Monitoring and controlling ink pressurization in a modular ink delivery system for an inkjet printer

An air pressurization system is incorporated as part of a replaceable auxiliary ink supply for an ink jet printer. The auxiliary ink supply cartridge includes a pressurized container having air, ink and electrical signal connections. The air pressure applied to the auxiliary ink supply is monitored to be maintained in a predetermined range in accordance with a start-up sequence, an operational sequence, a waiting time, and a close-down sequence.

FIELD OF INVENTION
 The present invention generally relates to print cartridges used in
 computer controlled printers, and more particularly, to methods and
 apparatus for delivering ink to such print cartridges.
 BACKGROUND OF INVENTION
 One problem in ink-jet printing is that some applications require a large
 supply of ink. For example, "large format" applications use large size
 printing media (for example, 22 inch.times.34 inch, 34 inch.times.44).
 Examples of large format applications include computer aided design
 (engineering drawings), mapping, graphic arts, and posters. The large
 format printed image can use a large amount of ink either because of the
 large printed area needing to be covered with ink or the use of 100
 percent filled-in image areas, or both. Therefore, it is desirable to have
 ink reservoirs that contain a large amount of ink to avoid replacing an
 empty ink reservoir in the middle of a printing cycle or the frequent
 changing of the ink reservoir between printing jobs.
 However, merely increasing the size of the ink reservoir in an on-board
 system to hold more ink has not proved to be an acceptable solution. The
 ink reservoir is supported on the printer carriage and moves with the
 printhead. Increasing the amount of ink in motion would necessarily
 require an increase in the size and weight of the structure that supports
 and moves the carriage back and forth. The increased mass of the carriage
 would also significantly increase the cost of the printer (for example,
 larger and more expensive electrical motors).
 In response, recently, relatively large ink reservoir systems have
 developed in which the reservoir is mounted off-board.
 In contrast to on-board reservoirs, printing systems using off-board ink
 reservoirs require means for delivering the ink from the off-board ink
 reservoir to the printhead. Pumps can be used for such delivery, but such
 pumps have problems associated with their use. For example, the
 ingredients in the ink can be incompatible with the pump components, and
 such components as diaphragms and seals can degrade when exposed to the
 ink solvents for extended time periods.
 A second problem in ink-jet delivery arises in color printing. Color
 printing typically uses multiple ink reservoirs, each containing ink of a
 different hue. Since each ink reservoir must be individually pressurized,
 multiple pumps can be used. However, the addition of each additional pump
 increases the cost of the overall printing system. Thus, it would be
 desirable to use one pump that can provide the necessary pressure for all
 the ink reservoirs individually.
 One other problem in ink-jet technology is that the customers have
 different purchasing criteria. Some customers, with high ink usage rate,
 may prefer the lower, "unit price" of a large ink reservoir. Other
 customers, may prefer a lower, "start-up" price of a smaller ink
 reservoir. Thus, it would be beneficial for the customers to have a
 printing system that is adaptable to ink reservoirs with different sizes.
 In addition, the manufacturer also benefits when the size of the ink
 reservoir is not a limiting factor in the design of the printer or the ink
 delivery system.
 SUMMARY OF THE INVENTION
 Briefly and in general terms, an apparatus for delivering pressurized ink
 to a printhead, according to the invention, includes a deformable bag for
 holding ink, a pressurizable container substantially surrounding the bag
 for exerting fluid pressure on said bag and pressurizing any ink within
 the bag, and a sealable ink outlet port for fluid communication with the
 ink bag. The port is fluidically connectable to the printhead so that
 pressurized ink is deliverable to the printhead.
 The invention contemplates a process having the steps of: providing a
 deformable bag for holding ink for a printhead; substantially surrounding
 the bag with a pressurizable container; exerting fluid pressure on the bag
 by pressurizing the container, thereby pressurizing any ink within the
 bag; and delivering pressurized ink to the printhead.
 In a presently preferred embodiment of the invention, the air pressure
 system is incorporated as part of a replaceable auxiliary ink supply as
 well as part of a replaceable ink delivery system having air, ink and
 electric signal connections to the auxiliary ink supply. The air pressure
 applied to the auxiliary ink supply is monitored to be maintained in a
 predetermined range in accordance with a start-up sequence, an operational
 sequence, a waiting time, and a close-down sequence.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring to FIG. 1A, reference numeral 310 generally indicates a
 pressurizable container for exerting fluid pressure on a deformable ink
 bag 313 which contains a liquid ink 316.
 The container 310 is an air impermeable rigid container which houses the
 ink bag 313. The container 310 is attached to a chassis 319 to form a
 hermetic seal. A method for securing such a seal is to choose the same
 material, such as HDPE (high density polyethylene), for both the chassis
 319 and the container 310 and to use an attachment process such as
 ultrasonic welding, or heat staking, or adhesive bonding. A gas inlet port
 355 allows pressurized air 373 to flow into the container 310. Later
 versions use an O-ring seal between the container and chassis.
 The ink bag 313 is constructed from a multi-layer metallized polymer film,
 such as metallized PET (polyethylene terephthalate), with a sealant layer
 made of LDPE (low density polyethylene). The bag 313 has a high barrier
 property to water diffusion and other solvents present in the ink 316. The
 ink bag 313 can be of any shape and size suitable for holding the ink 316.
 The ink bag 313 is flexible, deformable, and collapses when its contents
 are emptied.
 The ink bag 313 is heat staked onto an external surface 321 of a fin 322 to
 make a hermetic, fluid tight seal. Also, the fin 322 is attached to the
 chassis 319 to form a hermetic, fluid tight seal. A method for making the
 fin to chassis seal is to choose the same material, such as HDPE (high
 density polyethylene), for both the chassis 319 and the fin 322 and to use
 an attachment process such as ultrasonic welding, or heat staking, or
 adhesive bonding. In the preferred embodiment the fin 322 has a diamond
 shape for manufacturing ease. The fin 322 has two ports, an ink inlet port
 328 and an ink outlet port 331. The fin 322 is connected to a first ink
 conduit 334 at the ink outlet port 331. The first ink conduit has a
 sealable outlet port 325 and is connected to a second ink conduit 342 by a
 first male connector 337. The sealable ink outlet port 325 provides fluid
 communication with the print cartridge.
 The first male connector 337 is located on a base 346 of a printer 349. The
 first ink conduit 334 and the second ink conduit 342 are made of a
 material with high barrier property, such as FEP (fluorinated ethylene
 propylene), to diffusion of air and ink solvents (including water). The
 ink 316 is in fluid communication with a print cartridge 344 via the bag
 313, the fin 322, the first ink conduit 334 and the second ink conduit
 342. Thick LLDPE (linear low density polyethylene) tube material has been
 used more recently.
 Referring to FIG. 1A, reference numeral 344 generally indicates the print
 cartridge connected to the second ink conduit 342. The print cartridge
 also includes a printhead 340. The print cartridge is of conventional
 thermal ink-jet construction and operation. The print cartridge 344 also
 includes a pressure regulator 341 for maintaining a preset back pressure
 (for example, minus 2 inches of water) required for the printhead 340 to
 function. When the pressure inside the printhead 340 is lower than
 atmospheric pressure, a condition exists that is called back pressure (or
 negative pressure). Back pressure is necessary to keep ink from drooling
 out of the nozzles (not shown here) of the printhead 340. The pressure
 regulator 341 is in fluid communication with the ink 316 in the second ink
 conduit 342 on one side, and the printhead 340 on the other side.
 Depending on the pressure inside the printhead 340, the pressure regulator
 341 allows or stops the flow of the ink 316 to the printhead 340.
 Further referring to FIG. 1A, the container 310 is in fluid communication
 with a first gas conduit 356 having a sealable gas inlet port 352 and the
 gas inlet port 355. The gas inlet port 355 is received in the container
 310. The first gas conduit 356 is connected to a second gas conduit 364.
 The second gas conduit has a second male connector 358 that is insertable
 into the sealable gas inlet port 352. The sealable gas inlet port 352 and
 the second male connector 358 together, make a second quick disconnect
 valve 367. See FIG. 2B. The second male connector 358 is located on the
 base 346 of the printer 349.
 The container 310, the ink bag 313, the fin 322, the chassis 319, the first
 ink conduit 334, the first gas conduit 356, the sealable ink outlet port
 325, and the sealable gas inlet port 352 are collectively referred to as
 an ink containment device 311.
 Referring to FIG. 1A, reference numeral 361 generally indicates an air
 manifold. The air manifold 361 contains a first gas outlet port 370 for
 providing air 373 to the container 310 via the second gas conduit 364. The
 number of the first gas outlet ports 370 on the manifold is a matter of
 design to accommodate all the pressurizable containers 310 that house the
 ink bags 313. Only one container and ink bag is illustrated in FIG. 1
 avoid redundancy. In a typical color ink-jet printing device there are
 four ink reservoirs: black, magenta, cyan, and yellow. Thus, on such a
 color printer the air manifold 361 has four first gas outlet ports 370. An
 air compressor 376 is electrically connected to the printer 349 so that
 the compressor 376 is turned on when the printer 349 signals the air
 compressor. The air compressor 376 has a second gas outlet port 382 which
 is connected to an air chamber 385 in the air manifold 361 via a third gas
 conduit 388. The air compressor 376 can be any commercially available unit
 capable of providing air at a pressure of about 2 psi and at an air flow
 rate of about 150 cc/min. More recent innovations use a pressure sensor
 with a more powerful compressor as described in more detail below.
 The air manifold 361 has an air bleed vent 390 for providing a continuous
 bleed. The bleed vent is a commercially available ball 392 and spring 393.
 The purpose of the continuous bleed is to minimize the exposure of the
 seals in the system to an elevated pressure when the printer is not in
 operation and second, to equilibrate the system's pressure and to avoid
 over pressurization during operation. When the pressure inside the air
 chamber 385 exceeds the desired pressure of 2 psi, the ball 392 compresses
 the spring 393 to allow excess air to exit through the air bleed vent 90.
 Referring to FIG. 1A, in operation, the first male connector 337 and the
 second male connector 358 are inserted into the sealable ink outlet port
 325 and the sealable gas inlet port 352, respectively. These insertions
 bring the ink containment device 311 in fluid communication as shown in
 the drawings.
 When the air compressor 376 is turned on, the air 373 flows in turn through
 the second gas outlet port 382, the third gas conduit 388 and into the air
 chamber 385. The air 373 is then directed to the first gas outlet port 370
 and thereafter through the second gas conduit 364, the second quick
 disconnect valve 367, the first gas conduit 356, the gas inlet port 355
 and into the container 310.
 The pressure of the air inside the container 310 exerts a pressure on the
 ink bag 313 containing the ink 316. This pressure causes the ink 316 to
 flow through the ink inlet port 328 and thereafter through the fin 322,
 the ink outlet port 331, the first ink conduit 334, the first quick
 disconnect valve 343, the second ink conduit 342 and into the pressure
 regulator 341.
 As the ink is jetted out of the printhead 340, the pressure inside the
 print head 340 decreases until it reaches a preset back pressure. The
 difference between the back pressure on one side of the pressure regulator
 341, in communication with the printhead 340, and the more positive
 ambient air pressure creates a pressure differential that causes the
 pressure regulator 341 to open and to allow the ink 316 to flow into the
 printhead 340. When the pressure in the printhead 340 reaches the preset
 operating pressure, the flow of ink stops and the differential pressure
 across the pressure regulator is equilibrated.
 FIG. 3 illustrates another embodiment of the present invention. For the two
 embodiments like reference numerals indicate like components. In referring
 to FIG. 1B reference numeral 310' generally indicates a pressurizable
 container for exerting pressure on the deformable ink bag 313 which
 contains the liquid ink 316. A sealable fluid inlet 412, such as a septum,
 is located in a sidewall 415 of the container 310' for receiving a
 pressurized fluid 422 such as air. A pressurized fluid cylinder 418 holds
 the pressurized fluid 422. The pressurized fluid 422 is in fluid
 communication with the container 310 through a pressure regulator 431, a
 fluid conduit 425, and a hollow needle 428 which connects to the inlet
 412. The pressure regulator is commercially available and is set for a
 pressure of about 2 psi. The fluid conduit 425 is made of any material
 that can support an air pressure of about 2 psi.
 Referring to FIG. 1B, in operation, the hollow needle 428 is inserted into
 the septum 412. The pressurized fluid cylinder 418 is opened and the
 pressurized fluid 422 moves through the pressure regulator 431, the fluid
 conduit 425, the needle 428, and into the container 310. The needle 428
 can remain in the septum during normal operation. Upon inserting the first
 male connector 337 into the sealable ink outlet port 325, the system is
 ready for operation in the same manner as described above in connection
 with FIG. 1A.
 It should be appreciated that: any pressurizable fluid, including a liquid,
 that is compatible with the pressurization system can be used in place of
 the air 373 and the fluid 422; the fin 322 has a diamond shape but any
 other shape that can accommodate the ink bag 313 and the chassis 319 can
 be used; the preset back pressure is minus 2 inches of water but the
 pressurization system described here can accommodate any other back
 pressure requirements that the printhead 340 may have; only one type of
 air compressor 376 is described but any type of pump capable of providing
 the desired air pressure and flow rate may be used such as those pumps
 used in fish aquariums; and the desired pressure in the ink conduits, the
 gas conduits, and the containers 310 and 310' is 2 psi but pressures in
 the range from minus 10" of water to over 45 psi can be used.
 FIG. 3 depicts a schematic representation of a printing system 510 with a
 different ink container 512 of the present invention. Also included in the
 printing device 510 is a printhead 514 and a source of pressurized gas
 such as a pump 516. The pump 516 is connected by a conduit 518 for
 providing a pressurized gas such as air to the ink container 512. A
 marking fluid 519 such as ink is provided by the ink container 512 to the
 printhead 514 by a conduit 520. This marking fluid is ejected from the
 printhead 514 to accomplish printing.
 The ink container 512 which is the subject of the present invention
 includes a fluid reservoir 522 for containing ink 519, an outer shell 524,
 and a chassis 526. In the preferred embodiment the chassis 526 includes a
 air inlet 528 configured for connection to conduit 518 for pressurizing
 the outer shell 524 with air. A fluid outlet 530 is also included in the
 chassis 526. The fluid outlet 530 is configured for connection to the
 conduit 520 for providing a fluid connection between the fluid reservoir
 522 and fluid conduit 520.
 In the preferred embodiment the fluid reservoir 522 is formed from a
 flexible material such that pressurization of the outer shell produces a
 pressurized flow of ink from the fluid reservoir 522 through the conduit
 520 to the printhead 514. The use of a pressurized source of ink in the
 fluid reservoir 522 allows for a relatively high fluid flow rates from the
 fluid reservoir 522 to the printhead 514. The use of high flow rates or
 high rates of ink delivery to the printhead make it possible for high
 throughput printing by the printing system 510.
 The ink container 512 also includes a plurality of electrical contacts, as
 will be discussed in more detail with respect to FIG. 4. The electrical
 contacts provide electrical connection between the ink container 512 and
 printer control electronics 532. The printhead control electronics 532
 controls various printing system 10 functions such as, but not limited to,
 printhead 514 activation to dispense ink and activation of pump 516 to
 pressurize the ink container 512. In one preferred embodiment the ink
 container 512 includes an information storage device 534 and an ink level
 sensing device 536. The information storage device 534 provides
 information to the printer control electronics 532 for controlling printer
 510 parameters such as ink container 512 volume as well as ink
 characteristics, to name a few. The ink level sense device 536 provides
 information relating to current ink volume in the ink container 512 to the
 printer control electronics 532.
 As ink 519 in each container 512 is exhausted the ink container 512 is
 replaced with a new ink container 512 containing a new supply of ink. In
 addition, the ink container 512 may be removed from the printer chassis
 538 for reasons other than an out of ink condition such as changing inks
 for an application requiring different ink properties or for use on
 different media. It is important that the ink container 512 be not only
 accessible within the printing system 510 but also easily replaceable. It
 is also important that the replacement ink container 512 form reliable
 electrical connection with corresponding electrical contacts associated
 with the printer chassis 538 as well as properly form necessary
 interconnects such as fluid interconnect, air interconnect and mechanical
 interconnect so that the printing system 10 performs reliably. The present
 invention is directed to a method and apparatus for reliably engaging the
 ink container 512 into the printer chassis 538 to insure proper electrical
 interconnection is formed.
 It is important that ink spillage and spattering be minimized to provide
 reliable interconnection between the ink container 512 and printer 510.
 Ink spillage is objectionable not only for the operator of the printer who
 must handle the spattered ink container 512 but also from a printer
 reliability standpoint. Inks used in ink-jet printing frequently contain
 chemicals such as surfactants which if exposed to printer components can
 effect the reliability of these printer components. Therefore, ink
 spillage inside the printer can reduce the reliability of printer
 components thereby reducing the reliability of the printer.
 FIGS. 3 and 4 depict the ink container 512 of the present invention. The
 ink container 512 includes a housing or outer shell 524 which contains the
 fluid reservoir 522 shown in FIG. 1 for containing ink 519. The outer
 shell 524 has a leading edge 550 and trailing edge 552 relative to a
 direction of insertion for the ink container 512 into the printer chassis
 538. The leading edge 550 includes the air inlet 528 and the fluid outlet
 530 which are configured for connection to the air pump 516 and the
 printhead 514, respectively, once the ink container 512 is properly
 inserted into the printer chassis 538. The air inlet 528 and fluid outlet
 530 will be discussed in more detail below.
 A plurality of electrical contacts 554 are disposed on the leading edge 550
 for providing electrical connection between the ink container 512 and
 printer control electronics 532. In one preferred embodiment the plurality
 of electrical contacts 554 include a first plurality of electrical
 interconnects that are electrically interconnected to the information
 storage device 534 and a second plurality of electrical interconnects
 which are electrically interconnected to the ink volume sensor 536 shown
 in FIG. 3. In the preferred embodiment the information storage device 534
 is a semiconductor memory and the ink volume sensing device 536 is an
 inductive sensing device. The electrical contacts 554 will be discussed in
 more detail with respect to FIG. 4C.
 The ink container 512 includes one or more keying and guiding features 558
 and 560 disposed toward the leading edge 550 of the ink container 512. The
 keying and guiding features 558 and 560 work in conjunction with
 corresponding keying and guiding features on the printer chassis 538 to
 assist in aligning and guiding the ink container 512 during insertion of
 the ink container 512 into the printer chassis 538. The keying and
 aligning features 558 and 560 in addition to providing a guiding function
 also provide a keying function to insure only ink containers 512 having
 proper ink parameters such as proper color and ink type are inserted into
 a given slot printer chassis 538. Keying and guiding features are
 discussed in more detail in co-pending patent application Ser. No.
 08/566,521 filed Dec. 4, 1995 entitled "Keying System for Ink Supply
 Containers" assigned to the assignee of the present invention and
 incorporated herein by reference.
 A latch feature 562 is provided toward the trailing edge 552 of the ink
 container 512. The latch feature 562 works in conjunction with
 corresponding latching features on the printer portion to secure the ink
 container 512 within the printer chassis 538 such that proper
 interconnects such as pressurized air, fluidic and electrical are
 accomplished in a reliable manner. The latching feature 562 is a molded
 tang which extends downwardly relative to a gravitational frame of
 reference. The ink container 512 shown in FIG. 4B is positioned for
 insertion into a printer chassis 538 along the Z-axis of coordinate system
 564. In this orientation gravitational forces act on the ink container 512
 along the Y-axis.
 FIG. 4C depicts an electrical interconnect portion 570 which is the subject
 of the present invention. The electrical interconnect portion 570 includes
 electrical contacts 554 and upstanding guide member 572, and inner wall
 member 574, and an outer wall member 576. In the preferred embodiment, the
 plurality of electrical contacts 554 include electrical contacts 578 which
 are electrically connected to the fluid sensing device 536 shown in FIG. 3
 and electrical contacts 580 which are electrically connected to the
 information storage device 534. In the preferred embodiment, the
 electrical contacts 578 are defined in a flexible circuit 582 which is
 mounted to the ink container 512 by fastener 584. A circuit 586 on which
 contacts 580 and information storage device 534 are disposed provides
 electrical connection between the information storage device 534 and
 contacts 580. The circuit 586 is attached to the ink container 512 by
 fastener 584.
 The inner upstanding wall 574 and the outer upstanding wall 576 help
 protect the electrical circuit 586, information storage device 534, and
 contacts 578 and 580 from mechanical damage. In addition, the upstanding
 walls 574 and 576 help minimize inadvertent finger contact with the
 electrical contact 578 and 580. Finger contact with the electrical contact
 578 and 580 can result in the contamination of these electrical contacts
 which can result in reliability problems with the electrical connection
 between the ink container 512 and the printing system 510. Finally,
 inadvertent contact with the electrical contact 578 and 580 can result in
 an electrostatic discharge (ESD) which can result in reliability problems
 with the information storage device 534. If the information storage device
 is particularly sensitive to electrostatic discharge such a discharge may
 result in catastrophic failure of the information storage device 534.
 FIG. 5A depicts an ink container 512 of the present invention shown secured
 within an ink container receiving station 588 within the printer chassis
 538. Because ink container 512 is similar except for keying and guiding
 features 558 and 560 and corresponding ink properties contained within the
 respected fluid reservoir, the same reference numbering will be used for
 each ink container 512. An ink container indicia 590 may be positioned
 proximate each slot in the ink container receiving station 588. The ink
 container indicia 590 may be a color swatch or text indicating ink color
 to assist the user in color matching for inserting the ink container 512
 in the proper slot within the ink container receiving station 588. As
 discussed previously the keying and guiding features 558 and 560 shown in
 FIGS. 4A-B prevent ink containers from being installed in the wrong slot.
 Installation of an ink container in the wrong slot can result in improper
 color mixing or the mixing of inks of different ink types each of which
 can result in poor print quality.
 Each receiving slot within the ink container receiving station includes a
 corresponding keying and guiding slot 592 and a recessed latching portion
 594. The guiding slot 592 cooperates with the keying and guiding features
 558 and 560 to guide the ink container 512 into the ink container
 receiving station 588. The keying and guiding slot 592 associated with the
 corresponding keying and guiding feature 560 is shown in FIGS. 5A-B and
 the keying and guiding slot associated with the corresponding keying and
 guiding feature 558 on the ink container 512 is not shown. The latching
 features 594 are configured for engaging the corresponding latching
 features 562 on the ink container 512.
 FIG. 5B shows a cross-section of a single ink container receiving slot
 within the ink container receiving station 588. The ink container
 receiving slot includes interconnect portions for interconnecting with the
 ink container 512. In the preferred embodiment these interconnect portions
 include a fluid inlet 598, and air outlet 596 and an electrical
 interconnect portion 600. Each of the interconnects 596, 598, and 600 are
 positioned on a floating interconnect portion 602 which is biased along
 the Z-axis toward the installed ink container 512.
 The fluid inlet 598 and the air outlet 596 associated with the ink
 container receiving station 588 are configured for connection with the
 corresponding fluid outlet 530 and air inlet 528, respectively on the ink
 container 512. The electrical interconnect 600 is configured for engaging
 the plurality of electrical contact 554 on the ink container 512.
 FIG. 6A shows a large format printer 10 of the type which includes a
 transversely movable printhead carriage enclosed by a plastic or metal
 hinged cover 12 which extends over a generally horizontally extending
 platen 14 over which printed media is discharged. At the left side of the
 platen is a transparent hinged cover 16 which contains four removable ink
 reservoirs 20, 22, 24, 26 which, through a removable flexible tube
 arrangement to be described, supply ink to four inkjet printheads mounted
 on the moveable carriage.
 In the plan view of FIG. 6B which the carriage cover 12 has been removed,
 it is seen that the printhead carriage 30 is mounted on a pair of
 transversely extending slider rods or guides 32, 34 which in turn are
 rigidly affixed to the frame of the printer. Also rigidly affixed to the
 frame of the printer are a pair of tube guide support bridges 40, 42 from
 which front and rear tube guides 44, 46 are suspended. The printhead
 carriage 30 has a pivotal printhead holddown cover 36 fastened by a latch
 38 at the front side of the printer which securely holds four inkjet
 printheads, one of which is shown in FIG. 7 in place in stalls C, M, Y, B
 on the carriage. The front tube guide 44 is angled near the left bridge
 support 40 to provide clearance for opening the printhead cover when the
 carriage is slid to a position proximate the left side of the platen 14 so
 that the printhead holddown cover 36 can be easily opened for changing the
 printheads.
 A replaceable ink delivery tube system described in more detail below
 conveys ink from the four separate ink reservoirs 20, 22, 24, 26 at the
 left side of the printer through four flexible ink tubes 50, 52, 54, 56
 which extend from an ink reservoir connector 70 through the rear and front
 tube guides 44, 46 to a printhead connector 100 which is releasably
 affixed to the carriage 30.
 At the right side of the printer is a printhead service station 80 at which
 the printhead carriage 30 may be parked for servicing such as wiping,
 spitting or priming the printheads.
 As seen in FIG. 6A each of the four ink reservoirs 20, 22, 24, 26 is easily
 accessible from the front of the printer when the optional cover 16 (seen
 in FIG. 1) is open so that the reservoirs can be easily installed, removed
 or replaced with new reservoirs. As is known in the art, three of the
 reservoirs each contain a different base color of ink such as cyan,
 magenta and yellow and the fourth reservoir contains black ink so that a
 high number of colors can be produced as desired during printing. FIG. 11
 shows an ink connector 23, an air connector 25 and an electrical connector
 27 on the front end of an ink reservoir 20. The other reservoirs are
 similarly constructed.
 The replaceable ink delivery tube system is broadly comprised of the four
 flexible ink delivery tubes 50, 52, 54, 56 which are all permanently
 connected at one end to the printhead connector 100 which is a relatively
 rigid plastic part best seen in FIGS. 7A-B and, at the other end, to the
 reservoir connector 70 which is another relatively rigid plastic part best
 seen in FIGS. 9 and 12-15.
 Referring now to FIGS. 7 and 8, four printheads 140 (one of which is shown
 in phantom in FIG. 7A) are received in the four separate stalls C, M, Y, B
 on the carriage 30 and have ink reception ports which respectively mate
 with ink delivery connectors 110, 112, 114, 116 on the printhead connector
 100. Each stall has a different printhead lockout configuration comprised
 of various vertically extending lockout posts 120-125 formed on the
 printhead connector 100 in different positions around the ink delivery
 connector ends 110, 112, 114, 116 so that each stall is different and can
 only be mated with a printhead 140 of complementary configuration. By way
 of illustration only, the left stall C is configured to receive a
 printhead containing cyan colored ink. The adjacent stall M is configured
 to receive magenta, the next stall Y to the right is configured to receive
 yellow ink and the stall B at the right side of the connector 100 is
 configured to receive a printhead containing black ink.
 FIG. 8 shows a printhead 140 configured to be received in the cyan stall of
 the printhead connector 100. The printhead 140 includes two rows
 downwardly directed inkjet nozzles 142 and a pivotally mounted handle 144
 at the top for removing the printhead 104 from the carriage 30. The cyan
 ink delivery connector 110 on the printhead connector is received in a
 generally vertically extending ink receiving tube 146 on the cyan
 printhead. Proximate the lower end of the ink receiving tube 146 is a
 lockout collar 148 integrally formed with the printhead 140 with a portion
 shown in phantom which has been broken off or otherwise removed at the
 factory so that the cyan configured printhead 140 can only be receivable
 in the cyan stall C of the printhead connector 100 to properly connect the
 ink delivery connector end 116 tube with the cyan printhead 140. It will
 be appreciated that printheads may be mass produced with frangible collars
 148 extending generally all the way around the ink receiving tube 146 and
 that selected portions of the collars 148 can be easily removed at the
 factory to thus create cyan, magenta, yellow and black printheads each
 having different configurations which are uniquely receivable only in the
 appropriate stalls of the printhead connector 100. The partially removable
 or frangible collars 148 may be removed at selected locations whereby the
 remaining portions of the collars 148 are receivable only in the mating
 stalls on the printhead connector. Alternatively, it will be appreciated
 that the printhead connector lockout posts 120, 125 may be constructed so
 that they are easily broken off or otherwise removed in selected areas for
 mating with appropriately configured printheads.
 The replaceable ink delivery tube system of the present invention comprised
 of the flexible ink delivery tubes 50-56 and printhead connector 100 is
 completed by the ink reservoir connector 70 (FIGS. 9 and 12-15) which is
 permanently affixed to an ink supply end of the ink delivery tubes. The
 reservoir connector comprises a plastic frame 72 having guide channels 73
 which mate with guide rails on the printer frame and a vertically
 extending flange 74 to which a printed circuit board PCB, not part of the
 present invention, is rigidly attached. The frame 72 includes a pair of
 vertically extending sides 76, 78 and defines four parallel connector
 module stalls separated by vertically extending divider walls 80, 82, 84.
 The frame is open at the front and rear sides so that the ink delivery
 ends of ink reservoirs 20, 22, 24, 26 may be received in the stalls from
 the front side of the printer. The front side of the reservoir connector
 70 seen in FIG. 9 and shows modules, described below, having ink delivery
 inlets 50i, 52i, 54i, 56i, air connections 90, 91, 92, 93 and electrical
 connectors 94, 95, 96, 97 which mate with like connections 90, 91, 92, 93
 and electrical connectors 94, 95, 96, 97 which mate with like connections
 on the reservoirs, the modules being mounted in the module stalls and
 extending through the stalls in the frame 72 to the rear side of the
 printer.
 Four reservoir connector modules 200, 202, 204, 206 are resiliently mounted
 in each of the four stalls of the frame 72 such that the four modules are
 forwardly and rearwardly moveable with respect to the frame and slightly
 laterally moveable with respect to the frame under the influence of a pair
 of compression springs 208, 210 extending between each module and spring
 seats on the frame 72 to permit the modules to readily connect to and
 disconnect from the ink reservoirs 20, 22, 24, 26 which are manually
 inserted from the front of the printer. Each module ink port 90, 91, 92,
 93 receives ink from one ink reservoir 20, 22, 24, 26, and the air
 connections 90, 91, 92, 93 deliver compressed air to the reservoirs.
 The rear side of the reservoir connector 70 as seen in FIG. 12, includes a
 pair of quick release twist connectors 212, 214 which are easily gripped
 between the thumb and fore finger which can be rotated as desired to
 rotate locking shafts received in apertures in the printer frame to
 connect and disconnect the reservoir connector 70 from the printer frame.
 An air delivery manifold 216 is mounted on the rear of the upwardly
 extending flange 74 and includes a quick release connector for connecting
 and disconnecting the manifold 216 to a flexible air supply line which
 delivers air through four tubes 218, 220, 222, 224 to the modules 200,
 202, 204, 206 to pressurize each of the four ink reservoirs when connected
 to the modules to cause the ink reservoirs to deliver ink under pressure
 through the ink delivery connections 50i, 52i, 54i, 56i and the four ink
 supply tubes 50, 52, 54, 56 which are respectively connected to ink supply
 outlets 50o, 52o, 54o, 56o on the rear side of the modules. Also shown is
 a a main electrical connector 230 extending through an aperture 232 in the
 flange 74 which connects to the circuit board and four electrical
 connections 234, 236, 238, 240 of conductors 248, 246, 244, 242 extending
 from the circuit board through the frame 72 to the connectors 94-97 on the
 front of the modules. Disconnection of the main air supply line from the
 manifold 216 and disconnection of an electrical conductor strip from the
 main electrical connector 230 is quickly made by from the rear side of the
 printer so that the entire reservoir connector including the permanently
 connected ink delivery tubes 50, 52, 54, 56 can be removed from the
 printer merely by rotating the quick release connectors 212, 214. A rigid
 plastic tube clip 250 having a bayonet connector 252 which is readily
 slidably received in and removed from an aperture in the printer frame is
 also provided to hold the ink delivery tubes 50, 52, 54, 56 in the proper
 spaced relationship to each other proximate the reservoir connector 70.
 Ink reservoir lockouts 270 are provided to ensure that ink reservoirs are
 containing only one type of ink, for example pigment based ink, can be
 received in the reservoir connector. In the preferred embodiment, these
 lockouts take the form of four separate removable members 270 slideably
 received in slots 272 in the top portion of the frame 72 above the four
 modules. In the configuration shown, each lockout 270 has three
 horizontally spaced downwardly extending fins 274, 276, 278 which mate
 with ink reservoirs having four horizontally spaced upwardly extending
 fins 280, 282, 284, 286 (FIG. 11) to ensure that reservoirs containing one
 type (not color) of ink only, e.g. pigment based ink rather than dye based
 ink, can be received in the frame 72. Separate lockouts (not part of this
 invention) are also provided near the front end of the reservoir stalls in
 the printer frame to ensure that reservoirs containing only the
 appropriate color of ink may be received in the four reservoir stalls. As
 seen in FIG. 9 one of the lockouts 270 has been removed to more clearly
 show the slots 272 in the frame in which the lockouts 270 are slideably
 received. Also note in FIG. 9 that the lockouts 270 each have vertically
 upstanding bosses 288 integrally formed thereon which, when the lockouts
 270 are fully inserted into the slots 272 in the frame 72, provide and
 additional means of affixing the printed circuit board to the front of the
 upstanding flange 74 at the top of the reservoir connector frame.
 It is thus seen that an easily replaceable ink delivery tube system has
 been provided which is uniquely useable with ink of a selected type, e.g.
 pigment based ink or dye based ink but not both, due to the lockouts 270
 provided at the ink reservoir connector 70 and which is uniquely
 connectable to printheads of a selected color due to the lockout collars
 148 on the printheads and the lockout posts 120-125 provided on the
 printhead connector 100. Removal of the entire system from the printer
 when it is desired to change from, e.g. pigment based ink to dye based
 ink, prevents fouling of the ink delivery system in a foolproof manner by
 inadvertent use of ink of the wrong type therein. The replaceable delivery
 system is easily removed from the printer merely by disconnecting the air
 line and electrical connections at the reservoir connector 70 so that the
 reservoir connector can be removed from the printer, by removing the
 printheads from the carriage and then disconnecting the printhead
 connector 100 from the carriage 30 merely by squeezing the resilient
 finger tabs 102, 104 while pulling the printhead connector 100 from under
 the carriage 30 and by removing the ink delivery tube clip from the rear
 tube guide 46.
 It will be understood by those skilled in the art that the invention
 provides an integrated, modular and easily configurable flexible system to
 pressurize ink in order to deliver it to inkjet printheads at the required
 flow rate and pressure. This is especially relevant for the ink supply
 system of so-called regulator printheads that require continuous
 refilling.
 The air pressure system (APS) provides and controls the pressurization of
 the ink in the ink cartridges during a printing operation. This ensure
 that the ink supplied to the inlet to the printhead is at the correct
 minimum pressure to ensure correct printhead function. The internal
 pressure in the printhead should remain within necessary limits for the
 desired print quality at various respective print speeds. Pressurization
 is particularly useful for a system where the ink supply is remote from
 the printhead such as off the carriage, in order to overcome pressure
 losses with long connecting tubes and to allow machine design flexibility
 for ink cartridge location and especially ink cartridge height, as well as
 tube diameters, fluid interconnects, etc.
 The following components are particularly helpful in providing an
 inter-related system of air pressure monitoring and control. The air pump
 reliably pressurizes the air and thereby the ink to the required pressure
 in the required time. The pressure sensor provides measurement of the air
 pressure for its feedback control. The solenoid pressure valve enables
 rapid depressurization of the system. The mounting base locates the pump,
 sensor and pressure valve with associated tubing manifold, quick connect,
 while also providing a sump to contain possible ink leakage from the valve
 due to any ink leakage in the cartridge contaminating the air circuit.
 The flexible tubing enables easy connection of the distributed parts of the
 pressure system. The various manifolds provide secure interconnection of
 the multiple air tubes forming the air circuit. The outer sheet of the ink
 cartridges effectively forms part of the air circuit, and the flexible ink
 bag isolates the ink from the air whilst allowing pressure transmission.
 The small air leak vent allows pressure equalization with the atmosphere
 when not printing. The restraint frame around the member holding the ink
 cartridges helps to resist the forces developed by the high pressure in
 the ink cartridges. The quick connections for the air tubes facilitates
 the quick coupling for the two halves of the air circuit and also results
 in easy replacement of certain portions of the air tubes.
 It is important to note that the modular system allows for ease of
 modification or expansion. The programmable firmware which controls the
 ink pressure levels allows easy adjustment to suit individual product,
 printhead and ink needs. Such flexibility is enhanced by the use of an
 analog pressure sensor to control an oversized air pump. Also, all
 electro-mechanical components can be housed in the electronics shielding
 enclosure with the pneumatic power connection to the ink cartridges only
 by air, thus eliminating completely all electrical emission problems.
 The pressure relief valve is normally closed. This means that the valve is
 closed when no voltage is applied, so that the air system circuit is
 fail-safe--it is closed when the machine is turned off, or in reshipping,
 or between plots. The valve is the only possible opining for ink of the
 air circuit/secondary containment when the ink cartridges are fitted in
 the plotter.
 Each ink cartridge has its only slow leak vent with built-in filter that
 does not allow ink to pass. For the printer system this provides the means
 to avoid the system pressurizing itself with temperature or altitude
 changes in shipping or storage. This is also particularly useful for
 shipment of the individual ink cartridges separate from the printer.
 The air tubing is raised above the maximum ink level in the cartridges.
 This is to provide a simple gravity check against any ink leak in a
 cartridge entering the air circuit. Moreover each cartridge has a pair of
 exposed contacts on the outside of the ink bag to detect ink by change in
 resistance. The printer checks these on machine switch on and before
 pressurisation for any plot. If any leak is deteted the system will not
 pressurise and will notify the user to change that ink cartridge. This is
 to preven any ink getting into the air system at all. Also, at the outlet
 of the pressure relief valve is a sump to catch ink ejected from a
 contaminated air system. There there are three levels of ink containment
 which reduces the probability of ink ever being leaked into a customer's
 carpet or floor.
 As shown in the flow chart of the drawings, there is a specific sequence of
 steps which assures that the minimum ink pressure is reached quickly
 before the printing operation begins. The actual air pressure required is
 determined at the start of each plot dependent on the volume of ink left
 in the cartridge since a major pressure loss contributor is the ink bag
 when nearly empty, and which color, since the color masimum flow rate is
 lower. The pressure is maintained for a predetermined wiat time between
 plots, thus giving effectively no warm up time for the air pressure system
 for high throughput printing.
 The housing supports the ink cartridge sides by providing spacers between
 the cartridges and a structural reinforcing loop of metal around the
 outside of the entire cartridge group. The housing provides the base which
 together with a sheet metal frame clipped in from the top completes the
 closed loop. This allows the cartridge bottle to be blow moulded for low
 cost using generally low rigidity materials, thereby also achieving the
 industrial design needs for a book-shaped form factor.
 The following tables provide various data and operating ranges for the air
 pressure system:

Preferred Default Parameters
 For Air Pressurization System (APS)
 Parameter Name Value Unit
 Print pressure Pnormal 1.2 psi
 normal
 Print pressure Pblack 1.85 psi
 Black &lt; 80 cc absolute
 Print pressure Pcolor 1.4 psi
 Colour &lt; 80 cc absolute
 Stop pressure Pstop 2.25 psi
 Repump pressure Prepump 1.95 psi
 Pump pressure rate Ppump 0.2 psi/s
 Print pressure wait Tcheck 0.15 s
 time for fine checking
 Minimum pump on time Tmin 0.1 s
 to reach print pressure
 Post plot wait time with Twait 5 minutes
 pressure maintained
 Pressure sensor maximum offset Pcal +0.25 psi
 calibration allowed -0.25
 Maximum time to Pprint 20 s
 in first (coarse) check
 Maximum time to Pprint 10 s
 in fine check
 Min pressure allowed at start of Pprint psi
 swath (except first) during printing
 Depressurisation check: Max Tdep 0.3 psi
 pressure after valve open 20 s
 Valve open time for depressurisation Tvalve 30 s
 Pnormal: All cartridges operating in "normal" pressure loss range.
 Pcolor: Any color cartridge in "nearly empty" range, black in normal range.
 Pblack: Black in nearly empty range.
 Pressure Budget
 The required minimum air pressure at flow Q is given by:
EQU P(air)=P(printhead at Q)+P(head loss)+P(flow losses at Q)+P(ink bag)
 Where:
 P(air): The pressure measured by the sensor: effectively equal to the
 pressure in the ink bags
 P(printhead): The minimum inlet pressure defined by spec. at specified pen
 flow rate Q
 P(head): Pressure loss due to the height difference between the printhead
 inlet and the ink bag exit.
 P(flow): Pressure loss due to flow friction at specified flow rate.
 P(ink bag): Pressure loss due to bag collapse resistance
 TABLE
 Key Parameters
 Platform maximum 24 cc/min Printed platform
 flow rate
 black pen max 20 cc/min Printhead platform
 flow rate
 color pens max 6 cc/min Printhead platform
 flow rate
 min pressure.sup.1 Q (cc/min)/2 psi 0 to 20 cc/min
 to ensure PQ 10 psi 20 to 24 cc/min
 min pressure .sup.1 0 psi 0 to 24 cc/min
 no damage
 inks max 5 Centipoise platform inks
 viscosity (max)
 Ink bag pressure 0.15 psi Full to 80 cc
 loss.sup.2 (max) (abs) ink remaining
 0.69 psi 80 cc to empty (99%)
 1.05 psi 80 cc to empty (3.sigma.)
 Printhead inlet 137 mm Small bag
 height above ink (350 & 175 cc)
 bag outlet height 161 mm Large bag (700 cc)
 Pressure measurement 0.15 psi Sensor &
 error (max) electronics errors
 After zero offset
 calibration
 .sup.1) Defined at the inlet holes in the pen needle.
 .sup.2) Defined at the centre of the ink outlet septum.
 The time to pressure is directly proportional to the air volume to be
 compressed, and thus depends on the cartridge size and the ink remainin in
 each.
 The following duty cycle description explains the duty cycle curve shown in
 the drawings:
 The APS Duty Cycle
 A) System de-pressurized: pump off, valve closed. Air pressure equalisation
 through the Mirage vents.
 B) Incoming plot detected: pump on full speed to Pblack, printing allowed
 as soon as Pprint reached.
 C) Pblack to Pstop pump runs at half speed and stops at Pstop.
 D) Pressure decays to Prepump at rate dependent on system air volume,
 Mirage vent leaks, system leakage, and ink use rate.
 E) At Prepump pump on until Pstop reached.
 F) Repeat of (D) to (F) until plot finished.
 G) APS maintains (D) to (F) loop for Twait, unless plot received.
 H) Valve opened for Tvalve to de-pressurize system.
 Time to Pressure
 This is important for the time to reach print pressure only, since after
 this point the APS works in the background maintaining the ink pressure.
 This APS "warm up time" runs in parallel with the time used for servicing
 at the start of any plot when the APS is de-pressurized whichever is the
 longer defines the delay between plot detection and print start (assuming
 plot processing time is less).
 TABLE
 Time to Pressure Key Parameters
 RR warm up delay 5 seconds To meet RR
 from "cold" throughout goals.
 Time to print pressure 5 seconds Goal for pump
 for 4 empty selection for
 350 cc Mirage Roadrunner.
 to Pnormal
 Air volume range: min 395 cc Includes 17 cc
 350 cc Mirage max 1985 cc RR air circuit
 700 cc Mirage max 3680 cc
 Wait time pressurized 5 (tbc) mintutes To be optimised for
 Use Model.
 Air Leakage
 The total APS air leak rate is an important system variable for pump life
 and duty cycle, and for pressure checking frequency. In the APS design,
 the leak rates are defined as a flow rate at a pressure; the flow rate is
 always defined in terms of standard air (air at 14.7 psi absolute and
 60.degree. F.).
 The system's dominant source of leakage is the designed-in leakage of the
 four ink cartridges, followed by the pump, with the valve having at least
 an order of magnitude lower leakage. The rest of the air circuit is
 airtight.
 The effect of leakage on the pump life requirement is also dominant: more
 than a minimum of 50% of the air pumped is expected to be used to replace
 leaked air. Air vented to atmosphere each time the system de-pressurizes
 is the next major contributor. While the air actually used to replace the
 ink used is two orders of magnitude lower. The pump duty cycle is directly
 affected by the leakage, but the system air volume range is also
 significant in defining pump off time.
 Note that the vent is fitted in the cartridge to equalise pressure (and
 thus avoid creep of its shell) during transport. The APS uses this feature
 to allow pressure equalisation of the printer when de-pressurized, as the
 air circuit (in particular the relief valve) is normally closed.
 Air Pump
 This is a triple cylinder diaphragm pump using a swashplate mechanism
 driven by a DC motor. This provides a compact and quiet air compressor
 that allows speed control. The pump is used without an air filter on the
 inlet. The multiple cylinder configuration provides several important
 benefits of:
 Low pumping noise and vibration.
 Lowered pressure pulses in the air circuit (this affects pressure
 measurement algorithm).
 Increased reliability due to parallel system redundancy.
 The swashplate mechanism is extremely compact compared to the crank slider
 mechanism more commonly used in diaphragm air pumps.
 TABLE
 APS Pump Requirements
 Time to Pressure 2.5 seconds maximum Affects
 pressurization
 Over Life to 2.5 psi system "warm up
 time"
 for 500 cc rigid volume before printing can
 start.
 with 24 V nominal Supply voltage
 Leak rate: Life start 1 scc/min.sup.1 maximum Affects:
 system air use
 Life end 10 scc/min maximum
 at 2.5 psi
 Life 50,000 standard minimum
 liters.sup.2
 MVBF (mean volume 600,000 standard minimum During normal
 lifetime.
 between failures) liters To meet 1% AFR
 budget.
 Duty cycle for
 Life and MVBF
 Pressure capability 3.5 psi minimum 1 psi margin for
 platform future needs.
 15 psi maximum To avoid safety
 risks.
 Restart pressure 3 psi minimum To suit APS half
 speed repumping.
 at 12 V 1 psi margin for
 platform future needs.
 Operating voltage 24 V .+-.10% supply. Voltage of
 printer.
 0 to 100 pwm For speed control.
 .sup.1) SCC = cc of `standard air`: air at standard atmospheric pressure
 and temperature.
 .sup.2) liters of "standard air": air at standard atmospheric pressure and
 temperature
 Device selection notes: The APS design allows for relatively easy
 substitution of alternative pumps: since the mechanical functional
 connection to the APS is by air tube. In particular the use of alternative
 motors has been foreseen in the design of the pump mounting.
 Pressure Relief Valve
 This is a solenoid operated 2 way NC valve. Normally Closed means that the
 valve is closed when no actuating voltage applied. The valve has one port
 connected to the air circuit in the APS module; the exit port discharges
 into the ink sump. No air filtration is provided: hence, the air circuit
 cleanliness is important.
 TABLE
 APS Pressure Relief Valve Requirements
 Leak rate: over Life 0.2 scc/min maximum Affects system
 air use
 Operating voltage 24 V .+-.xx
 Flow xx cc/min .+-.xx Affects de-
 at 2.5 psi pressurization
 time and ink
 leak detection
 algorithm.
 Life 100,000 cycles minimum open/close
 MCBF (mean cycles 3,000,000 cycles minimum During normal
 between failures) lifetime
 To meet 0.1%
 AFR budget.
 Duty cycle 30 s ON (open)
 for Life and MCBF 5 cycles OFF
 Device selection notes:
 The APS design allows for the easy substitution of alternative valves:
 since the functional mechanical connection to the system is by flexible
 tube, and there is space to add alternative mounting clips (indeed a
 redundant clip to suit standard ISO size is already built in the support).
 Pressure Sensor
 This is a silicon piezoresistive device with integrated temperature
 compensation and signal conditioning (amplification). The sensor measures
 gauge pressure and hence has a single pressure port that is connected to
 the air circuit in the APS module.
 TABLE
 APS Pressure Sensor Requirements
 Pressure range 0 to 3.5 psi
 Accuracy .+-.0.1 psi
 Maximum pressure 15 psi No damage Equal to pump max
 possible pressure
 Supply voltage 5 V
 Device selection notes:
 Space is provided in the APS support for mountings for alternative sensors.
 Referring to FIGS. 16-17, an air system support frame 700 carries an air
 pump 702, a pressure sensor 704, and a pressure relief valve 706 which all
 connect through adaptor 708 to flexible conduit 710 having a locking
 connector 712 for attachment to the manifold on the back of the ink
 connector member. The frame is in a modified cup shape to create a sump
 714 under the pressure relief valve for collecting any ink which may leak
 from the ink container through the air lines. These air system components
 each have electrical power supply lines, with a three-wire line 716
 connected to the pressure sensor for transmission of data to the control
 electronics. The frame 700 includes hooks 715 and tabs 717 for mounting
 under the connector module at its front end as shown by dotted lines 719.
 The self-explanatory flow charts of FIGS. 18A-18D when combined with the
 data and information of the various previous tables show the sophisticated
 monitoring and control procedures which can be customized by merely
 changing firmware without having to change individual physical components
 in the system. Various protective steps assure that any malfunction in the
 system will be detected and appropriate error signals generated to alert a
 user and where necessary stop and/or close down the system until a problem
 is resolved.
 Additional flexibility is provided for different lengths (volumes) of ink
 containers as shown in FIG. 20. When a smaller container 720 is used, a
 slot 722 is engaged by the fastener to lock the connector module in a
 shortened position (See FIG. 5B). When a larger container 724 is used,
 another slot 726 is engaged the the fastener to lock the connector module
 in a lengthened position.
 Sturdy and leak-resistant construction for the ink connection is assured by
 a unique tower/humidor combination shown in FIG. 22. The humidor 728
 includes opposing raised fins 730 which initially slide down matching
 grooves 732 in a tower 734 until they reach matching slots 736 which cause
 the humidor to slightly rotate so that triangular fin 738 engages a
 matchin elongated notch 740 thereby holding the humidor in position
 against a biasing spring 742. The humidor itself covers needle 744 and its
 ink passage 746 until compressed by a septum of an ink supply container to
 expose the ink passage. A facing of different concentric layers 748 abuts
 the septum to help prevent ink leakage.
 Additional structural support for the ink containers when mounted and
 subjected to the rising air pressures in the containe is provided by a
 sheet metal loop 750 (See FIG. 5A).
 It will be appreciated that the latest embodiment of the air pressure
 system and related components provides very predictable and secure control
 of the ink pressure whether applied to normal printing operations, or to
 unusual events such as priming, air purging of the ink tubes and the like
 as shown in the table of FIG. 23.
 Various changes and improvements can be made to the illustrated embodiments
 disclosed herein without departing from the spirit and scope of the
 invention as set forth in the following claims.