Design and development of CSP techniques for finding robust solutions in job-shop scheduling problems with Operators

[ES] Se desarrolla una técnica CSP para buscar soluciones robustas en el problema job-shop scheduling. La técnica esta desarrollada en tres pasos. El primer paso resuelve el problema sin tener en cuenta operadores. El segundo paso introduce las restricciones de los operadores y obtiene soluciones teniendo en cuenta el makespan y la robustez. En el tercer paso se mejora la robustez redistribuyendo los buffers. Para probar las robustez de las soluciones obtenidas se aplican incidencias virtuales en las soluciones.[EN] A CSP technique have been developed for finding robust solutions in job-shop scheduling problems with operators. The technique is developed in three steps. The first step solve the problem without operators minimizing the makespan. The second step introduce the operator constraints and give solutions take into account makespan and robustness. The third step improve the robustness redistributing the buffer. Some virtual incidences are created and to check the robustness of the solutions.Escamilla Fuster, J. (2012). Design and development of CSP techniques for finding robust solutions in job-shop scheduling problems with Operators. http://hdl.handle.net/10251/18029Archivo delegad

Modern software project management

Escamilla Fuster, J. (2010). Modern software project management. http://hdl.handle.net/10251/8580.Archivo delegad

Eficiencia Energética y Robustez en Problemas de Scheduling

[EN] Many industrial problems can be modelled as a scheduling problem where some resources are assigned to tasks so as to minimize the completion time, to reduce the use of resources, idle time, etc. There are several scheduling problems which try to represent different kind of situations that can appear in real world problems. Job Shop Scheduling Problem (JSP) is the most used problem. In JSP there are different jobs, every job has different tasks and these tasks have to be executed by different machines. JSP can be extended to other problems in order to simulate more real problems. In this work we have used the problem job shop with operators JSO(n,p) where each task must also be assisted by one operator from a limited set of them. Additionally, we have extended the classical JSP to a job-shop scheduling problem where machines can consume different amounts of energy to process tasks at different rates (JSMS). In JSMS operation has to be executed by a machine that has the possibility to work at different speeds. Scheduling problems consider optimization indicators such as processing time, quality and cost. However, governments and companies are also interested in energy-consumption due to the rising demand and price of fuel, the reduction in energy commodity reserves and growing concern about global warming. In this thesis, we have developed new metaheuristic search techniques to model and solve the JSMS problem. Robustness is a common feature in real life problems. A system persists if it remains running and maintains his main features despite continuous perturbations, changes or incidences. We have developed a technique to solve the $JSO(n,p)$ problem with the aim of obtaining optimized and robust solutions. We have developed a dual model to relate optimality criteria with energy consumption and robustness/stability in the JSMS problem. This model is committed to protect dynamic tasks against further incidences in order to obtain robust and energy-aware solutions. The proposed dual model has been evaluated with a memetic algorithm to compare the behaviour against the original model. In the JSMS problem there are a relationship between Energy-efficiency, Robustness and Makespan. Therefore, the relationship between these three objectives is studied. Analytical formulas are proposed to analyse the relationship between these objectives. The results show the trade-off between makespan and robustness, and the direct relationship between robustness and energy-efficiency. To reduce the makespan and to process the tasks faster, energy consumption has to be increased. When the energy consumption is low it is because the machines are not working at highest speed. So, if an incidence appears, the speed of these machines can be increased in order to recover the time lost by the incidence. Hence robustness is directly related with energy consumption. Additionally, robustness is also directly related with makespan because, when makespan increases, there are more gaps in the solution, these incidences can be absorbed by these natural buffers. The combination of robustness and stability gives the proposal an added value due to since an incidence cannot be directly absorbed by the disrupted task and it can be repaired by involving only a small number of tasks. In this work we propose two different techniques to manage rescheduling over the JSMS problem. This work represents a breakthrough in the state of the art of scheduling problems and in particular the problem where energy consumption can be controlled by the rate of the machines.[ES] Muchos de los problemas industriales se pueden modelar como un problema de scheduling donde algunos recursos son asignados a tareas a fin de minimizar el tiempo de finalización, para reducir el uso de los recursos, el tiempo de inactividad, etc. Job-Shop scheduling (JSP) es el problema más utilizado. En JSP hay diferentes trabajos, cada trabajo tiene diferentes tareas y estas tareas tienen que ser ejecutadas por diferentes máquinas. JSP puede ser extendido a otros problemas con el fin de simular una mayor cantidad de problemas reales. En este trabajo se ha utilizado el problema job shop scheduling con operadores JSO(n, p), donde cada tarea también debe ser asistida por un operador de un conjunto limitado de ellos. Además, hemos ampliado el clásico problema JSP a un problema donde las máquinas pueden consumir diferentes cantidades de energía al procesar tareas a diferentes velocidades (JSMS). En JSMS las operaciones tiene que ser ejecutadas por una máquina que tiene la posibilidad de trabajar a diferentes velocidades. Los problemas de scheduling consideran indicadores de optimización tales como: el procesamiento de tiempo, la calidad y el coste. Sin embargo, hoy en día los gobiernos y los empresarios están interesados también en el control del consumo de energía debido al aumento de la demanda y del precio de los combustibles, la reducción de las reservas de materias primas energéticas y la creciente preocupación por el calentamiento global. En esta tesis, hemos desarrollado nuevas técnicas de búsqueda metaheurística para modelar y resolver el problema JSMS. La robustez es una característica común en los problemas de la vida real. Un sistema persiste si permanece en funcionamiento y mantiene sus principales características a pesar de las perturbaciones continuas, cambios o incidencias. Hemos desarrollado una técnica para resolver el problema JSO(n, p) con el objetivo de obtener soluciones robustas y optimizadas. Hemos desarrollado un modelo dual para relacionar los criterios de optimalidad con el consumo de energía y la robustez/estabilidad en el problema JSMS. Este modelo se ha desarrollado para proteger a las tareas dinámicas contra incidencias, con el fin de obtener soluciones sólidas y que tengan en cuenta el consumo de la energía. El modelo dual propuesto ha sido evaluado con un algoritmo memético para comparar el comportamiento frente al modelo original. En el problema JSMS hay una relación entre la eficiencia energética, la robustez y el makespan. Por lo tanto, se estudia la relación entre estos tres objetivos. Se desarrollan fórmulas analíticas para representar la relación estimada entre estos objetivos. Los resultados muestran el equilibrio entre makespan y robustez, y la relación directa entre la robustez y eficiencia energética. Para reducir el makespan, el consumo de energía tiene que ser aumentado para poder procesar las tareas más rápido. Cuando el consumo de energía es bajo, debido a que las máquinas no están trabajando a la velocidad más alta, si una incidencia aparece, la velocidad de estas máquinas puede ser aumentada con el fin de recuperar el tiempo perdido por la incidencia. Por lo tanto la robustez está directamente relacionada con el consumo de energía. Además, la robustez también está directamente relacionada con el makespan porque, cuando el makespan aumenta hay más huecos en la solución, que en caso de surgir incidencias, estas pueden ser absorbidas por estos buffers naturales. La combinación de robustez y estabilidad da un valor añadido debido a que si una incidencia no puede ser absorbida directamente por la tarea interrumpida, esta puede ser reparada mediante la participación un pequeño número de tareas.En este trabajo se proponen dos técnicas diferentes para gestionar el rescheduling sobre el problema JSMS. Este trabajo representa un avance en el estado del arte en los problemas de scheduling y en el problema donde el consumo de energía p[CA] Molts dels problemes industrials es poden modelar com un problema de scheduling on alguns recursos són assignats a tasques a fi de minimitzar el temps de finalització, per a reduir l'ús dels recursos, el temps d'inactivitat, etc. Existeixen diversos tipus de problemes de scheduling que intenten representar diferents situacions que poden aparèixer en els problemes del món real. Job-Shop scheduling (JSP) és el problema més utilitzat. En JSP hi ha diferents treballs, cada treball té diferents tasques i aquestes tasques han de ser executades per diferents màquines. JSP pot ser estès a altres problemes amb la finalitat de simular una major quantitat de problemes reals. En aquest treball s'ha utilitzat el problema job shop scheduling amb operadors JSO(n, p), on cada tasca també ha de ser assistida per un operador d'un conjunt limitat d'ells. A més, hem ampliat el clàssic problema JSP a un problema on les màquines poden consumir diferents quantitats d'energia per a processar tasques a diferents velocitats (JSMS). Els problemes de scheduling consideren indicadors d'optimització tals com: el processament de temps, la qualitat i el cost. No obstant açò, avui en dia els governs i els empresaris estan interessats també amb el control del consum d'energia a causa de l'augment de la demanda i del preu dels combustibles, la reducció de les reserves de matèries primeres energètiques i la creixent preocupació per l'escalfament global. En aquesta tesi, hem desenvolupat noves tècniques de cerca metaheurística per a modelar i resoldre el problema JSMS. La robustesa és una característica comuna en els problemes de la vida real. Un sistema persisteix si continua en funcionament i manté les seues principals característiques malgrat les pertorbacions contínues, canvis o incidències. Hem desenvolupat una tècnica per a resoldre el problema JSO(n, p) amb l'objectiu d'obtenir solucions robustes i optimitzades. Hem desenvolupat un model dual per a relacionar els criteris de optimalidad amb el consum d'energia i la robustesa/estabilitat en el problema JSMS. Aquest model s'ha desenvolupat per a protegir a les tasques dinàmiques contra incidències, amb la finalitat d'obtenir solucions sòlides i que tinguen en compte el consum de l'energia. El model dual proposat ha sigut evaluat amb un algorisme memético per a comparar el comportament front un model original. En el problema JSMS hi ha una relació entre l'eficiència energètica, la robustesa i el makespan. Per tant, s'estudia la relació entre aquests tres objectius. Es desenvolupen fórmules analítiques per a representar la relació estimada entre aquests objectius. Els resultats mostren l'equilibri entre makespan i robustesa, i la relació directa entre la robustesa i l'eficiència energètica. Per a reduir el makespan, el consum d'energia ha de ser augmentat per a poder processar les tasques més ràpid. Quan el consum d'energia és baix, a causa que les màquines no estan treballant a la velocitat més alta, si una incidència apareix, la velocitat d'aquestes màquines pot ser augmentada amb la finalitat de recuperar el temps perdut per la incidència. Per tant la robustesa està directament relacionada amb el consum d'energia. A més, la robustesa també està directament relacionada amb el makespan perquè, quan el makespan augmenta hi ha més buits en la solució, que en cas de sorgir incidències, aquestes poden ser absorbides per els buffers naturals. La combinació de robustesa i estabilitat dóna un valor afegit a causa de que si una incidència no pot ser absorbida directament per la tasca interrompuda, aquesta pot ser reparada mitjançant la participació d'un xicotet nombre de tasques. En aquest treball es proposen dues tècniques diferents per a gestionar el rescheduling sobre el problema JSMS. Aquest treball representa un avanç en l'estat de l'art en els problemes de scheduling i, en particular, en el problema on el consum d'energia pot ser controlat perEscamilla Fuster, J. (2016). Eficiencia Energética y Robustez en Problemas de Scheduling [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/64062TESI

A Dual Scheduling Model for Optimizing Robustness and Energy Consumption in Manufacturing Systems

[EN] Manufacturing systems involve a huge number of combinatorial problems that must be optimized in an efficient way. One of these problems is related to task scheduling problems. These problems are NP-hard, so most of the complete techniques are not able to obtain an optimal solution in an efficient way. Furthermore, most of real manufacturing problems are dynamic, so the main objective is not only to obtain an optimized solution in terms of makespan, tardiness, and so on but also to obtain a solution able to absorb minor incidences/disruptions presented in any daily process. Most of these industries are also focused on improving the energy efficiency of their industrial processes. In this article, we propose a knowledge-based model to analyse previous incidences occurred in the machines with the aim of modelling the problem to obtain robust and energy-aware solutions. The resultant model (called dual model) will protect the more dynamic and disrupted tasks by assigning buffer times. These buffers will be used to absorb incidences during execution and to reduce the machine rate to minimize energy consumption. This model is solved by a memetic algorithm which combines a genetic algorithm with a local search to obtain robust and energy-aware solutions able to absorb further disruptions. The proposed dual model has been proven to be efficient in terms of energy consumption, robustness and stability in different and well-known benchmarks.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research has been supported by the Spanish Government under research project TIN2013-46511-C2-1 for the Spanish government and the TETRACOM EU project FP7-ICT-2013-10-No 609491.Escamilla Fuster, J.; Salido Gregorio, MA. (2016). A Dual Scheduling Model for Optimizing Robustness and Energy Consumption in Manufacturing Systems. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture. 1(1):1-12. https://doi.org/10.1177/0954405415625915S1121

Rescheduling in job-shop problems for sustainable manufacturing systems

[EN] Manufacturing industries are faced with environmental challenges, so their industrial processes must be optimized in terms of both profitability and sustainability. Since most of these processes are dynamic, the previously obtained solutions cannot be valid after disruptions. This paper focuses on recovery in dynamic job-shop scheduling problems where machines can work at different rates. Machine speed scaling is an alternative framework to the on/off control framework for production scheduling. Thus, given a disruption, the main goal is to recover the original solution by rescheduling the minimum number of tasks. To this end, a new match-up technique is developed to determine the rescheduling zone and a feasible reschedule. Then, a memetic algorithm is proposed for finding a schedule that minimizes the energy consumption within the rescheduling zone but that also maintains the makespan constraint. An extensive study is carried out to analyze the behavior of our algorithms to recover the original solution and minimize the energy reduction in different benchmarks, which are taken from the OR-Library. The energy consumption and processing time of the tasks involved in the rescheduling zone will play an important role in determining the best match-up point and the optimized rescheduling. Upon a disruption, different rescheduling solutions can be obtained, all of which comply with the requirements but that have different values of energy consumption. The results proposed in this paper may be useful for application in real industries for energy-efficient production rescheduling.This research has been supported by the Seventh Framework Programme under the research project TETRACOM-GA609491 and the Spanish Government under research projects TIN2013-46511-C2-1, TIN2015-65515-C4-1-R and TIN2016-80856-R. The authors wish to thank reviewers and editors for their positive comments to improve the quality of the paper.Salido Gregorio, MA.; Escamilla Fuster, J.; Barber Sanchís, F.; Giret Boggino, AS. (2017). Rescheduling in job-shop problems for sustainable manufacturing systems. Journal of Cleaner Production. 162(20):121-132. https://doi.org/10.1016/j.jclepro.2016.11.002S1211321622

A Genetic Algorithm for Energy-Efficiency in Job-Shop Scheduling

Many real-world scheduling problems are solved to obtain optimal solutions in term of processing time, cost, and quality as optimization objectives. Currently, energyefficiency is also taken into consideration in these problems. However, this problem is NP-hard, so many search techniques are not able to obtain a solution in a reasonable time. In this paper, a genetic algorithm is developed to solve an extended version of the Job-shop Scheduling Problem in which machines can consume different amounts of energy to process tasks at different rates (speed scaling). This problem represents an extension of the classical jobshop scheduling problem, where each operation has to be executed by one machine and this machine can work at different speeds. The evaluation section shows that a powerful commercial tool for solving scheduling problems was not able to solve large instances in a reasonable time, meanwhile our genetic algorithm was able to solve all instances with a good solution quality.This research has been supported by the Spanish Government under research project MINECO TIN2013-46511-C2-1 and the CASES project supported by a Marie Curie International Research Staff Exchange Scheme Fellowship within the 7th European Community Framework Programme under the grant agreement No 294931. We would like to thanks Philippe Laborie (IBM ILOG CPLEX) for validating the CP Optimizer model for this problem. We also appreciate the significant efforts made by all the reviewers to improve this paper.Salido, MA.; Escamilla Fuster, J.; Giret Boggino, AS.; Barber, F. (2016). A Genetic Algorithm for Energy-Efficiency in Job-Shop Scheduling. 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Solving the job shop scheduling problem with operators by depth-first heuristic search enhanced with global pruning rules

The job shop scheduling problem with an additional resource type has been recently proposed to model the situation where each operation in a job shop has to be assisted by one of a limited set of human operators. We confront this problem with the objective of minimizing the total flow time, which makes the problem more interesting from a practical point of view and harder to solve than the version with makespan minimization. To solve this problem we propose an enhanced dept-first search algorithm. This algorithm exploits a schedule generation schema termed OG&T, two admissible heuristics and some powerful pruning rules. In order to diversify the search, we also consider a variant of this algorithm with restarts. We have conducted an experimental study across several benchmarks. The results of this study show that the global pruning rules are really effective and that the proposed algorithms are quite competent for solving this problem.We are grateful to the anonymous referees for their comments and suggestions, that made it possible to improve this paper. This research has been supported by the Spanish Government under projects MEC-FEDER TIN-20976-C02-01 and TIN-20976-C02-02 and by the Principality of Asturias under Grant FICYT-BP09105.Mencia, C.; Sierra, MR.; Salido Gregorio, MA.; Escamilla Fuster, J.; Varela, R. (2015). Solving the job shop scheduling problem with operators by depth-first heuristic search enhanced with global pruning rules. AI Communications. 28(2):365-381. https://doi.org/10.3233/AIC-140630S36538128