10.01.2013 Views

ComputerAided_Design_Engineering_amp_Manufactur.pdf

ComputerAided_Design_Engineering_amp_Manufactur.pdf

ComputerAided_Design_Engineering_amp_Manufactur.pdf

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!