A Novel Inductive Sensor For Simultaneous Linear and Angular Displacement Measurement

This article presents a new noncontact inductive sensor that can measure linear and angular displacements. The sensor system consists of a movable shaft and a stationary part around it. The movable shaft is capable of moving along the axis and rotating around the axis. A thin ferromagnetic core is attached to it. A pair of solenoidal coils is attached around the stationary part and two pairs of planar flexible coils are attached around it. The axial movement of the movable shaft modifies the inductance experienced by the solenoidal coils, whereas the radial movement of the shaft modifies the inductance experienced by the planar coils. The linear and angular displacement measurements are independent of each other, thereby reducing propagation of errors in measurement. The sensor is capable of measuring 360 degrees angular displacement and +/- 20 mm linear displacement. A prototype of the sensor has been developed and tested in the laboratory. The worst-case linearity error is 0.45% and a resolution of 45 mu m for linear displacement measurement. For the measurement of angular displacement, the worst-case linearity error observed is 0.86% and a resolution of 0.2 degrees.