Creators of Evenlite Vision Lighting Seminar Daryl Martin Midwest Sales & Support Manager Advanced illumination 734-213 213-13121312 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 3
Lighting Source Comparisons The lighting source with the largest envelope MAY be the most versatile! 2005 4
Lighting Intensity vs. Spectrum 100 Daytime Sunlight Mercury (Purple) Quartz Halogen / Tungsten Relative Intensity (%) 80 60 40 20 Xenon Fluorescent Red LED White LED 0 300 400 500 600 700 Wavelength (nm) 2005 5
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 6
Brief Review of Light and Optics for Vision Illumination 2005 7
The Visible Light Spectrum UV IR 390 735 400 nm 500 nm 600 nm 700 nm Human Visible Range Decreasing Frequency Decreasing Photon Energy Increasing Wavelength Increasing Photometric Output Increasing Penetration Depth 2005 8
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 9
Spectral Response - CCD vs. Human Vision Absolute QE (%) 80 60 40 20 IR Enhanced Analog Digital Interline Transfer Standard Analog CMOS UV Enhanced Analog Human Photopic Human Scotopic IR Block (Short Pass) 0 300 400 500 600 700 800 900 1000 Wavelength (nm) 2005 10
Where Does the Light Go? Total Light In = Reflected Light + Absorbed Light (may be re-emitted) + Transmitted Light Illumination Absorb Reflect Emit Transmit 2005 11
Reflection on Specular Surfaces Light reflects at the angle of incidence Just like a pool ball off the bumper Φ1 = Φ2 1 2 Surface Angle determines where light comes from in order to illuminate the surface 2005 12
Divergence and Intensity Intensity falls with the inverse square of the divergence radius I = 1/r 2 Use collimation and short working distances when possible 2005 13
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 14
OK, so where do we start? 2005 15
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 16
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 17
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 the part of interest and its immediate background! 2005 18
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 19
Using Color to our Advantage 2005 20
Using Color Use Colored Light to Create Contrast Use Like Colors or Families to Lighten (yellow light makes yellow features brighter) Warm R Cool V Use Opposite Colors or Families to Darken (red light makes green features darker) O Y G B 2005 21
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 22
Using Color for Selection White Light Monochrome Light Red Red + Green Color CCD Green B&W CCD Blue 2005 23
Using Geometry and Structure 2005 24
Common Lighting Techniques Partial Bright Field Dark Field Back Lighting Diffuse Dome Axial Diffuse Full Bright Field 2005 25
Lights for Partial Bright Field 2005 26
Lights for Full Bright Field 2005 27
Dark Field Illuminators 2005 28
Bright Field vs. Dark Field Camera Bright Field Image Bright Field Ring Light Mirrored Surface 2005 29
Bright Field vs. Dark Field Camera Dark Field Image Scratch Dark Field Ring Light Mirrored Surface 2005 30
Dark Field Angled light Used on highly reflective surfaces OCR or surface defect applications 2005 31
Result of Dark-Field Light Emphasize Height Changes Diffuse Surfaces are Bright Flat Polished Surfaces are Dark Shape and Contour are Enhanced 2005 32
Axial Diffuse Light directed at beam splitter Used on reflective objects 2005 33
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 35
Technique vs. Sample Surface Reflectiveness Matte Mixed Mirror Specular Flat Axial Diffuse Geometry Independent Area Bright Field Surface Texture / Shape Topography Dark Field Diffuse Dome / Cylinder Curved 2005 36
Wavelength vs. Composition Checklist Monochrome Doped w/ UV Fluorescing Agent UV B G R IR RGB X WHI Dark Rubber X X Dark Plastics X X Transparent Plastics / Glass Semi-metallic X X 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 37
Sample Applications
Stamped Date Code Recessed metal part Reflective, textured, flat or curved surface Bright Bright Dark Field field field Line ring spot light light 2005 39
Data Matrix Peened data matrix Flat, shiny surface Curved, matte surface May be viewed w/ a perspective shift Broad Bright Dark Area Field Standard Linear Ring Dome Light Array 2005 40
UPC Bar Code Printing beneath cellophane wrapped package Broad Axial Bright Dark Diffuse Area Field Linear Ring Illuminator Light Array 2005 41
Bar Code under Clear Wrap Coaxial BF Ring Light DF Linear Array - BALA Broad Area Linear Array 2005 42
Ink Jet OCR Purple Ink Concave, reflective surface Axial Bright Dark Diffuse Field Diffuse Illuminator Ring Dome Light 2005 43
Lighting Technique Requirements Partial Bright Field Dark Field Diffuse Axial Full Bright Field Diffuse Dome Full Bright Field Lighting Type Ring, Spot Angled Ring, Bar Diffuse Box Dome 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 ments -No WD limit -Light must be very close to part -Light 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 44
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 46
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 47
Imaging Beyond Visible Near IR Red 660 nm light reveals the blue dot matrix printed bottle date & lot codes. IR 880nm Back Light Red 660nm Back Light 2005 48
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 49
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 50
Filters are useful too! 2005 51
Pass Filters in Machine Vision Pass filters exclude light based on wavelength. Sunlight and mercury vapor light are reduced by 4X Fluorescent light is reduced by 35X 715 nm Long Pass 510 nm Short Pass 660 nm Band Pass 2005 52
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 53
Light Polarization 2005 54
Polarizing Filters in Machine Vision Coaxial Ring Light w/o Polarizers Coaxial Ring Light w/ Polarizers Off-Axis Ring Light w/o Polarizers Longitudinal Linear w/o Polarizers Transverse Linear w/o Polarizers BALA 2005 55
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 along the edge. Back Light - Crossed Polarizers 2005 56
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 57
Light Specification: Rules-of 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 58
Thank you! 24 Peavine Dr. Rochester, VT 05767 802-767-3830 www.advancedillumination.com