Robotracer Beetle: Normalization of infrared sensor outputs

This is my robotracer, Beetle, and I have almost finished checking its capabilities.  The only thing left is to write data to the flash memory of the microcontroller, dsPICmc806.

The followings are experimental results for its normalization of infrared (IR) sensor outputs.  The data of 7 IR sensor outputs is obtained when I push Beetle to cross a horizontal white line.

The first figure shows the results when the ground material is similar to that used in Taiwan's contest.

Currently, I have no idea about why the shape of the sensor outputs do not look like bell.  Is it because the angle between the emitting line of IR LEDs and the ground is about 60 degrees? This makes the projection of the light on the ground similar to the shape of a rain drop (according to theory, the shape should be an ellipse if the light emitted from IR LEDs are cones).

The following figure shows the theoretical prediction of the projection of my LEDs on the ground. (I write a MATLAB program to produce the figure)

All the maximum and minimum values of the sensor outputs are mapped using a linear function to 900 and 50, which is shown at the bottom half of the figure.

The mapping function is

$y = y_{min} + (y_{max} - y_{min})/(x_{max} - x_{min})(x - x_{min})$

The following are the results when I used a printed track on a poster, and the reflection ratio is larger than that of the contest ground.

03/20/2014

The previous experimental results seem to suffer residual voltage problem (D2 is the most obvious one), because I did not wait some time to let the residual voltage from the other LED reflected light dies out, and sample immediately after the previous sampling process ends.  The followings are revised version for both poster and contest ground normalization.

From tomorrow on, I will try to find out the impact of the differences on the estimation of the position of line tracks.