A Real-Time Approach to Risk-Free Control of Highly Redundant Cable-Driven Parallel Robots

In cable-driven parallel robots (CDPRs), the cable tension must be in an admissible positive range. The positive tension distribution (PTD) in CDPR is generally guaranteed using optimization-based methods, limiting their real-time applications due to the unpredictable worst-case computation time of such methods. In this study, we consider the PTD to be an integral part of the control system and introduce a computationally efficient control-based approach for generating positive tensions. This innovative approach offers several benefits for controlling redundant CDPRs. It significantly improves computation time compared to existing iterative methods, eliminates high sensitivity to kinematic uncertainties, and enhances trajectory tracking performance. Additionally, the proposed method keeps the robot on the boundary of the workspace when the trajectory exits the wrench-feasible workspace. To this end, we introduce a novel representation of CDPR dynamics as a nonaffine form, considering the tension of the cables as state variables. A robust unilateral constrained control structure is proposed using a third-order model, ensuring control efforts remain within a prescribed positive range. The computational efficiency of the method is investigated in a hyper-redundant CDPR and is compared with the conventional methods. It is also shown that for the desired trajectory out of the workspace, the proposed method keeps the robot at the boundary of the workspace while maintaining positive tensions.