Torque Sensor Based on Differential Air Pressure Using Volumetric Strain

This paper proposes a torque sensor based on the differential air pressure measurement method using the volumetric strain of a mechanical sensing structure. A model of the measurement system based on the differential air pressure from the volumetric strain of the mechanical sensing structure is proposed and theoretically discussed. The error sources are identified and an error propagation model is presented for the proposed torque measurement method. Considering these error sources, a prototype torque sensor is presented as a case study for the method verification. Both the mechanical and readout electronics designs are discussed and analyzed. The mechanical sensitivity, resolution, and maximum stresses are analyzed using finite-element modeling. Based on the results from the simulation, a prototype torque sensor is manufactured and experimentally verified using a readout electronics design. For verification, the sensor prototype is measured under static torque to have a sensitivity of 0.04272V/N·m and a range of ±117N·m. Compared with the nominal mechanical sensitivity result from the FEM simulation, this measured sensitivity has a difference less than 6%. The noise analysis of the designed readout electronics shows that the resolution of 0.006% can be achieved with this design. Furthermore, hysteresis analysis shows an error of 0.012% of full scale. From these results, it is also shown that the actual performance of the sensor is mainly limited by the differential pressure sensor and the readout electronics design and is not by the mechanical design of the sensor.