Basic considerations on transmission characteristics for tendon drive robots

Discusses force control for the tendon-sheath driving system typically used to actuate robotic finger joints. For a simple tendon-sheath model, the transmission characteristics were first formulated with apparent tendon-stiffness and equivalent backlash. An interesting aspect is that apparent tendon-stiffness changes when the tendon is pulled or loosened, while tendon-stiffness itself keeps constant under the absence of friction. This unexpected behavior is confirmed by simulations as well as by experiments. The authors show that the direction-dependent behavior of apparent tendon-stiffness eventually brings about a direction-dependent response in the force control system without carefully designed control strategy. Finally, a control strategy is introduced to remove the direction-dependent response.<>