Ink jet printing apparatus with air purge function

An ink jet printing system with a pen body having a first chamber and a second chamber. A print head on the pen body is connected to the second chamber, and an ink-transmissive barrier separates the second chamber from the first chamber. A pump is connected to the pen body in communication with the first chamber, and operates to generate a positive pressure in the first chamber to motivate ink from the first chamber, through the barrier, and into the second chamber. An ink supply cartridge may be provided that removably connects to the pen body, and which has openings in registration with corresponding openings in the pen body into the first and second chambers, respectively. A sliding shutter or other valve may be provided on each of the pen body and the cartridge to close the openings when the cartridge is removed from the pen body. An actuator portion of the cartridge may operate to engage the pump upon installation of the cartridge, and to displace any gas bubble from the second chamber to the supply cartridge; upon disengagement of the cartridge, the actuator may release the pump, drawing ink from the cartridge into the first chamber.

FIELD OF THE INVENTION
 This invention relates to ink jet printers, and more particularly to ink
 jet printers with replaceable ink supplies.
 BACKGROUND AND SUMMARY OF THE INVENTION
 Ink jet printers employ print heads that reciprocate over a media sheet and
 expel droplets onto the sheet to generate a printed image or pattern. In
 some ink jet printers, an ink supply connected to the print head
 reciprocates along with the print head. To reduce operating costs, some
 ink jet printers use ink supplies that are separately replaceable, so that
 the print head is not discarded when an ink supply is depleted. The
 connection between such a print head and replaceable ink supply faces some
 difficulties.
 First, it is important to make a disconnectable fluid connection between
 the ink supply and the print head that does not leak, either when the
 components are connected to each other, or when separated for ink supply
 replacement. A connection should be repeatable without degradation,
 readily aligned or tolerant of misalignment, compact, reliable, and
 inexpensive.
 A second concern with removable ink supplies involves the introduction of
 gas into the print head. Gas may be introduced by way of ink containing
 dissolved gas that outgasses in a print head chamber, or due to air
 entrapped upon connection of an ink supply. Gas bubbles can block the flow
 of ink, and can lead to ink degradation, drying, or crusting.
 Existing supply/print head interface systems may employ a foam-filled ink
 supply, and a mesh covered conduit on the print head that presses against
 the foam. While effective, foam systems reduce the volumetric efficiency
 of the supply cartridge, are subject to ink crusting at the openings when
 the components are separate, and are vulnerable to leakage without
 additional sealing.
 Other contemplated systems for a supply/print head interface involve the
 use of a needle and septum, with a hollow needle on the print head, and a
 septum on the ink supply sealing the opening. This requires additional
 sealing to prevent the needle from drying out when the supply is removed,
 and the system tends to be more bulky and complex than would be most
 desirable. The septums may be damaged or deformed, with a particular
 concern involving an inexperienced user repeatedly reinstalling a single
 ink supply due to a lack of confidence about whether the installation was
 correct. Further, such systems are intolerant of moderate misalignments,
 and rely on elastomeric components that can be troublesome to procure.
 The present invention overcomes the limitations of the prior art by
 providing an ink jet printing system with a pen body having a first
 chamber and a second chamber. A print head on the pen body is connected to
 the second chamber, and an ink-transmissive barrier separates the second
 chamber from the first chamber. A pump is connected to the pen body in
 communication with the first chamber, and operates to generate a positive
 pressure in the first chamber to motivate ink from the first chamber,
 through the barrier, and into the second chamber. An ink supply cartridge
 may be provided that removably connects to the pen body, and which has
 openings in registration with corresponding openings in the pen body into
 the first and second chambers, respectively. A sliding shutter or other
 valve may be provided on each of the pen body and the cartridge to close
 the openings when the cartridge is removed from the pen body. An actuator
 portion of the cartridge may operate to engage the pump upon installation
 of the cartridge, and to displace any gas bubble from the second chamber
 to the supply cartridge; upon disengagement of the cartridge, the actuator
 may release the pump, drawing ink from the cartridge into the first
 chamber.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
 FIG. 1 shows an ink jet printing system 10 having a pen assembly 12 and a
 removable ink supply cartridge 14. The pen assembly is mounted to a
 carriage (not shown) that reciprocates along a scan axis 16 above a media
 sheet 20. The media sheet is advanced along a feed axis 22 by a feed
 mechanism 24.
 The pen assembly 12 has three major moving parts. A pen body 26 is fixed
 with respect to the carriage, a sliding pen shutter 30 is slidably
 connected to an upper portion of the body, and a pump element 32
 reciprocates with respect to the body as will be discussed in detail
 below. An inkjet print head 34 is connected to a lower surface of the pen
 body.
 The ink supply cartridge 14 includes a body 36 defining an ink chamber 40,
 which is fully enclosed (except for some form of vacuum relief valve or
 mechanism), but which is shown open at its upper end for illustration
 purposes. A cartridge shutter 42 is slidably connected to a lower portion
 of the body, and a latch 44 is pivotally attached to a lower end of the
 body. As shown in FIG. 2, the cartridge shutter 42 is an elongated planar
 body that rests flat against the flat lower surface 46 of the cartridge.
 The shutter is held tightly against the lower surface by a pair of rails
 50, which constrain motion of the shutter to the single linear degree of
 freedom along the length of the shutter.
 The shutter defines a first opening 52 and a second opening 54, which are
 spaced apart and aligned on the median of the shutter. The shutter has a
 flat, smooth lower surface 55 in the regions of the openings so that each
 opening is entirely surrounded by the planar surface. At a free end of the
 shutter, in what will be described as the insertion direction, a flange
 portion 56 extends upwardly. The flange defines an aperture 60 for closely
 receiving a cylindrical boss 62 that extends horizontally from the
 exterior of the cartridge body in the insertion direction. The shutter
 includes four engagement feet 64 extending downward and in the insertion
 direction for engaging the shutter of the pen body, as will be discussed
 below. Each foot has a toe portion with a sloped upper surface that
 provides a wedging function when it engages a similar and oppositely
 oriented element on the pen shutter. The shutter 42 is spring biased
 toward the insertion direction by a coil compression spring 66 that
 encompasses the boss 62, pressing apart the shutter flange from the
 cartridge body.
 The pen shutter 30 is spring biased toward an extraction direction opposite
 the insertion direction by a tension spring 70, which connects an
 extending portion 72 of the pen shutter to an exterior surface of the pen
 body facing the insertion direction. Referring back to FIG. 1, the pen
 shutter 30 defines a first opening 74 and a second opening 76, which
 respectively correspond to the first and second openings 52, 54 of the
 cartridge shutter, and which have similar size and spacing so that they
 are in registration when the two shutters are engaged. The shutter has a
 flat, planar upper surface 78, particularly those portions entirely
 surrounding each of the openings. The pen shutter includes two upwardly
 protruding feet 80 adjacent the second shutter opening 76, and a tapered
 ledge 82, all extending in the extraction direction and having sloped
 lower surfaces that facilitate engagement of the two shutters, and to
 compress together the respective flat surfaces 55 and 78 to provide a
 fluid-tight seal about the openings.
 As further shown on FIG. 1, the pen body has a stanchion 84 that protrudes
 upwardly from a rearwardly extending portion of the body. The pump element
 has an intermediate portion 86 that is captured in a channel in the pen
 body, and which has an upstanding actuator portion 90. A tail portion 92
 of the pump element is connected to the pen stanchion 84 by way of a
 tension spring, which biases the pump to the illustrated retracted
 position.
 As shown in FIG. 3, the ink cartridge 14 is shown just prior to
 installation on the pen 12, with the ink chamber 40 filled to a full level
 94 with ink 96. At the lower wall of the cartridge body, a pair of
 cartridge openings 100, 102 are spaced apart and sized similarly to the
 shutter holes 52, 54. With the cartridge shutter 42 in the closed position
 illustrated, the cartridge openings 100, 102 are closed because the
 shutter openings are offset. As will be illustrated below, when the
 shutter is moved to an open position, the openings align, and fluid flow
 into and out of the chamber is provided. In either position, and in
 intermediate positions, the flat upper surface of the shutter and flat
 lower surface of the cartridge body prevent fluid from escaping between
 the components.
 The pen body 26 defines a first chamber 104 and a second chamber 106. At
 the upper surface of the pen body, a first aperture 110 connects to the
 first chamber 104 and opens to a first elongated basin 112 that is
 recessed below a flat pen body upper surface 114. A second aperture 116
 connects to the second chamber 106 and opens to a second elongated basin
 120 that is recessed below the upper surface 114, and which is separate
 from the first basin 112. The basins are positioned co-linearly along the
 midline of the pen shutter, and are spaced apart on-center comparably to
 the spacings of the apertures 110, 116, and of the shutter openings 74,
 76.
 The first aperture 110 is covered at its lower opening by a reed-type check
 valve 122 that admits fluid into the first chamber from above, but which
 prevents fluid from escaping the first chamber. The second aperture 116 is
 covered at its upper opening in the basin 120 by a reed-type check valve
 124 that admits fluid into the basin from the second chamber below, but
 which prevents fluid from entering the second chamber by way of the
 opening 116. Both check valves are normally closed, so that ink or air do
 not leak into or out of the pen when pressures are at equilibrium, such as
 when there is no ink supply cartridge installed.
 The first chamber 104 and second chamber 106 are separated from each other
 by a porous mesh barrier 126, such as is commonly used in existing ink jet
 devices. The mesh barrier has openings sized to prevent passage of
 anticipated contaminant particles. The mesh also serves to prevent passage
 of gas bubbles when wetted by ink. The barrier 126 is positioned largely
 beneath the first chamber and above a portion of the second chamber. It is
 tilted at an angle from the horizontal, and slopes upward toward the
 second aperture. Thus, an air bubble trapped in the second chamber below
 the barrier will float upward at an angle toward the opening 116, where it
 will come to rest as illustrated by bubble 130. Essentially, the upper
 portion of the second chamber is positioned laterally of part of the first
 chamber, and entirely above the level of the barrier. It serves as a sump
 to collect gas bubbles that occur in the second chamber.
 The pump element 32 has a piston element 132 that is closely received in a
 pump aperture 134 in a wall of the first chamber. The piston element has a
 constant rectangular cross section that maintains a fluid-tight seal with
 the wall as it reciprocates between the extended position shown, and a
 compressed position in which a major portion of the piston extends into
 the first chamber. Thus, the pump effectively changes the volume of the
 first chamber. Upon compression, it displaces unfiltered ink, which
 becomes filtered as it passes through the mesh barrier into the second
 chamber (and thereby expelling the gas bubble and/or ink out of the second
 chamber as discussed below); upon extension, it draws fluid into the first
 chamber via the first opening 110.
 FIG. 3 shows an initial condition in which the cartridge is not yet
 connected to the pen. In FIG. 4, the cartridge is in an initial stage of
 connection with the pen. The cartridge has been advanced in the insertion
 direction until the cartridge shutter 42 is fully engaged to the pen
 shutter 30. In the engaged condition, the shutter surfaces 55 and 78 are
 fully abutting around the shutter openings 52, 54, 74, 76. In this
 condition, the shutters are essentially connected as a single unit, and
 the contact surrounding the openings prevents leakage of ink at the seam
 of contact. The shutters are held in close contact by the engagement of
 the feet 64 of the cartridge shutter, with the feet 80 and ledge 82 of the
 pen shutter. The slopes at the toes of each foot prevent the toes from
 stubbing against each other, and provide a camming action that compresses
 the shutters together.
 In the FIG. 4 condition, the ink supply is full, and the pen chambers are
 filled with ink, except for the presence of the bubble 130. Each shutter
 is in a closed position as biased by the respective springs, so that the
 openings of the shutter are offset from the respective openings of the pen
 body and the cartridge. A tail portion 136 of the cartridge shutter
 remains spaced apart from the pump actuator 90, and the pump remains in
 the extended position allowing maximum first chamber volume.
 In FIG. 5, cartridge installation proceeds, with the cartridge tail portion
 136 having contacted the pump actuator 90, and with cartridge advancement
 having continued beyond the moment of such contact. Because the spring
 force of the pen shutter spring 70 is greater than that of cartridge
 shutter spring 66, the further cartridge movement causes the cartridge to
 move relative to the momentarily immobilized cartridge shutter,
 compressing spring 66 and bringing the cartridge apertures 100, 102 into
 registration with shutter openings 52, 54. With the cartridge shutter
 fully open, limited by the interaction of the shutter flange hole 60 with
 a shoulder on the boss, further advancement causes the pen shutter 30 to
 slide toward an open position. In this position, the pen shutter holes 74
 and 76 have just overlapped the pen basins 112 and 120. Thus, in the
 illustrated moment of installation just prior to actuation of the pump,
 there are two avenues for fluid communication between the ink supply and
 the pen chambers, limited only by the check valves, each of which is
 presently closed in the absence of a pressure differential in the
 appropriate direction.
 In FIG. 6, the cartridge is fully installed, and the latch 44 has dropped
 under its own weight to engage the pen stanchion 84, preventing the
 cartridge from being inadvertently moved from the installed position by
 the actions of the springs, all of which are providing a maximum biasing
 force in the installed position. In the installed position, the cartridge
 shutter 30 and pump 32 have advanced together until the pump has displaced
 ink from the first chamber 104 into the second chamber 106. Meanwhile, the
 shutter openings remain in communication with the pen apertures throughout
 the compression process between the moments of FIGS. 5 and 6. This is
 possible because the basins have adequate length comparable to the stroke
 of the pump, and is necessary because at least one of the openings must
 allow fluid flow to accommodate the volume displacement.
 Upon installation, the volume change caused by the pump is accommodated by
 expulsion of the air bubble 130 from the second chamber, past the check
 valve 124, and through the openings into the ink chamber of the cartridge;
 check valve 122 prevents ink flow through the other opening. Preferably,
 the pump displacement is calculated to be at least as great as the volume
 of the typical bubble. The displacement may be based in part on expected
 outgassing by the typical volume of ink in the cartridge over the life of
 the cartridge. Any pumping of ink back to the cartridge where the bubble
 is smaller than expected is not a problem, because the recirculated ink
 will be available for printing. This means that repeated pumping, such as
 might occur when an inexperienced user repeatedly installs and uninstalls
 a cartridge, does not waste ink.
 When fully installed, printing may proceed until the cartridge contents are
 depleted. In the preferred embodiment, the printing system uses drop
 counting or other means to estimate when the cartridge is nearly but not
 entirely depleted. This prevents "dry firing" of the print head, which can
 damage a component that is intended to be reused for a multitude of ink
 cartridges.
 FIG. 7 illustrates the condition in which the ink level has dropped from
 the full level 94 to a depleted level in which ink remains covering both
 cartridge apertures 100, 102. Through the process of the printing that has
 consumed the ink to deplete the cartridge, a new bubble has reformed in
 the pen, and will eventually be displaced upon installation of the next
 cartridge as described above. After receiving a signal from the printer,
 the user begins the process of removing and replacing the functionally
 depleted cartridge. On removal, the process of installation is reversed,
 with the sequence of operation of the shutters and pump proceeding in
 reverse order. The user lifts the latch 44, and extraction is made with
 the aid of the spring forces, particularly that of the pump spring.
 As shown in FIG. 8, the extension of the pump 32 by the pump spring 94
 increases the volume of the first chamber 104. The first chamber check
 valve 122 admits ink from the cartridge supply to fill the enlarged
 volume, slightly dropping the ink supply from level 140 to level 142. The
 check valve 124 on the second chamber ensures that unfiltered ink from the
 supply does not enter the "clean" second chamber, where contaminants might
 cause clogging of the print head. Throughout the shifting of the pump, the
 apertures remain open as the shutter apertures pass over the pen basins,
 as discussed above. In the moment illustrated by FIG. 8, the pump has
 completed its stroke. As extraction proceeds, the shutters move so that
 the pen shutter closes off the pen apertures. Then, the cartridge
 continues moving relative to the shutters to close off the cartridge
 apertures. Finally, the shutters disengage from each other, and the
 cartridge is removed.
 Until a new cartridge is installed, the pen openings are closed, and only
 the volume of the pen shutter openings are filled with ink exposed to air.
 Even if this ink is allowed to dry, it presents no contaminant concern
 because the second chamber check valve 124 prevents admission of any
 contaminants to the pen, and the filter barrier prevents contaminants from
 reaching the print head. Similarly, the small volume of the cartridge
 shutter openings contains only a minimal amount of exposed ink, limiting
 the risk of spillage before the depleted pen is disposed of.
 An new cartridge is installed as illustrated beginning in FIG. 3 by the
 same process.
 In the preferred embodiment, the shutters, the pump, and the pen and
 cartridge components that sealably contact the shutters are formed of a
 hydrophobic material such as Teflon.RTM.-filled plastic. This prevents ink
 from wicking via any microscopic planar gaps between the surfaces.
 Alternatively, elastomeric gaskets may be used to ensure a good seal in
 circumstances in which suitable materials or dimensional precision are not
 attainable. In other alternatives, the pump system may be used without
 sliding shutters, with the check valves in the pen providing closure, and
 another set of check valves or the like providing closure of the cartridge
 apertures. The check valves may be of any suitable type, including duck
 bill, ball-type, or any other type. The pump is shown as a sliding piston,
 but may be of any type, including one using a flexible diaphragm to
 provide a seal. Similarly, an elastomeric gasket or 0-ring may be employed
 where the use of a hydrophobic pump element material is inadequate to
 provide a reliable seal.
 The spring forces may be changed to select the sequence of operations
 during installation and removal. It is important that the openings between
 pen and supply cartridge be open during the entire stroke of pump motion,
 to avoid expelling ink or ingesting air via the print head. However, In
 embodiments in which the pump attempts to operate against a sealed
 chamber, it is believed that this may provide adequate resistance to stop
 pump actuation until an appropriate opening is available to allow ink
 flow. Also, it is preferable that the shutters mate before either the pen
 or cartridge shutters open, preventing ink from leaking between the
 shutters before they are fully engaged and sealed. Which shutter opens
 first, or whether the forces are designed so that they open simultaneously
 is unimportant.
 In the preferred embodiment, it has been observed that the following
 actions occur as the cartridge is installed and moved from a zero position
 in which the shutters are mated, toward the installed position, and beck
 to the removed position. Displacement distance are of the cartridge body
 relative to the fixed pen body.
 0.0 mm Shutters engaged, both shutters fully closed, cartridge shutter
 about to move.
 1.0 mm Cartridge apertures begin to open.
 2.6 mm Cartridge apertures fully open.
 3.6 mm Pen apertures begin to open.
 3.8 mm Pump motion begins.
 5.2 mm Pen apertures fully open.
 8.9 mm Pen shutter stops, pump fully compressed, latch engaged, cartridge
 fully installed. The pen is operational.
 Extraction then begins.
 5.2 mm Pen apertures begin to close.
 3.8 mm Pump motion ends, fully retracted.
 3.6 mm Pen apertures closed.
 2.6 mm Cartridge apertures begin to close.
 1.0 mm Cartridge apertures closed.
 0.0 mm Shutters engaged, both shutters fully closed, cartridge removable.
 While the above is discussed in terms of preferred and alternative
 embodiments, the invention is not intended to be so limited. For instance,
 the ink that cycles back into the cartridge during pumping may be sent to
 a waste chamber in systems with ink chemistry that has a limited shelf
 life, or which is otherwise unsuited to such recycling.