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