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.

A linear inchworm motor was developed for applications in adaptive, conformable structures for flow control. The device is compact (82 x 57 x 13 mm). and capable of unlimited displacement and high force actuation (150 N). The static holding three is 350 N. Four piezoceramic stack elements (two for clamping and two for extension) are integrated into the actuator.\khich is cut from a single block of titanium alloy Actuation is in the form of a steel shaft pushed through a precision tolerance hole in the device. Unlimited displacements are achieved by repetitively advancing and clamping the steel shaft. Although each step is only on the order of 10 microns. a step rate of 100 Hz results in a speed of 1 mm's. Since the input voltage can readily control the step size, positioning on the sub-micron level is possible. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/12/2015 Terms of Use: http://spiedl.org/terms 722 70 80 90 Clamp, Pusher Voltage (V) Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/12/2015 Terms of Use: http://spiedl.org/terms

This paper addresses a particular type of power harvesting in which energy in the periodic movement of structures is parasitically converted to stored electric charge. In such applications, tuning of the vibration power harvesters' resonance frequency is often required to match the host structures' forcing frequency. This paper presents a method of adjusting the boundary conditions of nonlinear stiffness elements as a means of tuning the resonance frequency of piezoelectric vibration power harvesters (altering the deformation mode from bending to in-plane stretching). Using this tuning method, the resonance frequency was experimentally varied between 56 and 62 Hz. For a vibration level of 2 mm/s, the harvester has a similar Q to a linear system but its Q is reduced by one third at a vibration level of 10 mm/s. This behavior is important for applications where high sensitivity is required for low vibration levels but mechanical robustness is required for high vibration levels.

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