Cable interference control in physical interaction for cable-driven parallel mechanisms

Cable interferences and collisions can lead to unpredictable behavior when a human physically interacts with a cable-driven parallel mechanism through its mobile platform. This paper presents an interactive control approach to prevent two cables in interference from folding onto one another, and thus preserve the cable-mechanism geometry. In this approach, the controller generates a repulsive force to prevent the cables from crossing. Therefore, the task is executed within the cable-driven parallel mechanism’s geometric limits. The repulsive force applied by the controller is derived from the gradient of the minimum distance between any pair of cables of the parallel mechanism. In turn, this minimum distance between cables is computed from the Karush-Kuhn-Tucker conditions of the associated optimization problem. The approach was tested and validated on a parallel mechanism driven by seven cables.