【作者】 张莹；

【导师】 王耀南；

【作者基本信息】 湖南大学 ， 控制科学与工程， 2010， 博士

【摘要】 大型冷凝器是火电厂和石化行业的大型换热设备的关键设备之一,在大型汽轮机装置的热力循环中起冷源的作用,能降低汽轮机排汽压力和温度,提高汽轮发电机组的循环热效率。冷凝器运行时,由于冷却水不洁净、热交换时伴随化学反应等原因,致使冷凝管内壁积聚了不利于传热的污垢,冷凝管的污垢将产生一系列危害：严重削弱冷凝器的换热能力,引起真空度降低、能耗增加,还可能导致冷凝管堵塞甚至造成管壁腐蚀穿孔而引发事故。论文首先探讨了冷凝器污垢产生的原因以及对冷凝器传热性能的影响,说明污垢监测、污垢清除的必要性；总结并分析了各种污垢清洗方法的优点与不足；提出了高压水射流清洗机器人在线工作的设计方案,详细介绍了视觉控制在机器人领域的研究方法和应用。在污垢系数大于某一设定值时,清洗机器人将自动运动到待清洗区域,对待清洗管口的中心坐标进行定位,实现对冷凝管的高压水射流清洗,所以知道机器人当前的位置具有十分重要的意义,而冷凝管管口的边缘检测是实现精确定位的关键步骤。在分析了现有的边缘检测算法后,凭借Canny提出的边缘检测三准则,对二维奇Gabor小波的阶跃边缘检测性能做了详细分析,并与现有的边缘检测算法做了仔细比较,实验结果证明了应用于冷凝器管口边缘检测的优越性。另外考虑到水下光线的复杂性,获取的图像经过检测处理有可能发生边缘缺失或不完整的现象,故对基于最小二乘法的边缘拟合进行了研究,提出了改进的随机Hough变换算法得到冷凝器管口中心坐标,最后利用P3P算法完成机器人的定位。清洗机器人要在冷凝器水箱体中自主运动,需要解决智能导航问题。由于一般的摄像机成像视角只有40-50度,不满足对空间的全方向成像要求,本文提出了基于双曲线的折反射全向相机的视觉导航,对折反射的成像原理,全向图像的展开,全向相机的极线几何等做了详细的推导,并利用Kruppa方程对摄像机的内部参数进行定标。机器人的导航是通过固定和移动两个全向相机获取目标图像,通过匹配的特征点计算极线几何后,根据特征点在成像平面的变化情况,从而得到当前位置点与理想位置的误差,经过计算得到移动机器人需要执行的旋转角度和平移距离,接着对在水下工作的机器人行走机构的受力情况做了分析,得到它的运动学和动力学方程,最后用反步法对清洗机器人驱动轮进行控制,实验证明机器人可以准确移动到指定位置。在清洗机器人到指定位置后,如果直接利用边缘检测得到的坐标对冷凝管进行定位,会因机械加工精度误差、水中流体力学的影响导致定位偏差,从而影响清洗效果。为了解决这个问题,本文提出了基于极线几何的机械臂视觉伺服控制,通过Gabor包络算法从管口图像中提取多个特征点进行匹配,再计算基本矩阵和特征点与极线的误差,利用任务函数将控制量分解为两个控制任务,首要任务是通过旋转使特征点收敛到极线上,然后使特征点沿着极线平移到期望位置,并根据上述原理设计机械臂的笛卡尔工作轨迹,即机械臂先从初始位置开始旋转,当获得与期望位置相同的方向相位后,然后平移到期望位置。这种控制方法不需要事先知道工作空间的三维信息,控制规则简单,能够得到比单纯手眼结构的机械臂更大的工作空间等优点。实验证明该方法能得到很好的控制效果,所有的特征点在有限时间能够到达期望的位置,误差能收敛到零。视觉伺服系统的视觉控制器性能依赖于系统所提取的图像特征,为避免局部图像特征超出视域所带来的问题,本文对全局图像特征--图像矩特征作为图像特征信息进行了研究,推导了基于矩特征的雅可比矩阵。控制算法避免了图像的特征匹配过程,在不需要知道目标的成像高度、摄像机焦距及不需要精确标定的摄像机外部参数的情况下,较好的实现了基于图像的视觉伺服控制系统仿真。最后,设计了冷凝器清洗机器人的总体结构,提出了基于局部加权偏最小二乘回归算法的污垢预测算法,即通过在训练集的污垢数据局部模型内对新测得的数据进行偏最小二乘回归分析,并采用自适应算法对模型参数、各模型之间的加权系数进行自动优化调整,能很好的解决新旧数据相互影响问题,以适应冷凝器水质及工况参数的动态变化。接着详细介绍了清洗机器人的运动机构,回转机构,主机架,电动推杆,机械臂,高压喷嘴等机械部件,对由工控机、触摸屏和PLC等组成的清洗机器人硬件系统,以及组态软件,故障报警系统和高压水控制等软件系统做了详细介绍,并给出了部分关键仪表设备的具体型号和性能参数,保证了清洗机器人完成高效、稳定的清洗任务。论文最后总结了全文的主要创新性研究成果,并对下一步研究工作进行了展望。更多还原

【Abstract】 Large condenser is one of the key heater exchange equipments in heat-engine plant and petrochemical industry. It plays the role of cold source in the thermodynamic cycle for large steam turbine which can decrease the exhausts pressure and temperature of the steam turbine in order to enhance the cycle thermal efficiency of the turbo generator. For the unclear cooling water and chemical reactions during heat exchange when the condenser is running, the fouling which is not favorable for heat transfer is accumulated in the inner wall of condenser tube. These fouling have produced such harm:severely decreases the heat exchange capacity of the condenser; lowers the vacuum degree; increases energy consumption and probably leads to accidence due to the blockage of condenser tube and followed by erosion and perforation.First of all, the paper explains the necessity of fouling monitoring and fouling cleaning by investigating the cause of fouling accumulation and the influence on heat transfer performance of condenser. Then it analyzes the advantage and disadvantage of the ordinary fouling measurement and cleaning methods. Afterward the concept of the cleaning robot is proposed and introduces the principle of cleaning robot for large condenser based on a mobile manipulator. In addition we describe the research methods and research content of visual control.When fouling factor is greater than a set value, cleaning robot would automatically move to the area waiting to be cleaned and using the center coordinates of tube to implement high-pressure water jet cleaning, so condenser tube edge detection is a key step to achieve precise positioning for condenser cleaning. We make analysis of the existing edge detection algorithm and depend on the edge detector three criteria proposed by Canny, make a detailed analysis for two-dimensional odd Gabor wavelet applied in step edge extraction and done a careful comparison with the existing edge detection algorithm. As a result, two-dimensional odd Gabor wavelet is proved better than edge detection algorithm when used in condenser nozzle edge detection. In addition, the complexity of the underwater light is taken into account, the images edge may miss or incomplete after the edge process; and then we studied the edge fitting algorithm based on least-squares method, finally proposed improved random Hough transform algorithm to get the condenser tube center coordinates.If cleaning robot is wanted to autonomic move in the condenser water tank, first of all, the key problem is to solve the intelligent navigation. As the general camera visual angle is only 40-50 degrees which can not meet the need of the Omni-directional requirements, the paper proposed Omni-directional camera visual navigation based on hyperbolic Catadioptric and deduced in detail the camera catoptrics’principle, epipolar geometry, image unfold model, then Kruppa equations is applied for camera parameters calibration. Robot navigation is obtain the target image by fixed and mobile Omni-directional cameras and calculate epipolar geometry by means of feature points matching which could obtain the error between current location point and ideal location point according to change in the imaging plane. And then we can calculate the rotation angle and translation distance which mobile robots need to carry out. Therefore analysis the kinematics and dynamics model for the underwater robot, finally, the cleaning robot left wheel and right wheel controlled by back-stepping control algorithm, simulation experiments show that robot can move to the specified location accurately and quickly.when the creeper truck arrive the designated location, if directly use the nozzle coordinate for mobile manipulator would lead to location deviation because the water hydromechanics and mechanics process precision, thus affecting the cleaning effect. In order to solve this problem, this dissertation proposed manipulator visual servo control algorithm based on epipolar geometry, which extracts the feature points from the nozzle edge by mean of Gabor envelope algorithm. After calculation the fundamental matrix and the error between feature points and epipolar line, the task function is applied to split the control variable into two decoupled tasks. The primary task is make feature points converge on the epipolar lines using the rotations only, the second task allows feature point to slide along the epipolar lines corresponding to the desired position, so the Cartesian trajectory of the robot’s manipulator is perfectly predictable, first of all the robot manipulator begin to rotate, when obtains the same orientations with the expectations location, then translate to the expect location. The new methods does not depend on anymore prior knowledge of the 3D structure scene, it only need simple control law and could get wider working space than eye-in-hand system. Simulation result on robotics toolbox for matlab and epipolar geometry toolbox shows that the method can obtain good control effect. All feature points finally convergence to the desired position and the total error converges to zero within a finite time. For the visual servo system, the visual performance of the controller depends on the system extracted image features, in order to avoid the problem of local image features beyond the visual scene. this paper using global image features-image moments as image feature information, avoiding the complex features match, Then deduced the jacobian matrix base on image moments. the visual control is realized with unknown depth of object, the camera focal length and does not require precise calibration of external parameters of the camera case. The simulation results show the image moments can used as image-based Visual servo control system.In the end, according to the specific requirements of cleaning robot, we proposed locally weighted partial least squares regression algorithm for prediction of condenser fouling, which fitting new measurement data by means of partial least squares regression analysis in old measured dada with a number of local models, then apply adaptive algorithm to adjust optimization model parameters and weighted coefficients of multi-model. The algorithm is a very good solution to the mutual impact of the new and old measurement data in order to adapt the condenser water quality changes and the device parameters dynamic changes. Then introduce in detail the cleaning robot motion mechanism, rotation mechanism, the chassis mainframe mechanism, electric putter, robotics manipulator, high-pressure nozzles and other mechanical component, and then introduce in detail the cleaning robot control system hardware composed by industrial computer, touch screen and PLC, as well as control system software composed by configuration software development, fault alarm systems, high-pressure water system, also provide specific model and parameters of some key instrumentation to ensure that cleaning robot fulfills cleaning task with high efficiency and stability。Finally, the main innovations of the thesis are summarized and the fields for further research are expected.更多还原