ComputerAided_Design_Engineering_amp_Manufactur.pdf
ComputerAided_Design_Engineering_amp_Manufactur.pdf
ComputerAided_Design_Engineering_amp_Manufactur.pdf
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has been developed as a neutral interface for the bi-directional communication of data between CAD<br />
systems and computer-controlled CMMs in a multi-vendor, computer-integrated environment. DMIS<br />
was developed by Computer-Aided <strong>Manufactur</strong>ing Incorporated (CAM-I) and it was approved in<br />
1990 by the American National Standards Institute (ANSI) as an American National Standard. The<br />
main advantages of DMIS is that it is APT-like and it allows measurement results to be carried back<br />
in the same neutral format. This is particularly important in computer integration to both quality<br />
and management information systems in a CIM architecture and is fast evolving as the main industry<br />
standard.<br />
DMIS carries two main types of statements: process-oriented commands and geometry-oriented<br />
statements. Process-oriented commands consist of motion statements, machine parameters statements,<br />
part alignment statements, probe calibration statements, and other statements related to the inspection<br />
process. Geometry-oriented statements are used to describe the geometrical elements, geometric dimension<br />
and tolerances, coordinate systems, and other types of data which may be included in a CAD<br />
database. DMIS has been designed to be compatible with complete part model definitions supporting<br />
simple geometrical features like point, circle, ellipse, arc, sphere, cylinder, cone, and plane—as well as<br />
more complicated ones like the general curve element, general surface element, pattern elements, rectangle<br />
element, parallel plane element, and general raw data element. It also supports GD&T specifications<br />
according to ANSI Y14.5M which is widely adopted in the industry. Another powerful feature of DMIS<br />
is its high level language capability. This allows for variable definitions as well as program control,<br />
providing for high flexibility in automated inspection planning. Although it has been reported that there<br />
are interfacing problems between the CAD system and the CMM, 44 DMIS will evolve as the main interface<br />
standard as further refinements are made.<br />
Computer-Aided Inspection Planning System for the Coordinate<br />
Measuring Machine (CAIPS-CMM)<br />
The development of a computer-aided inspection planning system for the coordinate measuring machine<br />
(CAIPS-CMM) is characterized by the generative approach with few reported instances of the variant<br />
approach. 45 In the generative approach, applications are broadly divided into:<br />
• Inspection of turned parts46 • Inspection of prismatic parts47–49 • Inspection of complex surfaces for molds. 50–52<br />
For turned and prismatic parts, the application of a feature-based technique is very apparent. Expert<br />
systems are also mainly used for the reasoning process in planning, coupled with techniques like objectoriented<br />
programming. For the inspection of complex surfaces, the focus of researchers is on minimization<br />
of inspection points and comparative analysis.<br />
Regardless of the applications, a CAIPS-CMM should generally cover the following areas in order to<br />
automate the task of CMM part programming in a computer-integrated environment:<br />
• An interface to a CAD product model for interpretation of measurement requirements. Inspection<br />
requirements for the CMM are driven by the GD&T specifications which usually refer to geometrical<br />
surfaces or datum on the product model. Hence a product model should ideally encompass<br />
complete geometric information as well as GD&T information. Higher level information like<br />
features can be incorporated which could help in the planning process. The structure of the product<br />
model representation is outlined in the next section.<br />
• A framework for inspection planning based on the knowledge of the operational procedures of<br />
the CMM is required.<br />
• Knowledge of the machine capabilities in terms of the machine configuration, the available sensor<br />
configurations, the accuracy, the operating speed, the supporting evaluation functions, etc., is<br />
essential for decisions such as selection of probes for the CMM.<br />
© 2001 by CRC Press LLC