Digital twins to enhance the integration of ergonomics in the workplace design

Recently, human-centered design has become one of the most promising approaches for improving the entire production process design. During the design phase, among the main important aspects to investigate, ergonomic performance of the workplace (WP) plays a key role. It is well known that design errors can lead to significant delays in the design and engineering of a production process, especially when it is related to a complex system such as the assembly line of an automotive industry. Prediction of the ergonomic performance, which is often coarsely considered during the design phase, can represent a fundamental step in preventing ergonomic issues since the early design phase of a production process, avoiding also negative consequences on line balancing. Based on a concurrent engineering (CE) approach, the aim of this paper is to present a framework that uses digital twins of stations in order to minimise the time necessary to develop and design a new assembly line. The application of this procedure will allow avoiding the possibility of realising a line that reveals ergonomic problems and correcting design errors during the design phase and not just during the production phase. In this way, it is possible to achieve great advantages in terms of cost avoidance for the correction of the design errors and in terms of time to market, which will be significantly reduced. A digital twin of a real station of a Fiat Chrysler Automobiles (FCA) assembly line is presented to validate the numerical procedure and the design approach proposed in this paper. Finally, numerical results, regarding the evaluation of an ergonomic index, were compared with experimental ones achieved by analysing data collected during an experimental session.     

Digital twin-based smart assembly process design and application framework for complex products and its case study

With rapid advances in new generation information technologies, digital twin (DT), and cyber-physical system, smart assembly has become a core focus for intelligent manufacturing in the fourth industrial evolution. Deep integration between information and physical worlds is a key phase to develop smart assembly process design that bridge the gap between product assembly design and manufacturing. This paper presents a digital twin reference model for smart assembly process design, and proposes an application framework for DT-based smart assembly with three layers. Product assembly station components are detailed in the physical space layer; two main modules, communication connection and data processing, are introduced in the interaction layer; and we discuss working mechanisms of assembly process planning, simulation, predication, and control management in the virtual space layer in detail. A case study shows the proposed approach application for an experimental simplified satellite assembly case using the DT-based assembly application system (DT-AAS) to verify the proposed application framework and method effectiveness.     

Assembly failures and action cost in relation to complexity level and assembly ergonomics in manual assembly (part 2)

Earlier studies have demonstrated strong relationships between manual assembly at high physical load levels and increased amounts of quality defects compared to assembly at low physical load levels. A recent Swedish interview study of engineers in design and manufacturing engineering indicated that assembly complexity factors are of additional importance for the assembly quality. The objective of this study was therefore to examine the significance of high and low complexity criteria and the relationships between assembly ergonomics and assembly complexity and quality failures by analyzing manual assembly tasks in car manufacturing. In total, 47 000 cars were analyzed and the results showed several significant correlations between assembly ergonomics and assembly complexity, assembly time, failures and action costs. The action costs for high complexity tasks were 22.4 times increased per task per car compared to low complexity tasks.     

An assembly oriented design framework for product structure engineering and assembly sequence planning

The paper describes a novel framework for an assembly-oriented design (AOD) approach as a new functional product lifecycle management (PLM) strategy, by considering product design and assembly sequence planning phases concurrently. Integration issues of product life cycle into the product development process have received much attention over the last two decades, especially at the detailed design stage. The main objective of the research is to define assembly sequence into preliminary design stages by introducing and applying assembly process knowledge in order to provide an assembly context knowledge to support life-oriented product development process, particularly for product structuring. The proposed framework highlights a novel algorithm based on a mathematical model integrating boundary conditions related to DFA rules, engineering decisions for assembly sequence and the product structure definition. This framework has been implemented in a new system called PEGASUS considered as an AOD module for a PLM system. A case study of applying the framework to a catalytic-converter and diesel particulate filter sub-system, belonging to an exhaust system from an industrial automotive supplier, is introduced to illustrate the efficiency of the proposed AOD methodology.     

A spatiotemporal information management framework for product design and assembly process planning reconciliation

This paper introduces an innovative framework for product design and assembly process planning reconciliation. Nowadays, both product lifecycle phases are quasi concurrently performed in industry and this configuration has led to competitive gains in efficiency and flexibility by improving designers’ awareness and product quality. Despite these efforts, some limitations/barriers are still encountered regarding the lack of dynamical representation, information consistency and information flow continuity. It is due to the inherent nature of the information created and managed in both phases and the lack of interoperability between the related information systems. Product design and assembly process planning phases actually generate heterogeneous information, since the first one describes all information related to “what to be delivered” and the latter rationalises all information with regards to “how to be assembled”. In other words, the integration of assembly planning issue in product design requires reconciliation means with appropriate relationships of the architectural product definition in space with its assembly sequence in terms of time. Therefore, the main objective is to provide a spatiotemporal information management framework based on a strong semantic and logical foundation in product lifecycle management (PLM) systems, increasing therefore actors’ awareness, flexibility and efficiency with a better abstraction of the physical reality and appropriate information management procedures. A case study is presented to illustrate the relevance of the proposed framework and its hub-based implementation within PLM systems.     

An approach to determine geometric feasibility to assembly states by intersection matrices in assembly sequence planning

In this article, an approach is described for the development of a process for the determination of geometric feasibility whose binary vector representation corresponds to assembly states. An assembly consisting of four parts is considered as an example. First, contact matrices generate the assembly's connection graph. The developing connection graph was used to model the example assembly. In the assembly's connection graph, each node corresponds to a part in the assembly, and edges in the graph of connections correspond to connecting every pair of nodes. Moreover, in the connection graph, each connection corresponds to an element in the binary vector representation. In the development of the approach, intersection matrices are used to represent interference among assembling parts during the assembly operation. Intersection matrices are defined to along the Cartesian coordinate system's six main directions. The elements of intersection matrices are constituted to Boolean values. Each element of binary vector representations includes a connection between a pair of parts. First, ordered pairs of parts are established. Then, Cartesian products, which are produced from these established ordered pairs of parts, are applied to Boolean operators. Finally, geometric feasibility of these binary vector representations is determined. In this work, some assembly systems are sampled and examined. Among these examples, six assembly sequences for a four-part packing system; two assembly sequences for a five-part shaft bearing system; 373 assembly sequences for a seven-part clutch system and assembly states have been investigated.     

Applying a fusion of wearable sensors and a cognitive inspired architecture to real-time ergonomics analysis of manual assembly tasks

High value manufacturing systems still require ergonomically intensive manual activities. Examples include the aerospace industry where the fitting of pipes and wiring into confined spaces in aircraft wings is still a manual operation. In these environments, workers are subjected to ergonomically awkward forces and postures for long periods of time. This leads to musculoskeletal injuries that severely limit the output of a shopfloor leading to loss of productivity. The use of tools such as wearable sensors could provide a way to track the ergonomics of workers in real time. However, an information processing architecture is required in order to ensure that data is processed in real time and in a manner that meaningful action points are retrieved for use by workers.In this work, based on the Adaptive Control of Thought—Rational (ACT-R) cognitive framework, we propose a Cognitive Architecture for Wearable Sensors (CAWES); a wearable sensor system and cognitive architecture that is capable of taking data streams from multiple wearable sensors on a worker’s body and fusing them to enable digitisation, tracking and analysis of human ergonomics in real time on a shopfloor. Furthermore, through tactile feedback, the architecture is able to inform workers in real time when ergonomics rules are broken. The architecture is validated through the use of an aerospace case study undertaken in laboratory conditions. The results from the validation are encouraging and in the future, further tests will be performed in an actual working environment.     

Soft computing framework for intelligent human–machine system design,simulation and optimization

 This paper proposes a novel soft-computing framework for human–machine system design and simulation based on the hybrid intelligent system techniques. The complex human–machine system is described by human and machine parameters within a comprehensive model. Based on this model, procedures and algorithms for human–machine system design, economical/ergonomic evaluation, and optimization are discussed in an integrated CAD and soft-computing framework. With a combination of individual neural and fuzzy techniques, the neuro-fuzzy hybrid soft-computing scheme implements a fuzzy if-then rules block for human–machine system design, evaluation and optimization by a trainable neural fuzzy network architecture. For training and test purposes, assembly tasks are simulated and carried out on a self-built multi-adjustable laboratory workstation with a flexible motion measurement and analysis system. The trained neural fuzzy network system is able to predict the operator's postures and joint angles of motion associated with a range of workstation configurations. It can also be used for design/layout and adjustment of human assembly workstations. The developed system provides a unified, intelligent computational framework for human–machine system design and simulation. Case studies for workstation system design and simulation are provided to illustrate and validate the developed system.     

Design of assembly lines with the concurrent consideration of productivity and upper extremity musculoskeletal disorders using linear models

Work-related musculoskeletal disorders (WMSDs) are common occupational diseases among assembly workers due to repetitive motions or heavy workloads. The conventional approaches to decreasing WMSDs in assembly workers usually focus on individual assembly work at the station level. These approaches, however, do not pay enough attention to work allocation at the whole assembly line level such as balancing ergonomic burdens among workers by proper work assignment. This paper presents a methodology that can be used to integrate ergonomic measures of upper extremities into assembly line design problems. Linear models are developed to link work-worker assignment to the upper extremity ergonomic measures based on a guideline from American Conference of Governmental Industrial Hygienists. These linear models allow ergonomic and productivity measures to be integrated as a mixed-integer programming model. The case studies of this paper show the new model can effectively balance and control exposure levels in the upper extremity while not significantly decreasing line efficiency. This research shows the potential to reduce the need of numerous task adjustments for ergonomic improvement after initial assembly line design in conventional trial-and-error based assembly task adjustment. Furthermore, these linearization methods can be generalized in order to incorporate other ergonomic measures in tabulated forms into assembly line design problems.     

Knowledge intensive Petri net framework for concurrent intelligent design of automatic assembly systems

The integration of design and planning of flexible assembly system has been recognized as a tool for achieving efficient assembly in a production environment that demands assembly with a high degree of flexibility. This paper proposes a concurrent intelligent approach and framework for the design of robotic flexible assembly systems. The principle of the proposed approach is based on the knowledge Petri net formalisms, incorporating Petri nets with more general problem-solving strategies in AI using knowledge-based system techniques. The complex assembly systems are modeled and analyzed by adopting a formal representation of the system dynamic behaviors through knowledge Petri net modeling from the specifications and the analysis of those models. A template is first defined for a knowledge Petri net model, and then the models for assembly system individuals are established in the form of instances of the template. The design of assembly systems is implemented through a knowledge Petri net-based function–behavior–structure model. The research results show that the proposed knowledge Petri net approach is applicable for design, simulation, analysis and evaluation, and even layout optimization of the flexible assembly system in an integrated intelligent environment. The integration of assembly design and planning process can help reduce the development time of assembly systems.     

新型防化发烟车RMST一体化设计与关键技术分析

针对我军装备可靠性维修性保障性测试性（RMST）设计中存在的问题,着眼防化发烟车任务特点和使用保障需求,提出将能执行任务率指标引入到新型发烟车RMST设计研制中,创建适用于防化发烟车的RMST设计流程、一体化设计定量指标体系和顶层参数数学模型,并对涉及到的系统工程设计、综合权衡优化、指标调整分配等关键技术进行分析。本文可为提高新型防化发烟车RMST设计水平提供一定的研究基础。     

基于构件模型的系统框架设计研究

研究利用Web Service技术思想和构件的强装拆性思想,将可复用的、基于构件的应用系统框架同内部的业务构件实现分离开来,研究目的是提高系统框架的可复用性.给出了一种对构件概念模型的定义,并命名为EC构件,同时定义了系统内部标准的构件概念模型;在分析基于构件的系统框架同构件模型之间关系的基础上,证明利用该系统框架可以实现构件的管理和互操作,从而使系统具有良好的可移植性、可复用性和可维护性.     

Measuring the physical demands of work in hospital settings: design and implementation of an ergonomics assessment

BACKGROUND: Assessing the physical demands of the heterogeneous jobs in hospitals requires appropriate and validated assessment methodologies. METHODS: As part of an integrated assessment, we adapted Rapid Entire Body Assessment (REBA), using it in a work sampling mode facilitated by a hand-held personal digital assistant, expanding it with selected items from the UC Computer Use Checklist, and developed a scoring algorithm for ergonomics risk factors for the upper (UB) and lower body (LB). RESULTS: The inter-rater reliability kappa was 0.54 for UB and 0.66 for LB. The scoring algorithm demonstrated significant variation (ANOVA p<0.05) by occupation in anticipated directions (administrators ranked lowest; support staff ranked highest on both scores). A supplemental self-assessment measure of spinal loading correlated with high strain LB scores (r=0.30; p<0.001). CONCLUSION: We developed and validated a scoring algorithm incorporating a revised REBA schema adding computer use items, appropriate for ergonomics assessment across a range of hospital jobs.     

Development of assembly system with quick and low-cost installation

ABSTRACT

Cell production systems for assembly operations generally require tool changes using several hands and a customized work table. The initial setting and resetting of the assembly system are costly. We implemented a system comprising the use of only two hands and without the requirement of tool changers. In addition, multiple sensors are used to perform tasks robustly to avoid errors. The peg-in-hole task is performed robustly against errors without the precise positioning of objects. The objective is to develop a system that is lean and agile and can be set up quickly. We evaluate this system based on the task-board and assembly tasks during the assembly challenge in the industrial robotics category of the World Robot Summit 2018.     

A new hybrid improvement heuristic approach to simple straight and U-type assembly line balancing problems

This paper presents a new hybrid improvement heuristic approach to simple straight and U-type assembly line balancing problems which is based on the idea of adaptive learning approach and simulated annealing. The proposed approach uses a weight parameter to perturb task priorities of a solution to obtain improved solutions. The weight parameters are then modified using a learning strategy. The maximization of line efficiency (i.e., the minimization of the number of stations) and the equalization of workloads among stations (i.e., the minimization of the smoothness index or the minimization of the variation of workloads) are considered as the performance criteria. In order to clarify the proposed solution methodology, a well known problem taken from literature is solved. A computational study is conducted by solving a large number of benchmark problems available in the literature to compare the performance of the proposed approach to the existing methods such as simulated annealing and genetic algorithms. Some test instances taken from literature are also solved by the proposed approach. The results of the computational study show that the proposed approach performs quite effectively. It also yields optimal solutions for all test problems within a short computational time.     

A PDES/STEP-based model and system for concurrent integrated design and assembly planning

Product data exchange and interfacing between different CAD/CAM systems are of great importance to the development of concurrent integrated design environments and computer integrated manufacturing systems. This paper presents a STEP-based method and system for concurrent integrated design and assembly planning. An integrated object model for mechanical systems and assemblies is first defined by a hierarchy of structure, geometry and feature. The structure is represented as a component-connector or joint multi-level graph with both hierarchical functional and assembly relations. These hierarchical relation models are then used for uniformly describing their causal relations both for assembly level and feature based single part level. The generic product assembly model is organized according to STEP, using mostly the entities of integrated resources and partly self-defined entities, which are necessary for design and assembly planning. Based on the generic product assembly model, STEP-based strategies and agent concepts are used for agent-based concurrent integration of design and assembly planning. A prototype system, consisting of a CAD system, a product modeling system, an assembly planning system, and an assembly evaluation system is developed, in which product data can be exchanged between these subsystems. Details about the implementation of the system are addressed. The integrated design and assembly planning system can support the introduction of a new product. The results of assembly planning are feedback to the stage of assembly design to improve on the design. A case study is carried out for assembly-oriented design of a gearbox, to illustrate the proposed approach and to validate the developed system.     

基于YII2框架的高校毕业设计质量管理系统设计

信息化时代,为提升高校教务管理水平,简化工作流程,基于当前毕业设计管理工作中存在的问题与不足,运用计算机与互联网技术,开发了一套毕业设计质量管理系统,实现论文指导工作的在线过程化管理。系统采用YII2框架实现业务逻辑功能,利用bootstrap前端技术实现手机页面自适应,使用FPDI_PDF-Parser文本分析技术实现文档水印生成,并连结MySQL数据库实现数据的存储与管理。在互联网环境中,允许师生通过电脑或手机随时随地地进行互动交流与信息查询,突破了传统论文指导工作在时间与空间上的限制。经过实际工作测试,系统运行稳定,扩展性强,能够满足高并发量的访问需求,方便师生开展论文指导工作的同时,也加强了管理部门对设计过程的监督与管理,具有较高的应用与推广价值。     

Impact of decision sequence of pricing and quality investment in decentralized assembly system

The quality and price of suppliers’ products directly influence the potential demand in the market. This paper studies the impact of decision sequence in a two-echelon assembly system with demand uncertainty: suppliers first decide wholesale price and quality investment for their components, and then the manufacturer decides product price after the uncertainty in demand is resolved. We consider three scenarios in the stage of suppliers’ decisions. In case 1, both suppliers simultaneously determine quality investment followed by the simultaneous setting of wholesale prices. In case 2, both suppliers make quality investment and wholesale price decisions simultaneously. In case 3, one supplier acts as a leader and moves first to announce quality investment and wholesale price, and the other supplier moves later. We compare all decision models from each firms’ perspective. Our analysis reveals that the second decision sequence is the best option for the manufacturer and the integrated supply chain and the first decision sequence is the best option for suppliers as a whole, but there is no clear dominating choice for each supplier. The optimal choices of suppliers are mainly determined by the cost structure. We examine and discuss the relation between system parameters and the incentives of suppliers in choosing decision sequence.     

Utilizing variant differentiation to mitigate manufacturing complexity in mixed-model assembly systems

A measure of product variety induced complexity has been proposed for mixed-model assembly systems with serial, parallel and hybrid configurations. The complexity model was built based on the assumption of identical parallel stations, i.e., same product variants are produced at all parallel stations in the same volume and with the same mix ratio. In this paper, the existing complexity model is extended to general mixed-model assembly systems with non-identical parallel stations in the presence of product variety. Then it is discussed that how to reduce the system complexity using the variant differentiation, based on which a mathematical formulation is developed to minimize the complexity of a mixed-model assembly system. The formulated problem is a non-linear programming problem and then solved by genetic algorithm. Last the developed complexity mitigation model is applied to the configuration selection of assembly systems, i.e., to identify the system configuration with the minimum complexity.