Cmm

coordinate Measuring Machine

1. –
–
CMM
Lectureby
Mr.C.Ramkumar,
Assistant Professor/Department of
Mechanical Engineering
KIT-KalaignarKarunanidhiInstitute
of Technology

2. A coordinate measuring machine (CMM) is a device for measuring the physical
geometrical characteristics of an object.
This machine may be manually controlled byan operator or it may be
computer controlled.
Measurementsaredefinedbyaprobeattachedtothethirdmovingaxisofthis
machine.Probesmaybemechanical,optical,laser,orwhitelight,among
others.
BasicPrinciplesof CoordinateMeasuring
machines

3. DESCRIPTION
•Thetypical"bridge"CMMiscomposedofthreeaxes,anX,Y
andZ.Theseaxesareorthogonaltoeachotherinatypical
threedimensionalcoordinatesystem.
•Eachaxishasascalesystemthatindicatesthelocationofthat
axis.Themachinewillreadtheinputfromthetouchprobe,as
directedbytheoperatororprogrammer.
•ThemachinethenusestheX,Y,Zcoordinatesofeachofthese
pointstodeterminesizeandposition.Typicalprecisionofa
coordinatemeasuringmachineismeasuredinMicrons,or
Micrometers,whichis1/1,000,000ofameter.

4. •Acoordinatemeasuringmachine(CMM)isalsoadevice
usedinmanufacturingandassemblyprocessestotestapartor
assemblyagainstthedesignintent.BypreciselyrecordingtheX,Y,
andZcoordinatesofthetarget,pointsaregeneratedwhichcanthen
beanalyzedviaregressionalgorithmsfortheconstructionoffeatures.
•Thesepointsarecollectedbyusingaprobethatispositionedmanually
byanoperatororautomaticallyviaDirectComputerControl
(DCC).DCCCMMscanbeprogrammedtorepeatedlymeasure
identicalparts,thusaCMMisaspecializedformofindustrialrobot.

5. CoordinateMeasuringMachines-Model

6. Basic Elements of CMM
Coordinate-measuring machines include three
major functional components:
1. The main structure (table & movable
frame) which include three axes of motion.
2. Probing system
3. Data collection system -typically includes
a machine controller, desktop computer and
application software

7. BLOCKDIAGRAMOFTHE
ELEMENTS OFACMM
CO-ORDINATE
MEASURING
MACHINE
DIGITAL
READ OUT
COMPUTER
SOFTWAREPROBING
SYSTEM

8. Usesof CMM
Theyareoftenusedfor:
1.Dimensionalmeasurement
2.Profilemeasurement
3.Angularityororientationmeasurement
4.Depthmapping
5.Digitizingorimaging
6.Shaftmeasurement

9. Feature BasedMeasurement
•Form
–straightness, flatness, roundness, cylindricity,
sphericity
•Orientation
–parallelism, perpendicularity, concentricity,
angularity
•Profile
–profile (scanning), surface (manual), output
(graphics)

10. ADVANTAGESOF USINGCMM
FLEXIBILITY:
Co-ordinate measuring machines are essentially universal measuring machines and
do not need to be dedicated to any single or particular measuring task.
They can measure practically any dimensional characteristic of virtually any
part configuration, including cams, gears, and contoured surfaces.
No special fixtures or gages are required; because electronic probe contact is light,
most parts can be inspected without being clamped to a surface plate.
REDUCED SETUP TIME:
Establishingpartalignmentandappropriatereferencepointsareverytime
consuming with conventional surface-plate inspection techniques.
These procedures are greatly simplified or virtually eliminated through
software available on computer-assisted or computer-controlled CMMs.

11. IMPROVEDACCURACY
AllmeasurementsonaCMM aretakenfromacommongeometricallyfixed
measuring system, eliminating the introduction and accumulation of errors that
can result with hard gage inspection methods and transfer techniques.
Moreover, measuring all significant features of a part in one setup prevents
the introduction of errors due to setup changes.
Inthepart-program-assistedmode,theoperatorpositionsthemachine;oncethe
initialpositionhasbeenset,themachineisunderthecontrolofaprogramthat
eliminatesoperatorchoice.
In the Computer Numerically Controlled (CNC) mode, motor-driven machines
run totally unattended by operators.
Also, automatic data recording, available on most machines, prevents errors in
transcribing readings to the inspection report.
This all adds up to the fact that less skilled operators can be readily instructed to
perform relatively complex inspection procedures.

12. IMPROVEDPRODUCTIVITY
All the factors previously mentioned help to make CMMs more productive
than
conventional inspection techniques.
Furtherdramaticproductivityimprovementsarerealizedthroughthecomputational
andanalyticalcapabilitiesofassociateddatahandlingsystems,including
calculatorsandalllevelsofcomputers.

14. •All CMMs will have three moving elements of which one is capable of moving in x-
axis, another in y-axis and another in z-axis with respect to each other.
•Eachmovingelementisalsofittedwithalinearmeasurementtransducerforpositional
feedback,withthehelpofwhichwecanhavetheco-ordinateofaparticularposition
withrespecttoareference.
•Themovingelementscanbemovedbymeansoffrictionlessairbearingsormechanical
bearings.
•TheJobtobemeasuredwillbemountedoveratablemadeofgranitebecauseof
itsstabilityinvarioustemperatures.
•The work table of the machine generally consists of tapped holes to facilitate clamping
and locating of parts.
•Atotalof11differentmachineconfigurationsexist;however,some
configurations are modifications of one of the five primary configurations:
ofthese

15. MACHINECONFIGURATIONS
Avarietyofmachineconfigurationsisavailablefrom
themanufacturersofCMMs.
Each configuration has advantages that make it suitable
for particular applications.
Atotalof11differentmachineconfigurationsexist;
however,someoftheseconfigurationsaremodificationsof
oneofthefourprimaryconfigurations:bridge,
column,gantry,andhorizontalarm.

16. TYPES OFCMM
1.
2.
3.
4.
5.
Cantilever type
Bridge type
Column type
Gantry type
Horizontal type.
1. CANTILEVERTYPE
1. The probe is attached to the vertical quill that moves in a Z-axis
direction relative to a horizontal arm that over hangs the work table.
2. The quill can be moved along the length of the arm to achieve y-axis
motion, and the arm can be moved to the work table to achieve x-axis motion.
Typesofcantilever
1.MovingTableHorizontalArmCMM
2.MovingArmHorizontalArmCMM
3.ColumnCMM
4.FixedTableHorizontalArmCMM

17. Types ofCMM
Moving Arm Horizontal Arm
Coordinate Measuring Machine
Moving Table Horizontal Arm
Coordinate Measuring Machine

18. Types ofCMM
FixedTableCantileverCoordinate
MeasuringMachine
MovingBridgeCoordinateMeasuring
Machine

22. COLUMN:
Column-typeCMMsaresimilarinconstructionto
accurate jig boring machines.
Thecolumnmovesinavertical(Z)directiononly,and
atwo-axissaddlepermitsmovementinthehorizontal
(XandY)direction.
Column-typeCMMsareoftenreferredtoas
universalmeasuringmachines ratherthan
CMMs bymanufacturersandareconsideredgage-
roominstrumentsratherthanproduction-floorm/c.

23. Column-typeCMM

25. Types ofCMM
Gantry Coordinate Measuring
Machine
L-shaped Bridge Coordinate
Measuring Machine

26. Gantry-typeCMM

28. X
Y
Z
Movingram Movingtable
Fixedtable
HorizontalarmCMMs

32. Probe Tips

34. ProbeSystems
Switching probe
system
Continuous measuring probe
system
Kinematictouchtriggerprobe

38. Data flowbetweenCAD/CAMsystemand CMM
CAD
CAM
NC
processor
CMM
processor
CMM
NC
machine
center
Part
CMMInspection
Update NC
part program
Flag tool room Tool
management
and planning
Theoriticalpart
PartProgram
for minor tooling wear
and machine
adjustment
formajorflaws

39. Measurement with a CMM
•Step1:Calibrationofthestylusorprobe tipwith respect to
theprobeheadreferencepointusingacalibratedball.
•Step2:
position
system.
Metrologicaldeterminationoftheworkpiece
inthemeasuringmachine-related
coordinated
•Step3:Measurementofthesurfacepointsonthe
workpieceinthemeasuringmachine-relatedcoordinate
system.
•Step 4:Evaluation of the geometric parameters of the work
piece
•Step5:Representationofthemeasurementresults
aftercoordinatetransformationintotheworkpiece
relatedcoordinatesystem.

40. Basic Geometric Elements
Circle:Requires 3 points for measurement: By
measuring 4 (up to 50) or more points form
deviation is determined
Plane:Planar measurements require 4 or more
points for form. The intersection of Planes 2 and
3 generate Line 5; Point 6 is the intersection of
Plane 4 and Line 5
Cylinder:To define a cylinder, 5 points are
necessary. Calculations provide its axis and
diameter. The intersection of the Cylinder 7 and
Plane 4 is Line 8.
Cone:The cone (or taper) requires at least 6
points for definition. Calculations determine the
cone’s included angle and its axis in space.
Sphere:The location of a sphere is found by
measuring 4 points is also calculated.

41. CalculatedSolution-Distance

42. CalculatedSolution-Distance

43. CalculatedSolutions-Angle

44. CalculatedSolutions-Plane

45. CalculatedSolutions-Circle