Type synthesis of the rotational decoupled parallel mechanism based on screw theory

With the gradual deepening of study on the parallel mechanism, the difficulty brought by the existence of coupling to the theoretical analysis and practical application of parallel mechanisms is becoming increasingly apparent. The research on the decoupled parallel mechanism is currently one of the hot fields. Though most of the rotational parallel mechanisms, which has been widely used in spatial orientation fields, are not decoupled. It is comparative difficult for the synthesis of fully decoupled rotational parallel mechanisms, and the number of the existing parallel mechanisms which can realize rotational decoupling is limited. In addition, most of the existing rotational decoupled parallel mechanism are obtained depending on the experience of the researcher, and don’t possess the general theoretical significance. Based on the screw theory, this paper presents the rotational conditions of the parallel mechanism through the analysis of the relationship between the degree of freedom of the parallel mechanism and its limbs. The synthesis rule of the limbs for decoupled rotational parallel mechanism is established according to the twist screw system of the limbs, which assures the decoupling of the rotations in each limb. The selection principle of the input pairs for the rotation driven limbs is proposed, then the type synthesis method for rotational decoupled parallel mechanisms is formed. With this type synthesis method, synthesis of the rotational decoupled parallel mechanisms is performed, which can provide a reference for the development of the novel type parallel mechanisms with independent intellectual property rights.