Research On Design Method For A High-Speed Grinding Motorized Spindle System Based On Mechanical-Electric Coupling Dynamics

Equipment & Manufacturing are the major industry of national economy.Machine tool industry is the base of Equipment & Manufacturing, and NationalDefense. The high-speed grinder, advanced machine tool is used to realizehigh-efficiency and precision machining, is also one of important marks to measurethe development of national industry level. However, high-speed motorized spindlesand high-frequency converting current drive units have been widely used inhigh-speed grinder field. The high-order harmonic mechanical-electric couplingvibration caused by high-frequency converting current, or the mechanical-electriccoupling induced by a bad match for parameters of a system will result in grindingbeing unstable, and bad surface quality. The design of a high-speed grindingmotorized spindle system has been performed by the static method. As for the method,there is inherent drawback. The independent design of key units which includeinverter, motorized spindle and grinding wheel is conducted. This leads to themechanical-electric coupling being difficult to be evaluated. Therefore, it is quiterequired to study the design method for a high-speed grinding motorized spindlesystem based on mechanical-electric coupling dynamics.On the basis of the traditional mechanical model for a grinding wheel rotor, themechanical-electric coupling dynamic model of a high-speed grinding motorizedspindle system is created, taking high-frequency converting current of power switchesinto further account. The created model consists of inverter, motorized spindle,grinding wheel, and grinding force. In terms of features of the created model, thenumerical method is proposed to make a study of the mechanical-electric couplingdynamical behavior of the system. Some typical transient processes of the system withtwo type supply including starting, speeding up, and grinding are simulated by usingthe created model. One is an ideal sinusoidal voltage source, the other is a voltagesource inverter controlled by SPWM (Sinusoidal Pulse Width Modulation).Experiment is also performed on a high-speed surface grinder. It is shown thathigh-order harmonics generated by high-frequency converting current are a newfactor which results in the mechanical-electric coupling vibration of the system.Based on revealing physical mechanism of the high-order harmonicmechanical-electric coupling vibration, match characteristics of the system amonginverter, motor, and grinding wheel are further researched. In order to explore an approach to suppressing the high-order harmonic mechanical-electric couplingvibration and improving match behavior of the system, the created model is adoptedto research the influences of inverter working parameters, electrical-magnetic designof motorized spindle motors, and grinding wheel parameters on pulsation torque andstator current spectrum. It is indicated that the high-order harmonicmechanical-electric coupling vibration can be effectively suppressed by optimizinginverter working parameters and electrical-magnetic design of motorized spindlemotors, and making a suitable choice of grinding wheels. The variation of pulsationtorque and power switch losses with the carrier wave frequency of an inverter isanalyzed to obtain the optimization region of inverter working parameters forsuppressing the high-order harmonic mechanical-electric coupling vibration. Theeffect of inverter working parameters on the stator current spectrum of motorizedspindle motors and surface quality of camshafts is experimentally studied. It istheoretically and experimentally proved that optimizing inverter working is feasibleto suppress the high-order harmonic mechanical-electric coupling vibration, andimprove surface quality.The harmonic analysis method for calculating iron losses of inverter-fed motorshas been widely applied in engineering field. However, the method is complicated,inefficient and restricted to manufacturers only providing limited performance curvesof silicon steel sheets with users. A traditional parameter estimation model is alsoused to predict iron loss characteristics of soft magnetic materials. However, there is abig error. In view of the above reasons, a modified parameter estimation model forpredicting iron loss characteristics of soft magnetic materials with SPWM voltagesource inverter supply is established. The modified model is to redefine and reassumethe coefficienct of eddy current losses in the traditional model. In order to validate themodified model, it is compared with the harmonic analysis method and the traditionalmodel. It is shown that compared to the traditional model, the modified model is morereliable and its error is smaller, but compared with the harmonic analysis method, themodified model is simpler, easier to compile codes, and its efficiency is higher. Theconventional iteration method of starting current is only suitable for calculatingstarting performance of a motor rated point, but is not suitable for calculating that ofhigh-frequency motorized spindle motors with low voltage and low frequency.Thereby, the method of dynamical simulation based on the createdmechanical-electric coupling model is proposed. It is indicated that a reasonableevaluation of starting performance for high-frequency motorized spindle motors is given by the proposed method. The significant heat generated by electrical-magneticlosses results in high-frequency motorized spindles being difficult to achievehigh-speed and high power. The model of electrical-magnetic design optimization forhigh-frequency motorized spindle motors is created.On the basis of the above research, the design and analysis soft of ahigh-frequency motorized spindle system with inverter supply is further developed.The function of the developed soft includes optimization of electrical-magnetic design,static performance analysis and dynamical behavior evaluation. A 10kW/18krpmmotorized spindle for internal cylindrical grinding, a 20kW/12krpm motorized spindlefor cylindrical grinding and a 120kW/10krpm high-speed and high-power motor aresuccessfully developed by adoping the developed soft. It is experimentally shown thatthe electrical-magnetic design of motorized spindles used for internal cylindricalgrinding and cylindrical grinding, respectively is exact. In addition, the design ofbearing span, dynamical balance of rotors and assembly are successful.The work offers important theories and effective approaches for suppression ofmechanical-electric coupling vibration, electrical-magnetic design and dynamicaldesign of a high-speed grinding motorized spindle system, and high-speed and highpower realization of motorized spindles.