Closed-Loop Control of a Complementary Clamp Piezoworm Actuator

The concept of the complementary clamp piezoworm actuator with a diode-shunted delay circuit was experimentally verified through prototype testing. One clamp uses high voltage to grip and low voltage to release while the other clamp operates in reverse fashion. The resulting piezoworm actuator can be driven by a two-channel controller with the two clamps sharing the first channel and the extender piezoelectric stack using the second channel. The piezoworm achieved a speed of 440 $\mu$m/s and had a force capacity of 12.5 N when driven in open loop with trapezoidal waveforms. A delay circuit improved the force capacity from 12.5 to 14.7 N using a resistance of 1000 $\Omega$. A closed-loop tracking controller was developed for the prototype. It is shown that the prototype closed-loop system has a repeatability less than $\pm$ 20 nm for a 100 $\mu$ m step input and can track a 100 $\mu$m, 0.05 Hz sine wave with a 1% peak error and less than a 200 nm average error.