A Spatial Spring-Loaded Cable-Loop-Driven Parallel Mechanism

A novel architecture of spatial spring-loaded cable-loop-driven parallel mechanism is introduced in this paper. In this mechanism, cable-spool actuating systems and actuation redundancy are avoided. By attaching springs to the cable loops, three degrees of freedom for spatial displacement can be controlled using only three actuators. This paper presents the inverse kinematics, the static equilibrium equations and the workspace analysis. Because all these equations are obtained based on the cable segment lengths, many square roots appear in the equations. The boundary equations for different arrangements, i.e., preload, non-zero stiffness and external forces, are obtained separately in order to simplify the analysis. The boundary equations of each cable force for any situation can be obtained by combining the equations based on the matrix superposition principle. It is verified that the mechanism has a significantly large workspace within which the cables and the springs can be maintained in tension compared to a standard mechanism actuated with three motors.