Negative Pressure Ink Delivery System

This invention relates to thermal ink-jet (TIJ) printers, and more particularly to improvements in the pens used therein.

TIJ printers typically include a TIJ pen which includes a reservoir of ink coupled to the TIIJ printhead. One type of pen includes a polymer foam disposed within the print reservoir so that the capillary action of the foam will prevent ink from leaking or drooling from the printhead. In such a foam-pen, an air-vented delivery system is provided wherein air enters the reservoir via a separate vent opening to replace ink which is dispensed from the reservoir through the printhead.

A different type of TIJ printer has an ink reservoir which is ordinarily maintained under a sub-atmospheric or negative pressure so that ink will not leak or drool from the printhead. Various types of ink reservoirs may be used including refillable ink reservoir cartridges which are mounted on the moveable printer carriage, throwaway replaceable cartridges which are mounted on the printer carriage, and remote or offboard ink reservoirs from which ink is brought to the printhead on the printer carriage by tubing.

A collapsible ink reservoir for a handheld inkjet-printer is disclosed in U.S. Pat. No. 4,422,084 issued Dec. 20, 1983 to Saito. Negative pressure is maintained in a polypropylene ink bag by various types of springs which bias the bag walls apart from each other. The springs may be mounted inside of or externally Qf the ink bag but the spring pressure regulator construction does not result in substantially complete emptying of the ink bag and the bag itself is not carried on a printer carriage.

Another ink reservoir which achieves constant negative back pressure through an external spring or an elastomeric bladder is disclosed in U.S. Pat. No. 4,509,062 issued Apr. 2, 1985.

The invention provides an improved negative pressure ink reservoir incorporated into a cartridge for use in a printing device such as a TIJ printer/plotter, facsimile machine, or the like. The unique features of the invention affords many benefits. The cartridge itself is relatively thin in one direction, and can be mounted in various orientations on a printer/plotter carriage to take advantage of such thin dimension and provide a smaller footprint/spaceprint for the printer/plotter. The ink delivery system is simple and efficient. Ink is held in a substantially airtight reservoir formed by two oppositely positioned pieces of thin flexible non-elastic plastic-like material that have been attached by thermal bonding or other suitable technique to a compatible plastic material on a frame. A pressure regulator inside the reservoir includes two spring-loaded pistons in order to provide the necessary backpressure to prevent ink from drooling out of the printhead. The frame is preferably made of two different plastic materials. One material is an engineering plastic forming the external surfaces and providing structural support and the second material provides the fluid path for the ink and is suitable for thermal attachment to the bag material. Strong metal sidecovers attached to the frame help form an outer casing to provide a protective cover for the ink reservoir inside and to provide rigidity to the cartridge. The aforementioned spring/bag reservoir construction inside a compact strong outer casing achieves a high degree of volumetric efficiency (volume of deliverable ink compared to the external volume of the pen.

The various principal ink reservoir components in the cartridge are all attachable to each other along the same axis, thereby facilitating the manufacturing and assembly of the cartridges, including the spring assembly, bag walls, filters, and sidecovers. The spring assembly includes the spring plates, protective cover, and bowed spring which are also assembled together along a common axis for attachment.

FIG. 1 is an exploded perspective view of a replaceable or throwaway ink cartridge of a presently preferred embodiment of the invention prior to assembly;

FIG. 2 is a sectional view of the cartridge of FIG. 1 and of FIG. 3, with the spring assembly not shown;

FIG. 3 is a cross-sectional view of the cartridge of FIG. 2, with partial enlargements at the sections shown thereon;

FIG. 4 is an exploded perspective view of another presently preferred embodiment of the the invention after assembly;

FIG. 5 is a perspective view of the cartridge of FIG. 4 after assembly, with sidecovers not shown;

FIG. 6 is a closeup perspective view of the cartridge of FIG. 4 after assembly, with sidecovers removed;

FIGS. 7A, 7B and 7C schematically show three stages of compression for the spring assembly of the present invention;

FIG. 8 shows three steps for installing the aforesaid cartridge in a multi-pen carriage; and

FIG. 9 is a perspective view showing multiple cartridges of the present invention mounted for use in a printer/plotter.

The drawing shows a replaceable ink cartridge comprising a rigid outer housing 10 having a pair of spaced cover plates 12, 14 intended to be affixed as by heat bonding, or adhesive, or preferably press fit through interlocking tabs to opposite sides of a plastic peripheral wall section 16. Snout portion 13 of the cartridge has an ink discharge aperture in its lowermost end wall (as seen in FIG. 1) to which is affixed an electrically driven print head, not shown.

An inner collapsible reservoir structure unit 25 comprised of a relatively rigid inner plastic frame 20 and a pair of ink bag sidewalls or walls 22, 24, at least one of which is flexible membrane such as plastic, attached thereto is mounted in the outer housing 10. Preferably, inner frame 20 is molded with the outer housing 10 in a two step injection molding process. Inner frame 20 is formed of a softer and lower melting point plastic than the plastic of housing 10 to permit heat bonding of the bag walls 22, 24 thereto. Alternatively, inner frame 20 may be separately constructed with some flexibility to assist in mounting it in the housing 10 but the frame 20 is rigid relative to the flexible ink bag membranes described below

The frame 20 has a pair of opposite side edges 21a21b to which the flexible plastic ink bag walls 22, 24 are respectively joined as by heat welding at their peripheral edges to form the reservoir structure 25. The reservoir structure 25 contains a pressure regulator 30 which in turn is preferably comprised of a pair of spaced substantially parallel metal sideplates 40, 50 urged apart by a bow spring 60 toward the flexible walls 22, 24. The assembled reservoir structure including the inner frame 20, membranes 22, 24 and pressure regulator 30 is then mounted inside of wall section 16 of the cartridge and side walls 12, 14 are then affixed to the cartridge housing peripheral wall 16. The snout portion 13 of housing 10 also contains an ink filter 18 which is placed in fluid communication with the flexible ink bag reservoir. The filter 18 may be mounted inside the reservoir structure or it can be positioned outside of the reservoir structure but inside outer housing 10 with minor porting and seal modifications to ensure fluid communication from the ink reservoir to the filter 18. The lowermost portion of the peripheral outer housing wall 16 (as viewed in FIG. 1) is provided with an ink discharge aperture 19 through which ink is downwardly discharged from the filter 18 to the print head, not shown.

The pressure regulator sideplates 40, 50 may be individually cut from a continuous metal strip of metal such as stainless steel, each plate being of generally rectangular configuration with rounded corners to minimize damaging the flexible bag membranes.

The bow spring 60 also may conveniently be cut from a common strip of metal such as stainless steel.

The bow spring 60 is affixed, preferably by spot or laser welding at the apexes of each of its bights centrally onto each of the sideplates 40, 50.

An edge guard in the form of a thin but tough polyethylene cover layer 41, 51 having an acrylic adhesive on one surface thereof may then be press- bonded to the outer surface of each side plate 40, 50 if desired. The cover layers 41, 51 are each sized slightly larger than the side plates,40, 50 so that a marginal width of approximately 1.2 millimeters of the cover layers extends beyond each edge of the metal plates 40, 50 to prevent those edges from contacting the comparatively delicate plastic bag wall membranes 22, 24.

The pressure regulator 30 is centrally positioned in the frame 20 and housing IO and the two flexible plastic ink bag walls or membranes 22, 24 are then heat bonded or cemented at their peripheral edges to the side edges 21a, 21b of the inner plastic frame 20, care being taken to maintain the central positioning at all times of the regulator and cover layers 41, 51 in the frame 20 between the flexible membrane walls 22, 24. The bag walls 22, 24 are then securely affixed to the pressure regulator 30 preferably by heat bonding the membrane bag walls 22, 24 to the cover layers 41, 51 in the area bounded by the broken line B. This heat bonding has the primary purpose of preventing relative motion between the pressure regulator 30 and preventing direct contact of the metal sideplates 40, 50 with the relatively delicate membrane bag walls 22, 24 to prevent the edges of the sideplates from cutting or puncturing the membranes. In the absence of any protective cover layers, the bag walls may be directly bonded by heat bonding or suitable adhesive to the pressure regulator. Either method of construction also reduces the area of ink contact with the walls 22, 24 which in turn minimizes the migration of moisture from the ink through the membranes. Such migration, over time, degrades the ink quality and this problem is thus minimized. In one embodiment the dimensions of the dashed line area of heat bonding are approximately 8 mm by 29 mm. and the heat bond area is centrally located on the sideplates 40, 50. In another embodiment, the regulator side plates and bag sidewalls are initially assembled to be in moveable contact with each other. Thereafter, a heated platen momentarily contacts the film and fuses the film to the plate. A slight vacuum must be applied to the inside of the frame to improve the quality of the fusion.

As ink is withdrawn from the reservoir bag, the flexible sidewalls 22, 24 of the ink bag and the pressure regulator sideplates 40, 50. Gradually move towards each other until the spring is in an essentially flat configuration with the two sideplates 40, 50 coming virtually into contact with each other so that the bag is substantially completely emptied of ink.

Persons skilled in the art will readily appreciate that various modifications can be made from the preferred embodiment thus the scope of protection is intended to be defined only by the limitations of the appended claims. For example, the cover layers 41, 51 may in some instances be unnecessary and an ink bag having a single flexible membrane wall instead of two flexible membrane walls might be constructed. In this instance, the pressure regulator need only have a single side plate urged into engagement by a spring with the single flexible membrane bag wall.

It is therefore understood from the foregoing description that the invention provides a bonding technique to assure that the regulator is centrally positioned and always held in its proper place between the flexible membrane bag walls, preferably by heat bonding of the bag walls to an edge guard layer covering the outer surface of the two side plates 40, 50.

In such a preferred embodiment of the invention, inadvertent puncture of the thin bag walls by the regulator is prevented by a protective edge guard in the form of a layer of tough plastic bonded to the outer surface of the side plates, the protective layers each having a peripheral edge which extends beyond the edge of the side plate to prevent the edges of the side plates from directly contacting the bag walls.

FIG. 2 illustrates a partially assembled ink cartridge embodying the invention, including an external pen case comprising a composite frame structure 16, 20 and a pair of side covers 12, 14. The frame structure defines an open area 315 for the ink reservoir. The pen snout 13 is formed at one corner of the cartridge, and a printhead 17 is attached at an end 23 of the snout 13. TIJ printheads are well known in the art, and include a plurality of orifice nozzles disposed in a printhead plane. In this exemplary embodiment, the nozzles eject ink droplets in a direction generally normal to the printhead plane.

The pressure regulator 30 is centrally positioned in the open area 315 of the inner peripheral frame 20 and the two flexible ink reservoir sidewalls 22, 24 are heat bonded or cemented at their peripheral edges to the outer edge walls 21 of the inner peripheral frame 20, with care being taken to maintain the central positioning at all time of the regulator in inner peripheral frame between the flexible sidewalls. The reservoir sidewalls may then be securely affixed to the sideplates, preferably by heat bonding in the area shown as 144. This heat sealing has the primary purpose of preventing relative motion between the pressure regulator 30 and the flexible sidewalls, as well as preventing direct contact of the metal sideplates 40, 50 with the relatively delicate reservoir sidewalls to prevent the edges of the sideplates from cutting or puncturing the sidewalls. As best shown in FIG. 6, each cover plate 146 is affixed to the outer peripheral frame through matching tabs 148 and slots 149.

The material used for reservoir sidewalls should be flexible, relatively puncture resistant, impermeable to moisture and chemically compatible and non-reactive with the ink contained therein to prevent leakage or migration of the ink out of the reservoir, and impermeable to external contaminants such as air, dust, liquids and the like.

The reservoir is filled with ink via port 122 which is subsequently plugged for shipment. The required means which fire the ink droplets through the orifices on the printhead is wail known in the art and causes progressive collapse of the spring reservoir such that its sidewalls both retract inwardly as the ink volume in the reservoir is decreased.

Referring to FIGS. 4, 5 and 6, peripheral outer frame is provided with a pair of spaced parallel slots 10a and 10b on opposite sides of reduced thickness channel 15. Cover plates include additional centrally located slots (not shown) aligned with slots 10a, 10b, respectively, to provide a passageway for ink level indicator strips 113 and 114 which are cemented or heated sealed to opposite reservoir sidewalls 124, 122, respectively. The joinder areas are shown as areas 142, 144 in FIG. 4. A window device/24 having a stationary viewing window 25 therein is placed over and aligned with the reduced thickness channel 15 to provide a passageway for movement of the indicator strips 113, 114.

The schematic drawing of FIG. 7 shows how the spring assembly is preloaded inside the cartridge in order to optimize the range of negative pressure exerted by the spring during depletion of the ink from the reservoir. The actual negative pressure required of the spring is based on various factors, including the nozzle orifice architecture, the geometry of the cartridge (including the outer expansion limits of the reservoir as determined by the thickness of the cartridge), and the static ink head in the reservoir as determined by the horizontal/vertical orientation of the cartridge when mounted in printing position in the carriage. In this regard it is important to emphasize that when ink is supplied to the ink reservoir through inlet hole 122, the spring force exerted against the flexible walls of the ink reservoir must be calibrated to provide sufficient back-pressure (i.e., negative pressure) to prevent any undesirable leakage of the ink such as drooling through the printhead during cartridge storage, during cartridge installation on the carriage, or during operation on the carriage. Thus the flexible walls should not contact the sideplates of the casing or the rigid frame member after the filling operation is completed, as best shown in the "pre-loaded" middle drawing of FIG. 7.

FIG. 9 illustrates a preferred embodiment of a TIJ printer incorporating a cartridge mounted in an upright position with the longest dimension of the cartridge in the Z axis, the intermediate dimension of the cartridge in the Y axis, and the thinnest dimension of the cartridge in the X axis. The printer includes a housing 232 which supports various elements including a platen 234 which supports a print medium 236 such as a sheet of paper. The printer includes a pen carriage 238 which is driven along a support shaft 240 to eject drops of ink from the pens 250 onto the print medium. As is well known in the art, the printer further includes media advancement mechanisms not shown to advance the medium in the Y direction arrow 242 along the medium advancement axis to position the medium for the next successive transverse swath carried out by the carriage 238 along the scan axis 244. According to one aspect of the invention, the carriage 238 holds a plurality of thin pens 250, and is relatively narrow due to the thinness of the pens along the X direction 244 of carriage movement. As a result, the required width of the printer 230 can be relatively smaller than in prior designs. Further, the depth dimension of the pen is smaller than the height dimension, thereby minimizing the pen footprint while providing a high volume pen. This permits further a reduction in the printer footprint size.

In the preferred embodiment, the carriage 238 includes compartments adapted to carry four pens, each of a different color, as for example black, cyan, magenta and yellow. The pens are secured in a closely packed arrangement and may be selectively removed from the carriage for replacement with a fresh pen (see FIG. 8). The printheads of the pens are exposed through openings in the pen compartments facing the print medium.

While the aforementioned exemplary embodiments are TIJ cartridges, the invention is adaptable for use with other print cartridges which incorporate an ink reservoir as part of the cartridge. Similarly, the invention is not limited to a two-material frame but would be adaptable to any unitary or composite frame member such that a flexible membrane could be heat staked, glued, bonded, or sealed by compression or the like to the frame.

Although specific embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various modifications and revisions can be made without departing from the spirit and scope of the invention as defined in the following claims.