Method of extending the life of a printbar of a color ink jet printer

#This invention relates to full width array, multicolor thermal ink jet printers, and more particularly, to a method of extending the life of a printbar in a four printbar, full width array color ink jet printer, by sensing problem nozzles which fail to eject ink droplets and by filling in the missing droplets with ink droplets of a different color ink from one of the other printbars.

#It is well known in the reading and/or writing bar industry to assemble pagewidth or full width array raster input scanning (RIS) bars and raster output scanning (ROS) bars from relatively short RIS/ROS subunits placed end-to-end on a structural support bar. Once assembled, the full width array RIS/ROS bars have the requisite length and number of image processing elements to scan or to write an entire line of information with a high image resolution. Image writing bars such as thermal ink jet printbars have a plurality of printhead subunits mounted end-to-end on a structural bar which also serves as a heat sink and may optionally be cooled by passing a liquid therethrough, such as water.

#Each thermal ink jet printhead subunit uses thermal energy selectively produced by resistors located in capillary filled ink channels near nozzles or orifices to vaporize momentarily the ink and form vapor bubbles on demand. Each temporary bubble expels an ink droplet and propels it towards a recording medium, such as, paper. The use of an array of printhead subunits is appropriate because full width array printheads cannot be practically fabricated on a single wafer. Full width array printbars may be composed of collinear arrays of printhead subunits or stagged printhead subunits on each side of a structural support bar and offset from one another.

#FIG. 1 is a partially shown, isometric view of a multicolor, full width array ink jet printer.

#FIG. 2 is an enlarged, schematic front elevation view of four typical printbars of the printer in FIG. 1.

#FIG. 3 is a pixel image printed by the printbar for black ink and showing the results of a defective nozzle.

#In FIG. 1, multicolor ink jet printer 12 is illustrated with four identical full width array printheads 14, 15, 16, and 17, disposed therein to produce printed output or images on a recording medium, such as sheet 18. The printheads each comprise a structurally supporting substrate 20 which also functions as a heat sink and may optionally be cooled by the passage of a liquid coolant, such as water, through internal flow paths (not shown). An array of printhead subunits 22 are affixed on the supporting substrate 20 in an abutted fashion, as taught by U.S. Pat. No. 5,198,054 to Drake et al. and incorporated herein by reference. Alternatively, individual subunits 22 may be spaced apart from one another by a distance approximately equal to the length of a single subunit and bonded to each opposing surface of a supporting substrate 20, the subunits on one surface being staggered from the subunits on the other surface of the supporting substrate. In one embodiment, subunits 22 may be similar in construction to U.S. Pat. No. 4,774,530 to Hawkins, the relevant portions of which are hereby incorporated by reference. The forward facing edges of the subunits contain the droplet ejecting nozzles 23 and are referred to as printhead subunit faces 24 (See FIG. 2). The subunit faces 24 are maintained in close proximity to the surface of recording medium or sheet 18. Also affixed to substrate 20, at a position behind the abutted subunit array, is printed wiring board 26. Printed wiring board 26 contains the circuitry required to interface and drive the individual heating elements (not shown) in the subunits to eject ink droplets from the nozzles 23. While not shown in FIG. 1, printed wiring board 26 is connected to individual contacts contained on the subunits via a commonly known wire bonding technique (See FIG. 7). The data required to drive the individual heating elements of the printhead subunits is supplied from an external system by a standard printer interface, modified and/or buffered by a printer micro processor (not shown) within the printer and transferred to the printheads 14, 15, 16, and 17 by ribbon cables 27, only one of which is shown, and pin-type connector 28.

#Ink is supplied to the individual subunit nozzles 23 of FIG. 2 through ink channels (not shown) which connect the nozzles to subunit reservoirs 29. The subunit reservoirs 29 have inlets 25 which are aligned and sealed with outlets 31 in ink manifolds 30. Further description of such an arrangement may be found in U.S. Pat. No. 4,929,324 to Drake et al., the relevant portions of which are hereby incorporated by reference. Ink is supplied to the manifold inlet connectors 32 to which flexible hoses (not shown) connect an ink supply (not shown) located within the printer 12. Also affixed to the surface of substrate 20 are locating or alignment pads 34 (See FIG. 1) which are used to accurately position the full width array printheads or printbars within the printer 12. Further description of alignment pads 34 and the locating reference points (not shown) in the printer may be found in U.S. Pat. No. 5,192,959 to Drake et al., the relevant portions of which are hereby incorporated by reference. The location of full width array printbars 14, 15, 16, and 17 is particularly important in order to accurately position the nozzles of abutted printhead subunits 22 comprising each full width array printbar, because multicolor printing requires accurate placement of the ink droplets from each printbar relative to one another in order to place one ink droplet on a previously ejected droplet on the recording medium 18, thereby achieving the desired final colored image.

#As further illustrated in FIG. 1, recording medium 18 is fed in the direction of arrow 36 as ink droplets are ejected from the nozzles in subunit face 24 of subunits 22 to produce output images 38 thereon. The paper is fed by conventional paper feeding mechanisms (not shown) and is maintained in close proximity to the subunit face of the subunits 22 making up the various full width array printbars by one or more paper guides 40 which may contain several idler star wheels (not shown) therein. The spacing between the front faces 24, which are all coplanar with one another, and the surface of the recording medium 18, commonly referred to as the Z-direction, is important to control the position of the ink droplets ejected from the individual nozzles. Furthermore, the spacing between the parallel and adjacent full width array printbars 14, 15, 16, and 17 must be maintained as close as possible and within very close tolerances, as discussed later with reference to FIG. 2.