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In manual assembly systems, workers' differences in terms of skills, level of expertise and perceived physical effort largely affect the assembly line balancing and system performance. Traditional long-term strategic decisions may not respond to workforce changes and needs, resulting in frequent requests for line rebalancing. In this study, we propose a methodological framework and an easy-to-use Assembly Line Worker Assignment and Rebalancing Problem with different options: workers' assignment considering their performance variability, integration of worker dependent physical exertion constraints and possibility to use trainers to assist inexperienced workers. A bi-objective linear programming model is proposed aiming to minimise the cycle time and the number of reassigned tasks to respect the initial design while integrating new workers with different characteristics. The ϵ -constraint approach is used to build Pareto frontiers for this bi-objective problem. This approach is applied to three real cases. The obtained results show that the developed model can be successfully used in manufacturing companies to help the production managers to deal with workforce turnover and skills heterogeneity. [ABSTRACT FROM AUTHOR]

In an assembly system, balancing the line and designing the part feeding setting play a fundamental role in guaranteeing efficiency and effectiveness. Although these two aspects are interrelated, they are usually performed subsequent to each other, with the part feeding decisions only being made once the line has already been balanced. However, the simultaneous solving of the assembly line balancing and part feeding problems can lead to interesting benefits. In this paper, an innovative approach for solving the Joint Assembly Line Balancing and Feeding Problem (JALBFP) is proposed, to achieve an integrated balancing of assembly tasks and parts picking/kitting and a fully synchronised assembly-feeding system. The aim is to minimise the operational system cost, including workforce, space and transportation costs. The Mixed Integer Linear Programming (MILP) model is applied to several instances and two case studies and compared to a hierarchical approach. The proposed model leads to a significant improvement in reducing the number of assembly stations required and the inventory level at the line, where space is notoriously scarce, also avoiding workforce oversizing in the feeding system. The strength of the model relies on its formulation and on its versatility, which makes it applicable to different assembly sectors. [ABSTRACT FROM AUTHOR]

Ergonomics has a significant impact on productivity and human safety in manual assembly lines. For this reason, several studies in recent years have proposed including ergonomics in assembly lines. However, most works are focused on simple assembly lines, while only a few studies exist for mixed-model assembly lines (MMALs). Thus, in this paper, we propose a new methodological approach to include physical fatigue and rest allowance (RA) as ergonomic parameters in MMAL problems. For the balancing problem, we propose a linear mathematical model that minimises the cycle time by including RA. For the sequencing decision, we develop a heuristic approach that assigns workers to workstations according to the workers' age and their related maximum physical capacity. Then, we propose a linear sequencing model that minimises the work-overload by also evaluating RA to assign each worker according to her or his features. Finally, to complete the study, we test the mathematical models in a real case application and provide a detailed discussion of the results to highlight the benefits we can achieve with this approach. [ABSTRACT FROM AUTHOR]

In several occupational sectors, workers are daily exposed to vibrations induced by automatic, pneumatic, or electric tools, with a consequent increase of musculoskeletal disorders. In this paper, a bi-objective manual assembly line design model is proposed, aiming to avoid excessive daily vibration exposures. The developed model allows to minimise both total equipment costs and vibration levels by respecting the threshold values defined in the ISO 5349-1. The ϵ-constraint approach is used to address both objectives and to find the Pareto frontier. The model is applied to several instances to evaluate the computational limit of the solving method, as well as to an industrial case to provide managerial guidelines. The results show that the method can solve small and medium size instances. Moreover, the case study points out that safe vibration exposure levels can be achieved also with a low additional investment and that solutions equal from an economic point of view can be different from a vibrations exposure one. [ABSTRACT FROM AUTHOR]

The effects of workforce differences on manufacturing systems have attracted the attention of a wide range of researchers in recent years. The differences between workers in terms of skills, age, gender and anthropometric measures have a large impact on production system performance. In this study, the workforce differences factors in production system design and modelling were investigated, with the aim of understanding how the differences between workers could influence a production system and how they had been considered in previous studies. The papers selected from the Scopus database were categorised based on whether how human factors are incorporated into manufacturing system optimisation and design approaches is discussed therein or is not. To find relevant papers, two sets of keywords were defined: (1) keywords relating to the differences between workers and (2) keywords relating to the kind of problem under study. Furthermore, the investigated papers helped highlight the strengths and weaknesses of the existing literature and derive a discussion on the possible future research steps. [ABSTRACT FROM AUTHOR]

Ergonomic aspects have a crucial role in manual assembly systems. They impact on the workers' health, final product quality and productivity. For these reasons, there is the necessity to integrate them into the assembly line balancing phase as, whereas, only time and cost variables are considered. In this study, human energy expenditures are considered as ergonomic aspects and we integrate them, for the first time, into the assembly line balancing problem type 2 through the rest allowance evaluation. We consider as an objective function the minimization of the smoothness index. Firstly, a new optimal method based on mixed integer linear programming and a new linearization methodology are proposed. Then, a heuristic approach is introduced. To complete the study, a computational experimentation is presented to validate the mathematical model and to compare the methodologies proposed in terms of computational time, complexity and solution. Additionally, we provide a detailed analysis of the impact that rest allowance evaluation can have on productivity comparing the results obtained, taking into account the rest allowance integration before, during and after the assembly balancing process. [ABSTRACT FROM AUTHOR]

The human-centered workplace design philosophy and the operator 5.0 concepts are gaining ground in modern industries moving through the personalization of the operators' workplace for improving workforce well being and capabilities. In such a context, new assistive technologies, such as passive exoskeletons, are good candidates to be wisely adopted in manufacturing and logistics systems. A growing interest in these devices has been detected over the last years, both from an academic and company perspective, with an increasing number of design solutions and tests according to their field of application. Aiming to investigate the current state of the art, we propose a literature review focused on passive exoskeletons for manufacturing and logistics (M&L) systems. We categorize the exoskeletons assessment in relation to the M&L tasks in which they are applied to give the reader an easy and direct insight into the exoskeleton performance in real settings. Further, the impact of the exoskeleton deployment from an efficiency perspective and its cost-effectiveness evaluation are provided. Finally, a maturity heat map is proposed to track the maturity level of different exoskeletons by focusing on a set of scientific and industrial domains. A discussion and a future research agenda are also provided by focusing on the managerial implications of investing in these devices. [ABSTRACT FROM AUTHOR]

The paper presents a systematic literature review on big size product manufacturing systems in MTO and ETO environments. In particular, the analysis is focused on highly customised, big and heavy products, calling for highly engineering solutions. This kind of products are characterised by low-volume demand, complex material bills, need of more than one worker in the same workstation (caused by the component dimensions and complexity), multi-skilled human resources and large floor space requirements. The analysis involved 587 research articles published from 1981 to 2017 from 118 international journals in the area of production research and operation management. Finally, 160 papers have been individuated and clustered in three main research topic area: specification processes and product design, production planning and control, project portfolio management. Results indicate that research focused on optimising and managing a large-size product manufacturing system is gaining growing attention in the last ten years. However, product/process design, production planning and control and project management techniques still lack innovations and ad hoc methods, capable to take into consideration both in-house part feeding problems, both ergonomics issues present in this kind of manufacturing environments. [ABSTRACT FROM AUTHOR]