Force Reduction of 3-RPS Parallel Manipulator Using Mechanical Springs

Abstract This paper presents the force reduction of a 3-RPS parallel manipulator using mechanical springs. Two design methods are proposed: one attaches a linear spring from the base to each cylinder-piston pair of P-joint, and the other implements a torsional spring to the R-joint of each leg. The significance of the proposed methods lies in their structural simplicity and ease of implementation. In these methods, the spring parameters are acquired using particle swarm optimization (PSO) to minimize the total actuator force of the manipulator when it tracks along the centerline of the workspace. In this work, a numerical example of a 3-RPS parallel manipulator is given to demonstrate the effectiveness of the proposed methods. Through four different trajectories, it is shown that the two methods can significantly reduce the actuation forces of the manipulator. The force reduction rate (FRR) of the manipulator can be achieved up to 95% with a linear-spring design and 88.2% with a torsional-spring design when it tracks along the centerline of the workspace. The lowest FRR for the linear-spring design is 70.8% and that for the torsional-spring design is 66.2%. The obtained results demonstrate the high performance of the proposed methods, along with design simplicity, making them have great potential applications.