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FUNDAMENTALS OF MACHINE VISION- LIGHTING
Part 3 in a Series: Illumination Terms and Techniques
© 2014, Pete Kepf, All Rights Reserved
Pete Kepf, CVPwww.kepf.me
Pete Kepf, CVPwww.kepf.me
Introduction
Overview: Lighting is critical variable Applications and their lighting schemes
Lighting Lenses Sensors
What do you want your image to look like? Software Part Attributes
Pete Kepf, CVPwww.kepf.me
What is Machine Vision?
Machine Vision is the use of a computer to acquire visual information and/or extract image information for purposes of data storage or automatic decision making.
+ =
Pete Kepf, CVPwww.kepf.me
What are some Typical Industrial Applications?
Motion/ Robot Guidance Defect/ Flaw Detection Inspection/ Grading/ Sorting Identification/ Verification Data Acquisition Measurement/ Gauging
Pete Kepf, CVPwww.kepf.me
What makes a Vision System?
Vision Components
Lens Camera Processor Input/ Output
Peripherals
Lighting Frame/ Enclosure Controls/ Software Part Handling/
Reject/ Sorter
Pete Kepf, CVPwww.kepf.me
Application Examples
Motion:Front LightingNear IR
Flaw:Front LightingBlue Filter
MeasurementBack LightingVisible
Sort:Front DiffuseVisible
MeasurementStructuredPattern Projector
CountFront LineVisible
Pete Kepf, CVPwww.kepf.me
Goals
• High S/N• High Contrast• Even Distribution• Repeatable
• Product Variability• Ambient
Conditions
Pete Kepf, CVPwww.kepf.me
Lighting Effects
Light Source Frequency Brightness Angle “Shape” Duration
Object Surface
Reflectivity Geometry
What do you need the image to look like?
Pete Kepf, CVPwww.kepf.me
How Light Works
Reflection: Angle of Incidence = Angle of Reflection
Absorption: Frequency Specific
Refraction: Affects angle and Frequency
Scattering: Multi-angle Reflection
Pete Kepf, CVPwww.kepf.me
How Optics are Affected
Reflectivity: Polish/ CoatingScattering: Dirt/ Scratch
Absorption: Lens MaterialRefraction: Lens Material
Pete Kepf, CVPwww.kepf.me
How Sensor is Affected
Reflectivity: Polish/ CoatingScattering: Dirt/ Scratch
Absorption: Sensor Material/FilterRefraction: Sensor Material
Pete Kepf, CVPwww.kepf.me
Lighting for Machine Vision
Back Light Pattern Projector
Line Light
Ring Light
Axial Light
Dome Light
Pete Kepf, CVPwww.kepf.me
Lighting Characteristics
Frequency/ Wavelength (Color) Polarization Intensity (Brightness) Direction (Soft/ Spectral/
Polarized) Duration (Constant/ Pulse)
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Polarization
Filter Source and Camera
Source: www.thermalcamerarentals.com
Pete Kepf, CVPwww.kepf.me
Lighting Source Frequency (Color/ Spectrum)
(Previous: Halogen- Fluorescent- Xenon; Now: LED)
Source: www.thermalcamerarentals.com
Wavelength (nanometers) = 3,000,000 / Color temp (Kelvin).
Pete Kepf, CVPwww.kepf.me
IntensityLumens vs. Lux: 1 lx = 1 lm/m2
Lumen = Light Emitted Total "amount" of visible light in a defined beam or
angle, or emitted from a source. Also depends on its spectrum, via the nominal response of the human eye.
Lux = Area Accounts for the area over which the lumens are
dispersed. 1000 lumens, concentrated into an area of one square meter provides an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square meters, produces a dimmer illuminance of only 100 lux.
Source: Wikipedia
Pete Kepf, CVPwww.kepf.me
DirectionSeite: 17
Top (or Front)
Light source and image sensor are on the same side of the part. Diffuse On-axis Dark/ Bright
Field
Back
Light source and image sensor are on opposite sides of the part.• Diffuse• Collimated
Structured
Light source has a known geometry.
• Line• Grid
Pete Kepf, CVPwww.kepf.me
Front (Spot) LightUses:
• Small Parts• Structured Light
Pete Kepf, CVPwww.kepf.me
Direction: Top Lighting
Diffuse On-axis Bright/ Dark Field
Pete Kepf, CVPwww.kepf.me
Bright Field/ Dark Field
Pete Kepf, CVPwww.kepf.me
Ring Light
Shadow-less illumination
Applications:• specular surface• diffused surface
General-purpose
Pete Kepf, CVPwww.kepf.me
Line LightApplications• imaging • web• line scanFeatures• adjustable lens• enhanced cooling • low current
consumptionUses• Road surface
inspection• Bottle inspection• Carpet Inspection• Print Inspection
Pete Kepf, CVPwww.kepf.me
Diffuse Work Envelope Light
Useful for:
• Robot Work Cells
• Top Light Assembly
• Reflective Parts
Pete Kepf, CVPwww.kepf.me
Diffuse Dome Light (“Cloudy Day Illuminator”)
Uses:• Metal and chromed bearing
surface inspection • CD / DVD assembly
inspection• Package inspection of glossy
plastics and finishes• Inspection of metal stampings
and parts with electrical contacts
• Automotive applications• Medical device packaging and
tray packs• Pharmaceuticals blister form
fill and trim• Cosmetics and makeup
packaging equipment and lines
• Diffused Tube Lights are meant for inspecting elongated parts
• Metal and chromed bearing surface inspection
Image of Sphere
Pete Kepf, CVPwww.kepf.me
Dual On-Axis Light (DOAL)
Uses:• Sphere inspection for
surface flaws• Ball bearing inspection• CD/DVD label inspection• LCD display inspection• Automotive part
inspection
Pete Kepf, CVPwww.kepf.me
Off Axis Ring LightUses• Illumination of scratches on reflective surfaces• Ball grid array (BGA) inspection• Water contamination inspection• Bottle Cap inspection• Microscopic stage illumination• Inspect molded epoxy parts to uncover
imperfections such as cracks, bubbles, and structural damage
Pete Kepf, CVPwww.kepf.me
Direction: Back Lighting
Diffuse CollimatedUses:• Absence/presence of objects• Defect detection in glass/plastic
containers• Object tracking (Fish in
aquarium)• PCB (printed circuit board)
board assembly through-hole lead detection
• Web inspection (pin-holes in web)
• Bottle cap detection• Bolt/Bolt thread inspection• Glass Sheet defect detection• Sub-pixel dimensional
inspection
Pete Kepf, CVPwww.kepf.me
Back Light
Useful for:
• Gauging• Measureme
nt
Pete Kepf, CVPwww.kepf.me
Direction: StructuredSeite: 29
Line Grid
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Pattern Projector
Useful for:
• Structured Light
• Height Derivation
Pete Kepf, CVPwww.kepf.me
Duration Constant
Non-Moving Parts Use Care with Ambient Typically large area No Controller
> 10 microseconds Line Speeds up to 1200 parts/ minute LED with Controller Configurable Form Factor
> 100 nanoseconds Part speeds up to 3500 feet/ second LED with Controller Configurable Form Factor
Pete Kepf, CVPwww.kepf.me
Summary Goals:
High S/N High Contrast Even Distribution Repeatable
Variables Frequency Brightness Angle “Shape” Duration
Other Components Lens Camera Sensor
Some Lighting Terms Top/ Front Back Structured On-axis Diffuse
Lighting “W”