Articles | Volume 6, issue 1
Research article
24 Apr 2015
Research article |  | 24 Apr 2015

Kinematic analysis of a novel 3-CRU translational parallel mechanism

B. Li, Y. M. Li, X. H. Zhao, and W. M. Ge

Abstract. In this paper, a modified 3-DOF (degrees of freedom) translational parallel mechanism (TPM) three-CRU (C, R, and U represent the cylindrical, revolute, and universal joints, respectively) structure is proposed. The architecture of the TPM is comprised of a moving platform attached to a base through three CRU jointed serial linkages. The prismatic motions of the cylindrical joints are considered to be actively actuated. Kinematics and performance of the TPM are studied systematically. Firstly, the structural characteristics of the mechanism are described, and then some comparisons are made with the existing 3-CRU parallel mechanisms. Although these two 3-CRU parallel mechanisms are both composed of the same CRU limbs, the types of freedoms are completely different due to the different arrangements of limbs. The DOFs of this TPM are analyzed by means of screw theory. Secondly, both the inverse and forward displacements are derived in closed form, and then these two problems are calculated directly in explicit form. Thereafter, the Jacobian matrix of the mechanism is derived, the performances of the mechanism are evaluated based on the conditioning index, and the performance of a 3-CRU TPM changing with the actuator layout angle is investigated. Thirdly, the workspace of the mechanism is obtained based on the forward position analysis, and the reachable workspace volume is derived when the actuator layout angle is changed. Finally, some conclusions are given and the potential applications of the mechanism are pointed out.

Short summary
This paper proposes a modified 3-DOF TPM 3-CRU. The mobility of the mechanism is analyzed based on screw theory. Both inverse and forward position analyses are performed, and the analytical solutions are obtained with respect to these two problems. The proposed TPM has explicit solutions for the inverse and forward kinematics issues. Both the path planning and control problems of the mechanism are very simple. The Jacobian matrix of the mechanism and reachable workspace are obtained.