Inverse dynamic and control of a hybrid parallel robot

In this paper, a new methodology for the development of the dynamic formulation for a hybrid parallel robot is introduced. The robot includes a tripod that is serially connected on top of a hexapod in order to increase its overall workspace, while maintaining sufficient accuracy and stiffness in motion. The robot will have applications involving gripping and manipulation of large aerospace components such as a wingbox structures and panels. The dynamic formulation of the system, based on Newton-Euler and inverse kinematic equations, is presented by identifying the position vector of the actuators during motion when the system follows certain point and orientation in space. Based on the velocity and acceleration, calculated by taking derivative of the motion equation, the force on the actuator is identified. Since the position vectors of all tripod joints can change through motion, the above methodology offers less complex calculations compared with the existing methods such as using forward dynamics. A MATLAB software was developed to create a set of comprehensive dynamic equations for the overall control system design. An experimental physical hybrid robot was built in order to verify the theoretical formulations. Force sensors, connected at each actuator joint, were used to obtain the applied force on each actuator through a number of given motions. The applied forces subsequently assist to calculate the acceleration of the moving platform. The experimental actuators' force results compare well with the proposed theoretical formulation.