Patent ID: 6229972
Filing Date: 2001-05-08
Classification: G03G

Abstract:
A densitometer for determining the optical density of a test sample, wherein said test sample is in the form of marking material on an endless supporting structure, and said test sample is at least sometimes in lateral motion advancing past said densitometer, said densitometer comprising:a photodetector;means to convert the output of said photodetector and provide a density output characteristic of the density of said test sample;means to receive encoder pulses, said encoder pulses being synchronous with the motion of said test sample, wherein said encoder pulses trigger the updating of said density output;means to receive a sync pulse signal signifying the passage of a reference mark on said endless supporting structure past a sensor, whereby a predetermined number of said encoder pulses are received between successive said sync pulses while said endless supporting structure advances; andstorage means for saving at least one of said density outputs;wherein during a run mode of operation, said sync pulse signal marks the beginning of a sequence of said density outputs, whereby said density outputs correspond respectively to successive defined spots on said test sample; andwherein during a calibrate mode of operation, said sync pulse marks the beginning of a reference sequence of at least one of said density outputs, and said reference sequence values are saved in said storage means, whereby reference density values can be retrieved at a later time.