Controlling vacuum flow for ink-jet hard copy apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to vacuum transport belt apparatus, such as useful in ink-jet hard copy apparatus and methods of operation and, even more specifically, to a restricted flow vacuum system providing media cockle control and having minimal airflow-induced ink drop trajectory effects.

2. Description of Related Art

The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the

Hewlett-Packard Journal

, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W.J. Lloyd and H.T. Taub in OUTPUT HARDCOPY [sic] DEVICES, chapter 13 (Ed. R.C. Durbeck and S. Sherr, Academic Press, San Diego, 1988). As providing background information, the foregoing documents are incorporated herein by reference. Further details of basic inkjet printing technology are also set forth below in the Detailed Description of the present invention with respect to FIG.

1

.

It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, transporting sheet metal, holding a sheet of print media temporarily to a transport system or platen, and the like. Hereinafter, “vacuum induced force” is also referred to as “vacuum induced flow,” “vacuum flow,” or more simply as just “airflow,” “vacuum” or “suction,” as best fits the context. Such vacuum holddown systems are a relatively common, economical technology to implement commercially and, in printing technology, can improve hard copy apparatus throughput specifications. For example, it is known to provide a rotating drum with holes through the surface wherein a vacuum type airflow through the chamber formed by the drum cylinder provides a suction force at the holes in the drum surface (see e.g., U.S. Pat. No. 4,237,466 for a PAPER TRANSPORT SYSTEM FOR AN INK JET PRINTER (Scranton) or U.S. Pat. No. 5,081,506 for a TRANSFER SYSTEM FOR A COLOR PRINTER (Borostyan)). The term “drum” as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term “platen” can be defined as a flat holding surface, in hard copy technology it is also used for curvilinear surfaces, e.g., the ubiquitous typewriter rubber roller; thus, for the purposes of the present application, “platen” is used generically for any shape paper holddown surface—stationary or movable—as used in a hard copy apparatus. Permeable belts traversing a vacuum inducing support have been similarly employed (see e.g., Scranton and U.S. Pat. Appl. Ser. No. 09/ 163,098 by Rasmussen et al. for a BELT DRIVEN MEDIA HANDLING SYSTEM WITH FEEDBACK CONTROL FOR IMPROVING MEDIA ADVANCE ACCURACY (assigned to the common assignee of the present invention and incorporated herein by reference)).

Generally in a hard copy apparatus implementation, the vacuum device is used either to support cut-sheet print media during transport to and from a printing station (also known as the “print zone” or “printing zone”) of a hard copy apparatus, to hold the sheet media at the printing station while images or alphanumeric text are formed, or both. In order to further simplify description of the technology and invention, the term “paper” is used hereinafter to refer to all types of print media and the term “printer” to refer to all types of hard copy apparatus; no limitation on the scope of the invention is intended nor should any be implied.

In essence, the ink-jet printing process involves digitized, dot-matrix manipulation of drops of ink, or other liquid colorant, ejected from a pen onto an adjacent paper. One or more ink-jet type writing instruments (also referred to in the art as an “inkjet pen” or “print cartridge”) include a printhead which generally consists of drop generator mechanisms and a number of columns of ink drop firing nozzles. Each column or selected subset of nozzles (referred to in the art as a “primitive”) selectively fires ink droplets (typically each being only a few picoliters in liquid volume) that are used to create a predetermined print matrix of dots on the adjacently positioned paper as the pen is scanned across the media. A given nozzle of the printhead is used to address a given matrix column print position on the paper (referred to as a picture element, or “pixel.”). Horizontal positions, matrix pixel rows, on the paper are addressed by repeatedly firing a given nozzle at matrix row print positions as the pen is scanned. Thus, a single sweep scan of the pen across the paper can print a swath of dots. The paper is stepped to permit a series of contiguous swaths. Dot matrix manipulation is used to form alphanumeric characters, graphical images, and even photographic reproductions from the ink drops. Page-wide ink-jet printheads are also contemplated and are adaptable to the present invention.

A well-known phenomenon of wet-colorant printing is “paper cockle,” the irregular surface produced in paper by the saturation and drying of ink deposits on the fibrous medium. As a sheet of paper gets saturated with ink, the paper grows and buckles in a seemingly random manner. Paper printed with images are more saturated with colorant than simple text pages and thus exhibit great paper cockle. Colors formed by mixing combinations of other color ink drops form greater localized saturation areas and also exhibit greater cockle tendencies.

As the ink-jet writing instruments—often scanning at a relatively high rate across the paper—expel minute droplets of ink onto adjacently positioned print media and sophisticated, computerized, dot matrix manipulation is used to render text and form graphic images, the flight trajectory of each drop is critical to print quality. Printing errors (also referred to in the art as “artifacts”) are induced or exacerbated by any airflow in the printing zone. Thus, use of a vacuum platen and vacuum transport device in the printing zone of an ink-jet printer creates an added difficulty for the system designer. One solution to the problem is set out in applicants' pending application 09/514,830, filed on Feb. 28, 2000, for a LOW FLOW VACUUM PLATEN FOR AN INK-JET HARD COPY APPARATUS. In essence, it employs a platen having an array of vacuum ports that are each filtered. The filter is constructed to provide restricted airflow such that media holddown pressure remains substantially uniform when the platen is either fully covered or partially uncovered. The filter mechanism provides airflow restrictions such that ink drop flight trajectories in the printing zone are unaffected, acoustic dampening of the vacuum pump is provided, and vacuum pressure is kept relatively high at the print media edges.

There is still a need for a commercial, low-cost, vacuum system for use in an ink-jet printing zone which will assist in minimizing cockle and provide a minimal airflow impact on ink-jet drop flight trajectory.

SUMMARY OF THE INVENTION

In a basic aspect, the present invention provides a vacuum platen system for transporting a sheet material, comprising: a platen having ports permitting airflow therethrough at predetermined positions of a surface thereof; a vacuum device associated with the platen and inducing the airflow; and a transport belt superjacent the surface, having an array of belt perforations such that each perforation through the belt has a diameter substantially less than the diameter of the ports.

In another basic aspect, the present invention provides a method for transporting print media across a vacuum platen associated with a vacuum inducing mechanism, comprising the steps of: drawing a vacuum through a plurality of vacuum ports distributed across the platen; and transporting ink-jet print media across the platen in a predetermined direction by a perforated belt associated with the platen so as to restrict flow by a combined construct comprising the platen and the belt.

In another basic aspect, the present invention provides an ink-jet hard copy apparatus comprising: an ink-jet writing instrument associated with a printing zone within the apparatus; an endless loop vacuum belt system for transporting print media to and from the printing zone; and a vacuum platen system located proximate the printing zone, the vacuum platen system having a platen, having a plurality of vacuum ports therethrough, a vacuum chamber, and a vacuum device for maintaining a negative pressure within the chamber such that an airflow is established through the vacuum ports into the chamber, wherein the vacuum belt system has a belt having perforations, each of said perforations being of a smaller size than each of said ports such that a uniform vacuum holding pressure is exerted on a sheet of print media carried by the belt across the platen and the airflow superjacent the belt in the printing zone is less than an airflow that affects ink drop flight trajectories.

In another basic aspect, the present invention provides a vacuum flow restricting print media transport apparatus comprising: a perforated belt and ported platen combination having an effective belt porosity less than platen porosity.

In another basic aspect, the present invention provides a method for controlling airflow in an ink-jet apparatus having a vacuum transport belt for transporting ink-jet media through a printing zone, comprising the steps of: suspending the vacuum belt across a vacuum source having essentially no physical support of the belt in the printing zone; and providing appropriate flow restriction in the printing zone by controlling the a real density of perforations in the belt based on specified design parameters and intended media usage.

In another basic aspect, the present invention provides for a method for controlling airflow in an ink-jet apparatus having a vacuum transport belt for transporting ink-jet media through a printing zone, comprising the steps of: suspending the vacuum belt across a vacuum source having essentially no physical support of the belt in the printing zone; and providing appropriate flow restriction in the printing zone by controlling the a real density of perforations in the belt based on specified design parameters and intended media usage.

Some of the advantages of the present invention are:

it provides a vacuum force sufficient for holding media in place against cockle deformation tendencies while being wetted by ink deposited thereon;

it provides a low flow vacuum system with minimal airflow induced ink drop directionality errors;

it provides a substantially uniform media holddown pressure when the platen is either fully covered or partially uncovered;

it provides a low flow platen that allows vacuum box pressure to remain relatively constant whether or not paper is fully covering the platen, thus compensating for different sized print media;

it allows for various media sizes and thicknesses to be held down with substantially the same pressure without requiring a large vacuum source;

it reduces acoustic levels caused by a vacuum induced airflow;

it provides a platen that is resistant to clogging by ink and paper dust;

it provides a belt that is available for cleaning off ink and paper dust;

it provides improved vacuum holding at paper edges;

it reduces platen construction complexity, resulting in less piece parts and lower manufacturing costs;

it eliminates vacuum leakage between ports;

it provides a media transport belt construct having better heat transfer characteristics;

it provides a media transport belt that is less subject to non-productive heat loss; and

it provides a more durable media transport belt.

The foregoing summary and list of advantages is not intended by the inventors to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic illustration of an ink-jet hard copy apparatus in accordance with the present invention.

FIG. 2

(Prior Art) is a planar, overhead view of detail of the top surface of a vacuum platen.

FIG. 3

is a schematic depiction of a vacuum platen system used in the present invention as also shown in FIG.

1

.

FIG. 4

(Prior Art) is an overhead view illustration of an exemplary platen surface have vacuum ports therethrough.

FIGS. 5 and 5A

are a schematic illustration (overhead view) of a section of a preferred embodiment of an endless-loop belt section in accordance with the present invention.

FIG. 6

is a schematic illustration (overhead view) of a section of a preferred embodiment of an endless-loop belt section (in transparency) riding over a section of a preferred embodiment of a channeled vacuum platen in accordance with the present invention for a hard copy apparatus as shown in FIG.

1

.

The drawings referred to in this specification should be understood as not being drawn to scale except if specifically annotated.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made now in detail to a specific embodiment of the present invention, which illustrates the best mode presently contemplated by the inventors for practicing the invention. Alternative embodiments are also briefly described as applicable.

FIG. 1

is a schematic depiction of an exemplary embodiment of an ink-jet hard copy apparatus

10

in accordance with the present invention. A writing instrument

12

is provided with a printhead

14

, having drop generators including nozzles for ejecting ink droplets onto an adjacently positioned print medium, e.g., a sheet of paper

16

, in the apparatus' printing zone

34

.

One type of printing zone input-output paper transport, and a preferred embodiment for the present invention, is an endless-loop belt

32

subsystem. A motor

33

having a drive shaft

30

is used to drive a gear train

35

coupled to a belt pulley

38

mounted on a fixed axle

39

. A biased idler wheel

40

provides appropriate tensioning of the belt

32

. The belt rides over a generic platen

36

in the print zone

34

; a specific platen subsystem in accordance with the present invention is described in detail hereinafter, but in general the vacuum platen subsystem is associated with a known manner vacuum induction system

37

(for simplicity of description referred to hereinafter sometimes as merely a “pump”). The paper sheet

16

is picked from an input supply (not shown) and its leading edge

54

is delivered to a guide

50

,

52

aligned for delivering a leading edge to the belt; an optional pinch wheel

42

in contact with the belt

32

may be used to assist transport of the paper sheet

16

through the printing zone

34

(the paper path is represented by arrow

31

). While vacuum release through the belt

32

downstream of the printing zone

34

(viz., off-platen) may be sufficient to transport the sheet

16

leading edge

54

toward the apparatus' output, an output roller

44

in contact with the belt

32

may optionally be used to receive the leading edge of the paper sheet and continue the paper transport until the trailing edge

55

of the now printed page is released.

Referring to both FIG.

1

and

FIG. 2

(Prior Art), a specific type of channeled platen

201

is illustrated. This platen

201

has a top surface

203

over which the belt

32

slides. Slots

205

in the surface

203

are coupled to the subjacent vacuum induction system

37

by through-holes

207

to distribute the vacuum force across the platen

201

to hold the sheet of paper

16

. A region

209

of the sheet of paper

16

is shown covering part of the surface

203

area. When a slot

205

is fully or partially open, as shown, airflow is high through the holes

207

of that slot

205

since the region

209

of paper is not closing the entire slot off from the local atmosphere. This can cause several problems. For example, the airflow into the vacuum box is high for smaller media sheets that leave a large percentage of the platen surface

203

open. This requires a relatively large vacuum pump

37

. If the surface

203

is mostly open (e.g., when a 3×5-inch card is on a 12×16-inch platen such that there is only about eight percent platen coverage), the pump

37

must provide a very large flow (e.g., 200 CFM or greater) before the appropriate vacuum level (e.g., at least 6-inches H

2

O) is produced in the slots

205

beneath the card. A large vacuum pump is undesirable since it leads to noise problems and increased cost of manufacture. The use of smaller holes

207

weakens vacuum levels in partially open slots

205

and leads to still other problems as smaller holes tend to clog with ink and paper dust. High airflow is induced around the edge

211

of the paper

209

also disturbs ink droplet flight trajectory from the pen

12

(

FIG. 1

only) to the paper. Moreover, the vacuum force exerted on the underside of the paper

209

is diminished in partially open slots which might permit undesirable paper flexing, cockle, or motion during a printing cycle.

Referring now to both

FIGS. 1 and 3

, illustrations of the details of the vacuum platen subsystem

301

for the hard copy apparatus

10

are shown. The system

301

fundamentally substitutes in the printing zone

34

of

FIG. 1

for elements

36

and

37

. Electrical power is supplied in any known manner; further details are not required for an understanding of the present invention.

A pump or exhaust mechanism

37

′ is mounted in any known manner in a vacuum box

307

(correlates in general position to

FIG. 1

, element

36

). A sheet

16

of paper is transported along paper path

31

to the printing zone by a perforated transport belt

32

′. A platen

311

member is mounted atop the vacuum box

307

. The platen

311

has a plurality of vacuum passageways, or ports,

315

coupling its outer surface with the vacuum source. The vacuum flow through the platen

311

and vacuum box

307

is represented by the arrows

305

. While in the shown embodiment it has been found that incorporating the pump

37

′ into the vacuum box

307

provides a commercially viable arrangement, it will be apparent to those skilled in the art that the vacuum pump can be remotely located in the printer

10

and coupled to the vacuum box if known manner manifolding is provided.

Turning also to

FIG. 4

, one embodiment of a substantially flat platen

311

, has a surface

313

that has vacuum ports

315

distributed across the surface. The distribution pattern can vary depending on the design specifics of a particular implementation. In the exemplary embodiment shown, the ports

315

comprise a linear array of substantially circular apertures. In a preferred embodiment, each port has a diameter which is essentially greater than that of perforations in the belt

32

which will ride over it as shown in FIG.

1

and which are separated by a port-to-port distance, “P—P,” a distance substantially greater than the distance between the perforations in the belt by a predetermined factor, generally at least double. In general, it is preferable that the platen vacuum ports

315

be large enough so that they do not clog with ink or paper dust or an aerosol mixture of the two. Ports

315

having a diameter in the approximate range of two to seven (2-7) millimeters have been found to be suitable to ink-jet printing conditions.

FIGS. 5 and 5A

illustrate a preferred embodiment for a perforated metal belt

32

′. Preferably, the belt

32

′ is fabricated of INVARN™ (commercially available from Specialty Steel and Forge company of Fairfield, NJ), having a thickness of approximately 0.005-inch, which makes it suitably flexible for a printer

10

(FIG.

1

). Other flexible metal, plastic, and fabric materials may be employed. The belt can be coated with PTFE, a nickel-PTFE blend, or any other commercial low friction substance in order to reduce drag forces and wear as the belt passes over the platen

311

. A thirty-two inch endless loop by twelve inch width implementation is a preferred embodiment for use with commercially available papers up to B-size; it will be recognized by those skilled in the art that any specific implementation may vary. An array

500

of individual belt perforations

501

is provided for transmitting the vacuum

305

from the platen

311

(see

FIG. 3

) through the belt to its outer surface

32

′.

For the platen

311

construct embodiment as shown in

FIG. 4

, the array

500

of perforations

501

is shown to be a staggered array and to have a cross-belt perforation separation, “CBPS,” of approximately 1.13-mm and a longitudinal perforation separation “LPS” of approximately 1.25-mm. Each perforation

501

has a diameter of approximately 0.3-mm. The array

500

of perforations

501

stops at border regions

503

of the belt

32

to ensure that the integrity of the entire belt is not compromised by perforations too near the edge.

In the shown embodiment, an approximate 4.0-mm wide border region

503

is provided along each longitudinal edge of the belt

32

′.

With the belt perforation array

500

as shown in

FIGS. 5 and 5A

and the platen port construct as illustrated in

FIG. 4

, the perforations

501

only allow the passage of air through them when they are over platen ports

315

. In other words, the design is tailored so that a sufficient flow through the belt is provided to limit wet paper positional changes and deformations yet low such that ink droplet trajectories are not affected and other problems related to the use of vacuum (see Background section above) are minimized.

It will also be recognized by those skilled in the art that in an alternative embodiment the ports may open into vacuum channels across the platen surface

313

. Such an arrangement is known to provide a more uniform vacuum across the width of the platen. See e.g., U.S. Patent application No. 09/292,838 by Wotton et al. for a VACUUM SURFACE FOR WET DYE HARD COPY APPARATUS (assigned to the common assignee herein and incorporated herein by reference).

FIG. 6

depicts a preferred embodiment combination of perforated belt

32

″ and platen

311

′ that has ported channels

601

. The belt

32

″ section is shown as transparent so that the subjacent platen

311

″ details are evident. A vacuum flow rate of approximately 33 cubic feet/hour/square inch is preferred. A vacuum flow rate in the range of about 6.0 to 103 cubic feet per hour per square inch should be employed. A vacuum induction force equivalent to about 8-inches-water-column provided beneath the platen

311

″ is preferred. Vacuum force in the range of 3-inches-water-column to 50-inches-water-column can be employed.

A series of platen channels

601

in the platen

311

″, each having a depth of about 0.5-mm and width of about 1.25-mm, separated from each other by about 5.0-mm in the paper path

31

direction, are oriented to be perpendicular to the transport belt motion, paper path

31

(FIG.

1

). A set of vacuum ports

315

through the floor of each channel

601

have a diameter of just slightly less than the channel width. The ports

315

within a channel

601

are separated by about 7-mm. As in

FIG. 5A

, a staggered array

500

of perforations

501

through the belt

32

″ are provided. The relative belt porosity is only about 2.5 percent. The relative platen porosity is about 20 percent. Thus, the total subsystem porosity is about one-half of one percent (0.50%). The total suited porosity is in the approximate range of twelve-hundredths to two percent (0.12% to 2.0%). The suited belt porosity is in the approximate range of twelve-hundredths to twenty percent (0.12% to 20%). The suited platen porosity is in the approximate range of ten to over ninety percent (10% to over 90%). The belt

32

,

32

′,

32

″ is providing the requisite flow restriction; therefore, the platen air flow passages

315

can be relatively large and close together without having an excessively large airflow affecting drop trajectory, pump requirements, and the like as discussed in the Background section above. Larger platen holes are less likely to clog and increased packing density can provide a vacuum closer to media edges. The area of each air flow passage

315

through the platen

311

,

311

′ should be substantially greater than the combined area of all air passages through the belt

32

,

32

′,

32

″ that couple the vacuum flow

305

to the paper transport surface of the belt. If not, a significant pressure drop will occur through the platen air passages. If a platen air flow passage

315

is approximately five times as great as the associated belt holes combined area, then the pressure drop through the platen will be approximately four percent (4%) of the pressure drop through the belt. It is preferable that at least 75% of the pressure drop occurs through the belt.

In another envisioned embodiment, the vacuum belt may be suspended across a vacuum source having essentially no physical support of the belt in the printing zone, providing appropriate flow restriction there by controlling the a real density of perforations in the belt based on the specific implementation's design parameters and intended media usage.

FIG. 5A

provides an exemplary implementation.

Thus, the present invention provides an ink-jet apparatus

10

with a vacuum type print media transport subsystem

301

for moving the print media

16

through a printing zone

34

. A transport belt

32

is provided with an array

500

of perforations

501

such that vacuum flow

305

is restricted. The perforations only pass a limited vacuum induced airflow

305

through the belt when over a platen

311

port

315

.

It will be recognized by those skilled in the art that while the present invention has been illustrated in a substantially planar embodiment, the concept is applicable to curvilinear platen implementation, including vacuum drum designs where the platen and vacuum box are concentric constructs.

The foregoing description of the preferred embodiment of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. Belt porosity and vacuum force requirements will be a function of a specific printer

10

design; actual induced vacuum force is a function of specific implementation design factors, such as sizes, shapes, thicknesses of the media, and the like as would be known to a person skilled in the art. Similarly, any process steps described might be interchangeable with other steps in order to achieve the same result. The embodiment was chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. Reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather means “one or more.” Moreover, no element, component, nor method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the following claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ”

Number	Name	Date
5197812	Worley et al.	Mar 1993
5582086	Kogame	Dec 1996
5664773	Sevcik et al.	Sep 1997
5706994	Welch et al.	Jan 1998
5717446	Teumer et al.	Feb 1998
5992994	Rasmussen et al.	Nov 1999

Controlling vacuum flow for ink-jet hard copy apparatus

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

US Referenced Citations (6)