I found a patent with a figure that looks an awful lot like FTIR. It’s 73 pages long and I haven’t read it yet. I believe this qualifies as prior art:
In December 1985, Richard Greene from San Francisco, CA used FTIR in a graphics tablet. He used a prism to block out external light, but did mention that the camera could be equipped with an IR filter and use IR as an input. It’s pretty clear that he was thinking about visible light FTIR, but his primary claim is for a camera that can only see FTIR light to be used as an input device. Infrared light and a rectangular prism seem to be reasonable extensions of this claim. His claim was also geared towards digital art (he used FTIR to mimick real brushes in computers). I don’t see any reason this couldn’t cover FTIR as a general input device.
I’m not a lawyer. Read it for yourself here: http://www.freepatentsonline.com/4561017.pdf
My last post got cut off. The 4th solution i referenced used one camera and FTIR. It triangulated a repsonse based on where an image was in air space vs. where the corresponding image was in the surface.
Here’s another from 1996 on rearlit diffused illumination:
This guy has a claim that looks an awful lot like FTIR and an external camera:
I haven’t read it yet. Pay special attn. to figure 10b. I don’t know if embedding the LEDs gets around his patent, but it shouldn’t matter using the Drawing Prism as prior art.
Another prior art: Danny Rozin built a canvas using IR light input and an external camera in 1998. I don’t know if he used FTIR, but he did use an external camera, IR light, and a projector on the canvas.
I’m tired and I’ve been reading patents quite a bit today. Hopefully this post is coherent. =)