[Robotgroup] Control systems

[Acy Stapp]

Thanks for the input, Edwin. I'm surprised I didn't remember the incidence
angle term. Maybe I could calculate some sort of correction factor lookup
that compensates for the range and angle attenuation (assuming a fixed head
angle and distance and a flat floor plane), giving me a more linear input
model.

The sensor is the AX-S1 forward IR sensor. I believe it has an IR
illuminator LED with a 40khz carrier. A bandpass at 40khz reports the active
illumination in one register and the remaining non-modulated IR is reported
in another register. The reported value seems to go down with the square of
the distance, from 0xFF at about 3 or 4 inches to 0x80 at about a 9-12
inches and 0x00 at a few feet. The passive IR sensor typically reports 0x03
or 0x04 seeing a human or 0x07 or 0x08 seeing a relatively warm surface. I'm
not sure whether the active sensor is including the energy from the passive
sensor but for a line-following robot it shouldn't make much difference.

Most of the precision is concentrated in the front of the view volume as
well but it clamps the result at 0xFF so I'm limited in to really about a 3
to 6 inch range of good precision. The eye seems to read a fairly narrow
cone, but probably wider than the tape at the distances I'll be reading.

Acy

On 9/10/07, Edwin Wise <edwin at simreal.com> wrote:
>
>
> On 10 Sep 2007, at 1:04 PM, Acy Stapp wrote:
>
> > * Separating the reflectance component from the distance component.
> > The
> > reported value seems to be proportional to emitterBrightness *
> > albedo / d^2.
> > I've tried tracking the largest negative and positive derivatives
> > as the
> > edges of the tape but there is a lot of sensor noise. Any ideas?
>
> Yeah, there will be ridiculous amounts of noise; the angle of
> reflection will matter a lot too, and the farther from the line the
> more information is going to be integrated across the lens (e.g. the
> line becomes a smaller and smaller fragment of the overall return).
> The farther away the "eye" is from the scene, the more "smear" you
> are going to get; edge detection will be nearly impossible.

 Question:  What kind of IR distance device?  Is it using the

> brightness for distance info, or is this a parallax sensor that also
> returns brightness?


See above.



-- 
Acy Stapp

"When I'm working on a problem, I never think about beauty. I think only how
to solve the problem. But when I have finished, if the solution is not
beautiful, I know it is wrong." -- R. Buckminster Fuller (1895 - 1983)