Abstract:
An inkjet printer includes at least one print cartridge mounted in a scanning carriage having an ink interconnect coupled, via a flexible tube, to an ink output of a stationary pressure regulator. An ink input of the pressure regulator is connected, via a tube, to a stationary ink supply having replaceable ink cartridges. The print cartridge contains one or more printheads and one or more ink interconnects, one interconnect for each color ink which is printable by the print cartridge. To avoid ink pressure spikes due to the momentum of the ink in the flexible ink tube as the carriage scans across the medium, a flexible diaphragm is incorporated in the ink chamber of the print cartridge. The print cartridge is inserted in the scanning carriage so as to create a fluid coupling between the printhead and the flexible tube leading to the scanning carriage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. application Ser. No. 08/179,866, now U.S. Pat. No. 5,625,396 filed Jan. 11, 1994, entitled “Ink Delivery System for an Inkjet Printhead,” by Keefe et al., which is a continuation of U.S. application Ser. No. 07/862,086, filed Apr. 2, 1992, now U.S. Pat. No. 5,278,584. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to inkjet printers and more particularly to an ink delivery system for an inkjet printer which supplies ink from an ink source to a printhead. 
     BACKGROUND OF THE INVENTION 
     Inkjet printers are well-known. In these types of printers, droplets of ink are ejected from orifices in a printhead as the printhead scans across a medium. In certain types of inkjet printers, disposable print cartridges, each containing a printhead and a supply of ink, are installed in a scanning carriage. When the supply of ink is depleted, the print cartridge is disposed of. This results in a fairly expensive cost per sheet of printing. 
     Another type of inkjet printer allows the user to replace the ink supply in the scanning carriage without disposing of the printhead itself. In both of the cases described above, the scanning carriage supports the ink supply for the printhead. Since the capacity of the ink container must be fairly large to avoid changing ink supplies frequently, the carriage must be fairly large. This large carriage places a limit on reducing the size of the inkjet printer. 
     To overcome the disadvantages of the “on-axis” ink supplies, printers with off-axis ink supplies have been developed which use an ink supply not carried on the scanning carriage. A flexible tube connects the off-axis ink supply to the scanning printhead. One problem with these off-axis ink delivery systems is that the height difference between the printhead and the ink supply is directly related to the ink pressure to the printhead. Therefore, there is a high likelihood that ink will drool out of the printhead nozzles if the printer is tilted or tipped over. Further, the momentum of the ink in the flexible tube as the carriage scans causes fluctuations in the pressure of the ink applied to the printhead. 
     What is needed is an ink delivery system for an inkjet printer which does not suffer from the various drawbacks of the existing inkjet printers described above. 
     SUMMARY 
     In the preferred embodiment of an inkjet printer, an ink delivery system includes a scanning carriage having an ink interconnect coupled, via a flexible tube, to an ink output of a stationary pressure regulator. An ink input of the pressure regulator is connected, via a tube, to a stationary ink supply having replaceable ink cartridges. A relatively small semi-permanent, but replaceable, or permanent print cartridge contains one or more printheads and one or more ink interconnects, one interconnect for each color ink which is printable by the print cartridge. The print cartridge is inserted in the scanning carriage so as to create a fluid coupling between the printhead and the flexible tube leading to the scanning carriage. Since the printhead receives ink from the stationary ink supply, the print cartridge does not need a large internal ink chamber and the print cartridge and carriage can be made small. 
     In the preferred embodiment, the ink pressure regulator is located proximate to the rest position of the carriage. This prevents drooling from the printhead should the printer be tipped to a non-level orientation. To avoid ink pressure spikes due to the momentum of the ink in the flexible ink tube as the carriage scans across the medium, a flexible diaphragm is incorporated in the ink chamber of the print cartridge. 
     A variety of pressure regulators are described, and a variety of print cartridges are described. In a preferred embodiment, since it is desirable to reduce the size of the carriage, each print cartridge has a dual chamber for containing two different colors of ink, so that only two print cartridges are needed for a full color printer printing black, cyan, magenta, and yellow inks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an inkjet printer incorporating an off-axis regulator. 
     FIG. 2 is a top down view of an alternative embodiment inkjet printer having one print cartridge installed and incorporating an off-axis regulator. 
     FIG. 3 is a perspective view of one embodiment of the scanning carriage. 
     FIG. 4 is a perspective view of one embodiment of the print cartridge and its ink interconnect. 
     FIG. 5 is a perspective view of the print cartridge of FIG. 4 showing its dual chambers. 
     FIG. 6 is a cross-sectional view along line  6 — 6  in FIG. 5 illustrating a flexible diaphragm in a wall of an ink chamber for reducing ink pressure spikes. 
     FIG. 7 is a cross-sectional view along line  7 — 7  in FIG. 4 illustrating the flow of ink around the edges of the printhead substrate to the ink ejection chambers. 
     FIG. 8 is a diagram of one embodiment of an ink delivery system. 
     FIG. 9 is a cross-sectional view of an ink accumulator which may be used in the embodiment of FIG.  8 . 
     FIG. 10 is a diagram of an alternative embodiment of an ink delivery system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view of one embodiment of an inkjet printer  10 , with its cover removed, incorporating various inventive features. Generally, printer  10  includes a tray  12  for holding virgin paper. When a printing operation is initiated, a sheet of paper from tray  12  is fed into printer  10  using a sheet feeder, then brought around in a U direction to then travel in the opposite direction toward tray  12 . The sheet is stopped in a print zone  14 , and a scanning carriage  16 , containing one or more print cartridges  18 , is then scanned across the sheet for printing a swath of ink thereon. 
     After a single scan or multiple scans, the sheet is then incrementally shifted using a conventional stepper motor and feed rollers  20  to a next position within print zone  14 , and carriage  16  again scans across the sheet for printing a next swath of ink. When the printing on the sheet is complete, the sheet is forwarded to a position above tray  12 , held in that position to ensure the ink is dry, and then released. 
     Alternative embodiment printers include those with an output tray located at the back of printer  10 , where the sheet of paper is fed through the print zone  14  without being fed back in a U direction. 
     The carriage  16  scanning mechanism may be conventional and generally includes a slide rod  22 , along which carriage  16  slides, and a coded strip  24  which is optically detected by a photodetector in carriage  16  for precisely positioning carriage  16 . A stepper motor (not shown), connected to carriage  16  using a conventional drive belt and pulley arrangement, is used for transporting carriage  16  across print zone  14 . 
     The novel features of inkjet printer  10  and the other inkjet printers described in this specification relate to the ink delivery system for providing ink to the print cartridges  18  and ultimately to the ink ejection chambers in the printheads. This ink delivery system includes an off-axis ink supply station  30  containing replaceable ink supply cartridges  31 ,  32 ,  33 , and  34 , which may be pressurized or at atmospheric pressure. For color printers, there will typically be a separate ink supply cartridge for black ink, yellow ink, magenta ink, and cyan ink. 
     Four tubes  36 , which may be flexible or rigid, carry ink from the four replaceable ink supply cartridges  31 - 34  to four pressure regulators within regulator housing  38 . The regulators convert the unregulated ink pressure from ink supply cartridges  31 - 34  to a regulated ink pressure. The regulated ink pressure will typically be set to between approximately −2 to −10 inches of water, depending on the printhead and other factors. In one embodiment, the printhead prints at a resolution between 300 and 600 dots per inch. Future printheads that offer higher resolution may require pressure setpoints in the range of −10 to −25 inches of water. The regulator pressure is also selected to support the ink path and mating architecture. The disclosed regulation system will accommodate all such pressure ranges. 
     The ink within ink supply cartridges  31 - 34  may be pressurized or non-pressurized. Additional detail of one embodiment of ink supply cartridges  37 - 34  is found in U.S. application Ser. No. 08/429,915, now U.S. Pat. No. 5,825,387 filed Apr. 27, 1995, entitled “Ink Supply for an Ink-Jet Printer,” by James Cameron et al., attorney docket no. 1094053-2, incorporated herein by reference. 
     Four flexible tubes  40  are connected from the outlets of the regulators in housing  38  to a manifold  42  on the carriage  16 . 
     Various embodiments of the off-axis ink supply, the regulators, the scanning carriage, and the print cartridges will be described herein. 
     FIG. 2 is a top down view of another printer  44  very similar to that shown in FIG. 1, but with the paper tray removed and one print cartridge  18  removed. Elements throughout the various figures identified with the same numerals may be identical. 
     In a preferred embodiment, the regulators in housing  38  are located as close as practical to the rest position  46  (FIG. 2) of carriage  16 . This will be proximate to the service station  48 , which performs functions such as priming the printheads and cleaning the nozzle plates of the printheads. This location of the regulators minimizes the distance between the rest position of the printhead nozzles and the pressure regulators. This proximity is not critical when the printer is flat. However, when the printer is tilted, the height difference between the pressure regulator and the nozzles will vary. If the regulator is moved a sufficient distance above the nozzles, then drooling will take place. By reducing this distance below a critical value, such drooling is prevented. This is best described by a formula, as presented below. 
     P p =gauge pressure setpoint within a pen printhead. 
     Gauge pressure is equal to the absolute pressure minus absolute atmospheric pressure. In the preferred embodiment, the gauge pressure setpoint is −4.5 inches of water. 
     H o =height of regulator minus height of printhead when printer is flat. Assume that the regulator is designed to be located 1 inch above the printheads when the printer is flat. 
     P r =gauge pressure setpoint of regulator=P p −H o . In our example, the regulator setpoint would be −5.5 inches of water to compensate for the height of the regulator above the printhead during normal operation. 
     ΔP=pressure variation expected among regulators. 
     In the above example, the regulator pressure can vary by ±1.5 inches of water due to a normal worst-case tolerance variation. Thus, under worst-case conditions, the regulator pressure can be as high as −4 inches of water. To avoid ink drool, the regulator can never be more than 4 inches above the printhead. Therefore, we must locate the regulator within 4 inches of the printhead to avoid drooling when the product is tilted to its worst-case drool-inducing orientation, which would typically be when the printer is placed on its side with the regulator above the printhead. 
     Thus, we have the following formula: 
     
       
           D   max   =P   p  (in inches of water)− H   o   −ΔP,   
       
     
     where 
     D o =maximum safe distance (in inches) between the rest position of the printhead and the regulator. 
     Each of the regulators in housing  38  essentially consists of a valve controlling an opening between the inlet and outlet of the regulator. The valve opens in response to an ink pressure drop on the outlet side of the regulator and closes in response to an ink pressure increase on the outlet side. The desired ink pressure at the outlet side is a predetermined difference between the pressure on the outlet side and ambient (atmospheric) pressure. A typical negative regulated pressure could be approximately −4 inches of water. As an example, when it is sensed that the ink pressure at the outlet side reaches a threshold of, for example, −5 inches of water, the valve opens until the pressure has reached, for example, −3 inches of water, which then automatically closes the valve. With smaller nozzle diameters, the optimum ink pressure is increasingly negative. Thus, threshold pressures of −10 inches of water or even more negative may be feasible. 
     When printer  10  or  44  is not being operated, the valve in each regulator will be closed. Additional details of the regulators will be described with respect to FIGS. 8-11. 
     In FIGS. 2 and 3, a single print cartridge  18  is shown installed in carriage  16 . Four tubes  40 , each connected to an outlet of a pressure regulator, are in fluid communication with a rubber septum  52  supported by carriage  16 . A hollow needle  54  (FIG.  4 ), formed as part of each print cartridge  18 , is inserted through the rubber septum  52  upon pushing the print cartridge  18  into its associated stall  55  (FIG. 3) within carriage  16  so that a fluid communication path exists between a particular ink supply cartridge  31 - 34  and a particular print cartridge printhead for providing a supply of ink to the printhead. 
     A flexible bellows  56  (FIG. 3) is provided for each rigid septum elbow  58  (FIG. 4) for allowing a degree of x, y, and z movement of septum elbow  58  when needle  54  is inserted into septum  52  to minimize the x, y, and z load on needle  54  and ensure a fluid-tight and air-tight seal around needle  54 . Bellows  56  may be formed of butyl rubber, high acn nitrile, latex, or other flexible material with low vapor and air transmission properties. In one embodiment, bellows  56  is a flexible diaphragm which is circular or rectangular in shape and may consist of a piece of film forming, or backed by, a resilient member. Alternatively, bellows  56  can be replaced with a U-shaped or circular flexible tube. 
     A spring (not shown) urges septum  52  upward. This allows septum  52  to take up z tolerances, minimizes the load on needle  54 , and ensures a tight seal around needle  54 . 
     An ink channel  59  extends from each needle  54 , over the top of print cartridge  18 , and into an ink chamber. 
     Additional detail regarding the ink interconnect is found in U.S. application Ser. No. 08/706,062, now U.S. Pat. No. 6,033,064 filed Aug. 30, 1996, entitled “Inkjet Printer With Off-Axis Ink Supply,” by Norman Pawlowski, Jr., et al., attorney docket no. 10960163-1, incorporated herein by reference. 
     FIG. 4 illustrates the bottom side of a multi-chamber print cartridge  18 . Two parallel rows of offset nozzles  60 , one row for each color ink printed by print cartridge  18 , are shown laser ablated through tape  62 . In one embodiment, there are 300 nozzles spaced to print a vertical resolution of 600 dots per inch. Ink fill holes  64  are used to initially fill the print cartridge ink chambers with ink. Stoppers (not shown) are intended to permanently seal holes  64  after the initial filling. 
     Metal contact pads  68  are electrically connected to electrodes on a substrate carrying the ink ejection elements. 
     FIG. 5 shows print cartridge  18  with its top removed to illustrate two ink chambers  72  and  73 , each for a particular color ink. Each ink chamber  72 ,  73  is in fluid communication with a respective needle  54  (FIG. 4) and an associated ink supply cartridge  31 - 34  via the tubing and ink interconnects, previously described. Each chamber  72 ,  73  is in fluid communication with a portion of a single printhead, or a separate printhead, associated with that chamber. 
     To mitigate the effects of ink pressure spikes due to the acceleration and deceleration of the scanning carriage  16 , a wall of each of the chambers  72 ,  73  has a flexible (e.g., rubber) portion identified as diaphragm  76 . Diaphragm  76  flexes outward a slight amount with an ink pressure spike to absorb any pressure increase of the incoming ink. Conversely, diaphragm  76  flexes inwardly into the ink chamber  72 ,  73  to absorb a negative pressure spike in the ink. The characteristics of diaphragm  76  would typically be empirically determined based upon the particular characteristics of the ink printer, taking into account scanning acceleration, the size of the flexible tubes  40 , the size of the ink chambers, and other factors. 
     FIG. 6 is a cross-sectional view along line  6 — 6  in FIG. 5 of the flexible diaphragm  76  which is adhesively secured or compression clamped to the plastic print cartridge frame  78 . In one embodiment diaphragm  76  has an area of about 1 cm 2  and is about 0.5 mm thick. The area and thickness depends on the flexibility of the material and the particular requirements of the system. 
     FIG. 7 is a cross-sectional view along line  7 — 7  in FIG. 4 illustrating the paths of inks A and B in the dual chambers  72 ,  73  around the outer edges of the silicon substrate  80  and into ink ejection chambers  82 ,  83 . A center wall  84  separates the two chambers. A heater resistor  85 ,  86  in each of the ink ejection chambers is selectively energized to eject a droplet  88 ,  89  of ink from an associated nozzle  60 . Additional detail of a printhead which may be modified to have the characteristics of FIG. 7 is described in U.S. Pat. No. 5,278,584, by Keefe et al., incorporated herein by reference. 
     In the preferred embodiment, the nozzle member  92  is a flexible tape  62 , such as Kapton™, having the nozzles  60  laser ablated through the flexible tape  62 . Contact pads  68  (FIG. 4) formed on the flexible tape  62  are connected to conductive traces on the back of the tape  62 . The other ends of the traces are connected to electrodes on the substrate  80 , which are ultimately connected to the heater resistors  85 ,  86 . In another embodiment, piezoelectric elements are used instead of heater resistors. The tape  62  is secured to the print cartridge frame  78  by an adhesive  94 . A barrier layer  96  forming the ink ejection chambers  82 ,  83  may be formed of a photoresist. An adhesive layer  98  secures the barrier layer  96  to the bottom of the flexible tape  62 . An adhesive  100  affixes substrate  80  to the center wall  84  and creates an ink seal between the chambers  72 ,  73 . 
     Although using two dual chamber print cartridges  18  has been shown in the preferred embodiment to reduce the size of the scanning carriage  16 , four single chamber print cartridges (without wall  84 ) can also be used. U.S. Pat. No. 5,278,584 by Keefe et al. shows a print cartridge for printing a single color. A smaller version of that print cartridge, but incorporating an ink inlet port, may be used in the printer of the present invention such that four print cartridges are used instead of two. FIG. 1 of the present disclosure illustrates the four print cartridges by dashed lines. Alternatively, a single black ink print cartridge and a tri-color print cartridge may be used, where the tri-color print cartridge incorporates three sets of nozzles, one for each color. 
     FIG. 8 is a diagram of an ink delivery system in accordance with one embodiment of the invention. In FIG. 8, the print cartridge  18  includes a single ink chamber or a dual ink chamber. Only one ink color path is shown for simplicity, and there will be a separate ink delivery system for each color ink. 
     Internal to each ink chamber in the print cartridge  18  is a relatively small accumulator of ink. The purpose of the small accumulator is to absorb carriage motion-induced pressure spikes. This accumulator, in one embodiment, consists of the flexible diaphragm  76  in FIGS. 5 and 6 forming a wall of the ink chamber. Another type of accumulator is shown in FIG.  9  and may hold anywhere from a few cubic centimeters of ink to a few tens of cubic centimeters of ink, depending upon the tolerable size of the print cartridge  18 . In one embodiment, the accumulator  110  shown in FIG. 9 comprises an ink bag  112  whose side walls  114 ,  115  are urged outward by an internal spring  118  so as to provide a negative pressure at an outlet  120 , opening into chamber  72  or  73 . Such a negative pressure will typically be on the order of −2 inches of water to −10 inches of water, depending upon the characteristics of the printhead. An inlet  122  receives the ink supplied to the print cartridge. 
     Ink is delivered to print cartridge  18  via flexible tubing  40 , which is preferably Polyvinylidene Chloride (PVDC), sold under the trade name Saran™ by DuPont. The flexible tubing  40  is connected to the output of a larger accumulator  124  (similar to accumulator  110 ), forming part of a regulator  125 , inside the regulator housing  38  (FIGS.  1  and  2 ). The accumulator  124  provides tolerance to air bubbles and allows for accurate pressure regulation of the ink from ink supply  31 . The large accumulator  124  is connected to the fixed tubing  36 , leading from the replaceable ink supply cartridge  31 , by the regulator valve  126 . The regulator valve  126  may be any form of valve, such as a rotary valve or a flapper valve. 
     In the preferred embodiment, the regulator valve  126  is a flapper valve which covers and uncovers a hole between the inlet  122  of the large accumulator  124  and the tube  36  to selectively allow an amount of ink to flow from the replaceable ink supply  31  to the large accumulator  124 . The opening and closing of the valve  126  is dependent upon the ink pressure at the outlet  120  of the large accumulator  124 . Such ink pressure may be determined by a diaphragm or, in the preferred embodiment, by monitoring the physical dimensions of the accumulator  124  of FIG.  9 . As the printhead ejects ink, the large accumulator  124  collapses. When the accumulator  124  collapses to a certain point, a position sensor connected to a sidewall  114  of the ink bag  112  triggers a controller circuit that opens the valve  126 . This position sensor may simply be a flag attached to the sidewall  114  of the accumulator  124  which interrupts a path between a photodetector and a LED when the ink bag  112  collapses to a certain point. While the valve  126  is opened, the accumulator  124  back pressure draws in a controlled amount of ink from ink supply  31 , determined by the open time of valve  126  and the flow rate of the ink. Since the collapsing of the spring  118  is related to the negative pressure at the outlet  120  of the accumulator  124 , actuating the valve  126  based upon the collapsing of the ink bag maintains the negative pressure at the outlet  120  at a fairly constant level. 
     Another method of sensing the collapse of the ink bag  112  is by positioning a metal leaf spring above or below the ink bag  112  which contacts a conductor. When the ink bag  112  collapses, the leaf spring loses contact with the conductor, signalling that it is time to open the valve  126  to refill the accumulator  124 . Other methods of sensing include capacitive sensing and inductive sensing. 
     Instead of sensing the physical collapsing of the ink bag  112 , the back pressure at the outlet  120  of the accumulator  124  can be sensed using a conventional pressure transducer at the outlet  120 . 
     The various means of sensing pressure are identified as the valve controller circuit  127  in FIG.  8 . 
     In the preferred embodiment, the pressure sensor, whether detecting the collapsing of the ink bag  112  or directly detecting the pressure at the outlet  120  of the accumulator  124 , also detects when the ink supply  31  is out of ink. When the system opens the valve  126 , the pressure should return to a less negative level, and the accumulator  124  should rebound. If it does not, this is detected, and the system thereby determines that the ink supply  31  is out of ink and the valve  126  should be closed to avoid air entering the tubing  40  and print cartridge  18 . Such a determination will also indicate to the printer to give the user an out-of-ink warning. 
     FIG. 10 illustrates another embodiment ink delivery system for an inkjet printer, where print cartridge  18  is connected via the flexible tubes  40  to a fixed mechanical pressure regulator  128 . Such a mechanical pressure regulator  128  may use more conventional techniques than the regulator described with respect to FIG.  8 . One such mechanical regulator  128  incorporates a moveable lever, where the position of the lever is based on the difference between atmosphere pressure and the pressure of ink in the regulator. The movement of the lever in response to the pressure differential mechanically opens and closes a valve at an inlet of the regulator (where opening the valve makes the regulator pressure more positive) to maintain the ink pressure at the outlet of the regulator relatively constant. Such a regulator will be well understood by those skilled in art after reading this disclosure. The particular characteristics of the regulator would be adjusted to achieve the desired negative pressure. 
     One type of mechanical regulator which may be used is similar as that described in U.S. application Ser. No. 08/550,902, now U.S. Pat. No. 5,872,584 filed Oct. 31, 1995, entitled “Apparatus For Providing Ink To An Ink-Jet Print Head And For Compensating For Entrapped Air,” by Norman Pawlowski, Jr. et al., attorney docket no. 1094910-1, incorporated herein by reference. Although the regulator described in that application is internal to the print cartridge itself, such a regulator without the printhead could also serve as the fixed regulator in FIG. 8 Another suitable mechanical regulator is described in U.S. application Ser. No. 08/518,847, filed Aug. 24, 1995, entitled “Pressure Regulated Free-Ink Ink-Jet Pen,” by Norman Pawlowski, Jr. et al., attorney docket no. 1093486-1, incorporated herein by reference. Another suitable regulator is found in U.S. application Ser. No. 08/705,394, now U.S. Pat. No. 5,736,992 filed Aug. 30, 1996, entitled “An Ink Delivery System for an Inkjet Pen Having an Automatic Pressure Regulator System,” by Winthrop Childers, et al., attorney docket no. 10960493-1, incorporated herein by reference. 
     Accordingly, a number of embodiments of an inkjet printer having a fixed regulator have been described. Placing the regulator at a fixed location off the carriage has two major advantages over having the regulator on board the carriage: 1) it allows the manufacture of very small printers, since the print cartridge size and the carriage size can be reduced; and 2) the regulator can be made more accurate and air-tolerant. By having the regulator off-board, we can increase regulator size, thus increasing the accuracy of the regulator, improving the accumulator capacity, and improving the regulator&#39;s tolerance to bubbles. 
     The regulator and/or ink supply station can be placed on either the forward side (shown in FIG. 1) of the carriage scan path or behind the carriage scan path. Also, the ink supply station can be located virtually anywhere internal or external to the printer, such as on the side opposite to the carriage rest position. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.