Design Strategies for the Geometric Synthesis of Orthoglide-type Mechanisms

Pashkevich A., Wenger P. and Chablat D. Belarusian State University of Informatics and Radioelectronics P. Brovka str, 220027 Minsk, Republic of Belarus [email protected] Tel. 375 17 239 86 73, Fax. 375 17 231 09 14 Institut de Recherche en Communications et Cybernétique de Nantes 1, rue de la Noë B.P. 6597, 44321 Nantes Cedex 3, France {Philippe.Wenger, Damien.Chablat}@irccyn.ec-nantes.fr Tel. 33 2 40 37 69 54, Fax. 33 2 40 37 69 30 ABSTRACT The paper addresses the geometric synthesis of Orthoglide-type mechanism, a family of 3-DOF parallel manipulators for rapid machining applications, which combine advantages of both serial mechanisms and parallel kinematic architectures. These manipulators possess quasi-isotropic kinematic performances and are made up of three actuated fixed prismatic joints, which are mutually orthogonal and connected to a mobile platform via three parallelogram chains. The platform moves in the Cartesian space with fixed orientation, similar to conventional XYZmachine. Three strategies have been proposed to define the Orthoglide geometric parameters (manipulator link lengths and actuated joint limits) as functions of a cubic workspace size and dextrous properties expressed by bounds on the velocity transmission factors, manipulability or the Jacobian condition number. Low inertia and intrinsic stiffness have been set as additional design goals expressed by the minimal link length requirement. For each design strategy, analytical expressions for computing the Orthoglide parameters are proposed. It is showed that the proposed strategies yield Pareto-optimal solutions, which differ by the kinematic performances outside the prescribed Cartesian cube (but within the workspace bounded by the actuated joint limits). The proposed technique is illustrated with numerical examples for the Orthoglide prototype design.