On the use of torque sensors in a space robotics application

Torque sensors in robotics are used in those applications where high precision positioning of the end effector is required. Technological difficulties often arise in the mechanical design as well as in the placement of the sensor. However the use itself of the torque sensor for feedback control, in all those cases where elasticity of the transmission is an issue, is maybe not completely understood. The main goal of this paper is to put the control problem in a clear and correct setting, both from the steady state and from the dynamic standpoints. The role of the zero in the origin of the complex plane in the transfer function from motor torque to output torque is thoroughly discussed. It is also shown, through analysis and simulations on a detailed model of the space robotic manipulator DEXARM, that a correct design of the torque loop allows to overcome some performance limitations in the control of the load position, that arise in the case of simple positional control.