Unbalanced Workload Allocation in Large Assembly Lines.

In modern production systems that perform under high cost environments, even small improvements in line efficiency represents large savings over the lifetime of an assembly line. In the beginning of modern production systems, it was thought that a `perfectly balanced\u27 line was the most efficient way to design the line. However in practice, the ideal perfectly balanced line seldom occurs, because some degree of imbalance is inevitable. Recent studies have found that unbalanced lines with a bowl shape workload configuration can yield performance in throughput as good as, or even better than those of a perfectly balanced line. This thesis studied the bowl phenomenon in large unpaced assembly lines under stochastic processing times. The control variables analyzed in this study were line length, buffer capacity, task time variability, and percentage of imbalance. A full factorial experiment was designed in order to characterize the main and interaction effects, and computational simulation was used to replicate the behavior of the unbalanced assembly lines. The results of the experiment suggest that unbalancing a large assembly line in a bowl shape workload configuration could provide statistical significant improvements in throughput. Moreover, the results also suggest that the Work in Process (WIP) and the Cycle Time (CT) increase linearly as the Throughput (TR) of the line increases. Even though, the rate at which the TR increases is greater than the rate at which the WIP and CT increases, line designers and production managers need to make an important managerial decision on how much they are willing to increase the WIP and CT of their lines in order to improve the throughput when implementing a bowl shape workload configuration. Furthermore, the results suggested that as the buffer capacity and the number of workstations in the line decreases, and the coefficient of variation of the workstations increases the benefits the bowl phenomenon and the percentage of imbalance of the best bowl configuration increases. In this research, the relationship between the production rate of large assembly lines with a bowl shape workload configuration and its line length, buffer capacity, task time variability, and percentage of imbalance has been studied for the first time. The results would provide valuable guidelines for line designers and managers that want to improve their assembly lines

The impact of unequal processing time variability on reliable and unreliable merging line performance

Research on merging lines is expanding as their use grows significantly in the contexts of remanufacturing, reverse logistics and developing economies. This article is the first to study the behavior of unpaced, reliable, and unreliable merging assembly lines that are deliberately unbalanced with respect to their coefficients of variation (CV). Conducting a series of simulation runs with varying line lengths, buffer storage capacities and unbalanced CV patterns delivers intriguing results. For both reliable and unreliable lines, the best pattern for generating higher throughput is found to be a balanced configuration (equal CVs along both parallel lines), except for unreliable lines with a station buffer capacity of six. In that case, the highest throughput results from the descending configuration, i.e. concentrating the variable stations close to the beginning of both parallel lines and the steady stations towards the end of the line. Ordering from the least to most steady station also provides the best average buffer level. By exploring the experimental Pareto Frontier, this study shows the combined performance of unbalanced CV patterns for throughput and average buffer level. Study results suggest that caution should be exercised when assuming equivalent behavior from reliable and unreliable lines, or single serial lines and merging lines, since the relative throughput performance of some CV patterns changed between the different configurations

Unbalanced manual flow line operating characteristics.

This thesis studies the operating behaviour of the manual unpaced lines, which are the most important of the flow lines' systems. The lines examined are unbalanced and six types of imbalance are considered, namely, the imbalances of mean service times, coefficients of variation (Covars), buffers'capacities, means and Covars, means and buffers, and Covars and buffers. It is argued that the deep understanding of the behavioural characteristics of such lines, contributes towards the achievement of practical solutions to many of their problems. The lines are simulated under both steady and non-steady states conditions, with positively skewed weibull work times distributions, different values of line length (N), buffer capacity (B), degree of imbalance (DI), and pattern of imbalance, utilizing full factorial designs.The data are subjected to the analysis of variance, multiple regression, multiple comparisons with control, pairwise comparisons, canonical correlation, and utilitv analysis A simple utility approach is also explored briefly.Some of the important conclusions for all the unbalanced lines' investigations are:(1) At least one unbalanced pattern generates superior idle time (I) and/or mean buffer level (ABL), over those of a balanced line. The superiority in I decreases as DI rises, whereas the advantage in ABL reduces as DI is decreased.(2) The DI of the best unbalanced pattern can substantially or moderately be increased and still yields approximately equal I to that of a balanced configuration.(3) If a line is unbalanced in the wrong direction, significantly inferior performance to that of a balanced design will result.(4) The unbalanced patterns' I tends to decrease, when N and DI reduce and B increases, while ABL falls directly with B.(5) The I's transient size increases as N and B become higher and DI increases, while the ABL's transient size rises whenever B reduces

A hybrid meta-heuristic approach for buffer allocation in remanufacturing environment

Remanufacturing system is complicated due to its stochastic nature. Random customer demand, return product rate and system unreliability contribute to this complexity. Remanufacturing systems with unreliable machines usually contain intermediate buffers which are used to decouple the machines, thereby, reducing mutual interference due to machine breakdowns. Intermediate buffers should be optimized to eliminate waste of resources and avoid loss of throughput. The Buffer Allocation Problem (BAP) deals with allocating optimally fixed amount of available buffers to workstations located in manufacturing or remanufacturing systems to achieve specific objectives. Optimal buffer allocation in manufacturing and remanufacturing systems not only minimizes holding cost and stock space, but also makes facilities planning and remanufacturing decisions to be effectively coordinated. BAP in a non-deterministic environment is certainly one of the most difficult optimization problems. Therefore, a mathematical framework is provided to model the dependence of throughput on buffer capacities. Obviously, based on the survey undertaken, not only there exists no algebraic relation between the objective function and buffer size but the current literature does not offer analytical results for buffer capacity design in remanufacturing environment. Decomposition principle, expansion method for evaluating system performance and an efficient hybrid Meta-heuristic search algorithm are implemented to find an optimal buffer allocation for remanufacturing system. The proposed hybrid Simulated Annealing (SA) with Genetic Algorithm (GA) is compared to pure SA and GA. The computational experiments show better quality, more accurate, efficient and reliable solutions obtained by the proposed hybrid algorithm. The improvement obtained is more than 4.18 %. Finally, the proposed method is applied on toner cartridge remanufacturing company as a case study, and the numerical results from hybrid algorithm are presented and compared with results from SA and GA

Human factors in the woollen industry: an investigation of inspection and mending performance with special reference to worsted and terylene/worsted cloth

This is an investigation into certain aspects of a process called burling and mending which is concerned with the inspection and repair of faults in cloth. The females who carry out this task represent a high proportion of the labour force in the textile industry. Three experiments were undertaken. The first of which established basic information on operator performance by testing the speed and accuracy of burlers and menders in carrying out cloth inspection on an evaluated piece of cloth, under four experimental conditions. The conditions prescribed inspection with: (1) eyes only; (2) hands only; (3) both hands and eyes (normal); and (4) hands and eyes plus supplementary angular lighting. A statistical analysis took into account the conditions described age differences performance in relation to eight different fault categories and the resultant interactions. [Continues.

Productivity and flexibility improvement of assembly lines for high-mix low-volume production. A white goods industry case

Las tendencias globales de la personalización e individualización en masa impulsan la producción industrial en serie corta y variada; y por tanto una gran variedad de productos en pequeñas cantidades. Por ello, la customización en masa precisa de sistemas de ensamblaje que sean a la vez altamente productivos y flexibles, a diferencia de la tradicional oposición entre ambas características. La llamada cuarta revolución industrial trae diversas tecnologías habilitadoras que podrían ser útiles para abordar este problema. Sin embargo, las metodologías para implementar el ensamblaje 4.0 todavía no han sido resueltas. De hecho, para aprovechar todas las ventajas potenciales de la Industria 4.0, es necesario contar con un nivel previo de excelencia operacional y un análisis holístico de los sistemas productivos. Esta tesis tiene como objetivo entender y definir cómo mejorar la productividad y la flexibilidad de las operaciones de montaje en serie corta y variada.Esta meta se ha dividido en tres objetivos. El primer objetivo consiste en comprender las relaciones entre la Industria 4.0 y las operaciones de ensamblaje, así como sus implicaciones para los operarios. El segundo objetivo consiste en desarrollar una metodología y las herramientas necesarias para evaluar el rendimiento de diferentes configuraciones de cadenas de ensamblaje. El último objetivo consiste en el diseño de sistemas de ensamblaje que permitan incrementar su productividad al menos un 25 %, produciendo en serie corta y variada, mediante la combinación de puestos de montaje manual y estaciones automatizadas.Para abordar la fase de comprensión y definición del problema, se llevó a cabo una revisión bibliográfica sistemática y se desarrolló un marco conceptual para el Ensamblaje 4.0. Se desarrollaron, verificaron y validaron dos herramientas de evaluación del rendimiento: un modelo matemático analítico y varios modelos de simulación por eventos discretos. Para la verificación, y como punto de partida para los análisis, se ha utilizado un caso de estudio industrial de un fabricante global de electrodomésticos. Se han empleado múltiples escenarios de simulación y técnicas de diseño de experimentos para investigar tres cuestiones clave.En primer lugar, se identificaron los factores más críticos para el rendimiento de líneas de montaje manuales multi-modelo. En segundo lugar, se analizó el rendimiento de líneas de montaje semiautomáticas paralelas con operarios móviles en comparación con líneas semiautomáticas o manuales con operarios fijos, empleando diversos escenarios de demanda en serie corta y variada. Por último, se investigó el uso de trenes milkrun para la logística interna de líneas de ensamblaje multi-modelo bajo la influencia de perturbaciones.Los resultados de las simulaciones muestran que las líneas paralelas con operarios móviles pueden superar a las de operarios fijos en cualquier escenario de demanda, alcanzando como mínimo el objetivo de mejorar la productividad en un 25% o más. También permiten reducir cómodamente el número de operarios trabajando en la línea sin afectar negativamente al equilibrado de la misma, posibilitando la producción eficiente de bajo volumen. Los resultados de las simulaciones de logística interna indican que los milkrun pueden proteger las líneas de ensamblaje de las perturbaciones originadas en procesos aguas arriba.Futuras líneas de investigación en base a los resultados obtenidos en esta tesis podrían incluir la expansión e integración de los modelos de simulación actuales para analizar las cadenas de montaje paralelas con operarios móviles incorporando logística, averías y mantenimiento, problemas de control de calidad y políticas de gestión de los retrabajos. Otra línea podría ser el uso de diferentes herramienta para el análisis del desempeño como, por ejemplo, técnicas de programación de la producción que permitan evaluar el desempeño operacional de diferentes configuraciones de cadenas de montaje con operarios móviles, tanto en términos de automatización como de organización en planta. Podrían incorporarse tecnologías de la Industria 4.0 a los modelos de simulación para evaluar su impacto operacional global ¿como cobots para ensamblaje o para la manipulación de materiales, realidad aumentada para el apoyo cognitivo a los operarios, o AGVs para la conducciónde los trenes milkrun. Por último, el trabajo presentado en esta tesis acerca las líneas de ensamblaje semiautomáticas con operarios móviles a su implementación industrial.<br /

Timing and Time Perception: Procedures, Measures, and Applications

Timing and Time Perception: Procedures, Measures, and Applications is a one-of-a-kind, collective effort to present the most utilized and known methods on timing and time perception. Specifically, it covers methods and analysis on circadian timing, synchrony perception, reaction/response time, time estimation, and alternative methods for clinical/developmental research. The book includes experimental protocols, programming code, and sample results and the content ranges from very introductory to more advanced so as to cover the needs of both junior and senior researchers. We hope that this will be the first step in future efforts to document experimental methods and analysis both in a theoretical and in a practical manner

Mechanisms of increased arrhythmogenic risk associated with acute regional ischaemia in rabbit: An optical mapping study

Acute coronary artery occlusion is the most common cause of sudden cardiac death. In some cases an acute myocardial infarction (MI) can immediately lead to lethal arrhythmias, but the factors that determine whether an MI precipitates arrhythmias are uncertain. In this thesis, I compare and contrast the detailed electrophysiology of hearts that develop arrhythmias post MI compared to those that do not using voltage sensitive fluorescent dyes in isolated rabbit hearts. In an attempt to improve the information from voltage mapping studies, initial work involved attempts to use ratiometric imaging of the fluorescence from the dye RH237. These identified optimal filter settings to collect voltage data at two distinct wavebands that would eliminate movement artefact and permit absolute voltage measurements. But routine implementation of this technique was prevented by additional technical issues related to uneven illumination levels and alignment of the two cameras. In initial studies the drug E-4031, a selective blocker of the delayed rectifier potassium current (IKr), was used to assess the contribution of this channel to repolarisation in rabbit ventricle, both in the steady state at a range of physiological and sub-physiological frequencies and in the transition between step frequency changes. The data suggests that IKr has a small but significant contribution to repolarisation at normal heart rates, 300ms pacing cycle length; a close to maximal concentration of E-4031 (0.03M) increased action potential duration (APD90) by 8.5 ± 1.7ms (P<0.01). This contribution is considerably larger at lower stimulation frequencies; at 1Hz E-4031 increased APD by 73.7 ± 13.7ms (P<0.05). The EC50 for E-4031 in this study was 0.01M which is similar to that reported in the literature. The recovery of the channel from inactivation appeared an important determinant of the rate of adaptation of the action potential duration. In the main experimental section, a novel snare technique was used to produce the acute coronary artery occlusion in the apical region of the left ventricle (LV) free wall. From control experiments (n=21), 47.6% of the hearts develop ventricular fibrillation (VF) within 30 minutes of coronary artery occlusion. On average, hearts with intrinsically longer epicardial action potential duration prior to ischaemia (mean APD50 168.8 ± 5.5ms) did not develop VF, and those with shorter APD (mean APD50 141.5 ± 3.5ms) during pre-occlusion period were more prone to VF (P<0.001). However, artificially prolonging the APD with the drug E-4031 (0.03 concentration) prior to coronary artery occlusion did not significantly change the incidence of arrhythmia. Brief and transient exposure to isoprenaline (0.3Mconcentration) before the occlusion shortened the average APD prior to occlusion but still did not increase the likelihood of VF. Therefore, I concluded that shorter epicardial APD values prior to ischaemia are associated with a higher incidence of arrhythmia but are not the cause. To investigate this further, a panoramic optical mapping technique was used to look at the electrophysiological properties across the entire ventricular surface of the hearts. The panoramic optical mapping study confirmed the correlation between shorter APD pre-occlusion and the incidence of VF during occlusion and indicated that the region of the LV exhibiting a shorter APD is confined to the apical half of the LV, and does not include basal LV or RV electrophysiology. Panoramic imaging also revealed a delayed activation time predominantly in the basal aspects of the LV. Both of these events – shorter APD in the apex and longer activation time in the base – were a feature of hearts that developed VF on ligation of the coronary artery. Future work will investigate the cellular/molecular basis for these differences in ventricular electrophysiology

Asymmetric interlimb coupling strength in rhythmic bimanual coordination

Beek, P.J. [Promotor]Peper, C.E. [Copromotor

Myocardial energy utilisation in relation to canine circulatory control, studied by multi-variate analysis and computer simulation

Imperial Users onl