Abstract: A spoke-type torque sensor mounted between the output of harmonic reducer and the link of robot is developed to control the vibration of flexible joint with harmonic reducer.The torque sensor is used to feed back the reaction torque exerted on the joint by the robot arm,and thereby obtain the vibration state information of the flexible joint directly.An approach to vibration suppression,which is capable of reducing the vibration quickly by means of adding a feed-forward compensation of nominal output torque to the conventional PD controller plus torque negative feedback,is proposed based on the feedback information from the designed torque sensor and the calculated nominal output torque of the joint.A series of vibration suppression experiments for tracking trapezoidal trajectories are carried out on an experimental platform newly designed for single joint control.The experimental results show that this approach can suppress the joint vibration quickly with a high degree of trajectory tracking precision.Hence,the difficulty that traditional PD controller plus torque negative feedback can't take into account both the effect of vibration suppression and the precision of trajectory tracking will be overcome by using the controller proposed.