Extreme configuration bifurcation analysis and link safety length of Stewart platform

The movement of parallel manipulator is carried out by controlling the length of links in usual condition. For a given set of motion input parameters, the Stewart platform is possibly at the states of configuration bifurcation. In order that the Stewart platform can move at will when the length of links changes in a determinate region, we discuss the problems about the manipulator configuration and link length. The extreme configuration is presented based on the idea of analyzing the movement state of parallel manipulator in link space. Sixteen kinds of extreme configurations for Stewart platform are described with the vector expressions of link lengths. In order to avoid configuration bifurcations, the bifurcation characteristics of extreme configurations are analyzed by homotopy method and static bifurcation condition. The safety length of links is solved, which makes the manipulator work safely in the safety length area of links. The relationship between the safety length of links and the structural parameters is analyzed by numerical examples.