Assembly Jobs Research Articles

A matheuristic-based multi-objective evolutionary algorithm for flexible assembly jobs shop scheduling problem in cellular manufacture

The flexible assembly job shop scheduling problem (FAJSP) and its extensions have received increased attention. However, multi-objective FAJSP in cellular manufacture (FAJSP-CM), a real-world extension of FAJSP with important applications in the mass customization of complex products, is barely considered in most previous studies. Hence, this study first addresses the multi-objective FAJSP-CM problem via a mixed-integer linear programming model (MILP). Then, a matheuristic-based multi-objective evolutionary algorithm (MMOEA), with a matheuristic decoding method, knowledge-guided initialization and learning-based local intensification method, is presented to efficiently tackle the FAJSP-CM problem in polynomial-time. The matheuristic decoding method, which hybrids a decomposition linear programming model (D-LP) that can quickly and optimally allocate the execution times of all operations, to search for the optimal solution in a specific space. The knowledge-guided initialization is extended to get a high-quality and great-diversity initial population for accelerated convergence. Meanwhile, the learning-based local intensification method is developed to adaptively coordinate five problem-specific local search operators to enhance the exploitation ability of the MMOEA algorithm. Finally, comprehensive experiments based on 720 instances are conducted to evaluate the proposed MILP model and MMOEA algorithm. The results of the first experiments illustrate the MILP model can obtain the Pareto solutions of small-scale instances. The remaining experiments demonstrate that the proposed MMOEA algorithm outperforms its competitors by 0.21 and 0.72 in hypervolume ratio and coverage indictors, along with approximately a 25 % improvement in success rate.

Bin packing problem with restricted item fragmentation: Assignment of jobs in multi-product assembly environment with overtime

This paper studies the assignment problem of multi product assembly jobs to days. The problem aims to minimize the amount of overtime while avoiding assembly delays for jobs that can be fragmented into smaller sub-tasks. When sequence-dependent setup times are negligible, the problem considered transforms into the bin packing problem with restricted item fragmentation where jobs represent items and days stand for bins. We present a mixed integer programming model of the problem by extending earlier formulations in the literature. Computational experiments show that the mathematical model obtained optimal solutions for majority of instances tested within reasonable computation times.

Multi-Agent Reinforcement Learning for Real-Time Dynamic Production Scheduling in a Robot Assembly Cell

As industry rapidly shifts towards mass personalisation, the need for a decentralised multi-agent system capable of dynamic flexible job shop scheduling (FJSP) is evident. Traditional heuristic and meta-heuristic scheduling methods cannot achieve satisfactory results and have limited application to static environments. Recent Reinforcement Learning (RL) approaches that consider dynamic FJSP, lack flexibility and autonomy as they use a single-agent centralised model, assuming global observability. As such, we propose a Multi-Agent Reinforcement Learning (MARL) system for scheduling dynamically arriving assembly jobs in a robot assembly cell. We applied a Double DQN-based algorithm and proposed a generalised observation, action and reward design for the dynamic FJSP setting. Using a centralised training phase, each agent (i.e., robot) in the assembly cell executes decentralised scheduling decisions based on local observations. Our solution demonstrated improved performance against rule-based heuristic methods, for optimising makespan. We also reported the impact of different observation sizes of each agent on optimisation performance.

Collaborative assembly of electrical cabinets through multimodal interaction between a robot and a human worker with cognitive disability

Assembly production activities consist of arrays of actions many of which can be executed by workers with cognitive disabilities (WCDs). However, figuring out sequences of assembly from technical documentation is an unsurmountable barrier for most WCDs to access assembly jobs. Partnering with a collaborative robot (cobot) can provide the assistance required to access the job while also promoting efficiency and quality of production, as well as worker satisfaction. A cobot cell for the collaborative assembly of electrical cabinets is discussed here. Using evaluative research methodologies, formative user studies are reported to assess if stepwise guidance from a cobot may make WCDs eligible for such assembly job. Two of the requirements obtained from earlier prototypes are studied: control of the worker over the amount of assistance received from the robot, and the use of redundant or complementary multimodal input and output channels for interaction. The assembly guidance solution is evaluated in user studies with WCDs for whom assembling electrical cabinets was, until then, out of their reach.© 2020 The Authors, Published by Elsevier B.V.Peer review under the responsibility of the scientific committee of CIRP.

Selection of an industrial robot for assembly jobs using multi-criteria decision making methods

Selection of an industrial robot for assembly jobs using multi-criteria decision making methods

Wheel design and motion analysis of a new heavy-duty AGV in aircraft assembly lines

PurposeThe flexible automatic transportation and manual assembly jobs for large aircraft components demand an automated guided vehicle (AGV) system with heavy-duty capacity and omnidirectional movability. This paper aims to propose a four driving-steering wheels-four supporting-steering wheels (4DSW-4SSW) layout plan to enhance the controllability and moving stability of AGV.Design/methodology/approachThe anti-vibration structure of DS wheels and high-torque steering mechanism of SS wheels with tapered rolling bearings are rigorously designed to meet the functional requirements. Based on the specific wheel layout and vehicle dynamics, the rotational kinematic model as well as the straight and rotational dynamic models of AGV are established by the authors. To well verify the motion characteristics of wheels under heavy load in three motion states including straight motion, self-rotation and rotation around a certain point, the simulations in ADAMS and factory experiments have all been conducted.FindingsSimulation results indicate that normal and friction forces of DS wheels and SS wheels are very stable except for some small oscillations, which are caused by non-center load distribution on AGV. Experimental results on driving speed of AGV have directly demonstrated that its positioning accuracy is enough for use in real aircraft assembly lines.Practical implicationsThe designed AGV system has been applied to the final assembly line of a certain aircraft in Aviation Industry Corporation of China, Ltd, whose assembly efficiency and flexibility have been significantly improved.Originality/valueA new layout plan of wheels for an omnidirectional heavy-duty AGV is proposed, which enhances the operating and moving capacity of AGV. A function of human-machine collaboration is also offered by the AGV for transporting large workpieces intelligently and economically in aerospace and other heavy industries.

Rolling horizon production scheduling of multi-model PCBs for several assembly lines

The joint task of allocating several PCB assembly jobs to a set of production lines, load balancing of the line machines and job scheduling is considered. The production facility includes a number of assembly lines of different kinds, the PCB jobs are of different types and they should be allocated to suitable (i.e. feasible) lines. Scheduling of the production should respect the predefined release and due dates, and the objective is to minimise the sum of job tardy times. The scheduling is of the rolling-horizon-type where at the beginning of each planning period new jobs are inserted in the current non-preemptive production programme of unfinished jobs from the past planning periods. A mathematical formulation and a two-phase heuristic (including initial job-to-line allocation and schedule improving steps) are given for the problem. Experimental tests with jobs from practice were convincing.

Human-robot collaborative work cell implementation through lean thinking

ABSTRACT Industry 4.0 stresses the importance of considering production automation as an integrated and collaborative teamwork process between human workers and intelligent machines and tools. Collaborative robotics is a recent field of study for industrial automation. Although fenceless robot systems are available, the actual implementation of collaborative schemes for the conduction of assembly jobs should be supported through dedicated procedures and guidelines. These procedures have yet to be found and defined in detail. In this work, the authors claim that it may be possible to approach the problem of collaborative cell design with the methods devised for lean thinking. In the paper, the most common lean strategies are listed and analysed from the viewpoint of setting up a collaborative work cell. The most suitable strategies and tools are then recommended in a methodology that has been proposed to redesign an industrial assembly cell. The methodology has then been adopted in the presented industrial use case which is focused on the steps of HRC design process such as tasks assignment and scheduling.

Empowering assembly workers with cognitive disabilities by working with collaborative robots: a study to capture design requirements

Collaborative robots and personalised human-automation load balancing strategies may be able to empower workers with cognitive disabilities to carry out complex assembly tasks. To design such assembly cells, it is necessary to investigate the human factors associated with this user group in relation to the technology proposed. We present a qualitative pilot user study in which an assembly worker with cognitive disabilities and multidisciplinary experts meet a collaborative robot in the context of routine assembly jobs. We draw requirements for the design of such cells and we contrast them with design requirements for regular workforce.

Integrated modelling and algorithm of material delivery and line-side storage for aircraft moving assembly lines

This paper considers the material supply problem for aircraft moving assembly lines. Distinguished from general automobile assembly lines, multiple parallel jobs are assembled concurrently and durations of assembly jobs are quite long, thus amounts of materials are orderly stored at the line-side space at the same time. In addition, the line-side space should be reused in the time dimension. With these characteristics, decisions on line-side storage of materials were introduced on the basis of material batching and tow-trains scheduling problems. An integrated decision–making mathematical model with the objective of minimising the number of deliveries was established. A hybrid endocrine-immune algorithm (HEIA) was proposed to jointly make decisions on the delivery batch, delivery time and storage positions of each job’s materials. Numerical experiments with the real-world data and randomly generated instances validate the effectiveness and efficiency of HEIA.

An Empirical Analysis of Export-Led Growth of Vietnam: Trade in Value Added (TiVA) Approach

This paper examines the long-run relationship between domestic value added exports and economic growth of Vietnam using ARDL bounds test of cointegration on annual data covering the period of 1995-2014.The bounds test establishes existence of both short-run and long-run relationship between exports and GDP of Vietnam and shows a substantial contribution of exports in the real GDP (0.73 percent for one percent changes in the domestic value added exports). The exports pattern of Vietnam portrays it following the footsteps of export-led growth model of Mexico, whereby it has turned itself into export production platforms for MNCs by suppressing the wages, rather than developing own indigenous industrial capacity. In such scenario, it seems challenging for Vietnam to sustain its export-led growth which it has achieved so far based on its cheap labour. With the rising living standards, ultimately the comparative advantages of cheap labour force would vanish in the future, which will cause a wave of assembly jobs to flow out of Vietnam. Moreover, two other low-cost countries in the region, Cambodia and Myanmar are likely to rise as close competitors of Vietnam in the low-cost assembly works in the near future. By that time, in case Vietnam fails to enter into higher value added activities, it will drag itself into the ‘middle income trap’. Therefore, the ‘assembly strategy’ shall be bonded with strategy to develop own indigenous industrial capacity, and national technological base. These will help Vietnam to upgrade its activities along value chains in forms of product upgrading, process upgrading, functional upgrading, and sectoral upgrading so that it can switch its role of ‘assembling agent’ to ‘indigenous producer’.

Risk Factors of Carpal Tunnel Syndrome for Male Patient Undergoing Carpal Tunnel Release.

Although the major cause of carpal tunnel syndrome (CTS) remains idiopathic, many male CTS patients are clinically different from female patients and often have specific risk factors associated with their conditions. An accurate analysis of such propensity has yet to be established. The purpose of this study is to compare male and female patients by analyzing the risk factors associated with CTS patients who underwent surgical treatment, with focus on their occupation. retrospective chart review of 818 patients with CTS was performed to identify the associated risk factors. Patients were stratified by gender: female (n = 707, 86.4 %) and male (n = 111, 13.6 %). The mean patient age was 54.5 (range: 16-85 yr.) for all groups. The medical history and risk factors of each patient was thoroughly reviewed by medical charts and telephone survey. We categorized the risk factors of CTS into 7 categories: anatomic, neuropathic, inflammatory, alteration of fluid balance, distal radius fracture associated, occupational risk factor related, and idiopathic. Occupations of CTS patients were divided into high risk occupations (vibratory tools, assembly jobs, and food processing and packaging jobs, and other occupations of repetitive wrist motion and forceful gripping) and nonrisk occupations. All variables were analyzed with chi-square or Fisher's exact test for differences between men and women. The number of individuals with known risk factors of CTS was greater in male, compared to that of female patients; 97 (87.4 %) male patients had the risk factors of CTS, while 361 (51.1 %) female patients (p < 0.001) did. In subgroup analysis of risk factors, male patients had frequent risk factors in neuropathic, inflammatory, and alteration of fluid balance (p < 0.001). Occupational risk was strongly associated with male gender (p < 0.001). Male CTS patients who underwent surgery are more likely to have a reason and have many occupational risk factors than women.

Global Displacements: The Making of Uneven Development in the Caribbean by Marion Werner

Reviewed by: Global Displacements: The Making of Uneven Development in the Caribbean by Marion Werner Benjamin F. Timms Marion Werner Global Displacements: The Making of Uneven Development in the Caribbean Malden, MA and Oxford, UK: Wiley Blackwell, 2015. xii + 215 pp. Figures, tables, notes, references, and index. $34.95 paper (ISBN 978-1-118-94198-0); $94.95 cloth (ISBN 978-1-118-94199-7); $27.99 electronic (ISBN 978-1-118-94195-9). As part of the Antipode Book Series, Global Displacements fittingly adopts a critical approach to analyzing contemporary restructuring of the global garment industry. While focused primarily on the Dominican Republic and Haiti, it highlights continuing uneven development and inequality at multiple geographical scales, from the global to the regional, national to the local, and even to the individual including racialized and gendered aspects. It is important to note that the study is not a comparative study of the garment free-trade zones between these two countries, but a relational study of this industry within, and between, the Dominican Republic and Haiti over the past three decades. Encompassing both the structural forces at play and the impacts they have on local agency, the book also utilizes primary field research on household and individual livelihood strategies aimed to mitigate the negative impacts of these structural forces related to restructuring of the global garment industry. The first quarter of the book highlights the rise, fall, and restructuring of the export processing garment industry in the Dominican Republic. The first decade of the 2000s saw [End Page 253] a major global restructuring of the garment industry that negatively impacted low-wage assembly, leading to restructuring away from merely assembly to "full-package" suppliers that expanded into other value-added components of production including design, cloth production, and some finishing aspects. Adopting feminist approaches, the author analyzes increased gender inequality as females tended to remain in the lowest-wage assembly jobs while males predominated in the newer value-added positions due to cultured gender stereotypes, both locally and globally, that viewed females as unfit for more flexible or labor intensive activities (which is debated well in the text). Relatedly, female labor has been devalued and became more disposable with higher layoffs, although the author acknowledges that male labor also suffered during restructuring, just to a lesser and different degree. After the structural analysis of global factors resulting in national and local gender inequalities in employment, the author turns to individual examples of livelihood strategies created by both women and men stemming from massive layoffs in the mid-to-late 2000s. This section of the book addresses gender and racial differences in post-free-trade-zone employment, underemployment, unemployment, and informal activities in both urban areas and the rural countryside. The author expertly presents individual experiences in highlighting the gendered and racialized differences in livelihood strategies sought in order to create personal "social worth," a process the author terms "embodied negotiations" (p. 87). The latter sections of the book turn to the relational geography between the Dominican Republic and Haiti in restructuring the garment industry as a "spatial fix" akin to David Harvey's concept (p. 114). Dominican and U.S. corporations shifted their involvement from the Dominican Republic to the Haitian border and, after the 2010 earthquake, further along the northern coast of Haiti to access cheaper labor. The ties to Naomi Klein's "disaster capitalism" in this section is an insightful addition. After the earthquake, Haiti's World Bank and IMF Poverty Reduction Strategy Paper, which called for a focus on agricultural development, was shelved as international institutions and corporate interests focused national development on export-oriented free-trade zones. However, the free-trade zones faced substantial contestation from labor groups that problematized the projects, which was another insightful and well-crafted section of the book. Building on these disparate results and experiences the author mentions a few alternatives championed to resolve the negative impacts restructuring and global production have on local livelihoods. Ethical consumption, including such movements as fair trade and other certifications, are argued to be inadequate as they are still embedded in colonial capitalist exploitation and modern uneven capitalist development. Instead, collective worker struggles through unions...

Parametric Design of Scalable Mechanisms for Additive Manufacturing

Additive manufacturing allows a direct fabrication of any sophisticated mechanism when the clearance of each joint is sufficiently large to compensate the fabrication error, which frees the designers of cumbersome assembly jobs. Clearance design for assembly mechanism whose parts are fabricated by subtractive manufacturing has been well defined. However, the related standard for parts fabricated by additive manufacturing is still under exploration due to the fabrication error and the diversity of printing materials. For saving time and materials in a design process, a designer may fabricate a series of small mechanisms to examine their functionality before the final fabrication of a large mechanism. As a mechanism is scaled, its joint clearances may be reduced, which affects the kinematics of the mechanisms. Maintaining certain clearance for the joints during the scaling process, especially for gear mechanisms, is an intricate problem involving the analysis of nonlinear systems. In this paper, we focus on the parametric design problem for the major types of joints, which allows the mechanisms to be scaled to an arbitrary level while maintaining their kinematics. Simulation and experimental results are present to validate our designs.

Spatial and Temporal Patterns in Sequential Precision Reach Movements.

Introduction: Sequential reach tasks are a common component of manual assembly jobs. These tasks typically involve manipulating a work object or material and reaching to successive target locations...

A survey of leaning and bracing behaviours in an automotive assembly plant

It is common for workers to use objects within the task environment to externally support themselves, when performing a task. We refer to this as ‘leaning’, when using the contralateral hand for support, or ‘bracing’, when using the trunk, hips or thighs for support. However, currently, ergonomists are unable to predict when these behaviours will occur when performing proactive ergonomic assessments, leading to incorrect estimates of how the jobs will be performed. The purpose of this survey was to quantify the types of external support used by workers during automotive assembly tasks. 250 automotive assembly jobs were observed, and the external support behaviours were documented using a 13-item survey adapted from Jones et al. (2008). We observed that 103 jobs (41.2%) were performed with the use of leaning and/or bracing. Of those, workers leaned, braced, or used both behaviours simultaneously 54.5%, 22.0%, and 23.5% of the time, respectively. Leaning was most prevalent at a height of 150 cm, while bracing was most prevalent at a height of 50 cm. This survey catalogues the leaning and bracing behaviours from a large array of assembly jobs. The trends we have identified can be used by ergonomists to predict whether or not external support is likely to be used by a worker during a certain task.

Analytical Approach for the Examination of the Feasibility of Rework in Flow Assembly Lines

Since the beginning of the 20th century flow assembly lines are a global standard for manufacturing companies to produce serial products. The standardization and the allocation of assembly jobs in certain cycle times along the assembly line ensure productivity. All work operations in each cycle are allocated ideally in such a way that every operator uses the complete cycle time for the assembly jobs.One disadvantage of these flow assembly lines is the lack of time for possible rework operations. If a human error occurs, there is hardly any time for its correction. The alternative is to stop the line until the rework is done. These situations cause an interruption of work for the whole line, which is unproductive. Consequently most errors become evident at the end of the line and cause rework, which diminishes productivity as well.This paper helps to examine the feasibility of rework in flow assembly lines with regard to technical and organizational restrictions.

Development and comparison of multiple genetic algorithms and heuristics for assembly production planning

Assembly jobs with tree-structured precedence constraints in their bill-of-materials structure are a generalized version of traditional jobs involving only line-structured precedence constraints. The assembly job shop scheduling problem deals with assembly jobs, in contrast to job shop scheduling which deals with only traditional jobs. This research explores the ability of different genetic algorithms (GAs) to solve the assembly job shop scheduling problem. The objective is to minimize the makespan (maximum completion time) of a given set of assembly jobs. Random key GAs are proposed which differ using three factors: decoding, schedule justification and individual rearrangement. The three factors have two, seven and two levels, respectively, resulting in 28 different GAs. Specifically, we have conducted a full factorial design of GAs using forward/backward decoding, 0–6 local steps of justification, with/without individual rearrangement. The aim is to test the performance of GAs using different factor settings. As benchmarks, two heuristics have been proposed. Lingo, a software tool for linear and non-linear optimization problems is also used for solution by setting the time limit to 30 min. The experiments have revealed significant effects of the aforesaid three factors on the performance of the GAs.

Optimal Posture and Supporting Hand Force Prediction for Common Automotive Assembly One-Handed Tasks

People often complete tasks using one hand for the task and one hand for support. These one-handed support tasks can be found in many different types of jobs, such as automotive assembly jobs. Optimization-based posture prediction has proven to be a valid tool in predicting the postures necessary to complete the tasks, but the related external support forces have been prescribed and not predicted. This paper presents a method in which the optimal posture and related supporting hand forces can be predicted simultaneously using optimization and stability analysis techniques. Postures are evaluated using a physics-based human performance measure (HPM) while external forces are assessed using stability analysis. The physics-based performance measures are based on joint torque. Stability is analyzed using criteria based on a 3D zero moment point (ZMP). The human model used in the prediction contains 56 degrees of freedom and is based on a 50th percentile female in stature. Tasks based on common automotive assembly one-handed tasks found in literature are considered as examples to test the proposed method. Overall, the predicted supporting hand forces have good correlation with experimentally measured forces.

Analysis of tremor in motor learning task

Abstract Hand-eye coordination is required in many skilled tasks. Individual differences affect the performance of people at work and leisure, for example, during assembly jobs or sports. The aim of this study was to determine whether motor learning can change the physiological action of hand tremor. Tremor is a repetitive and stereotyped movement, with regular frequency and amplitude, but there are different types of tremors with pattern variation. The results were calculated by participants’ time-on and time-off the target, the average distance from the center of the target, and the frequency of oscillatory movement of a cursor (tremor). The results of this study indicate a statistically significant (p&lt;0.05) influence of effect of task repetition on improvement of motor control and reduction of a high-amplitude tremor and an increase of a low-amplitude tremor. The assessed individuals achieved more than 50% better outcomes of a hand-eye coordination task in the final trials when compared with the initial trials. The dynamics of motor learning tend to rise, with a steady level of a 1-h interval between trials.