Thermal Error Measurement and Real Time Compensation System for the CNC Machine Tools Incorporating the Spindle Thermal Error and the Feed Axis Thermal Error

Thermally induced errors have been significant factors affecting machine tool accuracy. In this paper, the thermal spindle error and thermal feed axis error have been considered, and a measurement/compensation system for thermal error is introduced. Several modelling techniques for thermal errors are also implemented for the thermal error prediction; i.e. multiple linear regression, neural network, and the system identification methods, etc. The performances of the thermal error modelling techniques are evaluated and compared, showing that the system identification method is the optimum model having the least deviation. The thermal error model for the feed axis is composed of geometric terms and thermal terms. The volumetric errors are calculated, combining the spindle thermal error and feed axis thermal error. In order to compensate for the thermal error in real-time, the coordinates of the CNC controller are modified in the PMC program. After real-time compensation, the machine tool accuracy improved about 4–5 times. ID="A1" Correspondence and offprint requests to: Dr H. J. Pahk, School of Mechanical and Aerospace Engineering, Seoul National University, San 56–1, Shinlim-Dong, Kwanak-Ku, Seoul 151–742, Korea. E-mail: hjpahk@plaza.snu.ac.kr     

An Advanced Ultraprecision Face Grinding Machine

Cranfield Precision, Division of Landis Lund, has recently developed an ultraprecision face grinding machine which incorporates several automatic supervision features. The company supplied the machine to Cranfield University’s Precision Engineering Group in order that the group can undertake research, particularly in the area of damage-free grinding with high surface and subsurface integrity. The paper discusses the design of the machine, initial machining trials and potential research projects. Such projects will benefit from the availability of such an advanced machine system which incorporates many state-of-the-art features for the automatic supervision and control of the machining process. ID="A1" Correspondence and offprint requests to: Prof. J. Corbett, School of Industrial and Manufacturing Science, Cranfield University, Bedford MK43 0AL, UK. E-mail: j.corbett@cranfield.ac.uk     

A Structure-Oriented Product Data Representation of Engineering Changes for Supporting Integrity Constraints

This paper proposes a product data representation that can express and enforce integrity constraints on product structure during engineering changes (ECs). The representation adopts and extends the structure-oriented approach for managing EC data. Tightly integrated with product structure, it will enable designers to maintain and exchange consistent EC data throughout the product life cycle. To support operations for ECs properly, the representation provides the data, operations, and event–condition–action rules for nested ECs and simultaneous EC application to multiple options. In addition, the EC objects proposed in the representation integrate the data and integrity constraints into a unified repository. This repository will enable designers to access all EC data and integrity constraints through the product structure and relationships between EC objects. The paper also describes a prototype product data management system based on the proposed representation to demonstrate its effectiveness. ID="A1" Correspondence and offprint requests to: Dr N. Do, Division of Industrial System Engineering, Gyungsang National University, 900, Kajha-dong, Chinju City, 660–701, Korea. E-mail: dnc@nongae.gsnu.ac.kr     

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     

A Web-Based Remote Cooperative Design for Spatial Cam Mechanisms

Proliferation of the Internet has provided a great opportunity to exploit the advantages of distributed design and manufacturing. This paper presents an approach to component-based distributed cooperative design over the Internet where an extended multi-tier model (Browser/Server) is used to implement the web-based remote design system. As a case study, the system has been used to design spatial cam mechanisms based on mathematical models. Some experimental results are reported in order to illustrate the flexibility of the approach and the capabilities of the system. ID="A2" Correspondence and offprint requests to: Dr Gui Yun Tian, School of Computing and Engineering, University of Huddersfield, Huddersfield, HD1 3DH, UK. E-mail: g.y.tian@hud.ac.uk     

<Emphasis Type="Italic">Modelling of Five-Axis Machine Tool Metrology Models Using the Matrix Summation Approach</Emphasis>

Five-axis machining has been used widely in manufacturing freeform surfaces. The traditional approach of using a homogeneous transformation matrix (HTM) relies on heavy symbolic manipulation of the matrix multiplication. In this work, a new approach – the matrix summation approach – is developed and implemented for modelling the geometric errors of five-axis machine tools. This approach breaks down the kinematic equation into six components, each of which has clear physical meaning. It reduces the computations substantially and makes the five-axis kinematic model manageable and understandable. ID="A1"Correspondance and offprint requests to: Yin-Lin Shen, Academic Center T727, MAE Department, George Washington University, 801 22nd Street, NW, Washington, DC 20052, USA. E-mail: shen@seas.gwu.edu     

Optimal Control of a Multistage Machining Operation on a Computer Numerically Controlled Machine

A multistage machining operation ( MMO) model is proposed for a computer numerically controlled (CNC) machine to minimise the production cost of a deterministic order quantity under deadline constraint. Using the Lagrange method, the optimal machining time for each cutting tool is then achieved and the cost-related property of the Lagrange multiplier is also verified. In addition, a computer simulation of a numerical case using the MATLAB program is fully discussed, and the cost function of the machine for machining such operations with respect to the production deadline, is then obtained. Through this study, the project scheduling, production cost estimating, and even the contract negotiating of a deterministic quantity scheduled on the CNC machine can be further accomplished. This paper not only contributes an applicable operational strategy for a machine, but also provides a valuable approach for minimising the production cost for manufacturing engineers. ID="A1"Correspondance and offprint requests to: Chun-Hsiung Lan, 90-2,Nanya W. Road Sec. 2, Panchiao, Taiwan 220. E-mail: clan@mail-iem.tnit.edu.tw     

Forming Machine Qualification by Analysis of Manufactured Parts Geometry: Application to Aluminium Forming Process

Today, manufacturing companies work in a concurrent engineering context. In this paper, we develop a methodology to validate the modelling of an aluminium forming process based on dimensional characterisation and finite element comparison. Generally, finite element modelling (FEM) is used to validate die design in parallel with an experimental process. In this work, we use FEM to design forming tools in a first step. In a second step, measurement in the three dimensions gives the sheet metal process machine tool errors, and it is necessary to integrate the reasons for these defects in the process of concurrent engineering in the field of metal forming. Finally, we conclude that multiscale models should be used to model the mechanical process ID="A1"Correspondance and offprint requests to: R. Bigot, LGIPM, EA 3096, ENSAM Metz, Technopole 2000, 4, rue Augustin Fresnel, 57078 Metz Cedex, France. E-mail: regis.bigot@metz.ensam.fr     

Segmentation of the Measured Point Data in Reverse Engineering

Laser scanning is widely used because of its fast measuring capabilities and high precision. The segmentation of the scanned data is necessary for the fast and efficient surface modelling, but most segmentation techniques are based on very regular data, and the adaptation of previous techniques to process the scanned data does not usually produce a good result. In this paper, the solution of the segmentation of noise-free data and noisy data is proposed and compared. The solution for noise-free data is relatively simple having a small number of user-defined criteria. However, the solution for noisy data requires more criteria to produce a reasonable result when noise is globally distributed on the measured data. The approach is based on triangulated data and the result depends on some user-defined criteria. The result is illustrated to demonstrate its adaptability to measured data on a freeform surface and the results by the different criteria are compared. ID="A1" Correspondence and offprint requests to: Dr H.-C. Kim, Production and Automation Laboratory, Department of Mechanical and Intelligent Systems Engineering, Pusan National University, KeumJeon Gu, Pusan 609–735, Korea. E-mail: hchakim@hyowon.pusan.ac.kr     

The Development and Application of a Planar Encoder Measuring System for Performance Tests of CNC Machine Tools

In this paper, a measuring device with a planar encoder is developed to test the performance of a CNC machine tool. With the assistance of a PC, this system can be employed for both 2D contouring tests and 3D positioning tests for a CNC machine tool. The structure and the principle of the system, the applications for the general 2D contouring test, the drift test, and the specified geometric part path tests. An actual case study on improving the accuracy of machining a cam are described. Finally, a new 3D positioning method using the optic encoder is demonstrated. ID="A1"Correspondance and offprint requests to: Dr W. Jwye, 64 Wenhua Road, National Huwei Institute of Technology, Huwei, Yunlin, Taiwan 632. E-mail: Jywe@sunws.nhit.edu.tw     

Optimal Process Tolerance Balancing Based on Process Capabilities

An optimal approach for process tolerance balancing is presented. The new approach is based on process capabilities and is to be used in the stage of process planning. A nonlinear programming model is used to simultaneously optimise process tolerances of required operations. In the optimisation model, the objective function is to minimise the total manufacturing cost with different weighting factors. Using the estimated standard deviations of the dimensions and the manufacturing cost-tolerance functions, the constraint equations for the process tolerance chains and the manufacturing capability indices are established, together with a model for the economical tolerance bounds of machine tools. A practical example was used to verify the usefulness of the proposed approach. The results of the comparative study show that the proposed approach is more advantageous in relaxing tolerance requirements and in reducing scrap rates generally, compared with the existing methods. ID="A1"Correspondance and offprint requests to: Dr Y. Gao, Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. E-mail: meygao@ust.hk     

A Fast and Reliable Tool for Estimates for Plastic Blowing Moulds

This work presents a procedure to evaluate machining costs of dies made on CNC machines. Our survey deals with companies manufacturing plastic blowing moulds, and it is limited to the unit parts, that is, to the estimation step without going to the detail of process planning. To do this, we developed a process that uses the techniques of the semi-analytical method. This method is based on the decomposition of the shape required to manufacture the cavities; every cavity is decomposed in the same way for machining complex features, in order to determine the machining process and machining time, and the volume of metal to remove and the surface produced. ID="A1" Correspondence and offprint requests to: Dr Z. Bouaziz, Department of Mechanical Engineering, Route de Soukra Km3, BP W 3038, Sfax, Tunisia. E-mail: zoubeir.bouaziz@voila.fr     

WEB-BASED VIRTUAL CNC MACHINE MODELING AND OPERATION

A CNC simulation system based on internet for operation training of manufacturing facility and manufacturing process simulation is proposed. Firstly, the system framework and a rapid modeling method of CNC machine tool are studied under the virtual environment based on PolyTrans and CAD software. Then, a new method is proposed to enhance and expand the interactive ability of virtual reality modeling language(VRML) by attaining communication among VRML, JavaApplet, JavaScript and Html so as to realize the virtual operation for CNC machine tool. Moreover, the algorithm of material removed simulation based on VRML Z-map is presented. The advantages of this algorithm include less memory requirement and much higher computation. Lastly, the CNC milling machine is taken as an illustrative example for the prototype development in order to validate the feasibility of the proposed approach.     

A Study on Electrochemical Micromachining for Fabrication of Microgrooves in an Air-Lubricated Hydrodynamic Bearing

A specially built electrochemical micromachining/pulsed electrochemical micromachining (EMM/PECM) cell, a electrode tool filled with non-conducting material, a electrolyte flow control system and a small and stable gap control unit, are developed to achieve accurate dimensions for spindle recesses. Two electrolytes, aqueous sodium nitrate and aqueous sodium chloride are applied in this study. The former electrolyte has better machinability than the latter because of its ability to change appropriately to the transpassive state without forming pits on the surface of the workpiece. It is easier to control the machining depth precisely by micrometer with pulse current than direct current. This paper also presents an identification method for the machining depth by the in-process analysis of the machining current and interelectrode gap size. The interelectrode gap characteristics, including pulse current, effective volumetric electrochemical equivalent and electrolyte conductivity variations, are analysed, based on the model and experiments. ID="A1"Correspondance and offprint requests to: E.-S. Lee, Department of Mechanical Engineering, Inha University, 253, Yonghyun-Dong, Nam-Gu, Incheon, 402–751, Korea. E-mail: leees@inha.ac.kr     

Real-Time Deadlock Detection and Recovery for Automated Manufacturing Systems

The deadlock problems of automated manufacturing systems (AMS) are discussed in this paper. A dynamic-edge graph (DEG) with double labels was designed to model the AMS, to identify distinct part flows, to represent the states and capture the concurrent behaviour of the AMS. In the AMS, we assume that each resource has its own unit-capacity buffer to which it can be transferred when a deadlock situation occurs. The motivation of this research was to define the state of each part and propose a simple, dynamic and adaptable approach, based on double labels and some basic concepts in graph theory, for detecting a deadlock in real time and resolving deadlocks in the AMS. Through this approach both the utilisation of resources and the overall throughput can be improved. The proposed algorithmic procedure, in accordance with the states arrived at and generated from the model, can serve as a functional module for the operation of an AMS without the need to revise the original control extensively. In addition, the proposed procedure can be used cooperatively with a dispatching controller and expanded with little modification. ID="A1"Correspondance and offprint requests to: Dr W.-C. Yeh, Department of Industrial Engineering, Feng Chia University, PO Box 67-100, Taichung, Taiwan 407. E-mail: wcyeh@fcu.edu.tw     

Development of a System for Progressive Working of an Electric Product by Using Fuzzy Set Theory

This paper describes the development of a computer-aided design for a product with intricate bending and piercing operations for progressive working. The approach to the system is based on knowledge-based rules. Knowledge for the system is formulated from plasticity theories, experimental results, and the empirical knowledge of experts in the field. The system has been written in AutoLISP and AutoCAD on a personal computer. It is composed of four main modules, which are input and shape treatment, flat pattern layout, strip layout, and die layout modules. The system is designed considering several factors, such as bending sequence by fuzzy set theory, complexities of blank geometry, punch profiles, and the availability of press equipment and standard parts. The strip layout and die layout drawings, which are automatically generated by formulisation and quantification of experimental technology, will minimise trial and error and reduce the period for developing new products. The system could serve as a valuable system for experts and as a dependable training aid for beginners. ID="A1"Correspondance and offprint requests to: Professor J. C. Choi, Department of Mchanical Engineering, ERC for NSDM at Pusan National University, 30 Changjeon-dong, Kumjeong-Ku, Pusan 609-735, South Korea. E-mail: jcchoi@hyowon.pusan.ac.kr     

Agent- and CORBA-Based Application Integration Platform for an Agile Manufacturing Environment

A new application integration platform for an agile manufacturing environment is presented, which is based on agent and common request broker architecture (CORBA). CORBA enhances the system integration because it is an industry-standard for interoperable, distributed objects across heterogeneous hardware and software platforms. Agent technology is used to improve the intelligence of the integration system. The platform is open, distributed, and modular to enable the user to adapt its content to his requirements. This application integration platform supports the goals of agile manufacturing: rapid response to changing requirements, reduction in both time and cost of the product realisation process, and integration within a heterogeneous, wide-area-networked enterprise. In order to implement the application integration platform, we use a network integration server to integrate the network, design a generic database agent to integrate database, adopt a multi-agent based architecture to integrate application, and utilise a wrapper as a CORBA object to integrate the legacy code. Finally, a prototype framework is presented. ID="A1"Correspondance and offprint requests to: Dr F. T. S. Chan, Department of Industrial and Manufacturing Systems Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong. E-mail: ftschan@hkucc.hku.hk     

Application of the Maximal Spanning Tree Approach for Machine Cell Formation

This paper presents a comparative analysis of two methods for machine cell formation: 1. the maximal spanning tree (MST) approach 2. the CLINK method using a similarity coefficient matrix between machines as suggested by Seifoddini [18]. The results obtained from a sample of 16 data sets were compared for the two methods. The performance of these methods is compared, based on the total cell–load variation, grouping efficiency, and the total number of intercellular moves. ID="A1" Correspondence and offprint requests to: G. Prabhakaran, Department of Production Engineering, Regional Engineering College, Tiruchirap-palli 620 015, Tamil Nadu, India. E-mail: prabha@rect.ernet.in     

Intermittent Process Measurement of a Freeform Surface Profile with a Circular Triangulation Laser Probe on a Machining Centre

This paper describes the development of a non-contact type system for measuring a freeform surface on a machine tool. A laser probe, model OTM-3A20 made by Wolf & Back Co., was integrated into a CNC machining centre as a non-contact sensor. An adjustment device for the laser probe was designed to minimise the cosine error caused by assembly inaccuracy. An alignment test of the measuring laser beam was carried out using a calibrated specimen. The systematic accuracy of the circular triangulation laser probe and a standard triangulation laser probe, with respect to the surface roughness, surface slope, and coating colour of the workpiece, was investigated by using an HP5529A laser interferometer system. The measuring system, which consists of a personal computer, a CNC controller of a machining centre, a Renishaw MP10 touch-trigger probe system, and the controller of the laser probe system, was integrated information-technically. Automatic measuring software was developed for the purpose of measuring path simulation, generation of NC codes, and error analysis of the measured data. The profile error of the tested object, measured by the laser probe and the coordinate measuring machine respectively was found to be within 45 μm. In this case, the tolerance of the designed part is about 50 μm, so the developed system can be applied to the inspection of mould production in bakelite according to the experimental results. ID="A1"Correspondance and offprint requests to: Dr Fang-Jung Shiou, Department of Mechanical Engineering, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Rd. 106 Taipei, Taiwan. E-mail: shiou@mail.ntust.edu.tw     

Attribute Selection for Neural Network-Based Adaptive Scheduling Systems in Flexible Manufacturing Systems

System attribute selection is an integral part of adaptive scheduling systems. Owing to the existence of irrelevant and redundant attributes in manufacturing systems, by selecting the important attributes, better performance or accuracy in prediction can be expected in scheduling knowledge bases. In this study, we first propose an attribute selection algorithm based on the weights of neural networks to measure the importance of system attributes in a neural network-based adaptive scheduling (NNAS) system. Next, the NNAS system is combined with the attribute selection algorithm to build scheduling knowledge bases. This hybrid approach is called an attribute selection neural network-based adaptive scheduling (ASNNAS) system. The experimental results show that the proposed ASNNAS system works very well, when measured by a variety of performance criteria, as opposed to the traditional NNAS system and a single dispatching strategy. Furthermore, the scheduling knowledge bases in the ASNNAS system can provide a stronger generalisation ability compared with NNAS systems under various performance criteria. ID="A1" Correspondence and offprint requests to: Dr C.-T. Su, Department of Industrial Engineering and Management, National Chiao Tung University, 1001 Ta Hsueh Road, Hsin-Chu, Taiwan. E-mail: ctsu@cc.nctu.edu.tw