Pressure regulated free-ink ink jet pen

Abstract: The present invention relates to free-ink type ink-jet pens (FIG.1). A spring-loaded regulator mechanism is provided within the pen to allow ink from a pressurized ink reservoir to be fed to the pen while maintaining a predetermined set point back-pressure at the printhead (7) as needed for appropriate pen operation. A mechanism (e.g., 23, 223, 523, or 623) in communication with the ambient atmosphere is used in conjunction with a substantially constant force biasing mechanism (e.g. 29, 31, or 229, 231, or 529, 531, or 629, 631) to maintain the balance between the countervailing forces. Back-pressure is maintained substantially constant regardless of the ink flow rate from the ink reservoir into the pen.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to ink-jet technology, more particularly to free-ink reservoir type ink-jet pens, and specifically to pressure regulators for a free-ink ink-jet pen. 2. Description of the Related Art The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, 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, incorporated herein by reference. Generally, in the thermal ink-jet field, an ink-jet pen is provided with a printhead, having an orifice plate constructed in combination with heating elements. Thermal excitation of ink near nozzles at the orifice plate is used to eject ink droplets through the miniature nozzles and orifices onto a print medium, forming alphanumeric characters or images using dot matrix manipulation. Other types of ink droplet generators, such as the use of piezoelectric transducers, are also known in the art. The pen itself may have a self-contained reservoir for storing ink and providing appropriate amounts of ink to the printhead during a printing cycle. These self-contained, disposable pens are referred to in the art as print cartridges. Ink can be stored in a print cartridge in a contained medium, such as a permeable foam material (see e.g., U.S. Patent No. 4,771,295 (Baker et al.), assigned to the common assignee of the present invention and incorporated herein by reference). Alternatively, the pen can be a free-ink type print cartridge, where the ink is supplied to the printhead mechanism from a self-contained reservoir such as a biased ink bladder or bag as shown in U.S. Patent No. 5,359,353 ((Hunt et al.) assigned to the common assignee of the present invention and incorporated herein by reference). If a refillable type pen rather than a print cartridge is employed in the hard copy apparatus, ink is generally supplied from a remote, refillable, off-board, ink reservoir to a relatively permanent pen body and printhead mechanism. Early ink-jet printers used off-pen reservoirs as demonstrated in U.S. Patent No. 4,312,007 ((Winfield) assigned to the common assignee of the present invention and incorporated herein by reference). Moreover, it has been found that for some hard copy applications, such as large format plotting of engineering drawings and the like, there is a requirement for the use of much larger volumes of ink than can be contained within a replaceable print cartridge. Therefore, improved, relatively large, off-pen ink reservoir systems have also been developed more recently. As examples, refer to U.S. Patent No. 4,831,389 (Chan) which shows a multicolor off-board ink supply system; U.S. Patent No. 4,929,963 (Balazar) which demonstrates an ink delivery system for an ink-jet printer using a low pressure recirculating pumping system; and U.S. Patent No. 4,968,998 (Allen) which teaches an ink-jet pen which is refillable at a service station (each assigned to the common assignee of the present invention and incorporated herein by reference). Moreover, an ink-jet pen can be designed to have a substantially permanent printhead mechanism and an on-board (also referred to in the art as on-axis), detachable, reservoir that can be refilled or replaced as needed. While both print cartridges and free-ink ink-jet pens provide a reliable and efficient means of "jetting" droplets of ink from the printhead onto the print medium, the printheads generally require a mechanism to prevent the free flow of ink through the orifices when the printhead is not activated. Without such control, ink may leak, or "drool," onto the printing surface or into the printer mechanism. Such leaking ink may also build up and cake on the printhead itself, impairing proper operation. Complex pen service stations are often provided as part of the hard copy apparatus where printheads can be wiped or activated to "spit" away excess ink. To alleviate this problem, many ink-jet printers supply ink from the reservoir to the printhead at a slight under pressure (also referred to in the art as "back-pressure" or "negative pressure" operation), lower than the ambient atmospheric pressure at the printhead. To be effective, this pen back-pressure must be maintained consistently and predictably within a desired operating range. That is, the pen back-pressure must be large enough to prevent the unwanted free flow of ink through the orifices when the pen is not in use, yet at the same time small enough so that the printhead, when activated, can overcome the back-pressure and eject ink droplets in a consistent and predictable manner. This back-pressure will be affected by changes in either or both the ambient atmospheric and the internal pressure conditions. Likewise, temperature variations may cause the ink and air within the ink-jet pen to contract or expand, also affecting the back-pressure. Therefore, these factors must be accounted for and a mechanism incorporated into an ink-jet pen design to maintain the back-pressure within the predetermined, desirable operating range. In a foam reservoir print cartridge, the capillary action of the foam will generally be sufficient to create the desired back-pressure. In a free-ink reservoir type ink-jet pen, a variable volume, on-board, ink containment supply is often employed. For example, the reservoir may be of a biased, flexible material which can expand or contract, or an ink containment chamber may be provided which includes an internal pressure regulating device. In U.S. Patent No. 4,509,062 (assigned to the common assignee of the present invention and incorporated herein by reference), a spring pulls an ink-filled bladder membrane outwardly to create a slight negative pressure inside the ink reservoir. U.S. Patent No. 4,677,447 (assigned to the common assignee of the present invention and incorporated herein by reference) describes the use of a check valve in a printing device with an on-board ink reservoir that maintains a constant pressure difference between the ink reservoir and the ink-jet printhead. U.S. Patent No. 4,992,802 (assigned to the common assignee of the present invention) teaches the use of two pressure control mechanisms to extend the environmental operating range of an ink-jet pen. Related U.S. Patent Application Serial No. 08/065,957 (Seccombe et al.) describes a diaphragm type pressure regulator located on-board an ink-jet pen using an off-board ink reservoir. Back-pressure needs to be controlled within a specified tolerance limits so that the printhead can print properly. Print quality fluctuations are directly related to back-pressure fluctuations. Too little back-pressure can lead to poor print quality and ink leakage; too much back-pressure can starve the printhead which will also affect print quality and printhead life since running an ink-jet pen dry can damage the printhead mechanism. The back-pressure needs to be maintained regardless of the printing conditions, but in the prior art has fluctuated as a function of ink level in the on-axis supply or as a function of the ink flow rate. Therefore, improvements to back-pressure mechanisms are needed to effectuate these contrary operational requirements. EP-A-0339770 discloses an ink supply for an inkjet printer having a regulator including a diaphragm which flexes as a function of the pressure in the chamber to control the opening of a by-pass valve member. US-A-4,992,802 (referred to above) discloses a bladder mechanism for pressure control for a print head ejecting ink from an ink reservoir. Nevertheless further improvements are desirable to meet operational requirements. SUMMARY OF THE INVENTION The present invention is defined in the appended claims. It is an advantage of the present invention that back-pressure at the pen printhead remains constant despite fluctuations in ink flow rate from a main ink supply reservoir. It is an advantage of the present invention that an ink-jet pen into which it is incorporated receives ink from a remote or on-axis, detachable, pressurized reservoir at a constant, steady, printhead back-pressure set point. It is an advantage of the present invention that use of ink within a supply reservoir is maximized. It is another advantage of the present invention that it can deliver ink to an ink-jet pen at a relatively high flow rate without greatly affecting back-pressure at the printhead. It is another advantage of the present invention that back-pressure is controlled over a wide range of flow rates, inlet pressures, and pen orientations. It is another advantage of the present invention that the device can be designed with a footprint that makes for easy incorporation into an ink-jet pen mechanism. It is another advantage of the present invention that the device is designed to be manufacturable with a low part count and insensitivity to tolerance variations, leading to higher production yield and lower part cost. It is yet another advantage of the present invention that the regulator device is adjustable, providing post-manufacturing means by which to adjust the back-pressure set point. It is still another advantage of the present invention that ink solvent loss is minimized through the use of a vapor barrier member. It is a further advantage of the present invention that an ink-jet pen into which it is incorporated can be primed using the device. It is yet another advantage of the present invention that only one tube from the remote ink supply is required, reducing complexity and part count. It is still a further advantage of the present invention that frictional forces in the pressure regulator device are minimized, thus reducing variation in back-pressure at the printhead. It is still a further advantage of the present invention that inertial moments are reduced by designing components with specific gravities approximately equal to the specific gravity of ink. Other objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the FIGURES. DESCRIPTION OF THE DRAWINGS FIGURE 1 is an exploded, schematic, perspective drawing of a first embodiment of the present invention. FIGURE 2 is a schematic, perspective, cross-section drawing of a second embodiment of the present invention. FIGURE 3 is an exploded, schematic, perspective drawing of an embodiment of the present invention similar to that as shown in FIGURE 2. FIGURE 4 is another depiction of the present invention as shown in FIGURE 2 which demonstrates a valve and valve seat in a fully open position. FIGURE 5 is a schematic, perspective drawing of another embodiment of the present invention with a pen body cover plate removed. FIGURES 6 is a schematic, perspective drawing showing a "frictionless" pivot mechanism employed as a component of the present invention. FIGURE 6A is a detail of FIGURE 6. FIGURE 7 is a graphical comparison of back-pressure versus spring deflection for different types of spring mechanisms available for use in the present invention. The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted. DETAILED DESCRIPTION OF THE INVENTION Reference is made now in detail to specific embodiments of the present invention, which illustrates the best mode presently contemplated by the inventor for practicing the invention. While the present invention is described in terms of exemplary ink-jet pen structures, it will be recognized by a person skilled in the art that the invention is readily adaptable to other replenishable ink pens and, in fact, many fluid pressure regulating mechanisms. Therefore, no limitation is intended by the exemplary embodiments described nor should any be implied. Referring now to FIGURE 1, a pressure regulator device in accordance with the present invention is a valve lever adapted to regulate ink flow from a remote ink reservoir into a pen body by selectively opening and closing a valve based upon fluid pressure level within the pen body. A pen body 1 is provided which includes a partitioned ink containment chamber 3a, 3b and a printhead snout portion 5 for a printhead mechanism 7. A printhead mechanism 7, generally having a nozzle plate 6 and flex circuit 8 is adapted for cooperative mounting on the snout portion 5. A pen body crown 9, which includes a portion of the ink containment chamber portion 3a, is adapted to cap the pen body 1. A septum member 11 of the pen body crown 9 provides a coupling mechanism for a remote, positive-pressure, ink reservoir (not shown) by any suitable means as would be known in the art. In combination with a crown lid 13, the ink containment chamber 3a, 3b is substantially fluid tight. That is, ink flows under pressure from the remote ink reservoir through the septum member 11 and into the containment chamber portion 3a. Ink in the containment chamber portion 3a flows into the pen body containment chamber portion 3b and snout portion 5, controlled via a pressure regulator valving mechanism 12. From the pen body containment chamber portion 3b, ink is supplied directly into the printhead mechanism 7 via an ink outlet tube member 15. As shown in FIGURE 1, an ambient atmosphere vent 19 is provided in the form of a crown tube 21 through the pen body crown 9 and continuing through the crown lid 13, as a lid vent 19'. During assembly, an inflatable bag member 23 (shown in a deflated condition) is fixed in its substantially deflated state to a fitment 25. The fitment 25 includes an apertured pipe 27 with the inflatable bag member 23 substantially sealed around the fitment 25 and the apertured pipe 27 such that when mated with the pen body crown 9, the apertured pipe 27 is aligned with the ambient atmosphere vent 19, 19' through the crown tube 21. In this manner, the bag member 23 interior is open to the ambient atmosphere but sealed against the ingress of ink that flows under pressure from the ink reservoir through the septum member 11 and into the containment chamber portion 3a and then through the valving mechanism 12 and into containment chamber portion 3b. A pressure regulating valve actuating member 29 is mounted via a biasing spring 31 to the pen body crown 9. The spring-biased valve actuating member 29 acts as a lever and includes a valve seat 33 to regulate the flow of ink through the pen body containment chamber 3a, 3b, the valve opening and closing depending upon the use rate of the printhead mechanism 7 and subsequent pressure in containment chamber portion 3b. When assembled, the valve actuating member 29 is adjacent the inflatable bag member 23. Note that the spring 31 is a torsion spring that will exert a substantially constant spring force during deflections. With the inflatable bag member 23 mounted adjacent the valve actuating member 29 and coupled to ambient atmospheric pressure via the vent 19, 19', the bag member 23 inflates and deflates in response to the differential between ambient atmospheric pressure and the pressure level within ink containment chamber portion 3b, the valve seat 33 opening and closing the valving mechanism 12, respectively. In operation, the ink containment chamber portion 3b begins to run dry as printing continues via the printhead mechanism 7. As the depleting local supply of ink in the containment chamber portion 3b decreases, because the containment chamber portion 3b is sealed against the ambient atmosphere, a low pressure condition occurs. As the pressure drops within the containment chamber portion 3b, ambient air pressure via the ambient atmosphere vent 19, 19' inflates the bag member 23 based upon the increasing pressure differential. The bag member 23 in turn pushes on the valve actuating member 29, increasingly changing its relative position against the force of the spring 31 within the chamber portion 3b as the bag member 23 inflates. In other words, the spring 31 pushes the valve seat 33 against a valve (such as a molded orifice, pipe, needle-valve, or the like, hidden in the view of FIGURE 1) between the ink containment chamber portions 3a, 3b, shutting off the flow of ink. When the back-pressure at the ink-jet printhead mechanism 7 is less than the predetermined set point back-pressure, the inflating bag member 23 exerts a force on the valve actuating member 29, overcoming the spring force and causing it to act like a lever, moving the valve seat 33 such that ink can flow from the ink containment chamber portion 3a into the ink containment chamber portion 3b. The magnitude of the force exerted by the spring 31 will exceed the magnitude of the force exerted by the bag member 23, causing it to deflate when the back-pressure at the ink-jet printhead 7 is equal to or slightly exceeds the set point back-pressure. The valve actuating member 29 moves back under the force of the spring and the valve seat 33 shuts off the flow of ink. The use of a torsional spring has distinct advantages over prior art pressure regulators such as of the type disclosed in U.S. Patent Application Ser. No. 08/065,957 (Seccombe et al.) which uses a cantilever spring. Back-pressure fluctuations can be related to change in spring force and is sensitive to the ink flow rate through the valving mechanism 12. The ink flow rate through the valve increases as print density increases. Ideally, a constant back-pressure should be maintained regardless of printing conditions or ink level conditions. This goal is difficult to achieve since a spring-based system is predicated on the relationship: F = k * x, where F is the spring force, k is the spring constant, and x is the amount the spring is deflected. Thus, to reduce the amount the spring force increases for any given deflection, x, the spring constant, k, would need to be reduced. To obtain an acceptable back-pressure set point, the spring must be preloaded accordingly. In the present invention, the spring constant is reduced by use of a torsion spring which provides a means for combining a relatively large number of active coils within a compact space. Preloading thus occurs in a radial direction. Thus, the mechanism is preloaded to a predetermined set point without occupying extra internal volume more efficiently used for ink storage. Referring briefly to FIGURE 7, a comparison showing the substantial advantage in keeping a steady back-pressure using a torsion spring versus a cantilever, extension, or compression type spring in a spring-loaded regulator mechanism. While size might be a problem, a "negator" spring (e.g., as in a tape measure) also would provide a substantially constant spring force. Referring back to FIGURE 1, the valve actuating member 29 is also adapted to serve as an out-of-ink detector 17 in that when the ink supply runs dry and flow ceases through the septum 11 into the containment chamber 3a, 3b, the bag member 23 eventually fully inflates. A variety of electrical circuit devices can be integrated into the device to provide an indication that an out-of-ink condition has occurred when the valve actuating member 29 reaches a predetermined position within the in containment chamber portion 3b. For example, in the embodiment depicted in FIGURE 1, if the valve actuating member 29 is constructed of metal, two electrical contacts 51, 53 of an open circuit associated with the flex circuit 8 of the printhead mechanism 7 can be provided through the wall of the pen body 1. Traces from the contacts 51, 53 to the flex circuit 8 can be provided in a suitable manner as would be known in the art. In operation, as the bag member 23 inflates, the valve actuating member 29 eventually bridges the contacts 51, 53 and closes the circuit. In other words, the valve actuating member 29 acts as a circuit breaker device. Alternatively, the ends 55, 57 of a metal spring 31 could similarly be used to close a circuit. With the completion of the electrical circuit, an out-of-ink condition indicator (not shown), such as a lighted indicator, a tone producing device, or the like, can warn the user to replenish or replace the ink supply. Preferably, the contact is closed prior to complete starvation of the printhead so that the ink supply can be replenished prior to the pen reaching a de-primed condition. A first alternative embodiment is shown in two similar configurations in FIGURES 2 and 3. A pen body 201 includes an ink containment chamber 203. A printhead mechanism (not shown in this depiction, but see element 7, FIGURE 1) is adapted for attachment, such as at flex circuit 207 or another suitable ink outlet position, as dictated by design expediencies as would be known to a person skilled in the art. A pen body base member 209 includes a spring mounting post portion 241, a spring tension adjustment screw seat portion 243 having a threaded bore 245 therethrough, and a hollow ink inlet tube member 247. Within the containment chamber 203, a diaphragm 223 is mounted about its periphery 224 to substantially seal a complementary aperture 219 through the pen body base member 209. A vapor barrier lid 213, having an aperture 213' for access to a spring tension adjustment screw 249, completes a fluid-tight, pen body enclosure. The vapor barrier lid 213 is preferably vented by a long, relatively narrow channel 214 (FIGURE 3 only) to reduce vapor loss while leaving the diaphragm 223 susceptible to ambient atmospheric pressure. A near constant-force biasing mechanism, torsion spring 231, is mounted on the spring mounting post portion 241 of the pen body base member 209. The torsion spring 231 is adapted to have a first extremity 232 form a seat mated with the spring tension adjustment screw 249. The distal extremity 234 of the spring 231 is elongated and adapted to carry a plunger arm portion 230 connected to a plunger member 229 via an electrically conductive post member 235. The plunger arm portion 230 is further adapted to carry a valve seat 211 for mating with an ink inlet tube member 247, having a hollow bore 247' coupling to act as a conduit for ink from the remoter reservoir. In general, the valve mechanism can be a commercially obtainable needle and seat type and the valve can be actuated by any design expedient plunger arm assembly to which the seat is attached. The spring 231 exerts a force on the plunger arm portion 230 that equals the force exerted by the diaphragm 223 when the back-pressure equals the predetermined design back-pressure set point. Operation of the embodiment of FIGURES 2 and 3 is shown in FIGURE 4. Similarly to the operation of the embodiment shown in FIGURE 1, when the ink supply is depleted, the pressure inside the containment chamber 203 will fall. As the chamber pressure falls below ambient atmospheric pressure, the diaphragm 223 is flexed into the chamber 203. This pressure differential opens and closes the valving mechanism which lets ink from a pressurized remote reservoir enter the pen and printhead mechanism via the conduit that is inlet tube bore 247'. Forces are balanced in this spring-loaded regulator embodiment using a diaphragm 223 and a torsional spring 231. The diaphragm 223 creates its force from the pressure differential between the pen's interior ink containment chamber 203 and the ambient atmosphere. The torsional spring 231 is designed to counter-act the diaphragm force to achieve an equilibrium balance providing an appropriate predetermined back-pressure for the pen and printhead design. This balance set point (depending on the specific pen design printhead architecture requirements) can be roughly set and then adjusted by turning a provided adjustment screw 249 which also acts as the spring stop. All of the pressure regulator components are substantially hermetically sealed within the pen body enclosure. Note that the enclosure also acts as a travel limiter for the spring 231 and plunger arm assembly 229, 230, 235. Thus, when the pressure regulator is subjected to large negative pressures, the enclosure prevents large deflections which could damage the mechanism. The addition of the vapor barrier lid 213 limits evaporation of ink solvents; the lid 213 can be formed of a commercial material, such as a brass foil, that is impermeable to vapor outgassed from the ink in the containment chamber 203. Note also that the set point of the present embodiment can be adjusted once the device has been assembled using screw 249. This allows much tighter control over back-pressure and increases print quality and manufacturing yield. Referring back to FIGURES 2 and 4, as with the embodiment of FIGURE 1, the device can again be used as an out-of-ink- detection mechanism. Referring again to FIGURE 2, an electrical contact 251 is suitably mounted within the containment chamber 203. An electrical trace 254 connects the contact 251 to circuitry 253. Similarly an electrical trace 255 connects the torsion spring 231 to the circuitry 253 via conductive screw 249. If the reservoir is out of ink such that there is no longer any flow through conduit bore 247', the diaphragm 223 will flex until the post member extremity 235 abuts the electrical contact 251 as shown in FIGURE 4. In this manner, the combination of the post member extremity 235 and torsion spring 231 connected to the electrical circuitry 253 via trace 255 completes a circuit with the electrical contact 251 connected to the electrical circuitry 253 via trace 254. The completion of this circuit is used to trigger an out-of-ink condition as with the previous embodiment. The same resolution can be had using the torsion spring design of the present invention with a relatively large lever arm to provide a cantilever action in a smaller footprint design. The torsion spring configuration gives the spring system a lower spring rate which allows greater movement of the valve seat. This also gives the system the potential for higher flow rates when needed, whereas actual cantilever spring type regulator systems do no have enough throw to provide the same leverage ratio to obtain similar flow rates. As a general proposition, increasing the diaphragm area improves the performance of the regulator mechanism. To optimize performance, the size of the diaphragm should be maximized for any given pen body size. Several alternatives can be used to reduce the regulator mechanism footprint. The regulator mechanism diaphragm does not necessarily have to be round; effective area, not shape, is all that is needed in the force balancing equation of the pressure regulated pen system. Therefore, an oblong or oval or even square shaped diaphragm may be used. Such an embodiment is shown in FIGURE 5. A pressure regulated pen body 501 (shown with a cover or side plate removed) has a local ink containment chamber 503. An appropriate printhead mechanism, such as shown in FIGURE 1 is adapted for attachment as dictated by design expediencies for pen orientation with respect to the print medium platen (not shown). As in FIGURE 2, a spring mounting post 541 (see also FIGURE 2 element 241), a spring tension adjustment screw seat post 543 (see also 243, 245, 249), and a hollow, ink inlet tube member 547 (see also 247, 247') is provided. The ink inlet tube member 547 provides a channel for coupling the ink containment chamber 503 to a remote ink reservoir (not shown) such as with a simple tube or other ink conduit (not shown). Within the ink containment chamber 503, an oblong diaphragm 523 (see also 223) is mounted about its periphery to substantially seal a complementary cavity in the pen body 501 (hidden in this view; see also 224, 219). A port 519 connects the cavity to the ambient atmosphere. The port 519 is preferably a relatively long, narrow channel or labyrinth in order to reduce vapor loss while leaving the diaphragm 523 susceptible to ambient atmospheric pressure changes. A torsion spring 531 (see also 231) is mounted on the spring mounting post 541. The torsion spring 531 is mounted to have an extremity 532 proximate the spring coil and coupled to the spring tension adjustment screw seat post 543 and adjustment screw therein (not shown; but see FIGURE 2, elements 232, 245, 249). A distal extension member 534 (see also 234) of the torsion spring 531 extends through a plunger arm member 530. The plunger arm member 530 is coupled to a plunger post member 535 (see also 235) which is in turn coupled to a plunger member 529 (see also 229). The plunger arm member 530 also bears a valve seat mount 530'. The inner reach of the ink inlet tube member 547 has an opening, such as a molded orifice or the like, into the ink containment chamber 503 that acts in conjunction with the valve seat 533 and torsion spring assembly inside the chamber 503 to act as a valving mechanism. The operation of the embodiment as shown in FIGURE 5 is substantially the same as with the prior embodiment of FIGURES 2 through 4 as described above. Referring now to FIGURES 6 and 6A, it has been found that it is advantageous to make the diaphragm deflection mechanism as frictionless as possible. By doing so, variations in back-pressure are reduced and pen operation will be more consistent. A pen body base member 609 provides a similar mechanism for a diaphragm 623 and plunger 629 mechanism as in the embodiments shown in FIGURES 2 through 5. A plunger arm 630 is coupled to a free-floating torsion spring 631. A plunger post member 631' of the plunger arm 630 has a recess 631" (FIGURE 6A) or other mechanism for fixedly capturing one extremity 632 of the spring 631. Snaps 650, or other holding mechanisms along the plunger arm 630, fixedly secure a plunger arm spring extension member 634 to the plunger arm 630. A valve seat 633 and inlet valve mechanism 647 are provided in a manner substantially identical to the prior embodiments as already described. An opposite spring extremity 632 is fixedly captured (or designed for adjustment as shown in the embodiments of FIGURES 2 through 5) in a recess 643' of a base member mount post 643 such as with snaps 650'. Operation of the embodiment of FIGURES 6 and 6A is identical to the embodiment of FIGURES 2 through 5, only in this configuration where the spring is end mounted and the spring coil is free floating, frictional influences upon the diaphragm are minimized. Note that in addition to maintaining the pen ink containment chamber in a proper back-pressure balance, the apparatus can be used to "prime" the printhead. By manually pushing the diaphragm, such as by forcing a pressure through the vent (see FIGURE 4, element 214), the regulator valve could be held open and ink forced into the containment chamber until any air or gases from the ink is expelled through the orifice plate or a gas purge vent mechanism. The foregoing description of the preferred and alternative embodiments 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 disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. Similarly, any process steps described might be interchangeable with other steps in order to achieve the same result. The embodiments were chosen and described in order to best explain the principles of the invention and its best mode practical application to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims: An inkjet pen apparatus, adapted for use with an ink reservoir having a mechanism for supplying ink from said ink reservoir to said inkjet pen apparatus at a predetermined feed pressure, said inkjet pen apparatus characterised by : a pen body (1,201,501) having an ink containment chamber (3b, 203, 503); an inkjet printhead mechanism (7,207) coupled to said pen body (1,201,501) and in fluidic communication with said ink containment chamber (3b,203,503); coupling means (11,12,247,247',211,547,511,647,633) for coupling said ink containment chamber (3b,203,503) to said ink reservoir; and regulating means (12,211-249, 223-235, 623-650), mounted within said ink containment chamber (3b,203,503) and coupled to said coupling means (11,12,247,247', 211,547,511,647,633) for regulating flow of ink into said ink containment chamber (3b,203,503) from said ink reservoir via said coupling means (11,12,247,247',211,547,5111,647,633) while maintaining a predetermined, substantially constant, back-pressure set point at said inkjet printhead mechanism (7,207) during varying ink flow rates from said ink reservoir into said ink containment chamber (3b,203,503), wherein said regulating means (12,211-249,223-235,623-650) includes: valve means (12,33,211,511,633,647) for varying ink flow rate and preventing the flow of ink from said ink reservoir into said ink containment chamber (3b,203,503), and biassing means (29,31,55,57,231,232,234,235,629,631-650'), having a substantially constant bias force during varying ink flow rates from said ink reservoir into said ink containment chamber (3b,203,503), coupled to said valve means (12,33,211,511,633,647) for opening and closing said valve means, and comprising a torsion spring (31,55,57,231,232,234,531,532,631,632) having a substantially constant spring force, and at least one inflatable bag member (23) mounted on a valve seat mount (29) and coupled to ambient atmospheric pressure such that said bag member (23) inflates and deflates in response to the differential between ambient atmospheric pressure and said predetermined back pressure set point. The apparatus as set forth in claim 1, further characterised by : adjusting means (245,1249) for adjusting the predetermined back-pressure set point. The apparatus as set forth in claim 1 wherein said means for opening and closing (19,19',25,27,213,223,519,523,623) said valve means (12,33,211,511,633,647) is characterised by : a valve seat (33,211,511,633), movable to open and close said valve means, a valve seat mount (29,230,530',630), having said valve seat (33,211,511,633) mounted thereon, and wherein said biassing means (31,55,57,231,232,234,235,531-543,629,631-650') is coupled to said valve seat mount (29,230,530',630), for holding said valve seat (33,211,511,633) in a position closing said valve means until the biassing force is overcome by ambient atmospheric pressure.

Inventors: PAWLOWSKI NORMAN E JR, PAWLOWSKI, NORMAN E., JR.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1996
Main classification: B41J2
IPC codes: G01F23, B41J2