Passive Velocity Field Control of a Redundant Cable-Driven Robot with Tension Limitations

This paper proposes a novel dynamic control approach for a cable driven robot with high redundant actuation and cable tension limitations to perform tracking task while interacting with environment. In order for a cable-driven exoskeleton robot to execute the task smoothly and safely, it is necessary to consider the tracking motion performance as well as passivity when interacting with the environment under the conditions of the actuation cables' redundancy and the pulling limitation. With the additional consideration of the maximum limitation of the cable tension, cable-driven robot actually can only apply a certain range of feasible wrench on the external environment, which makes the task executed by robot be restricted. In order to make designed wrench be feasible and keep the desired trajectory tracking ability, we present a new control method by extending passive velocity field control (PVFC) method considering tracking stability and passivity. The approach augmented a higher dimensional virtual flywheel dynamics in a specific orthogonal complement space of the cable's actuation space. After the final adjustment of the designed wrench with respect to the cable's constraint, this method is capable of driving the cable robot to complete the trajectory tracking task and realize the passivity.