【作者】 姜培刚；

【导师】 陈建军；

【作者基本信息】 西安电子科技大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 弹性流体动力润滑(简称弹流润滑)为点、线接触机械零部件的主要润滑形式,其油膜厚度与形状是决定机械零部件润滑效率的主要因素。受各种因素的影响,机械零部件的弹流润滑油膜形状和厚度在工作期间通常是动态多变的。近年来,弹流润滑的实验研究,特别是动态条件下的油膜测量,已成为提高机械零部件润滑效率的研究热点。目前在非稳态条件和自旋条件下的弹流润滑实验中,尚存在测量装置的伺服控制手段简单和实际运动控制效果与实验设计存在较大差别等问题。为此,对现有变速变载等非稳态条件和自旋条件下的弹流润滑油膜测量装置的控制系统和控制算法进行改进,对于提高弹流油膜测量系统的测量精度,以及进一步探索苛刻条件下弹流润滑的基础实验研究和理论分析有较好的实际意义。现代数控技术的发展,为高精度弹流润滑油膜测量系统的研制提供了强有力的软硬件支持。在回顾弹流润滑研究现状的基础上,分析总结了目前国内外学者主要采用的弹流润滑实验研究方法。根据弹流润滑油膜测量系统对速度控制的特殊精度要求,结合现代数控技术提出了一种基于智能运动控制理论的弹流润滑实验伺服运动控制方法,对光干涉弹流油膜测量仪和光干涉自旋弹流油膜测量仪的运动控制系统进行改进,以探索非稳态和自旋条件下弹流润滑的真实工作状况,并在预定运动方式下开展弹流油膜厚度和形状随速度、载荷和旋滑比等因素变化的实验研究。在光干涉弹流油膜测量系统中,速度伺服系统的控制参数和结构参数是影响速度伺服系统性能的主要因素,且具有时变性和不确定性,采用单一的控制策略很难达到提高速度伺服系统的动态性能的目的。在综合自适应控制、模糊控制以及常规PID控制算法优点的基础上,按照模块化设计原则设计出自适应模糊PID(Self-adaptive Fuzzy PID, SAF-PID)智能双模伺服控制算法,对在不同工作状态下的模糊控制比例因子和规则因子利用Matlab仿真软件进行优化选择调整,使得整个控制器能够根据系统在不同的响应阶段和性能指标,自动调整控制参数、自动切换控制算法,以适应速度伺服系统在不同的工作状态下的动态性能要求。为验证本研究设计的SAF-PID智能双模速度伺服控制算法的有效性,首先利用Matlab仿真软件对速度伺服系统在实际工况下的性能进行模拟分析:通过仿真智能双模控制器的阶跃响应曲线和误差响应曲线验证整个控制算法的快速性、稳定性和准确性;通过人为在不同时间段加若干不同程度的干扰信号模拟控制结构参数和负载质量等主要参数的时变性和不确定性,以此验证整个控制器在不同响应阶段的控制参数自动调整、控制算法切换、系统的跟随精度和速度伺服系统的抗干扰能力。将此智能速度伺服控制算法用于控制纯滑动条件下的弹流润滑启动过程,以期与经典的实验结果和数值分析结果相比较,初步验证算法的有效性。将SAF-PID智能双模控制算法用于光干涉弹流油膜测量仪,在周期间歇卷吸条件下开展了弹流润滑的实验研究,发现了以下问题:周期性的间歇卷吸运动导致弹流接触区存在明显的封油现象;启动过程的速度干扰效应可产生局部增厚油膜,该局部油膜以卷吸速度通过赫兹接触区;在动态间歇卷吸条件下界面滑移仍可产生入口凹陷;入口凹陷的出现与速度和一个周期的高速段的持续时间有关;间歇卷吸运动中滑移产生的凹陷不随表面移动。在光干涉自旋弹流油膜测量仪上应用SAF-PID智能速度伺服控制算法,研究了自旋对油膜形成过程的影响并得出以下结论:通过实验验证了在传统滚动/滑动弹流润滑研究时钢球-玻璃盘接触条件下的自旋运动可以通过调节球盘接触中心与旋转中心间的偏心距的大小来进行抑制,并且旋滑比的大小亦由偏心距来控制;当旋滑比增大时,传统弹流润滑研究所观测到的经典马蹄型油膜形状发生了严重扭曲,并且旋滑比越大,油膜厚度越薄;油膜厚度对卷吸速度的依赖关系在很大程度上受旋滑比的影响,较低侧的油膜厚度具有较大的速度指数,并且随着旋滑比的减小,两侧的速度指数趋于相近,高速时,垂直于卷吸速度方向两侧的油膜厚度的差别也越大;实验结果表明,在弹流润滑接触条件下载荷的增加会加重旋滑的效果,导致两侧的油膜厚度差别加大,油膜厚度减小,马蹄型外观更加扭曲。更多还原

【Abstract】 Elastohydrodynamic lubrication (EHL) is the main lubricant style for those parts having point or line contacts. In this case, film thickness and shape are the major factors affecting the lubricating efficiency of machinery components. Influenced by some factors, the film shape and thickness in EHL for many machinery components are dynamic changed. In recent years, researches on elastohydrodynamic lubricated contacts under dynamic conditions have been focused. For most optical EHL test rigs, the current used servo control methods are so simple that the error between the reference and the actual motion is large to some extent. Therefore, the motion control system, as well as the control algorithm, is improved for the subsistent test rigs used under unsteady or spinning conditions. As a result, the measuring accuracy of film thickness and shape could be improved, and the following research on EHL problems under more rigor conditions could be carried on in future.The advancement of modern numerical control technique, fully support the development of high-accuracy EHL test rig in both hardware and software. Based on the review of EHL researches, many currently used EHL experimental methods are analyzed. According to the special accuracy of speed control in EHL experiment, a numerical controlled speed servo method is proposed, which is based on the intelligent motion control theory. Both multi-beam optical interference EHL test rigs without or with spin are redesigned using this new scheme, in order to reveal the real nature of EHL phenomena under unsteady or spinning conditions, and to perform the correlative experimental research on the film thickness and shape by changing speed, load and spinning-sliding ratio.In the film thickness measurement system, parameters of control and structure of the speed servo system are the main factors that affect the performance of the system, and are of time variation and uncertainty. As a result, a simple control method can not improve the dynamic performance of speed servo system. Integrated the advantages of self-adaptive control, fuzzy control and PID control, an intelligent dual module NC servo controller, called self-adaptive fuzzy PID (SAF-PID) controller is designed according to the modular design principle. Both fuzzy proportion and rule gene can be adjusted automatically by Matlab software under different working state. So the SAF-PID controller can change parameters and switch control methods automatically for the sake of adapting the system dynamic performances in the different work status.To validate the promoted SAF-PID controller, Matlab is used to simulate the speed servo control firstly. The step response and error response of SAF-PID controller can indicate the performance of rapid, steady and accuracy. Some disturbances are imported randomly to simulate the time variation and uncertainty of main parameters, such as control and load. So the interference killing features of speed servo control can be validated, such as the auto adjustment of control parameters, auto switch of control arithmetic, and the tracking precision of servo system. Then the proposed SAF-PID controller is used to control the start up process of EHL in pure sliding condition, in order to compare with the traditional results of experiment and numerical analysis, and to test this smart controller preliminarily.Experimental observation of EHL films under cyclic intermittent entrainment is carried out to validate the promoted SAF-PID controller, and three kinds of local film dimples have been identified. It is discovered that intermittent stops of the bounding surfaces generate clear lubricant entrapment and then film dimple due to squeeze effect, and pure rolling produced larger entrapment than that by pure sliding. Another local film dimple produced in the start-up process has also been demonstrated, which is attributed to the velocity perturbation. The peak velocity in the velocity oscillation results in an instantaneous larger lubricant entrainment and therefore local film dimple. The resultant crescent-shaped fringe moves through the Hertzian contact region at the entrainment speed. When pure disc sliding is employed, a cyclic inlet dimple appears due to boundary slippage effect. The results showed that the generation of the inlet dimple has strong dependence on the speeds and the time interval between two stops. Unlike those two dimples, the inlet dimple by the boundary slippage does not move through the contact region with the moving surface. In addition, the experiments displayed that the velocity perturbation effect from a sudden start-up was largely depressed under conditions of pure disc sliding. The observed phenomena can be explained by the squeeze effect, the entrainment effect and the wall slippage.Applied the SAF-PID intelligent speed servo control technology, the film thickness of a sliding EHL contact with spin has been measured by optical interference, and the effects of the spin on the film building up are studied. The main results are summarized as follows. It is demonstrated that in a ball-on-disc configuration spin motion can be superimposed on the conventional rolling/sliding EHL just by an offset of the contact center with respect to the disc rotation center, and the spin level is controlled by the offset. The EHL film shape is obviously skewed when spin motion is increased, and the symmetry of the conventional side lobes gets lost. Obvious film thickness reduction can be observed when spin level is high. The film thickness dependences on entrainment speeds are significantly influenced by the spin ratio Ssp. The film thickness at the low side lobe has the largest speed index. With decreasing spin motion, the speed indices of the two side lobes gets close. At high speeds, the film thickness difference of the two side lobes is large. In the present experiments, increasing loads can induce more effective spin effect within the EHL contact, and the difference between the two side lobe film thicknesses gets large and the horse-shoe film shape is more distorted. The spin raised by load decreases the overall film thickness.更多还原