Patent ID: 7394475

Claim:
An apparatus for image registration, the apparatus comprising: a first optical channel module configured to communicate light from a first image on a paper; a second optical channel module configured to communicate light from a second image on the paper; and a sensor module configured to receive light from the first optical channel and the second optical channel simultaneously, and to derive a signal based on the combined intensity of the light from the first optical channel and the light from the second optical channel, and to detect a light transition based on the signal in order to detect a registration, wherein the sensor module is configured to detect the registration by detecting the light transition as a first registration mark of the first image passes the first optical channel module and as a second registration mark of the second image passes the second optical channel module, wherein the registration marks are duplex page registration marks, wherein the sensor module is configured to determine a mis-registration has occurred upon detecting a plurality of light transitions when the first registration mark passes the first optical channel module and the second registration mark passes the second optical channel module, wherein the first optical channel module is configured to communicate light from the anterior side of the page and the second optical channel module is configured to communicate light from the posterior side of the page and wherein the sensor module comprises a single sensor, and wherein the sensor module further comprises: a light sensor circuit coupled to receive the combined intensity of the light from the first optical channel and the light from the second optical channel and adapted to generate a voltage level indicative of the combined intensity; a first edge detector circuit coupled to receive the voltage level and adapted to detect a first transition in the voltage level and adapted to generate a delay enable signal responsive to sensing the first transition; a delay circuit coupled to receive the delay enable signal and adapted to generate a delayed trigger signal after a predetermined period of time following the sensing of the generation of the delay enable signal; and a second edge detector circuit coupled to receive the delayed trigger signal and coupled to receive the voltage level and adapted to generate a mis-registration output signal to detect the mis-registration if a second transition in the voltage level is sensed following reception of the delayed trigger signal.