Development of an Integrated, Adaptable CNC System

Development of an Integrated, Adaptable CNC System

Xun Xu (University of Auckland, NZ)
DOI: 10.4018/978-1-59904-714-0.ch013
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Abstract

In order to prepare manufacturing companies to face increasingly frequent and unpredictable market changes with confidence, there is a recognized need for CNC machine tools to be further advanced so that they become more integrated with design models and adaptable to uncertain machining conditions. For a CNC system to be able to access any design information, this design information has to be at the task-level, that is what-to-do. For a CNC system to produce the final part, it has to turn the task-level information into method-level information which effectively is the machine control data. These topics are discussed at the beginning of this chapter. The rest of the chapter discusses a CNC native database used for converting the task-level data to method-level data, the methodology of converting the task-level data to methodlevel data, and implementation of the methodology to a conventional CNC machine that employs G-codes. Again both STEP-NC (ISO 14649-1, 2003) and function blocks (IEC 61499, 2005) are used.
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Task-Level Data Vs. Method-Level Data

An important feature of the STEP-NC concept is that of “machine tool independency”; this makes STEP-NC codes interoperable across various CNC systems. This is because a STEP-NC data model mainly captures the task-level or the what-to-do information. Although it is possible to define data at the method-level or the how-to-do level, such as machine tool trajectory, the main aim of STEP-NC is to allow these decisions to be made by a STEP-NC-enabled controller. This way, STEP-NC part programs may be written once but can be used on different machine tools providing that the machine tool has the required process capabilities. Figure 1 shows these two categories of data defined in the STEP-NC data model. The first two columns depict the manufacturing task information. The process-level data describe abstract manufacturing tasks at the macro-level. The geometry-level data are represented in terms of manufacturing_features. The how-to-do data are also divided into two types. Machine tool core data spell out the manufacturing requirements. Machine tool auxiliary data are method-level data and they are in fact defined in the STEP-NC data model as optional data. Both categories of how-to-do data take different forms when different machine tools are used.

Figure 1.

What-to-do and how-to-do data in STEP-NC ©2008, Taylor and Francis Journals, http://www.informaworld.com, used with permission from the authors.

The central issue is therefore the ‘transition’ from the task-level data to the method-level, or from the what-to-do data to the how-to-do data. Since STEP-NC is utilized as a CNC machining data model, implementation of STEP-NC is effectively a process of adapting its data model for different CNC systems. This is illustrated in Figure 2.

Figure 2.

Implementation of STEP-NC manufacturing ©2008, Taylor and Francis Journals, http://www.informaworld.com, used with permission from the authors.

Such a system may have three stages. First of all, a native version of STEP-NC program is generated based on the information in a generic STEP-NC program. Then, low-level, local NC commands can be generated based on the native STEP-NC information. This provides a direct interface with the targeted CNC machine, hence a “CAM-CNC transition”. This transition is intended to be hidden away from the user and ideally synchronised with the subsequent execution process. Finally, a STEP-NC enabled controller executes the STEP-NC program through the above native CNC commands.

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Generate A Native Step-Nc Program

The key in this phase is to “map” a generic STEP-NC program to a native one. In other words, the main task is to convert what-to-do information in a generic STEP-NC program, into the how-to-do information for a specific CNC machine. Different CNC machines have differing machining capabilities and native parameters. Until a STEP-NC program takes into account all the information specific to a CNC system, it will not be possible to execute the Workplan(s) specified in the STEP-NC program. The mapping process is also a “checking” process to evaluate the manufacturability of the job on a particular machine tool. In the distributed manufacturing environment, this “plug-and-play” feature gives a process plan the mobility and portability that are desired.

Figure 3 shows the logical structure of the system (Wang, Xu & Tedford, 2006). The three main functional units are the Native CNC database, Adaptor and Human-Machine (HM) interface.

Figure 3.

Logical structure of the system

Complete Chapter List

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Dedication
Table of Contents
Foreword
A.Y.C. Nee
Acknowledgment
Xun Xu
Chapter 1
Xun Xu
One of the key activities in any product design process is to develop a geometric model of the product from the conceptual ideas, which can then be... Sample PDF
Geometric Modelling and Computer-Aided Design
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Chapter 2
Xun Xu
Today, more companies than ever before are involved in manufacturing various parts of their end products using different subcontractors, many of... Sample PDF
CAD Data Exhange and CAD Standards
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Chapter 3
Xun Xu
Products and their components are designed to perform certain functions. Design specifi- cations ensure the functionality aspects. The task in... Sample PDF
Computer-Aided Process Planning and Manufacturing
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Chapter 4
Feature Technology  (pages 75-89)
Xun Xu
Throughout the course of the development of CAD, CAPP, and CAM systems, unambiguous representation of a design’s geometry and topology remain an... Sample PDF
Feature Technology
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Chapter 5
Feature Recognition  (pages 90-108)
Xun Xu
Conventional CAD models only provide pure geometry and topology for mechanical designs such as vertices, edges, faces, simple primitives, and the... Sample PDF
Feature Recognition
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Chapter 6
Feature Interactions  (pages 109-125)
Xun Xu
Feature interaction tends to have a wide range of consequences and effects on a feature model and its applications. While these may often be... Sample PDF
Feature Interactions
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Chapter 7
Xun Xu
Integrated feature technology promotes a closer connection between design and manufacturing through features. When machining features are... Sample PDF
Integrated Feature Technolog
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Chapter 8
CNC Machine Tools  (pages 165-187)
Xun Xu
The introduction of CNC machines has radically changed the manufacturing industry. Curves are as easy to cut as straight lines, complex 3-D... Sample PDF
CNC Machine Tools
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Chapter 9
Program CNCs  (pages 188-229)
Xun Xu
A CNC machine can be programmed in different ways to machine a workpiece. In addition to creating the cutting program, many other factors also need... Sample PDF
Program CNCs
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Chapter 10
Xun Xu
Technologies concerning computer-aided design, process planning, manufacturing and numerical control, have matured to a point that commercialized... Sample PDF
Integration of CAD/CAPP/CAM/CNC
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Chapter 11
Xun Xu
The integration model (Model B) as discussed in the previous chapter makes use of exchangeable neutral data formats such as IGES (1980). Neutral... Sample PDF
Integration Based on STEP Standards
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Chapter 12
Xun Xu
Function blocks are an IEC (International Electro-technical Commission) standard for distributed industrial processes and control systems (IEC... Sample PDF
Function Block-Enabled Integration
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Chapter 13
Xun Xu
In order to prepare manufacturing companies to face increasingly frequent and unpredictable market changes with confidence, there is a recognized... Sample PDF
Development of an Integrated, Adaptable CNC System
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Chapter 14
Xun Xu
A logical step after CNC machining is inspection. With inspections, Closed-Loop Machining (CLM) can be realized to maximize the efficiency of a... Sample PDF
Integrating CAD/CAPP/CAM/CNC with Inspections
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Chapter 15
Xun Xu
Today, companies often have operations distributed around the world, and production facilities and designers are often in different locations.... Sample PDF
Internet-Based Integration
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Chapter 16
Xun Xu
Companies that have been practicing CAD, CAPP, CAM, and CNC integration have now realized that there is a need to operate in a much broader scope... Sample PDF
From CAD/CAPP/CAM/CNC to PDM, PLM and Beyond
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Chapter 17
Key Enabling Technologies  (pages 354-393)
Xun Xu
While computers have proven to be instrumental in the advancement of product design and manufacturing processes, the role that various technologies... Sample PDF
Key Enabling Technologies
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About the Author