【作者】 刘学忠；

【导师】 路长厚；

【作者基本信息】 山东大学 ， 机械电子工程， 2008， 博士

【摘要】 非圆异型截面零件的加工在机械制造行业中占据着一个重要的地位。本文以动静压混合滑动轴承-转子系统的主轴运动轨迹控制为出发点,研究了主动节流混合滑动轴承系统及其转子运动轨迹的控制技术,以期为非圆异型机械零件的加工提供一条新途径,并相应地进行了有关的理论模型分析、仿真和实验研究。综合分析了传统的非圆零件加工和数控加工方法及各种微进给伺服机构装置,首次提出了通过控制混合滑动轴承-转子系统运动轨迹的方法,来实现主轴的非圆定轨迹回转运动的新思路,以期为非圆异型机械零件加工开辟新途径。其实现思路是通过主动伺服节流控制技术,实时调节流入动静压混合轴承油腔的流体流量和压力,进而影响轴承封油面上的油膜压力分布,得到可控的油膜合力,以达到控制主轴的运动状态和轨迹的目的。进行了动静压混合轴承系统的基本理论研究。基于典型的4油腔动静压混合轴承-主轴系统,研究建立了主动滑动轴承系统的理论模型,建立了主轴的运动模型和动力学模型,导出了主轴倾转情形下轴承油膜压力分布的Revnolds方程和小孔节流轴承各油腔的流量平衡方程。设计建立了一种适用的液压伺服控制结构,并相应地给出了雷诺方程边界条件的修正方式。为全文的研究工作提供了基本模型。研究了动静压混合轴承的可控性,为轴承系统设计提供理论依据。基于轴承的局部线性化模型,提出了一种可控性系数的概念来衡量混合轴承的可控性能,并分析研究了典型的4油腔混合轴承的参数对其静动态特性和可控性的影响。研究表明,轴承油腔面积对轴承的可控性有较为明显的影响,其中油腔轴向宽度的影响尤为显著。随着油腔尺寸的增加,轴承的静压效应增强,轴承的可控性得到明显提高。轴承的同心节流比以及速度参数、节流器类型对轴承的可控性系数影响不大,但对油膜的刚度、阻尼系数有较大影响,同样会影响到轴承的可控性。研究了混合轴承系统基于模糊逻辑的自适应变结构滑模控制方法。基于T-S动态模糊模型的系统分析方法,采用多个局部线性模型来近似逼近系统的整体非线性模型,得以用线性化的分析方法和较小的控制增益来构建滑模变结构控制(SMC),克服一般非线性动力学分析和求解的困难,有效改善模型的不确定性。进一步又采用模糊逻辑系统方法来逼近SMC中不连续的控制信号,且在线自适应调整模糊集合的参数,以补偿系统的不确定界,改善传统SMC中因控制切换所引起的抖振。通过对主动混合轴承-转子轨迹控制的仿真计算研究,验证了方法的有效性,在系统外部扰动和参数摄动情形下,主轴的轨迹跟踪均表现出了比较满意的效果,具有较强的鲁棒性,而且没有出现抖振现象。同时,对于无等效控制项方式的滑模控制也进行了仿真研究,其应用效果并无明显下降,而且更易于实现。研究了混合轴承-转子系统轨迹跟踪的离散变结构滑模控制方法。基于系统的线性化模型,采用离散趋近律的滑模到达条件,以一种在线估计的方法来预测系统的不确定性,并将其引入滑模控制算法中,同时给出一种自适应策略,在线调整离散趋近律参数,从而可以抵消掉系统的慢时变不确定量,以较低的控制增益获得系统的鲁棒性,有效降低准滑动模态区带的宽度。仿真结果表明,本方法对慢时变的系统参数摄动和外部扰动具有较强的鲁棒性,主轴的轨迹跟踪具有比较满意的效果。设计研制了混合轴承系统实验平台,进行了轴承-转子运动轨迹控制的实验研究。设计制造了一种典型的4油腔混合轴承,研制了适用的液压伺服控制系统。采用了无等效控制项的连续滑模控制方法,并对比研究了PID控制器的效果。实验结果表明,滑模控制方法效果优于PID方法。在低速旋转情形下,主轴的振动响应得到有效降低,得到了比较满意的轴心轨迹跟踪结果,验证了本文所提非圆轨迹控制方法的可行性,并发现和分析了进一步提高控制效果必须解决的关键问题。更多还原

【Abstract】 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.更多还原