An Online Reconfiguration Strategy of the Cable-Driven Parallel Robot for pHRI via APF-Adjusted Linear Approximation

Abstract

The simple and modular structure of cable-driven parallel robots (CDPRs) can enable effective real-time reconfiguration. In this paper, an online reconfiguration strategy is proposed for a 3-DOF point-mass CDPR to adjust the cable anchor positions and enhance its performance in physical human-robot interaction (pHRI). The reconfiguration problem, inclusive of all relevant constraints such as the wrench feasible condition (WFC) and the structural constraint on the cable anchors, is formulated as a non-convex optimization problem to determine the optimal positions of cable anchors. However, such original formulation poses a serious challenge to real-time determination, primarily due to the non-convex constraint imposed by the WFC and the non-convex objective function. To address this issue, the characteristics of the CDPR are considered, and a linear approximation method is employed to simplify the original optimization problem into a linear one, allowing it to be efficiently solved by the dual simplex method. Additionally, an artificial potential field (APF) is designed, considering both the inherent workspace properties and the interaction force, to adjust the solution of the linear optimization problem, which ensures that the optimal solution remains within a safe distance from the boundary of the solution space. Simulations validate the effectiveness of the strategy in improving the interaction metric while satisfying constraints.