Optimization of Tension Distribution for Cable-Driven Manipulators Using Tension-Level Index

Cable-driven manipulators (CDMs) are a special class of parallel manipulators driven by cables instead of rigid links. Due to the unilateral driving property of cables, CDMs require redundant actuation to maintain positive cable tensions. As a result of actuation redundancy, there exist an infinite number of possible cable tension solutions for a particular CDM pose. In this paper, a tension optimization method is proposed to obtain adjustable tension solution for CDMs. Adjustable tension solution is important because it enables the avoidance of tension limits and allows the stiffness of the CDM to be regulated. Tension-level indices are introduced to provide a systematic and practical way of setting the desired cable tensions level. The adjustable tension solution for each pose is obtained using a modified gradient projection method. The proposed method is generic and can be applied to CDMs with any number of redundant actuation. Simulation results show that the method is computationally efficient and the tension solutions can be manipulated by changing the tension-level indices. The simulation results have also been validated by experimental studies.