Kinematics, singularity, and optimal design of a novel 3T1R parallel manipulator with full rotational capability

Abstract

Parallel manipulators (PMs) with 3T1R (three translational and one rotational degrees of freedom) or Schonflies motion are very useful in industry. However, most 3T1R PMs have a limited range of rotation less than 90° while many practical tasks require a large range of rotation over 180°. Furthermore, there are no 3T1R PMs with full rotational capability that has small number of single-DOF joints and fixed actuators. A novel 2-(RRR)2RH PM with full rotational capability is proposed, where R and H denote a revolute joint and a helical joint, respectively. The moving platform is connected to the fixed base by two identical (RRR)2RH chains, where (RRR)2 denotes a 2- RRR closed chain. First, kinematic analysis of the proposed 2-(RRR)2RH PM, including mobility analysis, inverse and direct kinematics, singularity analysis, and workspace is presented. Second, the local conditioning index is used to evaluate the kinematic performance of the PM. Finally, optimal kinematic design of the 2-(RRR)2RH PM is investigated. The 2-(RRR)2RH PM has only 16 single-DOF joints and can be actuated by four fixed revolute joints. These features make it a good candidate in many applications.