| The magnetic suspension technique is a new hold technical method which with magnetic field force makes the object levitate without mechanical contact with other objects. With the advantages of zero friction, in gage, no pollution, low noise and long service life, it will be widely used in fields of traffic, navigation, machining, energy, chemical industry and high-tech areas. The magnetic suspension hold technical method is one of the best choices to realize the high precision, high-speed rotation and linear motion of the top grade NC machine tools. This paper mainly focuses on the study of the magnetic suspension hold technical method used in high-speed and high-precision kinematic mechanism of the top-grade NC machine tools, including the electric principal axis system (swivel bearing) held by magnetic suspension axile tree and the platform system (translational bearing) held by magnetic suspension guides.The paper made a comprehensive study of the current situation and developing trend of the magnetic suspension hold technical method at home and abroad as well as the operation significance, the importance and the feasibility of the study. On the basis of the equation of movement (mathematical model) of the magnetic suspension electrospindle and platform. By using the Ansys software, the author made an analog analysis of the magnetic field of the magnetic suspension milling electrospindle which was made under the project No.863. The purpose is to find out the orderliness of the magnetic field of thrust bearing and radial bearing, the reason of flux leakage, the changing rule of magnetic field and influencing factors, so as to optimize the structure of electromagnetic bearing and to choose the direction of the current. The paper made an analysis on the rule that the location rigidity coefficient and current rigidity coefficient of the electromagnetic thrust bearing and radial bearing will change in accordance with that of the deviant and the current of the magnetic suspension (thrust disc and rotor). A main control parameter base was also set up to provide data for the design of the control system of electromagnetic bearing and the realization of the intelligent magnetic bearing. The paper also made a study on exploiting the hardware system with a digital signal processor as the core to meet the hardware and sequential requirement of the control system. It will function in accumulating, controlling data and power outputting. The special control chip for magnetic bearing is being developed to cut cost, to increase the security and to realize the intelligent control. The paper also studied the method of making intelligent magnetic bearing and the key technology of designing and applying the magnetic bearing.As for the experiments, on the basis of the research results, the author has successfully developed the sensor transfer network, NC regulator, switch power amplifier and necessary machine, which forms 5-freedom-of-motion electric principal axis of magnetic suspension milling tool and a 6-freedom-of-motion platform of magnetic suspension (making analog feeding guides). The shaking state, accuracy of rotation and rigidity under different situations (eg: at different speed) were analyzed. Some questions and solutions in applying the magnetic suspension bearing into high-speed and high-accuracy machine tools were also put forth.Based on the above research, the technical criteria of the 5-freedom-of-motion electric principal axis of magnetic suspension milling tool and the 6-freedom-of-motion platform of magnetic suspension is quite advanced in China. The theoretic analysis has also been verified with correspondent experiments. What is worth mentioning is that the magnetic suspension platform is unique in China as the first platform model using 6-freedom-of-motion magnetic suspension bearing. The technical criteria also keep ahead. The 5-freedom-of-motion electric principal axis of magnetic suspension milling machine tool (22kw) is also unparalleled for its huge power though its rotate speed is only 27kr/min. These two models had been successfully displayed at the 6th World Industrial Fair of Shanghai during the Sept. 4 to Sept. 9 in 2004, which aroused public attention and received praise. The static suspension accuracy (amplitude of vibration) is less than 1μm, and the dynamic accuracy is less than 10μm. Its total bearing capacity reaches to 105.5kg, with the unit area bearing capacity larger than 0.3N/mm2, which has been verified by the 863 expert group on August 9, 2006. The development of the dedicated IC chip of magnetic suspension system has opened a new page of the study in this field. It will greatly improve the magnetic suspension technology as well as the intelligent process and serialization of the magnetic suspension bearing.
|
PDF Full Text Request