Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
A ribbon shield suitable for narrow throat impact printers is described having improved reliability and usability along with reduced ribbon drag.
shield suitable for narrow throat impact printers is
described having improved reliability and usability along with
reduced ribbon drag.
describes a partial side section view of a
state-of-the-art ribbon shield design used in a line matrix shuttled
print hammer unit.
A ribbon (3)
is shown passing between a first plate (1) and a
second plate (2) both having aligned holes to permit dot producing
impactors (4) attached to print hammers (5) to pass through while
driving ribbon (3) into paper (6) which is supported by a platen (7).
ribbon shield assembly keeps the ribbon out of
contact with the paper shown on the right side, thus reducing paper
smudge and shields the hammer mechanism on the left side.
Plate (1) is
somewhat rigid (.024" thick steel) and is
magnetically held against the hammer assembly at points (8) and (9)
and acts primarily as a mechanism shield for ribbon snag protection
on impactor tips. Plate (1) then supports plate (2) by the use of
double sided pressure sensitive tape (10). Plate (2) is .003 thick,
very flexible, and offers minimal resistance to forces toward or away
from the ribbon. Therefore when multi part outfolds pass through the
point of minimum throat clearance the force produced acts to pinch
the ribbon between the two plates which causes a drag force which can
stall the ribbon drive motor due to limited drive torque reserve.
undesirable condition is the tearing of single part
recycled paper having lumps and particles which add up to dimensions
which exceed the clearance (.003" Nominal) provided in the throat gap
with ribbon and paper installed. Typical one part recycled paper is
nominally .004" thick but lumps measuring .012" are not uncommon and
these lumps easily catch on the edge of the holes of plate (2) and
result in paper tearing and machine jams. Due to the small nominal
throat clearance (.003") any particle trapped in the recycled paper
which exceeds .007" total paper thickness has the potential of being
snagged and torn by the relatively sharp hole edge condition of plate
(2). Also plate (2) can only have a small degree of edge
conditioning due to its .003" thickness. This completes the
description of the prior art.