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铝电解槽阴极钢棒窄间隙旋弧焊接机器人的关键技术研究
毛一剑
Subtype工学博士
Thesis Advisor梁自泽 ; 景奉水
2018-05-24
Degree Grantor中国科学院大学
Place of Conferral北京
Keyword铝电解 阴极钢棒 窄间隙旋弧焊接 工业机器人 模型预测控制
Abstract       我国原铝产量位居世界第一,但是铝电解关键技术和基础理论研究薄弱,导致我国铝电解工业资源消耗高、能源利用率低、三废排放大。我国的铝电解槽寿命只有4到6年,比国外平均寿命少2年,因此每年有20%的电解槽需要停槽大修。大修质量的好坏,对延长槽寿命、降低铝生产成本具有重要意义。尤其是铝电解槽阴极钢棒和钢铝爆炸焊板连接质量的好坏直接影响到铝电解槽的电流分布、电能消耗、电流效率等经济技术指标。
       然而铝电解槽阴极钢棒和钢铝爆炸焊板连接处的作业空间狭窄,现有的自动化焊接机器人无法适应现场作业条件,目前完全依靠人工焊接。在高温、强磁场、高粉尘、大电流、有毒气体和高噪声等恶劣环境下,焊接作业人员劳动强度大、作业风险高、工作效率低。因此,研制强磁环境下替代人工作业的、自动化程度高的特种焊接机器人,对于提高生产稳定性、提升节能减排水平、促进铝电解行业的技术进步,具有重要的理论意义和工程价值。
       本文针对铝电解槽阴极钢棒焊接机器人的几个关键问题展开研究,主要工作如下:
       1.针对现有阴极钢棒和钢铝爆炸焊板连接方式存在的诸多问题,提出了一种新的技术方案:以阴极钢棒为基准的夹具对钢铝爆炸焊板进行定位,形成一个狭窄焊缝用于自动焊接。该技术方案具有节省焊接材料、提高焊接质量、改善电流均布性、降低生产运行中的安全隐患等优点。
       2.针对铝电解槽阴极钢棒和钢铝爆炸焊板之间狭窄焊缝的作业特点,提出了窄间隙旋弧焊接机器人系统的设计方案,建立了控制系统硬件框架、软件框架和机器人运动学模型,然后着重解决了几个关键技术难点:设计刚性固定夹具有效防止焊接变形;控制末端电弧旋转解决侧壁熔合问题;采用水冷滑块防止熔融金属溢流;焊接系统中机、电、水、气、磁、热等各个过程的综合考虑保证系统可靠运行;旋转电弧传感方式解决狭小作业空间窄间隙焊接的自动跟踪问题。
       3.针对旋弧焊接过程静态模型难以应用各类先进控制算法实现高精度高灵敏度焊缝跟踪的问题,基于焊接电弧物理、焊丝送给和熔化、电源回路模型、焊丝干伸长度、熔滴过渡及焊缝成形等过程的机理分析方法,建立了旋转电弧窄间隙焊接过程的动态模型。首先推导出系统模型的六阶非线性状态空间方程。然后在焊丝干伸长度远大于熔滴半径和熔滴过渡位移的条件下,系统方程解耦和降阶为三阶的四输入单输出系统。采用小信号线性化模型求得熔池形状和焊丝干伸变化时焊接电流响应特性。最后,对窄间隙旋弧焊中的焊道偏斜现象给出了新的定量解释。基于这一原理,提出最优的焊枪旋转控制策略。
       4.针对旋转电弧窄间隙GMAW过程的强耦合、高阶、扰动等问题,提出一种对开环电压和焊枪高度进行滚动时域优化的策略,设计了在状态可测假设下的预测控制系统。首先建立包含扰动的系统状态空间模型,并将其离散化、无量纲化和增量化。在状态空间模型的框架下,推导出旋转电弧窄间隙GMAW过程的预测方程,然后求得预测控制优化问题的数学描述和最优控制序列,所设计的预测控制器具有“前馈——反馈”结构。最后,求得考虑不可测扰动影响时预测控制系统闭环解,并证明其具有渐近稳定性和无静差跟踪特性。仿真验证了送丝机电枢电压冲击和位置斜坡偏差这两种扰动下所设计的闭环预测控制系统可以稳定运行,并且静态无差。
       5.针对旋转电弧窄间隙GMAW过程系统状态不可测的问题,提出一种反馈校正估计焊接系统状态的策略,设计了基于状态估计的预测控制系统。首先,建立了系统状态可观性判据,并推导出基于状态估计器的闭环预测控制系统的最优控制序列,通过配置闭环系统矩阵的极点改善系统动态性能。然后,针对极点未配置、消除单位圆上的极点、配置极点接近原点几种情况,得到闭环预测控制系统动态响应特性。最后,仿真验证了基于送丝机电枢电压冲击和位置斜坡偏差这两种扰动下所设计的闭环预测控制系统可以消除状态估计初值偏差。
       6.针对铝电解工业现场的作业环境,开发出一套窄间隙旋弧焊接机器人系统,对提出的控制策略和机器人系统进行了实验验证。焊接机器人完成单个接头焊接需要15分钟,比过去人工1—2个小时的效率大幅提升。机器人焊接接头压降低于7mV,比过去人工的10—30mV的压降大幅降低。机器人焊接质量的一致性和稳定性远远优于人工焊接。
Other Abstract        China is the largest countries producing primary aluminum all over the world. However, the research on basic theory and key technologies of aluminum electrolysis technology in China is weak, resulting in high resource consumption, low energy utilization and copious emission of three wastes. The service life of aluminum electrolytic cells in China is only 4 to 6 years, which is 2 years less than the average life expectancy in foreign countries. Therefore, 20% of electrolyzers need to be overhauled each year. The overhaul quality is of great significance for extending electrolytic cell life and saving the cost of aluminum production. In particular, the quality of the connection between the cathode steel busbars and the steel-aluminum explosive welding plates has a significant impact on economic and technical indicators such as current distribution, power consumption, and current efficiency.
        However, ready-made automatic welding equipment is impossible to apply because of the narrow operating space of the connection joint between the cathode steel busbars and the steel-aluminum explosive welding plates. Currently this work is mainly finished through manual welding. In terriblely bad environments such as high temperatures, strong magnetic fields, high dust, high currents, toxic gases, and high noise, welding workers are of high labor intensity, high work risks, and low work efficiency. Therefore, it has significant theoretical meaning and engineering value to develop automatic welding robot replacing human workers. It can improve production stability, increase level of energy conservation and emission reduction, and promote technological progress in the aluminum electrolysis industry.
        In this paper, several key problems of the cathode steel busbar welding robot for electrolytic aluminium cells are studied. The main work are summarized as follows:
        1. Aiming at many problems existing in the connection of existing cathode steel bars and steel aluminum explosion welding plates, a new technical solution is proposed: the steel-aluminum explosive welding plate is positioned by the clamp of the cathode steel busbars, and a narrow weld is formed for automatic welding. A narrow gap rotating-arc welding robot system is developed to weld automatically. This technical scheme can save welding materials, improve welding quality, ameliorate current distribution and decrease the safety security threat in production operation.
        2. Aiming at the working characteristics of the narrow weld between the cathode steel bars and steel aluminum explosion welding plates, the design scheme of the narrow gap rotating-arc welding robot system was proposed, and the hardware framework, software framework and robot kinematics model of the control system were established. Then several key technical problems have been solved: design rigid fixtures to effectively prevent welding distortion; control the rotating arc at the end to solve the problem of sidewall fusion; apply water-cooled sliders to prevent overflow of molten metal; make comprehensive consideration of mechanic, electricity, water, gas, magnetic, thermal and other processes in welding systems to ensure reliable operation; introduce rotary arc sensing to automatically track the narrow gaps in limited working spaces.
        3.Aiming at the problem that the static model of arc welding process is difficult to apply advanced control algorithms to achieve high-precision and high-sensitivity seam tracking, the dynamic model of narrow gap rotating-arc welding process was established,based on the principle of the following dynamic process: welding arc physics, welding wire feeding and melting, power circuit model, welding wire extension, droplet transfer and weld forming. First, a sixth-order nonlinear state space equation of the system model is established. Then, the condition that the wire extension is much longer than that of the droplet radius and the droplet displacement is established, and the system equation is decoupled and reduced to a third-order four-input single-output system. Based on the small-signal linearization model near the static equilibrium point of the system, the welding current response characteristics in the influence of the wire extension and the shape of the molten pool are determined. Finally, a novel quantitative explanation is proposed for the phenomenon of bead deflection in narrow gap rotating-arc welding. In addition, based on this principle, the optimal torch rotation control strategy is planned.
        4. Aiming at the problem of strong coupling, high order, disturbance and other factors in the narrow gap GMAW process of rotating arc, a receding horizon optimization strategy for open-loop voltage and welding torch height is proposed, and a predictive control system based on the assumption of states measured is designed. Firstly, a system state space disturbance model is obtained. Then, the model is discretely and dimensionlessly and incrementally processed. Fisrt, deduce predictive model of the narrow gap rotating-arc GMAW process in the framework of the state space model. Then the mathematical description and optimal control input sequence of the predictive control optimization problem are obtained. The designed predictive controller is with a “feedforward-feedback” structure. Finally, the closed-loop solution of the predictive control system is discussed when considering the influence of unmeasured disturbances. And it is of asymptotic stability and no tracking error characteristic. Then, the simulation verified that the closed-loop predictive control system designed under various perturbations of the wire feeding motor armature voltage impulse and positional slope deviation can operate stably, and there is no static difference.
        5.Aiming at the unmeasurable state of narrow gap rotating-arc GMAW process system, a feedback correction strategy for estimating the state of the welding system is proposed, and a predictive control system based on state estimation is designed. First,under the condition that the system is observable, the optimal control input sequence of closed-loop predictive control system based on state observer is deduced. Specifically discuss the closed-loop system dynamic response characteristics of several cases: the pole is not configured, the pole is configured in the unit circle, the pole is configured close to the origin of the situation. Finally, the simulation verified that the closed-loop predictive control system based on the two disturbances of the armature voltage impulse and position slope deviation can eliminate the initial value deviation of the state estimation.
        6. Aiming at the working environment of the aluminum electrolysis industry, a narrow gap rotating-arc welding robot system was developed. The proposed control strategy and robot system were verified by experiments. The robot is able to complete the welding of a single joint in 15 minutes, which is a significant increase over the previous 1-2 hours of manual labor. The robot welding joint voltage drop is reduced to 7mV, which is significantly lower than the artificial pressure drops of 10-30mV. And the welding quality consistency and stability are better than manual welding.
Language中文
Document Type学位论文
Identifierhttp://ir.ia.ac.cn/handle/173211/21166
Collection毕业生_博士学位论文
Affiliation中国科学院自动化研究所
First Author AffilicationInstitute of Automation, Chinese Academy of Sciences
Recommended Citation
GB/T 7714
毛一剑. 铝电解槽阴极钢棒窄间隙旋弧焊接机器人的关键技术研究[D]. 北京. 中国科学院大学,2018.
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