Vision Lighting Seminar

Transcription

1 Creators of Evenlite Vision Lighting Seminar Daryl Martin Midwest Sales & Support Manager Advanced illumination

2 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

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

4 Lighting Source Comparisons The lighting source with the largest envelope MAY be the most versatile!

5 Lighting Intensity vs. Spectrum 100 Daytime Sunlight Mercury (Purple) Quartz Halogen / Tungsten Relative Intensity (%) Xenon Fluorescent Red LED White LED Wavelength (nm)

6 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

7 Brief Review of Light and Optics for Vision Illumination

8 The Visible Light Spectrum UV IR nm 500 nm 600 nm 700 nm Human Visible Range Decreasing Frequency Decreasing Photon Energy Increasing Wavelength Increasing Photometric Output Increasing Penetration Depth

9 The Visible Light Spectrum Light is Seen Differently by film, humans and CCDs UV IR nm 500 nm 600 nm 700 nm Human Visible Range

10 Spectral Response - CCD vs. Human Vision Absolute QE (%) IR Enhanced Analog Digital Interline Transfer Standard Analog CMOS UV Enhanced Analog Human Photopic Human Scotopic IR Block (Short Pass) Wavelength (nm)

11 Where Does the Light Go? Total Light In = Reflected Light + Absorbed Light (may be re-emitted) + Transmitted Light Illumination Absorb Reflect Emit Transmit

12 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

13 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

14 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

15 OK, so where do we start?

16 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

17 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

18 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!

19 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?

20 Using Color to our Advantage

21 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

22 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

23 Using Color for Selection White Light Monochrome Light Red Red + Green Color CCD Green B&W CCD Blue

24 Using Geometry and Structure

25 Common Lighting Techniques Partial Bright Field Dark Field Back Lighting Diffuse Dome Axial Diffuse Full Bright Field

26 Lights for Partial Bright Field

27 Lights for Full Bright Field

28 Dark Field Illuminators

29 Bright Field vs. Dark Field Camera Bright Field Image Bright Field Ring Light Mirrored Surface

30 Bright Field vs. Dark Field Camera Dark Field Image Scratch Dark Field Ring Light Mirrored Surface

31 Dark Field Angled light Used on highly reflective surfaces OCR or surface defect applications

32 Result of Dark-Field Light Emphasize Height Changes Diffuse Surfaces are Bright Flat Polished Surfaces are Dark Shape and Contour are Enhanced

33 Axial Diffuse Light directed at beam splitter Used on reflective objects

34 Result of Axial Diffuse Illumination Surface Texture Is Emphasized Angled Elevation Changes Are Darkened

35 Diffuse Dome Similar to the light on an overcast day. Creates minimal glare

36 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

37 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

38 Sample Applications

39 Stamped Date Code Recessed metal part Reflective, textured, flat or curved surface Bright Bright Dark Field field field Line ring spot light light

40 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

41 UPC Bar Code Printing beneath cellophane wrapped package Broad Axial Bright Dark Diffuse Area Field Linear Ring Illuminator Light Array

42 Bar Code under Clear Wrap Coaxial BF Ring Light DF Linear Array - BALA Broad Area Linear Array

43 Ink Jet OCR Purple Ink Concave, reflective surface Axial Bright Dark Diffuse Field Diffuse Illuminator Ring Dome Light

44 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

45 Using Near IR and Near UV Light

46 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

47 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

48 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

49 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

50 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

51 Filters are useful too!

52 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

53 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

54 Light Polarization

55 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

56 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

57 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

58 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

59 Thank you! 24 Peavine Dr. Rochester, VT