Integrated sensors for PZT actuators based on thick-film resistors

A common problem when using piezoceramic actuators for precise positioning is their hysteresis. Either external sensors such as capacitive or inductive probes, optical sensors or strain gauges are commonly used. The latter are the most favorable solution in many cases, as they occupy the smallest volume and disturbances can mostly be avoided. Drawbacks are the assembly of these strain gauges on the target, their small gauge factor and their size. We propose a sensor based on thick-film technology which permits to avoid these problems. It will allow to increase the integration level of subminiature mechatronic systems. A piezoceramic element is covered with an electrode on either side. Afterwards, an insulating layer is patterned, followed by the required number of piezoresistive elements and the necessary electrode pads and conductive tracks. Experiments in the laboratory have shown that position control using these resistances is possible, taking advantage of the reliability, the intimate contact between sensor and actuator, a negligible creep and the stability. In this paper we present several possible sensor configurations, applications and measurement results.