Force trajectory generation for the redundant actuator in a pneumatically actuated Stewart platform

Force distribution is one of the advantage of a redundant parallel manipulator configuration, making the utilization of less powerful actuators feasible. In this contribution, a force trajectory for a redundant actuator in a seven-cylinder pneumatically-actuated Stewart platform is derived analytically using the inverse dynamic model to maximize the benefit of the additional actuator. A feed-forward scheme is proposed with a requirement of good position tracking control. An input/output linearization is applied for the redundant actuator force control design with good force tracking capability. The designed force trajectory generator is implemented in a full-size pneumatically-actuated Stewart platform, and the results show an improvement in form of force reduction on the six outer cylinders and better utilization of the redundant cylinder force capacity.