Patent ID: 7896460

Claim:
A method for detecting intermittent, weak or missing jets of a printer having a row of nozzles, the method comprising: sensing a test pattern using a sensor, the test pattern having an array of dashes produced by the row of nozzles; generating a first response profile that represents a first cross section of the sensed test pattern, the first cross section extending in and being parallel with a process direction in which a print medium advances, the first response profile containing illumination level variations in the process direction; obtaining a first metric for the first response profile based on the illumination level variations in the process direction, the first metric being a phase of a set of minimum illumination levels in the first response profile, obtaining a difference between the first metric and a reference, the reference being a reference phase; and wherein obtaining the difference between the first metric and the reference comprises: obtaining a second response profile based on a second cross section of the sensed test pattern, the second cross section extending in the process direction of the test pattern; obtaining a second metric for the second response profile, the second metric being a phase of a set of minimum illumination levels in the second response profile; obtaining a difference between the first metric and the second metric; and using the difference between the first metric and the reference and the difference between the first metric and the second metric to detect if any of the nozzles are clogged.