To obtain a new kind of parallel mechanism with bifurcated motion

the structural constraint

motion mode and input scheme are analyzed by using screw theory. The motion characteristics of a closed-loop linkage with bifurcated motion is firstly analyzed. In different motion modes

the closed-loop linkage with bifurcated motion has two kinds of single DOF(degree of freedom)finite rotational motions and one 2-DOF instantaneous rotational motion. A kind of hybrid limb with bifurcated motion is then obtained by integrating the closed-loop linkage with 4-DOF PPRR(P-prismatic pair

R-revolute pair )serial limb. The constraint exerted by the hybrid limb can switch among no-constraint

a constraint couple

and a constraint force. The constraint screws associated with the hybrid limb in different motion modes are identified. Lastly

a kind of parallel mechanism with bifurcated motion is constructed with three identical hybrid limbs connecting the fixed base and moving platform

and the actuation scheme for the parallel mechanism is discussed. The result shows that the parallel mechanism has the ability to perform variable motion modes such as 3T3R

3T

3R

2T1R(T-translation

R-rotation)and 1T2R.