Robotics and Computer-Integrated Manufacturing 23 (2007) 395–408 Kinematic analysis of a 3-PRS parallel manipulator Yangmin Li à , Qingsong Xu Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Av. Padre Toma´s Pereira S.J., Taipa, Macao SAR, PR China Received 6 October 2005; received in revised form 23 February 2006; accepted 7 April 2006 Abstract Although the current 3-PRS parallel manipulators have different methods on the arrangement of actuators, they may be considered as the same kind of mechanism since they can be treated with the same kinematic algorithm. A 3-PRS parallel manipulator with adjustable layout angle of actuators has been proposed in this paper. The key issues of how the kinematic characteristics in terms of workspace and dexterity vary with differences in the arrangement of actuators are investigated in detail. The mobility of the manipulator is analyzed by resorting to reciprocal screw theory. Then the inverse, forward, and velocity kinematics problems are solved, which can be applied to a 3- PRS parallel manipulator regardless of the arrangement of actuators. The reachable workspace features and dexterity characteristics including kinematic manipulability and global dexterity index are derived by the changing of layout angle of actuators. Simulation results illustrate that different tasks should be taken into consideration when the layout angles of actuators of a 3-PRS parallel manipulator are designed. r 2006 Elsevier Ltd. All rights reserved. Keywords: Parallel mechanism; Kinematics; Mobility; Workspace; Dexterity; Mechanism design 1. Introduction In recent years, parallel robots have become an active research direction due to the merits in terms of high accuracy, high stiffness, and high load carrying capacity over their serial counterparts. The principal drawbacks are their limited workspace and complex forward position kinematics problems. A parallel manipulator typically consists of a moving platform that is connected to a fixed base by several limbs or legs in parallel. A definite advantage of parallel manipulators is the fact that, in most cases, actuators can be placed on or near the truss, thus imposing a limited weight on the moving parts, which makes it possible for parallel manipulators to achieve high speed. Parallel mechanical architectures were first introduced in tire testing by Gough, and later were used by Stewart as motion simulators. An exhaustive enumeration of parallel robots’ mechanical architectures and their versatile appli- cations were described in [1]. Six degrees of freedom (DOF) parallel manipulators have many advantages mentioned above and many literatures introducing them; however, 6- DOF is not always required for many applications in practice. Recently, parallel manipulators with less than 6- DOF have attracted various researchers. Many 3-DOF parallel manipulators have been designed and investigated for relevant applications, such as the famous DELTA robot with three translational DOF [2] whose concept afterwards has been realized in many different configura- tions [3,4], the 3-UPU and 3-PRC architecture parallel robots with pure translational motions [5,6], the CaPaMan and HANA parallel manipulators with three spatial DOF [7,8], 3-RPS parallel mechanisms which are exploited as a micromanipulator [9] and as a coordinate-measuring machine [10], etc. Here the notation of R, P, U, C, and S denotes the revolute, prismatic, universal, cylindrical, and spherical joint, respectively. Although less-DOF spatial parallel manipulators present several advantages in terms of the device total cost reduction in manufacturing and operating, some issues become complicated since in many cases position and ARTICLE IN PRESS www.elsevier.com/locate/rcim 0736-5845/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.rcim.2006.04.007 à Corresponding author. Tel.: +853 3974464; fax: +853 838314. E-mail address: ymli@umac.mo (Y. Li).