The align platform function is another of the fuzzy logic functions. It calculates the
difference between the reported stair heading and the current heading of the Andros,
obtained from the Andros' onboard digital compass. The absolute value of the difference
is then compared against the defined fuzzy sets.
Total Length
Total Rise
Run -
Rise
Total Run
Figure 3-5: Stair data representation
If the absolute value is greater than 90 degrees, the Andros is rotated at its maximum
speed. If the absolute value is between 90 and 60 degrees of error, the Andros is rotated
at 75% of its maximum speed. If the absolute value is between 60 and 25 degree of error,
the Andros is rotated at 50% of its maximum speed. Finally, if the absolute value is less
than 25 degrees, the Andros is rotated at 25% of its maximum speed. This function has
an allowable angular tolerance of +/-4 degrees. The direction of the commanded rotation
is also dependent upon a fuzzy interpretation of the angular difference. If the absolute
value of the difference is less than 180 degrees and the actual difference is negative, the
Andros is rotated counterclockwise at the desired speed. If the absolute value of the
difference is less than 180 degrees and the actual difference is positive, the Andros is
rotated clockwise at the desired speed. The direction of rotation relative to the actual