Oki PACEMARK 4410, Service Handbook

Page: 37 / 189

40496501TH Draft Version
37
2.2.3 Head gap adjusting
The auto gap adjusting mechanism automatically adjusts the space between the platen and print
head according to the thickness of papers. This mechanism does this driving the platen back and
forth with the AG motor (pulse motor), and effects the auto gap motion after the reverse motion of
the platen. The platen is reversed at power on or off line when cover open or paper end is detected,
and the auto gap adjusting motion is performed when the printer returns to on line.
When the printer is shifted to off line at power on or detection of paper end, the platen reverses to
the position that the space to the print head becomes wider than the thickness of paper (gap open
position).
As the off line mode is released, shifted to on line after platen reverses, the AG motor drives the
platen to the direction that the space between the print head and platen becomes narrower.
The rotational force of tha AG motor moves the platen to the print head (in the direction that the
space becomes narrower) through various idle gears and adjusting cam.
After that, the AG plate impinges on the paper, and the AG frame is deflected, changing the core
gap of the auto gap sensor located on the AG frame. When the change of the core gap is detected,
the AG motor stops rotating.
Next, the AG motor reverse-rotates only a fixed step and stops. This allows the platen move
backward, obtaining an proper space with the print head.
The forward an backward motion of the platen is driven by the adjusting cam being rotated, and
the platen is always pulled to the reart of the unit by the spring.