Mobility analysis of lower-mobility parallel manipulators based on screw theory

Mobility analysis of lower-mobility parallel manipulators is of great importance in the context of analysis and design. A method is proposed for the mobility analysis of lower-mobility parallel manipulators based on screw theory. The limb structural constraint acting on the moving platform is first analyzed. Then the combined effect of all limb structural constraints is obtained by investigating the geometrical conditions of the linear dependency of them. Moreover, identification of the instantaneous mechanism is performed. The method is testified through examples including 4- and 5-DOF parallel mechanisms.