Printer assembly

A hybrid printing system adds color accents to documents produced by high speed black on white printers using wax based inks. The color indicia is printed while the moving documents are supported against a curved surface and the documents are heated to an appropriate temperature for use of a wax based ink between black printing and color accent printing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the processing of printed documents and, 
particularly, to the addition of indicia comprising one or more colors to 
previously printed black on white documents. More specifically, this 
invention is directed to a document processing system having a single 
paper path and the capability of being interfaced with a high speed 
monocolor printer and, especially, to apparatus employing multiple print 
heads to add colored indicia to text or graphics on documents exiting the 
interfaced printer without reducing document throughput rate or requiring 
redirection of the documents exiting the interfaced printer into multiple 
processing paths. Accordingly, the general objects of the present 
invention are to provide novel and improved methods and apparatus of such 
character. 
2. Description of the Prior Art 
While not limited thereto in its utility, the present invention enables the 
addition of indicia, in selected color(s), to printed documents exiting a 
high speed electrographic or xerographic printer, i.e., in a preferred 
embodiment the present invention is a high volume printer with accent 
color capability. There has been a long standing and unmet need in the art 
of the ability to provide color enhancement to conventional black on white 
printed documents. Previous attempts to satisfy this demand, as will be 
briefly described below, have been unsatisfactory. For example, there has 
been a failure to address the need to preserve the significant investment 
of potential users in their existing, installed black print data printers 
and, particularly, to recognize that this investment has been made with a 
primary objective of increasing printing speed. 
As an example of the prior art attempts to achieve high volume printing 
with multiple color capability, two color printing capability has recently 
been added to conventional xerographic apparatus by using two developers, 
one for black and one for a single accent color, operating at different 
voltages. This approach, however, has the disadvantage that it cannot 
offer full spectrum color capability on a high speed printer. 
For users requiring or desiring more than a combination of black plus a 
single accent color, the only previous alternatives have been low speed 
systems characterized by high labor intensity and/or expensive investment 
in equipment. By way of example, a xerographic process employing multiple 
developers may be employed. Printers utilizing multiple developers are 
slow, typically five pages per minute maximum, and expensive. Ink jet 
printer technology also offers multiple color capability. However, the 
prior art ink jet technology employed water-based inks which imposed 
restrictions on the choice of paper being processed and, generally, 
presented problems with permanency as a result of moisture absorption. It 
is to be noted that ink jet technology is available which employs print 
media which is liquid in the jet and solidifies upon impact, such media 
typically being wax based. While the use of wax based inks provides 
excellent full color range, previously available printers employing this 
technology were notoriously slow. 
Prior art transports for printing continuous forms employ rollers and web 
tension to drive the continuous form. Such transports are sensitive to 
changes in paper weight, moisture content, perforation strength and other 
paper characteristics and properties. Accordingly, previously available 
transports for continuous form paper were unsuitable for the overprinting, 
i.e., the addition of accent color, to previously printed documents 
because the requisite constancy of paper velocity could not be obtained. 
Prior art sheet feeders, similarly, had the inherent disadvantages that 
previously documents could not be consistently accurately positioned for 
the addition of color indication while achieving adequate throughout rate. 
SUMMARY OF THE INVENTION 
The present invention overcomes the above-briefly discussed deficiencies 
and other disadvantages of the prior art by providing a hybrid printer 
system, and particularly a combination of an electrographic or xerographic 
printing process and full color spectrum ink jet printing. The ink jet 
printing system is located immediately downstream of the electrographic or 
xerographic apparatus, which prints black text on white and, preferably, 
is interfaced therewith so as to define a continuous paper path. 
The present invention also encompasses a transport system which, in a first 
embodiment, reliably moves a continuous form or, in a second embodiment, 
reliably and serially moves individual sheets, comprised of various 
materials, sizes, thicknesses and textures. This transport system presents 
the documents, i.e., the pages to be printed, in orderly and predictable 
fashion for further processing. In accordance with a preferred embodiment, 
this further processing consists of high speed multi-color printing with a 
wax based ink. However, a transport system in accordance with the 
invention may be employed to deliver documents for imaging, 
personalization, labelling, etc. and these nondisclosed processing steps 
may be employed in conjunction with the multi-color printing. 
An accent color printing system in accordance with the present invention is 
comprised of an infeed module, a timing module, a placement module, a 
processing module which defines a convexly curved paper path, plural 
printheads juxtapositioned to the curved paper path, and a discharge 
module which may include a document stacker or other peripheral equipment. 
An object of the invention is to provide a printer capable of adding color 
indicia to a preprinted document. 
Another object is to provide a color accent printer capable of a throughput 
rate equal to the throughput rate of a high speed host printer. 
It is a further object of the invention to provide a printer capable of 
accurately depositing color indicia on a preprinted document. 
It is yet another object of the invention to provide a color accent printer 
capable of exercising sufficiently accurate temperature control over 
documents, particularly preprinted documents, to thereby permit high 
quality color printing by an ink jet print head employing a wax based ink. 
Still another object of the invention is to provide a paper transport 
system capable of accurate document positioning regardless of paper 
moisture content, paper thickness or other paper characteristics. 
It is still a further object of the invention to provide a paper transport 
path capable of supporting and positioning a document for high accuracy 
printing. 
These and other objects of the invention will be made clear from 
examination of the specification and drawings.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
With reference to the drawings, an accent color printer, indicated 
generally at 10 in FIGS. 1 and 5, receives a continuous form or web 16 of 
preprinted material for the addition of color indicia including text, 
and/or graphics and/or highlighting. An input interface 12, comprising a 
web control unit, functions to transfer the continuous form 16 of 
preprinted material from a xerographic or other type host printer 11 to 
the accent color printer 10. Typically, the host printer 11 will be a 
high-speed, single-color printing device reproducing multiple copies of 
the same document on a continuous form or web, or multiple copies of 
individual documents. 
The material comprising the continuous form or web 16 is typically a 
continuous length of paper having a row of tractor feed holes along each 
longitudinal edge. Documents are printed on the "pages" of the web in 
repetitive fashion. A predetermined number of tractor feed holes 
correspond to each page or document of the continuous form. Alternately, 
the continuous form may lack tractor feed holes, and the host printer 11 
will print a top of form mark on the continuous form 16 to designate the 
beginning of each document on the web. It should be recognized that the 
invention is not limited to accent printing on the same document or to 
accent printing only on a continuous form. As will be discussed below in 
the description of FIGS. 6-8, the invention is also applicable to single 
sheet printing of documents. For single sheet printing, alternative 
infeeds and outfeeds may be required. 
The input interface 12 serves as a buffer between the high-speed host 
printer 11 and the accent color printer 10. (See FIG. 5.) The input 
interface 12 is a mechanical connection which provides slack in continuous 
form 16 to compensate for variations between the throughput rates of the 
high-speed host printer 11 and the accent color printer 10. The input 
interface 12 is thus a web control which, in a manner known in the art, 
produces a free loop of continuous form 16 between the host printer 11 and 
the accent color printer 10. The input interface 12 further buffers 
differences in data transfer sequences and error recovery sequences for 
paper jams between the two printers 10, 11. 
The continuous form 16 exiting the input interface 12 is first fed into an 
in-feed system 18 of the accent color printer 10. (See FIG. 1.) The 
in-feed system 18 and the other components of the accent color printer 10 
are supported in a printer cabinet 24 having a cabinet frame 26. The 
in-feed system 18 comprises a plurality of rollers which cooperate to 
impart a continuous and consistent tension to the continuous form 16 
downstream of in-feed system 18. The continuous form 16 feeds through the 
in-feed system 18 in a generally S-shaped path over an upper in-feed 
roller 20 and around a lower in-feed roller 22. The upper in-feed roller 
20 is coupled to a chassis ground via a hysteresis clutch 21. The 
continuous form 16 is "grounded", i.e., held between, the upper in-feed 
roller 20 and pinch rollers 17. The pinch rollers 17 prevent slippage of 
the continuous form 16 on the upper in-feed roller 20. The hysteresis 
clutch 21 is a variable torque device settable at a preestablished level 
and embodied within the design to allow a web tension proportional to the 
torque. In operation, the hysteresis clutch 21 creates drag on the upper 
in-feed roller 20 to thereby tension the grounded continuous form 16. The 
tension added to the continuous form 16 should be low, typically 3/4 pound 
per inch of web. 
The continuous form 16 of preprinted material exiting the in-feed, i.e., 
tension control, system 18 is delivered to a heated roller 30. After 
passing over the heated roller 30, the continuous form 16 is guided to a 
vacuum belt conveyor, indicated generally at 32. 
The vacuum belt conveyor 32 supports, positions and moves the continuous 
form 16 for printing by a plurality of adjustable position print head 
systems 60 (only one of which is shown in FIG. 1). The vacuum belt 
conveyer 32 comprises a pair of parallel spaced apart, elongated generally 
D-shaped side frames 34. (See FIGS. 1 and 2.) The side frames 34 are 
substantially vertically oriented in the printer cabinet 24 and define an 
upper conveyor end and a lower conveyor end. The generally vertical 
orientation of the vacuum belt conveyor 32 permits a compact construction 
of the accent color printer 10; however, the accent color printer 10 is 
operable with the vacuum belt conveyor 32 at other orientations. Conveyor 
32 includes a lower belt drum 36 rotatably supported at the lower conveyor 
end between the side frames 34. An upper belt drum 38 is also rotatably 
supported between the conveyor side frames 34 at the upper conveyor end. 
The upper belt drum 38 is driven by a motor 40 through a drive belt 42. 
The speed of the motor 40 is controlled by the slack or a hanging loop of 
continuous form 16 created at the input interface 12. The length of a loop 
of the continuous form 16 is between the host and accent color printer and 
is monitored by the input interface 12. When the loop grows beyond a 
preestablished limit, the speed of the motor 40 is increased. When the 
length of the loop of the continuous form 16 falls below a preestablished 
limit, the speed of the motor 40 is decreased. Changes in speed of the 
motor 40 are made at a slow rate so as not to adversely affect print 
quality. 
Located between the side frames 34, and defining a curved or arced paper 
path between the belt drums 36 and 38, is a tension side sliding bed 44. 
The tension side sliding bed 44 comprises a platen which defines a 
generally arc-shaped, i.e., convex, surface over which a vacuum belt 50 
moves. Also positioned between the side frames 34, along the straight back 
edge of the frames, is a slack side sliding bed 48. The tension side 
sliding bed 44 is provided with a multiplicity of perforations 46. 
The side frames 34 are pivotally mounted to the cabinet frame 26 near the 
lower conveyor drum 36 to allow pivoting of the vacuum conveyor 32 away 
from the print head systems 60. The print head systems 60 are mounted to a 
print frame 62. The print frame extends from the top to the bottom of the 
cabinet 24. The print frame 62 is rigidly held in a fixed position by 
attachment to the cabinet frame 26 at the upper and lower ends of the 
print frame 62. 
The vacuum belt 50 is in the form of a continuous loop which travels over 
the upper belt drum 38, along the slack side sliding bed 48, around the 
lower belt drum 36 and along the tension side sliding bed 44 to return to 
the upper belt drum 38. The vacuum belt 50 provides a transport surface 51 
for moving the continuous form 16. The arc defined by the side frames 34 
and the tension side sliding bed 44 tensions the vacuum belt 50 over the 
tension side sliding bed 44 as the vacuum belt is driven by the upper belt 
drum 38. The tension in the vacuum belt 50 produces very smooth belt 
operation over the tension side sliding bed 44 without wandering or 
unevenness of belt motion. The vacuum belt 50 is provided with an 
arrangement of perforations 49 (see FIG. 3) over the entire surface of the 
belt. A belt tension adjuster 52 permits vertical motion of the lower belt 
drum 36 to adjust the tension in the vacuum belt 50 and to allow the axis 
of rotation of the lower belt drum 36 to be adjusted parallel to the axis 
of rotation of the upper belt drum 38. 
Accurate positioning of the upper and lower belt drums 36, 38 and the 
curved shaped of the tension side sliding bed 44 result in elimination of 
the requirement for edge registration of the vacuum belt 50. Consistent 
tracking of the vacuum belt 50 is significant since wander of the vacuum 
belt perpendicular to the paper path direction would cause lateral motion 
of the continuous form 16 with the result of deteriorated indicia print 
quality. Should edge registration of the vacuum belt 50 be desired, edge 
rollers (not shown) may be provided at an edge of the vacuum belt to 
continually stabilize the registration of the vacuum belt 50. Other 
methods of preventing belt wander, such as a fixed guide rail, could also 
be provided. 
The arc defined by the tension side sliding bed 44, in one reduction to 
practice, had a radius of approximately 96 inches. Modification in the arc 
radius can occur without compromising print quality, however, an 
approximate 96 inch radius has provided optimal results. Increases in the 
arc radius of over approximately 20%, or greater than approximately 120 
inches, result in a significant decrease in belt tension on the arced 
tension side sliding surface. Reduced tension leads to increased belt 
motion and therefore decreased print quality. The curved path of the 
vacuum belt 50 as it slides over the arced tension side sliding surface 
allows the continuous form 16 to remain in intimate contact with the belt 
50 for the length of the conveyor tension side. The curved path followed 
by the vacuum belt, furthermore, allows a very smooth running motion with 
little "hop" or displacement of the vacuum belt 50 from the tension side 
sliding bed 44 that could compromise print quality. The characteristic of 
intimate contact between the continuous form paper 16 and the vacuum belt 
50, combined with the smooth operation of the belt 50 on the conveyor 32, 
are critical for proper print registration and therefore high quality 
color indicia printing. 
The vacuum belt conveyor 32 supports the continuous form 16 on the vacuum 
belt 50 by creating a pressure differential across the form 16. This is 
accomplished by "evacuating" air from the interior chamber 56 of the 
vacuum belt conveyor 32, therefore drawing air in through the vacuum belt 
perforations 49 and tension side sliding bed perforations 46. Both 
conveyor side frames 34 define a series of air flow ports 53 which 
communicate with the vacuum chamber 56. A fan 54 is located over each port 
53 and affixed to a conveyor side frame 34. Ports 53 and fans 54 can also 
be provided on only a single conveyor side frame 34, depending on fan air 
flow capacity. The fans 54 exhaust air from the vacuum chamber 56, the 
chamber being defined in part by the side frames 34 and the sliding beds 
44, 48. 
The vacuum chamber 56 is separated into a series of vacuum compartments 73 
by perforated dividers 75. (See FIGS. 2 and 3.) The internal baffling of 
chamber 56 created by the dividers 75 reduces the overall requirement for 
vacuum. The use of separate but interconnected vacuum compartments 73 
results in a very uniform holding force over the entire transport surface 
51 of the vacuum belt 50. The uniform low pressure produced in the vacuum 
chamber 56 assists in preventing any wandering side to side by the 
continuous form 16 on the transport surface 51. The established pressure 
differential further allows the vacuum belt 50 to move the continuous form 
16 in the paper path direction. The curved shape of the transport surface 
51 and the uniform vacuum holding force on the transport surface 51 
results in an even tension on the continuous form 16, therefore providing 
an ideal surface for printing. 
Use of the vacuum belt conveyor 32 for transport of the continuous form 16 
further provides a transport system insensitive to changes in paper 
weight, moisture content, perforation strength and other variable 
characteristics of the paper comprising the continuous form 16. 
During the printing process, the vacuum belt conveyor 32 moves the 
transport surface 51 supporting the continuous form 16 past the multiple 
print head systems 60. For accurate and high quality printing, the 
transport surface 51 must provide highly accurate and wander-free dynamic 
positioning of form 16 as it moves past the print head systems 60. 
Vertical wandering, i.e., side-to-side movement perpendicular to the 
travel direction of the transport surface 51 of equal to or greater than 
0.003 inch will cause a visible print anomaly. 
The continuous form 16 containing the added color indicia printed in the 
manner to be described below, is drawn away from the vacuum belt conveyor 
32 near the upper belt drum 38. (See FIG. 1.) The continuous form 16 then 
travels downwardly to an outfeed system 98. The outfeed system comprises a 
single rotating outfeed drum 100, driven by a type AC motor 104, and 
multiple spring loaded contact rollers 102. The continuous form 16 is fed 
through a nip created by the outfeed drum 100 and the contact rollers 102. 
The AC motor 104 is coupled to the outfeed drum 100 by a drive belt 106. 
The outfeed drum 100 is driven so the nominal surface speed thereof is 
faster than the surface speed of the vacuum belt 50. The AC motor 104 is 
sized such that there is limited torque available and, accordingly, the AC 
motor 104 runs at a continuous slip angle so as to be at the same surface 
speed as the surface speed of the vacuum belt 50. The outfeed system 98 
thus maintains tension in the continuous form 16 as it exits the accent 
color printer 10. The continuous form 16 exiting the accent color printer 
10 via the outfeed system 98 is subjected to further processing such as 
cutting, stacking, compiling, etc. by post-printing document processors 
13. 
As noted above, color indicia, such as text, graphics and highlighting, is 
added to the documents that comprise the continuous form by an array of 
print head systems 60. The array of preferably eight print head systems 60 
are supported in juxtapositioned relationship to the tension side of 
conveyor 32 by the print frame 62. 
Referring to FIGS. 9 and 10, each print head system 60 comprises a print 
head support 64 and a print head 65. The print heads 65 each preferably 
employ an array of 96 ink jets to spray wax based inks. The print heads 65 
are evenly spaced along the paper path in the process direction by 
printhead supports 64 which are located in slots 66 on the printer frame 
62. Each print head support 64 comprises a print head carriage 180 mounted 
for movement on parallel printer tracks 182. The printer tracks 182 are 
oriented orthogonal to the travel direction of the transport surface 51. 
Backlashless actuator screws 184 precisely locate and fix the position of 
each print head carriage 180. Each actuator screw 184 is driven by a motor 
186 to position the printer carriages 180, and therefore the print heads 
65, orthogonal to the print path. The tolerance for the actuator screw is 
preferably at least 0.004 inches per foot to permit print head positioning 
of plus or minus 1/2 pixel or 0.0018 inches arranged in a direction 
orthogonal to the process direction. 
The print head positioning over the paper path utilizes an optical 
positioning sensor 188 and a reference gauge 189. The positioning sensor 
188 is mounted on the print head carriage 180. The reference gauge 189 is 
a precisely machined bar having indicator blocks 191 at precise positions. 
The positioning sensor 188 "reads" the position of the indicator blocs 
191. The reference gauge 189 is used to verify the position of the print 
head carriage 180 along the actuator screw 184. The position of the print 
head 65 must be verified to an accuracy greater than the industry 
tolerance for the actuator screws 184 employed to move the print head 
carriage 180. The positioning sensor 188 verifies the position of the 
print head 65 by edge detection of the very accurately manufactured 
reference gauge 189. It should also be recognized that a laser and an 
optical receiver, not shown, could be employed for sensing print head 
position. 
Each print head support 64 permits positioning of its single associated 
print head 65 along an axis orthogonal to the paper path, i.e., the 
process direction. In the typical use, once the print head support 64 has 
been adjusted to position the print head 65 for printing a particular 
document, the print head 65 remains in a fixed position relative to the 
paper path and does not move during the actual repetitive printing 
process. 
The print heads 65 are mounted to the print head carriages 180 at an angled 
orientation to the process direction or paper path. Each print head 65 is 
skewed at a defined angle A directly related to the printing resolution 
required. (See FIGS. 11a and 11b.) The angle is determined from the 
distance D between each ink jet 193 and the required resolution. The 
greater the required resolution for a given print head 65, the less the 
angle A from the paper path. In one reduction to practice the print heads 
65 each had ninety-six ink jets. The ink jets were spaced 0.269 in. from 
each other. The print heads 65 were angled at 82.degree., providing for a 
resolution of approximately 300 pixels/inch. Therefore, the accent color 
printer 10 provided for eight printed swaths of color indicia that could 
be added to a preprinted document, each swath having an approximate width 
of 3/10 of an inch. These combined eight swaths provided for a page 
coverage of about 1%. While it is preferable to mount a single print head 
65 to each print head carriage 180, it should be recognized that multiple 
print heads 65 may be mounted to a single carriage 180 as a method of 
increasing indicia printing width. 
The angle of the print heads in part defines the acceptable operational 
limits on the radius of the arc defined by the vacuum belt conveyor 32. 
The greater the angle A, the greater the required arc radius. This direct 
relationship arises from the linear orientation of the ink jets. Ink jets 
at the end of the linear array for a printhead 65 are positioned farther 
from the continuous document 16 on the vacuum belt conveyor 32 than ink 
jets at the center of the array. A solution is a curved array of ink jets 
having a radius commensurate with the array of the vacuum belt conveyor. 
In one reduction to practice for a linear array of 96 ink jets, at about 
82.degree., a radius of 96 inches is a practical minimum arc radius for 
the vacuum belt conveyor. An ink jet array, oriented so as to be generally 
orthogonal to the path direction, would permit a small or arc radius for 
the vacuum belt conveyor 32. It should be recognized that the invention is 
not limited to a curved vacuum belt conveyor of a constant radius, but the 
invention encompasses other convex curves for the tension side of the 
vacuum belt conveyor 32. 
The print heads 65 provide the ability to add up to eight separate colors 
of indicia to a document supported on the vacuum belt conveyor 32. The 
print heads 65 are supplied from a heated ink reservoir 67 that maintains 
the wax based ink in a fluid state. The ink reservoir 67 further 
pressurizes the fluid ink to the ink jets of the print head 65 over fluid 
lines 69 for printing. The reservoir 67 can comprise from one to eight 
chambers to provide one to eight possible colors. 
The ink jets employed in the invention require periodic cleaning in order 
to maintain high quality printing. Ink jet cleaning is a two step process 
involving first purging and then wiping the jets. A roller 220 is 
rotatably mounted near one end of the print head support 64. (See FIGS. 2 
and 9.) The roller 220 is preferably comprised of a synthetic material 
such as silicone or urethane having a durometer hardness of approximately 
40 Shore "A". The print frame 62 and the printhead support 64 have a width 
greater than the vacuum belt conveyor 32. The roller 220 is supported 
adjacent the side of the vacuum belt conveyor by a roller support 226 
extending from the side frame 34. The roller 220 is oriented to have the 
same angle "A" as the ink jets 193 of the print head 65. Therefore, the 
roller 220 and ink jets 193 are on the same centerline. The roller 220 is 
positioned to contact the ends of the ink jets 193 when the printhead 
carriage is moved beyond the edge of the vacuum belt conveyor 32. The 
printhead 65 is preferably moved to the cleaning position in response to 
motor 186 driving the actuator screw 184. The print head is positioned 
such that the ink jets 193 contact the surface of the roller 220. The 
roller 220 is positioned so the ink jets 193 are forced slightly into the 
roller surface 222. The angle of the roller 220 permits the roller 220 to 
at least partially seal all of the ink jets 193, therefore providing 
sufficient back pressure for the purging of the ink jets 193. 
After purging of the ink jets is completed, the printhead carriage 180 next 
moves the print head 65 past the roller 220 in a direction away from the 
vacuum belt conveyor 32. The printhead carriage 180 is then reversed in 
direction to pass the roller 220 a second time. The roller 220 is 
constructed to only rotate in a direction wherein the roller rotates when 
the printhead 65 initially passes the roller 220. When the printhead 65 
moves in the reverse direction, the roller 220 wipes the ink jets 193 of 
excess wax due to nonrotation of the roller 220. A blade 224 is positioned 
to contact the roller surface 222 and therefore scrape excess wax from the 
roller 220. The roller 220 is preferably constructed of silicone because 
of the superior release properties of wax from a silicone surface, 
therefore increasing scraping efficiency by the blade 224. 
Paper temperature is an important factor in maintaining consistent and high 
print quality with wax based inks. The required paper temperature is 
determined by the wax parameters of the wax based ink. The optimum paper 
temperature of 63.degree. C. maintains the wax in a slushy state to 
produce high quality printing results. Higher than optimum paper 
temperatures causes excess wicking of the ink into the paper fiber and 
therefore decreased print resolution. Lower than optimum paper temperature 
causes inadequate ink penetration and mere surface adhesion of the ink to 
the paper. For consistent high quality printing, the paper temperature 
needs to be maintained in the range of plus or minus 3.degree. Celsius. 
The temperature of the continuous form 16 arriving at the input of the 
color accent printer 16 is generally below the optimum paper temperature. 
Finned strip cabinet heaters 70 are provided at the bottom of the cabinet 
24 above and below the path of the continuous form 16 as the continuous 
form 16 moves from the infeed roller system 18 to the heated roller 30. 
The cabinet heaters 70 serve to heat the paper of the continuous form 16 
and, while so doing, to also raise the general ambient temperature inside 
the cabinet 24. The cabinet 24 is insulated with rigid foam insulation 72 
to reduce the energy requirements of the cabinet heaters 70. The cabinet 
24 is further sealed to provide increased retention of heated air within 
the cabinet 24. Heated roller 30 is provided with an internal quartz bulb 
heater 31 to provide additional heating by conduction to the continuous 
form 16. 
The vacuum chamber 56 of the vacuum belt conveyor 32 is also provided with 
a series of internal strip heaters 74 to maintain the vacuum belt 50, and 
therefore the continuous form 16, within the optimum temperature range. 
The internal strip heaters 74 are provided with heat shields 76 to prevent 
the creation of hot spots on the vacuum belt 50 (see FIGS. 2 and 3). An 
important function of the internal heaters 74 is to maintain the 
continuous form 16 at a consistent temperature past each of the eight 
print heads 65. Achieving and maintaining optimum paper temperature is 
further insured by ducts 55 directing heated air, drawn from the vacuum 
chamber 56 by the vacuum fans 54, towards the incoming continuous form 16. 
Temperature sensors monitor web temperature and control the cabinet heaters 
70, heated roller 30 and internal heaters 74 of the vacuum belt conveyor 
32 in response to the measured paper temperature. The heat sensors 
comprise an infeed temperature sensor 80, a lower conveyor temperature 
sensor 82, an upper conveyor temperature sensor 84 and a cabinet 
temperature sensor 86. The cabinet heaters 70 and the heated roller 30 are 
adjusted in response to the in-feed temperature sensor 80, the lower 
conveyor temperature sensor 82 and the upper temperature sensor 84. The 
internal heaters 74 are controlled in response to the cabinet temperature 
sensor 86. (See FIG. 6.) 
A significant factor for high quality, high speed printing is determination 
of exact document positioning to permit accurate integration of the 
desired color indicia into the preprinted document. Reliable and 
wander-free document placement orthogonal to the feed path direction is 
obtained by the previously described vacuum belt conveyor 32. Document 
position in the paper path direction is accurately determined by the 
combination of an encoder 90 and a pair of position readers 92, 93. (See 
FIGS. 1 and 12.) Paper position is initiated at the beginning of a 
printing run by manually adjusting the continuous form 16 to align with a 
registration mark on the vacuum belt conveyor 32. The encoder 90 and the 
upper and lower position readers 92,93 are then initialized to begin 
measuring document position on the continuous form 16. Document position 
is generally determined by the encoder 90 which comprises an encoder wheel 
94 in contact with the vacuum belt 50. 
With reference to FIG. 12, motion of the vacuum belt 50 causes rotation of 
encoder wheel 94, thereby generating an encoder signal 200 comprising a 
series of pulses, having a repetition rate commensurate with vacuum belt 
velocity, which is transmitted to the printer controller 95. Vacuum belt 
speed determines the continuous form position. To adjust for "creep" 
between the continuous form 16 and the vacuum belt, the upper and lower 
position readers 92, 93 directly read paper position. For conventional 
continuous forms or webs, a series of tractor feed holes are positioned 
along each edge of the web. The lower position reader 92 counts the number 
of holes to continuously determine the top or leading edge of each 
document or page of the continuous form 16. The lower position reader 92 
then transmits a first reader signal to the printer controller 95. The 
upper reader also reads the leading edge of the same document when the 
document is on the upper portion of the vacuum belt conveyor 32. The upper 
position reader 93 then transmits a second reader signal to the printer 
controller 95. The printer controller 95 is preprogrammed with the 
distance between the upper and lower position readers 92, 93. A 
computation circuit 202 in printer controller 95 measures the elapsed time 
between generation of the first reader signal and the second reader signal 
and utilizes the elapsed time and the known distance between readers 92 
and 93 to accurately determine document velocity. 
The readers 92, 93 can also read a top of form mark printed on each 
document of the continuous form, or the leading edge of individual 
separate documents. 
The belt velocity, determined by circuit 204 from the encoder 90 pulse 
train, is compared with the paper velocity as determined by circuit 202 in 
comparison circuit 206. If the velocities are not equivalent, circuit 206 
transmits a signal to a bit rate multiplier 208 to remove a pulse 210 from 
the signal 200 to create an accurate timing signal 212 that is transmitted 
to the print head firing circuit 214. The print head firing circuit 
signals each print head 65 when to fire. The deletion of a pulse 210 from 
the encoder signal 200 compensates for the small backward slip or "creep" 
of the continuous form on the vacuum belt 50. Accordingly, the ink jet 
firing enablement signal is continually adjusted to compensate for minor 
differences in the belt velocity, as measured by the encoder 90, and the 
actual continuous form velocity. The printer controller 95 can therefore 
determine an accurate position for each document on the transport surface 
51. 
Once the top of the document is determined, the printer controller 95 can 
accurately time the firing of the print head ink jets to properly position 
the color indicia. Accurate determination of document position and 
velocity permits the printer controller 95 to determine the printing 
timing sequence for one pixel relative to the speed of the transport 
surface 51. 
The printer controller 95 provides designation and timing signals to each 
print head 65. The designation signal indicates the particular print head 
ink jets which will fire. The host printer 11 transmits a compressed 
format bitmap of the required color accents to the printer controller 95. 
The printer controller 95 decompresses the bitmap, cues up the image for 
printing at the proper time and generates a designation signal for each 
print head 65. The timing signal generated by the print head firing 
circuit 214 controls the actual firing of the ink jets which are enabled 
by the designation signal. The printer controller 95 further permits the 
combination of the individual ink jet swaths to create multiple swath 
widths. More specifically, each print head 65 can, at the beginning of a 
print run, be physically adjusted to print precisely adjacent to the swath 
of another print head 65. The print controller then "matches" the edges of 
two or more print swaths together to allow the printing of larger and 
continuous indicia. 
Referring to FIGS. 6-8, in an alternative embodiment, the accent color 
printer 10' can add color indicia to separate individual documents 16'. 
The accent color printer 10' employs an alternative in-feed system 18' and 
a different outfeed system 98' when compared to the above-discussed 
embodiment. Individual documents 16' are received from an input control 
12'. Input control 12' can comprise a document stacker or other document 
handler. The in-feed system 18' serves to align the individual documents 
16' and place them on the vacuum belt conveyor 32. The individual 
documents 16' enter the input control 18' and are captured between an 
input roller 110 and an input belt 112 supported on belt rollers 114, 116. 
The input roller 110 and input belt 112 serve to redirect the individual 
documents 16' from a generally horizontal path to a generally vertical 
path. 
The vertically oriented individual documents 16' from the input roller 110 
are moved across the deck surface 128 of a sheet aligner 118. As may best 
be seen from FIG. 8, the sheet aligner 118 has an edge guide 120 located 
adjacent the deck surface 128 for aligning the individual documents 16'. 
The edge guide 120 is a formed sheet metal guide having a C- or J-shaped 
cross section. The deck surface 128 of the sheet aligner 118 is defined by 
a perforated metal platen 122. A housing 124 defines a vacuum chamber 119 
beneath the platen 122. A fan 126 evacuates air from vacuum chamber 119 
such that a pressure differential is created between the vacuum chamber 
119 and the outside air pressure. Therefore, when an individual document 
16' travels across the deck surface 128 of the sheet aligner 118, the 
individual sheet 16' is forced onto to the sheet aligner 118. 
The sheet aligner 118 further comprises a set of skewed aligner belts 130. 
(See FIG. 7.) The aligner belts 130 are driven on aligner belt rollers 
132, 134. The aligner belts 130 are oriented at an angle B from the 
direction of the paper path. The angle B for the aligner belts 130 has, in 
one reduction to practice, been found to be preferably approximately 
5.degree. with respect to the paper path direction. The aligner belts 130 
are further positioned to slide on the deck surface 128. The aligner belt 
rollers 134 and input roller 110 may be driven by a single motor 138. The 
motor 138 drives input roller 110 via drive belt 140 and input roller 110 
drives aligner rollers 134 via a drive belt 136. 
Individual documents 16' entering the sheet aligner 118 would free fall if 
no other force was placed upon them. However, the pressure differential 
created by the fan 126, evacuating the air from the vacuum chamber 119, 
supports the individual documents 16' against the deck surface 128. Due to 
the angle B of the moving aligner belts 130, the driving force on the 
individual documents 16' is toward the edge guide 120. The angled force of 
the drive belts 130 relative to the paper path thus edge registers the 
individual documents 16' against the edge guide 120. After the individual 
documents 16' register against the inner surface 121 of the edge guide 
120, the aligner belts 130 slip relative to the document as the document 
16' continues to move on a path defined by the edge guide 120. 
The aligner belts 130 are preferably overdriven with respect to the speed 
of the documents 16' in the paper path. In one reduction to practice, the 
aligner belts 130 were overdriven approximately 30 percent for reliable 
aligning results. 
A balance of force is required to properly align the document 16'. 
Insufficient vacuum permits free fall of the document 16' and therefore 
inadequate alignment. Excess friction between the aligner belts 130 and 
the individual documents 16' caused by an excessive pressure differential 
can result in a large driving force against the edge guide 120 and 
therefore may force the document 16' to climb up the edge guide 120 and 
produce misalignment. 
The sheet aligner 118 of the invention is unaffected by paper thickness. 
The sheet aligner 118 provides the vertical orientation for the documents 
16' by use of a pressure differential acting against the aligner deck 128. 
A pressure differential is preferred because a vacuum force does not 
require particular tuning of the sheet aligner 118 for varying paper 
thicknesses. 
Individual documents 16' aligned by the sheet aligner 118 are placed onto 
the vacuum belt 50 by a document placement system 142. The document 
placement system 142 comprises a placement belt 144 moving on placement 
rollers 146, 148, 150. The documents 16' from the sheet aligner 118 are 
captured between the placement belt 144 and the vacuum belt 50 as the 
vacuum belt 50 rolls around the lower belt drum 36. 
The documents 16' are printed with color-indicia in the same manner as the 
continuous form 16. However, for the individual documents 16', the 
position readers 92 consist of two retroreflective photosensors at a fixed 
distance from each other in the paper path direction. The position readers 
92 and 93 optically sense the leading edge of each individual document 
16'. The print controller 95 employs the signals of the encoder 90 and 
readers 92, 93 in the same manner as for continuous form 16 to determine 
document position for printing the color indicia by the printhead systems 
60. 
The documents 16' are withdrawn from the vacuum belt 50 by an outfeed 
system 98'. Individual documents 16' containing color indicia are carried 
toward the upper portion of the vacuum belt conveyor 32 on the transport 
surface 51. The vacuum belt 50 is accelerated away from the individual 
sheets 16' as the vacuum belt 50 approaches the upper belt drum 38. This 
acceleration is due to the sudden difference in curvature of belt 50 as it 
departs from the arc shaped tension side sliding bed 44 and passes about 
the upper belt drum 38. 
The individual sheets 16' which separate from belt 50 continue on a 
generally straight path toward the top of the cabinet 24 as the vacuum 
belt 50 accelerates around the upper belt drum 38. This separation, in 
part, is due to a drop in the pressure differential at the upper portion 
of the vacuum belt conveyor 32. The leading edges of the individual 
documents 16' are caught by an upper outfeed conveyor belt 152 and 
captured between the upper outfeed conveyor belt 152 and a lower outfeed 
conveyor belt 154. 
The upper outfeed conveyor belt 152 moves on rollers 156, 158, 160 and the 
lower outfeed conveyor belt 154 moves on rollers 162, 164, 166, 168. 
Roller 160 is driven to move the upper outfeed conveyor belt, and the 
contact with the upper outfeed conveyor belt 152 drives the lower outfeed 
conveyor belt 154. Individual documents 16' captured between the upper and 
lower outfeed conveyor belts 152, 154 are transported from the upper 
portion of the vacuum belt conveyor 32 to an outfeed position 170. The 
outfeed belts are driven at a linear velocity which is slightly greater 
than the speed of the vacuum belt 50 to aid in picking documents 16' off 
the transport surface 51. From the outfeed position 170, the documents 16' 
are collected for further processing. 
For documents 16' comprising relatively heavy paper, stripper fingers (not 
shown) may be required to assist in directing the individual documents 
into the outfeed system 98'. Alternately, the roller 156 for the upper 
outfeed conveyor belt 152 can be moved laterally in the direction of slack 
side sliding bed of the vacuum belt conveyor 32 in order to engage the 
leading edge of a document 16' in a position further around the upper belt 
drum 38. 
Individual documents 16' also require heating of the paper to obtain 
optimal print quality with the wax based ink employed by the print heads 
65. Heating of the incoming individual documents 16' is generally more 
difficult than for documents on a continuous form 16 because of decreased 
residence time of the individual documents 16' in the printer 10' before 
printing occurs. To raise paper temperature, the aligner deck platen 122 
is provided with an attached heater 172 and heats the individual documents 
in a manner similar to the heated roller 30 heating the continuous form 
16. The heater 172 preferably provides 10 watts per square inch of heating 
capacity and a total heating capability of approximately 1600 watts. The 
heater 172 is perforated in the same pattern as the platen 122 in order to 
permit air flow from the deck surface 128. The heater 172 is controlled in 
response to a platen temperature sensor 174. 
In order to further decrease the heating time required, heated air from the 
vacuum box 124 is directed from the fan 126 toward the incoming documents 
16'. Ducting 216 directs heated air from the fan 126 to the top portion of 
the sheet aligner 118. The air is directed over an air heater 218 for 
additional heating and then down across the incoming documents 16'. The 
heated air is then drawn back into the vacuum box 124 through the platen 
122 and the attached heater 172. This closed loop recirculation of the 
same heated air generally reduces the energy requirements of the heaters 
174, 218 and increases air temperature to permit a decreased heating time 
requirement for a document to be heated to a given temperature. The air 
heater 218 is regulated in response to an air temperature sensor 176. For 
optimum paper heating, the air temperature over the individual document 
should be maintained approximately 5.degree. higher than the platen 
temperature for even heating. For the accent color printer 10', the 
ambient temperature of the cabinet is increased by cabinet heaters 70 
located in the lower portion of the cabinet 24 and by the internal heaters 
74. Both heaters 70, 74 are regulated in response to the cabinet 
temperature sensor 86. 
While preferred embodiments of the foregoing invention have been set forth 
for purposes of illustration, the foregoing description should not be 
deemed a limitation of the invention described herein. Accordingly, 
various modifications, adaptations and alternatives may occur to one 
skilled in the art without departing from the spirit and the scope of the 
present invention.