【作者】 罗峰；

【导师】 张屹； 黄锐；

【作者基本信息】 湖南大学 ， 机械工程（专业学位）， 2019， 硕士

【摘要】 随着激光焊接技术的广泛应用,焊接生产的自动化程度越来越高。为了保证激光焊接过程的精度和效率,提高焊接工件的质量,开发一套焊缝自动跟踪系统十分必要。因此,本文基于同轴监测技术与龙门式三维运动平台,从图像采集模块、控制模块、执行机构模块和人机交互模块等几个方面,搭建了激光焊接过程监控系统。本系统采用“PC+运动控制器、PA数控系统”的主从式控制系统架构,PC机作为上位机负责信号采集处理、参数设置、发送命令及图形化显示等,运动控制器与PA数控系统作为下位机负责与执行机构通讯,完成各项命令的执行和反馈。其中,运动控制器通过PCI接口与主控系统PC进行通讯,并通过信号适配器与PA数控系统进行信号交互,以实现龙门式三维运动平台各个轴的同步运动。如何实时识别焊缝偏差信息并对其进行纠偏,是实现焊缝跟踪的关键。目前广泛采用线性结构光进行焊缝识别,它对焊缝坡口的类型依赖性比较强,并不适用于结构特征不明显的窄间隙焊缝激光焊接。对此,本文采用激光点光源作为辅助光源直接对焊缝区域进行照明,采取基于视觉传感的同轴监测方法获取了焊缝图像信息,并采用以阈值分割和寻质心为核心的图像处理方法提取到焊缝中心点坐标。通过数学建模对焊接头的运动状态参量横向偏差、切线角度偏差、方位角度偏差进行了定量分析,经过建模分析发现,在焊接头的运动状态参量中,横向偏差能够很好地反映焊接头与焊缝之间的相对关系,且利用本文提出的图像处理算法能够很容易地获取横向偏差,满足焊缝跟踪实时性要求。然后提出了基于均值限幅滤波的数字滤波算法,能够显著提高采集信号的精度。为提高焊缝跟踪精度,本文提出了基于积分分离的模糊自适应PID控制算法,以焊缝横向偏差e及偏差变化率ec为输入量,在内环以PID控制器的参数变化量△Kp、△Ki、△Kd为模糊控制器的输出量,建立两输入三输出的模糊控制系统模型,在外环以控制伺服电机的脉冲数量U为输出量建立PID控制系统模型。同时根据实时采集的焊缝偏差大小进行统计分析,提出了积分分离的思想,将焊缝跟踪过程分为模糊自适应PD控制、半模糊自适应PID控制和全模糊自适应PID控制,可以减小超调量、消除稳态误差、提高响应速度,避免系统由PD控制转换为PID控制时产生较大的震荡,使系统平滑过渡,提高控制精度。最后采用Simulink对模糊PID控制器及焊缝跟踪系统进行了仿真分析,并设计实验进行了验证,结果表明本文设计的均值限幅滤波算法和基于积分分离的模糊自适应PID控制算法可以有效地提高焊缝跟踪精度。更多还原

【Abstract】 With the wide application of laser welding technology,the automation degree of welding production becomes higher and higher.In order to ensure the precision and efficiency of laser welding and improve the quality of welding workpiece,it is necessary to develop an automatic seam tracking system.Therefore,based on the coaxial monitoring technology and the gantry 3D movement platform,this paper builds the laser welding process monitoring system from several aspects,such as image acquisition module,control module,executive mechanism module and humancomputer interaction module.This system adopts the master-slave control system architecture of "PC+ motion controller and PA numerical control system".PC as the upper computer,which is responsible for the signal collection and processing,parameter setting,sending commands and graphical display.The motion controller and PA numerical control system as the child controller,which are responsible for completing the execution and feedback of various orders.Among them,the motion controller communicates with the master control system PC through the PCI interface,and interacts with the PA numerical control system through the signal adapter,so as to realize the synchronous movement of each axis of the gantry 3D motion platform.How to identify and correct the deviation information of weld seam in real time is the key to realize the tracking of weld seam.At present,linear structural light is widely used for weld identification,which is strongly dependent on the type of weld groove and is not applicable to narrow welding seams with no obvious structural characteristics.In this paper,the laser point light source is used as the auxiliary light source to directly illuminate the weld area,the coaxial monitoring method based on visual sensing is adopted to obtain the weld image information.The image processing method based on threshold segmentation and centroid finding was used to extract the coordinates of the weld center.Through mathematical modeling,the transverse deviation,tangential angle deviation and azimuth angle deviation of the motion state parameters of welded joints are analyzed quantitatively,and found that lateral deviation error can well reflect the relative relationship between the seam and welding head.At the same time,using the image processing algorithm proposed in this paper can easily obtain lateral deviation,meet the real-time demand in seam tracking.Then a digital filtering algorithm based on mean limiting filtering is proposed,which can significantly improve the accuracy of the collected signals.In order to improve the precision of seam tracking,a fuzzy adaptive PID control algorithm based on integral separation is proposed in this paper.With transverse deviation e and deviation rate ec as the input,in the inner loop,PID controller parameter change delta Kp,delta Ki,delta Kd as the output of fuzzy controller,establish two input three output fuzzy control system model;in the outer loop,the PID control system model is established by taking the pulse quantity U of the control servo motor as the output quantity.At the same time,according to the real-time collection and statistical analysis of the size of the welding seam deviation,we proposed the idea of integral separation,in order to meet the requirements of response speed and tracking accuracy of the system.By this way,the seam tracking process is divided into fuzzy adaptive PD control,a half of fuzzy adaptive PID control and fuzzy adaptive PID control,which can reduce the amount of overshoot,eliminate the steady-state error and improve the response speed.It can also avoid larger oscillation when the system from PD control convert to PID control,so that the system can smooth transition and improve the control precision.Finally,we used Simulink to simulate the fuzzy PID controller and the welding seam tracking system,and design experiments.The results show that the mean and limiting filter algorithm and the fuzzy adaptive PID control algorithm based on integral separation can effectively improve the welding seam tracking accuracy.更多还原