Abstract
Milling stability not only reduces the surface quality of the workpiece but also seriously restricts the high-speed development of CNC machine tools. The electric spindle rotor system with the active magnetic bearing has a strong gyro coupling effect, and with the increasing rotor speed, it will become a major unfavorable factor for the stability of the system during high-speed milling. The strong gyro coupling effect makes the stability region narrow at the time of high-speed milling. So, a modal decoupling control method that can reduce the effects of the gyro effect on the magnetic levitation milling system under high-speed milling is proposed. The effects of the gyro coupling of the magnetic bearing rotor on the milling stability region before and after the decoupling control are studied, which show that the modal decoupling control technology can reduce the effects of the gyro effect on the magnetic levitation milling system.
Highlights
In the actual magnetic suspension electric spindle rotor system, the bandwidth of the power amplifier and the sensor is limited, which will lead to a time delay of the electromagnetic force, and the force produced by the magnetic bearing will put energy into the electric spindle rotor; the energy of the opposite precession mode will be put into the positive feedback and be accumulated, which will lead to a unstable milling system
Displacement sensor A Active magnetic bearing A Electric spindle rotor Active magnetic bearing B Displacement sensor B Workpiece ere is a cross-feedback control method based on the traditional PD controller, in which the cross-feedback can be divided into displacement crossover [7], velocity crossover, velocity and displacement crossover [8], and displacement crossover combined with electromagnetic force [9]. e advantage of cross-feedback, especially the speed cross-feedback method, is that the structure is simple and is easy to be implemented. e disadvantage is that there is still no effective cross-feedback parameter design method
When the traditional PD control is used, the characteristics of each mode are difficult to be independently adjusted because there is the strong coupling between the rotational mode and the translational mode of the magnetic electric spindle rotor. erefore, the control methods based on this have certain limitations
Summary
Received 6 July 2019; Revised September 2019; Accepted September 2019; Published May 2020. In order to reduce the gyro coupling effect of the highspeed magnetic suspension electric spindle rotor system on milling stability, it is necessary to suppress the positive precession mode and the opposite precession mode generated by the gyro coupling effect. In this regard, various solutions have been proposed, mainly including control methods based on modern control theory, such as sliding mode control [2], μ synthesis [3], gain-scheduled H∞ control [4], Cholesky decomposition reduction [5], and LQR control [6]. These control methods had played a role in suppressing the gyro effect, these algorithms are complex and computationally intensive and are difficult to implement in engineering due to hardware conditions
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