电阻点焊的控制系统设计与应用

方矩管生产最后环节需要将成品按规格数量集中,并通过打包带包装成捆。原打包带接头采用人工焊接,焊接完成后将成捆产品通过吊装入库,因此打包带的焊接质量和效率直接影响产品转运的安全性和生产节拍。为提高方矩管打包过程的自动化程度,设计了应用于方矩管打包带接头的电阻点焊自动控制系统。系统硬件主要采用PLC、伺服控制器和电阻焊机,软件采用工控软件实现。通过理论计算和调试得到满足打包带接头焊接需求的最佳焊接参数和运行参数,经过对焊接质量的可靠性测试分析,焊接打包带能够满足成捆产品转运负荷要求。该系统在原有半自动打包机的基础上实现了方矩管的全自动打包,组态软件运行状态良好,节省了人力成本,提高了方矩管打包的效率,焊接质量稳定,焊接方式更加环保。     

Online nugget diameter control system for resistance spot welding

The aim of this paper is to provide an integrated real-time control system for resistance spot welding (RSW), which is capable of producing welds with predetermined nugget diameters. Nugget diameter is a commonly used criterion for estimating the weld quality; thus, the system can be used for online quality control of RSW. The proposed system consists of two parts: a constant current controller and an online nugget diameter estimator. The constant current controller is used to guarantee the consistency of the nugget formation and growth during the welding process, while the online nugget diameter estimator can be used as a sensor for online estimation of the nugget diameter. The proposed online nugget diameter estimator is a mathematical function of the heat energy absorbed by the weld, which is taken into account only after the time when the first melting point of a weld appears. This time can be obtained by means of the dynamic resistance curve with a high resolution. A mathematical model of the online nugget diameter estimator is proposed and realized based on the experiment results and mathematical analysis. The welding process would be terminated when the difference between the actual nugget diameter and the predetermined desired value is within a given tolerance. According to a series of experiments, the welds used in the experiments had nugget diameters, which were well within the limits and the errors were within the given tolerance.     

Quality monitoring of resistance spot welding based on electrode displacement characteristics analysis

A new method is developed to monitor joint quality based on the information collection and process in spot welding. First, twelve parameters related to weld quality are mined from electrode displacement signal on the basis of different phases of nugget formation marked by simultaneous dynamic resistance signal. Second, through correlation analysis of the parameters and taking tensile-shear strength of the spot-welded joint as evaluation target, different characteristic parameters are reasonably selected. At the same time, linear regression, nonlinear regression and radial basis function (RBF) neural network models are set up to evaluate weld quality between the selected parameters and tensile-shear strength. Finally, the validity of the proposed models is certified. Results show that all of the models can be used to monitor joint quality. For the RBF neural network model, which is more effective for monitoring weld quality than the others, the average error validated is 2.88% and the maximal error validated is under 10%. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(10): 176–181 [译自: 机械工程学报]     

On-line evaluation of electrode wear by servo gun in resistance spot welding

More galvanized steels are being used in auto body assembly to improve safety and fuel efficiency of automobiles. However, spot welding these materials will result in a short electrode life due to serious and inconsistent electrode wear. Electrode radial wear during the electrode life test is the main factor leading to unacceptable nugget size. This paper firstly studied the feedback characteristics of servo guns to detect electrode axial wear online based on the developed system of an integrated servo gun with robot. Then a mathematical model of a spherical electrode was established to evaluate radial wear by detecting axial wear online at different electrode wear stages. The model was verified by experiments for welding different galvanized steels. It was shown that evaluation results of the model agreed well with the experiment results. The model revealed that a smaller radius of electrode face at beginning welds would result in a higher electrode wear rate. The method of evaluating electrode wear online based on the model also offered a guidance to determine the suitable time for tip dressing in real production.     

Quality control based on electrode displacement and force in resistance spot welding

The behaviors of electrode displacement and force during spot welding under various conditions, such as different weld currents, electrode forces, and welding times, were studied. Tests were conducted on a 170 kVA MFDC spot welder. Data were collected via a multichannel high-speed data acquisition system and were analyzed with MATLAB. Behaviors of 5182 aluminum and mild steel in spot welding were compared. Results show that nugget expansion rate does not reach zero for aluminium as it does for mild steel as nugget grew to a certain size. A linear relationship is found between the nugget size and maximum expansion that facilitates online weld quality evaluation. An electrode force peak is observed and believed relevant to the sufficient nugget size.     

Optimal design of high temperature vacuum furnace using response surface method

A new method using the response surface method and optimization technique has been developed instead of the original method based on trial and error. In order to construct a response surface, thermal analysis was performed under the condition of using the calculated thermal conductivity of the insulator in a previous study. In order to set up the response surface, the D-Optimal method was used in the process of selecting experimental points. Using a weighting factor, an optimization study was carried out under the condition of satisfying user requirements. Finally, the merits and drawbacks of the new method were described by comparing with the optimal design method based on the thermal analysis database which was developed in a previous study. The optimal results show that the developed method can be used to design an energy efficient, low manufacturing cost, high temperature vacuum furnace with avoiding unnecessary iterative manufacturing, and anticipating the performance before manufacturing. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon     

Development of fuzzy controller for inverter DC resistance spot welding using system identification

Journal of Mechanical Science and Technology - Adaptive Resistance spot welding (RSW) technologies have been developed and applied within the automotive industry to improve the weldability of...     

Forging force in resistance spot welding: analyzing the electrically generated forging force for two different electrode actuations

The forging force effect on resistance spot welding field is an ambiguity because it is believed to be just a mechanical force escalation in the classical theory. So far, the mechanically generated forging forces have been observed by many researchers and only the mechanical features have been considered for the investigation. Unfortunately, the journey of this exploration has not been continued after several superficial results were found for the past few decades. In real, there are still some cohesive existences of forces that have not been properly expounded yet, although it has frequently been noticed by other researchers. In this paper, the electrically generated forging force is introduced and also discussed for better realization. Several case studies for the fluctuation of electrode forces in terms of forces, vibrations, and acoustic emissions are primarily referred to support the classical concerns. With the inconstant and inaccurate force exertion, a computational analysis is derived as to distinguish the electrically generated forging forces with respect to the variation of process variables. Four types of metals are welded with two different electrode actuations and the corresponding force profiles are carefully measured. Only the stainless steel weld-based signals are presented in this paper to simplify the analysis because other materials too have similar phenomena. Experimental results show that the electrically generated forging forces are directly proportional to welding current, welding time, and compressing force but inversely proportional to electrode tips, provided the computation lies within welding lobe limits.

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Effects of welding parameters on electrode element diffusion during micro-resistance spot welding

Copper electrodes are commonly employed in micro-resistance spot welding (MRSW), a dominant process used to join ultra-thin metallic sheets. During welding, some copper from the electrodes inevitably diffuses into the spot welds, changing the chemical compositions and properties of the resulting welded joints. In this study, 0.05-mm-thick Ti alloy metallic sheets were welded via MRSW under various combinations of welding parameters (ramping time, welding time, holding time, welding current, and electrode force). The effects of these welding parameters on electrode elemental diffusion were investigated via elemental analysis. Elemental composition of welded joints was measured via energy-dispersive spectrometry after tensile-shear tests. No copper was detected in the heat-affected zone or base material, but the amount of copper in the welding nuggets varied significantly with the welding parameters. Moreover, comparing copper element and hardness maps in weld nugget, the welding nugget hardness increased when more copper diffused into it.     

一种基于模型的点焊电流有效值实时算法

焊接电流有效值是电阻点焊最重要的工艺参数和控制变量.现行的焊接电流有效值测量方法均不能同时满足测控的准确性和实时性,严重影响焊接过程控制的平稳性和焊接质量.基于电阻焊焊接回路数学模型,提出电阻焊电流有效值算法--过零导数法,使用微型洛氏线圈直接测量电流变化率并据此实时计算电流有效值.采用仿真数值离线训练的人工神经网络在线计算模型参数,简便的信号检测方法和简洁的计算形式保证该算法良好的实时性和准确性.在以DSP为核心的点焊质量实时监控系统中实现了基于神经网络拟合函数的实时计算.实验结果证明该算法是有效的.     

Optimal robot placement using response surface method

This paper is concerned with a new approach for optimal placement of a prescribed task in the workspace of a robotic manipulator. The approach is resulted by applying response surface method on concept of path translation and path rotation. A robotic optimization tool based on this approach is developed as an add-in to RobotStudio. The methodology has been carefully verified by optimizing the position of several kinds of industrial robots and paths in four showcases to attain minimum cycle time. The results indicate that an increase in productivity up to 37%, compared to the admissible location with the highest cycle time, is achieved by optimally positioning the task in the robot workspace.     

薄板点焊热过程的有限元分析

基于ANSYS有限元分析系统,建立用于点焊瞬态热过程分析的电热耦合有限元模型,考虑随温度变化的材料特 性参数、相变以及对流边界条件等,对点焊过程中的接触问题进行适当简化。通过对低碳钢薄板点焊过程的分析,得到 点焊接头的温度场及各部位的热历程,模拟了焊核形成过程,求得焊核及热影响区的形状和尺寸。     

Modeling small-scale resistance spot welding machine dynamics for process control

Electrode displacement is generally regarded as a variable that can provide real-time information useful for monitoring and controlling resistance spot welding (RSW) process quality. However, in small-scale RSW production, it is difficult to measure the displacement because its magnitude is very small. By contrast, force signals are relatively large and thus are less susceptible to measurement noise. In this article, an empirical model is proposed to simulate the dynamics of an SSRSW head with the objective of calculating electrode displacement from the variation of electrode clamping force measured during welding. The parameters in the model were determined by fitting experimental force and displacement signals with polynomials and then performing an optimization search for parameters of first-order dynamic models. To verify the models’ accuracy, they were subsequently applied to simulate the electrode displacement curves of welds with expulsion and without expulsion. The calculated displacement curves agreed well with experimental measurements, and the occurrence of expulsion was clearly indicated by the model predictions. A more comprehensive model is under construction with an objective to eliminate displacement sensor in the monitoring and control of SSRSW process.     

Optimal design of a variable stiffness joint in a robot manipulator using the response surface method

The response surface method combined with the design of experiment-based design optimization of a variable stiffness joint (VSJ) is presented in this article. A VSJ used in a manipulator of a robot arm to support 1 kg payload at the end is designed by considering the minimization of the total weight as the objective function. Owing to the requirement of large rotational stiffness of the VSJ, over 10 N · m, ring-type permanent magnets are adopted. First, a model composed of two permanent magnets was initially manufactured and tested for comparison with the analysis results. Then, a three-ring-type permanent magnet-based model is suggested and optimized to increase the torque of VSJ. The finite element method is used as a magnetic field analysis method to substitute for the expensive experimental process. Optimization results decrease the weight from 0.899 kg to 0.538 kg, still satisfying the requirement for the rotational stiffness. This paper was recommended for publication in revised form by Associate Editor Tae Hee Lee Jeonghoon Yoo received his B.S. and M.S. degrees in Mechanical Design and Production Engineering from Seoul National University, in 1989 and 1991, respectively. He then received his Ph.D. degrees from the University of Michigan, Ann Arbor, in 1999. Dr. Yoo is currently a Professor at the School of Mechanical Engineering at Yonsei University in Seoul, Korea. Dr. Yoo’s research interests include analysis and design of electromagnetic field systems. Myung Wook Hyun received his B.S. and M.S. degrees in Mechanical Engineering from Yonsei University, Korea, in 1995 and 1997, respectively. While studying for his M.S. degree, Mr. Hyun also studied variable stiffness unit design. He is now working at Samsung Electronics, Co. Ltd.. Jun Ho Choi received his B.S. and M.S. degrees in Mechanical Design from Hanyang University, Korea and his Ph.D. degree from the University of Michigan, Ann Arbor. He is currently a senior research scientist in the Korea Institute of Science and Technology. His research interests include nonlinear control, manipulator control, and safe-joint design. Sungchul Kang received his B.S., M.S., and Ph.D. degrees in Mechanical Design and Production Engineering from Seoul National University, Korea, in 1989, 1991, and 1998 respectively. Dr. Kang is currently a Principal Research Scientist in the Center for Cognitive Robotics Research, Korea Institute of Science and Technology, in Seoul, Korea. Dr. Kang’s research interests include mobility and manipulation of field and service robots and haptics. Seung-Jong Kim received his B.S. degree in Mechanical Engineering from Seoul University, Korea, in 1989, and his M.S. and Ph.D. degrees from KAIST in 1991 and 1998, respectively. Dr. Kim is currently a Principal Research Scientist at the Korea Institute of Science and Technology in Seoul, Korea. Dr. Kim’s research interests include the design, control, and dynamic analysis of mechatronic systems.     

基于响应面分析法的货叉关键尺寸参数优化设计

叉车货叉作为物流设备的重要组成部件,受载情况复杂多变,易产生高应力区域,甚至导致疲劳破坏。货叉的传统设计方法是通过经验法或实验法来确定货叉关键尺寸参数,该方法可靠性低,设计周期长。采用响应面分析法(Response Surface Methodology,RSM)对货叉关键尺寸参数进行优化。首先将货叉结构中各个加强筋的主要尺寸离散为7个关键尺寸参数,采用有限元灵敏度分析法得到了各个参数对货叉力学性能的响应关系;然后以货叉小变形、低应力和轻量化作为优化目标,采用响应面分析法中的中心组合设计(Central Composite Design,CCD)对80组样本进行了优化,在不增加货叉质量的情况下,最大应力减小了8.8%。基于响应面分析法的货叉关键尺寸参数优化设计方法已应用于诺力某型号叉车,取得了良好的优化效果,为类似的结构设计提供了一种有效可行的设计方法。     

双目立体视觉检测系统正向最优化设计方法研究

立体视觉技术在工业检测中的应用越来越广泛,如何提高检测精度、降低系统构建难度至关重要。本文提出了一种视觉检测系统正向设计最优化方法,以系统的检测精度为目标函数,以可选器件、工作环境、被检工件为约束条件,以光学参数和系统参数为决策变量,将系统设计问题转化为多目标不等式约束的非线性最优化模型,通过Kuhn-Tucker约束条件极值点的求解,获得最优的系统设计参数。本方法为立体视觉检测系统的设计提供了理论参考,可避免传统逆向设计方法中依赖主观经验而无法确认结果的最优性,以及大量反复试验而造成设计成本浪费等问题,实验验证了方法的可行性。     

一种气动点焊模拟系统

为模拟工业现场的工件焊接,采用典型气动元器件,开发了一套气动点焊模拟系统,该系统主要完成工件的传送和点焊。介绍了系统的整体结构、动作流程、气动回路以及采用可编程序控制系统的软硬件设计。所设计的气动点焊模拟系统典型美观,运行可靠,满足各项要求。     

响应面方法在机构设计中的应用

基于响应面方法和完全因子法在机构设计中的应用,以甜玉米脱粒机输送机构设计为例,利用MSC.ADAMS和Insight软件建立输送机构的虚拟样机模型.根据响应面模型,利用多项式回归分析将随机、不确定性参数对系统性能均值和波动性的影响综合起来考虑,优化了甜玉米脱粒机输送机构的设计参数,获得目标响应和参数的函数关系,为机构精确设计提供了依据.