A feasibility study on tension control of Bowden-cable based on a dual-wire scheme

A critical issue for Bowden-cable transmission is bending-dependent hysteresis that degrades control performance and limits the application. The relationship between input and output of the Bowden-cable varies with the changing bending angle of the cable. This paper proposes a novel method that can compensate the varying hysteresis of the Bowden-cable using an embedded auxiliary wire, called a sensing wire. The accumulated bend angle of the Bowden-cable can be estimated by measuring the displacement change of the sensing wire and the input tension of the actuation wire. The estimated bending angle of the sheath can be used to compensate the hysteresis of the Bowden-cable with a feedforward control scheme, even though it is subject to the varying shape of the Bowden-cable. The proposed system has a simple and fully embedded design inside the sheath and does not require any external shape sensor or output tension sensor, which keeps the size and complexity of the system low. The results show that the control error of output tension decreased from 4.22 N to 0.69 N when the bend angle of the Bowden-cable changes from 0° to 560°.