Research Of Magnetic Fluid Seals Applied In Wafer Handling Robot

Along with the rapid development of integrate circuit (IC), there is a high requirement of cleanliness and vacuum for the wafer processing environment, in which the wafer handling robot works. Compared with traditional mechanical seals, magnetic fluid seals have unique characters of high airtightness, minimal friction torque requirements, no pollution and long life-span. Considering above characters, magnetic fluid seal is appropriate for the sealing of torque transmission in vacuum wafer processing environments. So it is significant to research on the design of magnetic fluid seal and its application on wafer handling robot working in vacuum condition.Firstly, the development and research on wafer handling robot and magnetic fluid seal technology of china and abroad is introduced in this paper. According to the theory of ferrohydrodynamics, the seal differential pressure formulas of magnetic fluid seal are deduced. The formulas indicate that the magnetic field gradient in the sealing gap determine the seal capacity of magnetic fluid seal. To get a high sealing pressure, it is crucial to reasonably design the structure parameters of magnetic fluid seal to get a high magnetic field gradient.Secondly, the magnetic analysis model of dual magnetic fluid seal is established. The magnetic field distribution of dual magnetic fluid seal is calculated by ANSYS software, and the analysis results of magnetic flux density in the sealing gap of inner and outer shafts are got. On the basis of that, the influence of seal structure parameters on seal differential pressure is analyzed. The optimal taking value intervals of important parameters that affect the seal differential pressure are obtained.Afterwards, based on the gained conclusion of parameters selecting in the design of dual magnetic fluid seal, and according to the structural characteristics of wafer handling robot, a kind of wafer handling robot with dual magnetic fluid seal is designed. According to the radial expansibility and structural similarity that triaxial magnetic fluid seal compared with dual magnetic fluid seal, a kind of wafer handling robot with triaxial magnetic fluid seal is designed. The above two robots all have three degrees of freedom, which are R,θand Z, and can ensure the requirement of cleanliness and vacuum in wafer processing environment as well as meet the demand of wafer transmitting mission.Finally, a triaxial magnetic fluid seal experiment device is designed and manufactured. According to the sealing experiments, the static sealing pressure of triaxial magnetic fluid seal applied in wafer handling robot is 0.23MPa, and the dynamic sealing pressure is close to the static sealing pressure when the speed of robot's rotary shaft is 200-300r/min. The experiments prove that the design of triaxial magnetic fluid seal structure is correct and the application of triaxial magnetic fluid seal in wafer handling robot is feasible.