On Rotor Passing Through Critical Speeds And Dynamic Balancing By Controllable Electromagnetic Force

Nowadays the speed of rotating machinery is increasing,which makes more and more rotors work over several critical speeds.It's difficult to make these rotors pass through critical speeds and to make dynamic balancing.Traditional balancing methods,such as modal balancing method and influence coefficients method,need trial runs,resulting in a long process and a high cost of balance.Improving the dynamic balancing efficiency is a current research hotspot.Based on this background,this thesis presents a new method to assist a rotor to pass through critical speeds and to make dynamic balancing.It utilizes synchronous modal electromagnetic forces to suppress excessive vibration of a rotor-bearing system when the rotor is passing through critical speeds.The recorded electromagnetic forces information is used to reconstruct the correcting weights for the rotor.By adding or removing the calculated correcting weights,the rotor-bearing system is effectively balanced.In addition,by use of this method,a rotor can reach its working speed smoothly.Therefore some certain rotors can work properly if the rotors are assisted to pass through critical speeds in the process of start and stop.A rigid rotor-bearing model with elastic supports at both ends was used in numerical simulations.The rotating modal electromagnetic forces were successfully applied in assisting the rotor to pass through the 1st and 2nd critical speed.The correcting weights were deduced from the recorded forces.The vibration was significantly reduced after adding calculated correcting weights.The simulation results showed that this method was feasible.The influence of balancing speed and trial weight(size and direction)on the effect of one-time balancing was studied theoretically from the perspective of error tolerance.The optimal selection method of speed and trial weight was found.Dynamic analysis of a multi-section type long rotor was carried out.The influence of run-out and bending signal on balancing effect was explored.Rresults indicated that the run-out could be compensated by slow vibration vector while the bending rotor had to be repaired or assisted to pass through critical speeds.An E-type magnetic pole was designed and its electromagnetic force was calibrated.Under differential drive control mode,the control equations of DSP(Digital Signal Processing)command values were derived using magnetic flux in gaps as the intermediate variable.The electromagnetic force control system based on DSP was established,and the quantitative control of electromagnetic force was realized successfully.Experiments on a three-disk flexible rotor-bearing system were carried out.Firstly,the 1st and 2nd flexible modes was balanced respectively with electromagnetic forces,the resonance amplitudes was reduced by 80% and 50% respectively.Then the first two order critical speeds were passed successfully in one time by use of the method.The rotor vibration did not exceed the set limit in the whole running range.The maximum decrease of vibration reached up to 80% after only one-time balance.The results showed that the presented method is effective and promising in application.