Non-contact capacitive torque sensing on a rotating conductive axis

A capacitive torque sensor in which two angular displacement sensors are spaced a well-defined distance apart is proposed. The rotor of each of these capacitive displacement sensors is composed of an array of electrodes connected to sine waves with phase angles in the sequence -0°-90°-180°-270°. These voltages are capacitively coupled from the stator to the rotor. The stator is also equipped with a readout electrode. The phase angle of the sine wave on this readout electrode is proportional to the rotor-to-state electrode overlapping and thus is proportional to the angular position. The phase difference between the output signals of the two angular displacement transducers is a direct measure of the twist angle and thus of the torque in the axis. The sensor allows noncontact torque measurement on a 10-mm-diameter steel axis in the 0-100-N-m range, with a 1-N-m inaccuracy irrespective of the angular velocity of the axis