Design, modelling, implementation, and trajectory planning of a 3-DOF cable driven parallel robot

Cable tensions in cable robots make trajectory planning more complicated than in rigid-link robots. Since cables can only pull but not push, the cable tensions must be kept positive for a cabledriven system to maintain control. In this paper direct methods of trajectory planning including direct collocation and direct shooting are proposed to solve the two-point boundary value problem trajectory planning. Minimizing a robot's actuator force under cable constraints including positive forces and preventing severe changes in tensions are considered in this problem. The cable-driven robot consists of a 3-cable and a pneumatic cylinder, which betters robot tensionability. The direct methods are solved by the sequential quadratic programming algorithm and then compared with the GPOPS-II software package. The results designate that the direct methods of trajectory planning propose substantial benefits in satisfying essential continuity and smoothness of resulted profiles for a cable-driven robot with a multi-type actuation system. Experimental results confirm the numerical data, additional supporting the findings.