Study on torque measurement of revolving shaft based on capacitive grating sensing technology

The difficulties in torque measurement on revolving shaft are signal transmission, limited installation space, poor stability in long-term use and signal disturbance. In order to solve the problems above, an embedded capacitive grating torque sensor and measuring system have been developed. Through installing the capacitive grating sensors on both ends of the revolving shaft, electrodes of capacitive grating can be embedded respectively into the revolving shaft and the fixed support. When the revolving shaft is touched by torque, the capacitive grating outputs the signal of cyclical change. The phase difference between outputs of two capacitive grating sensors shows the size of twist angle. The outputs through the PLL processing in measuring circuit will be signal with the steady frequency and the twist angle can be worked out by it. Then the torque will be calculated by twist angle. The embedded installation of capacitive grating sensor least affects the structure of revolving shaft. Besides, it makes the capacitive grating sensor without the need for slip ring, radio or infrared to transmit signal and power, so it overcomes the shortcomings in installation and the signal being susceptible to interference in the ways above. By means of experiment it is proved that the capacitive grating sensor is highly reliable and can be used under the harsh environmental for a long time.