Wafer center finding

A method for finding a center of a wafer in a device having an interior and a plurality of entrances, the interior containing a robotic arm, and the device including a plurality of sensors, each one of the sensors adapted to detect a presence of the wafer at a predetermined location within the interior of the device, the method comprising:

• retrieving the wafer from outside the interior through a first one of the plurality of entrances;
• retracting the wafer into the interior and detecting a presence of the wafer with a first one of the plurality of sensors;
• rotating the robotic arm;
• extending the wafer out of the interior through a second one of the plurality of entrances and detecting an absence of the wafer with the first one of the plurality of sensors;
• and
• determining a location of a center of the wafer relative to the robotic arm using sensor data from the plurality of sensors and position data from the robotic arm.