Research And Design Of Magnetic Fluid Seals For Wafer Handling Robot

Generally a wafer's production is required a dust free vacuum environment in order to achieve higher IC integration levels and prevent the surface of the wafer from pollution. A reliable rotary hermetical technique is crucial for wafer handling robot within a vacuum chamber. Comparing to conventional mechanical seals, magnetic fluid sealed transmission can transmit rotary motion into a vacuum chamber with zero leakage, minimal contamination level and no maintenance required, so it is a significant work to do the research on principle and design method of magnetic fluid seal oriented to wafer handling robot under vacuum condition.Firstly, this paper introduces the development and current research on wafer handling robot and magnetic fluid seal technology at home and abroad. Then this paper points out the main design challenge of magnetic fluid rotary seal is how to preparative high performance magnetic fluid and the optimum structural design to improve seal capacity.Secondly, the principle of magnetic fluid seal is analyzed and seal differential pressure formulas of magnetic fluid seal is deduced and obtained according to the theory of ferrohydrodynamics. The seal capacity of magnetic fluid seal is depend on the saturation magnetization of the magnetic fluid and magnetic field gradient within the sealing gap. The mathematical model of rotationally symmetric magnetic fluid seal is established. Then the non-linear magnetic field distribution in magnetic fluid seal is calculated by ANSYS software through solving magnetic vector potential with appropriate boundary conditions, and the result is showed by magnetogram. Based on the distribution of magnetic flux density in the sealing gap, the influence of seal structure parameters on seal pressure differential is analyzed. A group of optimum parameters for sealing gap, pole width and slot width and slot height of the rectangular multi-tooth pole is obtained.Subsequently, the experiment device of magnetic fluid seal is designed and manufactured. The influence of magnetic field intensity, sealing gap and shaft speed are investigated on seal capacity. Both theoretical analysis and test results show that magnetic fluid seal is an effective and feasible method for designing the rotary feedthrough of wafer handling robot. There are many factors that can influence magnetic fluid seal performance. The seal capacity can be improved by optimizing the magnetic circuit parameters. Eventually, according to the task features of wafer handling robot, a designed dual coaxial magnetic fluid seal apparatus is applied to the transmission module of wafer handling robot which can achieve the radial linear stretching movement and rotation movement.