14 research outputs found

    Equivalent and efficient optimization models for an industrial discrete event system with alternative structural configurations

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    Discrete event systems in applications, such as industry and supply chain,may show a very complex behavior. For this reason, their design and operation may be carried out by the application of optimization techniques for decision making in order to obtain their highest performance. In a general approach, it is possible to implement these optimization techniques by means of the simulation of a Petri net model, which may require an intensive use of computational resources. One key factor in the computational cost of simulation-based optimization is the size of the model of the system; hence, it may be useful to apply techniques to reduce it. This paper analyzes the relationship between two Petri net formalisms, currently used in the design of discrete event systems, where it is usual to count on a set of alternative structural configurations.These formalisms are a particular type of parametric Petri nets, called compound Petri nets, and a set of alternative Petri nets. The development of equivalent models under these formalisms and the formal proof of this equivalence are the main topics of the paper.The basis for this formal approach is the graph of reachable markings, a powerful tool able to represent the behavior of a discrete event system and, hence, to show the equivalence between two different Petri net models. One immediate application of this equivalence is the substitution of a large model of a system by a more compact one, whose simulation may be less demanding in the use of computational resources

    Analysis of product shrinkage and waste in a potato bagging plant

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    Nowadays, an average of 2 kg of waste per person are generated in Spain. Furthermore, the household consumption is rising and, as a consequence, the waste production is also increasing. This trend presents a direct impact in the environment. Moreover, after two years of COVID-19 pandemic, it has been detected a stronger rise in consumption per person, while consumption through professional commercial channels for hospitality industry has been lower. This paper analizes the waste generation and product shrinkage in a potato bagging plant, which addresses its production to both final consumers and retailers. The raw materials washing line, as well as the production line, are taken into consideration in the analysis, while new uses to the produced waste are proposed, aiming at providing new useful life, such as the production of bioplastics or the production of biodiesel. As a consequence, the environment impact is minimized and new products are obtained

    Control predictivo con modos deslizantes

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    En los últimos 25 años, las estrategias de control avanzado por estructura variable (Variable Structure Control VSC), en particular las de Control por Modo Deslizante (Sliding Mode Control SMC), y las de Control Predictivo basado en Modelo (Model Predictive Control MPC), han experimentado una gran evolución. Sus buenas características operacionales y la superación de algunas de las desventajas que presentan cada una por separado motivaron la realización de esta tesis doctoral. A partir de los fundamentos teóricos de SMC y MPC, se presentan en esta tesis algunas leyes de control híbridas basadas en el modelo de POMTM del proceso a controlar, que caracteriza apropiadamente la mayoría de los procesos industriales y es de sencilla obtención. Además, dichas leyes son fácilmente programables en sistemas de control digital y son aplicables a sistemas modelables como de fase no mínima y con grandes retardos. Adicionalmente se han obtenido varias reglas de sintonización sencillas que proporcionan respuestas en bucle cerrado estables y suaves, incluso con alto grado de incertidumbre estructurada y no estructurada en el modelado. Los controladores han sido diseñados a partir de modelos exactos y sintonizados considerando cierto grado de incertidumbre. En varios apartados se han realizado análisis de estabilidad, admisibilidad y robustez con el fin de completar los apartados de síntesis. Se ha dedicado un capítulo a la simulación de las leyes propuestas con varios sistemas de interés, obteniéndose resultados favorables en cuanto a seguimiento de escalón y rechazo de perturbaciones en la salida, en comparación con GPC (C. Bordóns, 1994) y SMC (O. Camacho, 1996) e IM-SMC (O. Camacho y otros, 2003), obtenidos a partir del modelado de POMTM de los procesos. Por último se han programado y aplicado las leyes a dos sistemas no lineales con incertidumbres y perturbaciones: un intercambiador de calor en un circuito de recirculación de agua situado en la planta piloto del Departamento de Ingeniería de Sistemas y Automática de la Universidad de Sevilla y un campo de colectores de radiación solar distribuidos situados en la plataforma solar del Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas en Tabernas (Almería).In the last 25 years, the strategies of advance control known as Variable Structure Control, in particular Sliding Mode Control (SMC), and Model Predictive Control (MPC) have experimented a great evolution. Their good characteristics of performance and the goal to overcome some of their particular disadvantages have motivated the execution of this thesis. On the basis of the theoretical fundamentals of SMC and MPC, some hybrid control laws are presented that use the First Order Plus Dead Time Model (FOPDTM) of a process to control. This model characterizes appropriately the majority of industrial processes and it is easy to be identified. Moreover, it is easy to program the developed control laws using Digital Control Systems and they can be applied to control processes that can be modelled as systems of non-minimum phase and as systems with high delays. Additionally several simple tuning rules have been developed, and they provide stable and smooth responses, even with a high level of structured and unstructured uncertainty in the model. The controllers have been designed from exact models and they have been tuned taking into account uncertainties. In several sections an analysis of stability and robustness have been carried out in order to complete the sections with the synthesis of the controllers. A chapter is dedicated to the simulation of the control laws applied to several systems. The results have been satisfactory as regards the step tracking and the rejection of disturbances in the outlet. They have been compared to GPC (C. Bordóns, 1994) and SMC (O. Camacho, 1996) and IM-SMC (O. Camacho et al, 2003), which are controllers obtained from the FOPDTM of the processes. Finally, the control laws have been programmed and applied to two non-linear real systems with uncertainties and disturbances. First, a heat exchanger in a circuit for recirculation of water, situated in a pilot plant at the "Departamento de Ingeniería de Sistemas y Automática" in the University of Seville (Spain); second, a field of distributed collectors of solar radiation, situated in the "Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas" in Tabernas (Almería, Spain)

    Petri nets applied to the simulation of customer behavior in busy scenarios

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    [Resumen] El modelado y la simulación del comportamiento humano es una cuestión que ha sido abordada por medio de diferentes enfoques, entre los que pueden destacarse algunas metodologías basadas en agentes. En este contexto, el uso del formalismo de modelado de redes de referencia permite disponer de información detallada sobre el estado completo del sistema modelado y de los agentes en cualquier instante de la simulación. En la presente contribución se describe una aplicación de este formalismo al modelado y la simulación del comportamiento de los clientes potenciales en entornos comerciales con elevada concurrencia de público. En el marco de la red de referencia considerada, una red del sistema proporciona el contexto físico en el que los clientes, modelados por medio de las redes de marcas, desarrollan su actividad. La metodología propuesta, basada en el uso del formalismo mencionado, presenta una gran flexibilidad y una aplicabilidad potencial a muy diversos entornos, tales como supermercados, grandes superficies e incluso el comercio electrónico.[Abstract] Modeling and simulation of human behavior is a topic that has been considered from different approaches, as they are different methodologies based on agents. In the frame of this approach, the use of the formalism of reference nets, may provide with detailed information about the complete state of the modeled system and the agents at any stage of the simulation process. An application of this modeling formalims is described, leading to simulations of potential customers’ behavior in crowded shopping malls. In the frame of the reference nets, the system net models the physical context, where the customers, modeled by token nets, develop their activity. The proposed methodology shows large flexibility and potential applicability to very different environments, such as shops, supermarkets, shopping malls, as well as e-commerce.La investigación descrita en la presente contribución se enmarca en el proyecto de investigación “Modelos sostenibles y Analítica del Transporte en Ciudades Inteligentes”, PID2019-111100RB-C22, financiada por el Ministerio de Ciencia e Innovación.Ministerio de Ciencia e Innovación; PID2019-111100RB-C2

    Redes de Petri aplicadas a la simulación del comportamiento de consumidores en escenarios concurridos

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    Modeling and simulation of human behavior is a topic that has been considered from different approaches, as they are different methodologies based on agents. In the frame of this approach, the use of the formalism of reference nets, may provide with detailed information about the complete state of the modeled system and the agents at any stage of the simulation process. An application of this modeling formalims is described, leading to simulations of potential customers behavior in crowded shopping malls. In the frame of the reference nets, the system net models the physical context, where the customers, modeled by token nets, develop their activity. The proposed methodology shows large flexibility and potential applicability to very different environments, such as shops, supermarkets, shopping malls, as well as e-commerce.El modelado y la simulación del comportamiento humano es una cuestión que ha sido abordada por medio de diferentes enfoques, entre los que pueden destacarse algunas metodologías basadas en agentes. En este contexto, el uso del formalismo de modelado de redes de referencia permite disponer de información detallada sobre el estado completo del sistema modelado y de los agentes en cualquier instante de la simulación. En la presente contribución se describe una aplicación de este formalismo al modelado y la simulación del comportamiento de los clientes potenciales en entornos comerciales con elevada concurrencia de público. En el marco de la red de referencia considerada, una red del sistema proporciona el contexto físico en el que los clientes, modelados por medio de las redes de marcas, desarrollan su actividad. La metodología propuesta, basada en el uso del formalismo mencionado, presenta una gran flexibilidad y una aplicabilidad potencial a muy diversos entornos, tales como supermercados, grandes superficies e incluso el comercio electrónico

    Effects of Human Factors and Lean Techniques on Just in Time Benefits

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    A successful Just in Time (JIT) implementation is based on human resources integration (managers, operators and suppliers) and other lean manufacturing techniques applied in the production process. However, the relationship between these variables is not easily quantified. This paper reports a structural equation model that integrates variables associated with JIT implementation: management commitment, human resources integration, suppliers and production tools and technique, which affect the benefits gained, and are integrated into nine hypotheses or relationships among then. The model is evaluated with information from 352 responses to a questionnaire applied to manufacturing industry, and partial least squares technique is used to evaluate it. The direct effects, sum of indirect effects, and total effects are quantified, and a sensitivity analysis based on conditional probabilities is reported to know scenarios associated with low and high levels in variables’ execution and how they impact the benefits obtained. Findings indicate that managerial commitment is the most important variable in the JIT implementation process, since managers are the ones that determine the relationships with suppliers, integrate human resources, and approve the lean manufacturing techniques and tools that support the JIT
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