Using a bar code scanner to calibrate positioning of a robotic system

A method for teaching a robotic accessor the location of a target in an automated storage and retrieval system, the accessor being capable of motion in at least orthogonal x and y directions, the method comprising the steps of:

• a) moving the accessor to an initial position R.sub.xi,yi,zi proximate a nominal location of a target, the target having first and second opposing sides;
• b) activating a bar code scanner to sweep a light beam from an angle of .beta..sub.0 at a time t.sub.0 to an angle .beta..sub.3 at a time t.sub.3 in a y.sub.i plane toward the expected location of the target;
• c) determining whether the first side of the target is detected by the bar code scanner;
• d) if the first side of the target is not detected:
• d1) moving the accessor in a first direction to a new position R.sub.xi,yv,zi where Y.sub.v equals the previous y-coordinate of the accessor plus an incremental value;
• and
• d2) repeating steps b) and c) until the first side of the target is detected;
• e) when the first side of the target is detected, storing values Y.sub.v, t.sub.1 and t.sub.2, where t.sub.1 and t.sub.2 are measured from time t.sub.0 and are the times it takes the light beam to strike the first and second sides, respectively, of the target;
• f) moving the accessor in the first direction to a new position R.sub.xi,yv,zi where Y.sub.v again equals the previous y-coordinate of the accessor plus an incremental value;
• g) determining if the first side of the target is still detected;
• h) if the first side of the target is still detected, repeating said steps e) through g);
• and
• i) when the first side of the target is no longer detected, calculating the position of the center of P.sub.xc,yc,zi of the target.