Tech Briefs Magazine - March 2022 - PIT-17

newer LED light sources may be seen
as another albeit less mature alternative.
Bundled optical fiber also presents
a uniform light source. Much of what
interests the food-inspection industry
'reflects' at ranges beyond the visible,
which cuts out at around 700 nm. So
having a light source covering either
side of this point is vital.
Beyond being as cool as possible,
robust, and uniform, the light source
needs to fully traverse the width of
the inspection line. This edge-to-edge
capability takes advantage of the wide
field-of-view of the sensor, allowing inspected
product to be seen not only directly
beneath the sensor itself but off
to the edges. There's no regimentation
in a high-speed food inspection line because
product could be everywhere...
along the edges or bunched together
on the conveyor belt. Longevity of the
light source is also important since
many food-inspection lines run around
the clock.
Since the sensor is building a 'cube'
of image data one slice at a time and
the illumination itself is a very thin
strip, the region of interest (the 'slit
image') is what needs to be illuminated.
A white reflectance target is used
to calibrate the sensor prior to actual
operation. This is a crucial step because
the sensor is collecting image
data that a downstream robotics system
(e.g., vacuum, air knives, picking claw)
will use to segregate 'good' from 'bad.'
The objective is always to present the
right kind of light at the right intensity,
exactly where it's needed. Also, it is
important that documentation exists
providing wavelengths and intensity of
light across the field of projection, uniformity
of the light, and degradation
across standard distances. This way, the
exact positioning of the sensor relative
to the line can be determined should
some adjustment on the architecture of
the line be necessary.
Robotics
Robotic subsystems are a natural element
of many advanced machine vision
processing-line applications. The ability
to discriminate and eliminate depends
on the ability of the sensor and robotic
system to communicate rapidly and
faithfully, in real time. Hyperspec®
sensors
can run hundreds of frames per
second, meaning they are well-suited
from both an operational and economic
standpoint to work with high-speed
lines and the robotic systems embedded
in them.
The machine vision industry understands
that the wherewithal to integrate
a wide range of subsystems into a seamless
and continuously running line demands
that communication protocols
be industry-standard and fast. Gigabit
Ethernet is often used to tie everything
together from a data-flow perspective.
The HSI systems and computers that
manage the incoming data all work
with Gigabit Ethernet, but also other
very fast communication links such as
CameraLink.
Data Collection & Processing
Inspecting specialty crops such as
nuts and berries involves looking at
vastly similar-looking items with small
degrees of variability. Therefore, dividing
the signal or image into hundreds
of hyperspectral 'channels' is a benefit
to the industry.
Since ease-of-use is paramount and
steep yet rapid learning curves are necTime
of Flight vs. FMCW LiDAR Systems
ecent papers1-5
R
have presented a
number of marketing claims about
the benefits of Frequency Modulated
Continuous Wave (FMCW) LiDAR systems.
As might be expected, there is
more to the story than the headlines
claim. This article will examine these
claims and offer a technical comparison
of Time of Flight (ToF) vs.FMCW LiDAR
for each of them.
We understand that not all ToF and
FMCW systems are equal, so we will focus
on ToF as employed at AEye. Our hope
Photonics & Imaging Technology, March 2022
essary, Headwall's software is intuitive
and contains functions that allow users
to modify and adapt their inspection
processes based on what the sensors see.
The algorithm-based process pinpoints
the spectral characteristics users might
encounter. For example, almonds with
insect damage are nearly indistinguishable
from 'good' almonds under RGB
analysis. But the same scene classified
using HSI will call attention to the damaged
ones, which can be eliminated by
the downstream robotic system.
The combination of innovative sensors,
software, and workflow allows a
growing number of users access to HSI
with true solutions that use spectral data
to not only detect contamination, but
also 'grade' products so that less is wasted
and more is converted to revenue. Hyperspectral
imaging unlocks that possibility
within the machine vision industry.
Resources
1 " Food Safety Testing Market by Target Tested
(Pathogens, Pesticides, GMOs, Mycotoxin,
and Allergens), Technology (Traditional
and Rapid), Food Tested (Meat, Poultry,
Seafood, Dairy, Processed Foods, and Fruits
& Vegetables), and Region - Forecast to
2026 " , Markets and Markets, Food Safety
Testing Market, Published May 2021
2 " The effect of caffeine on the color-discriminating
function of the retina in volunteers " ,
Ovanesov KB. Vliianie. Eksp Klin Farmakol.
1998 Nov-Dec;61(6):17-9. PMID: 9929810
3 " Multispectral vs Hyperspectral Imagery explained " ,
GISGeography, 16 Feb 2018
4 " Handbook of Machine Vision " , Alexander
Hornberg, Wiley-VCH. p. 694, 2006. ISBN
978-3-527-40584-8
This article was written by Christian
Felsheim, Director Headwall Photonics
EMEA, and Dr. Will Rock, Senior Application
Engineer, Headwall Photonics (Bolton,
MA). For more information, visit http://info.
hotims.com/82319-222.
is that this article will outline some of
the difficult system trade-offs a successful
practitioner must overcome, thereby
stimulating robust informed discussion,
competition, and ultimately, improvement
of both ToF and FMCW offerings.
Competitive Claims
Claim #1: FMCW is a (New) Revolutionary
Technology
This is untrue.
Contrary to recent news articles,
FMCW LiDAR has been around for a
very long time, stemming from work
done at MIT Lincoln Laboratory in the
1960s8
itself was invented9
, only seven years after the laser
. Many of the lessons
learned about FMCW over the years-
while unclassified and public domain-
have unfortunately been long forgotten.
What has changed recently is the higher
availability of long coherence-length lasers.
While this has rejuvenated interest
in the established technology, as it can
theoretically provide an extremely high
signal gain, there are still several limita17
PIT
Application Briefs 0322_1.indd 17
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ToC
2/15/22 9:15 AM
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Tech Briefs Magazine - March 2022

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