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Imaging Through Bullet-proof Media

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OhioAviator

OhioAviator

Electrical
Sep 8, 2003
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Hi all,

I am a thermal imaging neophyte, so please bear with me. I hope someone can help. The situation is this...
We have a fixed-mount infrared video camera (Electrophysics Corp.) mounted above, and looking down into, an automobile shredder. The video image is used to enable the shredder operator to see through copious amounts of steam into the throat of the shredder so that he can see what he is putting into the shredder. We have the camera housed inside a substantial (read HEAVY) enclosure with a piece of expanded metal (1/2" mesh) covering the opening through which the lens looks down into the shredder.

The problem is that occasionally a piece of shrapnel will be shot up out of the shredder and make it through the mesh, striking the face of the camera lens. This, of course, destroys the lens.

Does anyone have any better ideas on how we can protect the camera lens and prevent it from being destroyed by flying shrapnel? We were thinking about using some type of bulletproof glass. Will this work? If so, what type do we need? Any other suggestions?

Much appreciated,

John R.
Cincinnati, OH.
 
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IR cannot see through ordinary glass. There are however clear Inspection covers that are used for scanning high voltage areas where opening enclosures present hazards. I don't think that they are "bullet proof" but are probably a heck of a lot cheaper than a new camera lense. You could do a web search for IR inspection ports to find a manufacturer and then see if they make one suitable for your application.
 
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Most infrared window material can tolerate only a limited amount of impact damage.

You might also need to look into hard carbon or diamond coatins to minimize chipping and gouging of the window itself.

TTFN
 
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A cheaper long term solution, if the situation permits, would be to get a longer lens (telephoto) and move the whole unit back far enough that the "shrapnel" does not reach it. Fix it once, right, and forget it.
Jack

Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

4011 Hillman Ave
Bronx, NY 10463

718-884-6644
866-884-6644 toll free
212-214-0919 fax and voice mail

JKEngineer@aol.com or JKEngineer@KleinfeldTechnical.com
come see what we can do for you:
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
 
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Thank you IRstuff and Mr. Kleinfeld. I'm finding out that the words "inexpensive", "tough", and "Infrared" all seem to be mutually exclusive of each other. I had considered Mr. Kleinfeld's approach, but found that to "fix it right, once, and forget it" required that the camera be located (no kidding) approximately 120 feet away and be elevated about 105' in the air, in order to obtain the proper viewing angle down into the shredder. Do-able, but not practical.

What about using some sort of periscope? Suggestions?

Thanks again.
--John R.
 
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Sure, that's another approach, the surface quality and finish are likely to raise the question of cost again, although they should be much cheaper, but durability may still be an issue. If the mirror gets hit, it will get damaged, although you may be able to tolerate more dings and scratches, since they'll be out of focus.

You could try just a single 45º fold mirror to keep the cost down. You might try to find a high polish flat, first-surface mirror to experiment with first

TTFN
 
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Ohio,
How about using highly polised stainless in place of glass mirror in this periscope apparatus. I have several "stainless" inspection mirrors that are very durable. You could probably make it yourself. I've made belt buckles using ss pipe and tubing then polished them to a "blinding" finish using ordinary jewelers rouge.
Kind regards,

Roy Gariepy
Maintenance and Reliability Dept.
Dorlastan Fibers LLC.
Goose Creek, South Carolina USA
 
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How about using a wide spaced mesh grid to cover over the camera lens. While some of the image woudl be obscured it might be an adequate cheap fix.

Not sure, really just throwing out a quick thought.
 
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I'd strongly suggest considering a thermal mirror. Aluminum actually works best, in my experience. It does not need a mirror finish, but should be thick enough (1/8") to not be distorted. Simply mount it so it reflects the scene into the camera. I'm sure ElectroPhysics can help you with this one too!


If I can be of further assistance, please feel free to contact me.
John Snell
Snell Infrared
 
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Hello IRJohn:

I looked into the plastic material available from infraredwindow.com and in fact I have a sample of the material. We are going to experiment with it by inserting(weaving is more accurate) it into a 15 lines/inch mesh grid of kevlar & stainless steel thread. We've done some preliminary tests and it will stop a pellet from a pellet gun 10 feet away.

As for the thermal mirror concept, I must admit that I like this approach better because it places the camera lens out of the direct 'line of fire'. I assume that we could simply use a flat piece of thick aluminum and set it at the appropriate angle to reflect the scene into the camera? However, would it not also deflect any shrapnel directly into the camera lens? What about using two mirrors in periscope fashion? The only drawback to that is that it makes our IP67 rated camera enclosure somewhat larger.

Comments appreciated!

--John R.
 
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"Why does the mirror or periscope have to be part of the enclosure?"....... I don't know. Maybe it doesn't. Maybe it can be mounted to the front surface of our existing enclosure. On second thought, there's no maybe to it. It definitely can be mounted on the outside or separately altogether.

Thanks JKEngineer. Often times it helps to have someone like yourself ask the basic common sense questions! Helps me to pull my head out of my .... er, sand!

Cheers,

--John R.
 
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It may be possible to use a rotating disk with gaps
to intercept moving particles while attenuate the IR
only with acceptable amount.



<nbucska@pcperipherals DOT com> subj: eng-tips
 
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I'm a builder of industrial process hardened cameras. Is there so much water vapor in suspension that you cannot see through the "steam" with a visible light camera? Is the steam always present when shredding is in operation?
I like the mirror idea. I'd suggest installing the mirror on a mounting so that if the shrapnel hits the mirror it will definitely flop out of the way. Vwalla. No reflected projectile. Let it hinge on one or two bolts using bellville washers to act as axial springs. Use lock tight on the threads though. We build a camera made for use in splattering areas but I can't mention that on this forum, or can I? Ours is however, only for visible light. Your IR camera (I assume it is sensitive beyond 1200 nanometers i.e. 1.2 microns) won't see through our optics. What wavelength are you using? Are you band limiting the light to the camera in any way?
cameraman1
 
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not knowing why you have to "look into the shredder", i would suggest looking at what goes into the shredder before it goes into the shredder (using either visable light or IR).

also, forget kevlar, it will stop blunt objects but sharp or pointed objects go thru it like a knife thru butter.
 
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Hello Eyec, and all the others...

Thank you all for your thoughtful and unique suggestions. I do appreciate it.

Eyec... you are correct, we actually do only look at what goes into the shredder. It just so happens that the best angle to see what goes into the shredder is the one that looks down into the shredder. We have to use IR since the whole shredder feed area is surrounded by steam, especially during the colder months.

Since late September we have been experimenting with a prototype lens protector that consists of a stainless steel mesh screen sandwiched between the expanded metal and the camera enclosure lens opening. It is approx. 10 mesh and actually is a piece cut from the side of a McDonald's french-fry fryer basket. It seems to be working well. The contraption has taken three direct "hits" from shredder shrapnel and has so far successfully protected the lens.

Again, thanks to all.

--J. Ruble
Cincinnati, OH
 
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