Inertial Stick-Slip Actuator for Active Control of Shape and Vibration

A newly proposed actuator concept, that uses an inertial mass driven by a piezoelectric element to cause stick-slip motion of a tube whose movement is resisted by friction, is found to be suitable for use as active struts in truss structures. The actuator is capable of performing shape control to correct for static and quasi-static distortion by changing its length by large amounts. It is also capable of controlling vibration by changing length by small amounts at varying speed. A simple, singledegree-of-freedom analytical model of the actuator is set up as a design tool and compared to the actual behavior of a prototype. Different driving waveforms have been investigated experimentally under various working conditions and it has been found that an asymmetric 2 kHz waveform produces good results over a wide range of different parameters. Finally, the open loop behavior of the prototype actuator has been measured by following triangular and sinusoidal paths at various frequencies. It is found that the actuator compares favorably with the best long stroke actuators available at present, and has two key advantages over them. It is mechanically much simpler, since it requires a single piezoelectric element and no high-precision machining, and its performance does not deteriorate after extensive use.