A Wide-Range Capacitive Sensor for Linear and Angular Displacement Measurement

A new capacitive sensor that is suitable for measuring both linear and angular displacements of a shaft over a wide range is reported in this paper. The sensor consists of a cylindrical shaft with a semi-hollow cylinder attached in the center; the shaft is capable of moving along the axis as well as rotating about the axis. Two pairs of semi-hollow-cylindrical electrodes surround the shaft, which is grounded. The amount of linear displacement and rotation is calculated by measuring the change in the capacitance of each of the four electrodes with respect to the shaft. A prototype sensor was constructed and tested; the rms error obtained is 0.6% for the linear displacement and less than 0.6% for the angular displacement. The proposed sensor has potential applications in several robotic, industrial, and automotive fields.