Study On The Active Control Of Hybrid Bearing Spindle Locus

Noncircular fine machining plays an important role in modern mechanical manufacturing. Addressing the locus control of an active hybrid bearing, an active lubricated sliding bearing and related spindle locus control techniques have been investigated theoretically and experimentally in this dissertation in order to provide a new method for noncircular machining.On the synthetically analysis of conventional and NC noncircular machining approaches and various servo feed devices, a novel idea which is expected to be used for noncircular machining is proposed for the first time. The method is that, by adjusting the oil pressure and fluid flow injected into the recesses of a hybrid sliding bearing using hydraulic servo systems, the pressure distribution on the bearing lands is altered at the same time and then the controllable oil forces are obtained. Thus the expected spindle locus is achieved and it will become possible for noncircular machining.The elementary theoretical research for the hybrid sliding bearing-rotor system is carried out based on a four-recess hybrid sliding bearing. The dynamic model of the bearing-rotor system is theoretically investigated and constructed. The Reynolds equation of oil pressure distribution and flow continuity equations for a rigid shaft under Kardan rotations are developed. The suitable hydraulic system is designed and constructed, and the relative boundary conditions for Reynolds equation are modified. Above research work provides the essential model for further researchs.The controllability of the hybrid sliding bearing system is theoretically investigated in order to guide the bearing design. An idea of controllability coefficients is proposed to evaluate the controllability of the hybrid bearing by means of local linearized model, and the influences of bearing parameters on the static and dynamic performance and controllability for a typical 4-recess hybrid bearing are studied. The results show that the bearing recess size, especially the axial size, has a significant influence on the controllability. The controllability increases with the increment of the recess size, due to the decrement of damping forces and the increment of hydrostatic effects. The concentric pressure ratio, journal speed parameter and restrictors have a little influence on the controllability coefficients but significant influence on the bearing stiffness and damping coefficients, and thus on the bearing system controllability.Combining the T-S dynamic fuzzy model and sliding mode control (SMC) technique, the adaptive fuzzy sliding mode control strategy for the hybrid bearing system is studied. The whole nonlinear model is approximated with multi local linear models, and the SMC can be constructed with linearizing method and lower feedback gain to overcome the problems for nonlinear dynamics and simultaneity to improve the uncertainties existed in practical system. A fuzzy logic system with online adaptive adjustment is utilized to approximate the discontinuous control signal and furthermore compensate for the system uncertainties, then the chattering phenomenon in classical SMC caused by discontinuous signal switching can be effectively alleviated. The numerical simulation for shaft locus control demonstrates the effectiveness of the proposed approach. The shaft locus tracking presents satisfied results and robustness without chattering phenomenon in despite of external disturbance and parameter variations. Meanwhile, the sliding mode control without equivalent control effort is studied and it is shown that the control effects descend little but apt to carry out.The discrete sliding mode control strategy for the bearing system is theoretically studied. The discrete reaching law is adopted to get the existing conditions of the quasi-sliding mode. An online estimation is used to predict the system uncertainties and compensate for the model error and slowly time-varying characteristics. Meanwhile an adaptive strategy is proposed to adjust the reaching law parameters and reduce the bound of the quasi-sliding mode. The simulation results show that the proposed method presents strong robustness to slowly time-varying external disturbance and parameter variations, and the shaft locus tracking also performs well.Finally, a test rig for active hybrid journal bearing is designed and manufactured for shaft locus tracking control experiments. A typical 4-recess hybrid bearing, along with suitable hydraulic servo system is designed and constructed. The sliding mode control strategy without equivalent control effort is adaopted and the comparative results of PID controller are given as well. The experimental results demonstrate the effectiveness of the sliding mode control in vibration control and shaft locus tracking. With low shaft rotating speed, the vibration response of the rotor declines effectively and a satisfied shaft locus tracking is obtained. Thus the feasibility of the proposed method is validated and meanwhile, the problems needed to be solved for improving shaft locus tracking performance are detected and analyzed.