Friday, September 18, 2009

new concept: putting the IR lights on a cable overhead

After thinking through the problems associated with constructing a floor mat system for tracking position of a student during cane travel training with a wii remote, I want to consider a new idea that may resolve many  problems.  This approach calls for creating an overhead string of LED lights on a three or four wire cable stretched tightly between two poles.  The poles would be floor-to-ceiling aluminum rods of the type I have here in the office to hold up the desks. These are telescoping poles from IKEA that extend up to 12'. I believe this could be easily installed in a wide variety of places. Even if they didn't have a full 30', they could use set up and use a shorter course.

Here are the pluses and minuses of the proposed system:

1. We can control the distance between the camera and the lights this way. In the floor mat arrangement,  the shortest cane held the Wii device only about 18" or so above the floor, so the portion of the floor that the camera could see at once was very small. If we point the wii device straight up instead of straight down, and if we string the lights on a single cable directly above the course, I believe that we should be able to be far enough from the lights that we would mostly always able to see one light, and usually more than that.  In the floor scenario, we were talking about making multiple rows of lights so that the cane would be seen even when the subject was not standing in the middle of the course. If we are far enough from the lights, we may only need one row. This has to be demonstrated experimentally.

2. The poles will be rigidly held in place, so, as long as they are padded, it won't pose too much of a hazard in the case of inevitable collisions. Because the poles are rigidly supported, we can draw the cables very tight, reducing the amount of sag. We will probably need some kind of mechanical tensioner in the cable for setting up the apparatus. While a little sag might not matter, a large amount of sagging could lead to measurement inaccuracies.  I think this set up is a fairly low hazard level.

3. This apparatus will be much easier to package and ship, much, much cheaper to produce and less prone to damage and wear, because no one will be walking on it.

4. The system will be very scalable. It will be relatively easy to extend or reduce the length of a course. It would also be possible to include additional legs, as long as the subject is prepared to negotiate a free-standing pole along the route.

5. There may be other applications for the set up that I am envisioning, such as Wii Fencing. I just googled it, and it does not appear that wiiFencing has been done. Here's a link to a thread on that subject. A cheap set up for tracking linear motion along a virtual course may have a range of uses in both therapeutic and gaming domains.

So...I am going to go shopping tomorrow and buy stuff to set this up. I will be ready to start testing next week, and if it looks promising, the next thing we have to do is to go to all of the sites and make sure that they have a location where the poles could be set up.



GB said...

ANYTHING that gets rid of the floor mat is a good idea to me. The mat was always a problem for the cane.

I wonder if the LEDs will string tightly across 30 feet?

The advantages are apparent and I like it . .. but I hear the clock ticking.

rafael said...

I think this change solves a lot of problems. I agree its certainly a lot less equipment and solves a number of problems. The user's feet don't occlue any lights. Its a lot less equipment.

I'm a little concerned that the sag across 30 feet might be a problem. Its not a predictable sag. The lack of a rigid bar means that each time its set up the sag will be slightly different. Most sites I imagine will have other lights on the cieling which might compete with the lights on the wire. If you have flourecent lights up there I believe those are it sources and may swamp the lights on the wire.

I suppose it will be solved empirically - have you tried it yet?

sl said...

I am not too worried about sag. We can make the cable very tight. the only thing that is tricky, I think, is to ensure that the lights are always pointing straight down. I have some ideas about how to do this. Gene, I agree that the clock is ticking, and that we have to work very, very quickly from here on out, but we can do it.

zeveland said...

I did a quick feasibility test at Steven's request and the results look good. I'll echo the concern about cable sag, but this new approach is promising.

About the test... We figure an approximate average six foot separation between Wii Remote and WiiCane lightstrip given eight foot poles. I hung a section of lightstrip vertically on a wall and checked the Wii Remote's view of the strip at 3-foot and 6-foot separation. The strip used consists of the 3mm package, 940 nm wavelength IR LEDs used previously on 6" centers.

The strip lights are clearly visible even with a reasonable ambient light level from indirect sunlight and incandescent room lighting. At the six-foot separation, the Wii Remote's field of view is about 60" horizontal, meaning that we should be able to report arc width with high accuracy out to about 30 inches of veering (or 30 inches combined veering and off-midline cane positioning). Beyond that, we'll still know arc width and veering amount but arc width measurement accuracy will decrease.