(57) An improved media axis image registration system for a multi-color inkjet printer/plotter
(10). The inventive system comprises a carriage assembly (100) for retaining multiple
inkjet cartridges (102, 104, 106, 108) or pens. Each cartridge (102, 104, 106, 108)
has a plurality of nozzles (502, 504, 506, 508) adapted to eject ink in response to
the application of an electrical signal thereto. A first mechanism (112) is provided
for moving the carriage assembly (100) in a first (scan) axis. A second mechanism
(152) is provided for moving print media (30) in a second (media) axis transverse
to the first axis. A position encoder (152) senses the position of the carriage assembly
in the media axis. A control circuit (300) provides electrical signals which cause
the nozzles (502, 504, 506, 508) in the inkjet cartridges (102, 104, 106, 108) to
eject ink onto the media (30) and create an image thereon in the form of a test pattern
(40) in response to timing signals. The inventive system includes a sensor module
(200) which optically senses the image and provides a set of sensed signals in response
thereto. The sensed signals are sampled in accordance with position encoder signals
to provide corrected timing signals. In a particular embodiment, the test pattern
(140) is illuminated by a light source (232) in the sensor module (200). The light
source (230) has spectral energy in the color bands of interest. The test pattern
(40) includes a plurality of vertically spaced bars which, when scanned by the sensor
module (200), allow the module (200) to generate an output signal of a given frequency.
The output signal is sampled and processed to provide the corrected timing signals
for activation of the nozzles. By detecting the position of the pattern (40), the
misalignment of a particular pen may be corrected.
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