Structure synthesis and analysis of a novel four-degree-of-freedom parallel manipulator

According to the principle of scaling ruler,6-DOF(degree of freedom) and 4-DOF rhombus kinematic chains with a large pantograph ratio have been constructed to form the parallel manipulator,and based on this,a novel 4-DoF parallel manipulator with a compact structure and a large workspace is proposed.Based on the equivalent substitution principle,an equivalent model of 4-DoF parallel manipulator can be designed by the way of replacing virtual axis of rhombus mechanism with the real axis of serial kinematic chains.In addition,screw theory was used to analyze the DOF.In the analysis of the kinematic screw system and reciprocal screw system of constraints in the equivalent model of parallel manipulator,two translational DOF and two rotational DOF can be confirmed in the parallel moving platform.