coordinate measuring machine

1. Coordinate Measuring
Machine (CMM)
S.DHARANI KUMAR
Asst.professor
Department of Mechanical Engineering
SRI ESHWAR COLLEGE OF ENGINEERING
,COIMBATORE ,INDIA

2. TYPES OF MEASURING MACHINES
1. Length bar measuring machine.
2. Newall measuring machine.
3. Universal measuring machine.
4. Co-ordinate measuring machine.
5. Computer controlled co-ordinate measuring machine.

3. Coordinate Measuring Machines
• Coordinate metrology is concerned with the measurement
of the actual shape and dimensions of an object and
comparing these with the desired shape and dimensions.
• In this connection, coordinate metrology consists of the
evaluation of the location, orientation, dimensions, and
geometry of the part or object.
• A Coordinate Measuring Machine (CMM) is an
electromechanical system designed to perform coordinate
metrology.

4. Coordinate Measuring Machine (CMM)
Measuring machine consisting of a contact probe and a mechanism to position
the probe in three-dimensions relative to surfaces and features of a work part
The probe is fastened to a structure that allows movement relative to the part
Part is fixture on worktable connected to structure
The location coordinates of the probe can be accurately recorded as it contacts
the part surface to obtain part geometry data

5. Coordinate Measuring Machines
• A CMM consists of a constant probe that can be positioned in 3D space
relative to the surface of a work part, and the x, y, and z coordinates of the
probe can be accurately and precisely recorded to obtain dimensional data
concerning the part geometry

7. accomplish measurements in 3D, a basic CMM is composed of the following
components:
 Probe head and probe to contact the work part surface.
 Mechanical structure that provides motion of the probe in three Cartesian axes
and displacement transducers to measure the coordinate values of each axis.
• In addition, many CMM have the following components:
 Drive system and control unit to move each of the three axes
 Digital computer system with application software.
Coordinate Measuring Machines

9. CMM
CMM – Coordinate Measuring Machine
Flatness
Roundness
Cylindricity

10. CMM Mechanical Structure
(a) Cantilever (b) Moving bridge (c) Fixed bridge

11. CMM Mechanical Structure
(d) Horizontal Arm (e) Gantry (f) Column

12. Cantilever type
• A vertical probe moves in the z-axis
• Carried by a cantilevered arm that moves in the y-axis
• This arm also moves laterally through the x-axis
• Advantage- a fixed table allows good accessibility to the
work piece
• Disadvantage- the bending caused by the cantilever design
• The cantilever design offers a long table with relatively
small measuring ranges in the other two axis.
• Suitable for measuring long, thin part

13. Moving bridge type
• Most widely used
• Has stationary table to support work piece to be
measured and a moving bridge
• Disadvantage- with this design, the phenomenon of
yawing (sometimes called walking) can occur- affect
the accuracy
• Advantage- reduce bending effect

14. Fixed bridge type
• In the fixed bridge configuration, the bridge is
rigidly attached to the machine bed
• This design eliminates the phenomenon of
walking and provides high rigidity

15. Column type
• Often referred to as universal measuring
machine instead of CMM
• The column type CMM construction provides
exceptional rigidity and accuracy
• These machines are usually reserved for gauge
rooms rather than inspection

16. Horizontal arm type
• Unlike the previous machines, the basic horizontal
arm-type CMM
• Also referred to as layout machine
• Has a moving arm, and the probe is carried along the
y-axis
• Advantage- provides a large area, unobstructed work
area
• Ideal configuration for measurement of automobile
parts

17. Gantry type
• The support of work piece is independent of the x and y axes,
both are overhead, supported by four vertical columns rising
from the floor
• This setup allows you to walk along the work piece with the
probe, which is helpful for extremely large pieces

18. CMM Operation and Programming
• Positioning the probe relative to the part can be accomplished in several ways, ranging from
manual operation to direct computer control.
• Computer-controlled CMMs operate much like CNC machine tools, and these machines must
be programmed.
CMM Controls
• The methods of operating and controlling a CMM can be classified into four main
categories:
1. Manual drive,
2. Manual drive with computer-assisted data processing,
3. Motor drive with computer-assisted data processing, and
4. Direct Computer Control with computer-assisted data processing.

19. CMM Controls
• In manual drive CMM, the human operator physically move the probe along the
machine’s axes to make contact with the part and record the measurements.
• The measurements are provided by a digital readout, which the operator can
record either manually or with paper print out.
• Any calculations on the data must be made by the operator.
• A CMM with manual drive and computer-assisted data processing provides some data
processing and computational capability for performing the calculations required to
evaluate a give part feature.
• The types of data processing and computations range from simple conversioons between
units to more complicated geometry calculations, such as determining the angle between
two planes.

20. CMM Controls
• A motor-driven CMM with computer-assisted data processing uses electric motors
to drive the probe along the machine axes under operator control.
• A joystick or similar device is used as the means of controlling the motion.
• Motor-driven CMMs are generally equipped with data processing to accomplish
the geometric computations required in feature assessment.
• A CMM with direct computer control (DCC) operates like a CNC machine tool. It
is motorized and the movements of the coordinate axes are controlled by a
dedicated computer under program control.
• The computer also performs the various data processing and calculation functions.
• As with a CNC machine tool, the DCC CMM requires part programming.

21. DCC CMM Programming
• There are twp principle methods of programming a DCC measuring machine:
1. Manual leadthrough method.
2. Off-line programming.
• In the Manual Lead through method, the operator leads the CMM probe through the various
motions required in the inspection sequence, indicating the points and surfaces that are to be
measured and recording these into the control memory.
• During regular operation, the CMM controller plays back the program to execute the inspection
procedure.
• Off-line Programming is accomplished in the manner of computer-assisted NC part
programming, The program is prepared off-line based on the part drawing and then
downloaded to the CMM controller for execution.

22. TYPES OF PROBES
• Two general categories
1. Contact (see figure)
• Touch-trigger probe
• Analog scanning probe
2. Noncontact
For inspection of printed circuit board, measuring a clay
of wax model, when the object being measured would
be deformed by the for of stylus
• laser probes
• video probes

23. Contact probes
1. Touch trigger probe
• As the sensor makes contact with the part, the difference in contact resistance indicates that
the probe has been deflected
• The computer records this contact point coordinate space
• An LED light and an audible signal usually indicate contact
• Touch probe assemblies consist of three components; probe head, probe and stylus
2. Analog scanning probe
• Use to measure contour surfaces, complex, irregular
• Remains in contact with the surface of the part as it moves
• Improve the speed and accuracy

24. Non-contact probe
1. Laser scanning probe
• Laser probes project a light beam onto the surface of a part
• When the light beam is triggered, the position of beam is read by triangulation through
a lens in the probe receptor
• Laser tool have a high degree of speed and accuracy
2. Video probe
• The feature are measured by computer ‘count’ of the pixels of the electronic image
• The camera is capable of generating multitude of measurements points within a single
video frame

25. Trigger type probe system

26. Measuring type probe system

27. Probe head, probes and stylus

28. Multiple shapes of sylus

29. CALIBRATION OF THREE CO-ORDINATE MEASURING MACHINE

30. APPLICATIONS
1) Co-ordinate measuring machines find applications in automobile, machine tool,
electronics, space and many other large companies.
2) These machines are best suited for the test and inspection of test equipment, gauges
and tools.
3) For aircraft and space vehicles, hundred percent inspections is carried out by using
CMM.
4) CMM can be used for determining dimensional accuracy of the components.
5) These are ideal for determination of shape and position, maximum metal condition,
linkage of results etc. which cannot do in conventional machines.

31. 6) CMM can also be used for sorting tasks to achieve optimum pairing of components
within tolerance limits.
7) CMMs are also best for ensuring economic viability of NC machines by reducing
their
downtime for inspection results. They also help in reducing cost, rework cost at the
appropriate time with a suitable CMM.

32. ADVANTAGES
• The inspection rate is increased.
• Accuracy is more.
• Operators error can be minimized.
• Skill requirements of the operator is reduced.
• Reduced inspection fix Turing 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.
• Reduction in off line analysis time.

33. 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 be square to each
other.
• There may be errors in digital system.

34. CAUSES OF ERRORS IN CMM
• The table and probes are in imperfect alignment. The probes may have a degree of
run out and move up and down in the Z-axis may occur perpendicularity errors. So
CMM should be calibrated with master plates before using the machine.
• Dimensional 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 and reversal error.
Error due to digitization.
Environment

35. • Other errors can be controlled by the manufacture and minimized by the
measuring software. The length of the probe should be minimum to reduce
deflection.
• The weight of the work piece may change the geometry of the guide ways and
therefore, the work piece must not exceed maximum weight.
• Variation in temperature of CMM, specimen and measuring lab influence the
uncertainly of measurements.
• Translation errors occur from error in the scale division and error in straightness
perpendicular to the corresponding axis direction.
• Perpendicularity error occurs if three axes are not orthogonal.

36. Comparison between conventional and coordinate measuring
technology
CONVENTIONAL METROLOGY COORDINATE METROLOGY
Manual, time consuming alignment of the test piece Alignment of the test piece not necessary
Single purpose and multi-point measuring instruments
making it hard to adapt to changing measuring task
Simple adaptation to the measuring test by software
Comparison of measurement with material measures,
i.e., gauge block
Comparison of measurement with mathematical or
numerical value
Separate determination of size, form, location and
orientation with different machines
Determination of size, form, location and orientation in
one setup using one reference system

38. Features of CMM Software
• Measurement of diameter, center distance, length.
• Measurement of plane and spatial carvers.
• Minimum CNC programmed.
• Data communications.
• Digital input and output command.
• Program me for the measurement of spur, helical, bevel’ and hypoid
gears.
• Interface to CAD software

39. • Generally software packages contains some or all of the following capabilities:
1. Resolution selection
2. Conversion between SI and English (mm and inch)
3. Conversion of rectangular coordinates to polar coordinates
4. Axis scaling
5. Datum selection and reset
6. Circle center and diameter solution
7. Bolt-circle center and diameter
8. Save and recall previous datum
9. Nominal and tolerance entry
10. Out-of tolerance computation

40. CMM
CMM – Coordinate Measuring Machine

41. CMM
CMM – Coordinate Measuring Machine

42. $$* IIT Delhi- DMIS File For Verifying Cylindricity:
Generated by Bhaskar
$$-> DMIS File Number - 1
$$-> Manifold Part / MFG001
DMISMN / DMIS Program
UNITS / MM, ANGDEC
$$-> FEATNO / 128
$$ Verify Gtol g01
T(CYLINDRICITY)= TOL / CYLCTY, 0.005000
OUTPUT / FA(M_CY1), TA(CYLINDRICITY)
$$-> END /
ENDFIL
$$* IIT Delhi- DMIS File For Verifying Conicity:
Generated by Bhaskar
$$-> DMIS File Number - 2
$$-> Manifold Part / MFG002
DMISMN / DMIS Program
UNITS / MM, ANGDEC
$$-> FEATNO / 88
$$ Verify Gtol g02
T(CONICITY)= TOL / CNCTY, 0.005000
OUTPUT / FA(M_CN02), TA(CONICITY)
$$-> END /
ENDFIL
DMIS

43. $$* IIT Delhi- DMIS File For Measuring A Cylinder: Generated by Bhaskar
$$-> DMIS File Number - 1
$$-> Manifold Part / MFG001
DMISMN / DMIS Program
UNITS / MM, ANGDEC
S(1)= SNSDEF / PROBE, INDEX, POL, 0.000000, 0.000000, $
0.000000, 0.000000, 1.000000, 100.000000, 4.000000
$$-> FEATNO / 128
MODE / PROG, AUTO
SNSLCT / S(1)
FEDRAT / MESVEL, MPM, 15.000000
FEDRAT / POSVEL, MPM, 20.000000
ACLRAT / MESACL, MPMM, 5.000000
ACLRAT / POSACL, MPMM, 10.000000
PRCOMP / OFF
SNSET / APPRCH, 5.500000
SNSET / RETRCT, 5.500000
SNSET / CLRSRF, 0.000000
F(M_CY01)= FEAT / CYLNDR, INNER, CART, $
0.000000, 0.000000, 0.000000, $
0.000000, 0.000000, -1.000000, 30.000000
F(BND_20)= FEAT / PLANE, CART, $
0.000000, 0.000000, 0.000000, $
0.000000, 0.000000, 1.000000,
F(BND_21)= FEAT / PLANE, CART, $
0.000000, 0.000000, -10.000000, $
0.000000, 0.000000, -1.000000,
BOUND / F(M_CY1), F(BND_20), F(BND_21)
MEAS / CYLNDR, F(M_CY1), 32
..........................
GOTO / 0.000000, 0.000000, -2.000000
PTMEAS / CART, 13.000000, 0.000000, -2.000000, $
1.000000, 0.000000, 0.000000
PTMEAS / CART, 9.192388, 9.192388, -2.000000, $
0.707107, 0.707107, 0.000000
$$* IIT Delhi- DMIS File For Measuring A Cone: Generated by Bhaskar
$$-> DMIS File Number - 2
$$-> Manifold Part / MFG002
DMISMN / DMIS Program
UNITS / MM, ANGDEC
0.000000, 0.000000, 1.000000, 100.000000, 2.000000
$$-> FEATNO / 88
MODE / PROG, AUTO
SNSLCT / S(2)
FEDRAT / MESVEL, MPM, 15.000000
FEDRAT / POSVEL, MPM, 20.000000
ACLRAT / MESACL, MPMM, 5.000000
ACLRAT / POSACL, MPMM, 10.000000
PRCOMP / OFF
SNSET / APPRCH, 0.249996
SNSET / RETRCT, 0.249996
SNSET / CLRSRF, 0.000000
F(M_CN02)= FEAT / CONE, INNER, CART, $
0.000000, 0.000000, -44.999981, $
0.000000, 0.000000, 1.000000, 36.870000
MEAS / CONE, F(M_CN02), 6.000000
RAPID / 1.000000
GOTO / 0.0000000000, 0.0000000000, 2.000000
RAPID / 1.000000
GOTO / 0.000000, 0.000000, 2.000000
RAPID / 1.000000
GOTO / 0.000000, 0.000000, -37.000000
PTMEAS / CART, 6.000008, 0.000000, -37.000000, $
-0.799999, 0.000000, 0.600001
PTMEAS / CART, 0.000000, 6.000008, -37.000000, $
0.000000, -0.799999, 0.600001
PTMEAS / CART, -0.000000, -6.000008, -37.000000, $
0.000000, 0.799999, 0.600001
DMIS

44. MACHINE VISION
VISION SYSTEM

45. VISION SYSTEM

46. Principle:

48. FUNCTION OF MACHINE VISION

49. INTEGRATION OF CAD/CAM WITH INSPECTION SYSTEM

50. FLEXIBLE INSPECTION SYSTEM