Modelling And Experimental Study Of Magnetic Couplings And Shafting Prototype For Vacuum Robot

The vacuum robot, a critical component to handle wafers among different chambers, is widely used in semiconductor cluster tool. The techniques of sealing isolation and power transmitting between atmosphere and vacuum environment are the bottleneck for developing a vacuum robot. Therefore, it is important to break through these key points and to design the prototype system of a vacuum robot. The theoretical objective of this dissertation is to analyze the characteristics of Permanent Magnetic Couplings (PMC) and to optimize its design. Moreover, the shafting of a vacuum robot which combines the rotary direct drive technique and the magnetic force transmission technique needs to be designed.Firstly, the mathematical models of the Equivalent Magnetic Charge (EMC) method and the Current Sheet Model (CSM) method for computing the torque of PMC are improved, and the magnetic flux leakage factor is introduced. The simplified formulas based on these analytical methods for computing the maximal torque of radial yoke-guided PMC with a gap between adjacent magnet blocks are obtained. The improved formulas greatly increase efficiency and accuracy. The results demonstrate that the accuracy of the improved CSM can be increased by 25% to 30% compared with the original CSM method, while the accuracy of the improved EMC increased by 4% to 30%, and the efficiency increased by over 100% compared with the original EMC method. Besides, a 3D Finite Element Analysis (FEA) model of PMC is established.Secondly, the influences of geometric parameters on the maximal torque T_max, the T_max/V, and the starting torsional stiffness K are analyzed systematically with the improved EMC, CSM and 3D FEA methods. Furthermore, simulations including the magnetic guiding effect of yoke iron, the coupling effect of multi-sets PMCs, and the effect of different PMCs'structures are completed. The conclusions are significant for optimal design of PMC. Thirdly, an example of simultaneously optimizing two sets of radial PMC with 3D FEA modeling is taken in this research. The preliminary design specifications are listed and a practical mathematical model with novel criterions is set up. Moreover, an optimizing strategy consisting of the 3D FEA, the Design of Experiments (DOE) and an exhaust algorithm in a small range is implemented to obtain the near-optimal parameter set. The proposed optimizing method can fulfill the requirements of practicability, higher precision, as well as strong stabilization. In this case, the evaluating indicator value is improved by 30% compared with the relative optimizing set obtained from DOE directly. The optimizing strategy can also be employed in various similar industrial applications.Fourthly, the prototype system of 2 DOFs vacuum robot shafting with coaxial arrangement is successfully designed, which combines the rotary direct drive technique and the magnetic force transmission technique. The isolation cover is designed as a setback type structure. The strength and the radial deformation are verified and the eddy current loss on the isolation cover is also analyzed. Besides, the design and fabrication of magnetic couplings used in a vacuum robot are discussed, and the assemble design of split type direct drive motor is studied, which has an important reference value on the development of next generation vacuum robot.Last but not least, the measuring equipment used to test the static and dynamic characteristics of PMC with different types of misalignment between driving and driven shaft is built. The results demonstrate that the variations of the transmitted torque and the tracking characteristic of radial PMC due to each type of misalignment are slight, and the dynamic characteristics of PMC are excellent. In this research, the response time is less than 0.01s at the starting stage; and the stabilization time is 0.35s when the peak velocity is 670deg/s and the acceleration is 1260deg/s2. Meanwhile, the maximal tracking error is about 20', and the steady state error is 2'under different types of misalignment. The dynamic property and precision of shafting is tested. The results show that the tracking characteristic of PMC is excellent, the steady state error is about 3', and the coupling effect between two sets of PMCs can be neglected.