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A d v a n c e d i l l u m i n a t i o n. c o m Fundamentals of Vision Lighting Daryl Martin Midwest Sales & Support Manager 734-213-1312

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Presentation on theme: "A d v a n c e d i l l u m i n a t i o n. c o m Fundamentals of Vision Lighting Daryl Martin Midwest Sales & Support Manager 734-213-1312"— Presentation transcript:

1 a d v a n c e d i l l u m i n a t i o n. c o m Fundamentals of Vision Lighting Daryl Martin Midwest Sales & Support Manager 734-213-1312 April, 2010

2 Topics  Review of Light for Vision Illumination  Vision Lighting Sources  Review of Illumination and Techniques  Sample Applications Examples  Using Near IR and Near UV Light  Filters are Useful, Too!  Standard Lighting Method  Optional Materials  Measuring and Specifying LED Light Power  Strobing Mini-tutorial

3 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 –lllumination Technique Requirements & Limitations 2) Familiarity with the 4 Cornerstones of Vision Illumination: –Geometry –Structure (Pattern) –Wavelength (Color) –Filtering 3) Detailed Analysis of: –Immediate Inspection Environment – Physical constraints and requirements –Sample – Light Interactions w/ respect to your Unique Sample

4 Review of Light for Vision Illumination

5 Characterizing Light for Vision Light: Photons propagating as a transverse electromagnetic energy wave and characterized by: - Frequency: Varies inversely with wavelength (Hz – waves/sec) - Measured Photon Intensity: Radiometric and Photometric (more later) - Wavelength (Most common for Machine Vision) - expressed in nanometers (nm) or microns (um) - 100 nm = 0.1 um = 1/10,000,000 th of a meter! - a human hair is ~ 100 um (100,000 nm) wide Photons: Energy packets exhibiting properties of waves and particles.

6 Light diffracts (bends) around edges – implications for back lighting. It moves more slowly, thus refracts (disperses) through media of different densities. The amount of refraction is directly proportional to its frequency, and thus inversely proportional to its wavelength. Example - violet light has a higher frequency, thus it is refracted more than red through a given medium. The amount of refraction also is directly proportional to the ratio of media densities and inversely proportional to the angle of incidence. Characterizing Light for Vision

7 Example Light is refracted as: n (glass) / n (air) 1.5 / 1.0 = 1.5 n = Index of Refraction Light Refraction n = 1.5 (glass) n = 1.0 (air) White Light Angle of Dispersion Courtesy Wikimedia Commons Visible light is a very small portion of the “electromagnetic spectrum” How small? ~ 1 / 1000 th of 1%!

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

9 Lighting Source Comparisons

10 Lighting – Intensity vs. Spectrum Wavelength (nm) 300400500600700 0 20 40 60 80 100 Relative Intensity (%) Daytime Sunlight Mercury (Purple) Quartz Halogen / Tungsten Xenon White LED Red LED Fluorescent

11 Brief Review of Light and Optics for Vision Illumination

12 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 The light type and technique tailored for the specific application that allows the vision system do its job better. Sample-Appropriate Lighting

13 400 nm 500 nm 600 nm 700 nm 390 455 470 505 520 595 625 660 695 735 The Visible Light Spectrum  Light is Seen Differently by film, humans and CCDs UV IR Human Visible Range

14 QE and LED Monochrome Light Camera vs. Eye Response Wavelength (nm) 300 400500600700 0 20 40 60 80 Absolute QE (%) 8009001000 Standard Analog Daytime Vision Night-adapted Vision Let your vision system determine sensitivity and wavelength!

15 Wavelength (nm) 300 400500600700 0 20 40 60 80 Absolute QE (%) 8009001000 IR Enhanced Analog Digital Interline Transfer Standard Analog CMOS UV Enhanced Analog Human Photopic Human Scotopic IR Block (Short Pass) Sensors and Wavelength

16 Where Does the Light Go? Illumination Reflect Emit Absorb Transmit  Total Light In = Reflected + Absorbed + Transmitted Light

17 Reflection on Specular Surfaces  Light reflects at the angle of incidence  Just like a pool ball off the bumper    Surface Angle determines where light comes from in order to illuminate the surface

18  Ring Light or Spot Light  Small Solid Angle  Dome, Axial Diffuse or Flat Diffuse  Large Solid Angle Note: Shorter WD and larger light increase the effective solid angle. Solid Angle and Geometry  Ring Light or Spot Light at greater WD  Smaller Solid Angle Solid angle: Effective surface area of a light / radius 2 of the cone.

19 Convergence of Concepts (Sample – Light – Lens**) Contrast Resolution Spatial Spectral Focal Length / Field of View Focus Working Distance / Stand-off Sensitivity **3-D Working Volume: Strong inter-relationship You cannot solve vision problems working in a vacuum! Light Interaction

20 Review of Lighting Techniques

21 3 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

22 4 Lighting Cornerstones  Change Light / Sample / Camera Geometry  3-D spatial relationship  Change Light Pattern (Structure)  Light Head Type: Spot, Line, Dome, Array  Illumination Type: B.F. – D.F. – Diffuse – B.L.  Change Spectrum (Color / Wavelength)  Monochrome / White vs. Sample and 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! How do we change contrast?

23 Common Lighting Techniques Partial Bright FieldDark FieldBack Lighting Full Bright Field Diffuse DomeAxial DiffuseFlat Diffuse

24 Typical Co-axial Ring Light – Sample Geometry Bright Field Bright Field vs. Dark Field Dark Field

25 Dark Field vs. Bright Field Dark Field Lights in Grey Areas Mirrored Surface Partial Bright Field Lights in White Area Scratch

26 Bright Field Lighting Bright Field vs. Dark Field Dark Field Lighting

27  Angled light – 45 degrees or less  Used on highly reflective surfaces  OCR or surface defect applications Dark Field Example

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

29 Reading under Cellophane UPC Bar Code Broad Area Linear ArrayDark Field Ring LightBright Field Ring Light Axial Diffuse Illuminator

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

31 Ink Jet OCR  Purple Ink  Concave, reflective surface Diffuse Dome Axial Diffuse IlluminatorDark Field Ring LightBright Field Ring Light

32 Diffuse Dome Illumination  Surface Texture Is Deemphasized  Best Choice for Curved Shiny Parts

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

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

35 Flat Diffuse  Diffuse sheet directed downward  Long WD and larger FOV  Hybrid diffuse (dome and coaxial) Coaxial BF Ring Coaxial DF RingDiffuse Coaxial Diffuse Dome Flat Diffuse

36 Backlight Illumination  Locates edges – Gauging  Internal defects in translucent parts  Hole-finding  Presence / Absence  Vision-Guided Robotics: Incl. Pick & Place  Useful for translucent materials

37 Light Diffraction: Bending around obstacles  D, where  is the diffraction angle and D is opening width High-accuracy gauging: Use monochrome light Shorter wavelengths best Use collimation – parallel rays Longer light penetrates samples better Backlight Illumination   Red Blue D D

38  Small Bottle – blue-green  Consider colors and materials properties also.  Longer wavelength isn’t always best for penetration! 660 nm Red Backlight 880 nm IR Backlight470 nm Blue Backlight Simple Back Lighting Example

39 Collimated Backlight Illumination Collimation No CollimationCollimation Film

40 High- Accuracy Gauging  Back lighting  Monochrome light better  Shorter wavelength a little better  Collimation even better  Optical collimation better than film  Minimal distortion lens  Telecentric lens best  Measurement calibration – CRITICAL*  Focus - CRITICAL* * Less critical if using a telecentric lens

41 Surface Reflectivity Surface Texture / Shape MatteMixedMirror Specular Flat Uneven Topography Curved Bright Field Dark Field Axial Diffuse Diffuse Dome / Cylinder Geometry Independent Area Flat Diffuse Technique vs. Sample Surface

42 Lighting Technique Requirements Partial Bright FieldDark FieldDiffuse Axial Full Bright Field Diffuse Dome Full Bright Field Lighting Type Ring, SpotAngled Ring, BarDiffuse BoxDome No SpecularNegate SpecularUse Specular When To Use -Non specular -Area lighting -May be used as a dark field light -Specular / Non -Surface / Topo -Edges -Look thru trans- parent parts -Specular / Non -Flat / Textured -Angled surfaces -Specular / Non -Curved surfaces -If ambient light issues Require ments -No WD limit (limited only to intensity need on part) -Light must be very close to part -Large footprint -Limited spot size -Ambient light may interfere -Light close to part -Large footprint -Ambient light minor -Beam splitter lowers light to camera -Light close to part -Large footprint -Camera close to light -Spot size is ½ light inner diameter

43 Using Color Lighting to our Advantage

44 Using Color Use Colored Light to Create Contrast Use Like Colors or Families to Lighten (green light makes green features brighter) Use Opposite Colors or Families to Darken (red light makes green features darker) WarmCool RV OB YG

45 Increasing Contrast with Color RedGreen BlueWhite Consider how color affects both your object and its background! White light will contrast all colors, but may be a contrast compromise. WarmCool RV OB YG

46 Using Near IR and Near UV Light

47 Imaging Beyond “Visible” – Near IR  Infra-red (IR) light interacts with sample material properties, often negating color differences. White light – B&W CameraIR light – B&W Camera

48 Imaging Beyond “Visible” – Near IR  Near IR light can penetrate materials more easily because of the longer wavelength. Red 660 nm Back LightIR 880 nm Back Light

49 Imaging Beyond “Visible” – Near IR  Red 660 nm light reveals the blue dot matrix printed bottle date & lot codes. Red 660nm Back Light IR 880nm Back Light

50 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

51 Imaging Beyond “Visible” – Near UV  Top Image: UV Light, B&W CCD  Near UV light fluoresces many polymers, including nylon.  Lower Image: UV Light, Color CCD

52 Filters are useful too! Blocking Ambient Light – Band Pass Blocking Glare – Polarization Avoiding Surface Glare w/o Polarization

53 Ambient Light: Any light, other than the vision- specific lighting that the camera collects. - Overhead plant lighting Mercury, HP Sodium, Fluorescent Tubes - Other nearby task lighting Incandescent, Fluorescent Tubes - Indicator status lights - Temporary lighting – construction, emergency - Sunlight – Weather and time-dependent - Interference from other nearby vision-specific lighting! Ambient Light

54 Controlling and Negating Ambient Light Turn off the ambient contribution Most effective... Least Likely! Overwhelm the ambient contribution w/ strobing Effective, but requires more cost and complexity Build a shroud Very effective, but time-consuming, bulky and expensive Control it with pass filters Very effective, but requires a narrow-band source light Ambient Light

55 510 nm Short Pass 715 nm Long Pass 660 nm Band Pass 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

56 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.

57 Avoiding Surface Glare  Change Geometry – 3D spatial arrangement of Light, Sample, and Camera (preferred)  Strobe to overwhelm glare from ambient sources  Use polarization filters (least preferred) Courtesy Wikimedia Commons

58 3-D Reflection Geometry: Light - Sample - Camera Avoiding Surface Glare

59 Polarizing Filters in Machine Vision Coaxial Ring Light w/o Polarizers Coaxial Ring Light w/ Polarizers Off-Axis Ring Light w/o Polarizers

60 Polarizing Filters in Machine Vision Back Light - No Polarizer Back Light - Crossed Polarizers  Top image: Without polarizing, the plastic material appears free of defects.  Bottom image: The use of crossed polarizers shows an internal strain field along the edge.

61 Standard Lighting Method  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

62 Develop the lighting solution early on in the vision system process Determine appropriate light geometry techniques Consider reflection geometry Be aware of and block ambient light Consider camera wavelength sensitivity Use monochrome light for high-accuracy gauging Remember that light MAY interact differently w/ respect to surface texture, color and composition Make the lighting solution robust Need more help? – Call your lighting professional!! Summary and Conclusions

63 Optional Materials Measuring and Specifying LED Light Power Strobing Mini-tutorial

64 Measuring and Specifying LED Light Power

65 Specifying Light Intensity - Units Flux: A measure of the rate of energy flow. flux ~ wavelength Flux Density: Flux measured at a specified WD Photometric - Intensity measures weighted to the human eye response Radiometric - Measures are not weighted Radiometric (Radiance)Photometric (Luminance) 1 W @ 555 nm (Yellow-green) = 683 lm 1 W @ 470 nm (Blue) = 62 lm 1 W @ 660 nm (Red) = 42 lm Measuring Light Power

66 Human Vision Sensitivity

67 QE and LED Monochrome Light Camera vs. Eye Response Wavelength (nm) 300 400500600700 0 20 40 60 80 Absolute QE (%) 8009001000 Standard Analog Daytime Vision Night-adapted Vision Let your vision system determine sensitivity and wavelength!

68 Photometric vs. Radiometric Units - Flux Density: Flux measured at a specified WD - Illuminance is Luminance @ WD Units: lm / m 2 (LUX) - Irradiance is Radiance @ WD Units: W / m 2, W / cm 2 or mW / cm 2  Illuminance is acceptable when comparing white consumer / commercial sources, such as fluorescent tubes.  Irradiance is BEST for comparing monochrome color LED light intensity for vision.  Consider camera sensor Quantum Efficiency. Measuring Light Power

69 MeasureLuminance (Luminous Flux) Illuminance (Luminance @ WD) Radiance (Radiant Flux) Irradiance (Radiance @ WD) Unitslumens (lm)lm / m 2 (LUX) Watts (W) W / m 2 W / cm 2 mW / cm 2 Weighted for Human Vision? XX Suitability: Commercial Light Comparison XXX Suitability: Vision Light Comparison X (White only) XX Photometric Radiometric Notes: 1) Compare monochrome sources by irradiance only @ common WD. 2) Consider camera sensor quantum efficiency and wavelength range.

70 Photometric Specification Measuring Light Power

71 Radiometric Specification Measuring Light Power

72 Irradiance @ 100 mm (uW / mm 2 ) Luminance (cd) Photometric vs. Radiometric Units Compare similar light sources w/ same Radiant Power units! CCD QE Curve Consider Sensor Efficiency Measuring Light Power

73 Strobing Mini-Tutorial

74 1) General Vision Definition: Flashing a light source, coordinated with a camera exposure period and/or in response to an external, timed event. 2) Advanced illumination Definition: Additionally, Ai can drive lights with controller internal timing, and also over-drive the lights. What is Strobing?

75 Strobe Flash Timing, Frequency and Duration (pulse-width) is Controlled by: 1) External Triggering Camera Top-of-Frame signal. Part-in-Place / Proximity signal. PLC / PAC Controller Timing Generator. 2) Internal Triggering Preset internal timing circuitry. Also presets in response to External Trigger. Built-in delays, pulse strings, pulse width, multi-channel outputs What is Strobing?

76 Freeze motion Sample singulated or indexed parts Minimize heat build-up Maximize lamp lifetime Overwhelm ambient light contribution Overdrive, or Turbo-Charge LED lights to compensate for short exposure times of fast-moving objects Why Strobe?

77 What is Overdriving? Short Duty Cycle (time on / total time x 100%) Large increase in current vs. DC mode per unit time Benefits of Overdriving: 2-10x more light intensity per unit time Short duty cycle Less heat build-up Longer light life Overdriving LED Lights


79 Ambient Light - 200 usec Strobe 4X Overdrive - 200 usec DC Continuous Level Current - 500 usec Boxed Pharmaceutical Ampules – FOV = 16” x 12” Strobe Example

80 Ai Company Contacts  US and International Sales, OE Contacts John Merva (Exec VP Sales and Marketing) – 603-493-3085,  Regional Sales and Apps Support – Midwest, Canada Daryl Martin – 734-213-1312,  Regional Sales and Apps Support – East, Southeast, South, West Coast Wanda Bilodeau – 617-283-9909,  Custom Quotations Joe Smith (Operations Manager) – 802-767-3830 x 221,  Inside and OEM Sales Support Megan Hudson – 802-767-3830 x 237,,  Factory Apps Support Mike Romano – 802-767-3830 x 227,  Communications, Advertising Harlen Houghton – 802-767-3830 x 231,

81 Thank you! 24 Peavine Drive Rochester, VT 05767 Corporate Phone 802.767.3830 Fax 802.767.3831;

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