Configuration bifurcations analysis of six degree-of-freedom symmetrical Stewart parallel mechanisms

The configuration bifurcations of Stewart parallel manipulators at singular positions induce the uncertainty of the moving trends of the manipulative platform. The Jacobian matrix method can determine the singular position of Stewart manipulators, but it cannot determine the configuration variation trend in the vicinity of the singular position. In order to investigate the concrete motion behaviors of the Stewart parallel manipulator at singular positions, we construct the algorithm for determining all the configuration branches and bifurcation points. Through detailed investigations of configuration bifurcation characteristics, we have found that with a decrease of the extensible legs' length, the bifurcation points of configuration branches of the movable platform get together gradually and the bifurcation type changes from turning to dual-point bifurcation, and then, finally, it becomes multiple-point bifurcation.