Part spectrum based methodology for cell sizing in flexible manufacturing systems

This paper describes a part spectrum based methodology which enables the determination of an optimum size for flexible manufacturing cells. The methodology incorporates a systems approach in that it enables the sizing of cells to achieve specified manufacturing objectives while maintaining a realistic level of flexibility and an acceptable level in terms of complexity of control.The proposed methodology for cell sizing is based on two component characteristics: processing time and number of operations. Furthermore, it is generalised in its implementation in that the effects of case specific factors such as processing sequence of components and location of machines in relation to each other are negated.The validation of the proposed methodology for cell sizing using data obtained from manufacturing companies implementing flexible manufacturing systems is also described.     

Impact of operation flexibility and dispatching rules on the performance of a flexible manufacturing system

Operation flexibility is one of the eight common types of flexibility that exist in flexible manufacturing systems. Dispatching rules are commonly used in loading the machines. This paper studies the effects of different levels of operation flexibility and various dispatching rules on the performance of a flexible manufacturing system. The system performance considered is mean flow time. Simulation results indicate that the mean flow time cannot be always improved by increasing the level of operation flexibility. Altering the dispatching rules seems to have a more significant effect on the mean flow time performance than changing the level of operation flexibility.     

An operational measure of routing flexibility in a multi-stage multi-product production system

The high degree of variety in customer demands causes mass production to become outdated and flexible production to be favored. Routing flexibility can be found in systems that implement general-purpose machines, alternative or identical machines, redundant machine tools, or the versatility of material handling systems. It is recognized that routing flexibility can be treated as a tool for enhancing system performance, such as lead time and inventory reduction. However, its implementation entails a huge cost of installation of flexible machines, automated tool changers and fixtures, and machine operators possessing multiple skills. Therefore, system managers must determine the appropriate level of routing flexibility for a specific system configuration in order to balance benefits and costs incurred. This paper presents a background to and a rational for a routing flexibility measure for a multi-stage flow shop. Instead of merely counting the number of available routes, this measure takes into account the loading balance between machines. Therefore, a manufacturing system with overloaded machines will have less routing flexibility as compared with one that is not overloaded, when both systems have the same number of available routes. An example for demonstrating the applicability of the proposed measure is also illustrated.     

A TQM approach for designing and building dedicated machines and equipment in-house

Many industries are responding to the need for major design changes in their manufacturing systems to include flexible and controllable systems that produce superior-quality products on time and at a lower cost. Maintaining flexibility while meeting the functional requirements of a manufacturing system often requires designing a machine that is unique. Consequently, a new trend in manufacturing systems design is to build such machines in-house. This paper describes a systematic implementation of total quality management (TQM) along with continuous improvement concepts to design and build a test-stand in-house. This project also involves creating a prototype for on-going machining design for future needs.     

Design principles of reconfigurable machines

Reconfigurable machines form a new class of machines that are designed around a specific part family of products and allow rapid change in their structure. They are designed to allow changes in machine configuration according to changes in production requirements. The reconfiguration may be related to changes in machine functionality or its scalability, i.e., the change in production volumes or speed of operation. Reconfigurable machines represent a new class of machines that bridges the gap between the high flexibility and high cost of totally flexible machines and the low flexibility and low cost of fully dedicated machines. The design principles of reconfigurable machines follow a similar philosophy, which was derived for reconfigurable manufacturing systems, and present an approach for the design of machines to be used mainly in high-volume production lines. This paper introduces design principles for reconfigurable machines, which may be applied in different fields of manufacturing. Based on these design principles, three types of reconfigurable machines were designed for various types of production operations such as: machining, inspection and assembly. This paper shows how the suggested design principles were utilized in the design of several full-scale machine prototypes and tested experimentally.     

工艺规划柔性评价及其在生产调度中的应用

多工艺规划是提高制造系统运行柔性的有效方法。在规则调度中，系统运行柔性与各决策点所选的加工操作有关。定义了多工艺规划柔性概念；研究了多工艺规划间的相互关系及其对系统运行柔性的影响；讨论了多工艺规划柔性评价指标；提出一种操作优先级判据，实现了多工艺规划中不同操作的优先级排序，并用于规则调度。仿真实验表明，根据该判据，调度系统在每一决策点能优先选择使系统运行柔性较大的加工操作，从而提高系统的运行性能。     

A finishing cutter selection algorithm for additive/subtractive rapid pattern manufacturing

The additive/subtractive rapid pattern manufacturing (RPM) process sequentially deposits thick material slabs and then machines them into desired geometries in a layer-by-layer manner. Although most rapid manufacturing systems mainly intend to increase flexibility in manufacturing rather than to reduce processing speed, it is still practical to choose the optimized sets of cutters and machining parameters specifically for each layer to improve both the machining quality and efficiency. This paper presents an algorithm to automatically select finishing cutter geometry, diameter, and calculate machining parameters for the RPM process. Inputs to this algorithm are StereoLithography file from a computer-aided design model and a cutter library. Finishing cutter selection is based on geometry accessibility and machining process efficiency analysis. The algorithm has been implemented in RPM automatic process planning software and the experimental result on a sample part is presented to show the efficacy of this algorithm.     

Application generator for the control of CNC machines

Computer numerical control (CNC) machines have brought about vast changes in the manufacturing process since their introduction into the engineering environment. The main advantage of CNC control is its flexibility, making small batch production possible as the changeover from manufacture of one type of board to another is much faster than with mechanically or electromechanically controlled systems. In the past these CNC machines have tended to be viewed as individual stand-alone pieces of equipment. However, with the emergence of CIM as a leading technology, it is important that these machines be totally integrated within the factory network. This paper examines two popular hierarchical models used within the context of CIM and describes an application generator which is under development for the control of automated manufacturing equipment.     

Inherently flexible cell communications: A review

The first generations of Flexible Manufacturing Systems (FMS) are flexible only with respect to implicity predefined types of parts and assemblies: determined by the machines and software comprising the FMS. A more radical form of flexibility is the ability to be readily adapted to produce unforseen product types. It is this inherent flexibility which is becoming a primary, rather than a secondary, requirement of new manufacturing systems architectures. The burden of this flexibility falls almost entirely on software which is the glue that defines what machines constitute an FMS and how they work together. This paper reviews current computer science research which addresses these issues. This paper explores the issue of devising programs and architectures that support their own replacement within the real-time, heterogeneous factory environment. Formal computable specifications for reconfiguration have been proposed as a way of producing flexibility, but this paper argues that self-referential systems based on independently communicating agents are both more flexible and more acceptable in practice. Requirements for long-term, inherent flexibility are shown to share more features with fault-tolerance and error recovery needs than with short-term flexibility. Five partial, complementary solutions are suggested which together should improve the inherent flexibility of future software systems: (1) global information services, (2) high-level standardization such that only the standards actually needed are generated, (3) distributed agent heterarchical architectures, (4) dynamic updating of configuration-oriented software, and (5) computational reflection.     

Machine loading in flexible manufacturing systems considering routeing flexibility

The key competitive strength of a manufacturing system lies in its flexibility, which represents the ability to respond effectively to changing circumstances. Flexible manufacturing systems (FMSs) react appropriately to change. The relevance of a particular type of flexibility depends upon the system and problem being considered. In this paper, the machine loading problem in a flexible manufacturing system is addressed. The loading problem is concerned with the allocation of part operations and required tools to the machines, so as to optimise some objective(s) subject to some technological constraints. Several objectives have been considered in the past such as maximisation of the utilisation of resources, minimisation of processing and tooling costs and maximisation of throughput rates. In such procedures, it is quite probable that a rigid loading schedule is obtained and in cases of machine breakdowns and tool failures alternate routeings are often not available. Therefore, in this paper, we develop a mathematical model which considers maximisation of the production routeings available for the parts and hence increases the routeing flexibility. The model is illustrated by examples.     

Evaluation of routing flexibility of a flexible manufacturing system using simulation modelling and analysis

Routing flexibility is a major contributor of the flexibility of a flexible manufacturing system (FMS). The present paper focuses on the evaluation of the routing flexibility of an FMS with the dynamic arrival of part types for processing in the system. A typical FMS configuration is chosen for detailed study and analysis. The system is set at five different levels of routing flexibility. Operations of part types can be processed on alternative machines depending upon the level of routing flexibility present in the system. Two cases have been considered with respect to the processing times of operations on alternative machines. A discrete-event simulation model has been developed to describe the operation of the chosen FMS. The performance of the system under various levels of routing flexibility is analyzed using measures such as mean flow time, mean tardiness, percentage of tardy parts, mean utilisation of machines, mean utilisation of automatic-guided vehicles, and mean queue length at machines. The routing flexibility for producing individual part types has been evaluated in terms of measures such as routing efficiency, routing versatility, routing variety and routing flexibility. The routing flexibility of the system has been evaluated using these measures. The flexibility levels are ranked based on the routing flexibility measure for the system. The ranking thus obtained has been validated with that derived using fuzzy logic approach.     

Three-half and half-axis patch-by-patch NC machining of sculptured surfaces

Despite the inbuilt advantages offered by five-axis machining, the manufacturing industry has not widely adopted this technology due to the high cost of machines and insufficient support from CAD/CAM systems. Companies are used to three-axis machining and their shop floors are not yet ready for five-axis machining in terms of training and programming. The objective of this research is to develop and implement a machining technique that uses the simplicity of three-axis tool positioning and the flexibility of five-axis tool orientation, to machine sculptured surfaces. This technique, 3½½-axis, divides a sculptured surface into patches and then machines each patch using a fixed tool orientation. This paper presents the surface partitioning scheme and the method of selecting an optimum number of sub-divisions along with actual machining experiments. For the example surface utilized in this study, the proposed hybrid method led to shorter machining time compared to traditional three-axis machining and comparable to simultaneous five-axis machining.     

A genetic algorithm approach to machine flexibility problems in an ion plating cell

For a long time, manufacturing industries have been concentrating on increasing productivity by increasing the size of the workforce, but this scenario has changed in last decade since the introduction of the term flexibility. Now, the manufacturers realize that flexibility of the machine environment can provide a better economic solution for improving productivity due to its quick response to the changing environment in the manufacturing industry. However, only very limited research on machine flexibility in the ion plating (IP) industry has been carried out and most of it has focused on product development and quality of coating. The aim of this paper is to determine the optimal level of machine flexibility in an ion plating cell (IPC) to improve the entire system performance. A machine loading sequencing (MLS) model based on a multi-objective genetic algorithm (GA) is developed and the case study of metal finishing company is discussed to validate the proposed model. Different levels of machine flexibility have been assigned to different machines to determine the optimal level to increase the overall system performance based on on-time delivery, quality of product and production cost. The results demonstrated that machine flexibility level in IPC should be zero under recent IP technology. However, when the IP technology is developed enough so that IP machine has the ability to produce different types of coating in high quality, machine flexibility should be introduced to enhance the overall system performance.     

Tool addition strategies for flexible manufacturing systems

The allocation of tools to machines determines potential part routes in flexible manufacturing systems. Given production requirements and a minimum feasible set of tools, the decision of how to fill vacant slots in tool magazines to maximize routing flexibility is shown to be a minimum cost network flow problem for the cases when routing flexibility is a function of the average workload per tool aggregated over tool types, or of the number of possible routes through the system. A linear programming model is then used to plan a set of routes for each part type so as to minimize either the material handling requirement or the maximum workload on any machine. The impact of these tool addition strategies on the material handling and workload equalization is investigated and computational results presented. The advantage of the overall approach is computational simplicity at each step and the ability to react to dynamic changes.This article is based upon work supported by the National Science Foundation under Grants No. DMC 85–44993 and DDM 92–15432.This work was done by the author while visiting the SIE Department of the University of Arizona.     

考虑机床闲置和工件绕路的可重构制造系统工件族构建相似性算法

针对可重构制造系统(Reconfigurable manufacturing system,RMS)需要兼顾柔性和效率问题,提出考虑机床闲置和工件绕路因素的RMS工件族构建方法。该方法首先提取不同工件工艺路线之间的最长公共子序列,然后以最长公共子序列为基础,考虑机床闲置和工件绕路因素将非最长公共子序列的工序合并到最长公共子序列中,形成最短混合工艺路线,通过分析最长公共子序列、最短混合工艺路线与工件相似性之间的线性关系,建立工件相似性系数求解算法,以此作为工件聚类成族的基础。最后,将该方法与已有方法进行对比分析,验证了该方法的准确性和实用性。     

Mathematical models for productivity and availability of automated lines

The basic attributes of any industrial machine are productivity rate, quality of products, as well as the cost and flexibility of manufacturing systems. Attributes of productivity are related to the theory of reliability, let alone the theory of efficiency of machines. The main attribute of reliability with any industrial machine is availability, which is the integrated index of the machine's reliability. The availability of industrial machines with complex designs should be a constituent of equations on productivity rate. This paper develops analytical equations of productivity rate with the availability of automated lines as a function of structural, technical and technological parameters of industrial machines. The equations allow for the output of automated lines to be modelled and their structures to be defined according to the level of productivity and availability.     

Logical Cell Formation in FMS, Using Flexibility-Based Criteria

Flexible manufacturing systems often are organized into a cellular architecture for ease of operation. The formation of these cells sometimes has been treated as an extension of the conventional cell-formation problem. This paper argues that, owing to the existence of flexible routing and transfer capabilities, the cell-formation problem in FMSs should be treated as quite distinct from that in conventional manufacturing systems and shows that a flexibility-based procedure is apt for overcoming the deficiencies of earlier forays into this area. Manufacturing cell flexibility is defined as a composite of three flexibility measures: producibility,processivity , and transferability. The problem of cell formation is modeled as flexibility maximization, and a procedure is developed for the simultaneous formation of machine cells and part families, while heuristically maximizing within-cell flexibility.     

A pattern-directed approach to flexible manufacturing: A framework for intelligent scheduling, learning, and control

The planning, scheduling, and control of manufacturing systems can all be viewed as problem-solving activities. In flexible manufacturing systems (FMSs), the computer program carrying out these problem-solving activities must additionally be able to handle the shorter lead time, the flexibility of job routing, the multiprocessing environment, the dynamic changing states, and the versatility of machines. This article presents an artificial intelligence (AI) method to perform manufacturing problem solving. Since the method is driven by manufacturing scenarios represented by symbolic patterns, it is referred to as pattern-directed. The method is based on three AI techniques. The first is the pattern-directed inference technique to capture the dynamic nature of FMSs. The second is the nonlinear planning technique to construct schedules and assign resources. The third is the inductive learning method to generate the pattern-directed heuristics. This article focuses on solving the FMS scheduling problem.In addition, this article reports the computation results to evaluate the utility of various heuristic functions, to identify important design parameters, and to analyze the resulting computational performance in using the pattern-directed approach for manufacturing problem-solving tasks such as scheduling.     

A machine vision system for tool wear assessment

Automated tool condition monitoring is gaining considerable importance in the manufacturing industry. This can be attributed to the transformation of manufacturing systems from manually operated production machines to highly automated machining centres. Modern image processing techniques and machine vision systems can now enable direct tool wear measurement to be accomplished in-cycle. Such a system, characterized by its measurement flexibility, high spatial resolution and good accuracy, is presented here. The system consists of a fibre-optic light source to illuminate the tool and a CCD camera (used in conjunction with a high resolution video zoom microscope) to capture the reflected pattern. The extent of the flank wear land has been determined using both textural and gradient operators; a texture operator has been implemented in the final system.     

A multi-agent RFID-enabled distributed control system for a flexible manufacturing shop

Flexible manufacturing systems are complex, stochastic environments requiring the development of innovative, intelligent control architectures that support flexibility, agility, and reconfigurability. Distributed manufacturing control system addresses this challenge by introducing an adaptive production control approach supported by the presence of autonomous control units that are cooperating with each other. Most of the currently distributed control systems still suffer from lack of flexibility and agility when the product verity is high and is not reconfigured in case of ad hoc events. To overcome this limitation, a drawback of an excessive dependence on up-to-date information about the products and other elements that move within the system is essential. Radio frequency identification (RFID) is a new emerging technology which uses radio frequency waves to transfer data between a reader and movable item for identification, tracking, and categorization purpose. This paper discusses the architecture devised to deploy RFID-enabled distributed control and monitoring system by means of a set of agents that are responsible for the realization of different control and monitoring tasks and for cooperating to enhance agility, flexibility, and reconfigurability of manufacturing system.