A Spatial Variable-Structure Cable-Driven Parallel Robot Through Cables Wrapping Over a Convex Polyhedron

The workspace of a cable-driven parallel robot (CDPR) in a complex environment is limited by obstacles and objects. To adapt a CDPR to a complex environment and enlarge the limited workspace, this article proposes a spatial variable-structure CDPR allowing cables to wrap over a convex polyhedron. A convex polyhedron can contain an obstacle or object approximately and guide cables to bypass the obstacle and object. This article investigates whether a cable wrapping over a convex polyhedron gets stuck by the edges from a statics perspective. An analytical approach to solving the path of a cable wrapping over a given sequence of edges is proposed. The concept of sequence-invariant space is proposed and an approach is developed based on the sequence-invariant space to track the wrapping edge sequence of a cable. Based on solving the path of cables, the inverse kinematics and statics of a spatial variable-structure CDPR are solved. An open-loop inverse kinematics-based control strategy is proposed for spatial variable-structure CDPRs. With the control strategy, the effectiveness of the proposed approaches in solving the path and tracking the wrapping edge sequence of a cable and in controlling a spatial variable-structure CDPR is verified, based on a CDPR prototype.