Patent ID: 8731718

Claim:
An end effector having a dual sensor for detecting presence of a wafer, comprising: an arm having a first end and a second end, the first end being connected to a pivoting joint, a first point and a second point being defined at the second end; a light emitter operable to generate a light signal; and a light sensor for detecting the light signal after the light signal is routed around the arm through a single light path, the single light path including a first segment and a second segment, the first segment being defined between the first point and the second point, and the second segment intersecting a wafer when loaded on the end effector; wherein a mapping function of a control module identifies presence of the wafer between the first point and the second point when the wafer is not loaded on the end effector and the wafer intersects the first segment blocking the light signal from reaching the light sensor; wherein a load function of the control module identifies presence of the wafer between the first end and the second end when the wafer is loaded on the end effector and the wafer intersects the second segment blocking the light signal from reaching the light sensor, wherein the control module determines if an interruption in the light signal corresponds to an interruption in the first segment or in the second segment, wherein the control module determines that the interruption of the single light path is in the first segment when the end effector is performing the mapping function, and the control module determines that the interruption of the single light path is in the second segment when the end effector is performing the load function.