A method of joint torque control for a tendon-driven system

It is hoped that robots are utilized in environments where human lives. Robots should work safely and perform complicated tasks. For safety, precise force control and lightweight mechanism are important because robots contact with human. In order to perform complicated tasks, multi-degrees-of-freedom system is needed. Tendon-driven system is able to achieve precise motion control and complicated tasks. In this system, wires are utilized as force transmission. Therefore, the system can achieve lightweight robot and can generate large joint torque. However, each joint torque interferes mutually because the tendons are attached to each link. Tendon tension must be kept over zero because the tendons can only generate traction force. In this paper, an inverse matrix of transposed Jacobian matrix with tension control was proposed in order to achieve tension control and torque control. This inverse matrix contains two conditions. One is the condition of joint torque control. The other is the condition that the minimum value of tendon tension is kept zero. In addition, the minimum value of tendon tension can be easily changed by bias force. Simulation results and experimental results show the validity of the proposed method.