value of the difference is reversed if the absolute value of the difference is found to be

greater than 180 degrees. This ensures that the Andros takes the shortest route possible to

reach the commanded heading.

 Once the Andros has been aligned, the IPD starts the skew alignment task. This is a

separate program thread, which runs parallel to the main stair control thread. The

purpose of the skew alignment task is to detect and counter any angular slippage of the

Andros upon the staircase. Slip detection is accomplished by monitoring the difference

between the current heading of the Andros and the heading of the stairs, similar to the

align platform function.



 Direction of Slip














 Direction of
 Adjustment

Figure 3-6: Skew alignment task correction

 If an angular slippage error is detected, the skew alignment task counters it by

rotating the Andros in the direction opposite of the slippage. (Figure 3-6) This, again, is

a fuzzy logic task as the slippage error is grouped into broad sets of possible angular

error. If the error is greater than 5 degrees but less than 10, the Andros is rotated at 15%