| Magnetic levitation bearings are becoming more and more widely used in spindles because of their special advantages of no mechanical contact and no friction.Because they are not subjected to the same preload as ordinary ball bearings during cutting,they increase the speed significantly and have higher cutting accuracy.However,while the magnetic levitation bearing has made a breakthrough in speed,it is inferior to the ball bearing in some aspects.In machine cutting,the magnetic levitation bearing support stiffness is far inferior to the ball bearing,and when the cutting force is too large,it may even fall off and break the solenoid due to loss of control.Although the speed breakthrough is great,but not suitable for cutting.For the above problems,the main research of this topic is:Firstly,considering the respective limitation problems of ball bearing supported electric spindle and magnetic levitation bearing supported electric spindle,a new support structure of magnetic/ball bearing double supported electric spindle is proposed.A 5-degree-of-freedom magnetic/ball dual-supported electric spindle experimental system was designed and built in-house.Using both experimental analysis and Maxwell simulation,the characteristics of the ball bearing and magnetic levitation bearing were analyzed in both radial and axial directions,the radial stiffness and axial stiffness of the ball bearing and magnetic levitation bearing were determined by comparing the magnitude of the theoretical and experimental values.Subsequently,the analysis of the first-order modal and second-order modal of the spindle rotor was completed to determine the maximum safe rotor speed.Next,the control problem of the magnet/ball dual-supported electric spindle is addressed.By analyzing the characteristics of the ball bearing,magnetic levitation bearing and rotor in the new support structure,the kinematic modeling and decoupling of the 5-degree-of-freedom magnetic/ball dual-supported electric spindle is carried out based on the traditional kinematic modeling method of the magnetic levitation bearing with 5 degrees of freedom.And the hybrid sensitivity H_∞controller is designed to address the decoupling error generated in the model building and the model inaccuracy caused by the low order instead of the high order.Using MATLAB simulations,it is verified that the designed controller can make the rotor of the magnetic/ball double-supported electric spindle track the given signal quickly,complete the offset as needed,and have good anti-interference capability when working at the set position.Finally,to further verify the rationality and advantages of this new support structure.After the introduction of the device principle and configuration of the electrical control part,an experimental platform with TMS320F28335 as the controller was built.By comparing the magnetic/ball double-supported electric spindle experimental rig with the ball bearing electric spindle experimental rig at different rotational speeds,it is proved that the magnetic/ball double-supported electric spindle controlled by the controller can effectively suppress the rotor vibration problem and make the rotor run more smoothly,and the amplitude is reduced by about 30%at different rotational speeds.It is further proved that this new structure is more suitable for high speed work while reducing the preload force on the ball bearing and prolonging the life of the ball bearing compared with the traditional ball bearing support;compared with the traditional magnetic levitation bearing support,the ball bearing provides stiffness guarantee for the magnetic levitation bearing while making the center of rotation of the magnetic levitation bearing much lower,and the air gap is reduced to 0.15mm in the experiment,so that the electromagnetic force can be more effectively utilized. |
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