【作者】 孔祥臻；

【导师】 王勇；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 气动系统以其结构简单、无污染、性价比高、维修方便以及抗干扰能力强等优点，被广泛应用于化工、医药、纺织、微电子、生物工程等工业自动化领域中。气动比例技术的出现，使气动系统从逻辑控制领域扩展到比例／伺服控制领域。但是由于气动系统固有的非线性、刚度小、阻尼比小以及固有频率低等缺点，使得气动比例系统定位技术进展缓慢，其控制精度和工作性能难以达到理想的效果，从而限制了气动系统在工业领域中的推广及应用。本文主要以提高气动比例系统的控制精度为目标，通过分析其摩擦力及动态特性，对系统的摩擦非线性补偿及智能控制策略进行研究。文中综述了气动比例系统的特点及发展状况，分析气动系统的摩擦补偿技术，阐述智能控制技术在该领域中的研究与应用。在深入分析气动比例系统的工作性能及特点的基础上，研究系统的摩擦机理，并且通过叠加高频低幅颤振信号补偿系统的摩擦力，结合气动比例系统的非线性特征，研究了智能混合控制器，获得系统良好的控制精度。首先，研究叠加高频低幅颤振信号补偿摩擦力的理论。为克服摩擦力给系统带来的稳态误差和低速爬行问题，通常是通过提高运动部件的加工精度和改进系统的润滑条件来减少系统的摩擦力。在气动比例系统中，可以通过改进气缸的机械结构，或者采用高精度新型气缸等措施来减少非线性摩擦对系统运动性能的影响，但是由于这种方法会使成本显著增加，也不可能最终消除非线性摩擦，从而影响系统的定位精度和轨迹跟踪精度。因此，必须从根本上对其进行研究，采用现代控制理论与摩擦补偿来减小非线性对系统运动精度的影响。基于粘弹性理论发展气动比例系统的摩擦数学模型。将该摩擦模型引入阀控缸系统的动态模型中，对系统的模态参数进行识别，建立系统完整的运动模型。通过研究系统的摩擦机理并对系统进行叠加颤振信号后的稳定性理论分析，系统部分静摩擦力转化为动摩擦力，最大静摩擦力减小，响应速度提高，从而将系统的粘滑运动转换为一种平稳运动。当颤振频率近似等于系统固有频率时，系统产生共振现象，当颤振频率为固有频率的3.3倍时，系统在不同的幅值下的定位精度均有提高。信号幅值与负载关系为A=0.005F+1.0333时，系统的滞后时间由原来的0.17s缩短为0.02s。其次，研究气动比例系统的智能混合控制策略，有效克服系统的非线性。智能控制采用各种智能化技术实现复杂系统和其它系统的控制目标，是一种具有强大生命力的新型自动控制技术。控制的目的就是根据控制对象的特性开发出适合系统特征的控制器，从而可以得到良好的控制性能。由于系统在运动过程中受工作负载、气源压力、气体流量和静态工作点等各因素的影响，气动比例系统属于典型的时变非线性系统。因此，严格地来讲，没有任何一种控制方法能够适用于被控对象的整个控制过程，控制策略单纯采用常规控制，很难取得令人满意的效果，必须根据不同的控制对象寻找最适合的控制策略。针对气动比例系统的非线性特点，将神经模糊控制引入到专家控制中，形成一种综合的实时智能混合控制策略。该控制器既具有专家控制的逻辑推理、模拟人的高级智能行为的能力，又具有神经模糊控制的直觉推理能力，将两种控制策略结合实现了并行控制与知识共享。研究发现，该混合控制结构响应快，控制性能高，兼顾快速性和灵活性，对于系统的任意轨迹跟踪具有较高的控制性能，对外干扰的鲁棒性较强。再次，研究气动比例阀控缸系统动态模型，描述系统的气源压力、气体流量及工作负载等工作参数对系统定位精度的影响规律。对影响系统动态特性的主要影响因素进行理论分析与实验研究发现，系统的控制性能受气源压力的影响最大，气体流量次之，工作负载最小。对不同的气源压力、气体流量及工作负载下的定位精度进行多元非线性回归分析，建立系统的定位精度与动态参数之间的关系方程，通过该方程可以近似计算出系统在不同状态下的定位精度。再次，对气动比例系统的数学模型进行系统辨识与稳定性分析。通过系统辨识，消除数学模型在机理建模及线性化过程中造成的误差，得到气动比例系统较为精确的数学模型。基于该模型进行稳定性分析，根据奈奎斯特稳定判据判定该气动比例系统属于稳定系统。最后，研制二自由度气动比例系统的控制程序及控制界面，实现气动比例系统在平面内的高精度轨迹跟踪研究。系统的“点-点”定位精度控制在±0.100mm以内，连续轨迹跟踪精度控制在±0.274mm以内，可以替代价格昂贵的伺服系统。更多还原

【Abstract】 Pneumatic systems have been used widely in industrial automation field such as chemical industry, medicine, textile, micro-electric and bioengineering for its advantages of simple in structure, anti-pollution, high performance to cost, easy to maintenance and anti-jamming. With the development of the pneumatic proportional system, pneumatic system control is extended from logical control to proportional/servo control area. However, the pneumatic systems have the disadvantages of inherent strong nonlinearity, low natural frequency and nonlinear influence of friction, it is difficult to obtain the satisfactory control performance, and its uses in industry area are limited. In this dissertation, the study on improving the positioning precision for the pneumatic proportional system is presented. The system friction nonlinear compensation and intelligent control method are developed based on the study of its dynamic Behaviors.In the paper, the features and development of pneumatic proportional system are presented, the friction compensation and the use of intelligent control technology in pneumatic are analyzed. Based on the study on working performance and features of the system, the friction mechanism is developed, the friction is overcome by adding chatter signal to the system, the intelligent hybrid controller is presented according to its nonlinear, the system tracking trajectory is realized.Theory on friction compensation based on high frequency low amplitude chatter signal is presented. To overcome the system steady-state error and scrawl under low velocity caused by friction, we usually improve the machining accuracy and lubricating of the move parts to reduce the system friction. However, in pneumatic proportional system, the nonlinear friction influence on the motion performance is reduced by improving the mechanical structure of the cylinder, or using high precision new cylinder, these methods will lead to high price, the nonlinear friction is not eliminated thoroughly, and the system positioning precision and low-velocity tracking precision are not improved finally. So it is necessary to combine modern control method with friction compensation to reduce the influence on movement precision of system nonlinear.Friction model of the pneumatic proportional system is developed based on the viscoelasticity method. Study on the system friction mechanism is developed, it is found that a part of static friction is turned into dynamic friction, the maximum static friction is reduced, the response speed is raised, and the stick-slip motion is transformed into a steady one by adding proper chatter signal. Based on the stability theory on the chatter signal added, it is found when the chatter frequency is 3.3times of the natural one, the positioning precision is the highest. And when the chatter frequency is equal to the system natural one, resonance happens. When the relationship between amplitude and load is A = 0.005F +1.0333 the hysteresis time is shorten from 0.17s to 0.02s.Intelligent hybrid control method is advanced to overcome the nonlinear of system. Intelligent control is a new automation technique which uses various intelligentized technology to realize the control of complicated system. The control purpose is to obtain good control performance by developing a controller which is suitable for the system Behaviors according to the controlled object. Influenced by the factors such as working load, pressure, flow and quiescent point, the moving pneumatic proportion system is nonlinear typically. So speaking strictly, there is no a control method which is suitable for the whole process of the controlled object, it is difficult to obtain famous control effect by use of conventional control method, and it is necessary to develop the most suitable control method according to different controlled-object.Based on the non-linearization of pneumatic system, the neural-fuzzy control is embedded in the expert control, a compositive real-time intelligent hybrid control method is produced. Not only has the controller ability of logical reasoning and advanced intelligent behavior of the expert control, but the instinct reasoning ability of the neural-fuzzy, the coupled control method realizes the parallel control and knowledge sharing. The experiments prove that the hybrid controller have the advantages of quick response, high control performance, it embodies both rapidity and flexibility, a high trajectory tracking precision and good robustness are obtained when the system work.The dynamic Behavior model of the pneumatic proportional valve-controlled cylinder system is developed, which describes the rules between positioning precision and dynamic parameters. Study on the main factors such as the pressure, flow and load which influence the system dynamic Behaviors is developed. The equation between positioning precision and dynamic parameters is provided by use of multiple nonlinear regression analysis, which describes the system positioning error under different working conditions.The system identification and stability analysis of the pneumatic proportional system is presented. To eliminate the errors caused by linearization and obtaining an accurate system model, the system identification process is designed, and the stablity study on system is done based on the identified model. Based on the model, study on the reliability is developed, the system is steady judged by Nyquist steady judgement.Finally, the control program and interface two-freedom pneumatic proportional system is presented, its high precision tracking trajectory is realized. The system positioning precision of point-to-point is within±0.100mm, and the continuous tracking trajectory control precision is within±0.274mm, it is expected to replace the expensive servo system.更多还原