A non-contact inductive sensor for high-accuracy tip deflection measurements of piezoceramic bending actuators

Abstract

Piezoelectric bending actuators are suitable for a wide range of applications that require deflections in range of hundreds of microns. A variety of applications can be found in almost all fields of electrical engineering, mechanical engineering, acoustics, automation, automotive, health care and in countless further application areas of industry and daily life. Piezoceramic compacts, piezoceramic actuators as well as complex units and systems are used. The development of high-efficient and lowcost piezoceramic materials optimized for technical applications allowed for a multiplicity of technical solutions for piezoceramic actuators. The so-called high-effective mass systems provide maximum gain at only 1 kV/mm resulting in a material strain of approx. 2 ppm. Therefore, high-effective piezoceramics show very large piezoelectric coefficients diq representing the ratio between strain and electric field. Inherent hysteresis, drift and creep characteristics are a disadvantage of high-effective piezoceramic materials. Therefore, piezoceramic bending actuators consisting of high-efficient piezoceramics are only suitable for a limited extent, as far as high-accuracy positioning is concerned. For applications, that require precise switching and exact position control, measures have to be taken for the compensation of the inherent piezoelectric effects such as creep and hysteresis and the compensation of external varying mechanical loads and vibrations. By means of a sensor attached to the bending actuator and an appropriate sensor electronics, the disturbing effects can be detected. The implementation of such a sensor-actuator system into a closed-loop control allows a compensation of negative effects, thus high-efficient piezoceramics can be used for highaccuracy positioning. In this paper, the focus is laid on a noncontact inductive proximity sensor its principle function is based on eddy current measurement effects offering the possibility of sensor integration in smallest spaces in combination with a high-accuracy electronic circuit. The essential structure and the operational mode of the non-contact inductive proximity sensor are discussed in detail.