  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 XYZ-machine. 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.
