Robust fixture layout design for multi-station sheet metal assembly processes using a genetic algorithm

The optimal fixture layout is crucial to product quality assurance in the multi-station sheet metal assembly processes. Poor fixture layout may lead to product variation during the assembly processes. In this paper, a genetic algorithm (GA)-based optimisation approach has been presented for the robust fixture layout design in the multi-station assembly processes. The robust fixture layout is developed to minimise the sensitivity of product variation to fixture errors by selecting the appropriate coordinate locations of pins and slot orientations. In this paper, a modified state space model for variation propagation in the multi-station sheet metal assembly is developed for the first time, which is the mathematical foundation of optimal algorithm. An e-optimal is applied as the robust design criteria. Based on the state space model and design criteria, a genetic algorithm is used to find the optimal fixture layout design. The proposed method can greatly reduce the sensitivity level of product variation. A four-station assembly process of an inner-panel complete for a station wagon (estate car) is used to illustrate this method.     

A Bayesian network approach for fixture fault diagnosis in launch of the assembly process

Verification and correction of faults related to tooling design and tooling installation are important in the auto body assembly process launch. This paper introduces a Bayesian network (BN) approach for quick detection and localisation of assembly fixture faults based on the complete measurement data set. Optimal sensor placement for effective diagnosis of multiple faults, structure learning of the Bayesian network and the diagnostic procedure are incorporated in the proposed approach. The effective independence sensor placement method is used to reach the desired number of optimal sensor locations, which provide the concise and effective sensor nodes to build the diagnostic Bayesian network. A new algorithm based on conditional mutual information tests is put forward to learn the Bayesian network structure. The body side assembly case was used to illustrate the suggested method and the simulation analysis was performed to evaluate the effectiveness of the diagnostic network. The work demonstrated that the proposed methodology composes a feasible and powerful tool for fixture fault diagnosis in launch of the assembly process.     

Risk-oriented assembly quality analysing approach considering product reliability degradation

Assembly process is a critical stage in the formation of product quality and reliability, but related consideration of the produced product reliability and accident risk has not attracted deserved attention in the most assembly quality analysis frameworks. To this end, this paper enhances risk analysis in assembly process quality control, which is advocated by ISO 9001:2015, and presents a risk-oriented assembly quality analysis approach considering the effects of assembly variations on the produced product reliability degradation and accident risk. First, a conceptual QRR chain is presented to illustrate the relationship among assembly process quality (Q), product reliability (R), and failure accident risk (R). Second, a risk-oriented and bidirectional framework for the analysis of assembly process quality is established based on the presented QRR chain aiming to quantitatively identify the risk sources in the assembly process and reduce the risk of failure accidents. Third, an assembly process quality risk model with key function reliability as its core is presented to establish the quantitative relationship between assembly variation and product failure accident risk. Finally, the presented approach is verified through a case study of an assembling quality risk analysing for acid-resistant grinder.     

A cost model for optimal mix of balanced stochastic assembly line and the modular assembly system for a customer oriented production system

A coat model is presented in this paper for balancing a stochastic assembly line where the incompletions on the line are handled on the basis of a modular assembly concept. The model proposed is a modification of the approach by Kottas and Lau and incorporates the provision of task times being greater than the cycle time for a customer oriented production system offering structural variations in the product. The assembly line was simulated using the balance obtained by the proposed model for estimation of in-process-atorage capacity for physical layout and design of the assembly line.     

基于VRML模型的协同装配工艺规划仿真方法

在研究了虚拟现实建模语言(VRML)模型特点以及协同装配工艺规划过程的基础上,将以VRML三维模型为设计信息载体的协同装配工艺规划仿真分为无约束的规划仿真和基于约束的规划仿真,并提出了相应的实现方法.所提方法使网络化的同步协同装配规划操作成为可能,通过实时交流,使产品装配工艺规划能够在集合多方设计经验的基础上方便快捷地实现.应用实例的应用结果表明,所提方法可快速发现设计缺陷并显著地缩短产品工艺规划周期.     

A quality control method for complex product selective assembly processes

Selective assembly is an important step during the manufacturing process for a complex product to meet precision requirements. The high precision requirement of complex product often results in producing a large number of surplus components in selective assembly process current practices. In this paper, we develop a comprehensive model which permits the integration of machining process parameters design, variation analysis and fault diagnosis, process adjustment and control strategy, process capability index calculation and matchable degree calculation. The model can be applied to evaluate and improve product, process and system design at early development stages, or support the improvement of matchable degree for a complex production selective assembly process. In this model, we have introduced a navel concept of general matchable degree for a multiple components selective assembly process. The implementation procedure and functional modules of the proposed model are given in details with an industrial case presented to illustrate the implementation of the proposed method.     

Linear and Integer Programming

Coordinate sensing systems have been widely used in various manufacturing processes to monitor product quality and automatically identify process faults. They play a crucial role in manufacturing quality improvement. For complex manufacturing processes, especially processes with multiple stages, typically not all process faults can be uniquely identified by a feasible sensing system. For these complex processes, a diagnosability study is an important issue for the evaluation and usage of coordinate sensing systems. This article conducts a diagnosability study of coordinate sensing systems based on matroid theory. The use of matroid theory improves understanding of existing results on diagnosability. In addition, new results and more efficient algorithms related to diagnosability study are investigated based on matroid theory. The developed theory and algorithms, which can be applied in a broad class of diagnosis problems, are demonstrated using a panel assembly process.     

基于机器视觉的电视机背板检测及自适应抓取研究

机器视觉广泛应用于装配、制造和加工等工业领域,用来保证产品质量,控制生产流程。将图像处理技术应用于自动化装配生产线,对电视机背板质量进行在线检测。为了实现对不同型号和尺寸的电视机背板的抓取,使用图像模板匹配方法确定当前背板的型号和检测当前背板的品质,并开发基于采集图像的视觉伺服自适应控制系统,该控制系统以西门子 PLC（programmable logic controller,可编程逻辑控制器）作为控制核心,通过串口通信实现PLC与Halcon软件的数据对接。使用Halcon中的工具箱对电视机背板采集图像进行运算以抽取目标的特征,并分析出抓取过程的坐标值,进而根据判别的位置坐标误差结果来控制步进电机调节偏移量以实现自适应抓取过程。针对图像处理后产生的电视机背板位姿累计误差,设计了一种标准模板中心参数值与增量误差值求差的方法,对背板位姿视觉定位误差进行补偿。通过抓取实验验证了视觉伺服自适应控制系统的可靠性较高,能满足自动化装配的工业生产需求。在生产实际中,电视机背板自动检测及抓取平台的应用能极大地提高电视机生产效率、节约人工成本、降低劳动强度和提高生产精度,该平台具有很好的应用前景。     

基于概率模型的光纤光栅传感网络优化布置

光纤光栅传感器相比与传统传感器,其特有的轴向敏感性决定了它的探测距离在传感器的不同方向上是有差异的,因此光纤光栅传感器的布置角度对于传感器网络的性能具有很大的影响。基于传统传感器的概率探测模型,本文提出了一种贴合光纤布拉格光栅传感器实际特点的探测模型,并通过实验验证了其正确性,继而利用这一模型,采用粒子群优化算法进行了光纤光栅传感网络的优化布置。最后,同不考虑布置角度的优化布置方法进行了比较,结果表明,在实际应用中考虑布置角度对于传感网络性能具有很大的提升。     

Quality design of tolerance allocation for sheet metal assembly with resistance spot weld

Tolerance directly influences the functionality of the products and the related manufacturing costs, and tolerance allocation is of great importance for improving the assembly quality. However, the information required to allocate tolerances for complex 3D assemblies is generally not available at the initial design stage. In this paper, a new quality design methodology is developed, which makes use of both original design data obtained by the response surface methodology and the extra interpolation data obtained by the Kriging method. The finite element modelling is presented for the sheet metal assembly process as no explicit relationship of the variations for key characteristic points are available. The robust tolerances can be allocated based on the quality design model. A case study with the typical assembly process of the rear compartment pan and the wheelhouse is carried out in the paper, the tolerance allocation results show that the developed quality design methodology is capable of determining the robust manufacturing tolerance before assembly, which satisfies the product requirements. This method enables a robust tolerancing scheme to be used in the sheet metal assembly process.     

民用航空发动机全生命周期全链路测量管理体系建设研究

为打破传统计量保障仅关注测量设备准确性而非测量结果可靠性的局限,构建了适用于民用航空 发动机全链路的测量过程控制管理体系。该体系以提升测量数据质量为目的,覆盖从部件设计到整机试验,从 适航取证到客户交付所涉及的全部产品测量过程。在测量过程设计阶段,根据测量需求及过程的关重程度,分 析测量能力,导出测量质量要求。在测量过程控制阶段,根据不确定度分析结果,锁定不确定度来源,利用测 量系统分析、控制图、测量能力审核等手段监控测量过程。在测量有效性验证阶段,结合科研阶段航空发动机 测量过程特点,建立同族测量过程归集,通过测量不确定度评定实现质量验证。该体系初期应用于厂内装配执 行过程“高压压气机转子装配”项目的测量分级、能力分析、过程监控、结果验证等,对实现包括试验验证、 生产制造等过程的全部相关方测量过程管理具有借鉴意义。     

Framework for designing a flexible cellular assembly system

Modern manufacturing companies have to face competition in a turbulent world market that requires them to improve their operating performances according to increasingly differentiated products with shorter life cycles, low volumes and reduced customer delivery times. The aim of the present paper is to develop a conceptual framework for the simultaneous design and control of a flexible, agile reconfigurable and robust assembly system in conjunction with the analysis and optimization of product, process, system structure, material-handling devices and plant layout. An effective solution for reconfigurability and agility in assembly to order and batch-type systems is a modular semi-automatic approach based on cellular flexible facilities: modularity, automation and human skills are combined to gain the advantages of mass production. Families of parts are produced in flexible cells, i.e. groups of various machines and resources that are physically close together and process one or more families of similar parts. The proposed approach is based on a multistage iterative procedure that integrates different supporting decision techniques and tools such as design for assembly, group technologies and cellular manufacturing. An application to the optimization of a semi-automatic flexible assembly system is illustrated: the system performances of example alternative solutions are presented and compared.     

Stochastic analysis and robust optimization for a deck lid inner panel stamping

FE-simulation and optimization are widely used in the stamping process to improve design quality and shorten development cycle. However, the current simulation and optimization may lead to non-robust results due to not considering the variation of material and process parameters. In this study, a novel stochastic analysis and robust optimization approach is proposed to improve the stamping robustness, where the uncertainties are involved to reflect manufacturing reality. A meta-model based stochastic analysis method is developed, where FE-simulation, uniform design and response surface methodology (RSM) are used to construct meta-model, based on which Monte-Carlo simulation is performed to predict the influence of input parameters variation on the final product quality. By applying the stochastic analysis, uniform design and RSM, the mean and the standard deviation (SD) of product quality are calculated as functions of the controllable process parameters. The robust optimization model composed of mean and SD is constructed and solved, the result of which is compared with the deterministic one to show its advantages. It is demonstrated that the product quality variations are reduced significantly, and quality targets (reject rate) are achieved under the robust optimal solution. The developed approach offers rapid and reliable results for engineers to deal with potential stamping problems during the early phase of product and tooling design, saving more time and resources.     

虚拟装配自动文本标注研究及在动车组中的应用

三维自动标注可明显提高复杂产品虚拟装配及虚拟样机技术的实用性。针对复杂产品虚拟装配实时文本标注复杂和效率低问题,提出交互式快速文本标注布局算法。算法通过预定义标注位置,建立文本压盖避让规则、动态调整标注规则,实现了移动三维模型点标注和左右标注快速自动布局。实例结果表明,该方法显著提高了复杂产品三维模型的可读性,增强了仿真的整体效果,提高了设计及培训效率。     

Assembly system facility design

This paper addresses the design of an assembly system facility consisting of multiple assembly lines of different shapes. In such a design problem there are two conflicting objectives: (i) to minimize the overall area of the facility; and (ii) to maximize the efficiency of the material handling transportation system. We first address the optimization problem of objective (ii) when replacing objective (i) with a constraint on the facility area. We propose a mixed-integer linear program to determine the layout of a facility with given dimensions and with given assembly line areas and shapes (that cannot be changed due to technological considerations). In the layout model, the physical placement of each line within the facility is a decision variable. The objective function of the layout model is to minimize the distances traveled by material flow. Our performance analysis provides an indication of the maximal problem size that can be solved in a reasonable amount of time and we examine the effect of the problem parameters on the solution run time. This layout model is then incorporated into an efficiency frontier approach for facility design to address both objectives. Examples are presented to illustrate the use of the proposed facility design model.     

Assembly systems layout design model for delayed products differentiation

Frequently changing customers’ needs and market pressures motivate manufacturers to offer a wide variety of their products. Poor demand prediction and increased manufacturing complexities and managerial burdens are just a few symptoms of products variety proliferation. Applying a postponement strategy is an effective method for mitigating the complexities arising due to increased products variety and customisation. Delayed product differentiation (DPD) is a prerequisite for applying form postponement strategies, where the unique features that distinguish each product are added at the final stages of production. This paper introduces an innovative design methodology to derive and represent an assembly line schematic layout for delayed products differentiation. The proposed methodology incorporates product commonality analysis and feasible assembly sequences to synthesise the assembly line layout in a single integrated logical design framework, without pre-defining either the number or the positions of differentiation points along the line. Products commonality analysis is performed using cladistics techniques commonly used for biological classification. The classical cladistics was modified to take into consideration the precedence constraints, which are required to ensure the feasibility of assembly sequences. Real product variants are used to validate the proposed DPD assembly line layout design methodology and demonstrate its merits.     

Stewart结构六维力传感器力矩各向同性研究

对于stewart并联结构的六维力传感器,应用并联机器人机构学理论,根据传感器的静态数学模型,研究当坐标系建立在下平台的几何中心处时,传感器的力矩各向同性指标。利用空间模型理论对力矩各向同性进行了图谱分析,并研究了坐标系变化时的力矩各向同性指标,以此作为该传感器的结构优化设计和应用的理论依据。     

复合材料胶层光纤布格光栅应变监测优化配置研究

航空航天用复合材料粘接胶层在制造和服役过程中不可避免会产生各种缺陷和损伤。针对其粘接胶层缺陷和损伤检测,基于光纤光栅应变传感原理,提出一种针对复合材料胶接层结构应变监测的光纤光栅传感网络优化配置的方法。通过仿真和实验研究了埋入复合材料构件胶接层的光纤布拉格光栅传感器在静载作用下的敏感区域分布特性,分析了载荷位移与布拉格波长漂移的关系,建立符合光纤布拉格光栅传感器实际特点的探测模型,采用粒子群优化算法进行光纤光栅传感网络的优化布置,研究结果表明光纤布拉格光栅传感器位置经优化后,覆盖率得到明显提高。     

基于遗传算法的传感器优化配置

讨论了以损伤诊断为目标的传感器优化配置问题,以模态置信度MAC矩阵的最大非对角元为目标函数,将目标函数的极小化问题转换为适应度函数的最大化问题,采用遗传算法对传感器的配置进行组合优化,针对满足组合优化中的约束条件问题提出了二重结构编码遗传算法,取得了满意的优化结果。算例表明,该方法应用于海洋平台模型损伤诊断的传感器优化配置是可行的,其结果优于序列法。