Visual inspection is a fundamental method for examining materials and components for flaws using the naked eye and light, with options for assisted techniques through optical and electronic devices. The effectiveness of visual inspections is influenced by factors such as lighting conditions, the quality of the inspector's detection capabilities, and their training. Machine vision technology has emerged as a valuable tool in automated inspections, particularly in production settings where consistent evaluations are necessary.

1. INSPECTION IS A N A TTITUDE
VERIFYING LONGITUDE TO LATITUDE
G . K . B H A R D W A J
VISUAL INSPECTION

2. VISUAL INSPECTION
VISUAL INSPECTION IS DEFINED AS
THE EXAMINATION OF A MATERIAL,
COMPONENT, OR PRODUCT FOR
CONDITIONS OF
NONCONFORMANCE USING LIGHT
AND THE EYES, ALONE OR IN
CONJUNCTION WITH VARIOUS AIDS.

3. VISUAL INSPECTION
VISUAL INSPECTION IS THE BASIC METHOD
OF INSPECTION.
IT IS THE PROCESS OF LOOKING OVER AND
AROUND AN EQUIPMENT OR PART OF THE
EQUIPMENT USING LIGHT, NAKED EYE TO
LOOK FOR FLAWS.
IT DOES NOT REQUIRE ANY EQUIPMENT OR
INSTRUMENT EXCEPT LIGHT, NAKED EYES
AND THE TRAINED OR EXPERIENCED
INSPECTION ENGINEER

4. VISUAL INSPECTION
VISUAL INSPECTION IS EMPLOYED TO
SUPPORT OTHER NDT METHODS.
DIGITAL DETECTORS AND COMPUTER
TECHNOLOGY HAVE MADE IT POSSIBLE
TO AUTOMATE SOME VISUAL
INSPECTIONS. THIS IS KNOWN AS
MACHINE VISION INSPECTION

5. VISUAL INSPECTION
VISUAL INSPECTION CONSISTS OF AT LEAST TWO MAJOR
PROCESSES.
THE FIRST IS A SEARCH PROCESS.
THE SECOND IS A PROCESS OF COMBINING RELEVANT
KNOWLEDGE, SENSORY INPUT, AND PERTINENT LOGICAL
PROCESSES TO PROVIDE AN IDENTIFICATION THAT SOME
ANOMALY OR PATTERN REPRESENTS A FLAW THAT
POSES A RISK TO THE PERFORMANCE, LIFE OF THE PART.
VISUAL INSPECTION OFTEN ALSO INVOLVES, SHAKING,
LISTENING, FEELING, AND SOMETIMES EVEN SMELLING
THE COMPONENT BEING INSPECTED

6. VISUAL INSPECTION
VISUAL INSPECTION CAN BE
CATAGORISED INTO :
AIDED VISUAL INSPECTION IS WITH USE OF
ANY OPTICAL ,OPTO-
ELECTRICAL,ELECTRONICS DEVICE OR
MECHANICAL INSTRUMENT
UN-AIDED VISUAL INSPECTION IS WITHOUT
USE OF ANY OPTICAL, OPTO-
ELECTRICAL,ELECTRONICS DEVICE OR
MECHANICAL INSTRUMENT

7. VISUAL INSPECTION
AIDED VISUAL INSPECTION
OPTICAL AIDS MECHANICAL AIDS
MICROSCOPES MICROMETERS
BORESCOPES CALLIPERS
FIBERSCOPES GAUGES-
VIDEO CAMERAS DEPTH
THREAD PITCH
WELD
FEELER

8. VISUAL INSPECTION
SEVERAL CHARACTERISTICS ABOUT THE PART
BEING EXAMINED MAY BE DETERMINED, WHICH
INCLUDE DIMENSIONAL CONFORMANCE, THE
PRESENCE OF DISCONTINUITIES, GENERAL FIT
AND WEAR, AND SIMPLE COSMETIC COMPLIANCE.
IT CAN BE PERFORMED BY DIRECT OR INDIRECT
METHODS DURING VARIOUS STAGES OF
MANUFACTURING OR AFTER THE COMPONENT
HAS BEEN PLACED IN-SERVICE.

9. VISUAL INSPECTION
THE QUALITY OF AN INSPECTION ARE AFFECTED
PRIMARILY BY FOUR FACTORS.
 THE QUALITY OF THE DETECTOR (EYE OR
CAMERA).
 THE LIGHTING CONDITIONS.
 THE CAPABILITY TO PROCESS THE VISUAL DATA.
 THE LEVEL OF TRAINING/EXPERIENCE AND
ATTENTION TO DETAIL.
VISUAL INSPECTION IS MOST IMPORTANT
TOOL WITH YOU UTILISE IT WITH ENGG
APTITUDE AND COMMON SENSE. CHECK FOR
SYMMETRY OF THE LOT, TWO ITEMS, EITHER
SIDE OF A COMPONENT, LEFT/REIGHT

10. VISUAL INSPECTION
MANUAL VERSUS AUTOMATED INSPECTION
 THE MAJORITY OF VISUAL INSPECTIONS ARE COMPLETED
BY AN INSPECTION ENGINEER, BUT MACHINE VISION IS
BECOMING MORE COMMON.
 THE PRIMARY ADVANTAGE OF AN INSPECTION ENGINEER IS
THEIR ABILITY TO QUICKLY ADAPT TO A VARIETY OF
LIGHTING AND OTHER NON-TYPICAL CONDITIONS, AND
THEIR ABILITY TO USE OTHER SENSES.
 THE PRIMARY ADVANTAGE OF A MACHINE VISION
INSPECTION SYSTEM IS THEIR ABILITY TO MAKE VERY
CONSISTENT AND RAPID INSPECTIONS OF SPECIFIC
DETAILS OF A COMPONENT.
 MACHINE VISION IS PRIMARILY USED IN PRODUCTION
APPLICATIONS WHERE A LARGE NUMBER OF COMPONENTS
REQUIRE INSPECTION AND THE INSPECTION CONDITIONS
CAN BE CLOSELY CONTROLLED.

11. VISUAL INSPECTION
BASIC PRINCIPLES THE HUMAN EYE
 LIGHT ENTERS THE EYE THROUGH THE PUPIL AND AN
IMAGE IS PROJECTED ON THE RETINA.
 MUSCLES MOVE THE EYEBALL IN THE ORBITS AND
ALLOW YOU TO FOCUS THE IMAGE ON THE CENTRAL
RETINA
 THE RETINA IS A MOSAIC OF TWO BASIC TYPES OF
PHOTORECEPTORS, RODS AND CONES.
 RODS ARE SENSITIVE TO BLUE-GREEN LIGHT AND ARE
USED FOR VISION UNDER DARK OR DIM CONDITIONS.
 CONES OPERATE ONLY IN RELATIVELY BRIGHT LIGHT,
BUT THEY PROVIDE US WITH OUR SHARPEST IMAGES
AND ENABLE US TO SEE COLORS

12. VISUAL INSPECTION
THERE ARE THREE TYPES OF CONES
 L-CONES ARE RED ABSORBING CONES OR
THOSE THAT ABSORB BEST AT THE
RELATIVELY LONG WAVELENGTHS
PEAKING AT 565 NM
 M-CONES ARE GREEN ABSORBING CONES
WITH A PEAK ABSORPTION AT 535 NM
 S-CONES ARE BLUE ABSORBING CONES WITH
A PEAK ABSORPTION AT 440 NM.

13. VISUAL INSPECTION
BASIC PRINCIPLES VISUAL ACUITY
(SHARPNESS)
 CONES PROVIDE US WITH OUR SHARPEST IMAGES
BECAUSE MOST OF THE 3 MILLION CONES IN EACH
RETINA ARE CONFINED TO A SMALL REGION JUST
OPPOSITE THE LENS CALLED THE FOVEA. THE MAXIMUM
CONCENTRATION IS ABOUT 180,000 CONES PER SQUARE
MM.
 OUR SHARPEST AND MOST COLORFUL IMAGES ARE
PRODUCED IN THE FOVEA/RETINA.
 OUTSIDE OF THIS REGION OUR VISION IS RELATIVELY
POOR BUT, SINCE WE CAN QUICKLY REDIRECT OUR EYES
WE TEND NOT TO BE AWARE OF OUR POOR PERIPHERAL
VISION.

14. VISUAL INSPECTION
BASIC PRINCIPLES VISUAL ACUITY(SHARPNESS)
THERE IS A LIMIT TO WHAT THE UNAIDED EYE CAN SEE.
 NORMAL VISUAL ACUITY OR 20/20 VISION IS DEFINED
AS THE ABILITY TO RESOLVE A SPATIAL PATTERN
SEPARATED BY A VISUAL ANGLE OF ONE MINUTE OR 1/60
OF A DEGREE OF ARC.
 ONE DEGREE OF A SCENE IS PROJECTED ON ABOUT 290
MICROMETERS OF THE RETINA.
 IN 290 MICROMETERS THERE ARE 123 CONES AND IN
1/60 OF A DEGREE THERE 2 CONES WHICH IS THE
NUMBER REQUIRED TO RESOLVE AN OBJECT.
 THE SIZE OF AN OBJECT THAT CAN BE SEEN AT A GIVEN
DISTANCE
WHEN VISUALLY INSPECTING AN OBJECT FOR A DEFECT,
A COMFORTABLE VIEWING DISTANCE D MIGHT BE AROUND 12
INCHES. AT 12 INCHES, THE NORMAL VISUAL ACUITY OF THE
HUMAN EYE IS 0.0035 INCH.
(IT MUST BE NOTED THAT THIS VALUE IS FOR THE
SITUATION WHERE THERE IS GOOD LIGHTING AND HIGH
CONTRAST BETWEEN THE OBJECTS BEING VIEWED.)

15. VISUAL INSPECTION
BASIC PRINCIPLES CONTRAST SENSITIVITY
 CONTRAST SENSITIVITY IS A MEASURE OF HOW FADED OR
WASHED OUT AN OBJECT CAN BE BEFORE IT BECOMES
INDISTINGUISHABLE FROM A UNIFORM FIELD
 IT HAS BEEN EXPERIMENTALLY DETERMINED THAT THE
MINIMUM DISCERNIBLE DIFFERENCE IN GRAY SCALE
LEVEL THAT THE EYE CAN DETECT IS ABOUT 2 OF FULL
BRIGHTNESS
 CONTRAST SENSITIVITY VARIES WITH
 THE SIZE OR SPATIAL FREQUENCY OF A FEATURE
 THE LIGHTING CONDITIONS
 WHETHER THE OBJECT IS LIGHTER OR DARKER THAN THE
BACKGROUND
 IT SHOULD BE NOTED THAT LARGER OBJECTS ARE NOT
ALWAYS EASIER TO SEE THAN SMALLER OBJECTS AS
CONTRAST IS REDUCED

16. VISUAL INSPECTION
BASIC PRINCIPLES LIGHT LEVELS
 UNDER NORMAL LIGHTING CONDITIONS THE CONES ARE
OPERATING AND THE EYE HAS GOOD VISUAL ACUITY AND
IS MOST SENSITIVE TO GREENISH YELLOW COLOR, WHICH
HAS A WAVELENGTH AROUND 555 NANOMETERS (PHOTOPIC
CURVE).
 WHEN THE LIGHT LEVELS DROP TO NEAR TOTAL
DARKNESS, THE RESPONSE OF THE EYE CHANGES
SIGNIFICANTLY
 AT THIS LEVEL OF LIGHT, THE RODS ARE MOST ACTIVE
AND THE HUMAN EYE IS MORE SENSITIVE TO ANY AMOUNT
OF LIGHT THAT IS PRESENT, BUT IS LESS SENSITIVE
TO THE RANGE OF COLOR.
 AT THIS VERY LOW LIGHT LEVEL, SENSITIVITY TO
BLUE, VIOLET, AND ULTRAVIOLET IS INCREASED, BUT
SENSITIVITY TO YELLOW AND RED IS REDUCED

17. VISUAL INSPECTION
BASIC PRINCIPLES LIGHT INTENSITY MEASUREMENT
 EFFECTIVE VISUAL INSPECTION REQUIRES ADEQUATE
LIGHTING.
 THE TYPE OF INSPECTION WILL DICTATE THE LIGHTING
REQUIREMENTS. INSPECTION OF COMPONENTS WITH FINE
DETAIL AND LOW CONTRAST WILL REQUIRE GREATER
ILLUMINATION THAN COMPONENTS WITH LARGE DETAILS
AND HIGH CONTRAST.
 LIGHT INTENSITY MAY BE MEASURED WITH A SUITABLE
LIGHT METER. THE UNIT OF MEASURE FOR WHITE LIGHT
IS CANDELA AND ILLUMINATION IS LUX
 INSPECTION OF COMPONENTS WITH FINE DETAIL AND LOW
CONTRAST MAY REQUIRE 100 FOOT-CANDLES OR MORE.
 SPECIFICATION REQUIREMENTS FOR LIGHTING SHOULD BE
REVIEWED PRIOR TO PERFORMING AN INSPECTION

18. VISUAL INSPECTION
BASIC PRINCIPLES LIGHT DIRECTIONALITY
 THE DIRECTIONALITY OF THE LIGHT IS A VERY
IMPORTANT CONSIDERATION.
 FOR SOME APPLICATIONS, FLAT, EVEN
LIGHTING WORKS WELL.
 FOR OTHER APPLICATIONS, DIRECTIONAL
LIGHTING IS BETTER BECAUSE IT PRODUCES
SHADOWS THAT ARE LARGER THAN THE
ACTUAL FLAW AND EASIER TO DETECT

19. VISUAL INSPECTION
BASIC PRINCIPLES PERSPECTIVE
THE EYE/BRAIN NEED VISUAL CLUES TO
DETERMINE PERSPECTIVE.
IS THE OBJECT FACING TOWARDS OR AWAY
FROM YOU?
BASIC PRINCIPLES OPTICAL ILLUSIONS
SOMETIME THE EYE/MIND HAS TROUBLE IN
CORRECTLY PROCESSING VISUAL INFORMATION.

20. VISUAL INSPECTION
BASIC PRINCIPLES VISION
 WHEN EVALUATIONS ARE MADE BY AN
INSPECTION ENGINEER, EYE EXAMINATIONS MUST
BE DONE AT REGULAR INTERVALS TO ASSURE
ACCURACY AND SENSITIVITY. THESE
EXAMINATIONS MAY CONSIST OF THE FOLLOWING
 NEAR VISION
 FAR VISION
 COLOR DIFFERENTIATION
 WHEN USING MACHINE VISION, DIFFERENT BUT
SIMILAR PERFORMANCE CHECKS MUST BE
PERFORMED

21. VISUAL INSPECTION
BASIC PRINCIPLES OF VISUAL INSPECTION
FOR BEST RESULTS THE INSPECTION ENGINEER OR
MACHINE VISION OPERATOR MUST HAVE
 A BASIC KNOWLEDGE OF MATERIAL PROCESSING,
FORMING, MACHINING AND JOINING PROCESSES.
 A GENERAL UNDERSTANDING OF DESIGN
FEATURES,APPLICATION AND SERVICE
REQUIREMENTS.
 SPECIFIC INSTRUCTIONS ON WHAT TO LOOK FOR
AND SPECIFIC ACCEPTANCE/REJECTION CRITERIA.

22. VISUAL INSPECTION
INSPECTION APPLICATIONS
VISUAL INSPECTION APPLICATION RANGE FROM LOOKING A
PRODUCT OVER FOR OBVIOUS DEFECT TO PERFORMING
DETAILED INSPECTIONS.
SOME OF THE COMMON APPLICATIONS INCLUDE
 DETECTION OF SURFACE ANOMALIES SUCH AS SCRATCHES,
EXCESS SURFACE ROUGHNESS, AND AREAS VOID OF PAINT
OR PLATING.
 CRACK, POROSITY, CORROSION OR OTHER FLAW
DETECTION.
 DIMENSIONAL CONFORMANCE.
 PRECISION MEASUREMENTS.
 FOREIGN OBJECT DETECTION.
 COMPONENT LOCATION.

23. VISUAL INSPECTION
INSPECTION APPLICATIONS FLAW DETECTION
 VISUAL INSPECTION OF MANUFACTURED
MATERIALS AND COMPONENTS IS A COST
EFFECTIVE MEANS OF IDENTIFYING FLAWS.
 VISUAL INSPECTION OF A CASTING REVEALS A
CRACK BETWEEN A THREADED OPENING AND A
PRESSED FIT.
 THE ALUMINUM SAND CASTING HAS HOT TEARS
AND SHRINKAGE AT THE TRANSITION ZONES
 WELD QUALITY REQUIREMENTS ARE COMMONLY
DETERMINED THROUGH VISUAL INSPECTION.
 MANY STANDARDS HAVE ESTABLISHED
ACCEPTANCE CRITERIA FOR WELDS

24. VISUAL INSPECTION
DIMENSIONAL CONFORMANCE
 VISUAL INSPECTION IS COMMONLY EMPLOYED FOR
GENERAL DIMENSIONAL CONFORMANCE, ASSEMBLY FIT,
AND ALIGNMENT BETWEEN COMPONENTS.
 COMMON APPLICATIONS INCLUDE DETERMINING
 WELD SIZE AND TOLERANCE.
 COMPONENT DIMENSIONS.
 MATERIAL ALIGNMENT AND ALLOWABLE DISTORTION.
 WELDS ARE COMMONLY INSPECTED FOR DIMENSIONAL
TOLERANCE.
 THERE ARE SEVERAL TYPES OF GAUGES USED TO INSPECT
WELDING FIT UP AND FINISHED WELDMENTS.
 THESE GAUGES ARE INTENDED FOR GENERAL INSPECTION
WHERE CLOSE TOLERANCES ARE NOT REQUIRED.
 THE GAUGE USED IS DETERMINED BY THE APPLICATION.

25. VISUAL INSPECTION
DIRECT AND REMOTE VISUAL INSPECTION
 MANY CODES REFER TO DIRECT VISUAL EXAMINATION AS
A VISUAL INSPECTION WHICH REQUIRES THAT ACCESS TO
THE AREA IS SUFFICIENT TO PLACE THE EYE WITHIN 24
INCHES OF THE SURFACE TO BE EXAMINED AND AT AN
ANGLE OF NOT LESS THAN 30º TO THAT SURFACE.
 IF THESE REQUIREMENTS CANNOT BE MET, THEN REMOTE
VISUAL INSPECTION MAY BE USED.
 REMOTE VISUAL INSPECTION MAY BE ACCOMPLISHED WITH
THE USE OF A NUMBER OF OPTICAL AIDS SUCH AS,
MIRRORS, MAGNIFIERS, AND RIGID OR FLEXIBLE
BORESCOPES.

26. VISUAL INSPECTION
OPTICAL AIDS
 MIRRORS ARE VALUABLE AIDS IN VISUAL INSPECTION, THEY ALLOW
THE INSPECTION OF THREADED AND BORED HOLES, INSIDE SURFACES
OF PIPES AND FITTINGS, AS WELL AS MANY OTHERS.
 MAGNIFIERS ASSIST THE VISUAL INSPECTOR BY ENLARGING THE SIZE
OF THE OBJECT BEING EXAMINED.
 COMPARATORS ARE A MAGNIFIER WITH A MEASURING CAPABILITY.
THE COMPARATOR HAS INTERCHANGEABLE RETICLES WHICH
PROVIDE MEASUREMENTS FOR THREADS, ANGLES, LINEAR
MEASUREMENT, DIAMETERS AND RADII.
 BORESCOPES ARE VISUAL AIDS USED FOR THE INSPECTION OF
INTERNAL SURFACE AREAS.
 THEY ARE DESIGNED FOR REMOTE VIEWING IN DIFFICULT TO REACH
AREAS SUCH AS JET ENGINES, CYLINDERS, TANKS, AND VARIOUS
ENCLOSED CHAMBERS.
 BORESCOPES ARE AVAILABLE IN MANY DIFFERENT DIAMETERS AND
LENGTHS, AND ARE CLASSIFIED AS RIGID OR FLEXIBLE.

27. VISUAL INSPECTION
MACHINE VISION BASIC PRINCIPLES
 MACHINE VISION TECHNOLOGY USES AN IMAGING SYSTEM
AND A COMPUTER TO ANALYZE AN IMAGE AND TO MAKE
DECISIONS BASED ON THAT ANALYSIS.
 IN INSPECTION APPLICATIONS, THE MACHINE VISION
OPTICS AND IMAGING SYSTEM ENABLE THE PROCESSOR TO
"SEE" OBJECTS PRECISELY AND THUS MAKE DECISIONS
ABOUT WHICH COMPONENT MEET A SPECIFIC INSPECTION
CRITERIA.
 MACHINE VISION CAN ELIMINATE HUMAN FACTOR ERROR
THAT MIGHT RESULT FROM DOING DIFFICULT, TEDIOUS,
OR BORING TASKS. IT ALSO ALLOWS PROCESS
EQUIPMENT TO BE UTILIZED 24 HOURS A DAY.
MACHINE VISION PROCESS
IMAGE ACQUISITION-IMAGE PROCESSING-FEATURE EXTRATION-
DECISION-CONTROL

28. VISUAL INSPECTION
MACHINE VISION - APPLICATIONS
AS MENTIONED PREVIOUSLY, MACHINE VISION IS PRIMARILY USED
IN PRODUCTION APPLICATIONS WHERE A LARGE NUMBER OF
COMPONENTS REQUIRE INSPECTION AND THE INSPECTION
CONDITIONS CAN BE CLOSELY CONTROLLED.
USES INCLUDE
 ASSEMBLY VERIFICATION (CAPS, FASTENERS,
ELECTRONIC BOARD COMPONENTS, ETC.)
 SURFACE INSPECTION (DENTS, SCRATCHES,
POROSITY.AND OTHER UNDESIRABLE FEATURES)
 VERIFICATION OF COLORS, GRADIENTS, PATTERNS IN
FABRICS AND LABELS.
 CONFIRMATION OF PROPER LABELING FOR MEDICATIONS,
FOODS AND OTHER PRODUCTS.
 INSPECTION OF COATING COVERAGE.
 FEATURE MEASUREMENTS.

29. VISUAL INSPECTION
MACHINE VISION - EQUIPMENT
 KEY SYSTEM ELEMENTS
A VARIETY OF COMPONENTS ARE INCLUDED IN A
MACHINE VISION SYSTEM, WHICH DEPEND ON THE
ENVIRONMENT, THE APPLICATION, AND THE BUDGET.
HOWEVER, THE FOLLOWING COMPONENTS ARE COMMON TO
ALL VISION SYSTEMS
 FRONT-END OPTICS THIS INCLUDES THE LIGHTING, THE
LENS, AND THE CAMERA.
 FRAME GRABBER THIS IS A COMPUTER PROCESSOR BOARD
THAT ACCEPTS THE VIDEO INPUT FROM THE CAMERA,
DIGITIZES IT, AND STORES IT FOR ANALYSIS.
 PROCESSOR A COMPUTER PROCESSOR IS REQUIRED TO
CONTROL THE VISION APPLICATION.
 CONTROL SOFTWARE COMPUTER SOFTWARE IS USED FOR
CONTROLLING AND EXECUTING VISION TASKS.

30. VISUAL INSPECTION
ADVANTAGES OF VISUAL INSPECTION
 READILY USED ON ALMOST ALL MATERIALS.
 SIMPLE TO PERFORM.
 LOW IN COST, (APPLICATION DEPENDENT).
 RELATIVELY QUICK.
 RESULTS MAY BE PERMANENTLY RECORDED.
 CAN BE AUTOMATED

31. VISUAL INSPECTION
LIMITATIONS OF VISUAL INSPECTION
 DIRECT INSPECTIONS ARE LIMITED TO SURFACES
ONLY.
 INDIRECT INSPECTIONS REQUIRE GREATER
INSPECTION ENGINEER KNOWLEDGE AND
TRAINING/EXPERIENCE.
 INSPECTION ENGINEER DEPENDENT, KNOWLEDGE
OF MATERIALS AND MANUFACTURING PROCESSES,
EYE SIGHT.
 STANDARDS (WORKMANSHIP) MAY BE DIFFICULT
TO OBTAIN.

32. THANK YOU
GK BHARDWAJ
JR.SUPV-RETD. DGM(IS)
RIO-DELHI(1)-HARIDAWR(8)-MUMBAI(6)-
HARIDWAR(18)-DELHI(4)-DELHI(2, ASSOCIATE)
AND
EICHER(3)-FLOWMORE(2)-LNT HOWDEN(1.5)