Vision system components
Strobecontroller
Camera
Illumination
PC system
Sample
Presentation and
sorting mechanics
PLC
Light
• Light is electromagnetic energy
conveyed through particles called
photons and though waves
• Quantum mechanics unites the two
types of behavior in the wave-particle
duality assertion
• The field concerned with the study of
light is called optics, a major research
area in modern physics.
Light properties
• The speed of light in vacuum denoted c
is 299,792,458 m/s
• The photon is a mass-less particle that
carries an energy E=h ν
• h=6.6262*10-34Js is called Planck’s
constant
• The spatial period or wavelength of the
light wave λ is found – in vacuum – by
the relation c=λν
Wavelength bands
VUV
10 nm -200 nm
Vacuum ultraviolet. Absorbed by oxygen.
UVC
200 nm – 280 nm
Very harmful to most forms of life. Absorbed by ozone layer.
UVB
280 nm – 315 nm
Over exposure causes sunburn and can damage the DNA in
the skin. May cause skin cancer. Induces vitamin D
production in the skin.
UVA
315 nm – 400 nm
Causes tanning. “Black light”.
Violet
380 nm – 450 nm
Blue
450 nm – 495 nm
Green
495 nm – 570 nm
Yellow
570 nm – 590 nm
Orange
590 nm – 620 nm
Red
620 nm – 780 nm
NIR
780 nm – 1400 nm
Near infrared.
SWIR
1400 nm – 3 µm
Water absorption 1450 nm
MWIR
3 µm – 8 µm
Used in heat-seeking missiles
LWIR
8 µm – 15 µm
Thermal infrared
FIR
15 µm – 1000 µm
Far infrared
Visible light
ultraviolet
(UV)
near-infrared
(NIR)
nm
200
300
400
500
600
700
800
900
1000
Illumination
• Light source
• Illumination geometry
Light sources
• Incandescence
– Light emission from hot bodies
– Continuous spectrum
– Wolfram lamps, halogen lamps, sun
• Luminescence
– Light emission from relatively cool bodies
– Flourescent lamps, CRT displays, LED
Luminescence
• Flourescence
– Instantaneous conversion of higher energy
light to lower energy light
• Phosphorescence
– Delayed conversion of higher energy light
to lower energy light
• LED
• Electroluminescence
• Cathodoluminescence
Luminosity
• Lux is a photometric term that
represents the amount of light per area
that falls on a surface
•
•
•
•
•
Bright sunlight: 100,000 lux
Cloudy day:
10,000 lux
Twilight: 5 lux
Full moon: 0.05 lux
Overcast night: 0.00005 lux
• Human eye is sensitive to this range!
Light source
• Choice based on
–
–
–
–
–
–
Spectrum
Intensity
Stability
Lifetime
Heat
Cost
Light source
• Choice based on
–
–
–
–
–
–
Spectrum
Intensity
Stability
Lifetime
Heat
Cost
Brightfield/darkfield
Brightfield frontlight
Darkfield frontlight
Darkfield backlight
Darkfield frontlight
Darkfield backlight
Brightfield backlight
Brightfield diffuse
backlight
• Easy to make
• Dependent on clean
surface
• Useful for count, size
shape, orientation and
transparency
Brightfield diffuse backlight
Brightfield collimated
backlight
• Dependent on clean surface
• Useful for precision
dimensional measurements
and more precise
transparency measurements
• Examples
• Direct sunlight
Brightfield collimated backlight
• Overhead projector
•Distant backlight
Light/material interaction
Incoming light
Specular reflection
Diffuse reflection
Absorption
Fluorescence / phosphorescence
Translucent transmission
Transparent transmission
Pinhole camera
Thin lens model
Thin lens formula
1
S1
1
S2
1
f
Focal length
Source: www.klt.co.jp/Nikon/LensGuide
Distance
Different distances – same field-of-view
Source: www.klt.co.jp/Nikon/LensGuide
Aperture
Aperture refers to the lens
opening through which
light rays pass.
Aperture blades determine
the size and shape of the
opening.
You can use the lens
aperture to control the
amount of light reaching
the film as well as the
picture's depth of field.
Source: www.klt.co.jp/Nikon/LensGuide
Camera
• A camera is a vision sensor that
captures the light to create a video
signal
Digital or analog
signal
Camera types
• Line scan camera
• Area scan camera
Line scan camera
• Line Scan is a linear or one
dimensional array of photoelements
• Line scan cameras can
generate 2D images if camera
or object is moving
• Common consumer
applications are the fax
machine and the photocopier.
Line Scan Applications
• Rotating parts
– Bottle surface inspection, impurity detection (vials)
Line scan applications
Web inspection
• Textile
• Plastic foil
• Steel/aluminum
• Paper
• Wood
• Glass
• Food
• Extruded profiles
Other line scan applications
• Linear measurements
• High resolution where area scan
cameras are infeasible and translational
movement is feasible
• Continuosly moving parts on a
conveyor
Line scan calculations
•
•
•
•
•
Horizontal Field of View (HFOV) :
Min. resolution (RES):
Number of pixels required = HFOV / RES:
Number of pixels (databook):
Max. velocity of movement (VOM):
• Required line-rate (VOM/RES):
• Gray level resolution:
• Data-rate:
1000mm
0.5mm
2000 pixels
2048 pixels
3000 mm/s
6 kHz
8 bit
12 MB/s
Area scan camera
• Consider area scan in all
other situations
• No movement
SW
SH
IH
IW
Area scan calculations
Camera sensor
Field-of-view (FOV)
SW
IW
SH
f
WD
IH
Exercise
A camera is made using a CCD-chip. The chip has the
following data:
Horizontal resolution
Vertical resolution
Pixels size
Pixels placement
:
:
:
:
768 pixels
576 pixels
11 μm * 11 μm
11 μm (centre to centre)
Given a focal length (camera constant) of 8 mm and a
working distance of 400 mm, find the field of view.
Area scan calculations
Camera sensor
Field-of-view (FOV)
IW
SW
SH
f=8mm WD=400mm
SH=576*11 m=6.336mm
SW=768*11 m=8.448mm
IH=6.336mm*(400/8)=316.8mm
IW=8.448mm*(400/8)=433.4mm
IH
Scanning system
• CCIR (B/W) and PAL (Colour) standard in
Europe: 625 lines / image, 25 images / second
1
2
3
4
5
6
7
8
9
10
20 ms = 1/50 sec
579
580
581
582
• EIA (B/W) and NTSC (colour) standard in
Japan/USA: 525 lines / image, 30 images /second
CCD image transfer
• Interline transfer CCD structure
Horizontal
shift register
Odd line
Even line
Pixel
(sensing area)
Vertical
shift register
CCD size
35mm Still
H=36.0
V=24.0
D=43.3
• 1980s: 1" and 2/3" sensors
1"
H=12.8
V=9.6 2/3"
D=16
H=8.8
V=6.6
D=11
• 1990s: 1/2", 1/3" and 1/4" sensors
1/2"
H=6.4
V=4.8
D=8.0
1/3"
• 2000s: 1/5", 1/6"...
H=4.4
V=3.3
D=5.5
1/4"
H=3.2
V=2.4
D=4.0
CCD size
• CCD size reduction helps:
– Smaller cameras
– Reduction of sensor price ( less rejected chips )
– Higher definition on the same size chip
• CCD size reduction helped by:
– Improvement of manufacturing processes
– Clean rooms
– Sensitivity constant or increased
CCD technology
• Micro-lens technology
– Sony Hyper HAD and
Power HAD
– improved sensitivity and
reduced smear
– 80% - 98% of light
captured by pixel
CMOS sensors
• CMOS is one of the standard processes
for ICs e.g. DRAM, logic,
microprocessors, A/D, D/A.
• Pixels are photo memory elements
• Very flexible readout
• FP noise but no jitter
• Easy interfacing
CMOS vs. CCD
CMOS
CCD
• Raster, random, ROI
• Analog+digital
• Reasonable signal
quality
• No jitter
• Easy interfacing
• Sequential pixels
• Analog signal
• Excellent signal
quality
• Jitter can occur
• Complex interfacing
Square pixels
• TV standard means non square pixels
• Square pixels simplifies measurements and
display
CCD
Non square pixels
CCD
Square pixels
CCD
Computer Display
Integration time
control
• Electronic shutter
– Integration time less than 1/50sec for blur-free
pictures of moving object
Without shutter
With shutter (1/2000s)
Integration time control
• Electronic shutter - Explanation
Saturation
level
Readout
Without
Bright light
Normal light
Pixel Charge
20 msec
With shutter
Shutter speed
– No need for external device (Strobe, mechanical
shutter)
Integration time control
• Restart-Reset
– Integration time controllable from
external device
– Applications:
• Long term integration
• Improved sensitivity
CCD Charge
in low light
conditions
20 msec to 30 sec or more
20 msec
Asynchronous shutter
• Synchronise picture acquisition with
Without external
external event
trigger
1
Trigger
2
3
Video out
1
2
3
Sensor
3
2
1
With external
trigger
Asynchronous shutter
• Explanation
External
trigger
Pixel
Charge
Integration time
Monochrome CCD Sensor
Spectral response
1.0
Relative response
0.8
0.6
0.4
0.2
0.0
400
500
600
700
800
Wave length (nm)
900
1000
Colour cameras
• 3CCD Vs 1 CCD
– 1CCD colour : specified colour filter is on
photo sensor
• Competitive price
• Compact camera
– 3CCD colour : Attach 3x B&W CCD with
Prism
• Excellent colour reproduction
• Back to resolution, S/N & contrast of B/W
1 CCD Camera
B/W
Colour
Each Pixel has a Colour Filter
CIE Colour Chart
Y
X
RGB CCD with mosaic filter
Relative response
1.0
0.8
B
G
R
0.6
0.4
0.2
0.0
400
IR stop
filter
500
600
700
800
Wave length (nm)
900
1000
Complementary Colour Filter
Complementary Colour/Mosaic filter
+ High sensitivity
+ High horizontal resolution
- Field integration Only
- Signal / Noise
- Colour accuracy
Applied in all consumer cameras, because of sensitivity
Primary Colour Filters
Primary Colour/Vertical stripe filter
+ Excellent colour reproduction
+ Full vertical resolution
+ Field/Frame integration
- Horizontal resolution
Primary Colour/Mosaic filter
+ Excellent colour reproduction
+ High horizontal resolution
- Frame integration Only
Primary Colour/Bayer array
+ Excellent colour reproduction
+ Same horizontal & vertical resolution
(-) Progressive scan only
Applied in scientific & industrial 1 CCD camera,
because of colour fidelity
3-CCD Camera
• How to get picture
Red
Green
Blue
Use 3x B&W CCD
Internal colour processing
• White balance
– Define which colour is ideal as “Standard” white
– Need to update according to lighting condition
Ex: Indoor: 3200K
Outdoor: 5600K
– Auto White balance detects white in the picture and
adjust accordingly
External calibration
Chromatic aberration
ED (Extra-low Dispersion)
glass minimizes chromatic
aberration.
Source: www.klt.co.jp/Nikon/LensGuide