Design and Prototyping of a Spherical Parallel Machine Based on 3-CPU Kinematics

the other. In one case, joints’ axes are set in space so that the mobile platform can freely translate (without rotating) inside its 3D workspace: this is easily obtained by arranging the universal joint of each limb so that the axis of the outer revolute joint is parallel to the base cylindrical joint; such three directions are mutually orthogonal to maximise the workspace and grant optimal manipulability. With a different setting of the joints, three degrees of freedom of pure rotation are obtained at the terminal of the spherical wrist: in this case the axes of the cylindrical joints and those of the outer revolute pairs in the universal joints all intersect at a common point, which is the centre of the spherical motion. This solution, at the cost of a more sophisticated controller, would lead to the design of simpler machines that could be used also stand-alone for 3-dof tasks and would increase the modularity and reconfigurability of the robotised industrial process. The two robots have been developed till the prototypal stage by means of a virtual prototyping environment and a sketch of the whole system is shown in Fig. 1: while the translating machine has been presented already elsewhere (Callegari & Palpacelli, 2008), the present article describes the design process of the orienting device and the outcoming prototype.

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