unit iv johnson

8/13/2019 Unit IV Johnson

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LASER AND ADVANCES INMETROLOGY

Unit 4


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Syllabus

Precision instruments based on laserPrinciplelaser interferometerapplication in linear, angular measurements and machine toolmetrology

Coordinate measuring machine (CMM)Constructional features types

Applicationsdigital devices

Computer aided inspection


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PRINCIPLE OF LASER

The sequence of triggered identical photon from stimulated atom is

known as stimulated emission

This multiplication of photon through stimulated emission leads to

coherent, powerful, monochromatic, collimated beam of light emission

The photon comes in contact with another atom or molecule in the

higher energy level E2 then it will cause the atom to return to ground

state energy level E1 by releasing another photon


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LASER INTERFEROMETRY

Two frequency Laser source

Optical elements

Beam splitter

Beam benders

Retro reflectors

Laser head s measurement receiver

Measurement display


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USE OF LASER

Laser Telemetric systemLaser and LED based distance measuringinstruments

Scanning Laser gaugeDiffraction pattern techniqueGauging wide diameter from the diffraction patternformed in a laser


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Laser Telemetric system


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LASER AND LED BASED DISTANCE MEASURINGINSTRUMENTS


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Scanning Laser gauge


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Diffraction pattern technique

These are used to measure small gaps and smalldiameter parts A parallel coherent laser beam is diffracted by a

small part and a lens on a linear diode array focusesthe resultant pattern.The measurement accuracy is more for smaller parts


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Gauging wide diameter from the diffractionpattern formed in a laser


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LASER INTERFEROMETER


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Beam splitter


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Various version of ACLI

Standard Interferometer Signal beamsInterferometer


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MICHELSON INTERFEROMETER


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TWYMAN-GREEN INTERFEROMETER


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MACHINE TOOL TESTING

The accuracy of manufactured parts depends on theaccuracy of machine toolsIt can be classified into

Static testsDynamic tests


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Static tests - If the alignment of the components ofthe machine tool are checked under static conditionsthen the test are called static test

Dynamic tests - If the alignment tests are carriedout under dynamic loading condition. The accuracyof machine tools which cut metal by removing chipsis tested by two types of test namely.

Geometrical testsPractical tests


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Geometrical tests : In this test, dimensions ofcomponents, position of components anddisplacement of component relative to one another ischecked.Practical tests : In these test, test pieces aremachined in the machines. The test pieces must beappropriate to the fundamental purpose for which

the machine has been designed


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PURPOSE OF MACHINE TOOL TESTING

The dimensions of any work piece

Surface finishes and geometry depends on the

accuracy of machine tool for its manufacture

High accuracy


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TYPE OF GEOMETRICAL CHECKS ON MACHINE TOOL

Straightness.

Flatness.

Parallelism, equi-distance and coincidence.

Rectilinear movements or squareness of straight line

and plane.

Rotations


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MAIN SPINDLE IS TO BE TESTED FOR

Out of round.EccentricityRadial throw of an axis.

Run outPeriodical axial slipCamming


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VARIOUS TESTS CONDUCTED ON ANY MACHINE TOOLS

Test for level of installation of machine tool in horizontaland vertical planes.Test for flatness of machine bed and for straightness andparallelism of bed ways on bearing surface.Test for perpendicularity of guide ways to other guide ways.Test for true running of the main spindle and its axialmovements.Test for parallelism of spindle axis to guide ways or bearingsurfaces.Test for line of movement of various members like spindleand table cross slides etc


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CMM


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Measuring machines are used for measurement oflength over the outer surfaces of a length bar or anyother long member

It is more useful and advantageous than verniercalipers, micrometer, screw gaugesThe co-ordinate measuring machine is used forcontact inspection of parts

Savings in inspection 5 to 10 percent of the time isrequired on a CMM compared to manual inspectionmethods


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TYPES OF MEASURING MACHINES

Length bar measuring machine

Newall measuring machine

Universal measuring machine

Co-ordinate measuring machine

Computer controlled co-ordinate measuring machine


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Types of CMM


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Working


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CAUSES OF ERRORS IN CMM

The table and probes are in imperfect alignment.The probes may have a degree of run out and move upand down in the Z-axis may occur perpendicularityerrorsDimensional errors of a CMM is influenced by

Straightness and perpendicularity of the guide ways.Scale division and adjustment.

Probe length.Probe system calibration, repeatability, zero point setting andreversal error.Error due to digitization.Environment


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The length of the probe should be minimum toreduce deflectionThe weight of the work piece may change the

geometry of the guide ways Variation in temperature of CMM


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CALIBRATION OF THREE CO-ORDINATE MEASURINGMACHINE


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APPLICATION

Automobile, machine tool, electronics, space etc.,Machines are best suited for the test and inspectionof test equipment, gauges and tools

Aircraft and space vehiclesdetermination of shape


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ADVANTAGES

The inspection rate is increased. Accuracy is more.Operators error can be minimized.

Skill requirements of the operator is reduced.Reduced inspection fixturing and maintenance cost.Reduction in calculating and recording time.

Reduction in set up time.No need of separate go / no go gauges for each feature.Reduction of scrap and good part rejection


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DISADVANTAGES

The table and probe may not be in perfect alignment.The probe may have run out.The probe moving in Z-axis may have some

perpendicular errors.Probe while moving in X and Y direction may not besquare to each other.There may be errors in digital system


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COMPUTER CONTROLLED CMM


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Types


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CNC-CMM


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FLEXIBLE INSPECTION SYSTEM


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MACHINE VISION

A Vision system can be defined as a system forautomatic acquisition and analysis of images toobtain desired data for interpreting or controlling anactivity

Machine vision can be defined as a means ofsimulating the image recognition and analysis

capabilities of the human system with electronic andelectro mechanical techniques


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Four types of machine vision system

Image formation

Processing of image in a form suitable for analysis by

computerDefining and analyzing the characteristic of image

Interpretation of image and decision-making


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Compiled by:

A.JOHNSON SANTHOSH

Assistant Professor,Department of Mechanical Engineering,PPG Institute of Technology,Coimbatore.

unit iv johnson

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