Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material

Definitions

• the present invention concerns printing.
• the printing art is quite mature. Vast amounts of research and expense have been dedicated to optimizing the quality and minimizing the cost of printers, particularly those intended for the consumer market. Given the difficulty of meeting the demands of the human eye, the results of these efforts have in fact been remarkable. Still, the techniques employed to achieve these results have tended to be complicated and expensive.
• Printers early employed in offices for small-computer output employed hammers and print-wire matrices. These were noisy and slow and produced low-quality output. Quality improved with the use of thermal printers, but these required special paper and tended to be slow, too.
• a greater quality advance accompanied the advent of laser printers, but their mechanisms are complicated, and they remain relatively expensive despite the high volumes in which they have been produced. And none of these technologies lend themselves well to color imaging.
• Ink-jet and ink-bubble technologies have addressed these shortcomings to a significant extent.
• Ink-jet printers squirt charged ink at the paper, deflecting the ink electrostatically to direct it to the desired location. This approach is simple in comparison with, say, laser printers, and it lends itself to color printing, since successive jets of different-colored ink can be applied to the same locations.
• Ink-bubble approaches are similarly direct: they employ explosive energy to propel ink drops to the paper from an array of sources. But the ballistic nature of the ink delivery in both of these approaches tends to make the image quality quite dependent on the type of paper or other image medium.
• the printing surface is provided by a print head that forms a plurality of capillaries terminating in an array of respective capillary outlets on the printing surface.
• the capillaries contain ink that capillary action ordinarily so retains in the capillaries that it does not mark paper brought into contact with the print sur- face. But the ink's dielectric constant exceeds that of air, and electrode pairs selectively apply potential differences across respective capillary outlets at which marks are to be made.
• the printer's marking mechanism does not itself require any moving parts at all; it requires only appropriate solid-state control circuitry and the print head, which can simply be a block that forms the capillaries and provides their associated electrodes.
• the ink column in a given capillary is required to move only a minute distance in order to make a mark.
• a single mark can be made in an ex- tremely brief period of time, and, since all that is required to make a mark is a single capillary and its associated electrode pair, the print head can readily be provided with a large number of capillaries and associated electrodes so that many pixels — typically, a whole row's worth or more — can be printed simultaneously. So the printing speed can be made relatively high with very little cost.
• the print quality is not as sensitive to paper type as it is when, say, ink-jet printers are employed.
• the invention lends itself to the use of hot-melt inks, which are well known for their lack of sensitivity to the type of image medium on which they are used. And hot-melt inks assume solid form when the printer is not in use, so they contribute further to the printer's operational robustness.
• the paper or other image medium is advanced past the print head by a reciprocating electrostatic gripper.
• the advancement gripper then releases the paper, typically after another, retention gripper grips it to hold it in place, and returns, grips the paper again, and again advances the paper after the retention gripper releases it.
• the distance by which the advancement gripper advances is typically so small — the spacing of one or two image rows — as to be visually imperceptible, and the retention gripper remains stationary. So the printer needs essentially no space to accommodate feed-mechanism motion.
• Fig. 1 is a perspective view, partly broken away, of a color printer that employs the present invention's teachings
• Fig. 2 is a cross-sectional view of the printer's print head taken at lines 2-2 of Fig. 1 ;
• Figs. 3A-D are more-detailed views of one of the print head's capillary outlets, illustrating the mechanism by which the printer marks the image medium;
• Fig. 4 is a cross-sectional view of one of the print-head modules that make up the print head
• Fig. 5 is an isometric view of the print head, illustrating the conductor paths by which control voltages are applied to the print head's capillary outlets;
• Figs. 6A and 6B are footprint diagrams that illustrate the cooperation of staggered capillary rows to provide a rectangular pixel layout;
• Figs. 7A and 7B are similar footprint diagrams illustrating the cooperation of staggered capillary rows to provide a hexagonal pixel layout
• Fig. 8 is a cross-sectional view of the print head illustrating the ink-supply ap- proach that the printer employs;
• Fig. 9 is a cross-sectional view of the printer showing the paper-feed mechanism that the printer uses;
• Fig. 13 is a simplified block diagram of capillary-driver circuitry for driving the capillary electrodes in a multi-bit-per-pixel version of the present invention.
• Fig. 1 illustrates a printer 10 that employs the present invention's teachings.
• grippers 12, 14, and 16 advance paper 18 from a paper supply 20 past a print head 22.
• the print head employs the present invention's teachings to apply an image to the paper by marking it with hot-melt ink from a cartridge 26.
• battery- powered circuitry 28 receives image-data signals from a source not shown and operates the print head 22 in accordance with the image data thus received. It also operates the grippers and vibrating print plate and supplies the power to melt the hot-melt ink.
• Fig. 2 which is a cross-section taken at lines 2-2 of Fig. 1 , partially illustrates the marking mechanism by which the illustrated embodiment operates.
• ink-supply channels 30, which extend the length of the print head 22, are filled with hot-melt ink that NiCr heating elements 32 keep molten.
• Each of the ink-supply channels forms a row of, say, 4000 capillaries 33 at its base.
• the illustrated printer is a color printer. It employs the conventional ink-color selection, namely, cyan, magenta, yellow, and black. Although Fig. 2 shows only a single capillary row for each color, more may be provided to speed printing or for other reasons, as will be explained below. None of these features is critical to the present invention.
• a piezoelectric actuator 34 causes the print plate 24 to reciprocate with a fre- quency of, say, 2 kHz through a vertical travel on the order of 75 ⁇ m between extended and retracted positions.
• the print plate's resilient core 36 urges the paper 18 into contact with the print head's bottom surface.
• Figs. 3A-C There it is marked by hot- melt ink that selectively applied electric fields have caused to bulge from selected capillaries' outlets despite the capillary action, as will now be explained by reference to Figs. 3A-C.
• Fig. 3 A diagrammatically illustrates a column of ink 38 held by capillary action in one of the capillaries 33. That drawing also shows two electrodes 40 and 42 disposed at opposite sides of the capillary outlet.
• Fig. 3A illustrates the situation in which there is no difference in electrical potential between the two electrodes 40 and 42. It can be seen that capillary action prevents the ink column from effectively marking paper that has been brought into contact with the bottom head surface.
• the printer of the present invention applies a voltage of, say, 200 V to electrode 40 while keeping electrode 42 at ground potential.
• the capillary outlet is on the order of only 40 ⁇ m across, so the applied potential difference causes electric fields on the order of millions of volts per meter at the capillary outlet.
• the attendant, similarly high field gradients cause the hot-melt ink, which has been chosen for its high dielectric constant, to bulge outward into the field thus formed and thereby mark the paper, as Fig. 3B illustrates.
• a hot-melt ink suitable for this purpose is Piccotex 75LC hot-melt ink, available from Hercules Incorporated of Wilmington, Delaware.
• the printer When the ink column comes into contact with the (relatively cool) paper, its tip solidifies in a matter of microseconds into a crust on the paper. As Fig. 3C illustrates, the printer then removes the electrodes' potential difference, so the (still-liquid) ink col- umn tends to withdraw back into the capillary. At the same time, the vibrating print plate 24 withdraws the paper into its retracted position with the help of a further gripper mechanism 46 (Fig. 2) embedded in its surface, as will be described in more detail below. This assists in breaking the contact between the crust thus formed and the withdrawing ink column. Grippers 12, 14, and 16 then advance the paper 18 by a small advancement distance.
• the spacing between capillary rows containing different-colored inks is chosen to be an integer number of advancement steps so that a paper location at which a capillary in one row has deposited ink of one color will eventually be positioned in registration with the corresponding capillary in the row that con- tains the next color so that ink of a different color may be deposited on top of the ink crust 47 that was deposited in the Fig. 3B operation.
• Fig. 4 depicts in more detail a single head module 48. which provides a single row of ink capillaries.
• the module includes a body 50 of insulating material such as an Al 2 O 3 -powder matrix in which the capillary 33 has been formed by one of the many known micro fabrication techniques.
• a NiCr resistor 52 deposited on one side of the head module 48 extends between the grounded electrode 42 and a similarly deposited power-supply rail 54.
• the ink that the head module 48 contains is in solid form when the printer is not in use, but turning the printer on applies power to the resistor 52, which thereupon heats the head module 48 and thus liquefies the hot-melt ink that it contains.
• Conductors 56 printed on the head module 48's opposite face connect the driven electrode 40 to a printed-circuit board backplane (not shown) that leads to drive circuits in the printer's circuit module 28 (Fig. 1). Since similar conductors are provided on the corresponding face of an adjacent head module, an insulating layer 60 insulates resistor 52 from the adjacent module's conductors.
• a printer employing the present invention's teachings may provide more than one capillary row for each color.
• Fig. 5 illustrates a head arrangement that provides two capillary rows per color for another purpose.
• the capillary outlets 64 that module 48 provides are staggered with respect to the adjacent module 62 's capillary outlets 66.
• the purpose of this arrangement is to enhance the printer's spatial resolution. If it proves inconvenient for a single capillary row to provide the number of capillaries per unit row length that the desired image resolution requires, one solution is to use different print-head modules to print different ones of a given row's pixels.
• module 48 can deposit, say, the odd-numbered pixels in a given row, and module 62 can deposit the even-numbered pixels in the same row.
• Fig. 6A illustrates this concept.
• the resultant pixel arrangement is illustrated in Fig. 6B, in which the module-62 capillaries' maarks are labeled A and the module-48 capillaries' marks are labeled B.
• Such a staggered relationship between capillary rows can also be used to achieve a different, hexagonal effect, as Figs. 7A and 7B illustrate by diagrams respectively cor- responding to those of Figs. 6 A and 6B.
• Figs. 7A and 7B illustrate by diagrams respectively cor- responding to those of Figs. 6 A and 6B.
• the spacing between adjacent capillary rows is the product of an odd in- teger and the distance between printed rows on the paper, and the paper-advancement mechanism advances the paper by two row spacings at a time. Consequently, a given module's capillaries print all of the pixels in a row, but only on alternate rows.
• footprints are depicted respectively as rectangular and hexagonal. These shapes reflect the conceptual pixels' shapes, and it may be beneficial for the capillaries' cross sections also to be so shaped. But some embodiments will employ circular capillary cross sections for all pixel arrangements.
• FIG. 8 illustrates, the cartridge 26 is snap fit into a receptacle 80 formed on the print head 22. It rests on a heater pad 82, which heats the cartridge 26 and thus the ink in longitudinally extending ink reservoirs 84. These reservoirs communicate at the cartridge rear with respective tubes 86 (Fig. 1), which fit into respective print-head openings 88 that communicate with respective supply channels 30.
• the tubes 86 are formed in a connector 90 that additionally provides an electrical con- nection between the heater 82 (Fig.
• Fig. 8 also shows that the print head 24 includes a cover 92 that closes a cavity 94 in which the individual head modules are mounted.
• the cover 92 forms a recess 96 that communicates both with the print-head exterior and with air holes 98 formed at the print- head modules' upper ends to permit air to be displaced as the capillaries' ink column extend and retract.
• the print-head modules' upper surfaces may also be provided with a Teflon coating 100 to discourage ink from bleeding out the air holes.
• Fig. 9 illustrates the illustrated embodiment's paper- feed mechanisms.
• a first set of elongated electrodes 102 is connected to a positive-voltage supply pad 104 and interdigitated with a second set of elongated electrodes 106 connected to a negative-voltage supply pad 108.
• the spacing between adjacent electrodes is on the order of mm, so the potential difference between the two supply pads, which is on the order of 200 V when the gripper is activated, sets up substantial electric fields above the gripper.
• the gripper thereby draws the first paper sheet tightly to itself. But the first sheet acts to shield all sheets above it, so it is only one that the gripper attracts.
• actuators 112 and 114 advance gripper plates 12 and 14 into engagement with the bottom sheet in the paper supply 20. Those plates' gripper electrodes are energized and thereby draw the bottom sheet 18 to their upper surfaces. Actuators 112 and 114 then retract the gripper plates and thereby pull the bottom sheet past retention lips 1 16 and 118. The printer then removes power from gripper 12 but not from gripper 14, which therefore retains its hold on the paper.
• piezoelectric actuator 114 advances gripper plate 14 and thus the paper sheet one advancement step to the right.
• the advancement step is one pixel-row spacing in the case of the pixel organization of Figs. 6A and B. In the case of Figs. 7A and B's pixel spacing, the advancement step is two pixel rows.
• Gripper 12 " s electrodes are then powered again to hold the paper sheet in place, and gripper 14's electrodes release the paper sheet. While gripper 12 holds the paper in place, gripper 14 * s actuator moves it back to the left, where it again grips the paper. Gripper 12 then releases the paper again, and gripper 14 again advances the paper sheet to the right as before.
• This advancing operation feeds the paper sheet into the space between the print head 22 and the print plate 24, which itself has gripper electrodes embedded in its upper surface.
• the print plate 24's electrodes are energized in synchronism with those of gripper 12 and so timed as to cooperate with the printing process, as Figs. 11 A-D illustrate.
• Fig. 11 A represents the energization state of the gripper electrodes on the retention grippers, i.e., the electrodes on gripper plate 12 and print plate 34.
• Fig. 1 IB represents the positions of the the print plate 24 and the activated capillaries' ink columns. Those drawings show that the capillaries' ink columns and the print plate 24 assume their advanced positions, in which the ink column can mark the paper, at time time t u while the retention grippers' electrodes are in the energized state. At time t 2 , the print plate and ink columns retreat to their retracted positions while the print plate's gripper is still energized and thus pulls the deposited ink crust out of contact with the still-liquid ink col- umn.
• Fig. 11C which represents the energization state of the advancement gripper' s electrodes.
• the retention grippers then release the paper at time t 4 so that the advancement gripper can begin advancing the pa- per to the right.
• Fig. 1 ID which represents the advancement gripper 14's position, shows that gripper 14 begins that advance at time t 5 .
• time t 6 the paper has been advanced to the point where the next marking is to take place, so the retention grippers grasp the paper again at time t 7 .
• the advancement gripper releases the paper at time t 8 , and it returns to the left at time t g .
• the cycle begins again at time t 10 and repeats until the entire image has been written on the paper sheet.
• the paper sheet advances beyond the reach of the first two gripper plates 12 and 14.
• a further piezoelectric actuator 120 (Fig. 9) moves advancement gripper plate 16 to the left and right in synchronism with the left-and-right movements of advancement gripper plate 14, its gripper electrodes being energized in synchronism with that plate's.
• Gripper plate 16 thus cooperates with print plate 24 just as advancement gripper plate 14 cooperates with retention gripper plate 12.
• Fig. 12 is a simplified block diagram that illustrates the data flow employed to drive the print-head electrodes that Fig. 3A's electrodes 40 and 42 exemplify .
• the electronics module 28 includes an image memory 126, which receives image data from the source of the image to be printed.
• the source will often be a personal computer or other device that can be supplied with driver software for process- ing the image data into the form most compatible with the hardware organization described above.
• the printer can itself be provided with circuitry that performs such processing.
• one row of image data (or, as was explained above, a subset thereof) is fetched for each capillary row and supplied to a respective one of several shift registers such as shift registers 128 and 130, which are associated with respective capillary rows.
• Each shift register receives its share of the image data for a full row between, say, times t 2 and t 10 of Figs. 11 A-D, and an ENABLE signal gates the shift registers' contents to respective electrode rows, as gates 132 indicate, with the timing at Fig. 1 IB illustrates.
• the Fig. 12 repre- sentation is merely conceptual; as was explained above, the voltages applied to the print- head electrodes ordinarily are nearly two orders of magnitude greater than conventional logic levels.
• Fig. 12 depicts the printer as employing single-bit pixels, whereas the present invention's teachings are readily adapted to multi-bit pixel data.
• the voltage applied to a capillary's outlet electrodes determines the distance by which the ink column protrudes from it. That distance, in turn, determines the size of the resultant printed dot.
• multi-bit pixel data can specify which of a set of predetermined voltages to apply to a given capillary's electrodes.
• a printer that employs the present invention's teachings in a multi-bit embodiment may use an arrangement such as that which Fig. 13 illustrates.
• Fig. 13 shows the shift register 134 for a single capillary row.
• One of its stages 136 may contain the data used to specify the voltage to the applied to electrode 40.
• Stage 136's contents may be, say, a four-bit number, which a decoder 138 uses to select among sixteen electronic switches 140 by which electrode 40 can be connected to a selected line of an electrode-voltage bus 142.
• the voltages on these lines are the outputs of respective taps of a voltage divider 144 whose input is the output of a gated voltage source 146.
• Source 146's output is a repetitive pulse whose timing Fig. 1 IB depicts and whose amplitude at least equals the voltage corresponding to the digital image data's full-range value.
• the print head is a simple manifold structure that has no moving parts. Ink application is controlled by arrays of electrodes, which can be provided on a simple flex-print substrate. It is well suited to use with hot- melt inks, so the method is not sensitive to the type of paper being used — and it contains no liquid ink when it is not in use. Moreover, the use of reciprocating electrostatic grippers greatly contributes to the compactness of the resultant printer package; since their travel is microscopic, a full-color printer can be made that is only slightly larger than the paper supply that it includes. The present invention thus constitutes a significant advance in the art.

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• Ink Jet (AREA)
• Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)
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• 1997
  • 1997-11-19 CA CA002277221A patent/CA2277221C/en not_active Expired - Fee Related
  • 1997-11-19 EP EP97948377A patent/EP0964783A1/de not_active Withdrawn
  • 1997-11-19 JP JP52837199A patent/JP2001508374A/ja not_active Ceased
  • 1997-11-19 AU AU54462/98A patent/AU5446298A/en not_active Abandoned
  • 1997-11-19 WO PCT/US1997/021124 patent/WO1999025557A1/en not_active Application Discontinuation

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