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金属粉末激光成形过程中的检测与闭环控制研究
Alternative TitleResearch on Measurement and Control in Metal Powder Laser Shaping Process
姜淑娟1,2
Department现代装备研究室
Thesis Advisor刘伟军
ClassificationTG665
Keyword金属粉末激光成形 熔池温度 熔覆高度 熔覆宽度 模糊pid控制
Call NumberTG665/J47/2009
Pages131页
Degree Discipline机械电子工程
Degree Name博士
2009-01-15
Degree Grantor中国科学院沈阳自动化研究所
Place of Conferral沈阳
Abstract金属粉末激光成形技术是基于快速原型(Rapid Prototyping,RP)技术基础上发展起来的一项新型金属零件加工技术。该技术利用高能量激光束直接作用在金属粉末上,可以直接成形高熔点、形状复杂或异质材料功能梯度零件,其成形过程是按照零件几何形状,利用金属粉末逐层逐道累积成形零件的。其独特的金属零件加工特点使其得到了迅速发展,在航空、军事、医学和汽车等众多领域得到了成功应用,并发挥了重要作用。作为一项新兴技术,金属粉末激光成形技术不可避免的存在一些问题,由于激光成形过程是一个多参数影响的过程,成形过程中各参数存在较强的耦合作用,参数的不稳定往往导致成形效果难以保证,例如成形零件外形尺寸精度低、内部组织性能不佳等。这一问题,引起了国内外许多学者的关注,对加工过程中的一些重要参数与成形效果之间的关系展开研究,通过对成形过程中的一些中间过程输出参数进行实时检测,并实现闭环反馈控制,从而达到改善成形产品质量的目的。本文正是在这种背景下进行研究的,本文对熔池场几何尺寸、熔池温度场、熔覆高度与熔覆宽度实时检测进行了深入研究并实现了切实可行的检测方法,在实践中取得了较好的效果,并进行了熔覆成形过程动态辨识,研究了成形过程控制方法,提出了具有较强自适应能力的模糊PID控制方法,取得了较好的仿真效果。本课题主要研究工作有以下几个方面。 1. 激光成形过程中的熔池场包含大量的过程信息,对熔池进行实时检测,并提取熔池特征信息,为熔池场的闭环控制提供依据。为此建立了熔池场实时检测视觉传感系统,实现了图像采集、图像处理和信息提取等功能,课题成功的进行了硬件系统构建和软件系统开发。 2. 实现了红外图像比色测温法在金属粉末激光成形过程中熔池温度场检测中的应用。研究了测温原理,完成了硬件双波长图像采集系统的构建,对滤光片波长进行了选择并对选择结果进行了仿真。阐述了软件测温实现过程。 3. 激光加工过程中,对熔覆高度进行实时检测,从而实现熔覆高度闭环控制是成形高质量零件的保证。加工过程是一个多参数耦合的非线性过程,在分析激光参数对熔覆高度影响的基础上,建立利用激光工艺参数预测熔覆高度的BP神经网络模型,为实现激光加工过程熔覆高度实时预测与闭环控制打下了基础。 4. 熔覆宽度是激光成形过程中与成形效果密切相关的中间过程输出参数,该参数的实时检测为调整扫描间距,确定合理搭接率,提高熔覆表面平整度具有重要作用。提出了一种基于卡尔曼滤波技术的激光熔覆宽度检测方法。利用视觉传感系统获取激光加工过程中的熔池图像,经过图像处理求熔池宽度作为参量建立系统状态方程和测量方程,应用卡尔曼滤波原理对图像上的熔宽和熔宽变化进行状态估计,得到最小均方差条件下的熔覆宽度最佳预测值,从而减小过程噪声和测量噪声引起的熔覆宽度测量偏差,实现加工过程熔覆宽度的精确检测。 5. 成形过程动态辨识,利用阶跃响应法进行了激光参数与熔覆高度、熔覆宽度的辨识实验,建立了激光功率、扫描速度、送粉速率与熔覆高度、熔覆宽度之间的数学模型,对成形过程有了基本了解,为控制器设计与动态过程调节规范确立打下良好基础。 6. 设计了PID熔覆高度控制系统,并利用遗传算法进行了PID参数寻优,寻优获得的参数可以实现较好的控制效果,但不适于实时控制过程。为此设计了模糊PID控制系统,利用模糊逻辑算法对PID参数实现在线自动调整,控制系统具有较强的适应能力和实时处理能力,对于金属粉末激光成形过程具有较好的控制效果。
Other AbstractThe Metal Powder Laser Shaping (MPLS) technology is a new manufacturing technology based on the theory of Rapid Prototyping. As one of the rapid prototyping techniques, the MPLS can manufacture high melting point parts, complex shape parts, or heterogeneous material functional graded parts with high power laser directly acting on metal powder without intermediate procedures or equipment. In virtue of the unique characteristics, the MPLS develops very fast. In recent years ,the MPLS has been brought into wide use in the region of aviation industry、military、medicine and automobile industry. However, there are still some weak points in it. A large number of parameters govern the MPLS process. These parameters are sensitive to the environmental variations, and they also influence each other. These unstable factors cause instability in the forming process, which results in bad quality of the shaped parts. For example, the geometrical accuracy and interior tissue performance cannot be guaranteed. In view of the serious influence on the geometrical accuracy and mechanical performance, effective measures must be taken in the process to optimize the parameters. Fortunately, it has drawn the technician and scholar’s great attention to the deterioration of formed parts. They commit themselves to investigating the effects of different processing parameters on the forming characteristics. Many scientific research academies and universities pursue the study for measuring and controlling some of the laser cladding process parameters in order to improve the fabricated metal parts. Our research is carried out in this background. The geometrical size of the molten pool, the temperature of the molten pool, the cladding height, and the cladding width are researched seriously, and effective real-time measuring strategies are fulfilled successfully. Furthermore, a real-time monitoring and feedback control system for the MPLS process has been constructed based on the process identification. The main parts of this thesis are described as follows. 1. The laser molten pool includes a great deal of process information. It is vital to real time monitor molten pool and to extract characteristic information to provide information for closed-loop control system. A vision sensing system for taking and processing the image of the molten pool has been setup. The hardware has been constructed successfully and the software has been developed effectively. 2. The application of infrared images colorimetric method is realized in measuring the molten pool temperature field in MPLS process. The measurement principle is researched and the hardware system for two-wavelength images collecting has been constructed. The wavelength selection and effect simulation is fulfilled. The software workflow for temperature measuring is illuminated. 3. The real-time detecting of the laser cladding height is necessary for forming high quality metal parts. Technological parameters are coupled and the forming process is a non-linear process. The influence of laser parameters on cladding height is analyzed. The prediction model of cladding height based on BP (Back propagation) neural network is build, which is the basement for real-time cladding height prediction and closed-loop control in laser forming process. 4. The cladding width is another important process parameter correlates to the quality of the formed parts. Precise sensing the cladding width is vital to improve the planeness of metal parts by adjusting scanning space or revising overlap. The application of Kalman filtering (KF) for the molten pool width detection in laser forming process is presented. The vision sensing system collects the images of the molten pool in laser forming process. The molten pool width calculated by image processing is used as a parameter to establish a state equation and a measurement equation. A Kalman filter recursively compute the solution over least squares approaches to equations which are established based on an estimation of the width and the displacement in width. The Kalman filter optimizes the estimation of the molten pool width at the next sampling time and reduces the measurement errors caused by the process and sensor noises. 5. The MPLS process dynamic identification is fulfilled by the method of experiment. Through step response experiments, mathematical models between the cladding height, the cladding width and the laser power, the scanning speed, or the powder flowrate are established respectively. From the identification, the MPLS process is understood, which is the basement for constituting technical specification and designing closed loop control. 6. A PID control system of laser cladding height is set up, and the Genetic Algorithms is used for optimizing PID parameters. The optimized parameters acquired perfect control effect, but it is not suitable for on-line control process. A fuzzy PID control system is fulfilled by fuzzy logical arithmetic optimizing PID parameters online. The fuzzy PID control system has great adaptability and can real time control the MPLS process perfectly.
Language中文
Contribution Rank1
Document Type学位论文
Identifierhttp://ir.sia.cn/handle/173321/382
Collection智能产线与系统研究室
Affiliation1.中国科学院沈阳自动化研究所
2.中国科学院研究生院
Recommended Citation
GB/T 7714
姜淑娟. 金属粉末激光成形过程中的检测与闭环控制研究[D]. 沈阳. 中国科学院沈阳自动化研究所,2009.
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