The effect of machine breakdowns and interstage storage on the performance of production line systems

Both machine breakdowns and interstage storage can significantly affect the efficiency of a production line. In this paper we use an exact analytic model to conduct a detailed study of how these two factors affect the throughput of a line. Based on the empirical results, a simple heuristic method is given to estimate the amount of storage space required to offset the negative effect of machine breakdowns. The results provide useful guidelines for designing or analysing production line systems.     

Hierarchical production control for a flow shop with dynamic setup changes and random machine breakdowns

In this paper, we study a manufacturing system consisting of two machines separated by two intermediate buffers, and capable of producing two different products. Each product requires a constant processing time on each of the machines. Each machine requires a constant non-negligible setup change time from one product to the other. The demand rate for each product is considered to be piecewise constant. Each machine undergoes failure and repair. The time-to-failure and time-to-repair are exponentially distributed random variables. The setup change and processing operations are resumable. We model our system as a continuous time, continuous flow process. An optimal control problem is formulated for the system to minimize the total expected discounted cost over an infinite horizon. To determine the optimal control policy structure, a discrete version of the problem is solved numerically using a dynamic programming formulation with a piecewise linear penalty function. A real-time control algorithm is then developed with the objective of maintaining low work-in-process inventory and keeping the production close to the demand. The algorithm uses a hierarchical control structure to generate the loading times for each product on each machine in real time and to respond to random disruptions in the system. The system is simulated using this algorithm to study its performance. The performance of the algorithm is also compared to alternative policies.     

Genetic algorithm for job-shop scheduling with machine unavailability and breakdowns

The job-shop scheduling problem (JSSP) is considered to be one of the most complex combinatorial optimisation problems. In our previous attempt, we hybridised a Genetic Algorithm (GA) with a local search technique to solve JSSPs. In this research, we propose an improved local search technique, Shifted Gap-Reduction (SGR), which improves the performance of GAs when solving relatively difficult test problems. We also modify the new algorithm for JSSPs with machine unavailability and breakdowns. We consider two scenarios of machine unavailability. First, where the unavailability information is available in advance (predictive) and, secondly, where the information is known after a real breakdown (reactive). We show that the revised schedule is mostly able to recover if the interruptions occur during the early stages of the schedules.     

The effect of breakdowns on U-shaped production lines

Consider a synchronized line performing assembly or fabrication tasks. Tasks are grouped into stations and stations are positioned on a line that is U-shaped. Stations may break down and be repaired. Small buffer inventories may be placed between stations to lessen the effect of breakdowns at one station on production at other stations. This paper investigates the effect of the U-shape of the line on the line effectiveness. We find that effectiveness increases when the line is U-shaped, compared with the traditional straight line shape.     

TDB-30W微层吹塑中空成型机生产线介绍

介绍了微层吹塑的原理、生产工艺,与传统技术相比具有的优点,以及本技术的未来技术创新点与市场前景。     

Predictable scheduling of a single machine with breakdowns and sensitive jobs

Production schedules released to the shop floor have two important functions: allocating shop resources to different jobs to optimize some measure of shop performance and serving as a basis for planning external activities such as material procurement, preventive maintenance and delivery of orders to customers. Schedule modification may delay or render infeasible the execution of external activities planned on the basis of the predictive schedule. Thus it is of interest to develop predictive schedules that can absorb disruptions without affecting planned external activities while maintaining high shop performance. We present a predictable scheduling approach, that inserts additional idle time into the schedule to absorb the impacts of breakdowns. The effects of disruptions on planned support activities are measured by the deviations of job completion times in the realized schedule from those in the predictive schedule. We apply our approach to minimizing total tardiness on a single machine with stochastic machine failures. We then extend the procedure to consider the case where job processing times are affected by machine breakdowns, and provide specialized rescheduling heuristics. Extensive computational experiments show that this approach provides high predictability with minor sacrifices in shop performance.     

Economic lot sizing for an imperfect production system subject to random breakdowns

This article considers an economic manufacturing quantity model for an imperfect production process that is subject to random machine breakdowns. The product is manufactured intermittently in batches to meet a constant demand. During a production run, the system is assumed to deteriorate over time. As a result, a fixed proportion of items produced are defective. The system is also subject to random breakdowns. A no-resumption inventory control policy is adopted. Under this policy, the production run is aborted when a breakdown occurs. Production will be resumed only when all on-hand inventories are depleted. Corrective maintenance is carried out immediately after a breakdown. The time-to-shift and the time-to-breakdown are two random variables following different exponential distributions. The objective is to find an optimal production lot size that minimizes the expected (long-run) total cost per unit time. Several models are investigated and a numerical approach is developed to obtain an optimal production lot size.     

The calculation of machine transient performance

In a recent paper the authors described the analysis of the transient field in the cross-section of a micro-generator during a field decrement test. Here results are presented for a similar calculation on a 4-pole 325 MVA machine. The complications arising from the conducting rotor body are discussed and suitable equations are formulated. A general transient machine formulation including stator currents is given.     

A real-time methodology for minimizing mean flowtime in FMSs with machine breakdowns: threshold-based selective rerouting

This paper presents the threshold-based selective rerouting (TSR) heuristic to minimize mean flowtime of parts in a flexible manufacturing system (FMS) with machine failures. Most of the available methodologies considering machine failures are either off-line methods or propose different versions of rerouting all the jobs to alternate machines. The objective of this methodology is to develop an efficient real-time rerouting strategy, which can be easily applicable in case of machine failures and is able to adapt to the dynamic features of an FMS. Parts in the queue of a failed machine are selectively rerouted to alternate machines when the benefit in terms of waiting time obtained from rerouting exceeds a specific pre-determined threshold value. The threshold concept and the performance of TSR in minimizing mean flowtime are tested with extensive simulation experiments. It has been shown that TSR provides significant improvements in system performance measures compared to other real-time rerouting methods and that the threshold value is dependent on system parameters. The relationship between the threshold value and system parameters has also been determined.     

A 3-DOF testing machine for in-plane behaviour of structures

A testing machine designed for studying the in-plane behaviour of structures controlling independently (either in load and in displacement) three degrees of freedom is presented. The main topics herein discussed are (i) limits of application, either due to the capability of jacks, transducers and rollers, and to local and global equilibrium; (ii) behaviour in the case of brittle failure, with particular regard to energy and displacement restitution due to the elastic behaviour of the machine itself and to oil deformability; and (iii) the control system, which is based on the classic scheme for feedback control systems and has a separate sub-system to keep under control the security devices.     

Operator allocation planning for reconfigurable production line in one-of-a-kind production

In a one-of-a-kind production (OKP) company, the operation routing and processing time of an order are usually different from the others due to high customisation. As a result, an OKP company needs to dynamically adjust the production resources to keep the production lines reconfigurable. Through a proper assignment of operators in different sections of a production line, bottlenecks and operator re-allocation during production can be reduced effectively. In this paper, a mathematical model is introduced for optimal operator allocation planning on a reconfigurable production line in OKP. The optimisation objectives are to minimise the total number of the operators, total job earliness and tardiness, and the average work-in-process storage. A branch-and-bound algorithm with efficient pruning strategies is developed to solve this problem. The proposed model and the algorithm are empirically validated by using the data of a windows and doors manufacturing company. A software system based on the proposed approach has been implemented in the company.     

Simple mathematical model for predicting the transient behaviour of an ice-bank system

The time-variable performance of a Refrigerant 22 ice-bank system was simulated by a dynamic model which was derived by assuming that heat transfer was always the limiting process, and which thus ignored hydrodynamic processes. The model comprised four ordinary differential equations describing the position of the ice front, the water temperature, and the refrigerant evaporation and condensation temperatures, each of which was derived by energy balance, plus a number of algebraic equations. Measured plant performance was accurately predicted except immediately after start-up, and in circumstances in which the assumption that the dynamics of refrigerant flow did not exert any controlling influence on the overall process dynamics was inadequate (for example, when the thermostatic expansion valve operation becomes unstable). The model requires only data that should be readily available or can be easily estimated, and thus it is suitable for analyses in the design of ice bank systems to handle time-varying conditions. Simple dynamic models ignoring hydrodynamics can be adequate in circumstances where the main source of variation arises beyond the refrigeration circuit itself.     

Virtual simulation of production line for ergonomics evaluation

To avoid ergonomic problems in the early planning stages of a production line and achieve more satisfactory planning and design, ergonomic simulation is
particularly important in digital production line planning. An ergonomics analysis method is presented by using two theories: Ovako working posture analysis system (OWAS) and Burandt-Schultetus hand-arm force analysis (BSHA). The processes of ergonomics analysis and simulation are discussed based on a platform of process simulation and process designer. As an example, the paper shows how ergonomics problems are considered in production line planning to make a better choice between different production line planning schemes.     

突然开孔结构风致瞬态内压极值研究

基于经典内压控制方程,对特定开孔时刻下的瞬态内压峰值响应进行了详细研究,分析孔口开启时间对结构瞬态内压峰值的影响。提出突然开孔结构瞬态内压极值的估算方法,并与精确算法进行对比。结果表明:门窗开启时刻的外压值越大,瞬态内压峰值越大,但两者最大值之间存在着一定的时差;瞬态内压极值与外压达极值时的瞬态内压峰值之间的比值可用放大因子G=1.17来描述;提出的极值计算方法能有效地估算突然开孔结构瞬态内压极值。     

The damped transient behaviour of finite beams and plates

The direct Finite Element Analysis which was successfully employed in the solution of dynamic flexural traveling wave problems is extended herein to provide the transient behaviour of finite beams and plates in which shear deformation and rotatory inertia are considered. The particle and angular velocities are exponentially damped so that the static solutions for these problems are obtained with the same analysis which provided the dynamic and transient cases. Three special cases are chosen as examples. In the first, a sinusoidally varying shear force is applied at the tip of a cantilever beam. The resonant characteristics of this beam for both the undamped and damped cases are studied. In the second, a step shear loading is applied to a cantilever beam and its damped dynamic history is studied. Finally, a circular plate whose outer edge is simply supported is impacted at its inner edge by a step moment and its damped transient behaviour is determined. The idea of the methods is potentially applicable to dynamic problems in general.     

Assessing comparative production efficiencies for product line management

Product line management involves product expansion or elimination depending on various factors, for example, production processes and demands in the market. This study focuses on measuring product performance for a firm’s product line management, using parametric and non-parametric approaches. First, we choose variables related to the production and demand of products and assess the comparative performance of product groups and individual products using data envelopment analysis (DEA). Second, we attempt to detect possible performance differences among the product groups using one-way analysis of variance. Third, we identify the sources of inefficiency using appropriate DEA scores and offer some managerial insights. Last, we try to confirm the determinants of product performance using Tobit regression analysis. The major contribution of this study is the use of a novel approach for product line management by measuring the performance of product groups and individual products using pertinent variables. The approach used in this study is applicable to various manufacturing and service industries. The limitations of this study are the number of product groups selected and examination of performance using cross-sectional data.     

生产浮动性对产线的影响分析及仿真

将生产线分成无缓存区、有缓存区两类,分别建立仿真模型,编写计算程序得到生产时间和产量等数据;结合图表分析数据,得到生产浮动性对单件生产时间及整体生产效率的影响特点;对比分析有无缓存区两种生产线,得到缓存区的设置对提高生产效率具有积极作用,以及在制品数量、总体生产效率随时间的变化趋势等结果;给出了对这些结果的解释,并用Flexsim软件对结果进行了验证.     

Assembly line system dynamic behaviour for high priority job order processing

Very often in a manufacturing plant, an important job order must be processed with higher priority than other regular jobs. It is vital for management to understand the impact on production performance of these high priority job orders. In this paper, this dynamic behaviour of assembly line systems is studied using computer simulation and derived metamodels in the form of mathematical expressions. An extensive computer simulation study is first conducted off-line. Next, analytical representations of the system lmetamodels) are fitted to the dynamic behaviour as simulated. These relatively simple equations can then be used on-line to estimate the impact of high priority job order processing when it occurs. The results indicate that the system response to this dynamic event can be described by first-order exponential delay functions captured in metamodels from simulation results. Using only the metamodels, the finish time of high priority jobs can be predicted and the number of delayed regular assembly products can be estimated in real time in the shop floor. This information is very valuable and useful for production scheduling.     

On the transient behaviour of a model for queues in series with finite capacity

Numerical studies have been carried out on the transient behaviour of a model for queues in series with finite waiting space. Poisson input and exponential service times have been assumed. On the basis of numerical results various conclusions have been drawn both for the transient and steady state situations concerning the servers arrangements, overflow probability, utilization etc