Applications of piezoelectric actuators range from active reduction of seismic loads on buildings to the accurate positioning of optical systems in cameras. This dissertation is concerned with small actuators that are capable of both comparatively large motions and fine resolution. Only one type of existing actuator, known as an "inchworm" fits this description , but inchworm actuators require very high-precision manufacture and are sensitive to mechanical wear.
As a result, a new type of high-resolution, long-stroke actuator has been recently developed at Cambridge University. The actuator consists of two separate parts. An outer holder and an inner sliding tube attached to a piezoelectric element that supports an inertial mass. To cause the sliding tube to move, the piezoelectric element is extended/contracted according to an asymmetric waveform.
A simple, one-degree-of-freedom dynamic model of the actuator is developed. Previous work has shown that the actuator works well at some frequencies but at other frequencies it does not perform as expected.
The main objective of this dissertation is to study the behaviour of the piezoelectric element, in order to explore a possible link between its non-linear behaviour and the observed unexpected behaviour.
Quasi-static and dynamic tests show significant non-linear coupling between piezoelectricity and the applied stress. Also, the piezoelectric behaviour changes as the frequency is increased.
A simulation based on experimental results is developed, and it is found that the new technique is able to predict the actual behaviour of the actuator.
A finite element study of the inner part of the actuator is carried out in order to show the significance of driving the actuator at resonance frequency, since this gives the best performance in terms of force, acceleration and velocity.
[Cambridge University | CUED | Structures Group | Geotechnical Group]
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