An investigation of piezoelectric ring benders and their potential for actuating servo valves

This paper describes the deformation of a piezoceramic disc shaped actuator due to two effects: inner edge mechanical loading and electrical excitation. A 2D axisymmetric coupled-field finite element model was constructed to represent the piezoceramic 'ring bender'. The model was used to predict actuator displacement due to a force applied to the inner edge, and also the piezoelectric induced strain due to an electric field applied in the poling direction of the piezoceramic. Results are compared with theoretical calculations of the deformation of a uniform thickness disc under mechanical load, and the displacement-voltage characteristics reported by the manufacturer. Experimental results for the displacement of the piezoelectric actuator, under a variety of constraint conditions, are also compared. The research presented provides an understanding of how the ring bender deforms under combined mechanical load and electric field. Each of these effects is considered and results show that the shape formed is different depending on whether the load is mechanical or electrical. This result provides an insight into how the actuator may be mounted for use as an actuator in servo valve pilot stage.