Patent ID: 8057115

Claim:
A disc printing system comprising: a disc carrier comprising: a disc retaining portion; a first surface spaced from the disc retaining portion at a predetermined location with respect to the disc retaining portion; and a recess adjacent the first surface; and a printer comprising: a print head a sensor comprising: a light emitter at a first angle offset from vertical; and an optical sensing element oriented at a second complementary angle offset from vertical; and a controller configured to determine a location of the carrier, based on first and second specular signals from the sensor as an area of incident light from the emitter is moved relative to and across the junction of the first surface and the recess, the first specular signal occurring when the area of the incident light is not received within the opening and impinges a first portion of the optical sensing element and the second specular signal occurring when the area of the incident light is received within the opening and impinges a second portion of the optical sensing element.