Mind / Iron
FOR THE
ROBOT
INNOVATOR
ERVO
by Bryan Bergeron, Editor ;
Working With Light
A good friend asked if I could
lend a hand developing a remote
optical sensing device for his robot.
The challenge was that
communications between the remote
environment and the local electronic
sensors had to be carried via a single
pair of optical fibers over several
meters. Intrigued, I quickly agreed.
After all — I asked myself — how hard
could it be? I’ve worked with IR
rangefinders, light radars, and even a
pair of high voltage HeNe lasers. Plus,
I had just finished experimenting with
the IR LIDAR from a Neato vacuum
teardown.
Well, the project that I assumed
could be handled in a weekend has
now stretched to over two months.
It’s one thing to work with off-the-shelf IR communications components
and cables, but quite another to
design an optical sensing system from
the ground up. For example, even
though most of my audio gear is
connected via TOSLink optical cable, I
had never tried to cut or splice the
cable, or alter the end-cap lenses. I
discovered that such an operation is
non-trivial.
A challenge in working with fiber
optics in general is the need for an
infrastructure significantly different
from that found in an electronics
shop. Lacking the equivalent of a
DMM or oscilloscope, I was virtually
testing for battery voltage by placing
the terminals on my tongue. That is, I
was initially limited to using my visual
perception of light intensity and area
of illumination in place of quantitative
tools.
I quickly learned that my drawers
of standard electronic tools were
useless when working with glass fiber.
Not only is it fragile, but snapped-off
ends have a tendency to seek out
corneas like a heat-seeking missile.
And once you break glass fiber, you
might as well toss the entire fiber.
That is, unless you have a $300 repair
6 SERVO 04.2012
kit and know how to use it.
After wasting several hours
polishing a few glass ends – the final
step in a repair – I moved to plastic
fiber. Plastic fiber is generally less
efficient at carrying light than glass
fiber, but is easier to work with. You
can cut it with a sharp blade and then
fire-treat the end to smooth it and
reduce internal reflection. Of course, it
helps to have a good pocket or even
desktop microscope to examine the
ends.
I love working with lasers, and
this project was an excuse to purchase
some hefty 100 m W IR red, green,
and blue laser diodes; 100 m W lasers
are “scary bright” – at least to me.
Actually, 100 m W IR lasers are just
plain scary. So, before powering up
any of the laser diodes, I went online
and ordered two pairs of laser
goggles. It took two pairs to cover the
four wavelengths of the lasers in my
set.
As with glass and plastic fibers,
laser diodes, and phototransistors,
goggles are designed to work at
specific wavelengths. Don’t even think
of using a pair of generic sunglasses
for protection if you experiment with
lasers of any significant intensity.
Although I found cheap no-name
goggles on the Web that cater to the
laser light show industry, I didn’t trust
the intensity reduction figures.
Instead, I went to Thorlabs
( www.thorlabs.com) for certified
goggles. You might gasp at spending
$150 or more for a pair of plastic
goggles, but you’d probably gasp
even more if you burned out your
retinas because you trusted a $10 pair
of no-name goggles. Another source
for quality certified goggles is Phillips
Safety Products ( www.ph
illips-safety.com).
A major infrastructure technology
is the perfboard equivalent in optical
work: the optical bench. Think of a
typical perfboard on steroids, with
regularly spaced holes about 1/4” in
diameter. Assuming you own standard
Published Monthly By
T & L Publications, Inc.
430 Princeland Ct., Corona, CA 92879-1300
(951) 371-8497
FAX (951) 371-3052
Webstore Only 1-800-783-4624
www.servomagazine.com
Subscriptions
Toll Free 1-877-525-2539
Outside US 1-818-487-4545
P.O. Box 15277, N. Hollywood, CA 91615
PUBLISHER
Larry Lemieux
publisher@servomagazine.com
ASSOCIATE PUBLISHER/
VP OF SALES/MARKETING
Robin Lemieux
display@servomagazine.com
EDITOR
Bryan Bergeron
techedit-servo@yahoo.com
CONTRIBUTING EDITORS
Jeff Eckert Jenn Eckert
Tom Carroll David Geer
Dennis Clark R. Steven Rainwater
Kevin Berry Gordon McComb
Michael Ferguson Robert Doerr
Mike Jeffries Morgan Berry
Greg Intermaggio
CIRCULATION DIRECTOR
Tracy Kerley
subscribe@servomagazine.com
MARKETING COORDINATOR
WEBSTORE
Brian Kirkpatrick
sales@servomagazine.com
WEB CONTENT
Michael Kaudze
website@servomagazine.com
ADMINISTRATIVE ASSISTANT
Debbie Stauffacher
PRODUCTION/GRAPHICS
Shannon Christensen
Sean Lemieux
Copyright 2012 by
T & L Publications, Inc.
All Rights Reserved
All advertising is subject to publisher’s approval.
We are not responsible for mistakes, misprints,
or typographical errors. SERVO Magazine assumes
no responsibility for the availability or condition of
advertised items or for the honesty of the
advertiser. The publisher makes no claims for the
legality of any item advertised in SERVO. This is the
sole responsibility of the advertiser.Advertisers and
their agencies agree to indemnify and protect the
publisher from any and all claims, action, or expense
arising from advertising placed in SERVO. Please
send all editorial correspondence, UPS, overnight
mail, and artwork to: 430 Princeland Court,
Corona, CA 92879.
Printed in the USA on SFI & FSC stock.