Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
.
This invention relates to pyrographic printers and,
more particularly, to exhaust systems for disposing of the
gaseous and solid waste products produced by electroresistive
printing processes and the like.
Electroresistive printing i5 one of the better known
pyrographic printing processes. It basically involves con-
trolling the current flow between a stylus and a conductive
substrate for an electroresistive recording medium to burn of~
localized areas o~ an overcoating on the recording medium,
thereby exposing a contrasting underlying layer in an image
configuration. As a general rule, there is relative motion
between the stylus and the recording medium so that the stylus
traverses the recording medium in accordance with a predeter-
mined scanning pattern. For example, in the Xerox* 400Telecopier* and Telecopier* 410 facsimile transceivers, which
are manufactured and sold by Xerox Corporation, electroresist-
ive paper is wrapped on a rotating drum to be more or less
helically scanned by a stylus which is advanced axially of
the drum.
Unfortunately, electroresistive and other pyrographic
printing processes are accompanied by the release of waste
products, including aromatic gases, visible smoke, and
particu~te matter. The aromatics create objectionable odors,
while the smoke and particulate matter tend to deposit a
soot-like residue.
Others have already recognized that the environmental
contamination attributable to the waste products of pyrographic
printing can be reduced, i~ not completely eliminated, by
suitable exhaust systems. A case in point is the Xerox*
Telecopier* 410 units which have exhaust systems of the type
described and claimed in a commonly assigned United States
* trade marks ~ ~
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Patent No. 3,840,880 which issued ~ctober 8, 1974 on an
application of Hans Peter Kramell entitled "Filtering
System for Pyrographic R~corders".
SUMMARY OF THE INVENTION
One of the primary goals of the present invention
is to provide methods and means for increasing the
efficiency of exhaust systems for pyrographic printers.
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More particularly, an important object of an aspect of
this invention is to provide methods and means for selectively
increasing the vacuum drawn in the immediate vicini-ty of a
stylus for an electrostatic printer or the like by an exhaust
system having an elongated inlet. A more detailed related
object of an aspect of the invention is to provide reliable
and economical methods and means for selectively reducing the
aerodynamic input impedance of the exhaust system in the
immediate proximity of the stylus as the stylus advances
lengthwise of the inlet to the exhaust system.
Briefly, to carry out these and other objects of this
invention, a pyrographic printer comprises an exhaust system
having an elongated inlet and a bifurcated throat. The inlet
is adjacent to and substantially coextensive with the path of
travel for the stylus, and the throat is configured to define
a main passage which leads away from the inlet and a branch
passage which loops back toward the inlet. To increase the
vacuum drawn in the immediate proximity of the stylus, the
input impedance of the exhaust system is selectively reduced
in that region. For that purpose, the stylus carriage carries
a baffle which extends into the throat to more or less seal a
stylus aligned segment of the branch passage.
In accordance with one aspect of this invention there
is provided in combination with a pyrographic printer having
a stylus mounted for movement along a predetermined path to
print an image on a recording medium, an exhaust system for
collecting waste products released by said recording medium
as the image is being printed; said exhaust system comprising
means for defining an elongated inlet opening substantially
adjacent to and coextensive with the entire path of movement
for said stylus; means for establishing a non-uniform vacuum
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substantially entirely along said inlet opening, including
means for maintaining a relatively strong portion of said
vacuum in alignment with said stylus as said stylus moves
along said path.
In accordance with another aspect of tnis invention
there is provided a method for collecting waste products
released in a pyrographic printer as a stylus moves along a
predetermined path to print an image on a recording medium,
said method comprising the steps of establishing a non-
uniform vacuum substantially adjacent to and coextensivewith the entire path of movement for said stylus, and main-
taining a relatively strong portion of said vacuum in align-
ment with said stylus as said stylus moves along said path.
BRIEF DESCRIPTION OF THE DRAWINGS
_ _ . _ _
Still further objects and advantages of the present
invention will become apparent when the following detailed
descrlption is read in conjunction with the attached drawings
in which:
FIGURE 1 is a fragmentary sectional view showing a
conventional exhaust system for an electroresistive printer;
EIGURE 2 is a fragmentary prospective view of an
exhaust system embodying the present invention;
FIGURE 3 is a fragmentary sectional view of an
electroresistive printer equipped with the e~haust system
shown in FIG. 2; and
FIGURE 4 is a fragmentary perspective view in
sectional form to illustrate the exhaust system of FIGS. 2
and 3 in additional detail.
DETAILED DESCRIPTION OF THE ILLUSTRATED _MBODIMæNT
While the invention is hereinafter described in
some detail with reference to a single exemplary embodi-
ment, it should be understood at the outset
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that there is no intent to limit it to that embodiment. On the con~rary, the aim is to
cover all modifications, alternatives and equivalents fallin~ within the spirit and
scope of the invention as defined by the appended claims.
Turning now to the drawings, and at this point especially to FIG. 1, there
is an electroresistive-type pyrographic printer 11 which is equipped with a
conventional exhaust system 12.
As illustrated, the printer 11 cornprises a drum 13 for supporting an
electroresistive recording medium (not shown) and a carriage 14 for supporting astylus 15. In operation, the recording medium is wrapped around the drum 13 and is
traversed in accordance with a substantially helical scanning pattern by the stylus
15. To generate that scanning pattern, the drum 13 is rotatable driven (by meansnot shown) and the carriage 14 is linearly driven (by additional means not shown) to
translate the stylus lengthwise of the recording medium along a path which is
essentially parallel to the axis of rotation of the drum 13. The printing is carried
out by controlling the current flow between the stylus 15 and the drum 13 so that
localized areas of an overcoating on the recording medium are burned away to
expose a cont~asting underlying area of the recording medium in an image configuration.
Gaseous and solid waste products released by the printing process are at
least par tially captured by the exhaust system 12. Those waste products are
released into an area of turbulent air flow because of the rotation of the drum 13
and the movement of the stylus 15. Thus, as taught by the aforementioned United
States Patent No. 3,840,880, the exhaust system 12 has a drum length inlet opening
21 which is advanced a few degrees ahead of but otherwise adjacent to the path of
travel for the stylus 15. A suitable air moving device (not shown) within the
exhaust system 12 maintains a partial vacuum along substantially the full length of
the drum 13 to continuously collect waste products from everywhere along the
Iength of the drum 13. -
As is known, an alternative for more sharply focusing the vacuum in the
area in which the waste products are released is to use an exhaust system having a
noz~le-like head which travels with the stylus. However, that eliminates the
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adYantage of being able to capture waste products which are temporally suspendedin the ~urbulent air.
Referring to FlGSr 2-4J in accordance with the present invention, there
is an exhaust system 12 a which synergistically combines the continuous waste
collection action of an elongated inlet with the vacuum focusing action of a nozzle-
like head. In many respects, the exhaust system 12 a is similar to the exhaust
system 12. Therefore, like reference numerals are used to identify like parts, with
the suffix a being added to distinguish between the two systems.
In keeping with this invention, the exhaust system 12 a has an elongated
inlet opening 21 a and a bifurcated throat 22 a. Again, the inlet 21 a extends
substantially the full length of the drum 13 a in position essentially adjacent to the
path of travel of the stylus 15 a. A suitable air moving device (not shown) within
the exhaust system 12 a draws a partlal vacuum along the full length of the drum13 a. However, the vacuum is stronger or more complete in the immediate
lS proximity of the stylus 15 a than elsewhere along the drum 13 a.
More particularly, to carry out this invention, there is an air flow
splitter 23 a which extends lengthwise of the throat 22 a just inwardly of the inlet
21 a to define a main air flow passage 24 a and a branch air flow passage 25 a. ^The
main passage 24 a leads away from the inlet 21 a, but the branch passage 25 a loops
back toward the inlet 21 a. Consequently, air drawn through the branch passage 25
a creates a countercurrent to the air drawn through the main passage 24 a, thereby
establishing a high aerodynamic input impedance for the exhaust system 12 a.
To selectively increase or strengthen the vacuum drawn in the
immediate proximity of the stylus 15 a, there is a baffle 26 a fbr at least partially
sealing a stylus aligned segment of the branch passage 25 a. The baffle 26 a is
mounted on the carriage 14 a for movement with the stylus 15 a and extends into
the throat 22 a to slidingly engage the branch passage side of the main passage 24
a. The extension of the baffle 26 a is generally perpendicular to the path of travel
of the stylus 15 a to maintain the desired alignment and is of sufficient length to
overlie the ports leading to and from the branch passage 25 a. Accordingly, the
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baffle 26 a dynamlcally reduces the aerodynamic input impedance of the exhaust
sys~em 12 a in a localized area surrounding the stylus 15 a, thereby strengthening
the vacuum drawn in that area.
(::ONCLUSION
In view of the foregoing, it will now be understood that the exhaust
system provided by this invention maintains a non-uniform vacuum along the path
of travel for the stylus of pyrographic printer and that the strongest portion of the
vacuum is maintained in alignment with the stylus as the stylus advances along arecording medium. That? of course, increases the efficiency of the exhaust system
by concentrating its air moving capacity on the area into which the gaseous and
solid waste products of the printing process are released. Moreover, it will be
evident that the exhaust system is economical to manufacture and reliable in
operation.
