Hybrid systems for planning and optimization of virtual assembly

Virtual assembly is the simulation of parts assembly processes by computer, analysing, evaluating and optimizing the feasibilities and procedures of assembly. It can thus avoid the potential problems and risks from designing to assembling. In this way, we can achieve the global optimization of the products and timely respond to the needs of the market. This paper presents a modelling framework for virtual assembly paths design and optimization of two objects on the basis of a class of hybrid system, which is applicable in many manufacturing environments. We propose an elementary hybrid machine containing time-driven and event-driven dynamics. We describe in detail a method of assembly paths design. The objective of optimization is evaluated in terms of time in the transition dynamics so as to make the problem more tractable. An explicit algorithm for deriving optimal assembly policies is developed. The optimal results indicate the feasibility and efficacy of the model and control algorithms.     

Multi-plant assembly planning models for a collaborative manufacturing environment

In a global supply chain, the components or parts of a product may be distributed and produced at various plants in a collaborative way for the purpose of expanding capacity and reducing costs. For an assembled product, the assembly operations for assembling the product may be performed at different assembly plants at various geographical locations. Therefore, in this collaborative manufacturing environment, it is required that one develops a multi-plant assembly planning model for organizing and distributing the assembly operations to the suitable plants for completing the final product. In this research, a multi-plant assembly planning model for generating and evaluating the multi-plant assembly sequences is presented. New graph-based models are developed to model and generate the assembly sequences. The feasible assembly sequences are analysed and evaluated based on several cost objectives. The multi-plant assembly planning model is formulated with the aim of minimizing the total of assembly costs and multi-plant costs. As a result, the optimized multi-plant assembly sequences can be obtained and each of the assembly operations is assigned to the suitable plant with a minimized cost. Example parts are tested and discussed.     

Augmented reality for assembly guidance using a virtual interactive tool

The application of augmented reality (AR) technology for assembly guidance is a novel approach in the traditional manufacturing domain. In this paper, we propose an AR approach for assembly guidance using a virtual interactive tool that is intuitive and easy to use. The virtual interactive tool, termed the virtual interaction panel (VirIP), is an easy-to-use tool that can be used to interactively control AR systems. The VirIP is composed of virtual buttons, which have meaningful assembly information that can be activated by an interaction pen during the assembly process. The interaction pen can be any general pen-like object with a certain colour distribution. It is tracked using a restricted coulomb energy (RCE) network in real-time and used to trigger the relevant buttons in the VirIPs for assembly guidance. Meanwhile, a visual assembly tree structure (VATS) is used for information management and assembly instructions retrieval in this AR environment. VATS is a hierarchical tree structure that can be easily maintained via a visual interface. It can be directly integrated into the AR system or it can alternatively act as an independent central control station on a remote computer to control the data flow of the assembly information. This paper describes a typical scenario for assembly guidance using VirIP and VATS. The main characteristic of the proposed AR system is the intuitive way in which an assembly operator can easily step through a pre-defined assembly plan/sequence without the need of any sensor schemes or markers attached on the assembly components. Several experiments were conducted to validate the performance of the proposed AR-based method using a monitor and a head-mounted display. The results show that the AR-based method can provide an efficient way for assembly guidance.     

An investigation of road crossing in a virtual environment

The reported study employed a virtual reality (VR) system, using a head mounted display (HMD), to investigate road crossing behavior in children and young adults. Younger children (aged 5-9 years) made the greatest number of unsafe road crossings and the oldest participants (aged >19 years) the fewest. Overall performance was better (fewer unsafe road crossings) in uniform speed than uniform distance trials, consistent with previous research suggesting that pedestrians base road crossing decisions on inter-vehicle distance rather than vehicle speed. Results are discussed in terms of road crossing behavior and the use of VR simulations in the study of pedestrian behavior.     

Stochastic assembly line balancing using beam search

This paper presents a beam search-based method for the stochastic assembly line balancing problem in U-lines. The proposed method minimizes total expected cost comprised of total labour cost and total expected incompletion cost. A beam search is an approximate branch and bound method that operates on a search tree. Even though beam search has been used in various problem domains, this is the first application to the assembly line balancing problem. The performance of the proposed method is measured on various test problems. The results of the computational experiments indicate that the average performance of the proposed method is better than the best-known heuristic in the literature for the traditional straight-line problem. Since the proposed method is the first heuristic for the stochastic U-type problem with the total expected cost criterion, we only report its results on the benchmark problems. Future research directions and the related bibliography are also provided in the paper.     

VRML虚拟现实网络互动仿真装配平台的研究

在计算机上实现了虚拟装配的流程以及运用VRML创建可视化的三维虚拟场景,提出了一种基于VRML和Java的虚拟现实构建方法,以增强VRML虚拟场景与外界的交互性,并通过实例提出了创建网络虚拟装配交互仿真的具体方案。该方法不仅可用于演示网络环境下的可视化装配,也适用于基于VRML的其它领域科学可视化。     

The Datum Flow Chain: A systematic approach to assembly design and modeling

Current CAD systems are part-centric and do not capture the underlying logic of an assembly at an abstract level. We need to make CAD systems assembly-centric. To be able to lay out, analyze, outsource, assemble and debug complex assemblies, we need ways to capture their fundamental structure in a top-down design process, including the designer's strategy for constraining the parts kinematically and locating them accurately with respect to each other. We describe a concept called the Datum Flow Chain to capture this logic. Most assembly problems occur due to ineffective datum logic or the choice of assembly procedures that are not consistent with the datum logic, if any, that was used to design the parts. The DFC relates the datum logic explicitly to the product's key characteristics, assembly sequences, and choice of mating features, and provides the information needed for tolerance analyses. Two types of assemblies are addressed: Type-1, where the assembly process puts parts together at their pre-fabricated mating features, and Type-2, where the assembly process can incorporate in-process adjustments to redistribute variation. Two types of assembly joints are defined: mates that pass dimensional constraint from part to part, and contacts that merely provide support. The scope of DFC in assembly planning is presented using several examples. Analysis tools to evaluate different DFCs and select the ones of interest are also presented.     

A comprehensive survey of augmented reality assembly research

In the past two decades, augmented reality(AR) has received a growing amount of attention by researchers in the manufacturing technology community, because AR can be applied to address a wide range of problems throughout the assembly phase in the lifecycle of a product, e.g., planning, design, ergonomics assessment, operation guidance and training. However, to the best of authors' knowledge, there has not been any comprehensive review of AR-based assembly systems. This paper aims to provide a concise overview of the technical features, characteristics and broad range of applications of ARbased assembly systems published between 1990 and 2015. Among these selected articles, two thirds of them were published between 2005 and 2015, and they are considered as recent pertinent works which will be discussed in detail. In addition, the current limitation factors and future trends in the development will also be discussed.     

基于网络的虚拟装配可视化技术研究

分析了在计算机上实现虚拟装配的流程及如何用VRML创建三维可视化的虚拟场景，提出一种基于VRML和Java的虚拟现实构建方法，用以增强VRML虚拟场景与外界的交互性，并以球阀为例给出了在网络上创建虚拟装配动画演示的具体方案．该方法不仅可用于演示网络环境下的可视化装配，也适合于其它领域基于Web的科学可视化。     

A modified multi-objective genetic algorithm for two-sided assembly line re-balancing problem of a shovel loader

This article deals with a real-life multi-objective two-sided assembly line rebalancing problem (MTALRBP) with modifications of production demand, line’s structure and production process in a Chinese construction machinery manufacturing firm. The objectives are minimising the cycle time and rebalancing cost, considering some specific constraints associated with the inevitable wait time, such as novel cycle time, idle time and balanced constraints. A modified non-dominated sorting genetic algorithm II (MNSGA-II) is proposed to solve this problem. MNSGA-II employs some problem-specific designs for encoding and decoding, initial population, crossover operator, mutation operator and selection operator. The great performance of MNSGA-II is demonstrated from two aspects: one is through the comparison between the representative results and current situation in the production system in terms of some ALs’ performance evaluation index, the other is utilising the comparison between the proposed MNSGA-II and two versions of initial NSGA-II in terms of ratio, convergence and spread.     

Case study: the impact of assembly reorientations on assembly time

Many prior-assembly planners have considered the number of assembly direction reorientations as an assembly sequence evaluation and selection criterion for assembly sequence planning. However, little study has been conducted to evaluate the effectiveness of the selected assembly sequences. This paper studies the impact of assembly direction reorientations on assembly time. Results of the case study show that, for both robot and human operator assembly processes, the number of reorientations in an assembly sequence has a significant impact on assembly time. The results support the study research hypothesis that using an assembly sequence which requires more assembly direction reorientations results in longer assembly time. The study conducted in this paper helps verify and quantify the importance and effectiveness of reducing the number of assembly direction reorientations in assembly sequence planning.     

A roadmap for Assembly 4.0: self-configuration of fixed-position assembly islands under Graduation Intelligent Manufacturing System

The layout of fixed-position assembly islands (FPAI) is widely used for producing fragile or bulky products. With the increasing customised demand and unique operation patterns, manufacturing practitioners are facing challenges on flexible and efficient production arrangement to meet customer demand, which lead to inappropriate assembly islands configuration, frequent setups and long waiting times in FPAI. Industry 4.0 comes with the promise of improved flexibility and efficiency in manufacturing. In the context of Industry 4.0, this paper proposes a 5-layer APICS (assembly layer, perception layer, interaction layer, cognition layer, and service layer) roadmap for transformation and implementation of Assembly 4.0. Following the 5-layer APICS roadmap, a Graduation Intelligent Manufacturing System (GiMS) is presented as the pioneering implementation in FPAI. A graduation-inspired assembly system is designed for FPAI at assembly layer. Internet of Things (IoT) and industrial wearable technologies are deployed for perception, connection, and collaboration among various manufacturing resources at perception and interaction layer. A self-configuration model is proposed at cognition layer for autonomously configuring optimal assembly islands and corresponding production activities to meet customer demand. Cloud-based services are developed for managers and onsite operators to facilitate their decision-making and daily operations at service layer. Finally, a demonstrative case is conducted to verify the feasibility of the proposed methods.     

虚拟环境中的产品装配技术

 利用虚拟环境作为人机界面来协助用户完成产品的装配活动是一个新的研究方向。本文主要介绍了在虚拟环境中进行产品装配所采用的一些技术,并着重讨论了虚拟装配的关键内容－虚拟装配规划系统的结构、功能、优点和存在问题。最后还了一个典型系统＝虚拟装配设计环境ＶＡＤＥ的体系结构和主要特点。     

基于虚拟装配的硬币自动包装机设计方法

为解决硬币处理困难的问题,研究和设计了一种新型台式硬币包装机.在开发过程中采用基于 3D 特征造型和虚拟装配等CAD 技术,应用Pro/E 软件实现了该硬币包装机的三维设计和数字化样机的建立;通过动态仿真和干涉分析,验证了设计方案的可行性.该方法为此种硬币包装机物理样机的制作,和日后产品结构的设计优化提供了快捷有效的途径.     

Modelling and analysis of selective assembly using Taguchi's loss function

An assembly is the integrative process of joining components to make a completed product. It brings together the upstream process of design, engineering and manufacturing processes. The functional performance of an assembled product and its manufacturing cost are directly affected by the individual component tolerances. But, the selective assembly method can achieve tight assembly tolerance through the components manufactured with wider tolerances. The components are segregated by the selective groups (bins) and mated according to a purposeful strategy rather than being at random, so that small clearances are obtained at the assembly level at lower manufacturing cost. In this paper, the effect of mean shift in the manufacturing of the mating components and the selection of number of groups for selective assembly are analysed. A new model is proposed based on their effect to obtain the minimum assembly clearance within the specification range. However, according to Taguchi's concept, manufacturing a product within the specification may not be sufficient. Rather, it must be manufactured to the target dimension. The concept of Taguchi's loss function is applied into the selective assembly method to evaluate the deviation from the mean. Subsequently, a genetic algorithm is used to obtain the best combination of selective groups with minimum clearance and least loss value within the clearance specification. The effect of the ratio between the mating part quality characteristic's dimensional distributions is also analysed in this paper.     

A framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance

Mechanical mechanisms with clearance abound in technological fields such as robotics, machine and steam turbine industry. The dynamic performance of these mechanisms in working condition can be achieved provided that the effects of the different on the mechanisms (such as mechanism dynamics, technological effects and thermal behaviour) are thoroughly understood. Virtual prototyping provides an integration of multi-domain dynamic simulation for the design and analysis process. In the current paper, a framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance is presented. A case study with such a simulation strategy is studied for the optimum design and analysis of the technological parameter.     

A framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance

Mechanical mechanisms with clearance abound in technological fields such as robotics, machine and steam turbine industry. The dynamic performance of these mechanisms in working condition can be achieved provided that the effects of the different on the mechanisms (such as mechanism dynamics, technological effects and thermal behaviour) are thoroughly understood. Virtual prototyping provides an integration of multi-domain dynamic simulation for the design and analysis process. In the current paper, a framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance is presented. A case study with such a simulation strategy is studied for the optimum design and analysis of the technological parameter.     

RFID-assisted assembly guidance system in an augmented reality environment

RFID technology provides an invisible ‘visibility’ to the end user for tracking and monitoring any objects that have been tagged. Research on the application of RFID in assembly lines for overall production monitoring and control has been reported recently. This paper presents a novel research on implementing the RFID technology in the application of assembly guidance in an augmented reality environment. Aiming at providing just-in-time information rendering and intuitive information navigation, methodologies of applying RFID, infrared-enhanced computer vision, and inertial sensor is discussed in this paper. A prototype system is established, and two case studies are presented to validate the feasibility of the proposed system.     

ASALBP: the alternative subgraphs assembly line balancing problem

Assembly line balancing problems basically consist of assigning a set of tasks to a group of workstations while maintaining the tasks’ precedence relations, which are represented by a predetermined precedence graph. However, one or more parts of a product's assembly process may admit alternative precedence subgraphs, which represent possible assembly variants. In general, because of the great difficulty of the problem and the impossibility of representing alternative subgraphs in a precedence graph, the system designer will decide to select, a priori, one of such alternative subgraphs. This paper presents, characterizes and formulates a new general assembly line balancing problem with practical relevance: the alternative subgraphs assembly line balancing problem (ASALBP). Its novel characteristic is that it considers the possibility of having alternative assembly subgraphs, with the processing times and/or the precedence relations of certain tasks dependent on the assembly subgraph selected. Therefore, solving this problem implies simultaneously selecting an assembly subgraph for each part of the assembly that allows alternatives and balancing the line. The potentially positive effects of this on the solution of the problem are shown in a numerical example. Finally, a simple mathematical programming model is described and the results of a brief computational experiment are presented.