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Tham khảo tài liệu 'parallel manipulators new developments part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 9 Design and Prototyping of a Spherical Parallel Machine Based on 3-CPU Kinematics Massimo Callegari Dipartimento di Meccanica Università Politecnica delle Marche Via Brecce Bianche Ancona Italy 1. Introduction Parallel kinematics machines PKMs are known to be characterised by many advantages like a lightweight construction and a high stiffness but also present some drawbacks like the limited workspace the great number of joints of the mechanical structure and the complex kinematics especially for 6-dof machines. Therefore Callegari et al. 2007 proposed to decompose full-mobility operations into elemental sub-tasks to be performed by separate minor mobility machines like done already in conventional machining operations. They envisaged the architecture of a mechatronic system where two parallel robots cooperate in order to perform a complex assembly task the kinematics of both machines is based upon the 3-CPU topology but the joints are differently assembled so as to obtain a translating parallel machines TPM with one mechanism and a spherical parallel machine SPM with 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 .
