Research On Dynamic Characteristics Of Motorized Spindle Assembly On NC Machine Tool

Motorized spindle has a compact structure, small vibration, low noise, high dynamic accuracy and good stability, and it is widely used in NC machine tools, machining centers and other manufacturing equipment. The application of motorized spindle is capable of boosting machining efficiency, reducing cutting force and improving the surface roughness of workpiece. Hence, the analysis and research on dynamic characteristics of motorized spindle assembly is very necessary. The calculation of critical speeds and unbalanced response, the effect of radial electromagnetic force and variation of some parameters on dynamic characteristics of motorized spindle are mainly researched.This dissertation introduces the basic theory and modeling method for dynamic characteristics analysis with rotor dynamic. The motorized spindle model is established by lumped mass method. Critical speeds are respectively calculated by Riccati transfer matrix method without damping and by transfer matrix method adding time factor with damping considering the factor of rolling bearing damping. The problems of numeric overflow and missing roots are solved and the computational accuracy is enhanced by the method of calculation. The calculation procedures are programmed by VB and Matlab software.The special structure of motorized spindle is the spindle built in motor. Radial unbalanced magnetic pull (UMP) is produced in rotor due to eccentricity when the motor is running. UMP causes the falling of critical speeds because it is equivalent to increase the quality of the rotor shaft section. The mechanism of production and main features of UMP are investigated, the result of UMP is obtained by extracting radial magnetic flux density in air gap with finite element method (FEM), and critical speeds are also calculated in the influence of UMP.Different influences of motorized spindle among axial preload of rolling bearing, UMP, and grinding wheel subassembly on dynamic characteristics are studied. The suggestion of improving dynamic characteristics of motorized spindle is presented, which provides reference for design and improvement of motorized spindle.