.1.BASIC CONCE4T OF LASER 4rin%i)le o& L"#er#
0 Laser stands for light amplification $# stimulated emission of radiation
0 :asers for measurement are lo" po"er gas lasers that emit light in the visi$le range 0 :aser light $eam
is- – 0ighl# monochromatic the light has a single "ave length – 0ighl# collimated the light ra#s are parallel
0 !hese properties have motivated man# applications in measurement and inspection A('"nt"ge# o& L"#er#
1. The installation is easy 2. )ccurac# is high
3. It has a long range optical path.
4. It has high repeata$ilit# of displacement measurement 5. !here is virtuall# no "ear and tear.
6. )s man# as six measurements can $e made simultaneousl# $# a single laser source.
Di#"('"nt"ge# o& L"#er#
1. It is expensive
2. !he measurement is not in traditional units
3. Conversion instrumentation is required as the measurement is in terms of "avelength.
.,.Inter&eroeter
Interferometer is optical instruments used for measuring flatness and determining the lengths of slip gauges $# direct reference to the "avelength of light.
.,.1.L"#er Inter&eroeter
It is possi$le to maintain the qualit# of interference fringes over longer distance "hen lamp is replaced $# a laser source. :aser interferometer uses )C laser as the light source and the
measurements to $e made over longer distance. :aser is a monochromatic optical energ#, "hich can $e collimated into a directional $eam )C. :aser interferometer.
.,.,.L"#er Teleetri% #y#te
!he laser s#stem of measurement is a noncontact s#stem. ) heliumneon laser $eam is ver#
narro" and travels for greater distance "ithout an# deviation.it produces a red $eam of light and is visi$le on the screen.
!he arrangement of laser telemetric s#stem is sho"n in fig. it mainl# consists of three main parts.
I !ransmitter ii =eceiver
iii rocessor electronics.
!he transmitter contains a heliumneon gas laser, collimating lens, a h#steresis s#nchronous motor and protective "indo"s.
!he receiver collects and senses the laser light transmitted past the o$'ect.
!he output is availa$le in digital form.therfore this s#stem can $e applied on production machines to control them $# feed$ac& loops.
!he processor electronics thus converts the received signal and displa#s the dimension $eing measured.
A('"nt"ge#.
1. 0igh speed scanning is possi$le 2. nline gauging can $e done.
3. !he output is availa$le in digital form.
..AC LASER INTERFEROMETER
It is possi$le to maintain the qualit# of interference fringes over longer distance "hen lamp is replaced $# a laser source. :aser interferometer uses )C laser as the light source and the
measurements to $e made over longer distance. :aser is a monochromatic optical energ#, "hich can $e collimated into a directional $eam )C.
:aser interferometer +)C:I has the follo"ing advantages.
1. 0igh repeata$ilit# 2. 0igh accurac# 3.:ong range optical path 4.(as# installations ear and tear
*chematic arrangement of laser interferometer is sho"n in fig. !"ofrequenc# /eeman laser generates light of t"o slightl# different frequencies "ith opposite circular polarisation. !hese $eams get split up $# $eam splitter ne part travels to"ards and from there to external cu$e corner here the displacement is to the measured.
!his interferometer uses cu$e corner reflectors "hich reflect light parallel to its angle of incidence. eam splitter 2 opticall# separates the frequenc# Q "hich alone is sent to the mova$le cu$e corner reflector. !he second frequenc# from 2 is sent to a fixed reflector "hich then re'oins f1 at the $eam splitter 2 to produce alternate light and dar& interference flic&er at a$out 2 ega c#cles per second.
8o" if the mova$le reflector moves, then the returning $eam frequenc# opplershifted slightl# up or do"n $# Uf. !hus the light $eams moving to"ards photo detector 2 have frequencies f2 and +f1 L Uf1 and 2 changes these frequencies into electrical signal.
hoto detector 2 receive signal from $eam splitter 2 and changes the reference $eam frequencies f1 and f2 into electrical signal. )n )C amplifier ) separates frequenc#. ifference signal f2 V f1 and )2 separates frequenc# difference signal. !he pulse converter extracts i. one c#cle per half "avelength of motion. !he updo"n pulses are counted electronicall# and displa#ed in analog or digital form.
..1.Mi%+el#on Inter&eroeter
ichelson interferometer consists of a monochromatic light source a $eam splitter and t"o mirrors. !he schematic arrangement of ichelson interferometer is sho"n in fig. !he
monochromatic light falls on a $eam splitter, "hich splits the light into t"o ra#s of equal intensit# at right angles. ne ra# is transmitted to mirror 1 and other is reflected through $eam splitter to
mirror 2, from $oth these mirrors, the ra#s are reflected $ac& and these return at the semi reflecting surface from "here the# are transmitted to the e#e. irror 2 is fixed and mirror 1 is mova$le. If $oth the mirrors are at same distance from $eam splitter, then light "ill arrive in phase and o$server
"ill see $right spot due to constructive interference. If mova$le mirror shifts $# quarter "avelength, then $eam "ill return to o$server 1ABB out of phase and dar&ness "ill $e o$served due to destructive interference
(ach half"ave length of mirror travel produces a change in the measured optical path of one
"avelength and the reflected $eam from the moving mirror shifts through 36BS phase change. hen the reference $eam reflected from the fixed mirror and the $eam reflected from the moving mirror re'oin at the $eam splitter, the# alternatel# reinforce and cancel each other as the mirror moves. (ach
c#cle of intensit# at the e#e represents lW2 of mirror travel. hen "hite light source is used then a compensator plate is introduced in each of the path of mirror 1 *o that exactl# the same amount of glass is introduced in each of the path. !o improve the ichelson interferometer 3i! Jse of laser the measurements can $e made over longer distances and highl# accurate measurements "hen compared to other monochromatic sources. 3ii!irrors are replaced $# cu$ecorner reflector "hich reflects light parallel to its angle of incidence.3iii! hotocells are emplo#ed "hich convert light intensit#
variation in voltage pulses to give the amount and direction of position change.
..,.A))li%"tion o& inter&eroeter 1. Linear measurement 2. Angular measurement
...U#e o& L"#er &or Alignent Te#ting
!he alignment tests can $e carried out over greater distances and to a greater degree of accurac# using laser equipment.
1. :aser equipment produces real straight line, "hereas an alignment telescope provides an imaginar# line that cannot $e seen in space.
2. !his is important "hen it is necessar# to chec& num$er of components to a predetermined straight line. articularl# if the# are spaced relativel# long distances apart, as in aircraft production and in ship$uilding.
. :aser equipment can also $e used for chec&ing flatness of machined surface $# direct
displacement. # using are optical square in con'unction "ith laser equipment squareness can $e chec&ed "ith reference to the laser $ase line.
..CO-ORDINATE MEASURING MAC*INES
X Coordinate metrolog# is concerned "ith the measurement of the actual shape and dimensions of an o$'ect and comparing these "ith the desired shape and dimensions.
X In this connection, coordinate metrolog# consists of the evaluation of the location, orientation, dimensions, and geometry of the part or o$'ect.
X A Coordinate Measuring Machine (CMM) is an electromechanical s#stem designed to perform coordinate metrolog#.
..1.Ty)e# o& Me"#$ring M"%+ine#
1.:ength $ar measuring machine. ,. 8e"ell measuring machine.. Jniversal measuring machine.. Coordinate measuring machine. /.Computer controlled coordinate measuring machine.
..,.Con#tr$%tion# o& CMM
) C consists of a constant pro$e that can $e positioned in 3 space relative to the surface of a "or& part, and the x, #, and / coordinates of the pro$e can $e accuratel# and
precisel# recorded to o$tain dimensional data concerning the part geometr#. !hese measurements can $e made $# positioning the pro$e $# hand, or automaticall# in more expensive machines.
...Ty)e# o& CMM 1. Cantilever t#pe
2. ridge t#pe1.moving 2.fixed 3. 0ori/ontal $oring t#pe
4. ertical $oring t#pe
3i! C"ntile'er ty)e: T+e cantilever t#pe is ver# eas# to load and unload, $ut mechanical error ta&es place $ecause of sag or deflection in Yaxis.
3ii! Bri(ge ty)e: ridge t#pe is more difficult to load $ut less sensitive to mechanical errors.
3iii! *oriont"l 8oring Mill ty)e: !his is $est suited for large heav# "or& pieces.
i'! 7erti%"l 8oring ill ty)e: vertical $oring mill is highl# accurate $ut slo"er to operate.
5or9ing 4rin%i)le
C is used for measuring the distance $et"een t"o holes. !he "or& piece is clamped to the "or&ta$le and aligned for three measuring slides x, # and /. !he measuring head provides a taper pro$e tip "hich is seated in first datum hole and the position of pro$e digital read out is set to /ero.
!he pro$e is then moved to successive holes, the read out represent the coordinate part print hole location "ith respect to the datum hole. )utomatic recording and data processing units are provided to carr# out complex geometric and statistical anal#sis. *pecial coordinate measuring machines are provided $oth linear and rotar# axes. !his can measure various features of parts li&e cone, c#linder
and hemisphere. !he prime advantage of coordinate measuring machine is the quic&er inspection and accurate measurements.
...COM4UTER CONTROLLED CO-ORDINATE MEASURING MAC*INE
!he measurements, inspection of parts for dimension form, surface characteristics and position of
geometrical elements are done at the same time.
echanical s#stem can $e divided into four $asic t#pes. !he selection "ill $e depends on the
application. 1. Column t#pe. 2. ridge t#pe. 3. Cantilever t#pe. 4. <antr# t#pe.
)ll these machines use pro$es "hich ma# $e trigger t#pe or measuring t#pe. !his is connected to the spindle in E direction. !he main features of this s#stem are sho"n in figure
../.4er&or"n%e o& CMM
<eometrical accuracies such as positioning accurac#, *traightness and *quareness.
!otal measuring accurac# in terms of axial length measuring accurac#. olumetric length measuring accurac# and length measuring repeata$ilit#. i.e., Coordinate measuring machine has to $e tested as complete s#stem.
*ince environmental effects have great influence for the accurac# testing, including thermal parameters, vi$rations and relative humidit# are required.
..0.A44LICATIONS
1. Coordinate measuring machines find applications in automo$ile, machine tool, electronics, space and man# other large companies.
2. !hese machines are $est suited for the test and inspection of test equipment, gauges and tools.
3. %or aircraft and space vehicles, hundred percent inspections is carried out $# using C. C can $e used for determining dimensional accurac# of the components.
4. !hese are ideal for determination of shape and position, maximum metal condition, lin&age of results etc. "hich cannot do in conventional machines.
5. C can also $e used for sorting tas&s to achieve optimum pairing of components
"ithin tolerance limits.
6. Cs are also $est for ensuring economic via$ilit# of 8C machines $# reducing their do"ntime for inspection results. !he# also help in reducing cost, re"or& cost at the appropriate time "ith a suita$le C.
A('"nt"ge#
1. !he inspection rate is increased. ,. )ccurac# is more. . perators error can $e minimi/ed.
. *&ill requirements of the operator is reduced /. =educed inspection fixturing and maintenancecost.
0. =eduction in calculating and recording time. . =eduction in set up time.
. 8o need of separate go W no go gauges for each feature.
. =eduction of scrap and good part re'ection. 1?.=eduction in off line anal#sis time.
11. *implification of inspection procedures, possi$ilit# of reduction of total inspection time through use of statistical and data anal#sis techniques.
Di#"('"nt"ge#
1. !he la$le and pro$e ma# not $e in perfect alignment. ,. !he pro$e ma# have run out.
. !he pro$e moving in Eaxis ma# have some perpendicular errors.
. ro$e "hile moving in Z and Y direction ma# not $e square to each other.
/. !here ma# $e errors in digital s#stem.
...CNC-CMM
Con#tr$%tion!he main features of C8CC are sho"n in figure has stationar# granite measuring ta$le, :ength measuring s#stem. )ir $earingsK control unit and soft"are are the important parts of C8C 7 C.
<ranite ta$le provides a sta$le reference plane for locating parts to $e measured. It is
provided "ith a grid of threaded holes defining clamping locations and facilitating part mounting. )s the ta$le has a high load carr#ing capacit# and is accessi$le from three sides. It can $e easil#
integrated into the material flo" s#stem of CI.
Lengt+ e"#$ring #y#te a 3 axis C is provided "ith digital incremental length measuring s#stem for each axis.
Air Be"ring the ridge cross $eam and spindle of the C are supported on air $earings.
Control $nitthe control unit allo"s manual measurement and programme. It is a microprocessor control.
So&t>"re !he C, the computer and the soft"are represent one s#stemK the efficienc# and cost effectiveness depend on the soft"are.
...Fe"t$re# o& CMM So&t>"re
3i! easurement of diameter, center distance, length. 3ii! easurement of plane and spatial carvers.3iii! inimum C8C programme. 3i'! ata communications. 3'! igital input and output command. 3'i! rogramme for the measurement of spur, helical, $evel9 and h#poid gears. 3'ii!
Interface to C) soft"are.
) ne" soft"are for reverse engineering complex shaped o$'ects. !he component is digiti/ed using C8C C. !he digiti/ed data is converted into a computer model "hich is the true surface of the component. =ecent advances include the automatic "or& part alignment and to orient the
coordinate s#stem. *avings in inspection time $# using C is 5 to 1B compared to manual inspection method.
...C"$#e# o& Error# in CMM
1 !he ta$le and pro$es are in imperfect alignment. !he pro$es ma# have a degree of run out and move up and do"n in the Eaxis ma# cause perpendicularit# errors. *o C should $e
cali$rated "ith master plates $efore using the machine.
2 imensional errors of a C is influenced $#
*traightness and perpendicularit# of the guide "a#s.
*cale division and ad'ustment.
ro$e length.
ro$e s#stem cali$ration, repeata$ilit#, /ero point setting and reversal error.
(rror due to digiti/ation.
(nvironment
3 ther errors can $e controlled $# the manufacture and minimi/ed $# the measuring soft"are. !he length of the pro$e should $e minimum to reduce deflection.
4 !he "eight of the "or& piece ma# change the geometr# of the guide "a#s and therefore, the "or& piece must not exceed maximum "eight.
5 ariation in temperature of C, specimen and measuring la$ influence the uncertainl#
of measurements.
6 !ranslation errors occur from error in the scale division and error in straightness perpendicular to the corresponding axis direction.
> erpendicularit# error occurs if three axes are not orthogonal.
./.C"li8r"tion o& T+ree Co-Or(in"te Me"#$ring M"%+ine
!he optical set up for the cali$ration is sho"n in figure !he laser head is mounted on the tripod stand and its height is ad'usted corresponding to the "or&ing ta$le of C. !he
interferometer contains a polari/ed $eam splitter "hich reflects %1 component of the laser $eam and the %2 Component parts through.
!he retro reflector is a polished trihedral glass prism. It reflects the laser $eam $ac& along a line parallel to the original $eam $# t"ice the distance. %or distance measurement the %1 and %2 $eams that leave the laser head are aimed at the interferometer "hich splits %1 and %2 via polari/ing $eaming splitter. Component %1 $ecomes the fixed distance path and %2 is sent to a target "hich
reflects it $ac& to the interferometer. =elative motion $et"een the interferometer and the remote retro reflector causes a opper shift in the returned frequenc#. !herefore the laser head sees a frequenc#
difference given $# %1%2 L U%2. !he %1%2 L U%2 signal that is returned from the external
interferometer is compared in the measurement displa# unit to the reference signal. !he difference U%2 is related to the velocit#. !he longitudinal micrometer microscope of C is set at /ero and the
laser displa# unit is also set at /ero. !he C microscope is then set at the follo"ing points and the displa# units are noted.1 to 1Bmm, ever# mm and 1B to 2BBmm, in steps of 1Bmm. !he accurac# of linear measurements is affected $# changes in air temperature, pressure and humidit#.
.0.M"%+ine 7i#ion
achine vision can $e defined as a means of simulating the image recognition and anal#sis capa$ilities of the human s#stem "ith electronic and electromechanical techniques.
7i#ion Sy#te
!he schematic diagram of a t#pical vision s#stem is sho"n. !his s#stem involves image acquisitionK image processing )cquisition requires appropriate lighting. !he camera and store digital image processing involves manipulating the digital image to simplif# and reduce num$er of data points. easurements can $e carried out at an# angle along the three reference axes x # and / "ithout
contacting the part. !he measured values are then compared "ith the specified tolerance "hich stores in the memor# of the computer.
!he main advantage of vision s#stem is reduction of tooling and fixture costs, elimination of need for precise part location for handling ro$ots and integrated automation of dimensional
verification and defect detection.
4rin%i)le
Fo$r ty)e#3OR! Eleent# o& "%+ine 'i#ion #y#te and the schematic arrangement is sho"n 3i! Image formation. 3ii! rocessing of image in a form suita$le for anal#sis $# computer. 3iii!
efining and anal#/ing the characteristic of image. 3i'! Interpretation of image and decisionma&ing.
!he surface of the o$'ect is to $e inspected $# using front lighting. %or inspecting three
dimensional feature structured lighting is required. )n image sensor vidicon camera, CC camera is used to generate the electronic signal representing the image. !he image sensor collects light from the scene through a lens, using photosensitive target, converts into electronic signal.
I"ge )ro%e##or: ) camera ma# form an image 3B times per sec at 33 m sec intervals. )t each time interval the entire image fro/en $# an image processor for processing. )n analog to digital converter is used to convert analog voltage of each detector in to digital value
I"ge An"ly#i#
!he distance of an o$'ect from a vision s#stem camera can $e determined $# tri"ng$l"tion te%+ni$e.!he o$'ect orientation can he determined $# the methods of e$i'"lent elli)#e. !he image can $e interpreted $# t"odimensional image. %or complex threedimensional o$'ects $oundar# locations are determined and the image is segmented into distinct region.
I"ge Inter)ret"tion: T+i# involves identification of on o$'ect. In $inar# s#stem, the image is segmented on the $asis of "hite and $lac& pixels. !he complex images can he interpreted $# gre#
scale technique and algorithms. !he most common image interpretation is template matching.
.0.1.F$n%tion o& M"%+ine 7i#ion
:ighting and presentation of o$'ect to evaluated.
It has great compact on repeata$ilit#, relia$ilit# and accurac#.
I.ighting source and pro'ection should $e chosen and give sharp contrast.
Images sensor compressor ! camera ma# he vidicon or solid state.
%or simple processing, analog comparator and a computer controller to convert the video
information to a $inar# image is used.
ata compactor emplo#s a high speed a"a# processor to provide high speed processing of
ata compactor emplo#s a high speed a"a# processor to provide high speed processing of