Abstract:
An apparatus and method for detecting ink leakage in a print head. Conductive material is provided on a print head substrate that functions as a detector for ink that has leaked out of the established ink well or conduit. The detector conductive material is preferably arranged in proximity to power and/or control signal conductors and senses when leaked ink is threatening these conductors.

Description:
FIELD OF THE INVENTION 
     The present invention relates to inkjet printers and, more specifically, to the detection of ink leakage in a print head of such a printer. 
     BACKGROUND OF THE INVENTION 
     Inkjet and like printers and cartridges are known in the art and include those made by Hewlett-Packard, Canon and Epson, amongst others. Inkjet printers include an ink supply and a print head to which ink is delivered for controlled discharge. Typically, an inkjet print head includes a substrate on or in which an expulsion mechanism is formed, a barrier plate that provides channels for delivering ink to the expulsion mechanism and an orifice plate positioned over the barrier layer such that ink is expelled through openings in the orifice plate. Power supply lines and signal processing or control lines are coupled to componentry in or on the substrate. 
     A disadvantage of known inkjet print head arrangements, however, is that the ink used therein is generally invasive and with time will leak outside of its confined area. For example, ink may leak in between the substrate and barrier layer or between the barrier layer and orifice plate, amongst other leakage channels. The escaped ink may seep onto the interconnect region(s) of the substrate where it can cause a short between the power and control lines or otherwise cause a malfunction of the print head. 
     Hence, a need exists for detecting when ink in an inkjet print head has escaped its confined area and may cause a malfunction of the print head. Furthermore, a need exists for a print head ink leakage detector that can be implemented in an economical, non-overly complex manner. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an inkjet print head that includes a mechanism that detects when ink has escaped its confined space. 
     It is another object of the present invention to provide such a print head that (1) can be economically implemented and (2) can uniquely identify itself when it has failed. 
     It is another object of the present invention to provide such a print head that utilizes conductive material adjacent the power and/or control lines to detect undesired leakage. 
     It is also an object of the present invention to provide an inkjet printer that incorporates such a print head. 
     These and related objects of the present invention are achieved by use of a ink leakage detecting apparatus as described herein. 
     The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cutaway isometric view of an inkjet printhead in accordance with the present invention. 
     FIG. 2 is a top view of an inkjet print head in accordance with the present invention. 
     FIG. 3 is a schematic diagram of a detection circuit in accordance with the present invention. 
     FIG. 4 is an alternative embodiment of a detection circuit in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a partial isometric view of an inkjet print head  10  in accordance with the present invention is shown. Print head  10  includes a substrate  20  to which a power line  12 , a control line  14  and a detect line  16  are coupled. 
     Substrate  20  includes an ink expulsion device  22  formed therein or thereon that they may be thermally, mechanically or otherwise actuated. In a preferred embodiment, the expulsion device is thermally (resistively) actuated as is known. Substrate  20  is preferably made of a semiconductive material such as silicon, Si, and includes a detection circuit  26  (not shown in FIG. 1; discussed in more detail below with respect to FIG. 3) and may optionally include a control circuit (i.e., on-chip as opposed to off-chip control logic; not shown in FIG.  1 ). 
     A passivation layer  21 , for example of Si02, preferably forms the top layer of the substrate. A plurality of other layers are formed in substrate  20  that permit operation of the thermal ink expulsion device and electrical connection to detection circuit  26 . These layers and the photolithographic steps or the like used to form them are known in the art and for clarity of the drawing these layers are not shown in FIG.  1 . 
     Power line  12 , control line  14  and detect line  16  are coupled to contact pads  13 ,  15  and  17 , respectively, which are typically formed of gold or a like conductive material. An interface conductive layer  19  as is known is provided to couple the contact pads to the passivation layer. Tantalum, Ta, or the like is a suitable interface conductive material. Power line  12 , control line  14  and detect line  16  are coupled to expulsion device  22 , control circuitry (not shown) and detection circuit  26  respectively. The power line connection is shown as a phantom line. 
     A barrier layer  40  is provided on substrate  20  and an orifice plate  50  having an orifice or nozzle  51  is provided over barrier layer  40 . Amongst other implementation, the orifice plate may be formed of kapton or a like material that is lazer abladed to form the nozzle orifices. The substrate, barrier layer and orifice plate combine to form an ink conduit or well  45  that directs ink over the expulsion mechanism. An ink supply (not shown) is coupled to ink conduit  45 . 
     As mentioned above in the Background of the Invention section, the ink used in conventional inkjet printers is invasive and with time (i.e., towards the end of life of the print head) will begin to seep between the orifice plate and barrier layer or between the barrier layer and substrate or through cracks in the passivation layer or through other channels. If this ink is permitted to flow across the substrate such that it electrically interconnects the power line and the control line, then the print head will malfunction. 
     In an effort to prevent this situation, the present invention provides detectors  30  adjacent to the power and control lines (an arrangement of detector  30  is better shown in FIG.  2 ). The detectors are coupled to detect line  16  and detection circuit  26  and when ink electrically interconnects the power or control line to a detector, a voltage is provided to detection circuit  26  which in turn generates an ink leakage signal (as discussed in more detail in reference to FIGS.  3  and  4 ). The generated signal uniquely identifies the print head that is failing and may be used to prompt a user to replace that print head. Unique identification, for example in a color printer having cyan, magenta, yellow and black color print heads, permits a user to replace only the failing print head. 
     Detectors  30  are formed of a conductive material and may be formed of the same conductive interface material  19  used to couple the power, control and detect contact pads to the substrate. The detectors  30  and material  19  may be put down in the same fabrication step. While not shown from the perspective of FIG. 1, detector  30  is coupled to layer conductive material or  19  under the detect contact pad. 
     Referring to FIG. 2, a top view of an inkjet print head in accordance with the present invention is shown. The layout of the print head of FIG. 2 is intended to illustrate a representative print head. It will be understood by those skilled in the art that inkjet layouts including such aspects as where conductors are connected, where the orifice plate is positioned, and how the orifices  51  are oriented may vary depending on a particular design. It should further be understood that the present invention is applicable to all print head arrangements and is in no way limited to the pedagogic embodiments disclosed in FIGS. 1-2. 
     FIG. 2 illustrates orifice plate  50  situated over substrate  20 . Connection regions ( 61 , 62 ) are respectively provided to the left and right of the orifice plate  50  and each connection region includes power contact pads  13 , control contact pads  15  and detect contact pads  17 . Contact pads  13  and  15  are coupled to substrate  20  by conductive interface material  19 . Contact pads  17  are coupled to the substrate by similar conductive material  19 , however, this material is formed integrally with the material that forms detectors  30 . These detectors or the “detector arrangement” is preferably formed about the power and control contact pads such that the leakage of ink onto both a detector and the power or control lines (as shown by phantom ink blot  70 ) causes a voltage to be propagated through the conductive ink to the detector. The detector is in turned coupled to the detection circuit which outputs an ink leakage signal upon receipt of a voltage from a power or control line or other source. While one arrangement of detectors is shown in FIG. 2 it should be noted that other arrangements could also be utilized. 
     Referring to FIG. 3, a schematic diagram of detection circuit  26  in accordance with the present invention is shown. Detection  26  preferably includes a MOSFET transistor  65  that receives a forward biased gate voltage (preferably 12V). The detect contact pad(s)  17  is/are preferably coupled to the drain MOSFET  65  and the source is preferably coupled through a resistor, R 1 , to ground. The detection circuit output  66  is preferably coupled at the source and buffered by an inverting buffer  67 . 
     Referring to FIG. 4, an alternative embodiment of a detection circuit (labeled  126 ) is shown. Detection circuit  126  preferably includes a MOSFET transistor  165  that has a gate which is coupled to detect contact pad(s)  17  through a resistor, R 3 , to ground. The drain is pulled through a resistor, R 2 , to the power supply voltage and the source is tied to ground. The output  166  is coupled to the drain and preferably buffered by inverting buffer  167 . While circuits  26  and  126  provide the same function, the circuit of FIG. 3 eliminates the input load caused by R 3 . 
     While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.