Rapid Prototyping Applications in Medicine. Part 2: STL File Generation and Case Studies

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prosthesis for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the expanded opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. This paper, Part 2, deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.     

Rapid Prototyping Applications in Medicine. Part 1: NURBS-Based Volume Modelling

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prostheses for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the extended opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In this paper, Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. Part 2 deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.     

Manufacturing process modelling using process specification language

The manufacturing process is one of the important processes in a product??s life cycle. The sharing of manufacturing process information among different functional application systems, such as process planning, manufacturing simulation, manufacturing execution and project management, has become difficult to implement due to the growing complexity of the manufacturing information of product, process, resource and plant. A unified representation of manufacturing process information for all applications can enable convenient integration between different application systems. The development of manufacturing-related ontology and the Process Specification Language (PSL) has provided a formal definition and structure of semantic concepts for the capture and the exchange of manufacturing information. This paper presents a manufacturing process information modelling method which builds a standard, complete and exact definition of manufacturing process data by applying current PSL specifications. New extensions of the concepts of the manufacturing process and the types of relationship for describing activities, materials and resources in a process are identified and developed. The completeness and adaptability of activity relation of the proposed manufacturing process information representation is verified using mathematical induction under a variety of complex manufacturing process situations. The ability of the modelling method in expressing complex process information is demonstrated by a machining process example.     

An adaptive agile manufacturing control infrastructure based on TOPNs-CS modelling

In this paper, an infrastructure for adaptive production control in an agile manufacturing environment is proposed. With this infrastructure, Virtual Production Systems (VPSs), each of which takes care of the production of a specific customer ordered product, can be dynamically and flexibly constructed. This can be achieved logically by product workflow and physically by the resources in one or more manufacturing systems, e.g. job shops. To respond to changes and disturbances to a VPS, architecture for the adaptive controller of a VPS is designed based on adaptive control principles and Temporised Object-Oriented Petri Nets with Changeable Structure (OPNs-CS) modelling. A case study is used in this paper to illustrate how adaptive production control of VPS functions can be conducted to cope with changes and disturbances to the production system.     

Push-pull production planning of the re-entrant process

Thin film transistor and liquid crystal display (TFT-LCD) fabrication manufacturing is characterised as a re-entrant process, in which a similar sequence of steps is repeated several times. Production control for the re-entrant process is complex, since, without intelligent control, it may incur the congestion of WIP or equipment idleness because of the work in progress (WIP) shortage. In this paper, three kinds of control policies are suggested: push, push-pull and pull types. Exact formulations using linear programming are given, and their performances of solutions are evaluated. It is shown that a pull type control policy gives stable throughput and delivery satisfaction at a small cost and with less production. A push type policy outperforms the other two types in the throughput and manufacturing cycle time.     

Object-oriented methods for manufacturing information systems

Object-oriented programming (OOP) is now widely used in application software development. OOP has advantages connected with handling complexity, reusability, extendability, modularity and data abstraction, enabling it to handle modern programming requirements more effectively than conventional programming methods. Successful advanced manufacturing systems demand increasing complexity, flexibility and integration between computer applications. An object-oriented approach is particularly promising for the design and development of manufacturing information systems. This paper outlines the concepts of object-oriented methods, and describes an object-oriented application development methodology for manufacturing information systems. A CASE (Computer-Aided Software Engineering) tool is used for system modelling and for direct source-code generation. A case study describing the development of a quality management information system is presented, which was implemented using a C++ development environment. Although the research described here is concerned with quality management information systems, the proposed design methodology is applicable to other areas of manufacturing, and conclusions are drawn concerning the uses of OOP in manufacturing information systems generally.     

Complexity of cellular manufacturing systems based on entropy models

Even structurally simple manufacturing systems can be operationally complex. This operational complexity can be colloquially defined as the uncertainty associated with managing the dynamic variations, in time or quantity, across information and material flows at the manufacturing systems interface. This paper proposes a means of measuring the information demands placed on cellular manufacturing systems, as a result of this uncertainty. A utility function for complexity is proposed according to the relationships between the complexity and utility in a manufacturing system and the underlying trend that the system becomes more and more complex in an everchanging environment is analyzed. This paper mathematically models the static entropy and the dynamic entropy of cellular manufacturing systems from an information-theoretic perspective. A unique feature of this measure is that it captures, in relative terms, the expected amount of information required to describe the state of the system. The measure provides flexibility in the scope and detail of analysis. Finally, an example is used to demonstrate the validity of the proposed methodology.     

<Emphasis Type="Bold">A Rapid Manufacturing Method for Water-Saving Emitters for Crop Irrigation Based on Rapid Prototyping and Manufacturing</Emphasis>

In order to build the complex built-in labyrinth design of an emitter which is a key element in water-saving devices, rapid prototyping and manufacturing (RP&M) is used to design the emitters and to manufacture corresponding rapid tooling (RT). Detailed CAD design of the emitter, CAD process design, and the generation of RT process modelling of the emitter have been carried out using parameterised design. Prototypes have been built using RP techniques to perform the rapid verification and modification of the emitter design; rapid tooling (RT) for the emitter has been fabricated using a metal spraying process to carry out trial-production. Finally, with the fabrication ofa precision mould as the basis, emitter mould design and manufacturing have been completed. As a result, the integration of design/verification/manufacturing of a mould and its products is realised.     

Object-Oriented Petri Nets with Changeable Structure (OPNs-CS) for Production System Modelling

We propose object-oriented Petri nets with changeable structure (OPNs-CS) in this paper for effective modelling of production systems with changing structures. Two mechanisms for carrying out the structural changes in OPNs-CS are defined. One is for the modification of message passing relationships between distinct OPNs and the other is for adding of OPNs to, and the removing of OPNs from, a model. A case study is provided to show that OPNs-CS can cope with both the uncertainties which may exist during the model-building phase of a one-of-a-kind production (OKP) system and the structural changes of the system which often occur while the production system is in operation.     

面向复杂零件协同制造的资源优化配置技术研究

面向复杂零件的异地协同制造，提出依据工艺流程进行制造任务分解，研究了以工艺流程为核心的逻辑制造单元（LMU）和逻辑加工路线（LMP）设计，有效利用LMP和LMU描述针对复杂零件的协同制造任务。对复杂零件异地协同制造的制造资源优化配置问题进行了数学分析和描述，阐述了问题的目标与约束条件，将资源优化配置问题归结为多目标优化问题，利用遗传算法进行求解，并进行了应用实例分析，证明了采用制造资源优化配置方法可以有效解决复杂零件网络化异地协同制造的资源优化配置问题。     

APPLICATION OF IMPROVED PRODUCTION ACTIVITY CONTROL ARCHITECTURE FOR SHOP FLOOR INFORMATION SYSTEM IN DIGITAL MANUFACTURING

Shop floor control (SFC) is responsible for the coordination and control of the manufacturing physical and information flow within the shop floor in the manufacturing system. Weaknesses of the production activity control (PAC) architecture of the shop floor are addressed by the Maglica's new system architecture. This architecture gives rise to unlimited number of movers and producers thus evolving more complex but decentralized architecture. Beijing Institute of Technology - production activity control (BIT-PAC) architecture introduces an idea of sub-producers and sub-movers thus reducing the complexity of the architecture. All the equipments including sub-producers and sub-movers are considered to be passive in the proposed shop floor information system. The dissemination of information from sub-producers and sub-movers is done manually through a PC. Proposed BIT-PAC SFC architecture facilitates the information flow from shop floor to the other area of the organization. Effective use of internet information services (IIS) and SQL2000 is done along with the ASP.NET technology to implement the application logic. Applicability of the software based on BIT-PAC architecture is checked by running application software on a network PC that supports the dynamic flow of information from sub-producers and sub-movers to the other parts of the organization. Use of software is also shown at the end for BIT training workshop thus supporting the use of SFC architecture for similar kind of environments.     

Simulation in process design

Simulation modelling can help managers understand the complexity of the interactions involved in manufacturing processes, from which they can derive strategies for improving systems and to plan for future design. If the limitations of the approach are considered and the required simulation skills are present, the technique can be a useful tool in the analysis of the complexity of modern manufacturing systems     

Modelling and Implementation of Internet-Based Virtual Machine Tools

A key factor for realising an Internet-based virtual manufacturing system (VMS) and virtual enterprise (VE) is how to represent the manufacturing elements and process mechanics precisely and effectively. This paper presents methods to represent the motion paths and operation of CNC machine tools on the Web. The method is composed of: 1. Geometrical modelling of the machine tools. 2. Kinematic modelling of the movements of machine tools. 3. Representation of the developed model in the internet infrastructure. 4. Development of a prototype Web-based virtual machine tools (WVMT). WVMT is available on the internet URL http://wvmt. postech. ac.kr, by which the client can interactively operate CNC machine tools, and verify the part program via graphic simulation. ID="A1"Correspondance and offprint requests to: Correspondence and offprint requests to: Professor S.-H. Suh, Department of Industrial Engineering, School of Mechanical and Industrial Engineering, POSTECH, San 31 Hyogja-dong, Pohang, 790-784, Korea. E-mail: shs@postech.ac.kr     

<Emphasis Type="Bold">Development of Divisional Parallel Scan Technology in Large-Scale Laminated Object Manufacturing</Emphasis>

Many technological difficulties exist in the field of rapid prototyping (RP) technology when making large-scale prototypes. The manufacturing efficiency is the main problem, and the process implemention and RP equipment also present difficulties. In this paper, the concept of divisional parallel scan is presented. Laminated object manufacturing (LOM) technology is used for the basic forming process and has been improved continuously through practice. Static divisional scan technology was also better developed to dynamic divisional scan technology, which can help in achieving the object of improving work efficiency and optimising design.     

Performance Modelling and Evaluation of Dynamic Tool Allocation in Flexible Manufacturing Systems using Coloured Petri Nets: An Object-Oriented Approach

Manufacturing systems are faced with ever-increasing customisation and unstable demand. The traditional hierarchical control structures for shop floor (pre-release planning, scheduling, dispatching and activity control) are often inflexible in responding to unexpected scenario changes and are thus not robust to system disturbances. In this paper, an object-oriented approach to modelling of FMS dynamic tool allocation and control under a non-hierarchical shop floor control scheme using coloured Petri nets is presented. A client–server paradigm is used in the proposed modelling method. The complete FMS model is partitioned into individual classes (machines, magazines, tool transport system, SGVs, tool storage, etc.) thereby significantly reducing the complexity of the model to a tractable size. The system performance under different tool request selection rules is also evaluated using coloured Petri net simulation. The proposed method can provide the designer of a tool management system with a high-level and structured representation of the tool-sharing control. It also provides an effective method for prototyping and evaluating performance of object-oriented shop floor control software.     

Optimisation of operations sequence in CAPP using an ant colony algorithm

Computer-aided process planning (CAPP) forms an important interface between Computer-aided design (CAD) and Computer-aided manufacturing (CAM). It is concerned with determining the sequence of individual manufacturing operations required to produce a product as per technical specifications given in the part drawing. Any sequence of manufacturing operations that is generated in a process plan cannot be the best possible sequence every time in a changing production environment. As the complexity of the product increases, the number of feasible sequences increases exponentially, and there is a need to choose the best among them. This paper presents an application of a newly developed metaheuristic called the ant colony algorithm as a global search technique for the quick identification of the optimal operations sequence by considering various feasibility constrains. A couple of case studies are taken from the literature to comparing the results obtained by the proposed method.     

A resource-based modelling approach to support responsive manufacturing systems

The manufacturing industry faces the challenge of responding quickly to the ever-changing requirements of customers. A key factor in these highly competitive environments is an ability for companies to master key production system dynamics such as change in the product types and variants and production quantities that they make, with high quality, low cost, and fast delivery. A novel approach to modelling manufacturing systems is introduced which is based on the provision of means for explicitly representing and computer executing dynamic producer units (DPUs). DPUs are defined as re-usable, change capable components of a manufacturing enterprise and have been described in the present authors’ previous publications. DPU concepts were conceived to support (1) the design of change capable manufacturing systems that can realise families of similar products in varying quantities and mixes and (2) the re-configuration of manufacturing systems in cases of withdrawal of a product family and introduction of a new one. To achieve this, a generic manufacturing system model is required to facilitate the systematic and timely alteration of production system designs and production plans. DPU modelling concepts facilitate these alterations through explicitly specifying the need for change capabilities so that rapid and cost-effective changeover responses can be made when production requirements change. This paper presents how DPU modelling concepts can be applied with reference to an industrial case study and describes a change decision-making framework in the form of a taxonomy and enabling tools.     

Object-oriented approach of MCTPN for modelling Flexible manufacturing systems

Manufacturing industry is facing a stricter challenge than ever before owing to the rapid change in market requirements. Flexible manufacturing systems (FMSs) have a much greater capability than traditional fixed-type production systems for coping with the rapid change. In this paper, a modified coloured-timed Petri net (MCTPN) is developed to model the dynamic activities in an FMS. The MCTPN provides an object-oriented and modular method of modelling manufacturing activities. It includes colour, time, modular and communication attributes. The features of object-oriented modelling allow the FMS to be modelled with the properties of classes, objects, and container trees. Since the system activities can be encapsulated and modularised by the proposed MCTPN, the manufacturing systems can be easily constructed and investigated by the system developers. It makes the concept of software IC possible for modelling complex FMSs. Once all of the MCTPN objects are well defined, the developers need to consider only the interfaces and operations relating to the MCTPN objects. In order to demonstrate the capability of the proposed MCTPN, the FMS in the Manufacturing Automation Technology Research Center (MATRC) of the National Taiwan University will be stimulated and justified by using the proposed MCTPN along with the G2 expert system.     

基于鼓-缓冲器-绳子理论的半导体晶圆厂车间层控制

为了将鼓-缓冲器-绳子理论应用于带回流的半导体晶圆厂车间的作业控制,通过设置回流缓冲,对传统鼓-缓冲器-绳子理论进行了修正,提出了一套适合带回流生产线的生产作业方法。针对瓶颈资源上的负荷堆积情况,提出了基于EDD和CR法则的推平原则,将瓶颈负荷推平。负荷推平后,根据瓶颈设备的实际可用情况,对瓶颈设备上的生产安排进行合理化,得到各订单的投料时间及出货时问安排。算例结果证明了该方法的可行性和有效性。