Patent Publication Number: US-6705716-B2

Title: Thermal ink jet printer for printing an image on a receiver and method of assembling the printer

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to printer apparatus and methods and more particularly relates to a thermal ink jet printer for printing an image on a receiver and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime. 
     An ink jet printer produces images on a receiver medium by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the ability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace. 
     In the case of ink jet printers, at every orifice a pressurization actuator is used to produce the ink droplet. In this regard, either one of two types of actuators may be used. These two types of actuators are heat actuators and piezoelectric actuators. With respect to piezoelectric actuators, a piezoelectric material is used. The piezoelectric material possesses piezoelectric properties such that an electric field is produced when a mechanical stress is applied. The converse also holds true; that is, an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing this characteristic are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, lead metaniobate, lead titanate, and barium titanate. With respect to heat actuators, a heater placed at a convenient location heats the ink and a quantity of the ink phase changes into a gaseous steam bubble. The steam bubble raises the internal ink pressure sufficiently for an ink droplet to be expelled towards the recording medium. 
     In the case of heat-actuated and piezoelectric actuated ink jet printers, a pressure wave is established in the ink contained in the print head. That is, in the case of piezoelectric actuated print heads, the previously mentioned mechanical stress causes the piezoelectric material to bend, thereby generating the pressure wave. In the case of heat-actuated print heads, the previously mentioned vapor bubble generates the pressure wave. As intended, this pressure wave squeezes a portion of the ink in the form of the ink droplet out the print head. Of course, if the time between actuations of the print head is sufficiently long, the pressure wave dies-out before each successive actuation of the print head. It is desirable to allow each pressure wave to die-out between successive actuations of the print head. That is, actuation of the print head before the previous pressure wave dies-out interferes with precise ejection of ink droplets from the print head, which leads to ink droplet placement errors and drop size variations. Such ink droplet placement errors and drop size variations in turn produce image artifacts such as banding, reduced image sharpness, extraneous ink spots, ink coalescence and color bleeding. 
     Therefore, in the case of piezoelectric and thermal ink jet printers, printer speed is selected such that the print head is activated only at intervals after each successive pressure wave dies-out. Such delayed printer operation is required in order to avoid interference of a newly formed pressure wave with a preexisting pressure wave in the print head. Otherwise allowing the preexisting pressure wave to interfere with the newly formed pressure wave results in the aforementioned ink droplet placement errors and drop size variations. However, operating the printer in this manner reduces printing speed because ejection of an individual ink droplet must wait for the preexisting pressure wave, caused by ejection of a previous ink droplet, to naturally die-out. Therefore, a problem in the art, for both heat-actuated printers and piezoelectric printers, is decreased printer speed occasioned by the time required to allow a preexisting pressure wave in the print head to naturally die-out before introducing a new pressure wave to eject another ink droplet. 
     Moreover, in the case of heat-actuated ink jet printers, a heating element, commonly referred to in the art as a “resistor”, is in direct contact with the ink in the print head to heat the ink. As previously mentioned, in the case of heat-actuated ink jet printers, a quantity of the ink phase changes into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. However, it has been observed that over time the ink droplet will “decel” or decelerate and experience a transient decrease in velocity and/or droplet volume after a relatively small number of print head firing cycles. At resumption of firing after a pause, droplet velocity and/or droplet volume recovers, only to decel again in the same manner. Although this phenomenon is not fully understood, the result of “decel” is interference with proper image formation. It has also been observed, in the case of heat-actuated ink jet printers, that resistor performance is decreased by a phenomenon referred to in the art as “kogation”. The terminology “kogation” refers to the permanent build-up of an ink component&#39;s burned residue on the resistor. This residue limits the resistor&#39;s energy transfer efficiency to the ink and causes the print head to permanently eject droplets with lower velocity or lower droplet volume. Therefore, quite apart from the problem of reduced printer speed, other problems in the art of ink jet printing are decel and kogation. 
     Also, in the case of heat-actuated ink jet printers, bubble collapse can lead to erosion and cavitation damage to the resistor. In other words, the repeated, relatively high speed collapse of the vapor bubble produces successive acoustic waves that impact the resistor. Over time, these successive impacts combined with the exposure of the resistor to chemical composition of the ink components corrode the resistor. Such cavitation leads to reduced operational life-time for the resistor. Therefore, another problem in the art is cavitation damage to the resistor. 
     In addition, in the case of heat-actuated ink jet printers, inks must function within a thermal or vaporization constraint. That is, the ink must vaporize at a predetermined temperature in order to form the vapor bubble when required. But for the vaporization constraint required by heat-actuated ink jet printers, various ink components could be included in the ink formulation to enhance printing characteristics. In other words, less soluble components, such as pigments, polymers, or certain surfactants, could be included at higher concentrations in the ink. In general, less soluble components in the ink provide better ink durability on paper because once the ink is deposited on paper, the ink is not easily resolubilized. Also, increasing viscosity or surface tension may improve ink/media interactions that affect print quality (e.g., dot gain, bleed, “feathering”, or the like), drytime and durability. Therefore, yet another problem in the art are limitations on types of ink useable in heat-actuated ink jet printers, which limitations are caused by constraints placed on vaporization limits of the ink. 
     Techniques to address the above recited problems are known. For example, an ink jet printer with a flexible membrane between ink and a working fluid is disclosed in U.S. Pat. No. 4,480,259 titled “Ink Jet Printer With Bubble Driven Flexible Membrane” issued Oct. 30, 1984, in the name of William P. Kruger, et al. and assigned to the assignee of the present invention. The Kruger, et al. patent discloses an ink-containing channel having an orifice for ejecting ink and an adjacent channel containing another liquid that is to be locally vaporized. Between the two channels is a flexible membrane for transmitting a pressure wave from a vapor bubble in the adjacent channel to the ink-containing channel, thereby causing ejection of a drop or droplets of ink from the orifice. According to the Kruger. et al. patent, a major advantage of the Kruger, et al. device is separation of the fluid to be vaporized from the ink. In this manner, according to the Kruger et al. patent, this separation permits use of conventional ink formulations, while at the same time making it possible to use special formulations of non-reactive and/or high molecular weight fluid in the bubble-forming chamber in order to prolong resistor lifetime. Moreover, as briefly indicated in the Kruger et al. patent, use of the membrane separating the ink and working fluid is intended to avoid erosion damage to the resistor. However, the Kruger, et al. patent does not address the problem of decreased printer speed occasioned by the time required to allow a preexisting pressure wave in the print head to naturally die-out before introducing a new pressure wave to eject an ink droplet. 
     A technique for damping a pressure wave to achieve increased printer speed and to prevent satellite ink droplet formation in a piezoelectric ink jet print head is disclosed in U.S. Pat. No. 6,186,610 titled “Imaging Apparatus Capable Of Suppressing Inadvertent Ejection Of A Satellite Ink Droplet Therefrom And Method Of Assembling Same” issued Feb. 13, 2001, in the name of Thomas E. Kocher, et al. An object of the Kocher, et al. patent is to provide an imaging apparatus capable of suppressing inadvertent ejection of a satellite ink droplet while maintaining printing speed. According to the Kocher, et al. patent, a print head defines a chamber having an ink body therein. A transducer (i.e., a piezoelectric transducer) is in fluid communication with the ink body for inducing a first pressure wave in the ink body. The first pressure wave squeezes an ink droplet from the ink body for ejection of the ink droplet from the print head. However, the first pressure wave is reflected from the walls of the ink chamber. Thus, the first pressure wave forms an undesirable reflected portion of the first pressure wave. This reflected portion of the first pressure wave may have amplitudes sufficient to inadvertently eject so-called “satellite” droplets following ejection of the intended ink droplet. Moreover, proper ejection of another ink droplet must await for the reflected portion to naturally die-out. Therefore, the Kocher, et al. device includes a thin piezoelectric sensor wafer spanning the ink channel for sensing the reflected portion of the first pressure wave. Once the sensor wafer senses the reflected portion, a second pressure wave is caused to be generated in the ink channel. According to the Kocher, et al. patent, the second pressure wave has an amplitude and a phase that damps the reflected portion, so that satellite droplets are not formed and so that printing speed is not reduced. However, the Kocher, et al. patent does not address pressure wave damping in a heat-actuated (i.e., non-piezoelectric) ink jet printer. In addition, the Kocher, et al. patent does not address separation of a working fluid from the ink to be ejected. 
     Therefore, what is needed is a thermal ink jet printer for printing an image on a receiver and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime. 
     SUMMARY OF THE INVENTION 
     The present invention resides in a thermal ink jet printer for printing an image on a receiver, comprising a print head defining a first chamber therein for receiving a working fluid and defining a second chamber therein; a flexible membrane separating the first chamber and the second chamber; a first transducer in communication with working fluid in the chamber for inducing a first pressure wave in the working fluid in the first chamber, so that said membrane flexes into the second chamber; and a second transducer in communication with the working fluid in the first chamber for inducing a second pressure wave in the working fluid in the first chamber, so that said membrane flexes into the second chamber. 
     According to an aspect of the present invention, the printer comprises a print head defining a first chamber and a second chamber therein. The first chamber contains a working fluid, such as water. The second chamber contains an ink body in communication with an ink ejection nozzle formed in the print head. A flexible membrane separates the first chamber and the second chamber. A first transducer is disposed in the first chamber and is in communication with the working fluid for inducing a first pressure wave that flexes the membrane into the second chamber. When the first membrane flexes into the second chamber, the first membrane transmits the first pressure wave into the ink body contained in the second chamber. When the first membrane transmits the first pressure wave into the ink body, an ink droplet is ejected out the ink ejection nozzle. A second transducer is disposed in the first chamber and is also in communication with the working fluid for inducing a second pressure wave that flexes the membrane into the second chamber. When the membrane flexes into the second chamber, the membrane transmits the second pressure wave into the ink body contained in the second chamber in order to damp the first pressure wave that was transmitted into the second chamber. The second pressure wave is sufficient to interfere with and damp the first pressure wave but insufficient to cause ejection of another ink droplet. The tranducers themselves may be thermal resistors, electromagnets, piezoelectric actuators, or similar devices for transforming energy input of one form (i.e., heat or electricity) into energy output of another form (i.e., hydraulic or mechanical movement). 
     A feature of the present invention is the provision of a first transducer separated from the ink body by a membrane, the first transducer generating a first pressure wave to flex the membrane and thereby transmit the first pressure wave to the ink body in order to eject an ink drop from the ink body. 
     Another feature of the present invention is the provision of a second transducer separated from the ink body by the membrane and spaced-apart from the first transducer, the second transducer generating a second pressure wave to flex the membrane and thereby transmit the second pressure wave to the ink body in order to damp the first pressure wave in the ink body. 
     An advantage of the present invention is that printer speed is increased. 
     Another advantage of the present invention is that the effect of “decel” is reduced. 
     An additional advantage of the present invention is that use thereof reduces the phenomenon known as resistor “kogation”. 
     Yet another advantage of the present invention is that resistor cavitation damage due to the combined effects of bubble collapse and corrosive inks are reduced. 
     Still another advantage of the present invention is that a wider variety of inks may be used for printing. 
     These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the specification concludes with claims particularly pointing-out and distinctly claiming the subject matter of the present invention, it is believed the invention will be better understood from the following description when taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a view in elevation of a thermal ink jet printer with parts removed for clarity; 
     FIG. 2 is a view in perspective of the thermal ink jet printer printing an image on a receiver; 
     FIG. 3 is fragmentation view in elevation of a first embodiment thermally-activated ink jet print head belonging to the printer, the first embodiment print head comprising a plurality of print head cartridges each defining a first chamber and a second chamber separated by a first embodiment membrane, the first chamber having a first embodiment first transducer and a first embodiment second transducer disposed therein; 
     FIG. 4 is a fragmentation view in elevation of the first embodiment ink jet print head, this view also showing the first embodiment first transducer and the first embodiment second transducer being activated to deform the first embodiment membrane; 
     FIG. 5A is a fragmentation view in horizontal section of the first embodiment print head, this view also showing the first embodiment first transducer and the first embodiment second transducer; 
     FIG. 5B is a fragmentation view in horizontal section of the first embodiment print head, this view also showing a first pressure wave induced by activation of the first embodiment first transducer; 
     FIG. 5C is a fragmentation view in horizontal section of the first embodiment print head, this view also showing the first pressure wave induced by activation of the first embodiment first transducer and a second pressure wave induced by activation of the first embodiment second transducer, the second pressure wave interfering with the first pressure wave to damp the first pressure wave; 
     FIG. 5D is a fragmentation view in horizontal section of the first embodiment print head, this view also showing the second pressure wave after having damped the first pressure wave; 
     FIG. 5E is a fragmentation view in horizontal section of the first embodiment print head, this view also showing ink refilling the second chamber after the first and second transducers have been activated and after the first pressure wave has been damped; 
     FIG. 6 is a fragmentation view in elevation of the first embodiment print head, this view also showing a second embodiment membrane; 
     FIG. 7 is a fragmentation view in elevation of the first embodiment print head, this view also showing a third embodiment membrane and further showing a second embodiment first transducer and a second embodiment second transducer; 
     FIG. 8 is a perspective sectional view in elevation of a print head cartridge belonging to a second embodiment print head; 
     FIG. 9 is an exploded view in elevation of the print head cartridge belonging to the second embodiment print head; 
     FIG. 10A is a fragmentation view in horizontal section of the second embodiment print head, this view also showing the first embodiment first transducer and the first embodiment second transducer; 
     FIG. 10B is a fragmentation view in horizontal section of the second embodiment print head, this view also showing a first pressure wave induced by activation of the first embodiment first transducer; 
     FIG. 10C is a fragmentation view in horizontal section of the second embodiment print head, this view also showing the first pressure wave and a second pressure wave induced by activation of the first embodiment second transducer, the second pressure wave interfering with the first pressure wave to damp the first pressure wave; 
     FIG. 10D is a fragmentation view in horizontal section of the second embodiment print head, this view also showing the second pressure wave after having damped the first pressure wave; 
     FIG. 10E is a fragmentation view in horizontal section of the second embodiment print head, this view also showing ink refilling the second chamber after the first and second transducers have been activated and after the first pressure wave has been damped; 
     FIG. 11 is an exploded view in elevation of a print head cartridge belonging to a third embodiment print head, the print head cartridge having a “pinch point”; 
     FIG. 12A is a fragmentation view in horizontal section of the third embodiment print head, this view also showing a first pressure wave induced by activation of the first embodiment first transducer; 
     FIG. 12B is a fragmentation view in horizontal section of the third embodiment print head, this view also showing the first pressure wave and a second pressure wave induced by activation of the first embodiment second transducer; 
     FIG. 12C is a fragmentation view in horizontal section of the third embodiment print head, this view also showing the second pressure wave and “pinch point” interfering with the first pressure wave to damp the first pressure wave; 
     FIG. 12D is a view in horizontal section of the third embodiment print head, this view also showing the second pressure wave after having damped the first pressure wave; 
     FIG. 12E is a plan view in horizontal section of the third embodiment print head, this view also showing ink refilling the second chamber after the first and second transducers have been activated and after the first pressure wave has been damped; 
     FIG. 13 is a view in perspective of a fourth embodiment print head; and 
     FIG. 14 is an exploded view in perspective of the fourth embodiment print head. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     The present invention will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     Therefore, referring to FIGS. 1 and 2, there is shown a thermal ink jet printer, generally referred to as  10 , for printing an image  20  on a receiver  30 . Receiver  30  may be paper or transparency or other material suitable for receiving image  20 . Printer  10  comprises an input source  40  that provides raster image data or other form of digital image data. In this regard, input source  40  may be a computer, scanner, or facsimile machine. 
     Referring again to FIGS. 1 and 2, input source  40  generates an output signal that is received by a controller  50 , which is coupled to input source  40 . The controller  50  processes the output signal received from input source  40  and generates a controller output signal that is received by a thermal ink jet print head  60  coupled to controller  50 . The controller  50  controls operation of print head  60  to eject an ink drop  70  therefrom in response to the output signal received from input source  40 . Moreover, print head  60  may comprise a plurality of print head cartridges  75   a ,  75   b ,  75   c , and  75   d  containing differently colored inks, which may be magenta, yellow, cyan and black, respectfully, for forming a full-color version of image  20 . 
     Still referring to FIGS. 1 and 2, individual sheets of receiver  30  are fed from a supply bin, such as a sheet supply tray  70 , by means of a picker mechanism  80 . The picker mechanism  80  picks the individual sheets of receiver  30  from tray  70  and feeds the individual sheets of receiver  30  onto a guide  100  that is interposed between and aligned with print head  60  and picker mechanism  80 . Guide  100  guides each sheet of receiver  30  into alignment with print head  60 . Disposed opposite print head  60  is a rotatable platen roller  110  for supporting receiver  30  thereon and for transporting receiver  30  past print head  60 , so that print head  60  may print image  20  on receiver  30 . In this regard, platen roller  110  transports receiver  30  in direction of arrow  112 . 
     Referring yet again to FIGS. 1 and 2, during printing, print head  60  is driven transversely with respect to receiver  30  preferably by means of a motorized continuous belt and pulley assembly, generally referred to as  120 . The belt and pulley assembly  120  comprises a continuous belt  130  affixed to print head  60  and a motor  140  engaging belt  130 . Belt  130  extends traversely across receiver  30 , as shown, and motor  140  engages belt  130  by means of at least one pulley  150 . As motor  140  rotates pulley  150 , belt  130  also rotates. As belt  130  rotates, print head  60  traverses receiver  30  because print head  60  is affixed to belt  130 , which extends traversely across receiver  30 . Moreover, print head  60  is itself supported by slide bars  160   a  and  160   b  that slidably engage and support print head  60  as print head  60  traverses receiver  30 . Slide bars  160   a  and  160   b  in turn are supported by a plurality of frame members  170   a  and  170   b  that are connected to ends of slide bars  160   a  and  160   b . Of course, controller  50  may be coupled to picker mechanism  80 , platen roller  110  and motor  140 , as well as print head  60 , for synchronously controlling operation of print head  60 , picker mechanism  80 , platen roller  110 , and motor  140 . Each time print head traverses receiver  30 , a line of image information is printed onto receiver  30 . After each line of image information is printed onto receiver  30 , platen roller  110  is rotated in order to increment receiver  30  a predetermined distance in the direction of arrow  112 . After receiver  30  is incremented the predetermined distance, print head  60  is again caused to traverse receiver  30  to print another line of image information. Image  20  is formed after all desired lines of printed information are printed on receiver  30 . After image  20  is printed on receiver  30 , the receiver  30  exits printer  10  to be deposited in an output bin (not shown) for retrieval by an operator of printer  10 . 
     In the case of thermal ink jet printers, a heater element causes boiling of the ink in the print head to produce a steam bubble that in turn produces a pressure wave in the ink. This pressure wave squeezes a portion of the ink in the form of an ink droplet out the print head in order to produce a mark on the receiver. The steam bubble then collapses. Of course, if the time between actuations of the heater element is sufficiently long, the pressure wave naturally dies-out before each successive actuation of the heater element. Thus, in the prior art, each pressure wave is allowed to die-out before successive actuations of the heater element. This is so because it is known that actuation of the heater element before the previous pressure wave dies-out interferes with precise ejection of ink droplets from the print head, which leads to ink droplet placement errors and drop size variations. However, operating the printer in this manner reduces printing speed because ejection of an individual ink droplet must wait for the preexisting pressure wave to naturally die-out. Therefore, it is desirable to damp the pressure wave without waiting for the pressure wave to naturally die-out, so that printer speed increases. 
     Moreover, in the case of prior art thermal ink jet printers, the heating element typically is in direct contact with the ink in the print head in order to form the steam bubble. However, it has been observed that over time the ink droplet will “decel”, thereby leading to a transient decrease in velocity and/or droplet volume. Also, heater element performance will decrease due to a phenomenon referred to in the art as “kogation”, which limits the heater element&#39;s energy transfer efficiency to the ink and also limits operational lifetime of the heater element. In addition, bubble collapse can lead to cavitation damage to the heater element. 
     Further, if it were not for the requirement that the ink be vaporized (i.e., vaporization constraint), various ink components could be included in the ink formulation to enhance printing characteristics. 
     It is therefore desirable to solve the hereinabove recited problems of the prior art by providing a thermal ink jet printer that increases printer speed, reduces occurrence of “decel”, reduces kogation, ameliorates cavitation damage to the heater element, and that does not require vaporization of the ink. 
     Therefore, turning now to FIGS. 3 and 4, there is shown first embodiment print head  60  comprising the previously mentioned print head cartridges  75   a/b/c/d  (only cartridges  75   a/b  being shown) coupled side-by-side in tandem. Each of cartridges  75   a/b/c/d  belonging to print head  60  defines an elongate first chamber  180  and an elongate second chamber  190  therein. For reasons disclosed more fully hereinbelow, first chamber  180  is capable of receiving a working fluid, which may be an aqueous liquid, such as water. Moreover, the working fluid may be a so-called “engineered” fluid that optimizes nucleation factors, such as vapor bubble temperature, bubble formation speed, and force exerted on the thermal resistor due to bubble collapse. Second chamber  190 , on the other hand, is capable of receiving an ink body from which image  20  will be formed. In addition, second chamber  190  has an outlet  195  for exit of ink drop  70  from print head  60 . Outlet  195  is preferably formed in an orifice faceplate  197  spanning second chamber  190 . 
     Referring again to FIGS. 3 and 4, a generally rectangularly-shaped flexible first embodiment first diaphragm or first membrane  200  separates first chamber  180  and second chamber  190 . Membrane  200  is elastic for reasons provided hereinbelow. In this regard, membrane  200  may be made from any suitable corrosion-resistant elastic material, such as a natural or silicon rubber and may be approximately 0.5 to 1.5 micrometer thick in transverse cross-section. Membrane  200  is preferably corrosion-resistant to resist corrosive effects of the working fluid and the ink body. Membrane  200  is sealingly affixed along an edge portion thereof to an elongate support member  210  that extends between first chamber  180  and second chamber  190 . Support member  210  supports membrane  200  and also serves to sealingly separate first chamber  180  and second chamber  190 . Membrane  200  may be sealingly affixed to support member  210  by any suitable means, such as by a suitable heat-resistant and corrosion-resistant adhesive. Moreover, membrane  200  is sealingly affixed along other edges thereof to an elongate lower ledge  215  that preferably creates second chamber  190  so as to define the ink body firing chamber. In addition, membrane  200  is sealingly affixed along edges thereof to an elongate upper ledge  216  that preferably creates first chamber  180  so as to define the working fluid firing chamber. The material forming upper ledge  216  can be the same material that forms lower ledge  215 . In this first embodiment print head  60 , membrane  200  is positioned over outlet  195  but is spaced apart therefrom to allow space for flexing of membrane  200 . Ledge  216  is sealingly connected to a horizontally-disposed die or rafter member  220 . Rafter member  220 , which is disposed in first chamber  180 , has an underside  225  for reasons disclosed hereinbelow. Thus, it may be understood from the description hereinabove, that membrane  200 , support member  210 , and ledges  215 / 216  cooperate to sealingly separate first chamber  180  and second chamber  190  and define the firing chambers for the working fluid and ink, respectively. In other words, membrane  200 , support member  210 , and ledges  215 / 216  cooperate to sealingly separate the working fluid and the ink body, for reasons disclosed hereinbelow. 
     Referring to FIGS. 3,  4 ,  5 A,  5 B,  5 C,  5 D, and  5 E, attached to underside  225  of rafter member  220  and therefore disposed in first chamber  180  is a first embodiment first transducer, which may be a first heater element or first resistor  240 , for locally boiling the working fluid. First resistor  240  is electrically connected to controller  50 , so that controller  50  controls flow of electrical energy to first resistor  240  in response to output signals received from input source  40 . First resistor  240  is in fluid communication with the working fluid, and thus membrane  200 , for inducing a first pressure wave  245  in the working fluid in order to flex membrane  200 . In this regard, when electrical energy momentarily flows to first resistor  240 , the first resistor  240  locally heats the working fluid causing a first vapor bubble  250  to form adjacent to first resistor  240 . Vapor bubble  250  pressurizes first chamber  180  by displacing the working fluid and causes generation of first pressure wave  245  in first chamber  180 . As first pressure wave  245  is generated in first chamber  180 , membrane  200  flexes or distends to squeeze ink drop  70  from the ink body residing in second chamber  190  and force ink drop  70  through outlet  195 , so that ink drop  70  will land on receiver  30 . In other words, first pressure wave  145  generated in first chamber  180  flexes membrane  200 , so that first pressure wave  245  is transmitted into second chamber  190  in order to pressurize second chamber  190 . After a predetermined time and as ink drop  70  passes through outlet  195 , controller  50  ceases supplying electrical energy to resistor  240 . Vapor bubble  250  will thereafter collapse due to absence of energy input to the working fluid. As vapor bubble  250  collapses, elastic membrane  200  will tend to return to its unflexed position to await re-energization of resistor  240  to eject another ink drop  70 . Also, as vapor bubble  250  collapses, the first pressure wave  245  propagates along elongate second chamber  190  in the working fluid as well as along first chamber  180  in the ink body. 
     Referring again to FIGS. 3,  4 ,  5 A,  5 B,  5 C,  5 D, and  5 E, attached to underside  225  of rafter member  220  and therefore disposed in first chamber  180  is a first embodiment second transducer, which may be a second heater element or second resistor  270 , for locally boiling the working fluid. First resistor  240  and second resistor  270  are off-set one to the other, as shown. The purpose of second resistor  270  is to damp first pressure wave  245  generated in both first chamber  180  containing the working fluid as well as in second chamber  190  containing the ink body. It is important to damp first pressure wave  245 . This is important because, as previously mentioned, first resistor  240  generates first pressure wave  245  in first chamber  180  and the “sympathetic” pressure wave  245  in second chamber  190  by means of membrane  200 , which first pressure wave  245  should be damped to increase printer speed by decreasing time between ejection of ink drops  70 . In this regard, second resistor  270  is energized by controller  40  a predetermined time after energization of first resistor  240 . To achieve this result, second resistor  270  is electrically connected to controller  50 , so that controller  50  controls flow of electrical energy to second resistor  270 . Second resistor  270  is in fluid communication with the working fluid and thus membrane  200  for inducing a second pressure wave  275  in the working fluid in order to flex membrane  200 . In this regard, when electrical energy momentarily flows to second resistor  270 , the second resistor  270  locally heats the working fluid causing a second vapor bubble  280  to form adjacent to second resistor  270 . Second vapor bubble  280  pressurizes first chamber  180  by displacing the working fluid and causes generation of second pressure wave  275  in first chamber  180 . As second pressure wave  275  is generated in first chamber  180 , membrane  200  flexes or distends. In other words, second pressure wave  275  generated in first chamber  180  flexes membrane  200 , so that second pressure wave  275  is transmitted into second chamber  190  in order to pressurize second chamber  190 . A predetermined time after second chamber  190  is pressurized, controller  50  ceases supplying electrical energy to second resistor  270 . Second vapor bubble  280  will thereafter collapse due to absence of energy input to the working fluid. As second vapor bubble  280  collapses, elastic membrane  200  will tend to return to its unflexed position to await re-energization of second resistor  270  to damp another first pressure wave  245 . As may be appreciated from the description hereinabove, second pressure wave  275  interferes with propagation of first pressure wave  245  along both first chamber  180  and second chamber  190 . As second pressure wave  275  interferes with first pressure wave  245 , first pressure wave  245  is substantially abated and force, momentum and speed of first pressure wave  245  is reduced (i.e., damped). Thus, re-energization of resistor  240  need not wait for first pressure wave  245  to naturally die-out. Rather, the hydraulic force of second pressure wave  275  damps hydraulic force of first pressure wave  245 , so that resistor  240  may be energized sooner, thereby increasing printer speed. After ejection of ink drop  70 , second chamber  190  is refilled with ink from an ink supply (not shown) as represented by an arrow  285 . 
     Referring to FIG. 6, there is shown a second embodiment elastic membrane  287 . Membrane  287  comprises a plurality of layers  290   a  and  290   b  constructed of predetermined elastic materials. In this regard, layers  290   a  and  290   b  may be made of an elastic natural or silicone rubber, each layer  290   a  and  290   b  having a different coefficient of elasticity for achieving a desired amount of asymmetric flexing of membrane  280 . 
     Referring to FIG. 7, there is shown a third embodiment membrane  300 . Moreover, in this embodiment of the present invention, a plurality of second embodiment transducers is also provided. Each second embodiment transducer comprises a first electromagnet  310  and a second electromagnet  312  both connected to a voltage source  315 . Voltage source  315  is in turn connected to controller  40  for controlling operation of electromagnets  310 / 312 . Each electromagnet  310 / 312  includes a metal core  317 . Each electromagnet  310 / 312  also includes an electrical conductor wire  318  that is capable of carrying an electrical charge and that is wound about core  317 . Membrane  300  includes a flexible substrate  320 , which may be made from natural or silicone rubber, to which is coupled a metallic layer  330  that is responsive to an electromagnetic force generated by electromagnets  310 / 312 . The material and thickness of metallic layer  330  are chosen so that metallic layer  330  will outwardly flex toward outlet  75  when electromagnetic force is applied to metallic layer  330 . However, as metallic layer  330  flexes, elastic substrate  320  will simultaneously flex in the same direction and the same amount because substrate  320  is coupled to metallic layer  330 . When first electromagnet  310  is energized, the flexing of membrane  300  causes first pressure wave  245  to be induced in the ink body residing in second chamber  190  to cause ink drop  70  to exit outlet  195 . Moreover, elastic layer  320 , as well as metallic layer  330  coupled thereto, will returned its unflexed state after ejection of ink drop  70  due to the elastic nature of substrate  320 . In addition, when second electromagnet  312  is energized, the flexing of membrane  300  causes second pressure wave  275  to be induced in the ink body residing in second chamber  190  in order to damp first pressure wave  245  in the manner previously mentioned. Of course, this embodiment of the present invention does not require the working fluid to be present. Thus, an advantage of this embodiment of the invention is that need for working fluid is eliminated. 
     Referring to FIGS. 8,  9 ,  10 A,  10 B,  10 C,  10 D and  10 E, there is shown ink cartridge  75   a  belonging to a second embodiment print head, generally referred to as  340 . In this regard, first resistor  240  and second resistor  270  are collinearly aligned and affixed to underside  225  of rafter member  220 . Collinearly aligning first resistor  240  and second resistor  270  may facilitate construction of print head  340 . Moreover, print head  340  includes an upper barrier member  350  defining first chamber  180  therein. Upper barrier member  350  also defines a first inlet  355  in communication with first chamber  180  for ingress of the working fluid into first chamber  180 . In addition, print head  340  further includes a lower barrier member  360  defining second chamber  190  therein. Lower barrier member  360  also defines a second inlet  365  in communication with second chamber  190  for ingress of the ink into second chamber  190 . First chamber  180  is vertically and collinearly aligned with second chamber  190 . Moreover, membrane  200  is interposed between upper barrier member  350  and lower barrier member  360 . 
     Referring to FIGS. 11,  12 A,  12 B,  12 C,  12 D and  12 E, there is shown ink cartridge  75   a  belonging to a third embodiment print head, generally referred to as  370 . In this regard, a first alcove or first blind cavity  380  is in communication with first chamber  180 , but is off-set from first chamber  180 . Also, a second alcove or second blind cavity  390  is in communication with second chamber  190 , but is off-set from second chamber  190 . Previously mentioned first resistor  240  is disposed in first chamber  180  while second resistor  270  is disposed in first blind cavity  380 . Thus, first resistor  240  and second resistor  270  are off-set from each other. As first resistor  240  heats the working fluid in first chamber  180 , vapor bubble  250  forms to flex membrane  200  in order to eject ink drop  70  out outlet  195 . Of course, as membrane  200  flexes, first pressure wave  245  propagates along second chamber  190 . Moreover, second resistor  270  is also disposed in first cavity  380  for flexing membrane  200 , which is in fluid communication with second cavity  190 . Second resistor  270  is actuated to produce second pressure wave  275  in second cavity  390  in order to damp first pressure wave  245 . Preferably, second resistor  270  is actuated before first pressure wave  245  passes second blind cavity  390 , so that first pressure wave  245  is precluded from entering cavity  390 . Moreover, according to this embodiment of the present invention, both first chamber  180  and second chamber  190  are provided with a “pinch point”  400   a  and  400   b,  respectively. In this regard, pinch points  400   a/b  are formed in upper barrier  350  and lower barrier member  360 , respectively. The purpose of pinch points  400   a/b  is to create an obstacle in the path of first pressure wave  245  in order to further damp first pressure wave  245 . Thus, it may be understood that third embodiment print head  370  is substantially similar to second embodiment print head  340 , except for the off-set of blind cavities  380 / 390 , presence of resistors  270  and the addition of pinch points  400   a / 400   b.    
     Referring to FIGS. 13 and 14, there is shown ink cartridge  75   a  belonging to a fourth embodiment print head, generally referred to as  410 . Fourth embodiment print head  410  is substantially similar to third embodiment print head  370 . However, according to this fourth embodiment print head  410 , first resistor  240  and second resistor  270  are off-set from outlet  195  and second chamber  190  includes a pinch-point  420  for obstructing first pressure wave  245  in order to damp first pressure wave  245  in second chamber  190 . According to this embodiment of the present invention, print head  410  is capable of controlling ink droplet volume as well as damping first pressure wave  245 . It may be appreciated by a person of ordinary skill in the art that this fourth embodiment of the invention will produce a plurality of different ink drop volumes (i.e., ink drop sizes) depending on the number and size of resistors present ad the firing combinations possible. Larger drop weights can be generated by timing the resistor firing events to amplify the pressure waves instead of damping them out as described in previously mentioned embodiments herein. 
     An advantage of the present invention is that printer speed is increased. This is so because there is no longer a need to wait for the first pressure wave to naturally die-out before re-actuating the transducer (e.g., resistor or electromagnet) that is used to successively eject ink drops. 
     Another advantage of the present invention is that the effect of “decel” is reduced. This is so because, although the effect of “decel” is not fully understood, it has been observed that separation of the ink body from the resistor by presence of the membrane reduces the effect of “decel”. 
     An additional advantage of the present invention is that use thereof reduces the phenomenon known as resistor “kogation”. This is so because the ink body is separated from the resistor and therefore cannot chemically react with the resistor. 
     Yet another advantage of the present invention is that resistor cavitation damage due to the combined effects of bubble collapse and corrosive inks is reduced. This is so because the ink body is separated from the resistor. 
     Still another advantage of the present invention is that a wider variety of inks may be used. This is so because the ink vaporization constraint can be relaxed so that less soluble components, such as pigments, or polymers, can be included at higher concentrations in the ink. Moreover, relaxing the thermal or vaporization constraint may allow use of inks with significantly different bulk properties. 
     While the invention has been described with particular reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements of the preferred embodiments without departing from the invention. For example, the invention is suitable for use in a piezoelectric ink jet printer as well as in a thermal ink jet printer. To effect this result, one or more piezoelectric transducers may be used rather that thermal resistors or electromagnets in order to produce the first pressure wave and the second pressure wave. 
     Therefore, what is provided is a thermal ink jet printer for printing an image on a receiver and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime. 
     Parts List 
       10  . . . thermal ink jet printer 
       20  . . . image 
       30  . . . receiver 
       40  . . . input source 
       50  . . . controller 
       60  . . . thermal ink jet print head 
       70  . . . sheet supply tray 
       75   a/b/c/d  . . . print head cartridges 
       80  . . . picker mechanism 
       100  . . . guide 
       110  . . . platen roller 
       112  . . . arrow (direction of receiver advance) 
       120  . . . belt and pulley assembly 
       130  . . . belt 
       140  . . . motor 
       150  . . . pulley 
       160   a/b  . . . slide bars 
       170   a/b  . . . frame members 
       180  . . . first chamber 
       190  . . . second chamber 
       195  . . . outlet 
       197  . . . faceplate 
       200  . . . first embodiment first membrane 
       210  . . . support member 
       215  . . . upper ledge 
       216  . . . lower ledge 
       220  . . . rafter member 
       225  . . . underside of rafter member 
       240  . . . first embodiment of the first transducer (i.e. first heater clement or first resistor) 
       245  . . . first pressure wave 
       250  . . . first vapor bubble 
       270  . . . first embodiment of the second transducer (i.e. second heater or second resistor) 
       275  . . . second pressure wave 
       280  . . . second vapor bubble 
       285  . . . arrow (representing ink refill direction) 
       287  . . . second embodiment membrane 
       290   a/b  . . . layers of second embodiment membrane 
       300  . . . third embodiment membrane 
       310  . . . first electromagnet 
       312  . . . second electromagnet 
       315  . . . voltage source 
       317  . . . metal core 
       318  . . . electrical conductor 
       320  . . . substrate 
       330  . . . metallic layer 
       340  . . . second embodiment print head 
       350  . . . upper barrier member 
       355  . . . first inlet 
       360  . . . lower barrier member 
       370  . . . third embodiment print head 
       380  . . . first blind cavity 
       390  . . . second blind cavity 
       400   a/b  . . . pinch points 
       410  . . . fourth embodiment print head 
       420  . . . pinch point