metrology and measurements unit iii
DESCRIPTION
UNIT IIITRANSCRIPT
3 MECH A & C
ASSIGNMENT DETAILS
35 & BELOW MARKS 1 TIME ALL DIAGRAM ( 1.5 UNIT)
30 & BELOW MARKS - 1 TIME ALL DIAGRAM ( 1.5 UNIT)
1 TIME WITHOUT CHOICE Q & A
25 & BELOW MARKS – 1 TIME ALL DIAGRAM ( 1.5 UNIT)
3 TIME WITHOUT CHOICE Q & A
UNIT III
ADVANCES IN METROLOGY
Basic concept of lasers Advantages of lasers – laser Interferometers – types – DC and AC Lasers interferometer – Applications – Straightness – Alignment. Basic concept of CMM – Types of CMM – Constructional features – Probes – Accessories – Software – Applications – Basic concepts of Machine Vision System – Element – Applications.
UNIT III
ADVANCES IN METROLOGY
Laser & Interferometers
CMM
Machine Vision System
LASER &
INTERFEROMETERS
LASER
LIGHT AMPLIFICATION BY STIMULATED
EMISSION OF RADIATION.
Why Laser instruments used ?
Laser Instruments are devices to produce
powerful, monochromatic collimated beam of
light in which the waves are coherent.
PRINCIPLE OF LASER
PRINCIPLE: When photon emitted during
stimulated emission has the same energy, phase &
frequency as the incident photon.
Photon comes in contact with another atom or
molecule in high energy level E2, then it will cause the
atom to return to ground state energy level E1 by
releasing another photon.
The sequence of triggered identical photon from
stimulated atom is known as stimulated emission.
PRINCIPLE OF LASER
This multiplication of photon through
stimulated emission leads to coherent,
powerful monochromatic, collimated beam
of light emission. This light emission is called
LASER.
BASIC CONCEPTS OF LIGHT
Distance between two trough
or crest are called
WAVELENGTH λ.
Time taken to travel one
wavelength λ is called time
period T.
Maximum disturbance of wave
is called amplitude (A).
Velocity of transmission is (
λ/T )
(1/T) is called Frequency.
LASER
Helium-Neon Laser source produces a 1 to 2 mm diameter
beam of pure red light having power of 1 MW. So, Very High
Intensity.
Laser is used for Interferometry.
Upto a great distance beam has no divergence , then it begins
expand at rate of about 1 mm/m.
Is visible & it can be observed easily. Its accuracy is of 1 mm
over 2 m.
Used for very accurate instruments in the order of 0.1
micron in 100m.
LASER METROLOGY
Commercially, It is projected onto position detector which is used for the method of alignment.
It is very convenient, collimated & high intensity source used, because for its Precision, Accuracy, No Contact and Hot moving parts.,
Laser diodes, Semiconductor lasers – More advantages, Lower cost.
Laser instruments – In surface Inspection & Dimensional Measurements.
LASER TELEMETRIC SYSTEM
Is a non contact gauge with a collimated laser
beam.
Measuring Rate – 150 Scans Per Second.
Three Components – Transmitter, Receiver,
Processor Electronics
LASER TELEMETRIC SYSTEM
TRANSMITTER – Produces a collimated parallel
scanning laser moving at high constant linear
speed. It appears as red line after scanning.
TRANSMITTER Components :
Low power helium neon gas laser.
Synchronous motor.
Collimating lens.
Reflector prism.
Synchronous pulse photo detector.
Replaceable Window.
SCHEMATIC DIAGRAM OF LASER
TELEMETRIC SYSTEM
ADVANTAGES
Possible to detect changes in dimensions when product
is in continuous processes.
There is no need to wait for measuring in hot
conditions.
Applied on production machines & controlled with
closed feedback loops.
Possible to write programs for microprocessor to take
care of smoke, dust & other airborne interference
around the work piece being measured.
LASER & LED BASED DISTANCE
MEASURING INSTRUMENTS
Can measure 1 to 2 m with accuracy of order of 0.1 to 1 % of measuring range.
It has two distance meter at equal distance on either side of object & control unit to measure thickness of object.
The angle at which the light enters the detector will change the distance between measuring head & object is changed.
Change in angle of deviation is measured & calibrated in terms of distance.
LASER & LED BASED DISTANCE MEASURING
INSTRUMENTS - ADVANTAGES
These types of instruments are very reliable
because there is no moving part.
Instrument response time is in milliseconds.
The output is provided
as 0 – 20 mA.
SCANNING LASER GAUGE
Used for Dimensional Measurements.
Has Transmitter, Receiver & Processor Electronics.
ADVANTAGES :
Accuracy of ±0.25 micron for 10-50mm diameter
objects.
It is used for objects of 0.05mm to 450mm diameter.
SCANNING LASER GAUGE
PHOTODIODE ARRAY IMAGING
Used for dimensional measurements.
Stationary part shadow is projected on a
solid state diode array image sensor.
Has four parts :
Laser source
Imaging optics
Photodiode array
Signal processor & Display unit
PHOTODIODE ARRAY IMAGING
ADVANTAGES
Used for large parts, two arrays.
Measurement accuracy is as high as
±0.05 micron.
DIFFRACTION PATTERN
TECHNIQUE
Used in dimensional measurements.
Parallel coherent laser beam is diffracted by
a small part & resultant pattern is focused by
lens on a linear diode array.
Distance between alternating light & dark
bands in diffraction pattern is direct function
of wire diameter, laser beam wavelength &
Lens focal length.
DIFFRACTION PATTERN
TECHNIQUE
ADVANTAGES
Used to measure small gaps & small
diameter parts.
Measurement accuracy is more for smaller
parts.
DISADVANTAGES
Not suitable for large diameters.
LASER TRIANGULATION SENSORS
For Dimensional
Measurements.
Quick Deviation
Measurement due to
Surface Change.
Perform Automatic
Calculation on Shell
Metal Stampings.
Can measure Bore
Diameter using 2 Sensor.
INTERFEROMETRY - BASICS
When light is made to interfere, it produces a pattern
of dark bands, which corresponds to a very accurate
scale of divisions.
A ray having a single frequency and wavelength is
produced generally known as monochromatic light.
This monochromatic light is used for measuring
flatness and determining the length of slip gauges.
It is the basic principle of interferometry.
LASER USES IN INTERFEROMETRY
To find accurate measurement of length.
Reduces time & Skill requirement like other
methods used for finding the length.
The Laser Measurement accuracy is order of
0.1µm in 100m.
In modified laser designs, a single frequency is
selected from the coherent beam and used for
interferometric measurement.
TWO FREQUENCY LASER
INTERFEROMETER
Two Frequency Laser Head
Beam Directing and Splitting Optics
Measurements optics
Receivers
Wavelength Compensators
Electronic Receivers
TWO FREQUENCY LASER
INTERFEROMETER
TWO FREQUENCY LASER
INTERFEROMETER - ADVANTAGES
For Measuring Linear Positioning, Straightness
in two planes.
High Sensitivity.
Free from Noise Disturbances ( Light, Electrical
Noise, Air turbulence).
Use of Single photo detector / Measurement
axis, Sensitivity to Optical Alignment is Less.
GAUGING WIRE DIAMETER FROM
DIFFRATION PATTERN USING LASER
LENGTH MEASUREMENT USING
FRINGE COUNTING
Incoherent Laser Beam illuminates three slits at
a time in the first plane which form Inference
fringes.
Fringe movement is determined by detector on
the other side of short length of grating.
The number of slits in the first plane is governed
by length over which measurement is required.
LENGTH MEASUREMENT
USING FRINGE COUNTING
LENGTH MEASUREMENT
USING FRINGE COUNTING
Using He-Ne laser at 0.63µm a fringe
spacing of 1µm will be obtained at 1.4µm
from the slits, if a separation of 1µm is used.
The spacing between the slits & distance of
the slit to the plane of grating depend on the
wavelength of the light used.
ADVANTAGES
Accurate measurements over relatively
short distances.
Wire diameters from 0.005 to 0.2mm
can be measured.
LASER INTERFEROMETRY
COMPONENTS
Two frequency laser source.
Optical elements.
Laser heads measurement receiver.
Measurement display.
TWO FREQUENCY LASER SOURCE
Generally, It becomes He-Ne type that generates
stable coherent light beams of two frequencies.
One is Polarized vertically and other one is
polarized horizontally relative to the plane of the
moving feet.
Laser slightly oscillates at two frequencies by a
cylindrical permanent magnet around the cavity.
TWO FREQUENCY LASER SOURCE
Beam containing both frequencies passes
through a quarter wave & half wave plates
which change the circular polarization, or
vertical and other horizontal.
Linearly polarized beam is expanded in a
collimating telescope, after which most of the
beam is transmitted through a 45 degree beam
splitter and one of the laser head.
OPTICAL ELEMENTS
The various optical elements are :
Beam Splitters
Beam Benders.
Retro reflectors.
BEAM SPLITTERS
Used to divide the laser beam into separate
beams along different axes.
Possible to adjust the splitted laser’s output
intensity by having a choice of beam splitter
reflectivities.
BEAM SPLITTERS USAGE ( DIVIDING EQUAL LASER OUTPUT )
BEAM BENDERS
Used to deflect the light beam around
corners on it path from the laser to each axis.
Beam benders are just flat mirrors, but having
absolutely flat and very high reflectivity.
Normally, the 90 degree beam deflection is
avoided for not to disturb the polarizing
vectors.
RETRO REFLECTORS
They are plane mirrors, roof prisms or cube
corners.
Cube corners are three mutually perpendicular
plane mirrors, and reflected beam is always
parallel to the incident beam in these devices.
In AC laser interferometer measurements, two
retro reflectors are used.
When plane mirror is used as retro reflectors in
plane mirror interferometer, it must be flat with
in 0.06 micron / cm.
LASER HEAD’S MEASUREMENT
RECEIVER
Used to detect the part of the returning beam
as F1 – F2 and a Doppler shifted frequency
component del f.
MEASUREMENT DISPLAY
Has microcomputer to compute & display results.
Signals from reference receiver & measurement
receiver located in the laser head are counted in two
separate pulse counters and subtracted.
Other input signals for correction are temperature
co-efficient of expansions.
Air velocity is also displayed.
AC LASER INTERFEROMETER
TYPES
Standard Interferometer
Single Beam Interferometer
STANDARD INTERFEROMETER
STANDARD INTERFEROMETER
The displacement is measured between the
interferometer & cube corner.
Measurement retro reflector for this
interferometer is a cube corner.
It is least expensive and can be used wherever
it is possible.
SINGLE BEAM INTERFEROMETER
SINGLE BEAM INTERFEROMETER
• As same as standard interferometer.
• Has outgoing and returning beam super
imposed on each other, giving the appearance if
only one beam travelling between the
interferometer and the retro reflector.
• Very much suitable when space for optics and
beam path is minimum.
LASER INTERFEROMETER
Uses AC Laser as light source.
Enable to measure over longer distance.
Laser – Monochromatic optical energy, (
Collimated into a directional beam ) – Exact
wavelength – Pure for highly accurate
measurements.
Utilize the principles of both optical
techniques & digital electronics.
AC LASER INTERFEROMETER
COMPONENTS – LASER
INTERFEROMETER
Two frequency zeeman laser.
Beam splitters.
Fixed internal cube corners.
External cube corners.
Photo detectors.
Amplifiers.
Pulse converter.
COMPONENTS – LASER
INTERFEROMETER
Two Frequency Zeeman Laser :He-Ne type
Beam Splitters : Adjust Output based on Reflectivities
Cube corners : Fixed & Movable external –Used to reflect
the laser beam
Photo detectors : To change beam splitters signal to electrical
signal
Amplifiers : Used to separate frequency difference.
Pulse converter : Used to extracts change in frequency.
MICHELSON INTERFEROMETER
Consists of monochromatic light source, a beam
splitter & two mirrors.
PRINCIPLE : Constructive & Destructive
Interference when one mirror remains fixed and
the other is moved.
Monochromatic Light from an extended source
falls on a beam splitter which splits the rays into
two equal rays of same intensity at right angles.
MICHELSON INTERFEROMETER
MICHELSON INTERFEROMETER
If both mirrors are kept at same distance from
beam splitter, the observer will see bright spot
due to constructive interference.
If Movable mirror M1, shifted by quarter ( half )
wavelength, then the beam will be returned to
observer 180 deg out of phase ( 360 deg in phase )
and darkness will observed due to destructive
interference.
MICHELSON INTERFEROMETER
IMPROVING CONDITIONS
Use of laser light for measuring longer distance.
Instead of using mirror the cube corner
reflector is suited for reflecting the light.
Photocells can be employed to convert light
intensity variation in voltage pulses to given
direction of position change.
DUAL FREQUENCY LASER
INTERFEROMETER
Used to measure displacement, high
precision measurement of lengths, angles and
refractive indices as well as derived static
and dynamic quantities.
DUAL FREQUENCY LASER
INTERFEROMETER - CONSTRUCTION
DUAL FREQUENCY LASER
INTERFEROMETER - WORKING
Laser source generates two frequencies. F1 & F2
Reference signal F1-F2 is detected in Photo detector
P2.
Measuring signal F1-F2 +- Del F for X(Y) direction by
photo detector P3(P4).
Environment correction is made by photo detector P1.
DUAL FREQUENCY LASER
INTERFEROMETER
DUAL FREQUENCY LASER
INTERFEROMETER -
APPLICATIONS
Used for both incremental displacement and
angle measurements.
Resolution 2nm in 10m measuring range.
TWYMAN – GREEN
INTERFEROMETER
Used as polarizing interferometer with variable
amplitude balancing between sample and reference
waves.
For exact test surface measurement, the instrument
error can be determined by absolute measurement.
This error is compensated by storing the same in
microprocessor system & subtracting from the test
surface measurement.
TWYMAN – GREEN
INTERFEROMETER ADVANTAGES
Permits testing of surface with wide varying
reflectivity.
Avoids undesirable feed back of light reflected
of the tested surface & instrument optics.
Enables utilization of the maximum available
energy.
Polarisation permits phase variation to be
effected with the necessary precision.
LASER INTERFEROMETER APPLICATIONS
LINEAR MEASUREMENT
LASER INTERFEROMETER APPLICATIONS
ANGULAR MEASUREMENT
MACHINE TOOL METROLOGY
Component parts accuracy depends on machine tool
accuracy.Parts quality depends on,
Rigidity & Stiffness of machine tool & its components.
Alignment of various components in relation to one
another.
Quality & Accuracy of the control devices and the
driving mechanism.
ALIGNMENT ACCURACY OF
MACHINE TOOL CHECKED BY
Geometrical Test :
Dimensions, Position and Displacement of
Component relative to one another are checked.
Static Test
Dynamic Test
Practical Test :
Test pieces are machined in machines. Test
pieces must be approximate to fundamental
purpose for which machine has been designed.
PURPOSE OF MACHINE TOOL
TESTING
Dimensions of any work piece, its surface &
geometry depend on machine tool accuracy
for its manufacture.
In mass production, various components
produced should be of high accuracy &
assemble to be on non-sensitive basis.
GEOMETRICAL CHECKS ON MACHINE
TOOL Straightness.
Flatness.
Parallelism, Equidistance & Coincidence.
Squareness of straight line & plane.
Rotations
Out of round.
Eccentricity.
Run out.
Periodical axial slip.
Camming.
GEOMETRICAL CHECKS ON
MACHINE TOOL
Movement of all the working components.
Spindle test for
Concentricity.
Axial slip.
Accuracy of axis & position.
LASER EQUIPMENT FOR ALIGNMENT
TESTING
Particularly suitable in aircraft production , shipbuilding etc., ( Flatness testing, Squareness checking etc., )
Consist of Laser of 10mm dia, Auto reflector.,
Laser has Helium-Neon Plasma Tube in heavy aluminum cylindrical housing.
Laser beam comes from its centre & parallel to housing within 10” of arc & alignment stability is of order of 0.2” of arc/hour.
LASER EQUIPMENT FOR ALIGNMENT
TESTING
Auto reflector consists of detector head & read
out unit.
No. of photocell are arranged to compare laser
beam in each half horizontally & vertically.
Detect the alignment of flat surfaces
perpendicular to a reference line of slight.
MACHINE TOOLS TEST
Test for level of installation of machine tool in
horizontal & vertical planes.
Tests for perpendicularity of guide ways to other
guide ways.
Test for flatness of machine bed & for
straightness & parallelism of bed ways on bearing
surface.
Test for true running of main spindle & its axis
movements.
MACHINE TOOLS TESTS
Test for line of movement of various members
like spindle, tables & cross slides.
Test for parallelism of spindle axis to guide
ways or bearing surfaces.
ALIGNMENT TESTS ON LATHE
Levelling of the machine.
True running of locating cylinder of main spindle.
Axial slip of main spindle & true running of
shoulder face of spindle nose.
True running of headstock center.
Parallelism of main spindle to saddle movement.
True running of taper socket in main spindle.
ALIGNMENT TESTS ON LATHE
Movement of upper slide parallel with main spindle
in vertical plane.
Parallelism of tailstock guide ways with the
movement of carriage.
Parallelism of tailstock sleeve taper socket to saddle
movement.
Pitch accuracy of lead screw.
Alignment of lead screw bearings with respect to
each other.
LEVELLING OF THE MACHINE
Done by sensitive spirit level.
Saddle is approximately kept in centre of the
bed support feet.
TRUE RUNNING OF LOCATING CYLINDER
OF MAIN SPINDLE
• Locating cylinder is provided to locate the chuck / face plate.
• Locating surface should be in cylindrical shape.
• Dial indicator is fixed to carriage & indicator feeler touches locating surface.
• Surface is rotated on its axis & indicator should not show any spindle movement.
ALIGNMENT TESTS ON MILLING
MACHINE
Cutter spindle axial slip or float.
Eccentricity of external diameter.
True running if internal taper.
Surface parallel with longitudinal movement.
Traverse movement parallel with spindle axis.
Centre T-slot Square with the arbor.
Tests on column.
Over arm parallel with spindle.
ALIGNMENT TESTS ON PILLAR
TYPE DRILLING MACHINE
Flatness of clamping surface of base.
Flatness of clamping surface of table.
Perpendicularity of drill head guide to the base plate.
Perpendicularity of drill head guide with plate.
True running of spindle taper.
Parallelism of the spindle axis with its vertical
movement.
Squareness of clamping surface of table to its axis.
Total deflection.
ACCEPTANCE TESTS FOR
SURFACE GRINDERS
Table top parallel to its movement by attaching the dial gauge in the stationary spindle and dial feeler touching the table top and traversing the table.
Spindle axis parallel to table top by fitting dial gauge on redial arm of the spindle & its feeler touching the square testing on table.
Slots parallel to table movement by fitting the dial gauge in the stationary spindle & dial feeler touching the slot & traversing the table.
ACCEPTANCE TESTS FOR
SURFACE GRINDERS
Vertical movement of the spindle square with
table top by fitting dial gauge in spindle & its
feeler touching the square resting on table.
Spindle axis square with the slot by fitting dial
gauge on an arm fitted to spindle & rotating
the spindle & rotating the spindle by 180 deg.
Practical tests.
CO ORDINATE
MEASURING MACHINE
CONTENTS
INTRODUCTION
TYPES OF MEASURING MACHINE
CMM AND TYPES OF CMM
PROBE
FEATURES
APPLICATION
ADVANTAGES
DISADVANTAGES
INTRODUCTION
Measuring machines are used for measurement
length over the outer surface of the length bar or
any long member.
The member may be either rounded or flat or parallel.
Measuring are more useful and advantages that
vernier calipers, micrometer etc..,
TYPES OF MEASURING MACHINE
Length bar measuring machine
New all measuring machine (spirit level)
Universal measuring machine (all)
Co-ordinate measuring machine
Computer controlled co-ordinate measuring machine
(inspect & measure)
CO ORDINATE MEASURING
MACHINE
Co-ordinate measuring machine is also called as CMM.
CMM is used for contact inspection the parts. When it is used for
computer integrated manufacturing, the CMM by computer
numerical control method.
A coordinate measuring Machine is a 3D device For measuring the
Physical geometrical Characteristics of an object.
CMM has movements in three axis .
This machine may be manually controlled by an operator or it may
be computer controlled.
BLOCK DIAGRAM OF THE
ELEMENTS OF A CMM
CO-ORDINATE
MEASURING
MACHINE
DIGITAL
READ OUT COMPUTER
SOFTWARE PROBING
SYSTEM
ELEMENTS OF CMM
A basic Co-ordinate Measuring Machine consists of four
elements.
The machine structure which is basically an X-Y-Z
positioning device.
The Probing system use to collect raw data on the part and
provide input to the control system.
Machine Control and Computer hardware.
The Software for three dimensional analysis.
CMM – BASIC PARTS
Description The typical 3 "bridge" CMM is composed of three axes, an X, Y and Z. These axes are orthogonal to each other in a typical three dimensional coordinate system. Each axis has a scale system that indicates the location of that axis. The machine will read the input from the touch probe, as directed by the operator or programmer. The machine then uses the X,Y,Z coordinates of each of these points to determine size and position with micrometer precision typically. Reference
FEATRUES OF CNC - CMM
According to control system
Manual CMM
CNC CMM or DCC CMM
According to design of main structure
CANTILEVER
MOVING BRIDGE
FIXED BRIDGE
HORIZONTAL ARM
GANTRY
COLUMN
According to mounting style
Bench top
Free Standing
Portable and Hand Held
TYPES OF CMM
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 • Two configuration: fixed table and movable
table
• Advantage- a fixed table allows good accessibility to the work piece
• Required small floor space
• Disadvantage- the bending caused by the cantilever design
• Suitable for measuring long, thin part
Moving bridge type
• Most widely used
• Has stationary table to support work piece to be measured and a moving bridge
• Stationary table and movable bridge: Allows high table load
• Advantage- reduce bending effect
• Disadvantage- with this design, the phenomenon of yawing can occur- affect the accuracy
Fixed bridge type
• Most widely used CMM
• In the fixed bridge configuration, provides better accuracy and rigidity.
• Disadvantage : Limited accessibility caused by the bridge
• Stationary bridge and movable table Leads to small measuring uncecertainty
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 production floor.
Horizontal arm type
• Have very large measuring range and low power consumption.
• Maximum accessibility has been achieved • Also referred to as layout machine
• Type of CMM: Moving arm and Moving Table
• Advantage- provides a large area, unobstructed
work area
• Ideal configuration for measurement of automobile parts
Gantry type
• supported by four vertical columns rising from the floor
• Employed three movable component moving along mutually perpendicular giudeways
• This setup allows you to walk along the work piece with the probe, which is helpful for extremely large pieces
• Used in measuring car body and wind tunnel Model
Gantry configuration with dual linear motor drives, laser scales an online compensation
According to mounting style
Bench top
Mounted on a bench or deck. Most CMM are this type
Free Standing
These machines can support themselves and do not required mounting
Portable and Hand Held
Moved freely and used almost anywhere
ADVANTAGES OF CMM
Flexibility
Reduced Setup Time
Single Setup
Improved Accuracy
Reduced Operator Influence
Improved Productivity
DISADVANTAGES OF CMM
The probe may not be in perfect alignment.
The probe may have run out.
The probe may moving in Z-axis may have
some perpendicular error.
There may have errors in digital system.
Common Applications
• Dimensional measurement
• Profile measurement
• Angularity or orientation
• Depth mapping
• Digitizing or imaging
• Shaft measurement
FEATURES CMM SOFTWARE
Measurement of the diameter, center
distance, length
Measurement of plane and spatial curves.
Minimum CNC program
Data communication
Digital input and output command
Interface CAD software
PROBE or Sensors
The measuring head that contact the job to
inspect and measure is called as probe.
The different kinds of probes like taper tip, ball
tip etc..,
The function of a CMM is to acquire information
about the measurand, usually in the form of
Cartesian coordinates. The devices used to explore
the area to generate this information are the
"sensors".
126
PROBE or Sensors • Two types of sensors:
“Tactile” sensors.
“Noncontact” sensors or "optoelectronic" sensors
• Tactile sensors distinguish:
“Rigid” or hard or fixed sensors .
“Point to point” or touch trigger sensors.
“Continuous” or measuring type or displacement sensors
• In non contact sensors ,Two main principles are used:
Triangulation 3D
Time of Flight
127
Sensors Tactile Sensor
Characteristic elements of a generic, tactile, fixed probing system
1. Co-ordinate measuring
machine ram (or spindle).
2. Probe extension.
3. Probe changing system.
4. Probe.
5. Stylus changing system
6. Stylus extension
7. Stylus shaft.
8. Stylus.
9. Stylus tip.
10. Tip diameter.
11. Generic, fixed probing system.
12. Stylus system (composed of
stylus system components).
128
Sensors The Rigid Sensor
Point measurement by means of a spherical rigid sensors
• Rigid sensor: “Touch finger” constituted by a shaft for the fitting of the touch
finger in the CMM probe holder.
• On the opposite extremity has either a sphere or a cone.
129
Sensors Point to Point Tactile Sensors
• The point to point type of measurement determines the position of points by
bringing in physical contact the tip of the sensors with the part and then
retracting.
• The point to point measurement represents a fast ideal solution to define
Dimension and Position.
Probing (point measurement) sequences
Legend:
1......: Starting point.
2......: Point probing.
3......: Disengagement
after point probing
130
Point to Point Tactile Sensors • Tactile sensors for point to point measurement are based on “Isostatic
support” concept.
• The spring still keeps the contact closed. the force of contact balances the force of the spring itself.
• Just before that the balance between the forces is reached, the force of contact between part and sensor causes a slight displacement of the stylus and the contact is opened.
• A signal is generated that allows the recording of the co-ordinates of the sphere centre at the moment of contacting the part surface. The point has been measured.
Isostatic support tactile sensor
The CMM starts to decelerate, while the spring preloaded mechanism follows the machine movement with a slight over-travel. Finally the machine retracts and the Isostatic support assumes its resting position in an extremely repeatable mode, ready to measure more points.
131
Sensors Continuous Tactile Sensors
Probing sequence in continuous measurement
• In the point to point measurement the sensor gets in contact with the part to be measured.
• In continuous measurement the sensor remains in contact with the part
• follows its profile and measuring points according to pre-determined laws in a single measuring path.
• Very accurate and relatively larger than point to point, the continuous sensors, can supply very complete information on the form of the measured feature.
132
Sensors Non Contact Sensors
• The non-contact sensors are based on optoelectronic techniques. These
types of sensors can measure an object without physical contact with it.
• the non-contact measurement technology allows:
To measure very small pieces not otherwise measurable.
For a faster measurement than a touch sensor.
To measure very soft pieces of material not otherwise measurable.
• Noncontact sensors are based on two principles
3D Triangulation Principle
Time of Flight Principle
133
Sensors Non contact sensor:3D Triangulation Principle
• It is a principle based on noncontact sensor.
• When object point C is lit by the laser, the
point becomes visible to the camera. Distance d between the laser source and the camera .
• the orientation a of the laser are known.
• line CB is determined by connecting the lens center to the image of point C in the image plane and finding its angle with line AB.
• In triangle ABC, by knowing d and angles a and b the position of point C on the object can be determined.
• Increasing angle g will increase depth accuracy, but that will increase self-occlusion, making determination of depth impossible.
The triangulation principle.
134
Continued… • Angle gamma determines the quantization accuracy of the scanner.
• When this angle is zero, objects at different depths cannot be distinguished from each other.
135
Sensors Non contact sensor: Time of Flight Principle
• The Time of Flight scanner is used to scan and investigate with laser light.
• The scanner rangefinder determines the distance from work surface by noting down the timing of round trip of the light pulse.
• The laser when emits light pulse detector has timed the reflected light.
• If c is known speed of light. If round-trip time t is known, then distance is (c* t)/2.
•
line of reference shown applications
MACHINE VISION
SYSTEM
MACHINE VISION SYSTEMS
Machine Vision::Computer Vision::Intelligent Vision
Automated Inspection of Manufactured products for Quality
and Process Control.
Definition:
Means of electro-optically simulating the image
recognition capabilities of the human eye/brain.
PRINCIPLE OF WORKING
Image Formation
Processing of image
Defining and Analysis of Image
Image interpretation and Decision Making
OVERVIEW OF MACHINE VISION PROCESS
FUNCTIONING OF
MACHINE VISION
SYSTEM
STEPS IN MACHINE VISION
SYSTEM Image Formation
Back Lighting
Diffused Front Lighting
Processing of image
Windowing
Image restoration
Defining and Analysis of Image
Distance measurement
Object orientation
Defining Object position
Image interpretation and Decision Making
CCD CAMERA
A CHARGE-COUPLED DEVICE (CCD) is a
sensor for recording images, consisting of an
integrated circuit containing an array capacitors.
MACHINE VISION SYSTEM
APPLICATION FIELDS
Inspection
Part Identification
Guidance and Control
HUMAN VS MACHINE VISION
HUMAN VISION
Recognition
Hand-eye coordination
Inspection
Find Position
Gather Information
Safety
MACHINE VISION
Identification
Robot guidance
Inspection
Find position
Measure
HUMAN VS MACHINE VISION
HUMAN VISION
Human Vision
High image resolution
Interprets complex scene
quickly
Operates in visible light
spectrum
MACHINE VISION
Machine Vision
Consistent, tireless
Operate in visible Infrared,
X-ray.
Operates in hostile
environments
Follows program precisely
MACHINE VISION APPLICATIONS
IN-LINE
Checking each item that passes the camera
RANDOM
Checking one item out of a series as it passes the camera on
the production line, and
OFF-LINE
Take an item off the production line for a test in a quality
assurance laboratory.
WHERE IS MACHINE VISION USED?
Semiconductor
Electronic
Automotive
Container
Pharmaceutical
Medical device
Plastic
Chemicals
Food
Footwear
Textiles
Printing
Wood / Forest
Fabricated Metal
WHY USE MACHINE VISION?
High speed production lines
Microscopic inspection
Clean room environments
Hazardous environments
Closed -loop process control
Robot guidance
Precise non-contact measurement
WHAT CAN MACHINE VISION DO?
PRESENCE - ABSENCE CHECKING,
ASSEMBLY VERIFICATION
Verify that part components are present and in the correct
locations
Dimensional Gauging
Calculate the distance between two or more points on an object
Defect detection
Identify defects and calculate defect characteristics such as position and size
ASSEMBLY VERIFICATION
DEFECT DETECTION
Golden Template Image Image with Defects Difference Image
GAUGING
ADVANTAGES
Lower inventories.
Fewer production overruns.
Reduced labor costs.
Less rework and production.
Avoidance of inspection bottlenecks.
Elimination of adding value to scrap conditions
ELIMINATES
Cost of Recruiting and Training.
Scrap - Rework created while learning a new job.
Average workers' compensation paid for injuries.
Average Educational grant per employee.
Personnel - Payroll department costs per employee
RESULT
Increased Market share.
Improved Customer satisfaction and lower warranty costs.
Penetration of New Niche Markets.
Pricing flexibility and participation in price Elastic markets.