In most Large Format printers, loaded substrates to be printed may present a defect
called skew, in which the substrate is not aligned in the paper axis. This implies that
the substrate advance and printing directions are not perpendicular and thus the
resulting image orientation is slightly wrong. It might cause paper jams in the printer,
as well as different image quality issues derived from corrections wrongly applied.
An Optical Line Sensor is mounted on the carriage facing downwards and consists of
a light source and a densitometer. It can obtain a numeric value representing the
darkness or lightness reflected by the surface measured.
The invention is composed of two optical line sensors mounted in the printing
carriage. These sensors can measure the distance to the edge of the substrate at
two different points, which allows the printer to calculate the skew and take actions in
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INC, HP, "SUBSTRATE LATERAL SKEW MEASUREMENT USING TWO LINE SENSORS", Technical Disclosure Commons, (October 12, 2021)