Type synthesis of 1T2R parallel mechanisms with parasitic motions

Finite motion analysis and type synthesis of parallel mechanisms with parasitic motions are great challenges in the fields of mechanisms and robotics. This paper proposes a finite screw based approach to handle this problem by taking one translational and two rotational (1T2R) parallel mechanisms with parasitic motions as examples. Firstly, 1T2R finite motion of the moving platform is categorized into four cases whose finite motions are described by finite screw analytically and then the reasons for producing parasitic motions are explored in this process. Based on this, available limbs are obtained algebraically by deriving formulas formed by triangle screw product. Finally, the assembly conditions among limbs, fixed base and moving platform are acquired in an analytical manner, leading to synthesize 1T2R parallel mechanisms with parasitic motions systematically. This paper solves a long-term problem that describes and analyzes finite motions of parallel mechanisms with parasitic motions and synthesizes their topology structures.