A new consideration on tendon-tension control system of robot hands

The authors discuss 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 factors called the 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 experiments. The authors also consider the effect of apparent tendon stiffness on force control and show that the direction-dependent behavior of apparent tendon stiffness eventually brings about a direction-dependent response in the force control system