This thesis presents precise position control methods of a 3-PRPS in-parallel manipulator for industrial applications such as assembly of highly integrated semiconductors and microsurgery.
Since real-time control is one of the most important issues required for industrial application, the experimental hardware is set up with a VME based DSP controller.
In the 3-PRPS parallel manipulator, structurally existing friction at three horizontal links considerably degrades the precise position control. In order to compensate the friction of the horizontal links in the joint space, three methods have been proposed and investigated.
The first method is to compensate the friction by joint torque feedback. However, the method resulted in unsatisfactory compensation due to noisy force-torque sensor signal.
The second one is newly proposed to compensate the friction by using the error information of the integrator of conventional PID position controller. This method is simple and very effective to periodical joint motions.
The thirdly proposed one is a disturbance compensation using disturbance and velocity observers. We analyzed the decision method of eigenvalues of the disturbance observer and the effects of the control resulted from the system model errors. Through a series of simulations and experiments, we see that the method is capable of compensating variations of the robot parameters such as inertia and damping as well as the joint friction.
Experiments show that the disturbance compensation method using disturbance and velocity observer is excellent to compensate the friction among three compared methods. Compared with conventional PID position control, it decreased position errors in a circular motion by approximately 70%.
keywords : 3PRPS parallel manipulator, Precise position control, Joint torque feedback, Integral error information, Disturbance and velocity observer.
