Control of a Bowden-Cable Actuation System With Embedded BoASensor for Soft Wearable Robots

Control of a Bowden-cable transmission requires dealing with varying frictional nonlinearity of the cable, which varies as the bend angle of the cable changes and degrades the performance of the output tension control if not compensated for. This article proposes a novel method of compensating for the changing nonlinearity of the Bowden cable. The method enables controlling the tension of a Bowden cable without directly measuring the output tension. The output tension differs from the input tension because of friction along the cable, which changes with the cable's bend angle. The bend angle can be estimated by using a Bowden-cable Angle (BoA) Sensor and the input tension of the actuation wire to compensate for the friction change. Friction compensation allows for feedforward control of the output tension of the Bowden-cable transmission despite the varying shape of the cable. The results show that the control error of the output tension decrease from 5.21 to 0.50 N when the bend angle of the Bowden cable change from 0° to 400°. The proposed control method can be fully embedded into a Bowden-cable system without redesigning the original device, minimizing the complexity and size of the actuation system. A Bowden-cable implementing the proposed control method is demonstrated with a soft wearable robotic hand.