Type synthesis and analysis of parallel mechanisms with sub-closed-loops

For the special needs of attitude adjustment and vibration isolation of precise instruments, parallel mechanisms with sub-closed-loops (PMWS) are proposed to eliminate the interferences that vary in frequency. First, the multi-drive units composed by sub-closed-loops are synthesized by two derivative methods, and the PMWS with diffident DOF are synthesized based on screw theory. Furthermore, proposing the concept of the sub generalized coordinate, and the first and the second order influence coefficients of each link of PMWS are established under the generalized coordinates and the sub generalized coordinates. Besides, based on the principle of virtual power and the Newton-Euler formula, meanwhile combining the kinematics analysis of PMWS, the dynamics formulas of PMWS are established separately in joint space and operational space. Finally, taking 6-(PRRR)US PMWS as numerical example, by comparing the results of theoretical calculation and simulation, the kinematics and dynamics formulas of PMWS are verified.