Position, Jacobian, decoupling and workspace analysis of a novel parallel manipulator with four pneumatic artificial muscles

Abstract

This paper firstly presents a novel 4-SPS/S (active chain/passive chain) parallel manipulator (PPM) driven by four pneumatic artificial muscles (PAMs). SPS denotes a spherical pair–prismatic pair–spherical pair chain and S denotes a spherical pair chain. The PPM proposed can be utilized as shoulder, wrist, waist, hip and ankle simulators or ankle rehabilitation robot. And we present a comprehensive analysis on the PPM proposed, including degrees of freedom (DOF), position, kinematic, Jacobian, singularity, decoupling and workspace analysis. In order to decrease the influence of the maximum angle of spherical pairs in four active chains on the workspace, a novel connector for PAM is proposed. The structure of the PPM is explicitly described, and DOF of the PPM are analyzed based on constraint screw theory. The posture of the moving platform (MP) of the PPM is obtained though Z–Y–X (α–β–γ) type Euler angles and the inverse position solution is obtained. When the MP moves toward any a single Euler angle direction, the closed-form direct position solution is presented by geometric analysis. A back propagation (BP) neural network model for the whole direct position solution is established. Two methods for the Jacobian matrix, one velocity composition, one differentiation, are addressed, and the acceleration inversion is obtained. Based on the Jacobian matrix, the singularity and kinematic decoupling of the PPM are both analyzed. The geometric model of expanded PAM is introduced, and the change of diameters of four PAMs in active chains is taken into consideration when chains of the PPM interfere. Based on length ranges of four active chains, the maximum angle of spherical pairs and possible interferences between chains of the PPM, the configuration workspace is presented. Finally, the characteristic of the workspace and the influence of the maximum angle of spherical pairs in active chains on the configuration workspace are both analyzed.