Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition The Coordinate Measuring System Unit 16

16-2 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

16-3 Coordinate Measuring System Measurements dimensioned from three rectangular coordinates – X, Y, and Z –High degree of accuracy To in. or mm Achieved using moiré fringe Machines widely used in field of measurement and inspection Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lathe equipped with coordinate measuring system

16-4 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 in. Transparent index grating mounted in reading head –Same resolution as Grating spar

16-5 Principle of the Moiré 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 over other at angle Lines cross, give dark bands As move top sheet to right, position of bands shift down (bands move vertically)

16-6 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 beam Beam strikes fringe pattern and reflected back to one of four photoelectric cells Reading head moved longitudinally, band moves vertically and picked up by next cell Signals from cells transmitted to digital readout display box – Signal from next cell + or in.

16-7 Operation of the Measuring Unit Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light Intensity on Photocells 3 and 4

16-8 Advantages of the Coordinate Measuring System Readout boxes provide clear, visible numbers Provides constant readout of tool position Reading indicates exact position of tool and not affected by machine or lead screw wear System eliminates need for gage blocks and measuring rods on jig borers and vertical milling machines

16-9 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 must be checked for one size only Reduces need for operator skill Eliminates scrap and rework Most machine tools can be fitted with system

16-10 Coordinate Measuring Machines Developed to speed up process of measuring parts produced on NC machine tools Can measure almost any shape with extreme accuracy and without use of special gages Computer controlled Installed on production lines –Automate inspection –Minimize operator error –Provide uniform part quality