Patent ID: 7552986

Claim:
A method for detecting a process direction registration error in a marking device, comprising: printing a test pattern of dashes, each dash extending in a process direction; obtaining a sensor profile from sensor responses to the test pattern, the sensor profile containing a plurality of minimum responses; converting the sensor profile to a minimum response profile based on the minimum responses in the sensor profile, the minimum response profile having approximately a shape of a sinusoidal curve; determining a first value, the first value being a phase of a first section of the minimum response profile, the first section of the minimum response profile obtained from a part of the sensor profile corresponding to dashes printed with a first printhead of the marking device; determining a second value, the second value being a phase of a second section of the minimum response profile, the second section of the minimum response profile obtained from a part of the sensor profile corresponding to dashes printed with a second printhead of the marking device; determining a phase difference between the first and second values; and determining a stitch in the process direction between the first and second printheads based on the phase difference between the first and second values.