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Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display.

PowerPoint to accompany

Krar Gill Smid

Technology of Machine Tools6th Edition

The Coordinate

Measuring System

Unit 16

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Objectives

The purpose of and how to apply the

coordinate measuring system

The main components and operation

of the measuring unit

The advantages of the coordinate

measuring system

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Coordinate Measuring System

Measurementsdimensioned from threerectangular coordinates

X, Y, and Z

High degree of accuracy To .000050 in. or 0.001 mm

Achieved using moir fringe

Machines widely used infield of measurement andinspection

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Lathe equipped with

coordinate measuring system

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Parts of the Measuring Unit

Three basic components

Machined spar with calibrated grating

Reading head Counter with digital readout display

Grating spar etched to .0001 in. resolution

Can have resolution of .000050 in.

Transparent index grating mounted inreading head

Same resolution as Grating spar

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Principle of the Moir Fringe

Example: Two pieces of plastic sheeting, each

with a series of equally spaced lines

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Place one sheet overother at angle

Lines cross, give

dark bands As move top sheet to right, position of bands

shift down (bands move vertically)

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Line Filament

Collimating Lens

Index Grating

Scale Grating

Photocell Strips

Principal Focus of Lens

Principle of the

Coordinate

Measuring Unit

Light from lamp passes

through lens converted

into parallel light beamBeam strikes fringepattern and reflected

back to one of four

photoelectric cells

Reading head movedlongitudinally, band

moves vertically and

picked up by next cell

Signals from cells

transmitted to digital

readout display box

Signal from next cell+ or - .001 in.

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Operation of the Measuring Unit

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Light Intensity on

Photocells 3 and 4

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Advantages of the Coordinate

Measuring System Eliminates need for operator calculations

and inherent possibility of errors

Machine setup time is greatly reduced

Production increased since workpiece mustbe checked for one size only

Reduces need for operator skill Eliminates scrap and rework

Most machine tools can be fitted with system

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Coordinate Measuring Machines

Developed to speed up process of measuringparts produced on NC machine tools

Can measure almost any shape with extremeaccuracy and without use of special gages

Computer controlled

Installed on production lines Automate inspection

Minimize operator error

Provide uniform part quality