DVT ADV Lighting Training - CA

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					                   Creators of Evenlite®




       Vision Lighting Seminar
                      Daryl Martin
            Midwest Sales & Support Manager
                 Advanced illumination
                     734-213-1312
                  dmartin@advill.com
                    www.advill.com


2005                                          1
                    Objectives


 • Lighting Source Comparison / Contrast
 • Machine Vision Illumination Principles &
   Techniques
 • Sample Applications
 • Imaging Beyond the “Visible” – Near IR & UV
 • “Pass” and Polarizing Filters in Vision
 • Toward a Standard Lighting Analysis Method

2005                                             2
                     Sources


       •   LED - Light Emitting Diode
       •   Quartz Halogen – W/ Fiber Optics
       •   Fluorescent
       •   Metal Halide (Microscopy)
       •   Xenon
       •   High Pressure Sodium
       •   Ultraviolet (Black Light)
       •   Infrared
       •   Electro-luminescent

2005                                          4
          Lighting Source Comparisons




       The lighting source with the largest envelope MAY be the most versatile!

2005                                                                         5
                               Lighting – Intensity vs. Spectrum
                                                                             Quartz Halogen / Tungsten
                                                    Mercury (Purple)
                         100
                                Daytime Sunlight

                         80                          Fluorescent
Relative Intensity (%)




                         60
                                                                                           White
                                     Xenon                                                 LED
                         40


                         20                                                               Red
                                                                                          LED


                          0
                               300           400          500          600          700


                                                   Wavelength (nm)
        2005                                                                                         7
           The right light helps the vision
                  system do its job

       • Sample-appropriate lighting is critical for a
         successful inspection.
       • Provides for a quality, consistent & robust
         lighting environment.
       • Saves development time, effort & resources
         better applied to other aspects of the vision
         system.
       • A Standard Method for Developing Machine
         Vision Lighting.

2005                                                     13
       Brief Review of Light and Optics for
                Vision Illumination




2005                                          14
          The Visible Light Spectrum

UV                                                                         IR

390                                                                        735




 400 nm                  500 nm                 600 nm                  700 nm

                              Human Visible Range



  Decreasing Frequency                  Increasing Wavelength

  Decreasing Photon Energy              Increasing Photometric Output
                                        Increasing Penetration Depth


  2005                                                                    15
          The Visible Light Spectrum

 • Light is Seen Differently by film, humans and CCDs

UV                                                               IR

390       455 470   505 520             595      625   660   695 735




 400 nm             500 nm                    600 nm          700 nm
                        Human Visible Range




  2005                                                          16
                             Spectral Response - CCD vs.
                                    Human Vision
                                                                       IR Enhanced Analog
                  80                                                   Digital Interline Transfer
                                                                       Standard Analog
                                                                       CMOS
                                                                       UV Enhanced Analog
Absolute QE (%)




                  60
                                                                       Human Photopic
                                                                       Human Scotopic
                                                                       IR Block (Short Pass)
                  40



                  20



                   0
                       300   400   500      600    700     800   900    1000


                                         Wavelength (nm)
          2005                                                                            17
        Where Does the Light Go?

 • Total Light In =
     Reflected Light +
     Absorbed Light (may be re-emitted) +
     Transmitted Light


       Illumination
                        Absorb



            Reflect
                 Emit            Transmit
2005                                        18
       Reflection on Specular Surfaces
• Light reflects at the
  angle of incidence
• Just like a pool ball off
  the bumper                  1      2
      F1 = F2

• Surface Angle
  determines where light
  comes from in order to
  illuminate the surface


2005                                     19
               Divergence and Intensity


       • Intensity falls with the inverse square of the
         divergence radius
       • I = 1/r2
       • Use collimation and short working distances
         when possible




2005                                                      20
                   Lighting Environment
                       and the Part


 • Ring Light
    – Small Solid Angle


Note: The solid angle of any light
source may be increased by placing
it closer to the object of interest.


 • Continuous Dome
    – Large Solid Angle



2005                                      21
       OK, so where do we start?




2005                               22
                  Standard Lighting Method
1) Knowledge of:
       - Lighting types and application advantages & disadvantages
       - Vision camera sensor quantum efficiency & spectral range
       - Illumination Techniques and their application fields relative to
            surface flatness & surface reflectivity
       - Illumination Technique Requirements & Limitations
2) Familiarity with the 4 Cornerstones of Vision Illumination:
       -   Geometry
       -   Structure (pattern)
       -   Color (wavelength)
       -   Filtering
3) Detailed Analysis of:
       - Immediate Inspection Environment – Physical constraints and
           requirements
       - Sample – Light Interactions with respect to your unique sample

2005                                                                        23
 Three Lighting Acceptance Criteria

       • It’s All About (creating) Contrast!
       • Feature Separation, or Segmentation
         1) Maximum contrast
            • features of interest
         2) Minimum contrast
            • features of no interest (noise)
         3) Minimum sensitivity to normal variations
            • minor part differences
            • presence of, or change in ambient lighting
            • sample handling / presentation differences


2005                                                       24
            Creating Contrast – 4 Lighting
                    Cornerstones
       • Change Light Direction w/ Respect to Sample and
         Camera (Geometry)
          - 3-D spatial relationship - sample, light & camera

       • Change Light Pattern (Structure)
          - Light Head Type: Spot, Line, Dome, Sheet
          - Illumination Type: B.F. - D.F. - Diffuse - B.L.

       • Change Spectrum (Color / Wavelength)
          - Monochrome, white vs. sample / camera response
          - Warm vs. cool color families – object vs. background

       • Change Light Character (Filtering)
          - Affecting the wavelength / direction of light to the camera

          Need to understand the impact of incident light on both
2005
           the part of interest and its immediate background! 25
       Immediate Inspection Environment

       • Physical Constraints
             - Access for camera, lens & lighting in 3-D (working volume)
             - The size and shape of the working volume
             - Min and max camera, lighting working distance and FOV
       • Part Characteristics
             - Sample stationary, moving, or indexed?
             - If moving or indexed, speeds, feeds & expected cycle time?
             - Strobing? Expected pulse rate, on-time & duty cycle?
             - Are there any continuous or shock vibrations?
             - Is the part presented consistently in orientation & position?
             - Any potential for ambient light contamination?
       • Ergonomics and Safety
             - Man-in-the-loop for operator interaction?
             - Safety related to strobing or intense lighting applications?


2005                                                                          26
       Using Color to our Advantage




2005                                  27
                          Using Color
           Use Colored Light to Create Contrast


                                         Warm       Cool

   • Use Like Colors or Families
                                                R   V
   to Lighten      (yellow light makes
   yellow features brighter)

                                         O                 B
   • Use Opposite Colors or
   Families to Darken       (red light
   makes green features darker)                 Y   G


2005                                                       28
        Increasing Contrast with Color



                                 Red                      Green




                                Blue                      White


       • Consider how color affects both your object and its background!

       • White light will contrast all colors, but may be a contrast compromise.
2005                                                                               29
       Using Color for Selection
       White Light                 Monochrome Light




                                             Red +
                           Red               Green



               Color CCD




                           Green




                B&W CCD
                           Blue



2005                                                  32
       Using Geometry and Structure




2005                                  33
          Common Lighting Techniques




  Partial Bright Field             Dark Field                        Back Lighting




                  Diffuse Dome                       Axial Diffuse
                                 Full Bright Field
2005                                                                                 34
       Lights for Partial Bright Field




2005                                     35
       Lights for Full Bright Field




2005                                  36
       Dark Field Illuminators




2005                             37
               Bright Field vs. Dark Field

                 Camera

                                 Bright Field Image




Bright Field
Ring Light




                                     Mirrored Surface
2005                                                    38
             Bright Field vs. Dark Field


               Camera               Dark Field Image

                          Scratch




Dark Field
Ring Light


                                         Mirrored Surface


2005                                                        39
       Dark Field

            • Angled light
            • Used on highly
              reflective surfaces
            • OCR or surface
              defect applications




2005                                40
              Result of Dark-Field Light


       • Emphasize Height Changes
       • Diffuse Surfaces are Bright
       • Flat Polished Surfaces are Dark
       • Shape and Contour are Enhanced




2005                                       41
       Axial Diffuse

         • Light directed at beam splitter
         • Used on reflective objects




2005                                    42
  Result of Axial Diffuse
      Illumination

• Surface Texture Is Emphasized
• Angled Elevation Changes Are Darkened
       Diffuse Dome

          • Similar to the light on an
            overcast day.
          • Creates minimal glare.




2005                                     44
                      Technique vs. Sample
                                        Surface Reflectiveness


                          Matte                    Mixed                   Mirror Specular

              Flat                                         Axial Diffuse

          Geometry
          Independent        Bright Field
          Area



Surface                                                Dark Field
Texture /    Topography
Shape


                                        Diffuse Dome / Cylinder




             Curved

   2005                                                                                      45
Wavelength vs. Composition Checklist
                                           Monochrome
                                      UV   B   G   R    IR   RGB   WHI
   Doped w/ UV Fluorescing Agent      X

              Dark Rubber                  X                       X
              Dark Plastics                             X          X
       Transparent Plastics / Glass                X    X
              Semi-metallic                        X    X          X
                 Metallic                          X    X          X
            Mixed Color Parts                                 X    X
            General Purpose                        X               X
         Ambient Light Problems            X   X   X
       Strobe / Ergonomic Problems                      X




2005                                                                     46
Sample Applications
              Stamped Date Code




  • Recessed metal part
  • Reflective, textured,
    flat or curved surface



                              Dark field ring light
                                           spot light
                             Brightfield Line light
                             Bright Field ring light



2005                                                    48
                    Data Matrix




  • Peened data matrix
  • Flat, shiny surface
  • Curved, matte
    surface
  • May be viewed w/ a
    perspective shift         BrightStandard Dome
                                     Field Ring Light
                              Dark Field Ring Array
                            Broad Area Linear Light



2005                                                49
                 UPC Bar Code


• Printing beneath
  cellophane wrapped
  package




                        Broad Area LinearLight
                         BrightField Ring Array
                         Dark Field Illuminator
                        Axial DiffuseRing Light




 2005                                             50
       Bar Code under Clear Wrap




                             Coaxial BF Ring Light




                             DF Linear Array - BALA


                         Broad Area Linear Array      51
2005
                  Ink Jet OCR


• Purple Ink
• Concave, reflective
  surface




                           BrightField Ring Light
                            Dark Field Ring Light
                          Axial Diffuse Illuminator
                                     Diffuse Dome



2005                                                  52
      Lighting Technique Requirements
             Partial Bright            Dark Field           Diffuse Axial          Diffuse Dome
                 Field                                      Full Bright Field       Full Bright Field


Lighting       Ring, Spot          Angled Ring, Bar         Diffuse Box                 Dome
  Type
              No Specular          Negate Specular         Use Specular            Use Specular

 When
  To       -Non specular          -Specular / Non       -Specular / Non         -Specular / Non
 Use       -Area lighting         -Surface / Topo       -Flat / Textured        -Curved surfaces
           -May be used as        -Edges                -Angled surfaces        -If ambient light
             a dark field light   -Look thru trans-                                issues
                                    parent parts
Require                           -Light must be very                           -Light close to part
ments   -No WD limit                close to part       -Light close to part    -Large footprint
          (limited only to        -Large footprint      -Large footprint        -Camera close to
          intensity need          -Limited spot size    -Ambient light minor      light
          on part)                -Ambient light may    -Beam splitter lowers   -Spot size is ½ light
                                    interfere             light to camera         inner diameter
   2005                                                                                          53
Using Near IR and Near UV Light
   Imaging Beyond “Visible” – Near IR

  • Infra-red (IR) light interacts with sample material
    properties, often negating color differences.


                                  Black




                                   Red


        White           Yellow

       White light – B&W Camera           IR light – B&W Camera

2005                                                              55
   Imaging Beyond “Visible” – Near IR

• Near IR light can penetrate materials more easily
  because of the longer wavelength.




       Red 660 nm Back Light       IR 880 nm Back Light
2005                                                      56
  Imaging Beyond “Visible” – Near IR

• Red 660 nm light reveals the blue dot matrix printed
  bottle date & lot codes.


                IR 880nm             Red 660nm
                Back Light           Back Light




2005                                                 57
   Imaging Beyond “Visible” – Near UV

• Near UV light when
  used w/ a matched
  UV excitation dye,
  illuminates codes
  and structural fibers.


• Top Image Set:
  Diaper
• Lower Image Set:
  Motor Oil Bottle
 2005                                   58
  Imaging Beyond “Visible” – Near UV

• Near UV light
  fluoresces many
  polymers, including
  nylon.


• Top Image: UV
  Light, B&W CCD

• Lower Image: UV
  Light, Color CCD
2005                                   59
       Filters are useful too!




2005                             61
Pass Filters in Machine Vision
• Pass filters exclude light     715 nm Long
  based on wavelength.               Pass
• Sunlight and mercury vapor
  light are reduced by 4X
• Fluorescent light is reduced
  by 35X
               510 nm Short                    660 nm Band
                   Pass                            Pass




  2005                                                 62
                Pass Filters

• Top Image: UV light w/
  strong Red 660 nm
  “ambient” light.




• Bottom Image: Same
  UV and Red 660 nm
  “ambient” light, with
  510 nm Short Pass
  filter applied.
2005                           63
       Light Polarization




2005                        64
Polarizing Filters in Machine Vision




       Coaxial Ring Light    Coaxial Ring Light   Off-Axis Ring Light
        w/o Polarizers         w/ Polarizers        w/o Polarizers




                                                          BALA

       Longitudinal Linear   Transverse Linear
         w/o Polarizers        w/o Polarizers



2005                                                                    65
Polarizing Filters in Machine Vision
• Top image: Without
  polarizing, the plastic
  material appears free
  of defects.
                              Back Light - No Polarizer



• Bottom image: The
  use of crossed
  polarizers shows an
  internal strain field
                            Back Light - Crossed Polarizers
  along the edge.

2005                                                          66
General Sequence for Lighting Analysis
        • Determine the Exact Features of Interest
        • Analyze Part Access / Presentation
              - Clear or obstructed, Moving / Stationary
              - Min / Max WD range, Sweet Spot FOV, etc.
        • Analyze Surface Characteristics
              - Texture
              - Reflectivity / Specularity
              - Effective Contrast – Object vs. background
              - Surface flat, curved, combination
        • Light Types and Applications Techniques Awareness
              - Rings, Domes, Bars, ADIs, Spots, Controllers
              - Bright Field, Diffuse, Dark Field, Back Lighting
        • Determine Cornerstone Issues
              - 3-D Geometry, Structure, Color & Filters
        • Ambient Light Effects / Environmental Issues
 2005                                                              67
 Light Specification: Rules-of-Thumb
• Need more part / background contrast? – Think B&W
  camera & color lights
• Ambient light issues? – Try monochrome light and a
  matched band pass filter
• Shiny, curved surfaces? – Try a diffuse dome light
• Shiny, flat, but textured surfaces? – Try axial diffuse
• See surface topography? – Think dark-field (low angle)
• When inspecting plastics – Try UV or IR light
• Need to see features through a reflective cover? – Try
  low angle linear lights (dark-field)
• Light combinations can solve problems too
• Strobing can generate up to 20x as much light
2005                                                   68
         Thank you!


24 Peavine Dr. Rochester, VT 05767
           802-767-3830
  www.advancedillumination.com

				
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