Dynamics On A Certain Type Roots Vacuum Pump Rotor System

The rapid development of electronics industry chemical industry and Semiconductor industry,many processes are required to be carried out in clean vacuum environment.So the requirements of the performance of the vacuum pump is gradually increasing.The roots vacuum pump is widely used in chemical industry Semiconductor industry and so on.Because of Bad working environment,the vibration problem of rotor system is easy to occur.And then affect its performance index and service life.The work efficiency will be reduced.(1)In this paper,a mathematical model of rotor bearing gear cavity system is established.The rotating shaft is regarded as the Euler beam of the elastic body.By using the vibration theory of beam,the equation of motion of the beam is pulled.The problem of meshing stiffness of the gears changing periodically with time is fully considered.The meshing stiffness of the gear is obtained by using the formula of Ishikawa.The plot of stiffness versus time is plotted;The motion differential equations of gears are listed by the method of concentrated mass.Gear translation and torsional freedom are considered,and the tooth surface friction is ignored;The bearing model is established,and the bearing force is calculated by Hertz contact theory.The model mentioned above is integrated with each other to establish the dynamic model of Roots pump.The ode45 method(Runge Kutta method)is used to solve the differential equations.The original Roots pump model was calculated by using the rotor model of Jeffcott and the mass of the rotating shaft was neglected.The correctness of the new model was verified by the comparison of the two calculation results.(2)Considering the difference of the Euler beam modal interception order will affect the accuracy of the calculation results,the vibration response of different truncation order is calculated.The number of stages is chosen which can guarantee the precision of calculation and will not take up too much computing resources.The influence of bearing clearance and support stiffness on the response of the rotor is studied by means of time-domain response,frequency spectrum and three-dimensional spectrum.The force model of the gear coupling misalignment is established.The expression of force is given.The force of the coupling misalignment was added to the Roots pump model to obtain the spectral characteristics of the misaligned fault.And provide a theoretical basis for fault diagnosis;The mechanism of rubbing between rotor and stator is analyzed.Roots pump model with rubbing fault is established,and the model is simulated.The spectrum characteristics of Roots pump rotor in the presence of rub-impact are analyzed.(3)Vibration tests were performed on Roots pumps with misaligned faults and rotor-to-chamber faults.FFT analysis is performed.The spectral characteristics of the fault are obtained,which provides the basis for fault diagnosis.And verify the rationality of the previously established model.