Research On Magnetic Fluid Seal Structure Of Laser Transmission Channel

Laser transmitting equipment is usually composed of laser source and theodolite.At present,the equipment is developing in the direction of high power and long distance.Theodolite usually includes azimuth axis and pitch axis system.There is a gap in the axis system when it works.If the sealing effect of the laser transmission channel is not good,water vapor and solid particles are easy to enter the inside.Water vapor and particles will affect the beam quality.In severe cases,high energy laser will destroy the surface film system of Kurdish mirror.Therefore,the performance of dynamic seal is challenged.In this paper,a variety of traditional dynamic sealing methods were compared,and the magnetic fluid sealing scheme was finally selected,which was applied to the dynamic sealing of laser transmission channel for the first time.This paper mainly studied the following aspects1.The static and dynamic seal pressure formula and friction torque formula were obtained through the knowledge of fluid mechanics.The pressure transfer process and failure mode were studied.The key factors affecting the withstand voltage were analyzed,including the withstand voltage series and the gap size.The influence factors of centrifugal force were calculated quantitatively.2.According to the design requirements,this paper adopted the short axis mode,which was the combination of bipolar shoe and monopole magnetic source.The key points of the design were the material selection of the magnetic fluid,the tooth shape design of the pole shoe,the size of the permanent magnet,the design of the outer cylinder and the inner cylinder,etc.The magnetic circuit of the structure was analyzed theoretically,the design formula of the permanent magnet was deduced,and the rationality of the parameters of the permanent magnet was proved.3.The simulation model was established to analyze the magnetic field,temperature and dynamics of the structure.The structure design of magnetic force line nephogram was reasonable.There were a few magnetic lines passing through the air layer,which indicates that there was magnetic flux leakage in the structure.4.The transient results of the temperature field showed that the temperature rise of the magnetic fluid was only 2.5°C under continuous operation for ten minutes,while the steady-state temperature rise was 5°C.The temperature rise was very small and would not affect the saturation magnetic induction intensity of the magnetic fluid.The dynamic analysis results showed that the first-order natural frequency of the outer cylinder component and the first inner cylinder was much greater than the on-board excitation frequency,and the second inner cylinder had a maximum deformation of 6.5microns at the on-board frequency under 3g acceleration in the x-axis direction.The deformation only accounted for 3% of the gap,which didn't affect the pressure resistance of the structure.5.Finally,an experimental turntable was designed.The turntable can be perfectly combined with the structure.The motor drove the shaft and then drove the inner cylinder to rotate to simulate relative motion.A total of 4 sets of experiments were arranged,including air tightness,torque,high and low temperature and vibration tests.Centrifugal force had almost no effect on the pressure resistance value because of the low speed.The air tightness test showed that the maximum withstand voltage value can reached 0.2MPa,which was not much different from the theoretical analysis results;the pressure resistance period at room temperature reached 30 days.The peak torque of the test motor was 28N·m,and the maximum starting torque of the structure was 3N·m.The rated torque of the engineering motor was much greater than that of the test motor,and the turntable would not creep during operation.In the extreme temperature of-40°C?50°C and the vehicle vibration of 0?500Hz,the structure can still maintain a good pressure holding effect.In this paper,theoretical simulation and experiment were combined to verify that the seal structure can meet the sealing requirements of the transmission channel.It can be well applied in actual engineering.This article had a guiding significance for the future research of laser emission channel sealing.