Design and Development of Torque- Controlled Joints

This paper discusses the effect of basic manipulator characteristics upon the implementation of high performance joint torque control. Two manipulators with very different characteristics (high and low gear ratios) are used in this analysis: The PUMA 560 manipulator and ARTISAN, a ten degree-of-freedom manipulator currently under development at Stanford. The experimental results obtained with a prototype link of ARTISAN are presented and compared to those previously obtained with the PUMA. This paper also describes conceptually a new type of torque sensor, developed during the course of this project. With this new sensor, using inductive contactless transducers, torques are evaluated by distance measurements of deflections in the sensor's structure. The new sensor provides a substantial increase in accuracy over conventional strain gauge sensors, achieves higher mechanical robustness, and presents lower sensitivity to electrical noise.