Modeling simulation & control of 6-DOF Parallel Manipulator using PID controller and compensator

This paper presents modeling simulation and control of stuart type 6-DOF parallel manipulator. Dynamic equations of the parallel manipulator are derived by using Kane's method, inheriting all the advantages while circumventing all the disadvantages of Newtown-Euler and Euler-Lagrangian formulations. In this modeling procedure at first all the inertial torques due to platform, motor and actuators are calculated and then this is equated with active torque supplied by the DC-motors in the form of electromagnetic torque. By this force-torque balance, calculation of time varying equivalent inertia of the motor is avoided. Normal PID principle based controllers are not very effective in achieving desired accuracy in trajectory tracking as reported in literature. Therefore, a novel control architecture has been proposed which not only has industry standard PID controller but also includes compensator for drastically improving tracking performance. Since, over all system of parallel manipulator is highly non-linear in nature with coupling terms and varying parameters, only PID controller alone could not reduce this resultant tracking error, even after best tuning. One lag compensator for each actuator has been designed in combination with PID controller, which resulted in significant improvement in trajectory tracking in comparison to former control methods (only normal PID based controller) for all the parameters of cartesian trajectory.