benefits of autofocus technology in manufacturing & logistics · 5 © 2020 cognex corporation...

© 2020 Cognex Corporation1

Benefits of Autofocus Technology in Manufacturing & LogisticsMatt Moschner


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


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”


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


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


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


Application example #1: High-speed focus sweeping with image fusion


Product feature: Cognex DataMan 374 with Torch light


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


Optotune LL Technology

Source: https://www.optotune.com/technology/focus-tunable-lenses

http://Sohttps:/www.optotune.com/technology/focus-tunable-lenses


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


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


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


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?


Questions?

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