Assembly line balancing problem is one of the most studied NP-Hard problems. NP-Hardness leads us to search for a good solution instead of the optimal solution especially for the big-size problems. Meta-heuristic algorithms are the search methods which are developed to find good solutions to the big-size and combinatorial problems. In this study, it is aimed at solving the multi-objective multi-model assembly line balancing problem of a company. A meta-heuristic algorithm is developed to solve the deterministic assembly line balancing problems. The algorithm developed is tested using the test problems in the literature and the the real life problem of the company as well. The results are analyzed and found to be promising and a solution is proposed for the firm.

In this study we focus on two-sided mixed-model assembly line balancing type-I problem. There is a production target for a fixed time horizon and the objective is to produce this amount with the minimum level of workforce. A mathematical model is developed to solve this problem in an optimal manner. For large scale problems, the mathematical model fails to give the optimal solution within reasonable computational times. Thus, a heuristic approach based on threshold accepting algorithm is presented. Both the mathematical model and the heuristic approach are executed to solve several example problems from the literature and a case study problem which is derived from the refrigerator production. Computational experiments are carried out using both approaches. It is observed that the heuristic procedure finds good solutions within very reasonable computational times.

In this study, we consider single model deterministic Assembly Line Balancing problem with task paralleling. The objective is to minimize the total cost which is composed of station opening cost and task dependent equipment cost. A branch and bound algorithm that allows two-level task paralleling is proposed. A heuristic algorithm is also developed both for obtaining efficient upper bounds to branch and bound and for achieving good approximate solutions for large sized problems. Computational experiments are conducted to investigate the effects of experimental parameters on the cost-related and algorithm-related performance measures. The exact algorithm results are compared to the proposed heuristic algorithm results, station paralleling results and optimal solutions without paralleling.

A diferença entre estações de trabalho é considerada desprezível em linhas de montagem tradicionais. Por outro lado, linhas de montagem heterogêneas consideram o problema de indústrias nas quais os tempos das tarefas variam de acordo com alguma característica a ser selecionada para a tarefa. No Problema de Balanceamento e Atribuição de Trabalhadores em Linhas de Montagem (do inglês Assembly Line Worker Assignment and Balancing Problem, ALWABP), os trabalhadores são responsáveis por estações de trabalho e de acordo com as suas habilidades, eles executam as tarefas em diferentes quantidades de tempo. Em alguns casos, os trabalhadores podem até ser incapazes de executar algumas tarefas. No Problema de Balanceamento de Linhas de Montagem Robóticas (do inglês Robotic Assembly Line Balancing Problem, RALBP), há diferentes tipos de robôs e o conjunto de tarefas de cada estação deve ser executada por um robô. Robôs do mesmo tipo podem ser usados múltiplas vezes. Nós propomos métodos exatos e heurísticos para a minimização do tempo de ciclo destes dois problemas, para um número fixo de estações. Os problemas têm características similares que são exploradas para produzir limitantes inferiores, métodos inferiores, models de programação inteira mista, e regras de redução e dominância. Para a estratégia de ramificação do método de branch-and-bound, entretanto, as diferenças entre os problemas forçam o uso de dois algoritmos diferentes. Uma estratégia orientada a tarefas tem os melhores resultados para o ALWABP-2, enquanto uma estratégia orientada a estações tem os melhores resultados para o RALBP-2. Nós mostramos que os limitantes inferiores, heurísticas, modelos de programação inteira mista e algoritmos de branch-and-bound para estes dois problemas são competitivos com os métodos do estado da arte da literatura. / The difference among workstations is assumed to be negligible in traditional assembly lines. Heterogeneous assembly lines consider the problem of industries in which the task times vary according to some property to be selected for the task. In the Assembly Line Worker Assignment and Balancing Problem (ALWABP), workers are assigned to workstations and according to their abilities, they execute tasks in different amounts of time. In some cases they can even be incapable of executing some tasks. In the Robotic Assembly Line Balancing Problem (RALBP) there are different types of robots and each station must be executed by a robot. Multiple robots of the same type may be used. We propose exact and heuristic methods for minimizing the cycle time of these two problems, for a fixed number of stations. The problems have similar characteristics that are explored to produce lower bounds, heuristic methods, mixed-integer programming models, and reduction and dominance rules. For the branching strategy of the branch-and-bound method, however, the differences among the problem force the use of two different algorithms. A task-oriented strategy has the best results for the ALWABP-2 while a station-oriented strategy has the best results for the RALBP-2. The lower bounds, heuristics, MIP models and branch-and-bound algorithms for these two problems are shown to be competitive with the state-of-the-art methods in the literature.

A diferença entre estações de trabalho é considerada desprezível em linhas de montagem tradicionais. Por outro lado, linhas de montagem heterogêneas consideram o problema de indústrias nas quais os tempos das tarefas variam de acordo com alguma característica a ser selecionada para a tarefa. No Problema de Balanceamento e Atribuição de Trabalhadores em Linhas de Montagem (do inglês Assembly Line Worker Assignment and Balancing Problem, ALWABP), os trabalhadores são responsáveis por estações de trabalho e de acordo com as suas habilidades, eles executam as tarefas em diferentes quantidades de tempo. Em alguns casos, os trabalhadores podem até ser incapazes de executar algumas tarefas. No Problema de Balanceamento de Linhas de Montagem Robóticas (do inglês Robotic Assembly Line Balancing Problem, RALBP), há diferentes tipos de robôs e o conjunto de tarefas de cada estação deve ser executada por um robô. Robôs do mesmo tipo podem ser usados múltiplas vezes. Nós propomos métodos exatos e heurísticos para a minimização do tempo de ciclo destes dois problemas, para um número fixo de estações. Os problemas têm características similares que são exploradas para produzir limitantes inferiores, métodos inferiores, models de programação inteira mista, e regras de redução e dominância. Para a estratégia de ramificação do método de branch-and-bound, entretanto, as diferenças entre os problemas forçam o uso de dois algoritmos diferentes. Uma estratégia orientada a tarefas tem os melhores resultados para o ALWABP-2, enquanto uma estratégia orientada a estações tem os melhores resultados para o RALBP-2. Nós mostramos que os limitantes inferiores, heurísticas, modelos de programação inteira mista e algoritmos de branch-and-bound para estes dois problemas são competitivos com os métodos do estado da arte da literatura. / The difference among workstations is assumed to be negligible in traditional assembly lines. Heterogeneous assembly lines consider the problem of industries in which the task times vary according to some property to be selected for the task. In the Assembly Line Worker Assignment and Balancing Problem (ALWABP), workers are assigned to workstations and according to their abilities, they execute tasks in different amounts of time. In some cases they can even be incapable of executing some tasks. In the Robotic Assembly Line Balancing Problem (RALBP) there are different types of robots and each station must be executed by a robot. Multiple robots of the same type may be used. We propose exact and heuristic methods for minimizing the cycle time of these two problems, for a fixed number of stations. The problems have similar characteristics that are explored to produce lower bounds, heuristic methods, mixed-integer programming models, and reduction and dominance rules. For the branching strategy of the branch-and-bound method, however, the differences among the problem force the use of two different algorithms. A task-oriented strategy has the best results for the ALWABP-2 while a station-oriented strategy has the best results for the RALBP-2. The lower bounds, heuristics, MIP models and branch-and-bound algorithms for these two problems are shown to be competitive with the state-of-the-art methods in the literature.

Purpose – The purpose of the study is to explore how productivity can be improved in an assembly line in manufacturing industry. In order to fulfill the purpose, following three research questions have been formulated: 1. How can an assembly line be designed? 2. Which potential improvement areas can be found in an assembly line? 3. How can assembly line balancing be used to improve productivity? Method – A case study was performed in order to answer the research questions. A combination of quantitative and qualitative data have been collected. To build an understanding of existing theories and research within the study area, a literature study was conducted which formed a theoretical framework. Parallel to the literature study, empirical data was collected through a case study. Data collection methods included observations, document studies, time measurements and focus group meetings. The reviewed theories and the collected data were later analyzed and a result was generated. Findings – In order to improve productivity, Theory of Constraints enabled the identification of potential improvement areas. To address the improvement areas, Assembly Line Balancing was found an appropriate method. Through the case study it was found that through Assembly Line Balancing, a reduction of takt time can be achieved which opens up the possibility to increase the production volume. Also, when re-allocating operators between work tasks, a reduction in numbers of operators is possible which results in lower costs. By lowering costs and increasing production volume, improved productivity is achieved. Implications – This study presents an application of the two improvement methods Theory of Constraints and Assembly Line Balancing in a manufacturing industry. Therefore, the thesis can be used as a basis when performing improvement work related to reduction of takt time in other manufacturing industries, to gain a better understanding for the implementation of the studied methods. Limitations – One limitation of the study was the pandemic Covid-19, which enforced restrictions on the case company. This disturbed the conduction of the case study since less focus group meetings were conducted, and suggested improvements could not be tested. Another limitation was the limited study time frame. Consequently, the collected time measurements were relatively few and the study scope was delimited to only packaging activities. To increase reliability, a more extensive time frame is necessary. The analysis has been adopted to the situation at the case company. The conclusions may hence be biased, which could restrict to what extent the study can be generalized.

In the automotive industry, assembly lines are used to produce vehicles. These assembly lines improve throughput, and need to be carefully planned. Planning, or balancing, an assembly line constitutes identifying precedence relationships between tasks in the assembly line, and assigning tasks to stations to fit some criteria. This procedure is costly to do by hand, and is well-suited for some level of automation. The problem of balancing assembly lines has been researched since the 1950’s, but modern assembly lines largely rely on engineers to balance the line by hand. This thesis proposes that the work flow of engineers planning the assembly line would be improved by a group decision support system. This group decision support system could supply engineers with proposals for assembly lines, which the engineers can choose to modify further, either by hand or with the decision support system. The group decision support system is realized with a distributed system, consisting of a front-end, a back-end, an application programming interface to balance assembly lines, and two databases. The front-end is a website, where the users can create problems with a precedence graph. The back-end allows data to be permanently stored in the two databases, and allows communication with the application programming interface. The contribution of this thesis is a proof of concept of a group decision support system that can solve two basic types of assembly line balancing problems, SALBP-1 and SALBP-2. During development it was found that the developed system was generic enough to support different types of tasks, such as planning cooking. Further development is needed to use the system in an industrial setting, as real assembly lines need more complex models than the current version support.

The global competitive environment and the growing demand for personalised products have increased the interest of companies in producing similar product models on the same assembly line. Companies are forced to make significant structural changes to rapidly respond to diversified demands and convert their existing single-model lines into mixed-model lines in order to avoid unnecessary new line construction cost for each new product model. Mixed-model assembly lines play a key role in increasing productivity without compromising quality for manufacturing enterprises. The literature is extensive on assembling small-sized products in an intermixed sequence and assembling large-sized products in large volumes on single-model lines. However, a mixed-model parallel two-sided line system, where two or more similar products or similar models of a large-sized product are assembled on each of the parallel two-sided lines in an intermixed sequence, has not been of interest to academia so far. Moreover, taking model sequencing problem into consideration on a mixed-model parallel two-sided line system is a novel research topic in this domain. Within this context, the problem of simultaneous balancing and sequencing of mixed-model parallel two-sided lines is defined and described using illustrative examples for the first time in the literature. The mathematical model of the problem is also developed to exhibit the main characteristics of the problem and to explore the logic underlying the algorithms developed. The benefits of utilising multi-line stations between two adjacent lines are discussed and numerical examples are provided. An agent-based ant colony optimisation algorithm (called ABACO) is developed to obtain a generic solution that conforms to any model sequence and it is enhanced step-by-step to increase the quality of the solutions obtained. Then, the algorithm is modified with the integration of a model sequencing procedure (where the modified version is called ABACO/S) to balance lines by tracking the product model changes on each workstation in a complex production environment where each of the parallel lines may a have different cycle time. Finally, a genetic algorithm based model sequencing mechanism is integrated to the algorithm to increase the robustness of the obtained solutions. Computational tests are performed using test cases to observe the performances of the developed algorithms. Statistical tests are conducted through obtained results and test results establish that balancing mixed-model parallel two-sided lines together has a significant effect on the sought performance measures (a weighted summation of line length and the number of workstations) in comparison with balancing those lines separately. Another important finding of the research is that considering model sequencing problem along with the line balancing problem helps algorithm find better line balances with better performance measures. The results also indicate that the developed ABACO and ABACO/S algorithms outperform other test heuristics commonly used in the literature in solving various line balancing problems; and integrating a genetic algorithm based model sequencing mechanism into ABACO/S helps the algorithm find better solutions with less amount of computational effort.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-08-03T11:05:17Z No. of bitstreams: 2 Dissertação - Carlos Alexandre Xavier da Silva - 2017.pdf: 2190162 bytes, checksum: 7c5e13d2301a93a75a0e2d68e1b9a893 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-08-03T11:06:02Z (GMT) No. of bitstreams: 2 Dissertação - Carlos Alexandre Xavier da Silva - 2017.pdf: 2190162 bytes, checksum: 7c5e13d2301a93a75a0e2d68e1b9a893 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-08-03T11:06:02Z (GMT). No. of bitstreams: 2 Dissertação - Carlos Alexandre Xavier da Silva - 2017.pdf: 2190162 bytes, checksum: 7c5e13d2301a93a75a0e2d68e1b9a893 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-06-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In one version of the Simple Assembly Line Balancing Problem (SALBP) tasks are assigned to stations along an assembly line with a fixed cycle time in order to minimise the required number of stations. It is assumed that the total work needed for each product unit has been partitioned into economically indivisible tasks. In practice, it may be that the minimal number of stations can be reduced when it is possible to further divide particular tasks in limited ways even with additional time penalty costs. Allowing task division leads to a new assembly line balancing problem, TDALBP (Task Division Assembly Line Balancing Problem) and a solution procedure for it. This work introduces a mathematical model for the TDALBP and presents promising computational results for the adaptation of some classical SALBP instances from the research literature. The results demonstrate that the TDALBP has the potential to significantly improve assembly line performance. / O balanceamento eficaz de uma linha de produção é importante para aprimorar a produtividade e reduzir custos de uma industria. O problema do balanceamento de linhas de produção (Assembly Line Balancing Problem - ALBP) envolve atribuir as tarefas necessárias para produzir cada unidade de um produto entre estações de trabalho ao longo de uma linha de produção, a fim de otimizar alguma medida de desempenho do sistema. Tradicionalmente, supõe-se que o trabalho total necessário para cada unidade de produto foi particionado em tarefas economicamente indivisíveis, de modo que uma maior divisão gera custos desnecessários. Assim, cada tarefa requerida não pode ser dividida e deve ser realizada em uma única estação. Na prática, no entanto, isso pode não ser sempre verdadeiro quando existe um objetivo orientado ao tempo, tal como a minimização do número de estações para um determinado tempo de ciclo. Neste caso, pode ser que o número mínimo das estações possa ser reduzido quando for possível continuar a dividir tarefas particulares de formas limitadas, mesmo se a divisão induzir custos adicionais de tempo. A permissão de tal divisão de tarefas nos leva a um novo problema de balanceamento de linhas de produção, o qual denotamos por TDALBP (Task Division Assembly Line Balancing Problem). Nós propomos um modelo de programação linear inteira binária para o TDALBP e procedimentos efetivos para solucioná-lo. Os procedimentos foram avaliados sobre adaptações de várias instâncias SALBP clássicas da literatura. Os resultados computacionais são promissores e mostram o potencial do TDALBP para a melhora significativa do desempenho de linhas de produção.

Future manufacturing will be characterized by the complementarity between humans and automation (human-robot collaboration). This requires new methods and tools for the design and operation of optimized manufacturing workplaces in terms of ergonomics, safety, efficiency, complexity management and work satisfaction. There have been some efforts in the recent years to propose a tool for determining optimal human-automation levels for load balancing. Although the topic is quite new, it shares some similarities with some of the existing research in the area of robotic assembly line balancing. Therefore, it is crucial to review the existing literature and find the most similar models and methods to facilitate the development of new optimization models and algorithms. One of the two contributions that this thesis gives to the research world in the RALBP context is a literature review that involves high quality articles from 1993 to beginning 2018. This literature review includes visual and comprehensive tables—and a label system— where previous research patterns and trends are highlighted. Visualization of data and results obtained by assembly line optimization tools is a very important topic that has rarely been studied. Data visualization would provide a: 1. better comprehension of patterns, trends and qualitative data 2. more constructive information absorption 3. better visualization of relationships and patterns between operations, and 4. better contribution to data manipulation and interaction. The second contribution to research found in this thesis is the use of a human modelling (DHM) tool (called IPS), which is proposed as an assessment to the ergonomic risk that a robotic assembly line may involve. This kind of studies are necessary in order to reduce one of the most frequent reasons of work absence in our today society i.e. musculoskeletal disorders (MSDs). MSDs are often the result of poor work environments and they lead to reduced productivity and quality losses at companies. In view of the above, IPS was used in order to resolve the load handling problem between human and robot, depending on their skills and availability, while fulfilling essential ISO standards i.e. 15066 and 10218:1 and :2. The literature review made it possible to select highly useful documents in developing assumptions for the experiment and contributed to consider real features detected in the industry. Results show that even though IPS is not capable of calculating an entire robotic assembly with human-robot collaboration, it is able to simulate a workstation constituted of one robot and one human. Finite and assembly motions for both human and robot are expected to be implemented in future versions of the software. Finally, the main advantages of using DHM tools in assessing ergonomic risks in RALB can be extracted from the results of this thesis. This advantages include 1. ergonomic evaluation for assembly motions 2. ergonomic evaluation for a full working day (available in future version) and 3. essential ISO standard testing (available in future version).