Unit III ADVANCES IN METROLOGY

1. UNIT-III
ADVANCES IN METROLOGY
PREPARED BY
L. DEVAKUMAR
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
KNCET

2. UNIT-III
ADVANCES IN METROLOGY
Basic concepts of laser, Advantages of laser –
laser interferometers – Types – DC and AC laser
interferometer – Applications – Straightness –
Alignment. Basic concept of CMM – Types of
CMM – constructional features – Probes –
Accessories – Software – Application – Basic
concepts of machine vision system – Element –
Application

3. LASER
• Laser stands for Light Amplification by Stimulated
Emission of Radiation.
• Laser instrument is a device to produce powerful,
monochromatic, collimated beam of light in which
the waves are coherent.
• Energy appears to be emanating from a very small
point.
• The laser is used extensively for interferometry
particularly the Helium- Neon gas type.
• This produces 1 to 2mm diameter beam of red light
power of 1MW and focused at a point of very high
intensity.

4. • Laser systems have wide dynamic range, low
optical cross talk and high contrast.
• Laser fined application in dimensional
measurements and surface inspection
because of the properties of laser light.
• These are useful where precision, accuracy,
rapid non-contact gauging of soft, delicate or
hot moving points.
• An electromagnetic radiation is emitted
whenever a charged particles such as an
electron drops from a higher energy state E2
to E 1

5. Terminology
• WAVELENGTH: the distance between the two
crest and two trough
• FREQUENCY: the number of waves passing in
a point in a certain time
• MONOCHROMATIC LIGHT: spectrum of visible
light having the same wavelength
• COHERENT: The distance over which the beam
stays in phase with itself

6. WORKINGPRINCIPLEOFLASER
A LASER work in the form of the processes that
consists of four importantprocesses:
1. Energy Absorption
2. Spontaneous Emission
3. Pumping and Population Inversion
4. Stimulated Emission of Electromagnetic Radiation
(Triggered photon)

8. COMPONENTS/ELEMENTS OF LASER
• ACTIVE MEDIUM – May be solid crystals such
as ruby, liquid dyes, gases as co2 or
Helium/neon semiconductors. It contain
atoms whose electrons may be excited to a
metastable energy level by an energy source.
• EXCITATION MEDIUM – Pump energy into
active medium. They are optical, electrical or
chemical methods.

9. • HIGH REFLECTIVE MIRROR – A mirror which
essentially reflects 100% of the laser light.
• PARTIALLY TRANSMISSIVE MIRROR – Reflects
less than 100% of laser light.

10. COMPONETS OF LASER

11. TYPES OF LASER SOURCE
• Optically pumped solid state laser
• Ruby laser
• Nd: Yag lasers (neodymium-doped yttrium aluminum garnet)
• Nd: Glass lasers
• Liquid Dye laser
• Gas laser( He-Ne, 632 wavelength)
• He-ne laser
• Argon laser
• Krypton laser
• Carbon Dioxide laser
• Excimer lasers
• Semiconductor laser(laser diode)

12. ADVANTAGES
• More intensive than any other monochromatic
source
• High precise, accurate
• It facilitates rapid non-contact gauging of soft,
delicate or hot moving parts
• Allow fabrication of fine structures with high
quality avoiding mechanical stress

13. APPLICATIONS
• MANUFACTURING- quality cutting, drilling,
welding
• DATA STORAGE- CD, DVD,
• COMMUNICATION
• DISPLAYS
• SCIENTIFIC APPLICATIONS

14. SCANNING LASER GAUGE

15. • TRANSMITTING UNIT
• PHOTO CELL OR RECEIVER
• MICROPROCESSOR OR CONTROL UNIT
• Used to measure the roundness and
diameter of hot steel bars
• Accuracy of 0.025mm for 5 - 25 mm dia
objects

16. SCANNING LASER GAUGE

17. Scanning laser gauge

18. LASER TELEMETRIC SYSTEM

19. • Used for high speed, non contact dimensional
and positional measurement and control
• The three components are TRANSMITTER,
RECEIVER, PROCESSSOR ELECTRONICS
• Laser beam moving at constant linear speed
• It measures at the rate of 150 scans per
second
• Object to be sensed photo electrically by the
receiver
• Received signals are converted by processor
electronics to convenient form

20. LASER TRIANGULAR SENSORS

21. LASER TRIANGULAR SENSORS

22. LASER TRIANGULAR SENSORS

25. DIFFRACTION PATTERN TECHNIQUE

26. WHAT IS DIFFRACTION?
• Which involves a change in direction of
waves as they pass through an opening or
around a barrier in their path.

27. • Above fig shows a method of measuring the
diameter of thin wire using the interference
fringes (edges, borders) resulting from
diffraction of the light by the wire in the laser
beam.
• A measure of the diameter can be obtained by
moving the photo detector until the output is
restored to its original value.
• Variation in wire diameter as small as 0.2%
over wire diameter from 0.005 to 0.2mm can
be measured.

28. TWO FREQUENCY LASER INTERFEROMETER

33. • This consists of two frequency laser head,
beam directing and splitting optics,
measurement optics, receivers, and
wavelength compensators and electronics.
• It is ideally suited for measuring linear
positioning straightness in two planes, pitch
(the place at the beam falls) and yaw
(deviation of beam)
• The two-frequency laser head provides one
frequency with P-polarization and another
frequency with S-polarization.
• The laser beam is split at the polarizing beam
splitter into its two separate frequencies.

34. • The measuring beam is directed through the
interferometer to reflect off a target mirror
or retro reflector attached to the object to be
measured.
• The reference beam is reflected from fixed
retro reflector.
• The measurement beam on its return path
recombines with the reference beam and is
directed to the electronic receiver.
• POLARIZATION – to produce different views
on different sides

35. • INTERFERENCE
The two waves suppose to form a resultant
wave of greater or lower amplitude is called
interference
• PRINCIPLE OF SUPERPOSITION
The two waves have same wavelength and
exactly in phase with each other – the resultant
wave is sum of the amplitudes which produces
increased brightness
if the phase not each other, the resultant
amplitude is the difference of the individual
amplitudes which results darkness

36. PRINCIPLE OF SUPER POSITION

37. INTERFEROMETER
• An instrument which generates and
compares the difference between the two
light waves which are reflected off two
different surfaces.
• Utilizes the effect of interference.
• INTERFEROMETRY: accurate measurement of
linear dimensions using a pure
monochromatic light source

38. • Laser Interferometer:
–the instrument used for high precision
measurements (distance, angles…. etc.)
–it uses the very small, stable and accurately
defined wavelength of laser as a unit of
measure

39. Applications
• Other Applications
– Measure angles, flatness, straightness, velocity
and vibrations, etc.
Xiaoyu Ding
Rearrangements
of the light paths

40. Linear Distance Measurement
The positioning accuracy is measured by
comparing the position value displayed by
machine with the actual position.

41. Straightness Measurements
Straightness and parallelism measurements with
moving board up to 20 mm.

42. • Measurement of lengths
• Small changes in lengths
• Optical testing
• Surface structure
• Measurement of pressure and
temperature difference in gas flows and
plasmas
APPLICATIONS OF INTERFEROMETERS

43. • Particle velocities and vibration
amplitudes
• Wavelength measurements
• Testing of optical components
• Calibration of slip gauges
• Co ordinate measuring machine

44. Principle of Michelson Interferometer
• Albert Michelson (1852~1931)
the first American scientist to receive a
Nobel prize, invented the optical
interferometer.
The Michelson interferometer has
been widely used for over a century to
make precise measurements of
wavelengths and distances.
Albert Michelson
Xiaoyu Ding

45. • Michelson Interferometer 1) Separation
2) Recombination
3) Interference
A Michelson Interferometer for use on an optical table

46. MICHELSON INTERFEROMETER

49. OBJECTIVE
• To determine the wave length of light derived
from certain sources by comparison to meter
bar.
• Based on the principle of constructive and
destructive interference
• The reflected rays back to beam splitter from
where they are transmitted to photo detector

50. Twyman green interferometer

52. TYPES OF INTERFEROMETERS
• Homodyne or single – frequency or DC laser
interferometer
• Hetrodyne or dual – frequency or AC laser
interferometer

53. AC LASER INTERFEROMETER
• OBJECTIVE
The A.C system mixes the beams of
slightly different frequencies, permitting the
distance information to be carried on a.c wave
form
a.c laser interferometer measures mirror
displacement by measuring the phase change
due to the doppler effect.

54. COMPONENTS
• Two frequency laser source
• Optical elements
i ) Beam splitters
ii ) Beam benders
iii ) Retro reflectors
• Laser head’s measurement receiver
• Wave plate
• Measurement display

55. STRUCTURE OF ACLI

56. • Using AC laser light source of quality
interference fringes over longer distance
• Two slightly different frequencies with
opposite circular polarization
• After reflection beams recombines at B2 to
produce alternate light and dark interference
• The photo detector p1 receives f1 and f2
• The photo detector p2 receives f2 and
(f1±Δf1)

57. • f2-f1 in Amplifier1
• F2- (f1±Δf1) in Aamplifier2
• The up and down pulses from the converter
are converted electronically and displayed In
analog or digital form on the indicator
• Has high repeatability and resolution of
displacement measurement
• High accuracy
• 60 m range
• Easy to install

58. SINGLE FREQUENCY DC LASER
INTERFEROMETER

59. COMPONENTS
• Laser source
• Beam splitter
• Retro reflectors
• Quarter Wave plate
• Photo detectors
• Measurement electronics

60. WORKING METHOD
• Single polarization state
• Wave plates or retarders – change the
polarization state of light
• Half wave plate will rotate the plane of
polarization
• Beam splitter – separates the beam source
• It is an improved version of Michelson
interferometer
• He – Ne gas type laser

61. • Beam having two opposing circularly
polarized components
• the two beams are reference beam and
transmitted beam
• These are recombines at beam splitter but
differently polarized but do not interfere
• Wave plate used to interfere with one
another to produce plane polarized beam
• The detectors used to distinguish the
direction of movement and the moveable
retro reflector is able to attach to the
required place for finding distance

63. COORDINATE MEASURING MACHINE
• OBJECTIVE:
To determine the geometrical
characteristics of an object operating in a three
dimensional space.
• Role of inspection process
• Measuring probe to determine coordinates of
points on an object surface.
• Design, testing, profiling
• 100% dimensional assessment.
• First developed in Ferranti in scotland

64. COORDINATE MEASURING MACHINE

66. CMM

67. WORKING
• Measuring machines are used for measurement
of length over the outer surfaces of a length bar
or any other long member.
• The member may be either rounded or flat and
parallel. It is more useful and advantageous than
vernier calipers, micrometer, screw gauges etc.
• The measuring machines are generally universal
character and can be used for works of varied
nature.
• The co-ordinate measuring machine is used for
contact inspection of parts.

68. • When used for computer-integrated
manufacturing these machines are controlled by
computer numerical control.
• General software is provided for reverse
engineering complex shaped objects.
• The component is digitized using CNC, CMM
and it is then converted into a computer model
which gives the two surface of the component.
• These advances include for automatic work part
alignment on the table. Savings in inspection 5
to 10 percent of the time is required on a CMM
compared to manual inspection methods.

69. TYPES OF CMM

72. Working Principle
• CMM is used for measuring the distance
between two holes. The work piece is
clamped to the worktable and aligned for
three measuring slides x, y and z.
• The measuring head provides a taper probe tip
which is seated in first datum hole and the
position of probe digital read out is set to zero.
• The probe is then moved to successive holes,
the read out represent the co-ordinate part print
hole location with respect to the datum hole.

73. • Automatic recording and data processing
units are provided to carry out complex
geometric and statistical analysis.
• Special co-ordinate measuring machines are
provided both linear and rotary axes.
• This can measure various features of parts
like cone, cylinder and hemisphere.
• The prime advantage of co-ordinate
measuring machine is the quicker inspection
and accurate measurements.

77. Performance of CMM
• Geometrical accuracies such as positioning
accuracy, Straightness and Squareness.
• Total measuring accuracy in terms of axial length
measuring accuracy.
• Volumetric length measuring accuracy and
length measuring repeatability. i.e.,
Coordinate measuring machine has to be tested
as complete system.
• Since environmental effects have great influence
for the accuracy testing, including thermal
parameters, vibrations and relative humidity are
required.

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

79. • CMM can also be used for sorting tasks to
achieve optimum pairing of components
within tolerance limits.
• 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.

82. PROBE SYSTEM

87. MACHINE VISION SYSTEM
• OBJECTIVE
A Vision system can be defined as a system
for automatic acquisition and analysis of images
to obtain desired data for interpreting or
controlling an activity.
It is a technique which allows a sensor to
view a scene and derive a numerical or logical
decision without further human intervention.
Machine vision can be defined as a means of
simulating the image recognition and analysis
capabilities of the human system with electronic
and electro mechanical techniques.

88. USES OF MACHINE VISION
• Functions like gauging of dimensions,
• Identification of shapes,
• Measurement of distances,
• Determining orientation of parts,
• Quantifying motion-detecting surface shading
• It is best suited for high production.
• These systems function without fatigue.
• This is suited for inspecting the masks used in
the production of micro-electronic devices

91. MACHINE VISION SYSTEM

92. MAIN ADVANTAGE OF VISION SYSTEM
• Reduction of tooling and fixture costs
• Elimination of need for precise part
• Location for handling robots and
integrated automation of dimensional
verification and defect detection

93. IMAGE FORMATION

94. FUNCTION OF MACHINE VISION
• Lighting and presentation of object to be
evaluated.
• It has great compact on repeatability,
reliability and accuracy.
• Iighting source and projection should be
chosen and give sharp contrast.
• Images sensor compressor TV camera may be
vidiocon or solid state.

95. • For simple processing, analog comparator
and a computer controller to convert the
video information to a binary image is used.
• Data compactor employs a high speed away
processor to provide high speed processing of
the input image data.
• System control computer communicates with
the operator and make decision about the
part being inspected.

96. • The output and peripheral devices operate
the control of the system.
• The output enables the vision system to
either control a process or provide caution
and orientation information two a robot, etc.

97. FUNCTION OF MACHINE VISION

98. ELEMENTS OF MACHINE VISION
SYSTEM
• The delivery system
• Light source(illumination)
• Lenses – Field Of View of working distance
• Image sensor and digitizer
1. Converting optical into electrical signal
2. Videocon camera, solid state, camera and
frame grabber, synchronizing sensor

99. • Preprocessor – greater degree of image
refinement and removing or enhancing
features
• Vision processor/ controller – preprocessed
can be analyze here
Programmable Logic Controller
• Communication links
• Output devices – to control machine function
according to communication received from
the processor

100. APPLICATION
• Machine vision can be used to replace
human vision for welding.
• Machining and maintained
relationship between tool and work
piece and assembly of parts to
analyze the parts.
• This is frequently used for printed
circuit board inspection to ensure
minimum conduction width and
spacing between conductors.

101. • These are used for weld seam tracking,
robot guideness and control, inspection
of microelectronic devices and tooling,
on line inspection in machining
operation, assemblies monitoring high-
speed packaging equipment etc.
• Automotive – to guid robots, identify
codes, engine block inspection.

102. • Semiconductor manufacturing
• Manufacturing industries
• Solar panel manufacturing
• Food and packaging
• Postal and parcel inspection
• Non destructive testing
• Inspections of continuous webs

103. MACHINE TOOL METROLOGY

104. True running of
locating of main
spindle
Axial slip of main
spindle

105. Parallelism of main spindle and
tail stock guide ways

107. DRILLING MACHINE