Conceptual Approach of Robustness in Logistical Control

The logistical control and order release of structurally dynamic systems represent a great challenge. In contrast to classical shop floor production, these systems can involve transitions between the two different organizational forms job shop production and flow production. This results in a system that is susceptible to turbulence and malfunctions. This paper presents an approach that improves the robustness of these systems and achieves a stable system state even under external influences. Decentralized stock control loops control the WIP of the individual stations in a closed loop. When organizational transitions occur, interlinking losses arise, which reduce the productivity of the system. Similar effects can cause disturbances and blockages. The introduction of a robustness controller adapts the input parameters of the order release to the current system status, so that an adapted reaction takes place in the event of strong disturbances

TOWARDS DIGITAL TWIN-DRIVEN PERFORMANCE EVALUATION METHODOLOGY OF FMS

The paper presents a method of automated modelling and performance evaluation of concurrent production flows carried out in Flexible Manufacturing Systems. The method allows for quick assessment of various variants of such systems, considering their structure and the organization of production flow of possible ways of their implementation. Its essence is the conditions imposed on the designed model, limiting the space of possible variants of the production flow only to deadlock-free variants. The practical usefulness of the model implemented in the proposed method illustrates the example, which describes the simultaneous assessment of alternative variants of the flexible machining module's structure and the planned multi-assortment production. The ability of the method to focus on feasible solutions offers attractive perspectives for guiding the Digital Twin-like scenario in situations caused by the need to change the production flow

Multi-job production systems: definition, problems, and product-mix performance portrait of serial lines

This paper pursues two goals: (a) Define a class of widely used in practice flexible manufacturing systems, referred to as Multi-Job Production (MJP) and formulate industrially motivated problems related to their performance. (b) Provide initial results concerning some of these problems pertaining to analysis of the throughput and bottlenecks of MJP serial lines as functions of the product-mix. In MJP systems, all job-types are processed by the same sequence of manufacturing operations, but with different processing time at some or all machines. To analyse MJP with unreliable machines, we introduce the work-based model of production systems, which is insensitive to whether single- or multi-job manufacturing takes place. Based on this model, we investigate the performance of MJP lines as a function of the product-mix. We show, in particular, that for the so-called conflicting jobs there exists a range of product-mixes, wherein the throughput of MJP is larger than that of any constituent job-type manufactured in a single-job regime. To characterise the global behaviour of MJP lines, we introduce the Product-Mix Performance Portrait, which represents the system properties for all product-mixes and which can be used for operations management. Finally, we report the results of an application at an automotive assembly plant

Incorporating working conditions to a mixed- model sequencing problem

Partiendo de una variante de un problema de secuenciación en líneas de productos mixtos (MMSP-W: Mixed-Model Sequencing Problem with Workload Minimisation), se proponen dos nuevos modelos que incorporan condiciones laborales a los puestos de trabajo de la línea. El primero tiene en cuenta la limitación de la saturación de los puestos de trabajo, mientras que el segundo contempla, además, la activación de los operarios a lo largo de la jornada laboral. Se realizan sendas experiencias computacionales, empleando un caso de estudio de la planta de motores de Nissan en Barcelona, con dos propósitos: (1) estudiar la repercusión que ocasiona la limitación de la saturación sobre la caída de la productividad de la línea, y (2) evaluar la recuperación de la productividad de la línea, mediante la activación de los operarios, manteniendo la misma calidad en las condiciones laborales conseguida al limitar la saturación.Beginning with a variation of the sequencing problem in a mixed-products line (MMSP-W: Mixed-Model Sequencing Problem with Workload Minimization), we propose two new models that incorporate the working conditions into the workstations on the line. The first model takes into account the saturation limit of the workstations, and the second model also includes the activation of the operators throughout the working day. Two computational experiments were carried out using a case study of the Nissan motor plant in Barcelona with two main objectives: (1) to study the repercussions of the saturation limit on the decrease in productivity on the line and (2) to evaluate the recovery of productivity on the line via activation of operators while maintaining the same quality in working conditions achieved by limiting the saturation. The obtained results show that the saturation limitation leads to suppose an important increase of work overload, which means average economic losses of 28,731.8 euros/day. However, the consideration of activity reduces these losses by 62.7%.Preprin

Work Organisation and Innovation in Ireland

[Excerpt] Innovations in work organisation have the potential to optimise production processes in companies and improve employees’ overall experience of work. This report explores the links between innovations in work organisation – under the broader label of high performance work practices (HPWPs) – and the potential benefits for both employees and organisations. It draws on empirical evidence from three case studies carried out in the Republic of Ireland, where workplace innovations have resulted in positive outcomes and where social partners played a significant role in their design and development

A research survey: review of flexible job shop scheduling techniques

In the last 25 years, extensive research has been carried out addressing the flexible job shop scheduling (JSS) problem. A variety of techniques ranging from exact methods to hybrid techniques have been used in this research. The paper aims at presenting the development of flexible JSS and a consolidated survey of various techniques that have been employed since 1990 for problem resolution. The paper comprises evaluation of publications and research methods used in various research papers. Finally, conclusions are drawn based on performed survey results. A total of 404 distinct publications were found addressing the FJSSP. Some of the research papers presented more than one technique/algorithm to solve the problem that is categorized into 410 different applications. Selected time period of these research papers is between 1990 and February 2014. Articles were searched mainly on major databases such as SpringerLink, Science Direct, IEEE Xplore, Scopus, EBSCO, etc. and other web sources. All databases were searched for “flexible job shop” and “scheduling” in the title an

Decentralised vs partially centralised self-organisation model for mobile robots in large structure assembly

Currently, manufacturing companies are heavily investing into the automation of manufacturing processes. The push to improve productivity and efficiency is increasing the demand for more flexible and adaptable solutions than the currently common dedicated automation systems. In this paper, the planning problem for mobile robots in large structure assembly was addressed. Despite near-optimal results, the previously developed hybrid agent behaviour model was found to lack responsiveness and scalability. For that reason, an alternative, fully decentralised agent behaviour model was developed and compared to the hybrid one. Through simulated experiments, it was found that the decentralised agent behaviour model achieved much higher responsiveness; however, it required additional spare capacity to compensate for its decision-making imperfections

Evaluating the performance of an AGV fleet in an FMS under minimizing part movement and balancing workload rules

The performance of an FMS with respect to AGV utilization is assessed using a simulation model. AGV fleets of different sizes are evaluated. Under OOM, an assignment rule designed to decrease time in system by minimizing part movements among machine tools, AGV utilization is lower than under WINO, an assignment rule that seeks to balance machine workload. For a given AGV fleet, machine utilization imbalance is more levelled under WINO than OOM, however comparing across the three AGV fleets, the maximum machine imbalance is smoother under OOM than under WINO. AGV utilization consistently decreases as the number of AGVs increases from eight to nine and then to 10. The system performance is adversely affected not only by too many AGVs but also by surplus spots in both inbound and outbound queues placed in front of the machine tools