trailing edge of the common clamp pulse. A fine positioning mode can be realized with the common clamp voltage set to 0V and continuous feedback control applied to the extender actuator. 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 surface displacement and force vs. time during the switching transient.