Thin, shallow-angle serrated hold-down with improved warming, for better ink control in a liquid-ink printer

The invention minimizes liquid-ink deposition on the top and edge of a guide-plate (or "hold-down" plate), and also minimizes running of deposited liquid ink along the top to the edge. Through these two effects together the rate of ink deposition on the top and edge of the plate is held below the volume of ink per unit time that can dry there. The invention also minimizes ink transfer from the edge onto the print medium. The deposition-minimizing provisions include two features: serration, and a very fine vertical dimension of the edge itself. These features enhance air flow, and thus transport of ink spray, rapidly across the edge--discouraging formation of a dead-air zone from which spray readily precipitates onto the edge. The thin edge also presents a smaller direct target for ink droplets. The serrations may enhance transport by (1) promoting a more-favorable balance between laminar and turbulent flow; or (2) enabling air passage between opposed surfaces of the plate--from underside to top surface--creating an updraft to lift the flow away from the edge; or (3) both. To minimize running of liquid ink along the plate, the plate is mounted essentially all exposed to heat from a heater whose main purpose is drying ink on the print medium: this raises the plate temperature and so promotes drying of ink on the plate too. To further minimize running of liquid ink along the plate toward the edge, the edge panel is at a very shallow angle; and the air-flow provisions mentioned above also help carry away liquid carrier, from whatever ink does fall onto the edge, thus accelerating drying. To minimize brushing off even a slight accumulation of ink (liquid or dry) onto the medium, the serrations also raise most of the edge away from the medium.

BACKGROUND 
1. Field of the Invention 
This invention relates generally to machines and procedures for printing 
text or graphics on printing media such as paper, transparency stock, and 
other glossy media; and more particularly to apparatus and methods that 
construct text or images from individual marks created on the printing 
medium, in a two-dimensional pixel array, by a pen or other 
liquid-ink-ejecting marking element or head that scans across the medium. 
The invention is particularly beneficial in printers that operate by an 
inkjet process. That process discharges individual ink drops onto the 
printing medium. 
2. Related Art 
U.S. Pat. No. 5,065,169, of Vincent et al., introduces the importance of 
controlling pen-to-printing-medium distance, and flatness of the medium, 
in an inkjet printer. Vincent discloses one way of performing those 
functions by means of a spacer formed as a skid, roller or the like that 
travels with the pen. 
Systems following Vincent addressed a more-difficult problem of performing 
like functions in staggered-multiple-pen systems--where traveling skids or 
rollers were problematic due to the tendency of the roller or skid on a 
trailing pen to smear the ink laid down by a leading pen. These later 
systems provided stationary hold-down plates, sometimes called "shims", 
intended to restrain the print medium against print-medium deformation 
such as curl or cockle. 
Such systems were not fully effective in controlling such deformation. As a 
result those systems were sometimes subject to print-medium crashes, 
particularly near the leading edge of each sheet, and degraded image 
quality due to curling and other flight-time-related errors--particularly 
along the lateral edges over the full height of each sheet. 
These limitations were especially noteworthy in conjunction with use of 
ink-drying heaters and ink-spray-removal blowers--modern developments 
whose objects are to reduce drying time for nonabsorbent media and to 
carry away waste ink spray, but which unfortunately have some tendency to 
aggravate curl and cockle. Waste ink is common in inkjet systems in the 
air above the print medium, whether persisting as minute spray droplets or 
present as recondensable vapor, and is advantageously carried off gently 
in an exhaust air stream to avoid its deposition onto the printing medium. 
The above-mentioned related patent document of Broder et al. heralded a 
significant improvement in hold-down-plate arrangements for controlling 
pen-to-print-medium distance and print-medium flatness. The Broder system 
accommodates operation of staggered multiple pens, without smearing of 
leading-pen marks by trailing pens. It also accommodates such pens when 
used to print on glossy media, and with a print-zone heater and 
spray-removal blower, while controlling print-medium deformation and 
avoiding so-called "paper crashes". 
Broder et al. obtained these improvements by introducing a dual guide 
system of central and lateral hold-down plates that restrain the print 
medium in a coordinated way. The central plate is upstream from the pen or 
pens, in part angled longitudinally down into contact with the print 
medium, and extends laterally across the width of the medium except in one 
or more regions that are laterally near the engagement of a print-medium 
advancing device. 
The other, lateral, guide system is positioned laterally outboard from the 
pen, and extends laterally across the medium only in one or more regions 
laterally near the engagement of the advancing device. These "one or more 
regions" preferably are only near the lateral edges of the medium. 
Thus the two guide systems complement each other in function. The first 
guide restrains the medium over an area that stops short of the lateral 
edges of the medium; and the second is preferably bifurcated and disposed 
laterally in two directions from the pen, restraining the medium across 
only its lateral edges. 
Despite these very favorable developments due to the teachings of Broder et 
al., certain imperfections have been noted in the quality of documents 
printed with the described system. In particular, spurious ink marks 
occasionally appeared in the printing--often transverse straight lines, 
generally at various regions of the printing-medium width and in the color 
of whatever ink was being used in the printer. 
The appearance of these linear markings was erratic in time, and seemed to 
neither correlate with any feature of the document being printed nor 
exhibit the characteristic pixel structure of the inkjet printing process. 
The marks, however, were very evidently associated with quantities of 
liquid ink seen on the top surface of the horizontal panel 121h (FIGS. 8 
and 9) and angled panel 121a of the central hold-down plate 121, and ink I 
which was seen running down the angled parts 121a of its top surface 
toward the straight edge 121e of the plate, and indeed on the edge 
121e--from which ink was being transfered from the edge to the printed 
sheets 30. The upper one of the angled panels 121a is particularly steep, 
about twenty-five degrees from horizontal. 
In the earlier configurations in which these phenomena were observed, the 
guide plate 121 was mounted above an adjacent plenum cover 50 (in this 
document not distinguished from the plenum generally) and pressed very 
lightly though firmly on the printing medium 30. The guide plate 121 
included a generally horizontal panel 121h, and downward angled panels 
121a--terminating in a straight, blunt edge 121e. 
A rear panel 121r served to stiffen or rigidify the guide plate 121. A 
section 50r of the plenum cover 50, roughly several centimeters from the 
print zone Z, was bent upward to help hold thin plastic paper guides (not 
shown) below the cover, leaving a narrow window 50w in the plenum cover 
50. 
The medium 30 advanced (from left to right in FIGS. 8 and 9) above a 
supporting grill 73 with orifices 74 and beneath the pens 10--while the 
pens 10 traversed along a direction which in FIG. 8 is in and out of the 
plane of the paper. Nozzles 11 forming part of each pen 10 discharged ink 
toward the top surface of the print medium 30 in the print zone Z. 
A preheater 78' and a heater 78 shown schematically to the left of and 
below the supporting grill 73 were provided to predry the print medium and 
to speed drying of ink deposited on the printing medium 30--to form a 
desired image. Air was moved slowly and gently from right toward left (as 
drawn in FIGS. 8 and 9) to carry away waste ink spray as droplets, and 
possibly components of the ink formulation in vapor form. This air 
movement was provided by a blower--not shown, but along a path that begins 
with the plenum structure 50 at left in the drawings--which sucked air 161 
away from the unprotected and already-imprinted regions of the print 
medium, across 162 the print zone Z and into the plenum 165 toward 168 the 
blower. 
In relation to the direction 33 of print-medium 30 movement, the hold-down 
guide 121 was at all times upstream from the pens 10. Thus it was not 
physically possible for the guide 121 to pick up ink by brushing it from 
the medium 30; and there was no path for ink migration directly from pen 
reservoirs to the guide plate 121. 
The source of this ink deposit was accordingly recognized as precipitation 
of waste ink from the air in the print zone Z. In a representative inkjet 
printer, as outlined above, a blower moves that air slowly away from the 
print zone Z to prevent significant amounts of the spray from falling, 
precipitating or otherwise being deposited onto the sheet being printed. 
This ink-spray-transporting air flow is preferably routed away from 
unprotected areas of the document--where the waste spray might settle onto 
those areas and so spoil the printed image. No protective structure is 
present or desirable in the downstream direction, which is to say the 
direction 33 of print-medium 30 advance; but the hold-down plate 121 
offers to serve as a shield over the print medium in the opposite, 
upstream direction. 
It is for this reason that advantageously the drying-air flow 161-168 is 
made to flow in that opposite direction, toward 162 and past (above) 165 
the hold-down plate 121--or in other words counter to the direction 33 of 
print-medium 30 movement. 
As can now be appreciated, this configuration was originally thought to 
have disposed of the waste-ink spray with some finality. In the 
more-demanding environment of close curl/cockle control and high image 
throughput, however, the same waste spray can come back to haunt the 
system. 
The plate 121, while thus upstream along the direction 33 of 
printing-medium 30 movement, is downstream along the direction 161-168 of 
air movement created by the drying blower. Hence the waste ink spray moves 
toward, and should move over and past, the plate 121--into the blower 
plenum structure 50 where it can harmlessly precipitate or be filtered out 
of the air stream, or both. 
As will now be understood, the above-mentioned ink deposits, ink flow I, 
and undesirable markings all resulted from failure of some of the waste 
ink to pass completely over and beyond the guide plate 121. 
Less clear, heretofore, was why this ink was building up where it was, on 
the plate 121 immediately adjacent to the print zone Z; and what could be 
done to prevent it from doing so or neutralize its effects; and how such 
preventive measures might be implemented. As can now be seen, important 
aspects of the technology which is used in the field of the invention are 
amenable to useful refinement. 
SUMMARY OF THE DISCLOSURE 
The present invention introduces such refinement. It resolves the 
mechanisms of ink appearance on the guide-plate top surface and edge--and 
goes on to offer simple but elegant arrangements for interfering with 
those mechanisms and so substantially eliminating the objectionable 
markings. 
Before offering a relatively rigorous discussion of the present invention, 
some informal orientation will be provided here. It is to be understood 
that these first comments are not intended as a statement of the 
invention. 
A portion of the creative contribution associated with the present 
invention is believed to reside in understanding and explaining the 
accumulation of ink on the guide plate, and its transference to the 
printing medium. To control print-medium deformation, the guide plate 121 
(FIGS. 8 and 9) must gently but firmly contact the medium 30; and in 
production of modern high throughputs the amount of spray generated is 
greater than ever before. 
The blower was provided to suck this relatively large quantity of fine ink 
spray, and perhaps some vapor, above and across the guide-plate edge 121e 
into the exhaust plenum structure 50. The desired air flow across the edge 
121e, however, was evidently perturbed by creation of a dead-air zone 163 
at the edge 121e of the guide plate 121. 
We believe that the relatively tall (0.2 mm), blunt edge 121e of the plate 
121 in earlier configurations tended to promote this dead-air region 163. 
It appears to us that ink particles or vapor, or both, were trapped in or 
at least decelerated by this dead-air zone 163. 
From this zone 163 the particles and/or vapor evidently dropped and/or 
condensed onto the top surface of the plate 121, near the edge 121, and 
also directly onto the edge 121e of the plate (and in some cases perhaps 
even directly onto the printing medium 30). Particles and/or vapor that 
were only decelerated at, rather than trapped in, the dead-air zone 163 
perhaps fell from the emerging stream 164 onto the top of the plate 121 
somewhat further from the edge 121e. 
As will be understood, air 164 just emerging from the dead zone or climbing 
to detour above it might well have a forward velocity component 
significantly lower than in other segments of the flow path. In any event, 
ink deposited on the top of the plate 121 and near its edge 121e, in 
liquid form--more quickly than it could dry there by evaporation of its 
liquid carrier. Also, at system startup the cool plate 121 promotes 
condensation. 
At the same time the blunt edge 121e of the guide plate 121 formed a 
relatively tall target of opportunity for stray ink drops or vapor. We 
believe that a part of the marking problem arose from direct deposition 
onto this edge 121e. 
In any event deposition on the top surface of the plate 121 continued until 
a critical accumulation of liquid was reached--at which point there was 
enough volume of ink to run as liquid ink I down the inclined surfaces 
121a of the plate, toward and to the edge 121e of the plate. Then the ink 
was transfered or brushed off from the straight edge 121e of the plate, 
either as liquid flow or as solid, dried ink, onto sheets 30 being 
printed. 
It will be appreciated that one satisfactory solution is not simply to 
reverse the blower direction 161-168. Clearly some other arrangement is 
needed if one intends to entirely prevent deposition of waste ink on the 
guide plate 121, for reversing the air flow would simply resurrect the 
originally recognized problem of ink-carrying air dropping waste spray 
onto finished parts of the printing. 
On first glance at FIGS. 8 and 9 it might be supposed that a solution to 
this problem could be found in rerouting the air flow upward into a 
tighter contour next to the pen or pens. In such a configuration for 
example the air might be moved in either longitudinal direction relative 
to the print-medium path, and/or perhaps even laterally (in and out of the 
plane of FIG. 8). 
Such solutions, however, would require a major restructuring of the system 
hardware--possibly including even the printer cabinet. Even beyond 
daunting cost considerations, the full repercussions of such a 
fundamentally different plumbing geometry would likely include a 
succession of other new difficulties involving noise, vibration, and 
operator and maintenance access to the pen, as well as myriad 
unanticipated problems. 
Instead a solution has been reached that is confined--in area, character 
and scope--to the dimensions of the problem. That solution recognizes the 
root problem as aerodynamic and liquid-dynamic, in particular relating to: 
entrapment of ink droplets or vapor, or both, in a dead-air zone 163 at the 
edge 121e of the guide plate 121, from which zone 163 (and the immediately 
following flow region 164) the droplets/vapor dropped/condensed onto the 
top and edge 121e of the plate 121; 
running of the thus-deposited liquid ink I from the top of the plate 121 
toward its edge 121e; and 
brushing/running off, of ink in liquid/dry form(s) from the edge 121e onto 
the medium 30. 
The solution further includes defending against each of these mechanisms by 
a relatively subtle restructuring of the guide system itself. This 
restructuring provides respective means for minimizing deposition of ink 
on the top and edge of the plate, minimizing running of ink along the top 
of the angled panels (and preferably eliminating the steeply angled 
panel), and minimizing transfer of ink from the edge onto the printing 
medium. 
These three means include in part an aerodynamic reconfiguration of the 
critical edge of the guide plate, and in part a related simple 
reconfiguration of the mounting of that plate. The earlier plate edge 121e 
is straight and continuous, providing no path for updraft of air from 
beneath the plate 121: such a path if present could have helped disrupt 
dead air 163 at the interface, as well as drying ink along the edge 121e 
itself. 
Furthermore the earlier positioning of the guide-plate 121h 
horizontal-panel attachment region at the top of the exhaust-plenum cover 
50 tended to isolate the plate 121 thermally from the paper-preheater 78' 
and the ink-drying heater 78 in its enclosure 71--it being understood that 
despite the solid walls 72, 77 about the heater space 71 considerable heat 
does radiate and convect 76 to the walls 72, 77 and thence toward the 
underside of the plenum cover 50. The result of this positioning was a 
relatively low guide-plate 121 temperature, and accordingly a tendency to 
keep the deposited ink in liquid form long enough for it to run as liquid 
ink I to the edge 121e. 
A comparatively steep angle B (FIG. 8) of the lower of the two angled 
panels 121a, relative to the horizontal, was another factor aggravating 
the tendency of the guide plate 121 to serve as a ramp for running of the 
liquid downward--leading liquid ink I toward the print medium 30. Steeper 
angles increase the rate of ink flow I toward the medium relative to the 
rate of ink-carrier evaporation; in earlier apparatus the edge angle B, 
when the edge was not deflected by contact with such printing medium, was 
in the range of eight to nine degrees. 
Further the upper of the two angled panels 121a was at a very steep 
inclination of about twenty-five degrees. This angle led to very rapid 
flow down that panel and liquid accumulation on the lower angled panel. 
Furthermore the plate 121 had a straight edge 121e, across the full width 
of the printing medium 30. As a result any ink arriving at the edge 121e 
of the plate--by the mechanisms just described--was essentially placed in 
contact with the print-medium 30 surface and very likely to be brushed off 
(as for example by movement of the medium 30 itself), or perhaps even 
shaken off, onto the printing medium 30. 
Reversing these several adverse influences provides several potential 
corrective factors. Such correcting effects in combination have been found 
to very greatly reduce or eliminate--depending on the quantities of ink 
discharged in a given user's applications--the incidence of the 
objectionable markings described above. 
In all cases the invention reduces ink deposition at least to the point 
that the problem is eliminated with occasional operator intervention to 
clean the plate. The invention also appears to facilitate such cleaning. 
Now with these preliminary observations in mind this discussion will 
proceed to a perhaps more-formal summary. The invention has several main 
aspects or facets, which are capable of practice independently of one 
another; however, for best enjoyment of the advantages of the invention 
they are preferably practiced together. 
In preferred embodiments of all these major facets or aspects, the present 
invention is apparatus for printing images, by marking with a liquid-base 
ink, on a printing medium. This apparatus includes some means for 
supporting the medium: for purposes of breadth and generality in 
describing the invention, these means will be called simply the 
"supporting means". 
The apparatus also includes a marking head disposed for marking on the 
medium; and some means for engaging the medium and for advancing the 
medium, in a particular direction, past the marking head. Again for 
purposes of generality and breadth of description we will call these 
last-mentioned means the "engaging and advancing means". 
In addition the apparatus has some means for vertically restraining the 
medium--in an area that is upstream from the marking head in relation to 
the above-mentioned "particular direction" of medium advance. For 
generality these means will be designated the "guide means". The guide 
means have a print-medium-contacting edge. 
Also included in the apparatus are some means for establishing, above the 
medium and the guide means, air flow to carry airborne waste ink away. 
These "air-flow establishing means" operate to carry the waste ink away 
from the marking head in a direction that is counter to that same 
"particular direction" of medium advance. 
Now we shall refer in particular to apparatus according to preferred 
embodiments of a first primary facet or aspect of the invention. In 
addition to the common elements introduced in the preceding four 
paragraphs, this apparatus also includes some means for minimizing 
deposition of ink from the air flow onto the guide means. Once more for 
breadth and generality, we shall refer to these means as the 
"deposition-minimizing means". 
The foregoing five paragraphs may be a description or definition of 
preferred embodiments of the first main aspect of the present invention in 
its broadest or most general terms. 
In preferred embodiments of a second main facet of the invention, the 
apparatus includes--in addition to the common elements already 
enumerated--some means for minimizing running of liquid ink along the 
guide means toward the edge. These will be called, for the reasons 
suggested earlier, the "liquid-running minimizing means". 
This may constitute a description or definition of preferred embodiments of 
the second main aspect of the invention in its most broad or general 
terms. 
In preferred embodiments of a third primary aspect or facet of the 
invention, in addition to the common elements the apparatus includes some 
means for minimizing transfer of ink from the guide-means edge onto the 
medium. These will be called the "transfer-minimizing means". 
This may serve as a description or definition of preferred embodiments of 
the third main aspect of the invention in its most general or most broad 
terms. 
In preferred embodiments of still a fourth major facet or aspect of the 
invention, the apparatus includes (together with the common elements) a 
plenum cover disposed upstream of the marking head in relation to the 
particular direction of medium advance; and the guide means are mounted to 
the undersurface of this plenum cover. The apparatus according to this 
fourth aspect of the invention also includes serrations defined in the 
guide-means edge. 
Further the edge has a very fine vertical dimension, and is at a very 
shallow angle of disposition relative to the horizontal. This may be a 
description or definition of preferred embodiments of the fourth major 
aspect of the invention in its broadest or most general form. 
Even in such general or broad forms, however, as can now be seen each of 
the main aspects of the invention resolves an important part of the 
previously outlined problems of the prior art. 
In particular by operation of the deposition-minimizing means discussed 
above in relation to the first main facet of the invention, the amount of 
ink depositing on and near the guide-means edge can be kept well below 
what can effectively dry there before it is able to run as liquid to the 
edge. As to the second primary aspect, the liquid-running-minimizing means 
defend against the overall problem at a different point in its 
development, by keeping to a very small value the amount of ink that is 
able to run to the edge. 
The transfer-minimizing means--introduced above in connection with the 
third main aspect of the invention--form still another line of defense. 
They mitigate the undesirable effects that arise from any ink that does 
arrive at the guide-means edge. 
As to the fourth main aspect of the invention, the mounting to the plenum 
cover, serrations, fine edge, and shallow angle all have beneficial 
effects as will be seen. Together they are successful in reducing the 
marking problem to an acceptable degree. 
Preferred embodiments of the several independent aspects of the invention 
in their broadest forms thus provide very significant advances relative to 
the prior art. Thus as noted earlier each of the main aspects of the 
invention may be practiced alone to gain a significant amelioration of the 
marking problem described above, and possibly for a given printing system 
any one alone, or any two alone, could be sufficient to provide 
satisfactory results. 
Nevertheless for greatest enjoyment of the benefits of the invention we 
prefer to use all the several independent aspects of the invention 
together in conjunction. Interestingly as will be seen at least one simple 
physical feature of apparatus according to our invention participates in 
forming more than one--and possibly all--of the beneficial means 
introduced in this section. (That physical feature is the serrated edge 
discussed below.) 
Moreover the invention is preferably practiced in conjunction with certain 
other features or characteristics which enhance its benefits. We prefer, 
for example, that the deposition-minimizing means of the first aspect of 
the invention include some means for enhancing air flow past the 
guide-means edge. 
These means--again in the interest of generality the "air-flow enhancing 
means"--aid in carrying ink spray rapidly away from the critical edge 
region. Thus they deter formation of a dead-air region from which ink can 
readily deposit onto the guide-means edge as in earlier apparatus. 
We further prefer that the air-flow enhancing means include serrations 
defined in the guide-means edge. With respect to only the air-flow 
enhancing means, we believe that these serrations operate advantageously 
by one or both of two mechanisms: 
enabling passage of updraft air between opposed surfaces of the guide 
means--i.e., from the underside of the guide means to the top surface of 
the guide means--thus potentially facilitating deflection of ink-bearing 
air flow away from the guide-means edge (and thus onward toward the 
exhaust plenum mentioned earlier); 
promoting a favorable balance as between laminar and turbulent flow, for 
purposes of moving the waste ink more smoothly and swiftly past the 
troublesome area (and safely into the plenum). 
The air-flow enhancing means further preferably comprise a very fine 
vertical dimension of the guide-plate edge; this further reduces the 
dead-air-zone tendency of the system. At the same time the fine edge may 
also present a less-probably-struck target for randomly falling spray 
droplets or condensing vapor, so that deposition directly onto the 
critical edge itself is minimized. 
Impingement of waste ink on the top of guide means, even closely adjacent 
to the edge, may be less severe than impingement on the very edge. (The 
reasons for this will become clear shortly in discussion of the 
liquid-running minimizing means associated with the second major aspect of 
the invention.) 
Even some very slight direct impingement on the print medium, just adjacent 
to the edge of the plate, may be less severe than impingement on the edge 
of the plate--since for each image area of the print medium such slight 
direct impingement would be extremely light and would be incremental 
rather than cumulative. If it is possible for ink to deposit directly on 
the edge (this possibility will be discussed below) then such a direct 
deposit, by comparison, is more likely to cause problems after protracted 
accumulation, when the quantity that can transfer onto the printing medium 
all at one time is large enough to create a severely conspicuous mark. 
The preceding paragraphs show that deposition in either direction from the 
vertical edge of the guide means may be preferable to deposition directly 
on the edge. Hence the small-"target"-edge phenomenon can possibly be a 
favorable and significant effect--although as noted elsewhere in this 
document the accuracy of this theory does not alter the effectiveness of 
our invention. 
Now we turn to preferable features related to the "liquid-running 
minimizing" means introduced above--in connection with the second aspect 
of the invention. These means are addressed to mitigating the effects of 
whatever ink does accumulate despite action of the deposition-minimizing 
means. 
As will be appreciated, these "liquid-running minimizing means" effectively 
serve as a second line of defense. We consider it preferable that the 
liquid-running minimizing means include a very shallow angle of 
disposition of the guide-means edge, relative to the horizontal. 
Quantitative evaluation of this condition is discussed later in this 
document. The mechanism by which the shallow angle deters running of 
liquid ink is simply to reduce the gravity-force component which is 
directed along the surface of the guide means--and so reduce the 
acceleration, due to gravity, of ink along that surface toward the edge. 
In principle the present invention is not limited to use in a printer 
system that includes a heater for applying heat to the print medium. A 
typical modern system, however, does include such a heater, for applying 
heat to the medium--generally at or near a print zone--to promote drying 
of ink on the medium. 
When our invention is used in such a system, we also deem it particularly 
preferable that the liquid-running minimizing means include disposition of 
substantially the entire guide means generally exposed to heat from the 
ink-drying heater. Such disposition promotes relatively rapid drying of 
ink that deposits on the guide means. The nature of this heat exposure is 
made more clear through discussion in greater detail later in this 
document. 
The operative mechanism here is to quickly dry, and thus stabilize, any ink 
on the guide-plate top surface: what dries in place cannot run to the 
edge. To enhance this effect, we prefer to attach the guide means at the 
undersurface of the plenum cover--rather than above the cover as 
previously. 
Still further the liquid-running minimizing means preferably include 
air-flow enhancing means such as already discussed above in connection 
with the deposition-minimizing means of the first major aspect of the 
invention. Enhancement of air flow does double duty in this way because 
the enhanced flow--in addition to deterring deposition--more effectively 
dries ink already deposited on the guide plate. 
Thus for example the serrated edge discussed earlier, whether its operative 
mechanism includes updraft generation or adjustment of 
laminar/turbulent-flow proportions, tends to help transport away liquid 
carrier from whatever quantity of ink does fall onto the guide-means edge. 
This effect amounts to rapid drying of that deposited material, and 
thereby deterrence of liquid flow along the guide means to the print 
medium. 
The air-flow enhancing means, operating in conjunction with the heater to 
rapidly dry ink at and next to the very edge of the guide means, make it 
relatively unlikely that ink can long persist on the edge in liquid form. 
It is this fact that makes impingement of waste ink on the top of the 
guide means--even immediately adjacent to the edge--relatively "less 
severe" as mentioned earlier. If such ink dries immediately next to the 
edge, there is some likelihood that it will never transfer to a sheet of 
print medium; but if it dries actually on the edge, then there is a fair 
likelihood that it will be brushed off onto the medium. 
As will now be understood, running-minimizing means in accordance with our 
invention actually can operate in part by controlling the relative rates 
of liquid running vs. liquid drying. 
Next we come to our preferences as to the "transfer-minimizing means" 
associated with the third main aspect of the invention. These preferably 
comprise serrations, formed in the edge of the guide means, that raise 
most of the edge out of contact with the print medium--so that even some 
liquid accumulation along much of the edge may escape being transfered to 
the medium. 
As can now be seen, serration is particularly useful in that it contributes 
to operation of: 
the deposition-minimizing means (by air-flow enhancement that carries ink 
past the dead air at the edge), 
the liquid-running minimizing means (also by air-flow enhancement--but in 
its role of promoting drying), and 
the transfer-minimizing means (by elevating nearly all of the guide-means 
edge out of contact with the print medium).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As FIGS. 1 through 7 show, in preferred embodiments the invention provides 
a guide plate 21 that is mounted preferably to the underside, or in any 
event below, an adjacent plenum cover 50. The guide plate 21 includes a 
generally horizontal mounting panel 21h, and very shallowly 
downward-angled edge panel 21a with serrations 21s and tips 21t. (No 
steeply angled panel is present.) 
This angled panel 21a is spring-mounted to press very lightly though firmly 
on the printing medium 30. A rear panel 21r serves to stiffen or rigidify 
the guide plate. 
A section 50r of the plenum cover 50, roughly several centimeters from the 
print zone Z, is bent upward and accommodates the stiffening panel 21r of 
the guide plate. This processing leaves a narrow window 50w in the plenum 
cover 50. 
The medium advances (from left to right in FIGS. 1 and 2) above a 
supporting grill 73, with apertures 74, and beneath the pens 10--while the 
pens 10 traverse along a direction which in FIG. 1 is in and out of the 
plane of the paper. 
The pens 10 meanwhile eject ink from nozzles 11 to form desired images on 
the top surface of the print medium 30, in the print zone Z. Flexible thin 
plastic fingers (not shown), below the guide plate help guide the leading 
edge 31 of the print medium smoothly under the angled panel 21a--and 
thence very reliably under the pens. 
A preheater 78' and heater 78 shown schematically to the left of and below 
the supporting grill 73 are provided mainly to predry the print medium and 
to speed drying of ink deposited on the medium 30 to form a desired image. 
In accordance with the present invention, however, the preheater 78' and 
heater 78 are also turned to the task of speeding the drying of ink that 
deposits--undesirably--onto the guide plate 21. 
Air 61-68 is moved slowly and gently from right toward left (as drawn in 
FIGS. 1 and 2) to carry away waste ink spray as droplets, and possibly 
components of the ink formulation in vapor form. This air movement is 
provided by a blower--not shown, but along a path that begins with the 
plenum structure 50 at left in the drawings--which sucks air away from the 
unprotected and already-imprinted regions of the print medium 30 and into 
the plenum structure 50. 
The guide-plate edge or tips 21t preferably are coined or ground down to a 
fine thickness, thereby reducing the surface area for deposition and 
minimizing the dead-air space formed by the edge functioning as a wall. 
The plate 21 is of stainless steel, and its resilience--particularly as to 
the vertical direction of movement of the angled panel 21a for the desired 
print-medium-retaining action--is enhanced and adjusted to precisely a 
desired degree. 
This enhancement and adjustment are provided by a pattern of transverse 
slits 22 and longitudinal slits 23, which define thin longitudinal strips 
24 serving as springs. This system also localizes the vertical flexure 
along, roughly, a line or region roughly 3 cm (11/4 inch) from the guide 
edge 21t--between the horizontal and angled panels 21h, 21a--while 
preventing lateral pivoting or rotation of that portion 21a of the guide 
21. 
Serrations 21s are formed at the edge 21s/21t of the guide plate 21, with 
one object of enhancing air flow across the guide-plate edge. It is 
difficult to say whether a prime mechanism for such enhancement is (1) 
favorable influence on the ratio of laminar to turbulent flow 63 over the 
plate edge 21s/21t; or (2) enabling of an updraft 69 from ambient, via the 
space beneath the guide plate, to join the primary air flow 61-65 along 
the top of the print medium and into 67 the plenum structure 50; or (3) 
both these effects; or (4) still other effects. 
In regard to the possible mechanism of an air updraft 69 through the 
serrations 21s, as can be appreciated from comparison of FIGS. 1 and 7 no 
such mechanism is unavailable in earlier configurations when a piece of 
printing medium 30 is present in the system. Under those circumstances in 
earlier configurations the medium 30 and straight edge 121t together 
obstruct air flow from the undersurface of the plate 121 into the air 
stream 161-168 above the medium 30 and plate 121. (FIGS. 1 and 8, which 
include the piece of printing medium 30, may accordingly make this 
relationship more clear than FIGS. 2 and 9.) 
The effectiveness of our invention does not depend upon determining which 
of the four above-enumerated theoretical interpretations (or combination 
of them) is correct. Observation of the finished apparatus and its printed 
images makes clear that the serrations 21s--by whatever mechanism--have a 
strong and apparently beneficial effect on the system operation. 
More specifically, such observation reveals a remaining pattern (not shown) 
of ink deposition on the top of the guide plate, when all the elements of 
the present invention are in use together. This pattern includes very 
conspicuous narrow longitudinal streamers or fingers of ink that are 
consistently aligned along the guide plate with the serration tips, 
respectively. 
These streamers in their entirety, at least after printing of some one 
hundred fifty to two hundred sheets, using the invention, are 
well-separated (along the direction 33 of print-medium 30 movement) from 
the serrated edge 21s and tips 21t. The ink deposition in the areas 
between streamers--which is to say, aligned with the cutaway areas 21s 
between serration tips 21t--is even further separated from the serrated 
edge than the streamers are. Hence the serrations 21s very evidently 
affect the air flow 63, 64 across the edge 21s, 21t in a significant way, 
a way which appears to be favorable. 
To the extent that an updraft 69 mechanism is operative, additional 
favorable results are thought to include particularly effective drying 
along most of the edge--i. e., again in the cut-away portions 21s, between 
the serration tips 21t. As will be understood this effect is in addition 
to introduction of an upward velocity component (not shown) to further 
smoothly lift the stream of ink vapor away from the edge--and so to 
minimize or help dissipate formation of dead air at the interface. 
A relatively small amount of ink spray which does deposit along and near 
the edge 21s/21t tends to dry very quickly. If desired for esthetic 
reasons--or in cases of rather heavy ink usage in which adverse quantities 
of ink eventually migrate near or to the edge--an operator of the 
equipment can periodically wipe away this ink deposit. 
It appears to us that the operator can do so much more effectively than 
before. This improvement is due to the fact that nearly all the edge of 
the plate is now defined along the portions 21s of the serrations that are 
drawn upward and rearward (relative to the medium-advance direction), out 
of contact with the medium 30 and therefore more accessible for cleaning 
efforts. 
Representative approximate dimensions for the guide plate 21 in the 
preferred embodiment are collected here: 
______________________________________ 
cm inch 
______________________________________ 
width (transverse to the medium 30) 
18.4 7.2 
length (parallel to the medium 30, 
5.5 2.2 
from the stiffening-panel 24r rear 
edge to the serration tips 21t) 
thickness of the body 21r, 21h 
0.02 0.008 
length of the: 
angled edge panel 21a 3.0 1.2 
horizontal panel 21h 1.4 0.55 
stiffener (rear) panel 21r 
1.1 0.43 
width of each spring 24 
0.25 0.1 
spacing between adjacent springs 24 
2.9 1.1 
length of each spring 24 
1.8 0.7 
number of serrations (cutouts) 21s 
24 24 
serration 21s periodicity 
0.8 0.3 
serration 21s depth 0.3 0.11 
radius (about a vertical axis) 
0.03 0.01. 
of the serration tips 21t 
______________________________________ 
The upper steeply angled panel of the earlier configurations is entirely 
eliminated. Liquid accumulation due to rapid flow down that panel is 
correspondingly avoided. 
The edge panel 21a of the guide plate 212 is advantageously at a very 
shallow--but nonzero--angle A to the horizontal. In some contexts the term 
"very shallow" might be regarded as merely a relative concept and left to 
subjective considerations, but that is not so in this case as the value of 
the angle is preferably selected on the basis of objective criteria as 
follows. 
We believe that the panel 21a should not be horizontal, as that would 
remove the beneficial effects of the serrations in raising the cut-away 
portions 21s of the edge out of contact with the medium 30. Use of a 
horizontal panel could also render very difficult the achievement of good, 
uniform control of the vertical spring force against the medium 30. 
On the other hand, to provide improvement from the earlier configurations 
discussed above, this angle A--when the edge panel 21a is not deflected by 
contact with the supporting grill 73 or the printing medium 30--is 
advantageously made less than the eight to nine degrees of those earlier 
configurations. (As will be understood, to determine the angle of the 
panel 21a relative to the horizontal when the edge is not deflected by 
contact with the grill 73 or medium 30, it is necessary to consider a 
free-standing guide plate 21 held with its mounting panel 21h at the angle 
(e. g,, here nominally horizontal) which that panel 21h assumes when in 
assembled position against the plenum cover 50.) 
Further in order to make a significant difference the edge angle A, when 
the edge panel 21a is not deflected by contact with the grill or medium, 
is preferably less than a value that may likely be critical, about six to 
seven degrees. The criticality in this regard arises from a tradeoff or 
compromise. 
One consideration is the need for an angled, nonhorizontal panel 21a; a 
contrary consideration is the adverse effects of steep angles. We consider 
an ideal value to be approximately six degrees--or, when the angled edge 
panel 21a is deflected by contact with the grill 73 or medium 30, 
approximately four to five degrees. 
Analogously the guide-plate edge and particularly tips 21t in accordance 
with our invention should have a very fine vertical dimension d (FIG. 7). 
This terminology does not leave the value of the dimension as a relative 
or subjective concept, for as a practical matter and for purposes of this 
document we mean a dimension selected in accordance with a tradeoff. 
On one side of this tradeoff is the desirability of minimizing the height d 
of the edge and particularly tips 21t. This consideration has aerodynamic 
and "target"--minimization ramifications as previously explained. 
Primary considerations on the other side of the tradeoff are, primarily, 
the cost of producing a very thin edge or tips 21t and, secondarily, the 
need for some mechanical or structural integrity in holding down the 
printing medium. Thus for example an edge height d of 0.03 mm (0.0012 
inch)--for each serration tip 21t--is readily provided by grinding, but is 
considerably more expensive than an edge height d of 0.06 mm (0.0024 inch) 
that can be obtained by coining (an impact process). 
Our preference is for the coined edge, which turns out to serve adequately, 
at least when used in conjunction with the several other features 
described in this document. To make an improvement over earlier 
configurations in this regard, the vertical dimension d of the tips should 
be significantly less than about 0.2 mm (0.008 inch)--which was the edge 
height in earlier configurations, the same as the full thickness D (FIG. 
7) of the stock. 
Further to optimize this improvement with respect to performance, the 
dimension d should be less than a value, which may likely be critical, of 
about 0.1 mm (0.0.004 inch). We consider the ideal value, taking cost into 
account, to be the above-mentioned 0.06 mm (0.0024 inch) for a coined 
edge. 
We regard it as particularly useful to attach the guide means 21 at the 
undersurface of the plenum cover 50--or in any event for this purpose 
equivalently below the cover--rather than above the cover as in earlier 
configurations. In the earlier geometries the cover 50 tended to insulate 
the guide plate 21 from the preheater 78' and heater 78, thereby 
discarding the potentially beneficial effects of heating upon the 
reevaporation of liquid-ink components from the plate 21. 
As mentioned in a preceding section, we prefer in this regard to dispose 
substantially the entire guide means 21 generally exposed to heat from the 
preheater 78' and ink-drying heater 78. By this we mean to encompass, 
among others, configurations in which the plenum cover 50 is not 
interposed to insulate the guide means 21 from the preheater 78' and the 
heater 78. 
As can be seem from FIGS. 1 and 8, the heater 78 has a compartment wall 72, 
77 of its own which to some extent does shield the guide means 21 from 
exposure to the heater 78 itself, directly. In accordance with our 
invention, however, the guide means 21 are exposed to heat 76 radiated 
(and convected) from the wall 72, 77, as well as whatever heat may issue 
through the support grill 73 and from the preheater 78'. 
It will also be recognized that during much of the system operation some 
piece of printing medium 30 is interposed between the heater 78 and the 
guide means 21. For present purposes, however, the print medium 30 is not 
always present and is not an effective insulator; thus substantially the 
entire guide means are effectively, adequately warmed by heat 76 issuing 
despite the presence of the medium 30. 
In configurations not incorporating any of the features of the present 
invention, objectionable marking of the print medium 30 was seen regularly 
after printing as few as five pages. Furthermore, wiping the accumulated 
ink from the guide-plate edge 121e was very awkward and relatively 
ineffective because the entire edge 121e (FIG. 8) was pressed against the 
support grill 73 or print medium 30. 
In practice of the present invention that figure is now elevated well 
beyond two hundred sheets. In addition, as mentioned earlier operator 
efforts to clean the plate are significantly facilitated by the function 
of the serrations 21s in moving most or nearly all of the guide-plate edge 
up away from the support 73 or medium 30. 
While various examples and embodiments of the invention have been shown and 
described, it will be appreciated by those skilled in the art that the 
spirit and scope of the invention are not limited to the specific 
description and drawings herein, but extend to various modifications and 
changes all as set forth in the following claims.