Reference is made to commonly assigned, co-pending U.S. patent application Ser. No. 12/974,038, filed concurrently herewith, entitled: “Forming an Ink Tank with Capillary Breather”, the disclosure of which is incorporated herein.
The present invention relates generally to an ink tank for an inkjet printhead, and more particularly to pressure regulation for an ink tank having a spring-biased flexible wall.
An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector consisting of an ink pressurization chamber, an ejecting actuator and a nozzle through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the pressurization chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the recording medium is moved relative to the printhead.
A common type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the recording medium and the printhead is mounted on a carriage. In a carriage printer, the recording medium is advanced a given distance along a media advance direction and then stopped. While the recording medium is stopped, the printhead carriage is moved in a direction that is substantially perpendicular to the media advance direction as the drops are ejected from the nozzles. After the carriage has printed a swath of the image while traversing the recording medium, the recording medium is advanced; the carriage direction of motion is reversed, and the image is formed swath by swath.
The ink supply on a carriage printer can be mounted on the carriage or off the carriage. For the case of ink supplies being mounted on the carriage, the ink tank can be permanently integrated with the printhead as a print cartridge so that the printhead needs to be replaced when the ink is depleted, or the ink tank can be detachably mounted to the printhead so that only the ink tank itself needs to be replaced when the ink tank is depleted.
One type of detachable ink tank includes a porous member (also called a wick or scavenger member) at the ink supply port. The printhead inlet port can include a standpipe, for example, with a filter member at its inlet end. When the ink tank is mounted onto the printhead, the ink tank wick is held in contact with the filter member on the standpipe of the printhead inlet port. The ink supply port of the ink tank includes a rim having a face that seals against a gasket surrounding the inlet port of the printhead when the ink tank is installed. The gasket seal provides a substantially airtight ink pathway from the ink tank to the printhead. Once the printhead is primed so that liquid ink fills the various ink passageways between the wick and the nozzles on the printhead, capillary action provides the force necessary to supply the ink to the nozzles as needed for printing. Such an ink tank facilitates easy and clean installation onto the printhead
Some types of ink tanks also include capillary media such as felt or foam that is used to retain ink inside the ink tank and provide a slight negative ink pressure so that ink does not drip out of the nozzles of the printhead. This ink-retaining capillary media thus serves as a pressure regulator and provides ink to the wick at the ink supply port.
It has been found that pigment particles in a pigmented ink can settle out in ink tank designs where ink is stored in a capillary media pressure regulator, partly due to the restriction of motion of pigment particles within the small passages of the capillary media, as described in more detail in US Patent Application Publication Number US20090309940. Such settling of pigments particles, especially for larger pigment particles (e.g. larger than 30 nanometers), can result in defective images during the printing process. As a result, an ink tank using capillary media to store ink can lead to a limitation in pigment particle size that can be used. Such a limitation can be disadvantageous because such larger particles can be beneficial for providing higher optical density in printed regions.
A different type of pressure regulator for an ink tank is a bag (or flexible wall) with a spring that provides pressure regulation for a supply of liquid ink within a reservoir of the ink tank. Such ink tanks can have less tendency for settling out of pigment particles than for the case of ink stored in capillary media. In addition, as disclosed in U.S. Pat. No. 7,086,725, an ink tank having a flexible wall or a bag and a spring for pressure regulation can provide ink from the reservoir more efficiently (i.e. less ink trapped in the depleted reservoir) than an ink tank using capillary media ink storage to perform pressure regulation.
In conventional ink tanks having a spring-biased flexible wall, no vent is provided to the ink-filled reservoir. In order to provide pressure regulation for nearly empty reservoirs as well as nearly full reservoirs, it is necessary in such ink tanks for the spring-biased flexible wall to be able to collapse substantially completely in the case of a nearly empty ink reservoir. This requires the flexible wall to have a high degree of flexibility. However, it is also desirable for the flexible wall to have low permeability to air, in order to keep air from passing through the flexible wall and being absorbed into the ink, which can result in air bubbles in the printhead. However, additional layers for low air permeability can reduce the degree of flexibility of the flexible wall. U.S. Pat. No. 6,773,099 discloses an ink tank with a spring-biased flexible wall and a one-way valve to allow air bubbles to enter the reservoir for maintaining a stable negative pressure as ink is used. However, typically such a one-way valve has a substantial cracking pressure at which the valve opens, leading to fluctuations in the regulated pressure, as the negative pressure in the reservoir needs to build up sufficiently to open the one-way valve. U.S. Pat. No. 6,830,324 discloses an air-permeable film provided at one end of an air path to allow air to pass through, but not ink. The air path has an air introduction port in the ink container sized to form an ink meniscus that breaks to allow air into the reservoir when the pressure in the reservoir becomes sufficiently negative. However, it has been found that such an air introduction port would need to have an opening diameter of approximately 50 microns in order to operate satisfactorily for allowing air into the reservoir as described. A difficulty in providing such a small hole in an ink container is that ink containers are typically injection molded, and a 50 micron molding pin to provide such a hole in the container would not be sufficiently robust for injection molding large numbers of ink containers.
What is needed is an ink tank having a spring-biased flexible wall in which air can enter the ink reservoir at a more gradual rate to keep the regulated pressure more uniform. In addition, a method is needed for making such an ink tank in a low cost way that is compatible with high-volume manufacturing methods.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the invention, the invention resides in an ink tank comprising a reservoir for holding ink, the reservoir including a flexible wall for adjusting an internal volume of the reservoir; a biasing element for applying a force to the flexible wall that tends to increase the internal volume of the reservoir; an ink supply port for delivering ink from the reservoir to a printhead; and a breather element, at least a portion of which is disposed inside the reservoir, including a capillary material in contact with ink in the reservoir, wherein the breather element is configured to allow air to enter the reservoir in response to an internal pressure of the reservoir being less than atmospheric pressure outside the ink tank by an amount that is related to a property of the biasing element and a capillary pressure of the breather element.
These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.
Referring to
In the example shown in
In fluid communication with each nozzle array is a corresponding ink delivery pathway. Ink delivery pathway 122 is in fluid communication with the first nozzle array 120, and ink delivery pathway 132 is in fluid communication with the second nozzle array 130. Portions of ink delivery pathways 122 and 132 are shown in
The drop forming mechanisms associated with the nozzles are not shown in
Also shown in
Printhead 250 is mounted in carriage 200, and multi-chamber ink tank 262 and single-chamber ink tank 264 are installed in the printhead 250. A printhead together with installed ink tanks is sometimes called a printhead assembly. The mounting orientation of printhead 250 is rotated relative to the view in
Paper or other recording medium (sometimes generically referred to as paper or media herein) is loaded along paper load entry direction 302 toward the front of printer chassis 308. A variety of rollers are used to advance the medium through the printer as shown schematically in the side view of
The motor that powers the paper advance rollers is not shown in
Toward the rear of the printer chassis 309, in this example, is located the electronics board 390, which includes cable connectors 392 for communicating via cables (not shown) to the printhead carriage 200 and from there to the printhead 250. Also on the electronics board are typically mounted motor controllers for the carriage motor 380 and for the paper advance motor, a processor and/or other control electronics (shown schematically as controller 14 and image processing unit 15 in
Also as shown in
Outer cover 285 is attached to one side of housing 270 (
As shown in
Flexible wall 230 and spring 232 plus the breather element that includes capillary member 267 provide pressure regulation to ink enclosed in reservoir 265. In particular, pressure within reservoir 265 decreases as ink is withdrawn for printing or maintenance operations. As a result of the reduced internal pressure within reservoir 265, flexible wall 230 is pulled inward toward back wall 287, compressing spring 232. Once the amount of negative pressure in the reservoir 265 relative to ambient pressure outside the ink tank reaches the capillary pressure of capillary member 267, air from outside the housing 270 enters through capillary member 267 and into reservoir 265. Since the negative pressure in reservoir 287 also depends upon the biasing force of spring 232 (i.e. to the spring constant times the spring displacement), air is allowed into reservoir 265 in response to an internal pressure of the reservoir 265 being less than atmospheric pressure outside the ink tank 264 by an amount that is related to a properties of the spring as well as the capillary pressure of the breather element. Flexible wall 230 remains tautly drawn against plate 234 and is capable of being pushed back outward by the spring 232. After ink withdrawal ceases, pressure changes due to thermal changes or outside barometric changes are buffered by the flexible wall 230 that is biased by spring 232. For a nearly full ink tank, pressure regulation is provided only by the spring-biased flexible wall 230. After enough ink is withdrawn that the capillary pressure of capillary member 267 is reached, pressure regulation is done primarily by air bubble entry through capillary member 267 during ink withdrawal, and by the spring-biased flexible wall 230 at other times. Because the capillary pressure of capillary member 267 is less than the cracking pressure of a typical one-way valve, air can enter the ink reservoir at a more gradual rate through capillary member 267 to keep the regulated pressure more uniform. Fluctuations in pressure are less, relative to the ink tank disclosed in U.S. Pat. No. 6,774,099, thus providing a very stable operating pressure for the printhead. In addition, because air bubbles are allowed to enter reservoir 265 as ink is withdrawn, it is not required that flexible wall 230 be able to collapse entirely toward back wall 287 in order to empty reservoir 265. The decreased requirement of flexibility (since maximum deformation of the wall is reduced) is more compatible with a desirable material choice for flexible wall 230 that has less permeability to air. Requirements on spring 232 are also lessened relative to spring-biased flexible wall ink tanks that do not have a capillary member 267 because the spring does not need to be fully compressed for an empty reservoir 265.
When reservoir 265 is filled to a first internal volume corresponding to a maximum ink fill volume, the flexible wall 230 is located at a first distance from the rigid back wall 287. The spring constant of spring 232 and the capillary pressure of capillary member 267 of the breather element are chosen such that when flexible wall 230 has been displaced to a distance from rigid back wall 287 less than a predetermined second distance that is less than the first distance (the second distance corresponding to a second internal volume less than the first internal volume of reservoir 265), air is allowed into the reservoir 265 through capillary member 267 if the ambient conditions outside the ink tank are at 20 degrees Centigrade and one atmosphere. The precise distance of the flexible wall 230 from the rigid back wall 287 at which pressure in reservoir 265 becomes sufficiently negative so that air is allowed into reservoir 265 through capillary member 267 depends to some extent upon ambient conditions. For example, if the ambient air pressure is greater than one atmosphere, air will enter through capillary member 267 when the flexible wall has been displaced to a distance from the back wall that is correspondingly greater than the predetermined second distance. Also if the ambient conditions cause the ink temperature to be greater or less than 20 degrees Centigrade, thermal expansion effects can change the distance of the flexible wall 230 from the back wall 287 at which air will enter through capillary member 267. However, if the flexible wall 230 is located at a distance from the rigid back wall 287 that is greater than or equal to the second distance (i.e. for reservoir internal volumes that are greater than or equal to the second internal volume), no air is allowed into reservoir 265, if the ambient conditions outside the ink tank are at 20 degrees Centigrade and one atmosphere. Typically, the second distance is between about 80% and 95% of the first distance. Similarly, the second internal volume is typically between 80% and 95% of the first internal volume of the reservoir 265 corresponding to the maximum ink fill volume.
A method of filling single chamber ink tank 264 with ink is shown schematically in
In some embodiments as shown in
In other embodiments as shown in
Flexible wall 230 can be formed into a convex shape by thermo-forming a flat piece of plastic film stock into the desired shape, conforming the plastic around a member having the desired shape and applying heat. In addition to a bondable layer (such as a weldable layer of polyethylene) to be adhered to the edge 289 of side wall 283 of housing 270, flexible wall 230 can also include an oxygen-transmission-resistant barrier layer of nylon or EVOH (ethylene vinyl alcohol) that is not placed into contact with edge 289.
As in the example of the previous embodiment shown in
In some embodiments a second capillary member, such as porous wick 276 is provided at ink supply port 275, e.g. by inserting wick 276 into ink supply port 275. When the ink tank 264 is assembled onto printhead 250, wick 276 transfers ink from ink supply port 276 to inlet pipe 242 of printhead 250, as described above with reference to
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
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