Abstract: Tendon-sheath actuation system in pull-pull configuration is widely used in surgical and search/rescue robots, because it can provide a kind of simple yet dexterous remote transmission. The undesirable nonlinear characteristics arising from the friction between contact surfaces and the tendon compliance are the major obstacles for robot control. Considering the limitation that the existing tendon-sheath transmission model is only applicable to elastic load, the torque transmission model under any load conditions is proposed. An experimental setup is established to verify the torque transmission characteristics and discuss the influence factors of torque transfer efficiency. The looseness phenomenon of the system is analyzed in order to calculate the required minimum preload. A friction torque compensation controller without distal-end feedback is designed to ensure that the output of the system can effectively track the expected torque trajectory, and the effectiveness of the scheme is validated by experiments. Thus, studies on the torque transmission characteristics have provided theoretical bases for the torque control of the tendon-sheath actuated robots.

Key words: friction compensation, minimum preload, tendon-sheath actuation system in pull-pull configuration, torque transmission model, transfer efficiency