Patent Publication Number: US-6981753-B2

Title: Glass-fiber thermal inkjet print head

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a divisional of application Ser. No. 10/074,565 filed on Feb. 11, 2002, now U.S. Pat. No. 6,565,760 which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to ink jet printers. In particular, this invention relates to a novel design and method of manufacture of a thermal inkjet print head. 
     BACKGROUND OF THE INVENTION 
     Thermal inkjet printers have become ubiquitous. 
     These printers typically use semiconductor-based print heads which have individually-controlled ink-ejecting printing elements that heat water-based inks to vaporization. Vaporizing the ink causes it to be propelled onto a print media through microscopic holes formed in a plate or shield. Thermal energy to vaporize ink is supplied from electric current driven through small thin film resistors that are in thermal contact with ink, which is otherwise held in place within the print head by capillary effect. 
     Prior art thermal inkjet printers form images on print media by repeatedly passing a print head over the media. Small quantities of ink are “sprayed” onto the paper by turning on and turning off the thermal ink jet printing elements as the print head moves across the paper or print media. 
     At least one problem associated with existing inkjet printers is the speed at which these printers can produce acceptable quality output levels. Because a finite time is required for ink droplets to traverse the distance between the media and the print head, there is an upper speed limit for the print head beyond which further speed increases are not possible. Instead of moving the print head across the media, a method and apparatus by which an entire line of a page might be printed at once could provide a significant overall printing speed increase. 
     SUMMARY OF THE INVENTION 
     A page-wide printer head formed from glass fiber nozzles onto which are deposited semiconductor heating elements, and current driving circuitry, can print an entire line of a single page at one time using thermal ink jet action. Narrow glass tube ink conduits are formed from hollow glass fibers which are sintered together, drawn to constrict the diameters of the hollow fibers and then longitudinally sliced to provide an array of glass tube nozzle assemblies. By using semiconductor processing techniques, heater resistors and control circuitry is formed onto the glass surfaces The heater resistors are deposited into the interior of the hollow glass fibers where they are used to heat liquid-based ink and ink components to vaporization. 
     The current drive circuitry is comprised of transistor-controlled silicon controlled rectifiers (“SCRs”) deposited onto the print head. The SCRs drive current through the heater resistors deposited into the open ends of the glass fibers. Hundreds or even thousands of individual current drive circuits, each circuit being comprised of a pair of SCRs wired in a series fashion, are fired by a control pulses delivered to a control transistor for each drive circuit. The current drive circuits of the SCRs are wired in a totem pole arrangement such that successive drive circuits are addressed by successive pulses on only two control lines wired to all of the series-connected drive circuits. 
     Predetermined individual SCRs are first latched “on” in sequence by a predetermined pulse in a synchronous train of pulses that are applied to the drive circuits. Individual drive circuits can be turned on or left off, i.e. in the SCR&#39;s non-conducting state. A single power pulse delivered to all of the drive circuits after the circuits are provided with the addressing pulse stream provides the electrical energy through the SCRs latched “on,” to vaporize ink. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a top view of a single hollow glass fiber tube section. 
         FIG. 2  shows a side view of a hollow section of glass fiber tube. 
         FIG. 3  shows an isometric view of several hollow glass fiber tube sections after sintering, drawing and slicing. 
         FIG. 4  shows a simplified representation of a glass fiber, thermal inkjet print head in a cutaway view through several glass fiber tube sections coupled to an ink reservoir. 
         FIG. 5  shows a perspective view of a four color ink cartridge including four different ink reservoirs and four different print heads formed using sintered drawn and sliced glass fiber tubes. 
         FIG. 6  shows a cross sectional view of a single glass fiber tube section and the semiconductor components deposited at the outlet side of the tube from which ink is ejected. 
         FIG. 7  shows a cutaway section of one end of a glass fiber tube section of that shown in  FIG. 6  in greater detail. 
         FIG. 8  shows a simplified block diagram of the positioning of a sintered drawn and sliced glass printer head and a source of material used to form semiconductor materials in the ends of the sintered glass tubes. 
         FIG. 9  shows a simplified representation of how materials might be deposited into the interior portions of the tube sections using an apparatus such as that shown in  FIG. 8 . 
         FIG. 10  shows a section of a glass substrate print head. 
         FIG. 11  shows how the several layers deposited into the interior of the glass tubes might appear after manufacturing. 
         FIGS. 12A–12D  show the progression of a droplet of ink as it is ejected from one of the glass tube sections. 
         FIG. 13  shows a schematic diagram of the control circuitry by which individual heater resistors are addressed sequentially. 
         FIG. 14  shows printer that might employ the glass print head disclosed herein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Glass fiber technology is well known.  FIG. 1  shows a top view of an exemplary hollow glass fiber  100  having an inner tubular section  102  formed by etching away a differently formulated glass material inside the glass annulus  104 . By forming the glass fiber  100  with a first type of glass around a second type of glass, it is possible to chemically etch or dissolve the second glass from within the first glass thereby leaving a hollow glass tube through which liquids (including gases) can flow. 
       FIG. 2  shows a side view of a section of glass fiber  100  and the length or extension of the hollow portion  102  through the length of glass tube  202 . 
       FIG. 3  shows an assembly of hollow glass tube sections  300  that is preferably formed by first bundling together several glass tube lengths, such as the length  202  shown in  FIG. 2 . The bundled glass fibers are then heated to a temperature at which the glass tube sections are sintered together thereby forming a monolithic, honeycomb-like structure of numerous orifices of some diameter D. The sintered tube sections are preferably drawn so as to significantly neck or decrease the inside diameter D of each tube section  302 . After sintering and drawing, the tube sections are laterally sliced across a plane  304  to form a thin matrix of small-diameter glass tubes or capillaries  306  such as that shown in  FIG. 3B . The resulting diameter of each glass tube must be sufficiently small so as to hold liquid based ink and ink components within the tubes by capillary effect. The largest-permissible diameter of the tubes to accomplish this will of course be affected by the composition and viscosity of the ink to be used. The diameter must also be sufficiently large so as provide a quantity of vaporized ink that will provide acceptable ink drop gain (drop spreading on the print media) without unduly large currents to heat unduly large ink volumes. 
     In  FIG. 4 , a section of a glass fiber print head  400  and the included glass capillary sections  402  are shown coupled to an ink reservoir  408 . As set forth above, the diameter of the ink capillaries is sufficiently small such that ink  408  in an ink reservoir  408  is retained by capillary action in the tubes yet can be expelled by thermal energy supplied by resistors  412  that are deposited near the open ends of the tubes, using techniques described below. 
     Semiconductor electronic control circuitry  412  deposited on the glass print head  402  (not visible in  FIG. 4 ) enables individual heater resistors in individual capillaries to be individually addressed so as to precisely control which capillaries have ink ejected from them. If the glass print head  402  extends across an entire page, printing a line of text on the page requires that ink be selectively ejected from some capillaries and not ejected from others so as to selectively deposit ink to form an image. An image or text can be formed one line at a time, across the entire page, by moving only the page being printed, i.e. without moving the print head  402 . The spacing S between adjacent capillary tubes  406  in the preferred embodiment is typically small: center to center distance of adjacent nozzles are expected to be 10 to 200 microns, (20 microns is normal for a 1200 dpi design. A 150 to 1500 dpi device is believed to be achievable with this design. The design can also be made so a specific address row could address every 5th to 15th nozzle (the exact skip rate to be determined by the addressing circuit rate and the total print head length, and print head resolution in dpi). 
       FIG. 5  shows a simplified perspective drawing of a multi-color page-wide inkjet print cartridge formed to have four different colored ink reservoirs  502 ,  504 ,  506  and  508  coupled to a single glass-fiber print head that includes four distinct print head assemblies. (At least one alternate embodiment would include using an assembly of four individual glass fiber structures  512 ,  514  and  516 .) Each reservoir holds a different color of ink. By separately controlling the ink deposition by the electrical signals applied to the glass fiber assemblies coupled to the respective colors, full-color, high-resolution, page-wide printing is achievable. 
     Each of the glass print head structures is comprised of an assemblage of individual glass fiber tube sections, such as those shown in  FIG. 3 , each of which has been sintered, drawn and sliced. After such processing, the individual glass fiber tube sections are subjected to further processing by which semiconductor manufacturing techniques are used to deposit thereon, heater resistors and control circuitry (not shown in  FIG. 5 ) by which the individual orifices of the individual tubes can be separately addressed. 
     As shown in  FIG. 5 , each of the print head sections  510 ,  512 ,  514  and  516  has emanating from it, three leads or terminals, each set being identified by reference numerals  518 ,  520 ,  522  and  524 . Electrical signals impressed upon the three terminal inputs, are used to control ink ejection from individual capillaries. 
     Ink ejection on a tube-by-tube basis is accomplished in the preferred embodiment by way of semiconductor current-latching circuits formed by depositing appropriate layers of semiconductor material into the interior or face of one end of each of the glass tube sections. Each current latching circuit is separately addressed and controllable. 
       FIG. 6  shows a simplified cross sectional view of one glass tube section  600 . It can be seen in  FIG. 6 , that there is a first semiconductor layer  602  followed by a series of other layers  604 ,  606  and  608 . Each of the semiconductor layers is used to control the heating and ejection of liquid based ink and ink components. Those skilled in the semiconductor fabrication art will recognize that various layers are required to form even a passive device and that the layers might require masking and etching. At least one layer is a conductive layer carrying electrical signals to semiconductor devices fabricated within the interior of the glass tube section  600  that is used to heat the used to heat liquid based ink and ink components to boiling. Layers  604 ,  606  and  608  might be isolation layers as well as semiconductor layers used to develop resistances, each of which is used to form control circuitry and resistive heating elements. The topology of the circuit formed on or in the glass tubes is shown in subsequent figures and described hereinafter. 
       FIG. 7  shows an enlarged view of an inverted portion of a single glass tube section  700 . Ink flows down (up as shown in the figure) the tube section in the direction indicated by the arrow  702 . Semiconductor layers,  704  deposited on the interior portions of the tube  700  form conductive traces, semiconductor layers, insulating isolation layers and resistive layers used to address the semiconductor drive circuitry and to provide current to a heater resistor also formed within the tube section. Both the heater drive circuitry and heater resistors can be formed using well-known semiconductor processes. The current through the resistor heats the ink (normally held in place by capillary action) to boiling which causes the ink to be ejected in small droplets that land on the print media. As happens in prior art thermal ink jet printers, the droplets land on the print media and then dry to a solid state. 
     Vacuum deposition techniques, evaporation and sputtering among others, are used to create semiconductor circuit elements within the interior of the glass tube sections. A mechanism such as that shown in  FIG. 8  can be used to deposit material into the actual interior sections of the tubes. A glass tube substrate (after sintering, drawing, sectioning and etching)  802  can be mounted onto a platen  804  that rotates at some predetermined rate about an axis  806 . A source of material  808  to be deposited into the tubes is provided such that the trajectory of the ions or particles follow a trajectory at an angle of theta by which a small portion of material is deposited at or near the top of one end of the tube section such as that shown in  FIG. 9 . The resultant deposition in the hollow tubes is typically an annular (an annulus) deposition of material although alternate embodiments would include crescent-shaped depositions. 
     The tube section  900  shows an amount of material  902  deposited onto at least the upper and top interior sections of the glass tube  900 . By appropriately masking interior annular sections of the glass tubes, it is possible to form a complete semiconductor device, such as an SCR, transistor and resistors, on the interior of the glass tube, small enough to allow the ink to continue to flow through that individually controllable from external circuitry. 
       FIG. 10  shows a section of a substrate formed from sintered drawn glass fiber tubes the diameter of which is on the order of 20 micrometers. Each of the several tube orifices shown in  FIG. 10  might be used to carry ink of a particular color such that the failure of one orifice by clogging, or semiconductor failure would not adversely affect the print quality as adjacent tube sections would presumably continue to function. 
       FIG. 11  shows how the multiple layers might appear after deposition at the top of one section of the glass tube sections.  FIG. 12A  shows the appearance of one of the tube sections prior to the ejection of an inkjet droplet.  FIG. 12B  shows the formation of a bubble within the tube section by heating the water based ink under the control of semiconductors deposited into the interior of the tube  12 B.  FIG. 12C  shows the ejection of the droplet and collapse of the air pocket until the tube is finally refilled as shown in  FIG. 12D . 
     A problem with controlling the individual nozzles of that structure shown in  FIG. 10 , is that individually addressed nozzle control circuitry would require hundreds or even thousands of different logical addresses requiring accompanying address decoding logic. Such numerous connections make the device susceptible to numerous failures. An alternate solution to this control problem is to individually address each of the nozzle heads by way of a totem pole series of current latching circuits, such as that shown in  FIG. 13 . 
     In  FIG. 13  three (3) individual control lines  1302 ,  1304  and  1306  can be used to individually address an unlimited number of control circuits  1308 ,  1310 ,  1312  and  1314  by means of synchronized pulsed trains impressed upon the P and S control lines  1304 ,  1306  that are operatively coupled to (electrically connected in the preferred embodiment) to each of the control circuits  1308 ,  1310 ,  1312  and  1314 . 
     Each of the control circuitry elements  1308 – 1314  is comprised of two, series connected SCR&#39;s. One of the series-connected SCRs is fired by a control pulse delivered through a transistor  1316  to the gate terminal of a second of the two SCR&#39;s  1318  and  1320 , causing both SCRs to turn on. An inherent characteristic of an SCR is that once it is triggered to the “on” state by positive voltages on the gate and anode, the SCR stays on until it is reverse biased or the voltage is removed from the anode. 
     In  FIG. 13  a pulse applied to both the P and S lines synchronously, causes the first SCR  1320  to forward conduct and to apply a voltage to the gate of the second SCR  1318 . By maintaining a relatively small residual bias voltage on the P line, both SCR&#39;s can be held in a forward biased “on” condition indefinitely. By minimizing this bias voltage, only a small amount of current flows through the heater resistor  1322 , which is deposited into the interior portion of one of the annular sections shown in the aforementioned figures. 
     The first pulse applied to the P and S terminals acts only to turn on the first current switch circuit  1308  (comprised of the two SCR&#39;s  1318  and  1320  and the transistor  1316 .) The subsequent current switching stages are not affected because at the instance of the first pulse and throughout its duration no signal is available at the gate of the first SCR  1324  of the second current latching circuit  1310 . Similarly, because there is no potential available at the cathode of the SCR  1324  the second SCR  1326  of this second current latching circuit  1310  can also not turn on. 
     Once the first SCR current latch  1308  is turned on, another voltage pulse is applied to the gate  1328  of the SCR  1324  such that upon the application of another subsequent voltage pulse to the P terminal, SCR  1324  will also turn on forward conducting and applying a voltage to the cathode of the SCR  1326 . If a pulse is simultaneously applied at the S lead, transistor  1330  will also turn on causing the SCR  1326  to forward conduct driving current through yet another heater resistor  1332 . 
     During the occurrence of the first two pulses, the third current switch stage  1312  remains deactivated because the gate of the SCR  1334  had no voltage applied to it nor did the gate or cathode of the SCR  1336  have any bias voltage applied thereto. 
     On the application of a third synchronous pulse to both the P and S leads, the third current switch stage  1312  also will turn on also driving a small amount of current through the third heater resistor  1338 . 
     In like fashion, subsequent stages of the totem pole arrangement shown in  FIG. 13  can be latched to an on state whereby the SCR&#39;s are put into a forward biased conducting state driving current through the heater resistors coupled to the cathode terminal of the second SCR stage of each current latch. The pulse train applied to the totem-pole connected current sources can be considered to a stream of addressing pulses in that the precise timing, duty cycle and frequency of the pulses can select which current driving circuit is latched on. After they are latched on, a small bias voltage can maintain the SCRs in the on state but if that bias voltage is kept relatively low, it will not produce currents through the heater resistors that is sufficiently large to vaporize ink in the capillary tubes where the resistors are deposited. 
     By applying a large-amplitude voltage pulse to all of the SCRs, those in the on state will deliver significant amounts of current to the heater resistors. Fluid in contact with the resistors will be vaporized and ejected from the capillary tubes onto the print medium. The firing voltage and current might need to be one to two orders of magnitude greater than the control pulses. 
     By appropriately selecting the pulse width and the frequency of the control pulses applied to the P and S lines, it is possible to individually address individual current latching circuits to either an on state or to remain in an off state. Distributed capacitance and inductance existing between the various elements of each current latch will determine the time constant needed to be counted for in the frequency, duty cycle, and voltage level of the pulse train used to address the individual stages. Once the stages are latched to an on state, the magnitude and duration can be determined from empirical data. 
     By individually addressing the current switch stages  1308 ,  1310 ,  1312  and  1314  it is possible to individually address individual current latching circuits that could be formed into the interior regions or on the surfaces of a glass substrate formed using the methods described above by sintering, drawing and slicing and thereafter vacuum depositing the SCR&#39;s, transistors and heater resistors onto either the surfaces of the glass structure or into the interior portions of the nozzles themselves. 
     By using semiconductor manufacturing techniques, which are well known to those skilled in the art, the geometries involved in the glass print head structure readily would accommodate the formation of multiple SCR&#39;s, transistors and resistors within the orifices of the glass structures themselves. Deposition of P type and N type semiconductor material, which would be required to form the individual transistors, could be accomplished by sputtering, evaporation or gas deposition techniques. Dielectric layers which would be required between the various N and P type semiconductor layers could also be achieved by other gas deposition or sputtering. Excess material might be etched away to form individual circuit traces by a reactive ion etch sputtering or gas etching using CF4. The structure shown in  FIG. 5  might be used with either a face shooter or edge shooter print head design although the preferred embodiment of the invention contemplates use as a monolithic-type print head. 
     Photolithographic masking techniques would also enable the precise positioning of circuit traces to contact surfaces by which the lead lines  518 ,  520 ,  522  and  524  of  FIG. 5  might be attached to connection areas of the substrate for connection to appropriate control circuitry controllers. 
     By sequentially addressing each of the nozzles of the glass print head structure for use in a page wide print head, it is possible to address hundreds or perhaps thousands of individual nozzle elements using only three control lines as shown in  FIG. 13 . Alternative embodiments would of course include parallel and asynchronous serial addressing schemes but these might require individual address lines and/or decoding circuitry in order to individually address and enable current driving devices for each orifice. 
     The preferred embodiment of the glass print head structure is expected to be only 200 microns in thickness, fragile enough to require a carrier during the manufacturing process. The center to center spacing for adjacently placed drops could be 10 to 200 microns, but the edge to edge spacing is zero microns because the glass fibers are sintered together. The matrix does not need to be, (and probably will not be) entirely open honeycomb pattern. Some fibers will be filled with the same type of glass as the outer sheath and so will remain filled after the etching process. Spacing between the individual glass fiber orifices would be quite small, and likely less than one micrometer. 
     By use of the foregoing glass fiber structure, and method of manufacturing and method of control, it is possible to realize a page wide print head structure that includes individually addressable print head elements. A number of advantages might be realized by such a structure. Overall printing speeds might be significantly increased beyond that which is currently possible using moveable print heads. Even if the sequential pulse trains required to address individual print head elements works slow, the increase in speed that would be achieved using a page wide print head would likely overcome any timing constraint imposed upon the sequential addressing of the control circuits. 
     The failure of one or even more individual print elements in a glass honeycomb print head could readily be compensated by increased firing rates of adjacent printing elements. Nozzle failure however is preferably compensated for by a duplicate nozzle array and circuit assembly of the same color. Fine resolution would also be achievable because of the close spacing of the glass fiber orifices. 
       FIG. 14  shows an exemplary printer  1400  that might use the glass print head and control circuitry disclosed above. 
     A series of rollers or platens  1402  rotates under the power of a platen motor  1404  so as to position a print media  1406  at a position below the print head  1408  described above. As shown in  FIG. 14 , the print head  1408  is moveable with respect to the media  1406  under the control of a carriage motor  1410  the rotation of which acts to wind and unwind a drive belt or cable  1414  to which the print head  1408  is attached. Movement of the belt or cable  1414  acts to slide the print head  1408  along a rod  1416  over which the print head  1408  moves. 
     Electrical control signals are delivered to the print head and the electronics thereon from the control circuitry  1412  described above through a flexible ribbon cable or equivalent  1418 . The position controller  1420 , which in the preferred embodiment is an appropriately programmed microprocessor, micro-controller, ASIC or equivalent, acts to move the platen motor  1404  and the carriage motor to position the print head  1408  at the proper location with respect to the media  1406 . At least one alternate embodiment of the printer shown in  FIG. 14  would be a fixed print head the dimensions of which would substantially cross the media  1406  so that virtually the entire page width might be printed. 
     Additional advantages and combinations will be apparent and are within the scope of the appended claims.