Static And Dynamic Performance Analysis And Experimental Detection Of High Speed Motorized Spindles

High speed motorized spindles, one of the most important part among the key technologies of the high speed machining, are now used increasingly in a broad range of CNC machining centers and high-performance spindles. A high speed motorized spindle has multivariate, non-stationary and complex coupling characteristics as well as considerable complicated interactions between dynamic performance and electromagnetic conversion of the spindle. Therefore, to understand and control this relationship has always been the key part of the high speed motorized spindle investigation. However, it is difficult to conduct dynamic test with load since the spindle speed can go up to very high in operation conditions. The knowledge of the relations between spindles'dynamic performance and electromagnetic conversion are limited, as the lack of fundamental information on high speed motorized spindles and the foreign monopoly of advanced technology, which hinders the in-depth investigation and application of high speed motorized spindles in high speed machining industry. Thus, this project puts forward a set of relative complete dynamic performance test methods based on the electromagnetic characteristics of high speed electric spindles, and the following conclusions can be obtained by comparing experimental data with theoretical analysis:①Dynamic performance test of high speed motorized spindles includes testing electrical and mechanical properties parameters. A dynamometer and a three-phase high frequency electrical parameters instrument et al. auxiliary equipments are used to obtain mechanical and electrical parameters of high speed motorized spindles, such as input voltage, current, power factor, output torque, speed and efficiency, whilst the value of dynamic stiffness can be obtained by exerting a force and testing the force and the displacement in the force direction. Two methods of testing high speed motorized spindles'torque and dynamic stiffness, mechanical and electromagnetic testing method, are given in this paper. For the mechanical contact load means, when a dynamometer is used for obtaining torque, problems of dynamic balance among dynamometer, spindle and coupling necessitate to be addressed. For another, using a non-contact eddy current dynamometer, one need to ensure that load magnetic field is stable and electromagnetic heat of the dynamometer dissipates in time. When testing dynamic stiffness of high speed motorized spindles, if the mechanical contact load mode is selected, problems related with contact wear including failure load, wear debris and friction heat dissipation need to be considered; if the electromagnetic loading mode is employed, not only the stability of the magnetic field but also the magnetic field interference with the displacement sensor needs to be considered to avoid failure data collection.②As the output mechanical energy depends on the electromechanical energy conversion in magnetic field of high speed motorized spindles, the magnetic field control is the emphasis of the study of dynamic performance of high speed motorized spindle, involving establishing mathematical model and selecting the control method for high speed motorized spindles. According to high speed motorized spindles'characteristics, two models are put forward in this paper: a steady-state mathematic model based on effective value of electromagnetic parameters and a process-control-based dynamic mathematic model. With the aim of controlling the air gap magnetic field, when the load changes, the steady-state model control the stator current to maintain the excitation current approximate stable to make sure the relationship between the rotor current and the load is linear. The control method with the steady-state model is very simple and the control accuracy is not high, and it is subjected to the U/f control mode. The process-control-based dynamic mathematic model focuses on controlling the rotor flux and the stator flux, corresponding with vector control mode and direct torque control mode, respectively. In this paper, analysis and experiment of vector control is conducted. The theory of speed sensor-less vector control and the dynamic performance of high speed motorized spindle under this condition are introduced, and the strategies used for maintaining the magnetic flux constant and resisting the external interference when the spindle load changes are described as well as experimental verification is performed.③To ensure the flux is stable when high speed motorized spindles are operated at low frequencies, the input voltage with U/f control should be compensated according to the level of back electromotive force of the stator windings of high speed motorized spindles in rated condition. However, under the vector control mode, the control accuracy of exciting current and torque current depends on the decoupling effects of coupling voltages in the dynamic mathematical model of high-speed motorized spindles. Therefore, effective voltage compensating methods at low frequencies with U/f control are discussed in detail, and validated by experiments. Decoupling means and effect of cross coupling voltages under vector control are compared, and anti-disturbance ability and dynamic speed tracking accuracy of high speed motorized spindles under vector control are verified experimentally.④How the harmonic magnetomotive force of harmonic magnetic field superimposes on the spindle flux, the way in which it affects the spindle electromagnetic torque and output speed, thereby exerting severe influences on the spindle static and dynamic performance, is elaborated. The impacts of different harmonics on spindles vary: the lower the harmonic orders, the more serious the impacts; the lower the frequencies of high speed motorized spindles, the higher the harmonics necessitate to be suppressed. As harmonic interference limits the scope of the actual rotational speed of high speed motorized spindles, the spindle actual speed with load cannot be too low.⑤The principles of electromagnetic heat and friction heat of high speed motorized spindles are analyzed on the basis of electrical machines and kinematics, and the heat transfer coefficient and the thermal resistance of the spindle each part are determined according to heat transfer theory. An integrated dynamic thermal model of high speed motorized spindles is established. The experimental results show that the spindle temperature increases with the spindle speed increases, while there is an optimum range for air pressure and lubricant volume where they exert the lest impact on the spindle temperature rise.In conclusion, some significant achievements in both theoretical and experimental terms can be obtained, including: the methods how to test dynamic performance of high speed motorized spindles are illustrated, the static and dynamic mathematic models are established, the relationship between the control method and the mathematic model is revealed, the decoupling effect of the cross-coupling voltages and its effect on spindles'dynamic performance are described, an integrated dynamic thermal model of high speed motorized spindles is developed and the factors related to the temperature rise of spindles are also determined. To investigate how the structural parameter design and electromagnetic parameters of high speed motorized spindles exert effects on spindles'dynamic performance, systematic analysis and experimental researches are performed, and some useful conclusions and experimental datum are obtained. These investigations constitute the basis for further studies of high speed motorized spindles, and thus they have academic significance and social and economic benefits to a large extent.