Analysis of position-level forward kinematic singularities of planar RPRPR parallel robots

Abstract

Parallel robots have many advantages over their conventional serial counterparts. High accuracy and high payload-to-weight ratio are the main ones of these advantages. The main factor underlying the success of parallel robots is their closed-loop construction. However, this architectural feature also causes a characteristic singularity problem, which constitutes their biggest disadvantage. Being different than serial robots, singularities known as Type II occur in the forward kinematic solution of parallel robots. Unlike Type I singularities encountered in inverse kinematics, these singularities of second kind are located within the workspace and around them the magnitude of the inverse dynamic solution goes to infinity. Therefore, in the vicinity of Type II singularities, the actuators get saturated and lose the control of the robot. Consequently, the entire available workspace is not usable by the robot. Due to these facts, singularity analysis has been one of the most important research topics in parallel robotics. The aim of this paper is to analyze the forward kinematic position singularities of a commonly used parallel robot, namely the RPRPR-type planar parallel robot. The paper examines the degeneracies of the position-level forward kinematic solution of the said parallel robot and explores the relations of these degeneracies with the forward kinematic motion singularities. Keywords - Parallel robot, planar parallel robot, forward kinematics, singularity, position singularity