by the structure housing the staircase, no position information will be acquired.

Therefore, the stair counter assembly was designed to provide the relative position of the

Andros upon the staircase by counting the number of stairs that the Andros has passed

and is able to account for a step while moving in either direction upon a staircase. For

example, while climbing the stairs, the Andros passes four steps. While attempting to

move to the fifth step, a slippage error occurs and the Andros slides back down two steps.

The stair counter is able to take this error into account and update the current position of

the Andros upon the stairs. In this case, the Andros would now be located at the second

step.

 Mounting Plate



 infrared
 Sensors





 \ Shroud












Figure 2-7: Stair counter assembly

 The stair counter assembly consists of an array of two Sharp GP2D 12 infrared object

detectors. These sensors take continuous distance readings up to 80 cm, have an update