Thursday, October 8, 2009

Course construction complete

This picture shows the WiiCane experimental set up at Touch Graphics' office. The apparatus consists of two poles at either end of a 32' course.  A pair of overhead cables supports a plastic strip that houses wiring and electronics for 64 infrared LED's on 6" spacing.  We added the second cable after observing 8" of sag at the mid-point of the single cable set up; the second cable takes the shape of a catenary (like in a suspension bridge), and hangers drop from the upper cable to the lower one that carries the light strip (like the roadway in a bridge). This ensure that the light strip is flat, and that should simplify algorithms for determining position and cane movement. The second cable also appears to stabilize the light strip and to reduce sway from air currents. Immobilizing the lights is key to ensuring our system's measurement accuracy.

In the detail picture, we see the two cables at the start of the course, a support pole, and the plastic channel that holds the electronics. The underside of the channel is printed with a metric distance scale that will help us to calibrate the algorithm for calculating linear position on the course. To do this, we will mount a laser pointer on the body-worn Wii device, and (hopefully) we will be able to visually observe the red dot from the pointer when it appears on the measurement scale. It's not clear whether this scale will be of use in an actual Wiicane product.

We have tried out the apparatus in our office with a Wii device mounted to a cane, with very promising results: as we walked along the course, the system was able to easily see the lights.  We could watch the lights moving on the video screen we had mounted on the goal-end pole, and it seemed to work for cane swings that were quite wide. The only remaining problem, in my view, is that the user must not roll his or her wrist while running the course, because then the camera is not pointed up at the lights, and we lose position awareness. But, since our second (body-mounted) Wii device will always tell us where the traveler is in relation to the lights, we will know that  wrist rotation has occurred if the person is under the lights but the cane-mounted Wii doesn't show any lights visible. Then we can provide spoken feedback to encourage the user to straighten his or her wrist, and we can let them know when this has been done successfully before resuming travel.

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