© 2020 Cognex Corporation1
Benefits of Autofocus Technology in Manufacturing & LogisticsMatt Moschner
© 2020 Cognex Corporation2
Agenda
• Overview of lenses and how to think about selection / tradeoffs
• The benefits of autofocus?
• What autofocus technologies exist – and do they have tradeoffs?
• Introduction to liquid lens technology for the purpose of autofocus
• Benefits of next generation liquid lenses
• Application examples
© 2020 Cognex Corporation4
Typically four considerations when picking the “right” lens
Focal length (FL) or lens “power” Aperture
Sensor compatibility Focal point
1
4
2
3
Description: Controls the opening angle (small FL = wide FOV) & magnification of lens (small FL = more magnification)
Description: Where in the field of view the lens has the best focus, resulting in the clearest image
Description: The size of the opening through which light travels in a lens, also affecting natural depth of focus.
Description: CMOS image sensor designs must be considered such as size, aspect ratio, pixel size, pixel chief-ray-angle (CRA)
Example:Short FL, wide FOV
Large FL, more magnification
Example:
Example:
Example:
Smaller # = larger opening, more light, less depth of focusLarger # = smaller opening, less light, more depth of focus
sensor sensor
1/18” imager size2.5 um pixel size
1200 x 1600 format
1” imager size3.50 um pixel size
1200 x 1200 format
“Tune”
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Autofocus technology allows for easier setup, dynamic adjustment
“One-click” setup
Dynamic refocusing
Description: When setting up a new application, being able to adjust the camera focus through software
“Tune”
RefocusDescription: Having the ability to adjust the focus point from frame to frame, depending on the distance from object to camera
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Three main technologies to ‘autofocus’ a lens
Electro-Mechanical Liquid LensMulti-camera
Description: Using a series of motors and gears to adjust the focus of the lens.
Very common in DSR cameras
Description: Insert a liquid lens within the lens assembly, adjustable based on voltage
Machine vision systems
Description: Install multiple cameras with different lenses, and select best for each image
Consumer devices e.g., phones
Liquid Lens
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Liquid lens technology has traditionally come with tradeoffs
Speed between focus points
Optical quality
Stability with temperature
variation
Legacy technology State of the art
Typically requiring 30-50% more resolution than c-mount lenses
20-30ms to refocus and “settle”, a measure of
focus stability
~0.1 diopter per oC
Diopter is a measure of focus power
Same optical quality as c-mount lens
2-3ms to refocus and “settle”, faster than most imager frame
rates
~0.025 diopter per oC, or about a 4x improvement
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What could the next LL project get us?Varioptic Optotune EL-3-10 Why it matters?
Time to change focus
Temperature stability*
Max aperture
Max focal distance
Max sensor size
~20-30ms ~2.5ms
0.10 diopter / degree C
0.025 diopter / degree C
2.3 3 mm
24 mm 35mm
1.2 MP 5MP
• Replace FF lenses in Logistics• * w.o. additional SW compensation
• Needed to support smaller pixel sizes (avoid diffraction limit)
• Support > 35mm focal lens lenses which are needed for large sensors
• Accommodate future products
• Refocus at frame rate
Unit to unit variation +/-0.6 diopter +/- 0.6 diopter • Focus based on distance input
Zoom compatible No No • Accommodate future optics innovation
Optical Range -5..+13 dptr -18..+18 dptr • Accommodate future optics innovation
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Optotune LL Technology
Source: https://www.optotune.com/technology/focus-tunable-lenses
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Distance Based Triggering• Triggers the reader when a part is detected within a certain distance• Supports all external trigger types (continuous trigger mode recommended)• Reduces the need for photo eyes and other trigger signals• Can report no reads in presentation applications
500mm 1000mmMin Trigger Distance: 500mmMax Trigger Distance: 1000mm
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Distance Based Read Setups• Enables and disables read setups based on distance• Good for applications with parts containing different materials and different heights• Helps in cases where you can get each part to read individually but struggle to get them together
500mm 1000mmMin Trigger Distance: 500mmMax Trigger Distance: 1000mm
Read Setup 1Code 128: EnabledData Matrix: DisabledActive Lights:8
Read Setup 2Code 128: DisabledData Matrix: EnabledActive Lights:16
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Indicator LED on a process error or system event
• Right indicator LED provides a visual queue on process errors e.g., validation errors, % interval time, decode time, code quality
• Provides more feedback to operators• Saves an output line that would otherwise be used to provide indication to
operators
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Single, top side solution with integrated trigger + dynamic autofocus
Verify application after the printer
DM374 + 16mm HSLL + Torch
160 fpm speed
Distance-based dynamic autofocus
Distance-based integrated trigger?
Illuminate scene based on code quality?