Closed-Form Forward-Position Solution for a 6-Dof 3-PPSP Parallel Mechanism and Its Implementation

Closed-form forward/reverse position solutions for a 6-degree-offreedom (DoF) parallel mechanism that has some type of nonsymmetric geometry are derived in this study. Particularly, the derived forward-position analysis is applicable to the mechanisms in which three passive joints are constrained to move parallel to the moving plate. Its kinematic and dynamic characteristics are investigated via isotropic index of the Jacobian matrix and isotropic index of the output effective inertia matrix, respectively. From this investigation, it is found that the mechanism has fairly uniform kinematic/dynamic characteristics throughout its workspace. To examine the effectiveness of the proposed 3-PPSP-type mechanism, a prototype is designed, implemented, and tested experimentally under various operating conditions. A simple PID controller is applied to the system, and its joint positions are servo-controlled. The controlled system showed a good trajectory performance. Noting that a more advanced controller requiring a forwardand/or reverse-position solution can be applied to the system in real time, it can be contended that the manipulator is a candidate for the high-precision manipulator. KEY WORDS—parallel manipulator, closed-form solution, 6-DoF, 3-PPSP The International Journal of Robotics Research Vol. 20, No. 1, January 2001, pp. 85-99, ©2001 Sage Publications, Inc.