Monday, December 31, 2007

Capaciflector

If you look at even relatively simple animals, like bumblebees, they are equipped with loads of complimentary sensors (vision, hearing, chemoreception, and touch). It seems to me the lofty goal of the robotics hobbyist to build a sizable robot that doesn't run into jutting coffee tables, moving cats, and other confounding domestic obstacles, let alone does anything remotely interesting, is to have a similar variety and multitude of sensors (not to mention being able to interpret all the signals).

Most robotics hobbyists know sensors react differently to different targets. The Cruiser's IR sensors can't detect a messy stack of papers or a bag of trash and it detects cardboard boxes about an inch farther away than semi-clear plastic boxes. Unless the cardboard is colored black. In information security, the key word is correlation: from multiple intrusion detectors in an intrusion detection system to determine if a hacker is up to no good. Clearly animals correlate their senses. The other night one of our cats was camped out on the bed next to me. I knew this because I could feel his warmth and the pressure of the sheet on my leg from his weight. I could move my leg and detect him. I never had to look.

The other thing in intrusion detection is you can't just stick one sensor on one computer host or network subnet. You have deploy sensors everywhere to see the whole picture or you will miss really important stuff. Surely the same is true in robotics? But the more sensors you add, the more cost, complexity, and required computing power you're dealing with (picture a robot with 10,000 IR detectors and driving circuitry). I was wondering if there was some simple, elegant, and economical way to use an electrostatic field to detect proximity.

Enter the capaciflector. Maybe everyone's heard of this but me. It was developed at Goddard Space Flight Center, NASA. A particularly attractive feature is the ability to use the robot's shell as the sensor(s) achieving an economy of purpose, and potentially giving the robot obstacle detection in essentially all directions and with whatever level of granularity you desire. I would think even a small robot with a basic microcontroller could gain a lot of perception without much processing cost. A few interesting tidbits on the capaciflector here. More articles on the subject here, here and here. Here's a capaciflector camera. But will this type of sensor work like I hope?

The big question is whether you can detect objects at any reasonable distance, say, 6 inches. For some reason the capaciflector reminds me of lateral lines on fish, but this is an active rather than passive sensor, and detects objects, not just living beings. Even if the distance is limited, this approach could provide another type of touch sense, like the hairs on our arms, and offer a last resort collision detection. Something, anything better than bumpers...

Have a happy and safe New Year!

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