无摩擦气缸及高精度气动负载系统研究

发布时间：2018-06-07 08:58

本文选题：气体润滑 + 静压气体轴承　；参考：《浙江大学》2016年博士论文

【摘要】：气缸是气动系统中最常用的执行元件,在生产制造领域得到了最为广泛应用。传统气缸在气动伺服控制场合下面临着新的挑战,气体介质的可压缩性使得对气缸的精确控制更加困难,摩擦力的存在使得气缸在低速运行时性能下降。由于气体介质不具备自润滑特性,摩擦力给气动控制系统带来了很大的麻烦。为了提高伺服控制效果,研究人员除了在控制策略、控制元件等方面展开研究外,还不得不对摩擦力展开细致深入的研究。摩擦力除了给气动伺服控制增加困难外,还给气缸本身带来了一些问题,比如发热、噪声、振动、粉尘、影响寿命等,给气动系统带来安全隐患。因此,除了致力于研究影响摩擦力的因素、建立更准确的数学模型之外,有效降低气缸的摩擦力无疑会带来更为直接的好处。如何减小气缸的摩擦力,开发出新型低摩擦气缸乃至无摩擦气缸已经成为气缸发展的一个新方向。本文提出了一种基于静压气体轴承的气浮式无摩擦气缸,采用静压气体轴承的原理设计气缸的活塞,在活塞两侧的端盖上对称布置了单向阀,使得轴承内腔始终与气缸高压腔一侧连通,解决了气浮轴承的供气问题。同时,这种带有单向阀的轴承结构还能在气缸换向过程中起到保压的作用,使气浮轴承工作更稳定。在建立了气浮轴承数学模型的基础上,提出了一种基于Matlab的气膜压力分布的数值求解方法,利用此方法研究了轴承的气浮特性,并结合电容测微原理对轴承的耗气量模型进行了研究,以Matlab/Simulink仿真和试验相结合的方法对气缸换向特性进行了研究。设计了一套以气浮式无摩擦气缸为执行机构的高精度气动负载系统,采用带有稳态输出预测的模糊PID控制器实现了对系统的高精度恒压控制,稳态压力波动小于50Pa,活塞运动达到1 000mm/s时系统的稳态压力波动小于150Pa,达到较高的精度。建立以高精度气动负载系统为基础的常规气缸负载性能测试系统,解决了当前国标难以具体实施的问题。文章最后利用高精度气动负载系统对常规气缸的摩擦力测试方法做了一些新的探索,利用本文提出的方法能够方便快速的测试出气缸匀速运动时的摩擦力。本文共有七章,现将各章节的主要内容概括如下:第一章,详细介绍了无摩擦气缸的研究现状、气体润滑相关技术的研究进展以及相关气动技术的发展状况,指出基于静压气体轴承技术的无摩擦气缸仍是未来无摩擦气缸的发展方向,简述了气动伺服控制技术的研究现状。最后概括了本课题的研究意义、研究难点以及主要研究内容。第二章,详细介绍了气浮式无摩擦气缸的机械结构、工作原理及技术难点。分析了气浮轴承的工作特性,提出了一种浮动连接机构用于解决活塞与活塞杆存在径向偏差或角度偏差而可能引起的卡死问题。建立气浮轴承气膜压力分布的数学模型,并对求解该模型的不同方法进行了分析,指出传统基于一维流简化的计算法不够准确以及基于Fluent的有限元仿真方法不适合于研究多结构参数对轴承气浮特性的影响。第三章,提出了一种基于Matlab的有限元数值求解方法,详细介绍了该方法所需的公式推导、气膜边界及边界条件的初始化、循环更新边界条件的流程、节流孔出口压力的迭代求解过程、轴承耗气量及承载力的计算方法等过程。得到气膜压力分布数据,并研究了均压腔及均压带对轴承径向承载力和耗气量的影响,指出了均压腔对提高气浮轴承的性能具有重要作用;并利用Fluent对气浮轴承进行了仿真,分析了气体在节流孔及均压腔中的流动特性,证实了均压腔内部压力相等这一假设的有效性。第四章,提出了利用电容测微原理对活塞泄漏模型进行研究的新方法。活塞外圆周面与气缸筒内壁构成了偏心圆柱电容器,将微小位置的变化转化为电容器电容的变化可以把对位置的测量转化为对电容的测量,利用电容值来衡量活塞的偏心率避免了对运动中的活塞偏心进行直接测量。利用该方法了建立基于离线数据的活塞耗气量模型,并提出了判断轴承是否正常工作的指标。研究了无摩擦气缸的换向特性,仿真和实验都表明,这种带有单向阀的活塞结构在气缸换向过程中具有保压的作用;指出了换向时间是影响换向过程中活塞内腔压力的主要因素,活塞处于气缸中位时是气缸的最佳换向时机。第五章,以气浮无摩擦气缸为基础设计了气浮式高精度气动负载系统,详细介绍了系统的结构、工作原理、控制系统的软/硬件结构。利用可变容积的压力动态模型、气浮式无摩擦气缸的泄漏模型以及比例方向阀的流量模型建立系统的数学模型。设计带了稳态输出预测的模糊PID控制算法,并通过实验对系统的稳态和动态特性展开了研究。实验结果显示,系统的稳态压力波动小于50Pa,在气缸活塞以1000mm/s的速度快速往复运动过程中仍能保证150Pa以内的压力波动,活塞停止运动后系统能够快速的回复到较高的控制精度。第六章,以高精度气动负载系统为基础构建了符合标准要求的常规气缸负载性能测试平台,根据标准对气缸负载性能和测试流程的规定对气缸的负载性能进行了测试。结果表明,标准指定的基于出口节流调速的气缸负载性能测试系统不能有效的控制被测气缸的速度,测试过程中有较大的冲击,不能准确的反映气缸在负载下真实的运动状态,并提出了采用进口节流调速的方式控制被测气缸的运动速度的改进方案。根据测试过程中被测气缸的运动速度和两腔压力变化曲线分析了在轴向负载作用气缸的运动特性,并研究了不同负载对气缸运动稳定性的影响,结果显示气缸的无爬行最低运行速度随着作用于被测气缸的轴向负载的增大而减少。以高精度气动负载系统为基础构建了一套常规气缸的摩擦力测试系统,通过被测气缸左右两腔的压力及预加负载计算出气缸的运动过程中的动摩擦力。实验表明,这种方法能够方便、快捷的获取气缸的摩擦力,为气缸摩擦力的测试提供了新思路。第七章,对本论文的主要工作、研究结论和创新点进行了总结,并对未来的研究工作进行了展望。
[Abstract]:Cylinder is the most commonly used actuator in pneumatic system, which has been widely used in the production and manufacturing field. The traditional cylinder faces new challenges in pneumatic servo control. The compressibility of the gas medium makes the precise control of the cylinder more difficult, and the friction force keeps the cylinder performance down at low speed. The friction force has brought great trouble to the pneumatic control system. In order to improve the effect of the servo control, the researchers have to study the friction force in detail in addition to the control strategy and the control element. The friction force is difficult to increase the pneumatic servo control. It also brings some problems to the cylinder itself, such as heating, noise, vibration, dust, and affecting the life of the pneumatic system. Therefore, in addition to the research on the factors affecting the friction force and the establishment of a more accurate mathematical model, the effective reduction of the friction force of the cylinder will undoubtedly bring a more direct benefit. The development of the new low friction cylinder and even the frictionless cylinder has become a new direction for the development of the cylinder. In this paper, a air floating type air cylinder based on the static pressure gas bearing is proposed. The piston of the cylinder is designed by the principle of static pressure gas bearing. The unidirectional valve is arranged symmetrically on the end cover of the two sides of the piston to make the bearing of the bearing. The inner cavity is always connected to the side of the high pressure chamber of the cylinder to solve the gas supply problem of the air bearing. At the same time, the bearing structure with a one-way valve can also play the role of pressure protection in the process of cylinder reversing, and make the air bearing work more stable. On the basis of establishing the mathematical model of the air floating bearing, a kind of gas film pressure based on Matlab is proposed. The method of numerical solution of distribution is used to study the air floating characteristics of bearing. The air consumption model of bearing is studied with the principle of capacitance micrometer. The change of cylinder reversing characteristics is studied by combining Matlab/Simulink simulation and test. A set of high precision with air floating cylinder without friction cylinder is designed. The system has high precision constant pressure control with a fuzzy PID controller with steady-state output prediction. The steady pressure fluctuation of the steady state pressure is less than 50Pa. The steady state pressure fluctuation of the system is less than 150Pa when the piston movement reaches 1 000mm/s, and the high precision is achieved. The conventional cylinder negative is based on the high precision pneumatic load system. The performance testing system has solved the problem that the current national standard is difficult to implement. At the end of this paper, a high precision pneumatic load system is used to make some new exploration on the friction testing method of the conventional cylinder. The method proposed in this paper can easily and quickly test the friction force when the cylinder is moving at uniform speed. In this paper, there are seven chapters. The main contents of each chapter are summarized as follows: in the first chapter, the research status of the frictionless cylinder, the research progress of the related technology of gas lubrication and the development of the related pneumatic technology are introduced in detail. It is pointed out that the frictionless cylinder based on the static pressure gas bearing technology is still the development direction of the frictionless cylinder in the future, and the pneumatic servo control technique is briefly described. In the second chapter, the mechanical structure, the working principle and the technical difficulties of the air floating type frictionless cylinder are introduced in detail. The working characteristics of the air floating bearing are analyzed, and a floating connection mechanism is put forward to solve the existence of the piston and the piston rod. The mathematical model of gas film pressure distribution of air bearing is established and the different methods for solving this model are established. It is pointed out that the traditional method based on one dimensional flow simplification is not accurate and the finite element imitation method based on Fluent is not suitable for the study of the multi structure parameter pair axis. In the third chapter, a finite element numerical solution method based on Matlab is proposed. The formula derivation, the initialization of the boundary and boundary conditions of the gas film, the flow of the cyclic updating boundary conditions, the iterative solution process of the outlet pressure of the throttle outlet, the calculation method of the bearing capacity and bearing capacity of the bearing are introduced in detail. The influence of the pressure distribution on the radial bearing capacity and gas consumption of the bearing is studied. It is pointed out that the pressure sharing chamber plays an important role in improving the performance of the bearing, and the air bearing is simulated with Fluent, and the flow characteristics of the gas body in the throttle hole and the pressure mean cavity are analyzed. The validity of the assumption that the internal pressure of the pressure equalizer is equal. In the fourth chapter, a new method is put forward to study the piston leakage model by using the principle of capacitance micrometer. The outer circumference of the piston and the inner wall of the cylinder form a eccentric cylindrical capacitor. The change of the change of the tiny position to the capacitor of the capacitor can turn the measurement of the position to the position. To measure the capacitance, the eccentricity of the piston is measured by using the capacitance value to avoid the direct measurement of the piston eccentricity in the motion. This method is used to establish the piston gas consumption model based on the off-line data, and the index to determine the normal work of the bearing is proposed. The change characteristics of the frictionless cylinder are studied, the simulation and the experiment are studied. It shows that the piston structure with a one-way valve has the function of holding pressure in the process of cylinder reversing. It is pointed out that the changing direction is the main factor affecting the internal pressure of the piston cavity during the reversing process. When the piston is in the middle of the cylinder, it is the best change time of the cylinder. In the fifth chapter, the air floating high precision gas is designed on the basis of the air floating cylinder without friction. The structure of the system, the working principle, the soft / hardware structure of the control system are introduced in detail, and the mathematical model of the system is established by using the variable volume pressure dynamic model, the leakage model of the air floatation type frictionless cylinder and the flow model of the proportional directional valve. The fuzzy PID control algorithm with the steady-state output prediction is designed and passed. The experimental results show the steady state and dynamic characteristics of the system. The experimental results show that the steady state pressure fluctuation of the system is less than 50Pa, and the pressure fluctuation within 150Pa can still be guaranteed in the process of fast reciprocating movement of cylinder piston at the speed of 1000mm/s, and the system can quickly recover to a higher control precision after the piston stops moving. Sixth chapters A conventional cylinder load performance testing platform is built on the basis of high precision pneumatic load system, and the load performance of cylinder is tested according to the standard cylinder load performance and testing process. The results show that the standard specified cylinder load performance testing system based on the exit throttle speed regulation can not be effective. To control the velocity of the cylinder, there is a great impact in the test process. It can not accurately reflect the real motion state of the cylinder under the load, and puts forward an improved scheme to control the velocity of the cylinder by the way of inlet throttle speed regulation. The motion characteristics of the cylinder in the axial load are analyzed, and the effect of different loads on the cylinder motion stability is studied. The results show that the minimum running speed of the cylinder is reduced with the increase of the axial load acting on the cylinder. Based on the high precision pneumatic load system, a set of friction force measurement for the conventional cylinder is built. The test system, through the pressure of the two cavities around the cylinder and the load preloaded, calculates the dynamic friction force in the movement of the cylinder. The experiment shows that this method can easily and quickly obtain the friction force of the cylinder, and provides a new idea for the test of cylinder friction force. Seventh chapters, the main work of this paper, the research conclusions and the innovation points are carried out. Finally, the future research work is prospected.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH138.51

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