Design, analysis and fabrication of a novel three degrees of freedom parallel robotic manipulator with decoupled motions

Most of the existing parallel robotic manipulators have coupled motion between the position and orientation of the end-effector. The complexity of the multi-axial manipulation produces the difficulty to control. This research deals with a lower mobility parallel manipulator with fully decoupled motions. The proposed parallel manipulator has three degrees of freedom and can be utilized for parts assembly and light machining tasks that require large workspace, high dexterity, high loading capacity, and considerable stiffness. The manipulator consists of a moving platform that is connected to a fixed base by three pairwise orthogonal legs which are comprised of one cylinder, one revolute and one universal joint respectively. The mobility of the manipulator and structure of the inactive joint are analyzed. Kinematics of the manipulator including inverse and forward kinematics, velocity equation, kinematic singularities, and stiffness are studied. The workspace of the parallel manipulator is examined. A design optimization is conducted with the prescribed workspace. It has been found that due to the special arrangement of the legs and joints, this parallel manipulator possesses fully isotropic. This advantage has great potential for machine tools and coordinate measuring machine. The experiment on the prototype verifies its feasibility as a portable parallel robotic machine tool.