Application of TOC embedded ILP for increasing throughput of production lines

Under fairly special circumstances, there are some special methods that can be used to attempt to increase the production rate of some production line systems. In this paper an attempt has been made to use the theory of constraint (TOC) approach to identify the critical machines. Various design alternatives are considered to increase throughput of the critical machine. This process is continued till the required throughput is achieved for the entire system. For large production line systems this approach will be tedious and time consuming. Hence we have attempted to generalize the TOC approach by integer linear programming (ILP) to increase the throughput. Data has been collected from an automobile ancillary manufacturing industry to validate the model. The TOC embedded ILP has been used to increase the throughput with minimum investment.     

Transient functioning mode of manufacturing systems with operation time constraints

Changing the periodic cycle time of a manufacturing system leads to transient functioning. In this paper, we propose to determine a transient schedule due to the throughput rate modification of a manufacturing cell with operation time constraints. This modification does not require a new allocation of resources or a new sequence of tasks. This method uses a P-time Petri net as a model and, paradoxically, the properties of the periodic controlled functioning mode, in order to build the transient schedule. As the duration of the transient functioning can be bounded by an upper value, the transient temporal schedule is obtained by solving a linear program whose constraints stem from the P-time Petri net model. Disturbances in the input rate of the system are considered in order to specify the properties of the setting corresponding to the target throughput rate, but other criteria can be used.     

Note: automatic mass-flow configuration method for evaluating turbomolecular pump performance

An automatic mass-flow configuration method is presented for the evaluation of turbomolecular pump performance. This configuration method is used to obtain an effective mass-flow rate. In addition, the throughput, inlet pressure, and compression ratio are evaluated. The throughput increases with the mass-flow rate. Moreover, the compression ratio increases almost linearly with the outlet pressure for mass-flow rates from 2.97 × 10(-9) to 3.96 × 10(-7) kg/s. Finally, empirical correlations are proposed for the throughput and inlet pressure.     

基于GSPN的过程建模分析方法研究

针对过程模型执行的不确定性特点,对基于广义随机Petri网(GSPN)的过程建模和仿真分析技术进行研究和讨论。该方法适用于使用随机变量,特别是分布函数描述过程模型中的活动、状态和转移这些基本特征。它可以最终通过稳定状态概率求解制造系统过程模型或子过程中等待时间、资源的利用率以及过程模型吞吐量等性能参数。建立了流程重构的定量分析技术基本方法,它为动态制造模型过程建模提供了持续改进的机制和计算方法。最后通过一个质量保证的工作流给出了分析的实例与步骤。     

基于流程的制造绩效评价体系研究

面向制造业企业,引入制造绩效指标评价体系和生产能力测量,并在此基础上提出了制造绩效测量系统的概念设计及基于流程分析的制造绩效评价系统模型,在系统的3个层次上分别设计了绩效指标群、网络层及协议层的指标,分析了网络层中评价指标间的交互关系,并提出协议层中各个绩效指标的测量和报告规范。     

Optimal production policy for a manufacturing system with volume flexibility in a supply chain under lumpy demand

A batch production system with volume flexibility in a supply chain where a manufacturer procures raw materials and/or component parts from multiple suppliers in a lot and processes them into a single product, is considered in this research. First of all, a decision-making model is developed for an optimal production rate selection in the volume-flexibility production system, where a single type of finished products is delivered periodically in fixed quantities within a fixed interval of time. In this model, the production rate is perceived as a decision variable and unit production cost becomes a function of production rate. This model takes into account not only inventory costs of raw materials and finished goods, but production costs as well. Then, a pragmatic computation approach is presented to solve the proposed model for special unit-production-cost functions. It is used to determine an optimal production rate, and thus to decide an optimal ordering policy for procurement of raw materials from suppliers and an optimal manufacturing batch size. Some observations are made for optimal production rate analysis. Finally, a numerical study is conducted to illustrate the solution and a set of data with ten problems is tested and compared.     

可重组制造系统缓冲区容量的优化研究

为了确定可重组制造系统中的缓冲区容量,通过分析机床工作状态、生产需求量等因素对缓冲区容量的影响,建立了缓冲区状态数学模型.在此基础上,提出了缓冲区容量、机床可用度和任务需求率之间的函数关系.以满足生产任务为前提,将重组后加工域缓冲区容量最小化作为优化目标.通过粒子群优化算法,利用非可微精确罚函数法处理约束条件,采用可变惯性权重平衡搜索,以求得各工序间缓冲区容量.最后结合仿真实例,探讨了该生产线重组后系统缓冲区容量的最优配置.     

A high throughput inductive pulse sensor for online oil debris monitoring

A high throughput inductive pulse sensor based on inductive Coulter counting principle for detecting metallic wear debris in lubrication oil is presented. The device detects the passage of metallic debris by monitoring the inductance change of a two-layer planar coil with a meso-scale fluidic pipe crossing its center, which is designed to attain high throughput without sacrificing the sensitivity. The testing results using iron and copper particles ranging in size from 50 to 150 μm have demonstrated that the device is capable of detecting and distinguishing ferrous and non-ferrous metallic debris in lubrication oil with a high throughput.     

两种多层穿梭车系统的性能比较分析

物流配送中心订单响应速度的加快,对订单拣选系统提出了更高的要求。多层穿梭车系统因其柔性强、效率高等特点,近年来得到了广泛应用。多层穿梭车系统具有两种形式——基于转载车和基于环形输送线,二者均可实现货物的快速拣选,但在系统吞吐量和订单完成周期方面存在差异,致使企业决策者难以进行系统选择。基于上述原因,本文比较两种多层穿梭车系统的性能差异。建立两个系统的开环排队网络模型,然后求解系统吞吐量、订单完成周期,通过仿真验证了排队论模型的准确性,通过试验对两种系统的性能进行对比分析。结果表明,系统吞吐量与层数、巷道数相关,层数越多,巷道数越少,转载车系统相对于环线系统优势越显著;订单完成周期与层数、订单到达率相关,层数越多,订单到达率越低,转载车系统相对于环线系统越具优势。     

A VXI instrument for real-time tracking of impedances

A VXI instrument for impedance measurements, equipped with a TMS320C30 Digital Signal Processor, is presented. It implements two measurement techniques: the first, based on an image model approach, allows accurate impedance measurements, while the second, based on an amplitude-phase approach, is mainly oriented in increasing the instrument throughput. The hardware architecture and the software strategies adopted in the VXI instrument implementation are then described in detail. Experimental tests for a wide range of impedance values are then carried out for the instrument metrological characterization and throughput evaluation. Concluding remarks are finally reported.     

Performance comparison of assembly systems with fixed and flexible cycle times

The traditional assembly system consists of a series of balanced workstations operating at the same rate with fixed cycle times. Recent advances in technology allow more flexible assembly systems, in which workstations operate independently and cycle times vary from job to job.This article develops an analytical model for comparing the throughputs (jobs per hour) of assembly systems with fixed and variable cycle times. The throughputs are compared on a common basis by requiring that both systems allow sufficient processing time to ensure product quality and that they have the same total times in system per job.Results indicate that an assembly system with variable cycle times can operate at a significantly higher throughput than one with fixed cycle times, provided there is sufficient buffer storage space between workstations to accommodate queueing. This benefit must be weighed against possible increased capital investment and practical considerations associated with system control.     

Simulation Analysis of a PCB Factory using Factorial Design – A Case Study

This study describes simulation modelling and analysis of a serial production line in a printed circuit board (PCB) factory. Simulation technique is applied to evaluate the performance of the existing manufacturing system, which requires modification to achieve two conflicting objectives, i.e. to maximise the average throughput rate and to minimise the average lead time. Based on a full factorial design, the computer model, which is developed using SIMFACTORY, has been used for finding out the active factors that have a great impact on the current operational problems. Then, a new system design is proposed to enhance the overall performance and is verified using a simulation model. The simulation approach presented here is also applicable to a wide variety of complex operational problems. ID="A1"Correspondance and offprint requests to: Dr F.T.S.Chan, Department of Industrial and Manufacturing Systems Engineering, University of Hong Kong, Pokfulam Road, Hong Kong. E-mail: ftschan@hkucc.hku.hk     

Single-machine-based predictive maintenance model considering intelligent machinery prognostics

As an increasing number of manufacturers are beginning to realize the importance of maintaining throughput, many maintenance models have been developed to enable machines to achieve near-zero downtime. However, previous maintenance models usually ignore machine’s deterioration process. Therefore, this paper develops a novel data-driven machinery prognostic approach for machine performance assessment and prediction. With this prognostic information, a predictive maintenance model is proposed for a repairable deteriorating machine. As machine performance can be assessed, once it reaches the maintenance threshold, a maintenance operation is performed to restore the machine. Moreover, an operational cost is introduced to meet real manufacturing process. In this predictive maintenance model, the optimal maintenance threshold and maintenance cycle number are obtained with the aim to minimize the long-term average cost. Finally, a case study is presented. The computational results show the efficiency of this proposed predictive maintenance model.     

Upgrade of the lithium beam diagnostic at JET

A 60 kV neutral Li beam is injected into the edge plasma of JET to measure the electron density. The beam observation system has been improved by replacing a Czerny-Turner spectrometer with a high-resolution transmission-grating spectrometer and a fast back-illuminated frame-transfer camera. The larger throughput of the spectrometer, the increased sensitivity, and the faster readout of the new camera allow inter-ELM (edge localized mode) measurements (frame rate of 100 Hz). The calibration of the setup, as well as an improved spectral fitting technique in the presence of carbon background radiation, is discussed in detail. The density calculation is based on a statistical analysis method. Results are presented for different plasma scenarios.     

优化结合二叉树和帧时隙ALOHA的防碰撞算法

分析和比较了现有无线射频识别（RFID）中采用的防碰撞算法存在的问题,提出了一种优化结合二叉树（BT）和帧时隙ALOHA的新的防碰撞算法。提出的算法在阅读器与标签开始通讯时采用帧时隙的ALOHA算法,当有时隙发生碰撞时采用BT算法对其进一步识别。该算法根据曼彻斯特译码得到碰撞位,通过估算一帧中可能出现的碰撞情况,运用数学推导并通过R软件编程计算给出数学期望值。仿真实验显示：提出的算法充分发挥了两种算法的优点,其搜索次数、传输时延、吞吐率等重要指标都明显优于ALOHA算法,尤其是新的防碰撞算法的吞吐率比ALOHA算法提高了近50%。另外,传输负担的减小还使数据传输的安全性有了更高的保障。     

A linear programming model for the control wafers downgrading problem

This paper considers the control wafers downgrading problem (CWDP) in the wafer fabrication photolithography area. The objective of the research is to minimize the total cost of control wafers, while maintaining the same level of production throughput. For the problem under a pulling control production environment, a linear programming model is presented to set the supply rate of new control wafers and the recycle and downgrading rates so as to minimize the total cost of control wafers. A numerical example is given to illustrate the practicality of the model. The sensitivity of the linear programming model solution to changes in the underlying parameter values is also investigated. The results demonstrate that the proposed model is an effective tool for determining the control wafers downgrading policy.This paper presents a linear programming model that considers the cost of new control wafers, recycle and downgrading control wafers in wafer fabrication. The proposed model improved the performance of control wafers management, and served as the basis for setting the usage rates of control wafers.     

Modelling and analysis of multiple cluster tools system with random failures using coloured Petri net

Semiconductor manufacturing is among the most complicated and expensive operation systems encountered today and multiple cluster tool system has become an important technology in semiconductor manufacturing systems with the advantages of higher yields and shorter cycle times. Modelling and simulation has become a standard methodology in order to understand and predict performance of semiconductor manufacturing systems. Resources random failures during process execution are one major concern regarding system performance measured in terms of throughput and cycle time. This study aims to models and analyse random failures of processing modules of multiple cluster tool systems using coloured Petri net method. The impact of different input factors on system throughput and cycle time is presented.     

Measurement of performance impact of SSL on IP data transmissions

Secure socket layer (SSL) provides networking security at session layer of the ISO/OSI reference model. The paper deals with the problem of developing a measurement instrument for evaluating the performance of a communication system based on SSL 3.0 implemented by the SSLeay library. The developed measurement instrument is able to evaluate the maximum throughput obtainable in such a communication system and allows users to carry out an experimental investigation on the throughput variations when the encryption algorithms used for confidentiality are changed. Moreover, for the various ciphers analyzed, the performance improvement gained by increasing the CPU clock frequency has been estimated.     

Simulation of flexible automated systems for the discrete production of metal components by forging and machining

The integration of metal forming and metal removal operations in a single flexible manufacturing cell will advance further the area of application of the flexible manufacturing system and will contribute to the flexible automation of traditionally high volume applications. Forming operations will first be employed to achieve a near net shape of the components, so that only a minimum of subsequent machining operations will be required to manufacture the final forms. The efficient use of these systems depends considerably on the proper design of the system. A simulation model written in the PASCAL language is presented, capable of simulating a mixed type FMC. With the aid of this model the effect of the batch size and the carrying capacity of the pallets on utilisation of the machine tool and the throughput times of the orders is examined.     

Design of a field programmable gate array-based platform for real-time de-noising of optical imaging signals using wavelet transforms

In this study, the design of a low-cost, field programmable gate array (FPGA)-based digital hardware platform that implements wavelet transform algorithms for real-time signal de-noising of optical imaging signals is presented. The proposed digital hardware de-noising platform can achieve a throughput of 25 Msamples per second, with a latency from input to output of 1.5 μs. The system fits on a 10K20, one of the smaller field programmable gate arrays from the Altera Flex 10K family, and represents a low-cost approach to signal de-noising. Preliminary experimental results clearly indicate the potential of the presented FPGA-based digital platform for real-time de-noising of signals utilized for the detection and imaging of surface defects and discontinuities.