"Adding the motors basically made it a push-button operation," said Daniel Montgomery, vice president of engineering at RedX. "The user does not have to think about what their environment is or what they need. They just turn the unit on and push the 'activate' button, and no matter where they are, they're going to get good detection."
It wasn't easy, of course. The 18-inch x 12.5-inch x 4.25-inch unit had a signature look and form factor that the company wanted to preserve, both from an efficiency standpoint and from a branding perspective. The problem was that the design was already as compact as possible. Now, the designers needed to fit a motor, gearbox, drive, and wiring inside a housing that was already full, particularly around the sampling baton.
At first blush, it would seem that the application would not present significant torque requirements, but a sampling baton loaded with a full roll of paper can weigh as much as 350g. The motors needed to be small enough to fit in the constrained space while overcoming inertia and reaching target rpm rapidly and reliably, no matter how cold the environment. The motors also needed to be efficient enough to support the analysis of a minimum of 50 samples on a single charge from a 7.2V rechargeable battery, even at freezing temperatures. "That was basically the big trade-off, size versus power," said Montgomery.
Automating the baton
The team went with a Micromo brushed motor that delivered 16mNm of torque, adding a planetary gearbox that brought the total reduction ratio to 14:1. Including a 512 line magnetic encoder helped ensure accuracy. Although performance was important, perhaps the biggest worry at the beginning was reliability.
"When we first proposed the motorized approach to our management, there was some pushback to creating a critical dependence on a fairly complex electromechanical component. If the motor failed or performed unexpectedly, the XPAK would be compromised, leaving our users with no capability when they needed it," said Montgomery.
Wow, this is really cool. I've done some research on explosive detection and actually helped build an <a href="http://www.securityproductsolutions.com/explosive-detector.html">explosive detector</a> kinda like this one, just not as nice..lol It's amazing how far technology is taking this field.
You are correct. The XPAK is very effective in detecting Military Grade Explosives and also Homemade Explosives. We can teach users to effectively detect explosives in a couple hours and since the system has no warm up time or calibration requirement, it's ready when needed. Deploying large numbers of systems will help gather intelligence on individuals involved in bomb-making activities. We need to be offensive when dealing with this threat. Thanks for your comments.
Thanks for the kind comments. I always get a kick out of talking to engineers about the process – reminds me of my days on the other side of the table.
To your question about sensors, the unitactually makes use of an external biologicalsensor – the human eye. The paper has a coating that, when sprayed with the contrast-enhancing ink and irradiated in the UV, demonstrates color change in the presence of explosive materials. The user looks in the viewfinder -- if we see dark patches, they know there is something amiss.
As far as I am aware, there is no additional sensor. They could probably easily rig one up with a linear CMOS image sensor coupled with some sort of a graphics processor chip, but that would increase size, cost, and detection time. The focus for these guys was to develop a simple, robust, cost-effective unit that would provide near-real-time results at checkpoints, etc. It's a clever bit of minimalist engineering, I'd say.
Kristin, I think this hand held explosive detectors is very helpful to cops, who are serving in sensitive areas. We know that now a day's terrorism is a major headache for almost all governments/countries, where suspicious materials like TNT are using widely for Bomb blasts. I hope this machine can help the cops for an early detection of TNT presence.
This is a story in the old tradition of Design News -- where the writers would get into the heads of the engineers and reveal their thought processes as they stepped through the design. Nice job by the author. I am curious, though: What kind of sensor is used for an application like this?
I agree Ann and Beth, this is scary. So I'm all the more glad to see this product. Anything we can do to make attacks less likely and to make attacks less harmful is good news. Tools like this could have the effect of discouraging the use of explosives.
I agree, it's unfortunate that the design of this detector is necessary. But I'm sure glad to see it, and it will no doubt come in very handy. Getting the motors' weight down while still providing enough torque looks like it was quite a challenge. I like the addition of a sensor.
Scary that we have to think about ruggedizing and packaging a handheld explosives dectector so that it is sturdy enough to use on the job as opposed to in controlled, scientific environments. Scary state of the world, but I suppose a harsh reality. It was interesting to follow the logic of their various design choices as they took a technology and tried to make it more commercially viable.
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