[CART360] Fiber Optic Bend Sensors

[Morgan Sutherland]

Hello List,

Faiq and I will be using fiber optic bend sensors (as mentioned in Tom
Igoe's article that we read at the beginning of class[1]) for our project.

If you need to sense the bend of the finger, you can attach flex sensors
> along the length of the fingers. This is how the Power Glove detects finger
> bending. I’ve also seen a couple variations that used an LED at each
> fingertip, a photocell or photodiode at the wrist, and a length of fiber
> optic cable connecting them. If the fiber optic is scored at each knuckle,
> it allows light to escape proportional to the bend of the finger.


I spoke to a couple of people who have done this before and they both had
the same exact recommendations. If you're interested in using these, the
parts you'll need can be purchased from a company called Industrial Fiber
Optics:

http://www.i-fiberoptics.com/

First you'll need and LED and a photodiode that attach easily to either end
of a fire optic cable with minimal light leakage. You can find a red LED
(IF-E96) and a photodiode (IF-D91) with screw-tight housing on this page:
http://i-fiberoptics.com/Fiber_optic_led_photodetectors.php
You definitely want a colored LED, not an infrared one (industry standard)
as this will give you some reference when you're scoring the cable.

The cable to get is Mitsubishi Eska CK-40 (jacketless), a 1mm plastic fiber
with no outer jacket to strip off. Jacketed cable is fine, but in order to
score the core, you'll need to cut it off carefully with a razor blade and
risk slicing the core:
http://i-fiberoptics.com/fiber-detail.php?id=106

Once you've got the cable, you can cut down it with a razor blade so that
light can leak out on one side and polish it down afterward. We haven't done
this yet, but we'll get the cable in the mail soon, so once we've done it,
hopefully we'll have found a good method. We've been advised to create a jig
for a more accurate cut. Apparently it's very difficult to get two sensors
to behave the same way, so we're expecting to do some calibration in
software.

The only distributor for Industrial Fiber Optics is Digikey, but they don't
stock the Eska cable in small lengths. It's best to order that directly from
Industrial Fiber Optics (with $14 shipping!) We also bought some jacketed
cable from Abra and we'll see how hard it is to strip the jacket.

a+,
M

1. http://www.tigoe.net/blog/category/physicalcomputing/176/
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