Methods of application of piezoelectric multilayer actuators to high-speed clutching, using displacement amplification
The suitability of electromagnetic actuating devices for application to machines with ever more demanding response time specifications is discussed, with the proposal that piezoelectric actuator technology can produce practical devices with faster response times than solenoids, for example. This thesis discusses and validates the proposition that the performance of piezoelectric ceramic actuators makes them viable devices for inclusion in high-speed machine applications, where rapid clutching using two-state actuation is required. Further, techniques are devised and explored for the design and application of these devices using displacement amplifying structures, which lead to the utilisation of engineering methods of relatively low precision. This is highly advantageous as to date, the piezoelectric multilayer actuator has usually been associated with high precision engineering. Applications of piezoelectric ceramic technology are reviewed, and the mechanical and electrical properties of these materials are discussed. Literature covering applications of piezoelectric actuators in relation to clutches, motors and positioners is also reviewed. This data search revealed many devices or systems where the displacement amplification of piezoelectric actuators was exploited in some way, but failed to show any devices where the high efficiency of these amplifying structures was either primary or even necessarily achieved. Indeed, it was concluded that in the absence of such applications or methodologies, a fruitful area of research might be to explore these methodologies. This work is a core element of this thesis. Using two basic topologies, devices producing efficient transformation of high-force, small movement two-state actuation, to larger movement with lower force, have been designed (using flexural hinge methods), manufactured, tested and analyzed. Hydraulic transformers have been briefly investigated and ultimately rejected on the grounds of comparative complexity. For any displacement amplifying or transforming device, applications for these systems are widely varying, but criteria for advantageous employment of the piezoelectric approach, as opposed to electromagnetic, are established. Design techniques which are partially analytical and partially experiential are proposed, which in practice exhibit adeptness for producing well-optimised designs. These methods are incorporated into special purpose structure-designer computer programs. Several design examples are detailed, and their performance analyzed in comparison with the modelling techniques and design program predictions. The application of these displacement amplifiers is discussed by example, to two discrete motion machines, both of which have been designed specifically to demonstrate the possibilities of using piezoelectric technology to regulate discrete motion drives. It is shown that the speed of response of the devices is such, that the concept of zero-velocity clutching with the intention of minimising wear, is feasible.