Abstract
The cost and power consumption of DC power amplifiers are much greater than that of AC power converters. Compared to a motorized spindle supported with DC magnetic bearings, a motorized spindle supported with AC magnetic bearings is inexpensive and more efficient. This paper studies a five-degrees-of-freedom (5-DOF) motorized spindle supported with AC hybrid magnetic bearings (HMBs). Most models of suspension forces, except a “switching model”, are quite accurate, but only in a particular operating area and not in regional coverage. If a “switching model” is applied to a 5-DOF motorized spindle, the real-time performance of the control system can be significantly decreased due to the large amount of data processing for both displacement and current. In order to solve this defect, experiments based on the “switching model” are performed, and the resulting data are analyzed. Using the data analysis results, a “full prediction model” based on the operating state is proposed to improve real-time performance and precision. Finally, comparative, verification and stiffness tests are conducted to verify the improvement of the proposed model. Results of the tests indicate that the rotor has excellent characteristics, such as good real-time performance, superior anti-interference performance with load and the accuracy of the model in full zone. The satisfactory experimental results demonstrate the effectiveness of the “full prediction model” applied to the control system under different operating stages. Therefore, the results of the experimental analysis and the proposed full prediction model can provide a control system of a 5-DOF motorized spindle with the most suitable mathematical models of the suspension force.
Highlights
Suspended high-speed motorized spindles display the advantages of being contact-free and wear-free; they exhibit low noise, high rotational speed, compact structures, high mechanical efficiency, low vibration, and high precision, which has aided the further development of high-speed machining processes
Fcn 1j is the classical nonlinear model of the radial suspension forces of the AC 2-DOF hybrid magnetic bearings (HMBs); x1 and y1 are positive displacements of the rotor in the x- and y-directions; φ1j is the radial resultant magnetic fluxes in the air-gap corresponding to each pole; Sr1 is the face area of the radial magnetic pole; δr1 is the length of the uniform air-gap without rotor eccentricity; Fm1 is the magnetomotive force provided to the outer circuit of the AC 2-DOF HMB; ij1 is the radial three-phase control current; j = A, B, C; Nr1 is the number of turns that the radial control coils
Magnetic bearings and the radial suspension subsystem of a bearing-free motor, a new modeling method based on the Maxwell tensor method for the radial suspension force of an AC magnetic bearing was presented in [13], and the AC 2-DOF HMB was modeled by this method
Summary
Suspended high-speed motorized spindles display the advantages of being contact-free and wear-free; they exhibit low noise, high rotational speed, compact structures, high mechanical efficiency, low vibration, and high precision, which has aided the further development of high-speed machining processes. Energies 2017, 10, 75 and mature classical control technologies [17] These two magnetic bearing models are highly reliable, not all model generations have been applied to the 5-DOF motorized spindle. As for the full area of the motorized spindle, the most comprehensive and adversely affect the real-time performance of the control system due to the large amount of data practical model is the “switching model”. If a model based a different operating state in [16], a “switching model” applied to a 5-DOF motorized spindle mayon adversely affect the real-time can be set in advance, the model efficient andof achieve better real-time performance in performance of the control systemwill duebetomore the large amount data processing for displacement and practice. The effectiveness of the prediction to the controltest system can be verified different operating stages.of the performance test experiments under different operating stages
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