•We address the multi-skilled worker assignment problem in the context of seru production system.•Differences in workers’ skill sets and proficiency levels are taken into consideration.•A ...mathematical model with objectives of improving inter-seru and inter-worker workload balance is proposed.•The impact of differences in workers’ competency on workload balance is analyzed based on the computational results.
The flexibility of production systems is becoming more and more important for manufacturers facing various changes. As an effective way to increase the flexibility in a short time with a small investment, multi-skilled workers have received more attention in recent years. In this paper, a multi-skilled worker assignment problem is solved in the context of seru production systems, in which differences in workers’ skill sets and proficiency levels are taken into consideration. Worker grouping, cell loading, and task assignment are solved concurrently in the problem. A mathematical model with objectives of improving the inter-seru and inter-worker workload balance is proposed to solve the problem. In order to verify the proposed model, a numerical example is presented and solved by a sum weighted method. Due to the NP-hard nature of the model, a meta-heuristic algorithm based on NSGA-II is developed. The algorithm is tested by several numerical examples and the impact of differences in workers’ competency on workload balance is analyzed based on the computational results.
This paper deals with the development of a
distributed multi-agent system
(
DMAS
) for scheduling and controlling
Robotic Flexible Assembly Cells (RFAC)
. In the proposed system, an approach for ...solving one of the most challenging decisional problems in RFAC is proposed and implemented. This problem is related to the products operations scheduling which requires their allocation and sequencing on the robots, while satisfying products and robots constraints under makespan minimization. The proposed
DMAS
addresses this challenge by using a cooperative approach supported by three kinds of autonomous control agents:
supervisory agent
,
local agents
, and
remote agents
. These agents interact by a negotiation protocol based on common dispatching rules for coordinating their individual decisions, satisfying their local objective and providing an optimized global solution. Moreover, because of the dynamic nature of the assembly systems, it is imperative to consider external disturbances on production scheduling and to solve the related issues. Consequently,
DMAS
has the ability to respond and manage some dynamic events that may occur in the cells such as unexpected robot breakdown or dynamic products arrivals. Computational results on benchmarks show the effectiveness and the robustness of the proposed system.
•To our knowledge, this is first study that addresses dynamic scheduling in RFACs.•Cell utilisation and due date tightness are the significant scheduling factors.•Percentage of prediction error (9%) ...confirms the efficient of proposed methodology.•The results of confirmation run improved by 11% compared to initial experiments.
This paper presents Taguchi method coupled with fuzzy logic for dealing with multi-objective optimisation problems for dynamic scheduling in robotic flexible assembly cells (RFACs). This is the first study to address these particular problems. In this study, Taguchi optimisation method has been applied to reduce the number of experiments required for scheduling RFACs. The experiments are implemented with four different scheduling factors, namely sequencing rule, dispatching rule, cell utilisation and due date tightness. These factors are difficult to optimise considering the objectives of multiple functions instead of a single objective. Therefore, a multiple performance characteristics index (MPCI) based fuzzy logic approach has been developed to derive the optimal solution. The predicted results of MPCIs have been verified via a confirmation test. Results of the confirmation test show significant improvement in MPCI using the optimal levels of the scheduling factors.
Production cells are considered a flexible production system capable to face new market demands. In most cases, this is provided by their capability of reconfiguration, i.e., by removing/adding new ...equipment needed and/or reusing the existent equipment for the new demand. Nevertheless, some companies are not conveniently exploring this opportunity. What happened, many times, is the design of a complete new cell replacing all the equipment and sending the existent machinery to the warehouse. This is a decision that, economically and environmentally, is costly. Furthermore, knowing that some equipment could be reused for a new product. In a Lean Thinking, this is waste and a Lean company should promote a more efficient and sustainable production. This paper introduces a study in a Lean company that has developed practices to reuse equipment. The reasons for the non-reuse of the existent equipment were studied and some strategies were proposed to turn this equipment available and visible for reuse. Also, the benefits of reusing equipment related with saved costs and contribution to the environmental sustainability, are discussed.
The adoption of a lean production model means a systematic implementation of various management methods and practices. Such a model presents the human element as a key factor in continuous ...improvement efforts, influencing workers’ job content and the quality of work. However, there are few evidences regarding research on quantitative assessment of the work demand, either psychological or physical, in a lean production environment. Therefore, this study aims to analyze from an ergonomics perspective the psychophysical demand and workers’ perceived workload within assembly cells undergoing a lean production implementation. The proposed method integrates complementary concepts of widely known techniques, enabling the consolidation of several assessment criteria into one particular index for both psychological and physical demands. Such a diagnostic method is illustrated in a case study from the automotive parts manufacturing sector, whose application is performed in three critical assembly cells selected by senior management. Our findings show systemic gaps between work demand and employees’ profile, indicating improvement opportunities in order to provide a better work environment.
► We investigate the problem of how to reconfigure conveyor assembly line to serus. ► A mathematical model in the view of makespan is developed to solve this problem. ► The proposed model is ...investigated by an industrial case. ► The propose model is compared to Kaku's model with respect to the selected plan. ► The computation results validate the model is more suitable to analyze the problem.
Confronted with the dynamic and complex market environments, the traditional conveyor assembly line can no longer meet customers’ demands effectively. The way of reconfiguring conveyor assembly line to a more flexible manufacturing system has been attracting considerable attention both in the academics and production practices. Seru system, also called assembly cell system, is regarded as one of the most successful innovations of manufacturing system in reconfiguring conveyor assembly line. Such a manufacturing system merges considerable flexibility of job shops and high efficiency of conveyor assembly lines to some extent. In this paper, we investigate the problem of how to reconfigure conveyor assembly line to serus. A comprehensive mathematical model incorporating two issues of how many serus should be established and how many workers should be assigned to each seru is developed. Then the model is investigated by an industrial case and compared to Kaku's model with respect to the selected plan. The computation results validate that the proposed model is more suitable to analyze the reconfiguration problems from conveyor assembly line to serus.
Due to increasing competition in the developing global economy, today's companies are facing greater challenges than ever to employ flexible manufacturing systems (FMS) capable of dealing with ...unexpected events and meeting customers' requirements. One such system is robotic flexible assembly cells (RFACs). There has been relatively little work on the scheduling of RFACs, even though overall scheduling problems of FMS have attracted significant attention. This paper presents Taguchi optimisation method in conjunction with simulation modelling in a new application for dynamic scheduling problems in RFACs, in order to minimise total tardiness and number of tardy jobs (N
T
). This is the first study to address these particular problems. In this study, Taguchi method has been used to reduce the minimum number of experiments required for scheduling RFACs. These experiments are based on an L9 orthogonal array with each trial implemented under different levels of scheduling factors. Four factors are considered simultaneously: sequencing rule, dispatching rule, cell utilisation and due date tightness. The experimental results are analysed using an analysis of mean to find the best combination of scheduling factors and an analysis of variance to determine the most significant factors that influence the system's performance. The resulting analysis shows that this proposed methodology enhances the system's scheduling policy.
Assembly cells often depend on the human elements when an extended automation is not (economically, even if technologically) possible. The workers’ natural variability is impossible to avoid in a ...manual assembly system. Usually when simulating an assembly system, a given task time distribution is assumed as the representation of the workers time performance. Workers have variations in their performance that can incur in the shifting of this distribution relative to the expected performance time distribution, as well as in the widening of this distribution, by the increase or decrease of dispersion. This paper presents a discrete event simulation model of an assembly system where the operators have different time distributions, aiming to assess their influence in the overall system performance. Those time distributions were obtained in industrial context, in a previous study, by observing workers in an assembly cell, so representing real performance of workers. The results indicate that the worst performing worker will “pace” the output system performance to a slower rhythm, while better performances of a single worker will only increase very slightly the system productivity.
This study aims to develop an efficient rule for scheduling robotic flexible assembly cells (RFACs). The proposed scheduling rule is called fuzzy sequencing rule (FSR) which is constructed by ...combining different input variables: processing time, due date, batch size and number of required assembly stations, using the fuzzy logic (FL) technique. Two independent performance measures are considered: makespan and maximum of tardiness. Simulation software named SIMPROCESS is used to examine the performance of FSR compared with existing scheduling rules. Simulation results show that the proposed rule outperforms the common scheduling rules.
This paper presents the results of a simulation-based performance comparison between assembly lines (AL) and assembly cells (AC) manufacturing systems with real-time distributed arrival time for ...just-in-time (JIT)-oriented production environment. This research adds to the sparse body of literature in this area. The previous performance comparisons were made in smaller scalability because of the combinational problem. In addition, the comparisons were addressed in centralised and hierarchical systems. In this paper, the distributed arrival time control (DATC) system is used to make performance comparison of two manufacturing systems scalable and practical in the heterarchical manufacturing system. It expands the range of the comparison between AL and AC into a real-time environment. In addition, this research includes four levels of the number of stations, four levels of assembly task time standard deviations, and two levels of system types. The results indicate that assembly cells have the ability to outperform assembly lines for the orientation of JIT production and to handle a wide range of variability with little change in mean squared deviation. It also shows that distributed arrival time control system can provide the stability of the scheduling of the manufacturing system.
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