Control of robot arms using joint torque sensors

This paper is basic study on vibration control, disturbance rejection and friction compensation in robots with flexible driving systems. Firstly, the system gain characteristic at the antiresonance frequency is introduced to evaluate the vibratory behavior of the control system. Secondly, the joint torque negative feedback which has a good effect on vibration suppression is discussed, while it is shown that the property of disturbance rejection is easily deteriorated when using high-gain joint torque feedback. Based on the assignment of pole-distribution, the relations between the vibration suppression and the disturbance rejection are analyzed. Thirdly, a feedforward compensation control based on a friction observer is proposed, it is shown that the tracking error is effectively decreased by this friction compensation. Lastly, a position control system considering the trade-off between vibration suppression and disturbance rejection is presented, and experimental results are also given.