Workspace analysis of an underconstrained cable-driven parallel robot with four cables

A cable-driven parallel robot is controlled by varying the cable lengths. When the moving platform of an underconstrained cable robot, suspended using four cables and acted upon by only the cable forces and weight of the platform, is moved to a particular position in a workspace, it can have only a limited variation in orientation. The feasible range of orientations at different positions in a cuboidal workspace is obtained in this work. It is not attempted to find the poses where the mobile platform is in complete static equilibrium. The range of poses, when the net force in all directions and the moment of forces about vertical axis are all equal to zero, and the moments about two horizontal axes are limited to specified limits, are mapped. Static simulation of the cable-driven robot at different positions along a prescribed path, as it transfers a payload, is conducted. The set of cable lengths corresponding to a position and orientation is given as input to the simulation and the equilibrium position is found. It is observed that when the cable lengths correspond to a feasible orientation, the moving platform stays on the intended path and when cable lengths corresponding to infeasible orientation are given as input, the center of the platform drifts away from the desired position. Knowledge of the feasible range of orientations will be useful in avoiding this drift and guiding the platform along a desired path.