Linearizing the joint torque characteristics of an electric direct-drive robot for high performance control of in-contact operations

To enable the application of high-performance in-contact control algorithms to commercially available robots, and thereby facilitate technology transfer from the robot control research community to commercial applications, a practical methodology has been developed to linearize the torque characteristics of electric motor-amplifier combinations. A four degree-of-freedom Adept II robot, with pulsewidth modulation amplifiers and both variable reluctance and brushless DC motors, was converted to operate from joint torque commands to demonstrate the methodology. The average percentage torque derivation over the command and position ranges was reduced from as much as 76% to below 5% for the direct-drive joints 1, 2, and 4, and was reduced by more than 50% in the remaining ball-screw driven joint 3