An integrable capacitive angular displacement sensor with improved linearity

Abstract

Abstract A novel type of high-resolution absolute angular encoder is presented. The operation is based on the capacitive coupling between four driving electrodes on a stator and a rotor electrode. The four driving electrodes are connected to four sinusoidal voltages with equal amplitudes and relative phase differences of 90 degrees. A sinusoidal voltage arises on the rotor electrode, which is due to the capacitive coupling of these voltages and results in a phase shift that depends on the angle of rotation. The voltage on the rotor is capacitively coupled back to the pick-up electrode on the stator to enable a contactless measurement to be made. In this way a dimensionless transduction of the angle of rotation of the rotor with respect to the stator into an electrical phase shift is possible. This transduction can be linearized by means of a special patterning of the driving electrodes. The resolution of the phase measurement is usually the limiting factor, so an improved sensor structure has been designed with a high-resolution incremental encoder part combined with a low-resolution absolute encoder structure. The combined operation results in a high-resolution absolute angular encoder. The rotor should be aligned with respect to the stator for proper operation of the sensor and an alignment technique is implemented, which is based on the same principle as that used in the sensor and gives information on both the magnitude and the direction of the misalignment, thus enabling automatic alignment to be carried out during assembly. The main source of error is buckling of the sensor parts.