Torque Sensor For Direct-Drive Manipulators

This paper describes the development of a joint torque sensor for the second direct-drive manipulator at Carnegie-Mellon University (CMU DD Arm II). The approach taken is to develop the sensor using static design considerations and then test it to verify its dynamic performance. Several design considerations applicable to semiconductor strain-gage torque sensors are presented. These are strain capacity limit, nonlinearity, sensitivity, and stiffness specifications. Associated design equations have been developed in the present work. A numerical example is given to illustrate the use of these design considerations. The development of a circular-shaft torque sensor for the CMU DD Arm II, that employs semiconductor strain gages, is described. Typical results from a static calibration test and from step and impulse tests are presented. Test show that the torque sensor performs well under dynamic conditions in a bandwidth of 100 Hz.