Abstract:
A printhead for a hardcopy apparatus is calibrated by a separate device before being installed in the hardcopy apparatus. The calibration information produced is stored in a memory located in the printhead, in the device, in the hardcopy apparatus or in an external device. A carriage and several printheads may be calibrated simultaneously.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to installing printheads in a hardcopy apparatus. In particular the present invention relates to preparing for use one or more replacement printheads in a printer.  
         BACKGROUND OF THE INVENTION  
         [0002]    When a hardcopy apparatus is in use, it may become necessary to replace a printhead. This may be due to a printhead cartridge running out of ink. Alternatively, it may be due to the printhead becoming defective, for example the number of blocked nozzles has exceeded a predetermined number.  
           [0003]    With conventional hardcopy apparatus, when it is necessary to replace a printhead, the existing printhead is removed, the replacement printhead is inserted and then specific routines are undertaken to ensure that the printhead will operate satisfactorily in the apparatus.  
           [0004]    Specific examples of these routines are:  
           [0005]    Routines to determine whether the printhead has been used before;  
           [0006]    Energy routines to determine the electrical characteristics of the printhead and modify the signal to the printhead to ensure optimal performance;  
           [0007]    Start-up routines to ensure that all nozzles are firing and that they are firing correctly.  
           [0008]    Routines to ensure nozzle alignment with the other printheads;  
           [0009]    Routines to ensure color calibration with the other printheads.  
           [0010]    The time during which these routines are undertaken represents downtime for the hardcopy apparatus. For example, for large format printers and industrial printers the downtime can amount to as long as twenty minutes. Thus printhead replacement is a costly exercise for the user, especially for expensive industrial hardcopy apparatus and hardcopy apparatus subject to heavy use.  
           [0011]    Failure to perform the above routines causes a reduction in print quality.  
         SUMMARY OF THE INVENTION  
         [0012]    Certain aspects of the present invention seek to overcome or reduce the above problems.  
           [0013]    According to a first aspect of the present invention, there is provided a method of installing at least one printhead in a hardcopy apparatus, wherein said printhead is subjected to a calibration and/or start up procedure before it is installed in the hardcopy apparatus.  
           [0014]    According to a second aspect of the present invention, there is provided a method of installing a plurality of printheads in a hardcopy apparatus, wherein the printheads are subjected to a calibration procedure relative to each other before they are inserted in the hardcopy apparatus.  
           [0015]    According to a third aspect of the present invention, there is provided a method of installing a carriage with one or more printheads mounted in said carriage in a hardcopy apparatus, wherein the printheads mounted in said carriage are subjected to a calibration procedure before the carriage is installed in the hardcopy apparatus.  
           [0016]    According to a fourth aspect of the present invention, there is provided a device for calibrating at least one printhead for a hardcopy apparatus, said device including a memory and means for subjecting said printhead to a calibration process, said calibration process producing calibration information, said calibration information being stored in said memory.  
           [0017]    According to a fifth aspect of the present invention, there is provided a system for calibrating at least one printhead for a hardcopy apparatus, said system comprising a device including means for subjecting said printhead to a calibration process, said calibration process producing calibration information, and said system further including an external device, said external device including a memory, said calibration information being stored in said memory.  
           [0018]    According to a sixth aspect of the invention, there is provided a system for calibrating at least one printhead, said system comprising a device including means for subjecting said printhead to a calibration process, said calibration process producing calibration information, and said system further including a hardcopy apparatus suitable for receiving said printhead, said hardcopy apparatus including a memory, said calibration information being stored in said memory.  
           [0019]    According to a seventh aspect of the present invention, there is provided a device for calibrating one or more printheads for a hardcopy apparatus, said device including means for receiving a carriage with said printhead(s) mounted therein, a memory, and means for subjecting the printhead(s) mounted in said carriage to a calibration procedure, said procedure producing calibration information, said calibration information being stored in said memory. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which:  
         [0021]    [0021]FIG. 1 is a schematic, perspective view of a peripheral device in accordance with an embodiment of the present invention;  
         [0022]    [0022]FIG. 2 is a perspective view of a user interface for use with embodiments of the present invention; and  
         [0023]    [0023]FIG. 3 is a block diagram indicating the connections between components of apparatus according to the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    Referring to the drawings, FIG. 1 shows a peripheral device  10  in accordance with the present invention. Basically, the device  10  resembles the corresponding parts of an ink-jet printer in which a printhead is to be inserted. The replacement printhead is first inserted in a corresponding printhead pocket  11  of the device  10 . The printhead incorporates its own memory. The necessary calibration and/or start up routines are then applied to the printhead while it is in pocket  11 . The printhead is then removed from pocket  11  and inserted in an inkjet printer ready for use.  
         [0025]    Device  10  comprises a carriage  20  which is displaceable in a scan direction  12  along slider rods  21 ,  22 . Pockets  11  are provided to receive printheads to be prepared for subsequent use. It will be appreciated that although only two pockets  11  are shown, any number of pockets may be provided, depending upon the number of printheads it is desired to prepare. Each pocket  11  contains datums, fluid interconnects, electrical connections and a latch to secure the printhead in place.  
         [0026]    A media supply roller  24  feeds print media  25  to a media take-up roller  26  and nozzles of the printheads deposit ink on the media as it passes underneath the carriage  20 . LED sensors  31 ,  32  are mounted on carriage  20  to scan the ink deposited on media  25  by the printhead nozzles. Any desired number of LED sensors may be provided. Part of the path of each of the LED sensors  31 ,  32  lies over a respective registration mark  33 ,  34  on a reticule  36 . Reticule  36  is mounted on a fixed part of the device  10  and is calibrated during manufacture of the device to a known relationship with the datums of the print pockets  11 .  
         [0027]    A service station  40  is provided for the printheads inserted in the device  10 . Service station  40  comprises a spittoon  41  and wipers  42  for each of the printheads, the wipers being provided with a drive system to move them relative to the printers. A cap  44  is provided for each of the printheads. Depending on the printhead to be serviced, the cap may be used for priming.  
         [0028]    The device  10  further comprises an electronics board  50 , incorporating a central processing unit (C.P.U.).  
         [0029]    In use of the device  10 , one or more printheads to be used in an inkjet printer are first inserted in pockets  11 . The preparation of a single printhead will first be described. At the completion of the insertion, the printhead is connected electrically (power and memory chip to the electronics board  50 ) and is aligned and held firmly in place through mechanical means. The pocket  11  and associated latch undertake these operations.  
         [0030]    The following routines are then undertaken:  
         [0031]    1. New Printhead Detection and Servicing  
         [0032]    Check if the printhead is a new or used printhead. If it is a used printhead, then skip operation 1a (Turn on energy) and perform a Servicing routine for a used pen. This consists of firing a prescribed number of drops from each printhead and wiping the printhead to assure cleanliness.  
         [0033]    If it is a new pen, perform the following steps:  
         [0034]    1a) Printhead energy algorithm  
         [0035]    Perform printhead energy algorithm to assure enough energy is given to all nozzles in the printhead so each one fires a drop. Store the information of printhead energy for use during printing. This may be done through encoding this into the memory of the printhead, by sending the information to the device CPU which then sends it to the printer software, or though any other information storage and retrieval system such that the information is usable by the printer when it is time to print with the printhead.  
         [0036]    1b) Servicing routine for a new or used pen  
         [0037]    Initiate a servicing routine consisting of firing a prescribed number of drops from each printhead into the spittoon  41  or onto the media  25  and wiping the printhead to assure cleanliness.  
         [0038]    2. Nozzle Health Check  
         [0039]    Check the nozzle health—i.e. for detecting missing or severely mis-directed nozzles. This can be done by firing onto the media  25  and scanning the resulting pattern with the LED sensors  31 ,  32 . If the number of missing or defective nozzles exceeds a pre-set threshold, the pen is serviced using the primer and wiper. After these operations, nozzle health checking is repeated.  
         [0040]    Store the information of nozzle health for use during printing. This may be done through encoding this into the memory of the printhead, by sending the information to the device CPU which then sends it to the printer software, or though any other information storage and retrieval system such that the information is usable by the printing machine when it is time to print with this printhead.  
         [0041]    3. Nozzle and Printhead Alignment  
         [0042]    Precise location of the printhead relative to the device  10  occurs through firmly holding the printhead without deflecting it. Alignment is achieved by using algorithms which are similar to the algorithms used in existing printers.  
         [0043]    The method used for printhead alignment is to align it to the precisely-located reticule  36  with registration marks  33 ,  34 . The sensors  31 ,  32  scan this reticule and store the locations of the registration marks  33 ,  34 . All alignments are done with respect to these registration marks. The inserted printhead prints a pattern which gives the following information:  
         [0044]    Nozzle position with respect to the registration marks  33 ,  34  of the reticule.  
         [0045]    Overall swath height with respect to the registration marks  33 ,  34 .  
         [0046]    Absolute distance of the odd/even separation of the nozzles for a given scanning speed of the carriage  20 .  
         [0047]    Other operations may be performed according to the specific algorithms for a given printhead. In other words, the device should be capable to be upgraded to accommodate new algorithms as new printheads are developed.  
         [0048]    Since the alignment is dependent on a good location of the printhead with respect to the datum, the above procedure may be performed a number of times and the device will calculate the average value of the positions for each of the different printhead insertions. This average will be used for nozzle and printhead to printhead alignment during actual printing in the inkjet printer.  
         [0049]    4. Color Calibration  
         [0050]    Color calibration is performed in a fashion similar to the way in which the color calibration is performed on a conventional printer when all the printheads are mounted. Patterns are printed with a variety of densities. The device  10  correlates the printed optical density to known optical densities printed with known printheads and records an adjustment factor for that printhead.  
         [0051]    As with the other information relating to the printhead, the information for alignment and color calibration are stored for use during printing. This may be done through encoding this into the memory of the printhead, by sending the information to the device CPU which then sends it to the printer software, or though any other information storage and retrieval system such that the information is usable by the printer when it is time to print with this printhead.  
         [0052]    An advantage of the above-described arrangement is that a user does not have to wait for the operations to be performed by the printer when a printhead is replaced. The printer need only be stopped long enough to replace a printhead and yet it has all the operations listed already done when it is replaced. Printing can begin immediately. With embodiments of the present invention, downtime is minimized. Downtime during printhead replacement is a severe problem for printing machines that are in high usage or which have a very high acquisition cost.  
         [0053]    Use of the device can even be an advantage in association with printers which are not in heavy use or with relatively low-cost printers since it enables a quicker restart of printing than the prior art. A single device  10  may be used in turn to set-up printheads for a plurality of different printers. The device  10  may actually be constituted by a special printer kept for this purpose. The method could be performed by having a printer in a print room but which is not used for actually printing  
         [0054]    Various modifications may be made to the above-described arrangement. In particular, although the device  10  shown in FIG. 1 has so far been described as a stand-alone device, it may be used in conjunction with the user interface device  60  shown in FIG. 2. The user interface device  60  is connected to device  10  via input/output cables  61 . Device  60  has a display  62  and a panel  63  with which a user may send instructions to device  10 . The user may select an automatic mode. Alternatively the user may select instructions from a menu. The instructions may include an indication of whether a full calibration routine is to be implemented or only a partial routine or only a start-up operation. The instructions may include the type of printhead and/or the type of printer in which the printhead is to be installed. The user interface device  60  may be used to store information during the calibration by device  10  for subsequent supply to the printer. This will be explained in more detail later in connection with FIG. 3.  
         [0055]    Instead of using reticule  36 , a different method may be employed to achieve printhead alignment. One alternative method involves the use of a so-called “golden pen”  11   a  which is a printhead or other marking device which is used as a “master” for calibrating the position of the printheads which are inserted in device  10  and which are subsequently removed. Except for periodic maintenance or replacement the golden pen remains installed in device  10 , e.g. in a respective pocket  11 . The golden pen is highly-accurately machined and is predictable under environmental changes. In use, the golden pen prints a pattern with each alignment and the inserted printheads each print a similar pattern, which gives the following information:  
         [0056]    Nozzle position with respect to the pattern printed by the “golden pen”.  
         [0057]    Overall swath height with respect to the “golden pen”.  
         [0058]    Absolute distance of the odd/even separation of the nozzles for a given scanning speed of the carriage.  
         [0059]    Whether the reticule  36  or the golden pen method is employed the device needs to be calibrated periodically. This can be done during a normal servicing of the printer or through contacting a service technician. For either method of alignment, the reticule  36  or the “golden pen”, is reset to have precise alignment to the device printhead datum in the device printhead pocket  11 .  
         [0060]    The printheads and the golden pen when used, may incorporate their own ink supply or have ink supply tubing attached thereto.  
         [0061]    The printheads may not have their own memories, in which case the calibration information is stored elsewhere, e.g. in the CPU in board  50 , in the printer where the printhead is to be installed, in the user interface  60 , or elsewhere.  
         [0062]    The arrangements described so far have printheads where the nozzle arrangements is parallel to the media movement and the operation of printing is done by scanning the head over the media for successive passes. However, the printheads may have their nozzles arranged perpendicular to the media axis. Here, the operation of printing is done by keeping the printheads fixed while the media moves perpendicularly to the array of nozzles. The device  10  is particularly advantageous for calibrating a printbar corresponding to a page wide array since this calibration process can be lengthy.  
         [0063]    In an alternative color calibration process, the printhead is calibrated analytically to an absolute scale of densities or L*A*B* values.  
         [0064]    Other types of sensors than the LED sensors  31 ,  32  may be employed. For example the detection of the presence or non-presence of a drop may be performed electronically, visually, or by the use of sound. In each case, the appropriate detector is mounted on device  10  beneath the printheads. The electronic circuitry to operate the sensors may be mounted on the carriage  20  (e.g. on board  50 ) or elsewhere.  
         [0065]    Although carriage  20  may be constructed similarly to a printer carriage, it may alternatively have a relatively heavy-duty construction to allow the frequent replacement of printheads without deterioration in accuracy of performance. The electrical interconnect arrangement may also be different.  
         [0066]    Although described in connection with an inkjet printer, device  10  may be used in connection with other forms of printer. Moreover, it can also be used in connection with other types of hardcopy apparatus including plotters, photocopiers, facsimile machines and scanners.  
         [0067]    [0067]FIG. 3 shows the connections in a system comprising a calibration and/or set up device  10  with its own electronics board  50 , a user interface device  60  and a printer  70 . The calibration information can be sent directly by board  50  to the printer  70 . Alternatively the calibration information may be stored in device  60  and forwarded to printer  70  subsequently. For example, at the time of calibrating the printhead, it may not yet be known for which printer it is intended. One of the types of information which it is particularly advantageous to store in device  60  in this way is so-called “mask reshuffle” data where the printing instructions for the nozzles need to be modified to account for defective nozzles. The supply by device  60  to the printer of this information saves time, after installation of the printhead in the printer, since the printer no longer needs to process the mask reshuffle.  
         [0068]    If desired, a short calibration procedure for an inserted printhead may still be undertaken by the printer. For example, it can be useful to check the alignment of the printhead and to take any necessary correction in case an error has been introduced during the transfer of the printhead.  
         [0069]    Device  10  may be used to undertake a calibration routine and a start-up routine or only a start-up routine. Performing both routines is preferred since, even if the printhead was correctly calibrated during manufacture, it is possible that changes occurred during transport and storage. At least a start up procedure should be undertaken since this prepares the printhead for immediate use. It is possible for device  10  to undertake the calibration procedure and for the printer to undertake the start-up procedure, although this does not save as much time as with the preferred embodiment. The start-up procedure may include setting-up the printhead for a particular power supply environment at its location of use.  
         [0070]    Device  10  may handle a plurality of printheads at the same time e.g. a black printhead and three color printheads or a black printhead and five color printheads. A suitable number of pockets  11  are provided. The printheads may be calibrated independently of one another. Alternatively, the characteristics of one or more of the printheads may be taken into account when calibrating one or more of the other printheads. For example, in operation of a four printhead printer, one of the printheads may need to be exchanged for a new one. In this case all four printheads are removed from the printer, the defective one is disposed of, and the three other printheads together with a new printhead, of appropriate type, are inserted in respective pockets  11  of device  10 . The new printhead is then calibrated taking into account the existing characteristics of the three printheads; for example it is known that drop volumes can change with age. Alternatively, all four printheads could be completely recalibrated. The particular choice of procedure can be selected by user interface device  60 .  
         [0071]    Similarly any number of nozzle arrays or modules, or printheads may be calibrated together.  
         [0072]    In a final modification, a printer carriage and all its printheads are calibrated together, removed together from device  10  and then inserted together by mounting the carriage in the printer. The old printer carriage can then be used as the carriage  20  on device  10 . Total carriage replacement has the advantage that no loss of alignment occurs due to physical transfer of the printheads from the device  10  to the printer. In addition alignment can be performed in a relative manner without using a separate standard such as reticule  36  or the golden pen. Moreover, color calibration can also be undertaken on a relative basis and all colors may be balanced at once.  
         [0073]    Total carriage replacement can be used even in the event of failure of only a single printhead. If the printer has a carriage which can relatively quickly be removed and replaced, this may be a quicker operation than replacing the faulty printhead and then calibrating it and starting it up in the printer.  
         [0074]    What has been described and illustrated herein is a preferred embodiment of the invention along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention, which is intended to be defined by the following claims—and their equivalents—in which all terms are meant in their broadest reasonable sense unless otherwise indicated.