Study On Vibration Control Of Milling Spindle With Active Magnetic Bearings

Complex surface workpieces are widely used in aerospace,automotive industry,medical equipment and energy,etc.The requirements for manufacturing quality and efficiency are increasing gradually,which makes turning-milling compound processing technology faces new challenges.The motorized spindle,which provides direct power for milling,is especially critical for the core components of B-axis power tool rest.The magnetic suspension motored spindle has attracted much attention because of its little mechanical wear,low energy consumption,low noise and good mechanical properties.Based on its active vibration suppression characteristics,this paper studies the vibration control technology of AMB milling spindle,aiming at effectively mitigating the vibration and chatter generated in the milling process of complex surface workpieces with low rigidity and strong coupling.The main research contents include:1.By studying the support principle and open-loop stability of active magnetic bearings,the inherent mathematical model is illustrated,and the stiffness damping characteristics of active magnetic bearings are deduced according to the model.It can be adjusted by changing the control current in the stator coils,providing a theoretical basis for active control of vibration by AMB motorized spindle.2.Aiming at the unbalanced vibration caused by the eccentricity of the rotor mass,a 2-DOF magnetic motorized spindle-rotor dynamics model is established with the rotor regarded as a rigid rotor,Then the LQR is proposed as the system state feedback control method and MPGA is designed to optimize the weight matrix.Besides,the simulation in Simulink further verified the stability of optimization effect3.A specific AMB milling spindle is customized to investigate its eddy effect and resonance problem caused by it.The steady-state eddy differential equation of AMBrotor(flexible)is established,and the mode shapes at critical speed are obtained in the Workbench.According to the simulation data,and combined with the control variable method,the relationship between the electromagnetic structure parameters of AMB and the critical speed is qualitatively analyzed.Starting with avoiding resonance,the intrinsic correlation and mechanism between the harmonic response analysis result and the motorized spindle parameter design are obtained4.Considering the vibration control system of uncertainty milling machining with input constraints,a model predictive control method under the spindle-tool coupling model is proposed to mitigate the milling chatter.In particular,by zero order Fourier approximation,system state variable expansion and discretization,the self-excited vibration system is transformed into a linear time-varying system with input constrains.combined with the invariant set theory,the optimal control input solved by the rolling optimization algorithm iteration makes the closed-loop control system converge;the numerical simulation show that the constructed model predictive control strategy is(progressive)stable.The sample working point is selected for experiment,and the obtained tool end displacement response curve shows different convergence,examining the validity of the model.