Abstract: When torque sensors are connected between shafts, the precision of torque measurement will be reduced due to loading effect, and then the commonly used torque sensors can only test static torque or dynamic torque. In order to achieve high-precision measurement of static and dynamic torque, a dynamic-static torque sensing method based on strain measurement is proposed. Firstly, the torsional deformation model of shaft is established and the relationship between torque and rotational angle is deduced. The principal strain distribution of the torsional shaft is analyzed by finite element simulation, and the optimal location of strain measurement is determined. Four strain gauges are connected in the Wheatstone full-bridge manner to obtain the torsional principal strain signal under torsional loading, and the principal strain signal is modulated in the designed sensing system to realize the transformation from torsional principal strain to torque signal, which can realize the high precision measurement of static and dynamic torque. Finally, the experiments of static and dynamic torque are carried out based on the material testing machine (MTS) and friction test table, respectively. The results show that the test results of static torque are consistent with the theoretical torque and quasi-static loading torque of MTS, which possess high linearity, and the measurement error is less than 0.47%. Meanwhile, the experimental results of dynamic torque at rotational speeds of 60 r/min, 100 r/min, 200 r/min and 300 r/min have good agreement with the dynamic torque loaded by the friction testing machine, whose measurement error is less than 5%, which indicates that the low rotational speed has little influence on the dynamic torque measurement and proves the dynamic stability of the torque test. Therefore, the proposed dynamic-static torque sensing method based on strain measurement can realize the high precision measurement.

Key words: strain measurement, sensing, static torque, dynamic torque