Showing papers in "The International Journal of Advanced Manufacturing Technology in 1998"

Deadlock prevention and avoidance in FMS : A Petri net based approach

Abstract: The use of structure theory of Petri nets to develop efficient deadlock prevention and deadlock avoidance methods for flexible manufacturing systems (FMSs) modelled by S4R nets is demonstrated Major synchronisation patterns, such as generalised parallel and sequential mutual exclusion, frequently observed in FMS contexts can be represented by this class The liveness property of a given S4R net (deadlock-freeness in the context of FMSs) is characterised in terms of structural Petri net elements called siphons An efficient method for controlling minimal siphons of a given S4R net is developed where local control places are added to the net A sufficient condition for liveness of the augmented net is provided This constitutes a deadlock prevention approach When the net liveness condition is not satisfied, an on-line controller, using a dynamic resource allocation policy, is developed for the augmented net The performance of the proposed approaches is illustrated using several examples

Optimisation of the weld bead geometry in gas tungsten arc welding by the Taguchi method

Abstract: In this paper, determination of the welding process parameters for obtaining an optimal weld bead geometry in gas tungsten arc welding is presented. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each welding process parameter on the weld bead geometry, and to predict the optimal setting for each welding process parameter. Experimental results are presented to explain the proposed approach.

NURBS curve and surface fitting for reverse engineering

Abstract: Reverse engineering is an approach for constructing a computer-aided design (CAD) model from a physical part through dimensional measurement and surface modelling. This paper presents alternatives for reverse engineering of free-form parts using Non-Uniform Rational B-Spline (NURBS) surfaces. A two-step linear approach is employed for fitting NURBS curves and surfaces using the measured points. During the first step, the weights of the control points are identified from a homogeneous system using symmetric eigenvalue decomposition. The control points are further processed in a way similar to B-spline curve and surface fitting. Some examples are presented to illustrate both the steps of reverse engineering and the process of NURBS curve and surface fitting.

Computer-aided process planning : A state of art

Abstract: During the last decade, computer-aided process planning (CAPP) has received much attention both from researchers and practitioners. One of the reasons for this is the role of CAPP in reducing throughput time and improving quality. An attempt has been made in this paper to review the existing literature with the objective of gaining insights into the design and implementation of CAPP systems. The literature available (1989–1996) on CAPP has been reviewed based on the types of systems. The advantages and disadvantages of such systems are presented. Finally, future research directions are indicated.

A study of the state-of-the-art rapid prototyping technologies

Abstract: Each rapid prototyping (RP) process has its special and unique advantages and disadvantages. The paper presents a state-of-the-art study of RP technologies and classifies broadly all the different types of rapid prototyping methods. Subsequently, the fundamental principles and technological limitations of different methods of RP are closely examined. A comparison of the present and ultimate performance of the rapid prototyping processes is made so as to highlight the possibility of future improvements for a new generation of RP systems.

The development of a CAD environment to determine the preferred build-up direction for layered manufacturing

Abstract: Stereolithography is a process used to produce polymer components rapidly directly from a computer representation of the part. There are several factors to be considered in order to make efficient use of the process. In particular, the build-up orientation of the part critically affects the part accuracy, the total build time and the volume of the support structures. The purpose of this study is to determine the optimal build-up part orientation for the StereoLithography Apparatus (SLA) process to improve part accuracy, and minimise the total build time and the volume of the support structure. Additionally, an algorithm is developed to calculate the staircase area, quantifying the process errors by the volume of materials supposed to be removed or added to the part, and the optimal layer thickness for the SLA system which can handle the variable layer thickness. Thus, the optimal part orientation is determined based on the user's selections of primary criteria and the optimal thickness of layers is calculated for any part orientation.

Integrated knowledge-based assembly sequence planning

Abstract: This paper presents a novel approach and system for the automatic generation, selection and evaluation, optimisation, and simulation of assembly plans. The information and knowledge about a product and its assembly (e.g. assembly constraints, solid model and CAD database, heuristic rules) are described using a hybrid approach and model with numeric and symbolic representation. A new methodology is presented to generate all feasible assembly sequences of the product by reasoning and decomposing the feasible subassemblies, and representing them by the assembly Petri net modelling. Qualitative strategic constraints are then used to evaluate the feasible assembly sequences. In order to obtain a good assembly sequence, some quantitative criteria such as assembly time and cost, workstation number, operator number, and part priority index are applied to select the optimal assembly sequence. Based on DFA analysis, MTM time analysis, and assemblability analysis, estimates are made of the assembly time and cost of the product when each of these sequences is used. A knowledge-based system KAPSS has been developed to achieve the integration of generation, selection evaluation, and visualisation of the assembly sequences.

Side milling of ruled surfaces : Optimum positioning of the milling cutter and calculation of interference

Abstract: Side milling is a process that enables machining time and thus costs, to be reduced. This type of machining is particularly well suited to ruled surfaces and all surfaces where one of the principal curvatures is very small compared to the tool radius and changes little oiler the entire surface. These surfaces must be treated with great care, as they are often on parts with high added value such as turbine blades, aircraft wings or helicoidal parts as used in fluid dynamics. We then need to calculate and minimise interference that may arise if the I ruled surface cannot be developed. Whereas machining is usually carried out by setting the tool according to a rule, we suggest a new setting of the tool allowing interference to be reduced considerably. The computation algorithms for this setting were developed so as to be used in real-time by CAD/CAM software. A comparative study of errors made with each type of setting is also presented. This shows a considerable reduction in errors when the setting we suggest is implemented.

Discrete event control system design using automation Petri nets and their ladder diagram implementation

Abstract: As automated manufacturing systems become more complex, the need for an effective design tool to produce both high-level discrete event control systems (DECS) and low-level implementations becomes more important. Petri nets represent the most effective method for both the design and implementation of DECSs. In this paper, automation Petri nets (APN) are introduced to provide a new method for the design and implementation of DECSs. The APN is particularly well suited to multiproduct systems and provides a more effective solution than Grafcet in this context. Since ordinary Petri nets do not deal with sensors and actuators of DECSs, the Petri net concepts are extended, by including actions and sensor readings as formal structures within the APN. Moreover, enabling and inhibitor arcs, which can enable or disable transitions through the use of leading-edge, falling-edge and level of markings, are also introduced. In this paper, the methodology is explained by considering a fundamental APN structure. The conversion of APNs into the IEC1131-3 ladder diagrams (LD) for implementation on a PLC is also explained by using the token passing logic (TPL) concept. Finally, an illustrative example of how APNs can be applied to a discrete manufacturing problem is described in detail.

Error modelling and measurement for the rotary table of five-axis machine tools

Abstract: Rotary tables are widely used with multi-axis machine tools as a means for providing rotational motions for the cutting tools on the three-axis machine tools used for five-axis machining operations. In this paper, we present a comprehensive procedure for the calibration of the rotary table including: geometric error model; error compensation method for the CNC controller; error measurement method; and verification of the error model and compensation algorithm with experimental apparatus. The methods developed were verified by various experiments, showing the validity and effectiveness of the presented methods, indicating they can be used for multi-axis machine tools as a means of calibration and precision enhancement of the rotary table.

A genetic algorithm for scheduling flexible manufacturing systems

Abstract: General job shop scheduling and rescheduling with alternative route choices for an FMS environment is addressed in this paper. A genetic algorithm is proposed to derive an optimal combination of priority dispatching rules “pdrs” (independentpdrs one each for one Work Cell “WC”), to resolve the conflict among the contending jobs in the Giffler and Thompson “GT” procedure. The performance is compared with regard to makes-pan criteria and computational time. The optimal WCwise-pdr is proved to be efficient in providing optimal solutions in a reasonable computational time. Also, the proposed GA based heuristic method is extended to revise schedules on the arrival of new jobs, and on the failure of equipment to address the dynamic operation mode of flexible manufacturing systems. An iterative search technique is proposed to find the best route choice for all operations to provide a feasible and optimal solution. The applicability and usefulness of the proposed methodology for the operation and control of FMS in real-time are illustrated with examples. The scope of the genetic search process and future research directions are discussed.

Integrated intelligent design and assembly planning: A survey

Abstract: This paper reviews the relevant literature of the development of methodologies and systems for integrated intelligent design of assembled products and processes. Based on a combination of the concurrent engineering approach and artificial intelligence techniques, an assembly oriented intelligent scheme for the integration of design and planning is proposed, in which the following components or activities are considered and carried out concurrently and intelligently: assembly modelling and design (conceptual design; preliminary design; detailed design), assembly process planning, assembly system layout and design, assembly simulation, econo-technical (e.g. assembl-ability, assembly time and cost) and ergonomic analysis and evaluation. The literature is reviewed and discussed in relation to the methodologies and systems of implementing the above components or activities and an integrated environment to support them. In addition, some research of our group on this topic is introduced.

A vision system for surface roughness assessment using neural networks

Abstract: In this study we use machine vision to assess surface roughness of machined parts produced by the shaping and milling processes. Machine vision allows for the assessment of surface roughness without touching or scratching the surface, and provides the flexibility for inspecting parts without fixing them in a precise position. The quantitative measures of surface roughness are extracted in the spatial frequency domain using a two-dimensional Fourier transform. Two artificial neural networks, which take roughness features as the input, are developed to determine the surface roughness. The first network is for test parts placed in a fixed orientation, which minimises the deviation of roughness measures. The second network is for test parts placed in random orientations, which gives maximum flexibility for inspection tasks. Experimental results have shown that the proposed roughness features and neural networks are efficient and effective for automated classification of surface roughness.

Rapid prototyping assisted surgery planning

Abstract: In recent years, new surgical techniques have been developed to improve the quality of operations, reduce the risk to patients and reduce the pain experienced by patients. Prominent developments include minimally invasive surgery, robot-assisted hip operations, computer-assisted surgery (CAS) and virtual reality (VR). These developments have helped surgeons operate under difficult visual conditions. Rapid prototyping (RP) technology has also found applications in medicine. The RP technique is able to fabricate a representative, physical 3D model. This 3D model can enhance interpretation, visual and physical evaluation, and the rehearsal and planning of the surgical steps before a surgical operation is carried out in order to eradicate the trauma. This paper presents the procedures involved in the conversion of computerised tomography (CT) scan data to a useful physical model. A case study of a CT scanned file of a patient who had an injury to the right eye socket is presented. Three different RP systems (SLA, SGC and LOM) are benchmarked for comparison in terms of the surface finish, accuracies, visual appearance and processing speed. Because of the ability of RP to fabricate models that are complex in design with intricate features that may be hidden by undercuts, as demonstrated in this paper, the results of this research can be extended to applications in general engineering. One specific area of application would be reverse engineering.

Temperature measurement in orthogonal metal cutting

Abstract: Orthogonal cutting experiments were carried out on steel at different feedrates and cutting speeds. During these experiments the chip temperatures were measured using an infrared camera. The applied technique allows us to determine the chip temperature distribution at the free side of the chip. From this distribution the shear plane temperature at the top of the chip as well as the uniform chip temperature can be found. A finite-difference model was developed to compute the interfacial temperature between chip and tool, using the temperature distribution measured at the top of the chip.

A comprehensive method for calibration of volumetric positioning accuracy of CNC-machines

Abstract: A comprehensive method for measuring the systematic errors of CNC-machine tools has been studied. The method used for measurement and calibration of machine tool errors should be general and efficient. The objectives of this study include: 1. Volumetric error modelling. 2. Experimental procedure for error measurement. 3. A tool position and path compensation method. 4. The verification method.

Calculation of tool paths for a torus mill on free-form surfaces on five-axis machines with detection and elimination of interference

Abstract: Within the framework of a study carried out in cooperation with the Sapex Company, we sought to develop an overall machining program for free-form surfaces on a 5-axis NC machine tool. This program comprises a certain number of general cases that will then have to be adapted to specific situations. In this paper, we present the algorithms allowing the following cases to be dealt with:

An investigation into the implementation of computer integrated manufacturing in small and medium enterprises

Abstract: Small and medium enterprises (SMEs) play an increasingly important role in all aspects of competitiveness e.g. for both products and production techniques, but also management methods, the organisation of the firm and human resource training. Obtaining and, just as importantly, mastering scientific and technological information is therefore essential to competitiveness of all SMEs. During the last two decades, several factors have forced global manufacturers to make dramatic changes in their products, markets, and manufacturing strategies. One of the ways by which SMEs can achieve a competitive advantage in manufacturing is through the implementation of computer integrated manufacturing (CIM). Realising the importance of SMEs, an attempt has been made in this paper to study the implementation of CIM in SMEs. First, the characteristics of CIM have been studied with reference to the application and infrastructure of SMEs. Secondly, a framework has been presented for the implementation of CIM in SMEs with the help of a conceptual model. Finally, future research directions on CIM in SMEs are indicated.

AGV schedule integrated with production in flexible manufacturing systems

Abstract: Flexible manufacturing systems (FMS) comprise, automated machine tools, automated material handling, and automated storage and automated retrieval systems (AS/RS) as essential components. Effective sequencing and scheduling of the material handling systems (MHS) can have a major impact on the productivity of the manufacturing system. The material handling cannot be neglected while scheduling the production tasks. It is necessary to take into account the interaction between machines, material handling systems and computer. In this context, this paper attempts to link the operation of automated guided vehicles (AGV) with the production schedule and suggests a heuristic algorithm that employs vehicle dispatching rules (vdr) for conflict resolution. The vdrs considered in this paper are: shortest operation time (SPT), longest operation time (LPT), longest travel time (LTT) and shortest travel time (STT). The performance of the vdrs in the proposed heuristic is compared with makespan criteria. The results show that the STT provides the best solutions compared to other vdrs.

An Intelligent Sensor System Approach for Reliable Tool Flank Wear Recognition

Abstract: An intelligent sensor system approach for reliable flank wear monitoring in turning is described. Based on acoustic emission and force sensing, an intelligent sensor system integrates multiple sensing, advanced feature extraction and information fusion methodology. Spectral, statistical and dynamic analysis have been used to determine primary features from the sensor signals. A secondary feature refinement is further applied to the primary features in order to obtain a more correlated feature vector for the tool flank wear process. An unsupervised ART2 neural network is used for the fusion of AE and force information and decision-making of the tool flank wear state. The experimental results confirm that the developed intelligent sensor system can be reliably used to recognise the tool flank wear state over a range of cutting conditions.

A computational system for process design of injection moulding: Combining blackboard-based expert system and case-based reasoning approach

Abstract: The process design of injection moulding involves the selection of the injection moulding machine, mould design, production scheduling, cost estimation, and determination of injection moulding parameters. Expert system approaches have been attempted to derive the process solution for injection moulding in the past few years. However, this approach has been found to be incapable of determining the injection moulding parameters owing to the difficulty in setting the moulding parameters. In addition, the existing expert systems for process design lack the proper architecture for organising a heterogeneous knowledge source. In this paper, the combination of a blackboard-based expert system and case-based reasoning approach is introduced to make up the deficiencies of the existing expert-system approach to the process design, from which a computational system for process design of injection moulding, named CSPD, was developed and described. CSPD first derives the process solution including the selection of injection moulding machine and mould base, tooling cost, and processing cost estimation, and production scheduling based on the blackboard-based expert-system approach. It is then followed by the determination of the injection moulding parameters based on the case-based reasoning approach and the previously derived partial solution.

Characteristics of chip generation by ultrasonic vibration cutting with extremely low cutting velocity

Abstract: Recently, mirror-surface machining of brittle materials such as ferrite, glass, and optical plastics has become more important, as these materials are used in optical communications and precision devices. Non-ferrous metals such as aluminium and copper were readily turned with diamond tools, but as the need for both infra-red and reflective optics escalated, the need to machine brittle materials arose. In this paper, ultrasonic vibration cutting at 20 kHz at extremely low cutting velocity for the precision machining of brittle plastics used for optical lenses is suggested and tested. The mechanism of chip generation, and characteristics of surfaces in the ductile mode, machined by ultrasonic vibration cutting are investigated. As a result, when micro cutting by ultrasonic vibration, it was confirmed that the chips generated by ductile mode cutting are obtained at 1/40 of the critical cutting velocity of the ultrasonic vibration cutting system, which is an extremely low cutting velocity.

A decision tree of neural networks for classifying images of wood veneer

Abstract: Artificial neural networks for the classification of wood veneer by an automatic visual inspection system are presented. Initially, a single large neural network is implemented with eleven image features as inputs and thirteen outputs — one for each class of veneer. In order to improve on the classification accuracy of this single network, a decision tree of smaller and more specialised modular neural networks is introduced to achieve a classification by successive refinement. This results in a substantial improvement in classification accuracy. A key process in the design of a modular neural network is the use of “normalised inter-class variation” in the selection of the most appropriate image features to be used for its particular specialised classification task.

Multiaxis machining with additional-axis NC system: Theory and development

Abstract: Four and five axis machining is advanced technology for dealing with complex shaped parts but its application is restricted owing to the high investment cost. The additional-axis method, typically obtained by attaching a rotary/tilt table to an existing three-axis machine, is a powerful alternative for achieving multiaxis machining. However, owing to insufficient study of the additional-axis method, its capability is limited to simple applications, such as multiface milling or drilling. In this paper, we attempt to establish a theoretical background and implementation methodology for achieving a genuine multiaxis NC system. The research is composed of: 1. Hardware set-up for implementing an additional-axis NC system. 2. Interface study for implementing multiaxis machining with the required hardware configuration. 3. Versatile CL-data generation algorithms for NC machining. 4. Implementation of the algorithms for developing a multiaxis CAM system using the additional-axis NC system.

Product and process dimensioning and tolerancing techniques. A state-of-the-art review

Abstract: Dimensioning and tolerancing are important engineering processes in the different phases of a product development cycle. The two main phases in a product cycle where dimensioning and tolerancing techniques are extensively employed are in the areas of product design and process planning. Tolerance and dimension assignment in both product design and process planning has an equally important role in keeping the production cost down and, hence, requires equal attention as far as research into these areas are concerned. Another important motivating factor for research is that manual dimension and tolerance assignment is often tedious, time-consuming and requires a considerable amount of skill and experience on the part of the engineer, resulting in inconsistencies and errors. Extensive research, in the area of dimensioning and tolerancing in both product design and process planning, has been carried out with the advancement in computers since the 1970s. The purpose of this paper is to review the state-of-the-art dimensioning and tolerancing techniques in both product design and process planning and explore the opportunities for future research in these areas.

An integrated experimental approach to link a laser digitiser, a CAD/CAM system and a rapid prototyping system for biomedical applications

Abstract: This study is carried out to develop a direct link between a laser digitiser and a rapid prototyping system for biomedical applications. Two CAD/CAM systems, DUCT and Pro-Engineer, are investigated and the DUCT system is found to be more suitable for this purpose. A laser digitiser is used to capture three-dimensional surface data for the object. With the aid of the CAD/CAM system, the data can be manipulated in a number of ways for display, modification and enhancement. In addition, the object scanned by the laser digitiser can be physically produced relatively quickly and accurately using StereoLithography Apparatus (SLA), a leading rapid prototyping system. Feasible and practical solutions to the problems encountered in the CAD surface model construction are proposed and illustrated. Two case studies, a facial and a breast model, are presented. Results show that this integrated approach can be applied effectively in the biomedical field.

A consideration of modelling techniques that can be used to evaluate manufacturing strategies

Abstract: Practising engineers frequently seek to understand what the effects of various manufacturing strategies will be on the performance of their production facilities. In this situation a computer model can help to provide insight and form predictions about future manufacturing system performance. Various types of modelling methods exist and each provide models that have distinct characteristics. This paper presents a review of popular modelling techniques and, based on the results of a structured experimental study, summarises their capabilities to support the evaluation of manufacturing strategies.

A method for assessing geometrical errors in layered manufacturing. Part 1: Error interaction and transfer mechanisms

Abstract: Geometric accuracy of components is one of the most important quality characteristics in layered manufacturing processes on which most rapid prototyping (RP) techniques are based. Layered manufacturing is an approximate fabricating process in which the final geometric error of the physical part is affected, not only by the approximation technique used, but also by the fabrication process. Errors that occur in one layer could propagate and transfer to other layers causing an accumulated error effect in the process. In this paper, a concept of disturbance error is introduced to describe the effect of accumulated errors in the fabrication process. A physical model is presented to describe error interactions and error transfer mechanisms in the layered manufacturing process. A geometrical model is developed using surface approximation techniques to describe the relationships of the geometrical errors. It is shown that although the complexity of the part geometry is not directly related to the manufacturing process, it will affect the geometrical errors of the part produced.

Material flow and control sequence specification of flexible production systems using coloured Petri nets

Abstract: Starting with the specification of each resource and the whole structure of a flexible production system, in this approach a special kind of coloured Petri nets is used for performing the modelling and the validation of the coordination control structure of the systems. In a second phase, it is proposed to modify the first models to synchronised Petri net schemas to facilitate the supervision and the interaction of the coordination model with the physical components of the system as well as the development and maintainability of the discrete-event control structures. The final result is a formal specification of coloured Petri net based coordination control of resources of the system, and logic control structures for control sequencing based on the use of synchronised subPetri net structures derived from the first one by refining transitions, i.e., their occurrence. Based on the proposed approach, the coordination control model of resources and a first skeleton of the logic control structures of a flexible assembly cell located at the Institute of Manufacturing Automation and Production Systems at the University of Erlangen-Nuremberg, Germany is elaborated and then the correctness of the obtained models with regard to material flow and control sequence specifications is validated by means of the structural analysis of the coloured Petri net-based models.

Process Capability-Based Tolerance Design to Minimise Manufacturing Loss

Abstract: In this paper we propose a nonlinear programming model, composed of a cumulative standard normal probability function and manufacturing cost, to design process tolerances. The tolerances are standardised in conjunction with the process capability of the machinery to minimise the total manufacturing loss that occurs owing to non-conforming parts. The proposed model has been applied to a workpiece manufactured through ten operations and solved by GINO (General INteractive Optimizer). A comparison between the results obtained by the proposed model and other methods indicates that robust process tolerances can be obtained by the new formulation.