Directional performance optimization of cable anchor layout for hybrid cable-driven parallel robots

Condition-number-based optimization of hybrid cable-driven parallel robots (HCDPRs) generally favors isotropic designs and therefore does not explicitly address task-dependent directional requirements. To overcome this limitation, this paper proposes a directional performance optimization method for HCDPRs based on directional manipulability and directional stiffness indices. In the present study, the optimization is restricted to the cable-driven subsystem, in which the cable anchor layout is taken as the design variable, while the manipulator is treated as a standard component and modeled as an external load. Accordingly, the proposed method should be understood as a direction-oriented geometric optimization of the CDPR subsystem rather than a holistic coordinated redesign of both HCDPR subsystems. A case study is carried out along a prescribed trajectory by comparing the proposed method with conventional condition-number optimization. The results show that the proposed method improves the target-direction performance, yielding about 20% enhancement in directional manipulability and about 25% enhancement in directional stiffness along the prescribed task direction. At the same time, the comparison also reveals measurable performance trade-offs in some non-target directions. These results indicate that the proposed method is particularly suitable for task scenarios in which the directional performance in prescribed directions is of primary concern.