Emilio Jiménez

Applicability of lean production with VSM to the Rioja wine sector

Lean production arose as a step towards a new era in production systems. It is a working philosophy designed to produce better products using fewer resources to obtain greater benefits. It has been applied to a wide variety of sectors different from the original automotive industry, in which it was developed. However, its application to continuous manufacturing processes of continuous products has been less, especially to the wine-production sector. The wine sector differs greatly from the automobile sector in various fundamental aspects, but it also has common fundamental aspects in its production and logistics systems. An important part of this work has consisted in studying the wineries of the Rioja region. This article analyses the applicability of lean production in the La Rioja wine sector and the results that may be obtained from its application, using value stream mapping as the main tool to identify opportunities for improvement. This piece of research shows that most of the production problems in the wine sector can be tackled using a lean production system, making certain adjustments according to the type of production. It shows the main properties of wine production from the lean viewpoint, and it improves the production and logistics systems.

On Observability and Design of Observers inTimed Continuous Petri Net Systems

This paper is devoted both to the study of observability criteria and the design of observers in the continuous Petri net setting. The concept of structural observability, regarding the possibility of estimating the marking of places, i.e., the system state, for any speed of the transitions is introduced and studied for the subclass of join-free Petri nets (JF). For non-join-free Petri nets, conditions to compute suitable state estimates are established. The proposed observers are piecewise linear systems that assure the continuity of the estimate even when a switch occurs. The system simulation may allow us to estimate even the unobservable space of the net system during a given time period.

Relaxed continuous views of discrete event systems: considerations on Forrester diagrams and Petri nets

Petri nets (PNs) constitute a formal paradigm for discrete systems. Some discrete models can be relaxed into continuous models. Infinite server semantics continuous Petri nets (ISSCPNs) is one of the most relevant timed interpretation of continuous PNs. ISSCPNs can be seen as piecewise linear systems. Forrester diagrams (FD) are specific modelling tools inside system dynamics, a methodology for the analysis of complex continuous systems. This paper explores and compares the modelling power of both formalisms, ISSCPNs and FD. Previous comparative views focused on the formalisms and on positive and compartmental systems, constitute the basis of this work. The comparison is complemented taking into account the interpretation of linear ordinary differential equation systems (LODES), the information delays and some methodological considerations. ISSCPNs permit to model any LODES when known upper and lower bounds of the state variables exists. Therefore systems with cyclic behaviour or delays in the information can be modelled.

Methodological approach towards sustainability by integration of environmental impact in production system models through life cycle analysis: Application to the Rioja wine sector

This paper proposes the integration of life cycle analysis within the production system models as a tool for decision making (whether at the strategic, tactical or operational levels) attending not only economic and technical criteria but also the environmental impact. This methodological proposal advances over the traditional approach of calculating the value of the environmental impact of a particular product, by proposing the use of models to determine the environmental impact of the product, according to the decisions made in the production system. That is, it does not provide an impact value of the product, but rather a model to determine the impact in terms of the decisions made in the production process; therefore, it can be used, especially by means of simulation, for the optimization of the production system, based on multiple criteria (including environmental impact). The methodological approach is exemplified by a case study, which is used to validate the proposal and to expose it more precisely and clearly, although the methodology is equally applicable to any production process, especially processes highly automated or with different alternative production techniques. This case study, based on the wine production sector of the Rioja Qualified Designation of Origin, in Spain, was made with actual data after several years of research in representative wineries; therefore, besides an application example, it is a support tool for sustainability in wineries, by reducing the environmental impact of wine production (especially in La Rioja and Spain, but generally throughout the world).

Forrester diagrams and continuous Petri nets: a comparative view

Forrester diagrams (FD) and Petri nets (PN) are formalisms introduced in the sixties to model complex systems. This paper explores similarities and differences between FDs and the continuous relaxation of the originally discrete PNs. Historically speaking, the approaches were quite different: the PNs paradigm was introduced at a very abstract level, without timing interpretation, while FDs led to a modelling methodology where the systematic simulation of a set of differential equations was the goal. Strict flow conservation around valves, non explicit fork and join operations, separation of information and material flows, are peculiarities of FDs. In PN models the existence of global conservation laws is a potential for structural analysis.

The optimization problem based on alternatives aggregation Petri nets as models for industrial discrete event systems

The construction, set-up and operation of many systems of interest in sectors such as industry, supply chains and communications are complex processes, which may require significant investment of resources. For this reason, the automation of the decision making for achieving the best design and operation of such systems, which may be regarded as discrete event systems (DESs), constitutes an active research field. In this paper, we present a methodology to cope with this process in an efficient way, optimizing not only the behaviour of the DES but also its structure. This kind of problem is usually associated with the so-called combinatorial explosion, since the number of alternative configurations for the DES might be huge. We present an improved algorithm to transform a set of alternative Petri nets, representing alternative structural configurations, into a more compact model called an alternatives aggregation Petri net. In real decision-making problems, where the different alternative structural configurations may share common subnets, this compact model may allow the development of a much more efficient optimization problem than the classic approach of ‘divide and conquer’. The achievement of this objective is performed by developing a single and compact model for all of the alternative structural configurations of the DES and the simulation of the most promising of them. In this paper, the mentioned methodology is introduced and its advantages and drawbacks are described in relation with the classic approach.

On observability in timed continuous Petri net systems

Fluidification is a classical relaxation technique for approximated performance evaluation of discrete systems. In this paper we deal with T-timed fully continuous Petri Nets working under infinite servers semantics, what leads to (deterministic) piecewise linear differential systems. Switches among dynamic linear systems are triggered by internal events through minimum operators on marking variables. The observability problem consists of estimating the (initial) marking from a partial measure. This paper is devoted to observability concepts and criteria in this particular class of systems, not to the observers design. The concept of structural observability, regarding to the possibility of estimating the marking of places for any speed of the transitions is introduced and studied for the subclass of join-free Petri nets (JF). For non join-free Petri nets, conditions to compute suitable estimates will be established.

Mining association rules from time series to explain failures in a hot-dip galvanizing steel line

This paper presents an experience based on the use of association rules from multiple time series captured from industrial processes. The main goal is to seek useful knowledge for explaining failures in these processes. An overall method is developed to obtain association rules that represent the repeated relationships between pre-defined episodes in multiple time series, using a time window and a time lag. First, the process involves working in an iterative and interactive manner with several pre-processing and segmentation algorithms for each kind of time series in order to obtain significant events. In the next step, a search is made for sequences of events called episodes that are repeated among the various time series according to a pre-set consequent, a pre-established time window and a time lag. Extraction is then made of the association rules for those episodes that appear many times and have a high rate of hits. Finally, a case study is described regarding the application of this methodology to a historical database of 150 variables from an industrial process for galvanizing steel coils.

Simulation-based optimization of discrete event systems with alternative structural configurations using distributed computation and the Petri net paradigm

Decision-making on discrete event systems with alternative structural configurations is a field with application to the efficient design and operation of many systems, ranging from manufacturing facilities to communication networks. The solution of this problem may be afforded by its transformation into an optimization problem. A variety of statements for this optimization problem can be presented by using different formalisms able to describe the model of the system. These different statements allow developing diverse optimization algorithms for solving the problem, which may be very demanding for a computer. In this paper, several approaches are presented in order to reduce the computing requirements needed by the mentioned algorithms, some of them are implemented in one processor and others are based on distributed computing. In particular, this paper presents a new distributed methodology, which associates sets of alternative structural configurations of the system to different alternative aggregation Petri net (AAPNs), regarding the number of available processors. Under certain conditions, this methodology alleviates the computational requirements for every processor and speeds up the optimization process. A case-study is presented and different techniques are applied to solve it, for illustrating diverse distributed and non-distributed methodologies, regarding the available processors, as well as for comparing their relative performance.

Environmental impact of mushroom compost production

BACKGROUND This research analyses the environmental impact of the creation of Agaricus bisporus compost packages. The composting process is the intermediate stage of the mushroom production process, subsequent to the mycelium cultivation stage and prior to the fruiting bodies cultivation stage. RESULTS A full life cycle assessment model of the Agaricus bisporus composting process has been developed through the identification and analysis of the inputs-outputs and energy consumption of the activities involved in the production process. The study has been developed based on data collected from a plant during a 1 year campaign, thereby obtaining accurate information used to analyse the environmental impact of the process. CONCLUSION A global analysis of the main stages of the process shows that the process that has the greatest impact in most categories is the compost batch preparation process. This is due to an increased consumption of energy resources by the machinery that mixes the raw materials to create the batch. At the composting process inside the tunnel stage, the activity that has the greatest impact in almost all categories studied is the initial stage of composting. This is due to higher energy consumption during the process compared to the other stages.