HP 1055CMHP - Manual (Page 296)

Functional Overview
10-10
HP DesignJets 1050C and 1055CM Printers Service Manual
Cap
The purpose of the caps is to prevent the nozzles from drying out
while the printer is idle. The caps seal off the printhead, forming a
closed, high humidity chamber with small volume that is vented to
ambient through a long and narrow passage. The caps self-align to
the printheads by referencing features on each printhead.
Wiper
The function of wiping is to remove ink residue and external debris
from the printhead so that good drop ejection and nozzle
performance is maintained throughout the life of the printhead.
Linear wiper motion will occur in the direction of the nozzle rows
(orthogonal to direction of carriage motion) at 0.2 to 6.0 ips
programmable speed. The maximum wiping force is 2N.
Spittoon
Spitting is the act of firing all the print head nozzles into a container
(spittoon). Spitting into the spittoon is done routinely to clear the
nozzles of viscous plugs and to clear any loose debris from the
nozzles. PHC Spittoon is designed to hold 50 cc of spat ink (which
has almost no water content due to evaporation).
In order to avoid ink spills when replacing PHC, color spittoons
have foam that will keep the ink escaping due to capillary effect.
Black ink does not have foam. The Black ink is pigmented, and it
has been proven that pigmented inks build up over any surface when
spat, including foams, creating stalagmites that may hit the
Printhead and cause some nozzles out.
Fortunately, black ink dries very fast, creating a solid block of ink
that will not fall out off the spittoon when tilted. For most users, the
probability of seeing enough liquid ink in the spittoon to create a
spills problem is very low.
To prevent the growth of tall and narrow stalagmites that may
reduce spittoon life, the Printhead spits in four different locations
(Scan-axis), randomly.