Study And Implementation Of Trajectory Planning For R-Theta Type Wafer Transfer Robot

In recent years, driven by mobile Internet, cloud computing and other emerging industries, IC industry has obtained a new development opportunity.Wafer transfer robot is key equipment in the IC manufacturing. This paper focuses on the research of trajectory planning of the R-Theta type wafer transfer robot to achieve fast and stable control scheme for the robot.Firstly, mechanical structure of the R-Theta type wafer transfer robot is analyzed. The driver mode and transmission method of every freedom is achieved.Based on those basic concepts, kinematics equations and dynamic equations of the robot are derived by using D-H coordinate representation method and Lagrangian mechanics respectively to provide theoretical support for robot trajectory planning.Secondly, the time optimal trajectory planning along a specified path problem of the R-Theta type wafer transfer robot is studied. By using the path parameter variable, dynamics equations, joint torque constraints and joint velocity constraints of the robot are parameterized and the time optimal trajectory planning problem is transformed into a optimal control problem with constrains of a second order differential dynamical system. Then, this optimal control problem is solved using numerical integration algorithm in the phase plane. In order to overcome shortcomings of the numerical integration algorithm, a novel nonlinear transformation method is proposed and original non-convex optimal control problem is transformed into a convex optimal control problem. For the purpose of obtaining smooth and time-optimal trajectory, energy item and torque jitter item together with the time item are considered to get a comprehensive optimal cost function. By using direct transcription method, the convex optimal control problem is discretized and reformulated as a large sparse optimization problem. Moreover, by introducing some auxiliary variables, the large sparse optimization problem is transformed into a second order cone programming.Finally, the second order cone programming can be solved by using YALMIP&Se Du Mi method. A smooth and time-optimal trajectory is obtained.Thirdly, the hardware and software platform for control of the wafer transferrobot is designed and implemented. In the hardware part, a four-axis motion control card based on PCIe bus is developed, and the FPGA logic code of the PCIe motion control card is designed and debugged. In the software part,software of the control system is developed based on RTX real-time operating system, including the hardware driver of the PCIe motion control card under RTX environment, the real-time control program of the robot and the interface program for debugging.Finally, based on the developed software and hardware platform, trajectory planning problem of the wafer transfer robot is realized. The smooth and time-optimal trajectory planning algorithm is verified on the platform. The experiment results show the effectiveness on the fast and smooth control of the wafer transfer robot.