Research On The Robust Control Technology For The Wafer Transfer Robot

Integrated Circuit industry is the foundation of the social economy development and the social progress, which can improve international competitiveness and provide guarantee for the national security. IC manufacturing equipment is the pillar of Integrated Circuit industry. As an important part of IC manufacturing equipment, wafer transfer robot undertakes the transit of wafer precisely, fast and steadily. According to the national 973 project"Highly efficient and stable transmission principle and the realization for lager-size thin wafers in complex environment"(2009CB724206), this paper studies the control technologies of wafer transfer robot from the stable and precise control.Traditional wafer transfer robot uses decelerating mechanism to connect the motor and the drived axis. This mechanism has the disadvantages of lower precision, poor reliability,lower stiffness. Based on the structure of foreign direct-drive wafer transfer robot, this paper designs a R-T direct-drive wafer transfer robot, and analyzes the transmission principle. In order to control the robot, the paper builds kinematics model and dynamics model of the wafer transfer robot. Also, after analyzing the error of trajectory tracking, this paper includes that it is important to improve the precision of motor control in order to improve the precision of trajectory tracking of end-effector.Because of the robot system parameter error and the dynamic characteristics which is ignored when build model, the built dynamics model must have a certain error. Also, the existing external disturbance and the particularity of direct-drive motor control effect the control performance of the wafer transfer robot. So it is difficult to obtain high precision control using conventional PID control. The paper studies on the PD control with feedforward compensation and the computed torque method focusing on R-T wafer transfer robot. On the basis of that, the robust control is introduced in. The expression of robust controller and the convergence performance of error of robust control method are derived.In order to meet the requirement of control algorithm to hardware, open controller , which is applied to direct-drive wafer transfer robot, based on digital signal processor(DSP) is designed. This controller adopts a hierarchy which consists of upper layer PC and lower layer DSP units. Upper layer mainly monitors the status of robot system real-timely, calculates inverse kinematics, and so on. The control algorithm is realized in DSP. The lower layer mainly completes direct and precise closed-loop control of every joint motor. The data is transferred between upper layer PC and lower layer DSP with serial port.Experiment system of wafer transfer robot is established, and debugging program is compiled. When T axis and R axis of wafer transfer robot is drived alone, robust experiment is carried out. The results demonstrate that robust control algorithm improves the precision of preconceived trajectory tracking for this direct-drive wafer transfer robot. So the algorithm realizes stable and precise wafer transfer.