Calculation and Analysis of Constant Stiffness Space for Redundant Cable-Driven Parallel Robots

In this paper, a new concept of the constant stiffness space (CSS) of cable-driven parallel robots (CDPRs) is presented to meet the requirement for the constant stiffness plane of CDPRs in ground simulation spacecraft landing addressing experiments. First, the previously studied stiffness model and cable tension feasible region are reviewed. Then, the concept of the stiffness relative contribution coefficient is proposed, which can directly reflect the influence of controllable stiffness on system stiffness and guide the selection of driving cables and the setting of cable tension limiting values. Further, a method to calculate the CSS is proposed. This method can effectively obtain the CSS of robots according to the target stiffness. Next, an evaluation index for the local and global stability of the CSS is presented to analyze and evaluate the stability of the CSS of CDPRs. The influences of the load and posture of the end-effector of a CDPR on the volume and stability of the CSS are analyzed. The analysis results can serve as guidelines for determining the CSS in practical applications. The correctness and efficacy of the proposed method are verified through the experimental and theoretical analyses. The results show that the proposed method is computationally efficient and can obtain the CSS of CDPRs within a given accuracy range.