Patent Application
20060227157
The disclosure relates to methods and apparatus for extending the reliability and usefulness of a full width printhead by providing a redundant temporary replacement printhead module that can be positioned to compensate for missing or faulty jets.
Printers using full width printheads (i.e., printbars) are known and offer several advantages over conventional printheads that must travel back and forth across a print medium to achieve printing of a page. Advantages include faster printing speed, quieter operation, improved reliability due to less moving parts, etc. However, full width printheads suffer from certain drawbacks.
One particular drawback is a problem with defective nozzles. High productivity printers achieve enhanced productivity by employing a large number of nozzles. However, more nozzles result in greater opportunity for nozzle failure. For instance, a full width ink jet printhead array spanning a typical 8.5″ wide sheet of paper may have 7200 or more discrete individual jet nozzles, each of which must operate properly for the printer to produce a quality print. The problem is increased in high speed production architecture ink jet systems that can have a combined printhead width of up to 24″ or more.
Partially due to manufacturing limitations and partially to reduce the cost of replacement, many pagewidth or full width printheads use a number of smaller replaceable printhead modules rather than a large single head. The printhead modules are either butted together to form a single linear array, or offset and staggered in length to provide full width functionality. Such full width printheads may also include multiple printhead modules arranged in series (but offset by a partial pixel width to achieve an effective increase in resolution of the head itself).
For example, a prototype 24″ full color printer uses a first set of 32 modules (eight (8) three inch (3″) long 300 dpi staggered print modules for each of four colors C, Y, M, and K) to achieve 300 dpi printing. A second set of 32 printhead modules is offset by ½ pixel from the first set to effectively double the resolution of the printhead assembly to 600 dpi. Thus, 64 total printhead modules are present. This represents a total of 57,600 individual nozzles in the full width, full color printhead array. Having such a large number of individual jets increases the probability that any single ink jet will fail. This, coupled with very high printer usage in high speed production makes the probability and frequency of nozzle failure a significant problem.
A simplified example of this is shown in
In this simplified example, a defective nozzle 220 is present within printhead module 200B. As is evident from the vertical lines, nozzles from the offset printhead module 300B do not overlap with the single defective nozzle 220 shown. Accordingly, once at least one defective nozzle is present, the collective printbar 100 consisting of various printhead modules with nozzles is no longer capable of reproducing a complete image. Instead, the printbar 100 will print with a band or streak at the location of the defective nozzle where no printing can occur. Thus, once one or more nozzles become defective, image quality suffers.
Failed ink jet detection systems are known in the art. Such technologies include, for example, drop sensors that recognize missing or misdirected drops. One such drop sensing device uses a light beam that is projected across the width of the printing medium and between the printhead and the printing medium to a detector. Based on the timing and degree of occlusion caused by an ink droplet passing through the light beam, the device can sense the size and directional accuracy of the ink droplets. A laser may also be provided for such detection. Examples of suitable detectors include U.S. Pat. No. 5,179,418, the subject matter of which is hereby incorporated herein by reference in its entirety, as well as Japanese Patent Publication No. 4-315914 and Japanese Patent Publication No. 4-276446.
Even though nozzle failures, such as defective nozzle 220, can be detected, no practical method exists to repair individual failed printheads, other than minor problems that can be fixed through routine cleaning or maintenance. Rather, typical repair requires a complete replacement of the printhead module containing one or more defective print nozzles. This, however, is problematic for at least three reasons. First, the failed printhead module is typically thrown away, which represents a significant investment in cost, even though only a single nozzle or jet may be defective. Second, a replacement printhead may not be readily available, which can increase printer down time. Third, typical replacement and necessary alignment must be performed by a qualified technician, which requires additional printer down time to schedule and complete the replacement. Particularly when the printer involved is used for high volume production runs, there is a very high cost associated with the necessity to stop the current production run and make such necessary printhead repairs.
Various methods and attempts to improve the reliability of such printers are known, including for example, those disclosed in U.S. Pat. No. 5,581,284 to Hermanson, U.S. Pat. No. 6,089,693 to Drake et al., U.S. Pat. No. 6,462,764 to Kubelik, and U.S. Pat. No. 5,587,730 to Karz. Each of these four patents is commonly assigned to Xerox Corporation and hereby incorporated herein by reference in their entireties.
There is a need for a more cost-effective system to compensate for defective ink jets.
There also is a need for a system and method that can extend the life of a printer before servicing or printhead replacement is necessary.
There further is a need for a system and method that can enable compensation for defective ink jets on an array that includes nozzles with different alignment offsets using only a single replacement module.
To provide redundancy at reduced cost, various exemplary embodiments provide one or more extra temporary replacement printhead modules in addition to the modules already provided to achieve fullwidth printing. These one or more replacement modules are not necessarily used during normal operation of the device and instead are mainly activated when one or more nozzles in the primary printhead modules are determined to be defective.
If the circumstances are that the printhead module with a failure has more than one defective jet, this extra temporary spare module can obviously operate to replace two or more jets in the defective module.
In order to take advantage of a single extra printhead module and to be able to compensate for more than a single failed jet, it is also possible that the module can be located to compensate for failed jets in two or more modules. If the modules are adjacent modules and the distance between failed jets is less than the length of the replacement printhead module, the module can be aligned to cover both defective jets. Alternatively, additional print passes could be added to compensate for more defective jets if they are not closely spaced.
In order to further take advantage of a single extra printhead module and to be able to compensate for more than a single failed jet, it is also possible that the module can be provided with roll capability around at least one axis to compensate for failed jets in different modules having non-aligned or non-uniform spacing.
In various exemplary embodiments, at least one extra printhead module is mounted on a separate translating x-axis or is otherwise adjustable along the x-axis. This architecture requires the addition of only a single printhead module because the x-axis translation ability allows alignment with any of the nozzles of the full width array.
In various exemplary embodiments, one replacement module can be positioned to compensate for two or more missing jet nozzles. In a preferred embodiment, the replacement module can be rotated or rolled about one axis in addition to x-axis translation to align with one or more defective ink nozzles. This may be particularly useful when defective nozzles are on modules that are offset or otherwise non-aligned with other printbar modules.
When one or more jets of a full width printhead is irreparably lost or otherwise defective, the jet(s) can be automatically detected by a suitable jet detector. An example of such known detection can be found, for example, in U.S. Pat. No. 6,089,693 to Drake et al. At this time, the printing process can be temporarily stopped and a spare temporary replacement printhead module moved into an x-direction position that covers the missing jet. The printing process can then be restarted and the printing of the image covered by the defective nozzle can be achieved using a nozzle from the spare replacement printhead module aligned with the defective nozzle. Conventional image processing techniques can provide the substituted drop by compensating the timing and placement of the replacement drop based on the known positional orientation of the spare replacement printhead module. This enables continued operation of the printer without the need for an extended stop to perform a complete replacement of a defective printhead module.
Although printing could proceed indefinitely through use of the spare module, the defective printhead module may be replaced at an appropriate time, such as after completion of a production run or until service can be scheduled. At this time, it may not be necessary to purchase or install a new printhead module. Rather, because the temporary spare module only needs to have at least one jet that fires, the first time the “replacement” printhead module is used, it can itself be used to replace the defective printhead module having one or more defective nozzles. Then, the defective printhead module can be mounted as the new “replacement” temporary spare printhead module. This “replacement” module can theoretically be used for the life of the product, since it only needs to have one operational jet to serve its purpose as a temporary spare.
The provision of more than one redundant print head module will further increase the average time between repairs of the printer. However, each added printhead adds additional cost and complexity.
Exemplary embodiments will be described with reference to the drawings, wherein:
The disclosure is directed to compensating missing or defective elements in spot imaging reading and/or writing bars. In particular, it pertains to full width array raster input scanning (RIS) and raster output scanning (ROS) bars. These are formed from either a single full width array or more preferably a series of relatively short modules assembled together to have a requisite length and number of elements to scan or write an entire line of information with a high image resolution. In exemplary embodiments, the spot imaging bars are writing devices, preferably liquid ink jet printers, but can also include reading devices, such as LED bars.
Exemplary printers can be of the continuous stream or drop-on-demand types, such as piezoelectric, acoustic, phase change wax-based or thermal, and have at least one printhead containing an array of nozzles from which droplets of ink are directed toward a medium, such as paper. The particular type of ink jet delivery methodology is not of particular concern, so long as temporary replacement printhead modules are compatible for use with any failed printhead modules in the main array.
In addition to the single color print bar 100 printing black ink, additional full width array printheads may be provided for printing a respective color, for instance cyan, magenta, and yellow. The appropriate ink can be supplied to the associated printhead by inclusion of an attached printhead ink tank coupled to the printheads themselves or by ink containers attached to the printheads through flexible tubing as used in connection with the black printbar. Alternatively, multicolor printheads could be utilized whereby two or more colors coexist within the same printhead. In this case, the alignment replacement jets on the replacement head would of course have to be of the same color as any given defective jet.
To print an image, a controller 54 receives bit map images from a print driver which is either resident in the printer or is resident in an image generating device such as a personal computer, or a combination of the two. The bit mapped images are manipulated by the controller 54 such that the appropriate signals are transmitted to the printbar 100. The drive signals generated by the controller 54 are conventionally applied via wire bonds to drive circuitry and logic on each of the printhead dies 200A, 200B, 300A, 300B, etc. of each printbar 100 (and any optional color printbars). Signals include pulsing signals that are applied to heat generating resistors or transducers formed in the heater dies or any other conventional or subsequently developed structure used by the printbar to eject ink from a select nozzle.
The controller 54 may take the form of a microcomputer including a central processing unit, a read-only memory for storing complete programs and a random access memory. The controller 54 also controls other machine functions such as rotation of the drum 11 and movement of a positioning device 440 (to be described later in detail) associated with a carriage 410 to advance a temporary replacement printhead module 500 in position to compensate for missing or defective jets in the printbar 100.
Defects resulting from the failure of certain nozzles to eject ink during the printing process can generate images that are unacceptable. Such defects are considered a significant failure mode and can result in a user not printing with the printer until the non-printing nozzle is remedied either through a maintenance operation or by replacement of the printbar.
In view of such printing defects, various embodiments provide a defective nozzle detection system 90 (
The carriage assembly 400 includes a translatable carriage 410 that is driven by lead screws 420 and 430 by a drive motor 440. The carriage 410 includes curved frame members 450 and 460, which support at least one temporary replacement printhead module 500. Carriage 410 may include threaded apertures through which the lead screws 420 and 430 are threaded. The carriage 410 moves in the X-direction shown to traverse the printer parallel to the length of the printbar 100 and perpendicular to a direction of paper advancement. The replacement printhead module 500 can be conventional in construction and fabricated in accordance with the same techniques used to form individual print modules 100A within printbar 100. In preferred embodiments, replacement modules 500 are identical to modules 100A and are thus suitable for eventual permanent replacement of malfunctioning printhead modules 100A.
When a defective nozzle is discovered through use of defective nozzle detector 90, a user may consider whether to continue printing. A user interface 80 may be provided, which typically appears on a display device, for instance, a cathode ray tube or liquid crystal display of the image input device 74. The user interface may include the selection of two or more document resolutions. For instance, the user interface 80 may include a draft mode selector 82 and a high resolution mode selector 84 which, once selected, are transmitted to a resolution control circuit 85. In addition, the user interface may include an image mend selector 86 that enables the user to select the option of filling in the missing data on a printed page due to one or more defective nozzle(s).
Suitable selectors can include pushbuttons, touch sensitive screens, or mouse selectable items in menus as non-limiting examples. If the user does not select the image mend selector 86 function, the user can either decide not to print with the printer until the defective nozzle is corrected (i.e., stop current usage of the printer) or continue to print at reduced image quality (i.e., while retaining the current detected nozzle defect(s)). It is also possible to include a defective nozzle visual indicator 87 in the user interface. The indicator 87 indicates to the user that one or more defective nozzles are present. In various embodiments, the printing system may include a default setting where once a defective nozzle is identified, the system automatically enters the image mend mode 86 until otherwise changed by the user. This can allow near seamless automatic compensation for faulty jets.
If the user selects the image mend selector 86 (or the feature is automatically enabled), then a signal responsive thereto is transmitted from the image input device 74 over the bus 71 to the controller 54. Either prior to selection or in response thereto, defective nozzle detector 90 identifies which of the nozzles are defective. The defective nozzle detector 90 is incorporated as part of printbar control circuits 92, which are coupled to the printbar 100. In one example of a defective nozzle detector, the defective nozzle detector circuit detects when there is no current being carried by a particular drop ejector, which would indicate, for instance, an open heater or thermal transducer. It is also possible that other defective nozzle detection devices including ink sensing conductors placed within a channel could be used. In addition, a print of a diagnostic test pattern could be made to manually assess missing or faulty jets. The test pattern would allow the user to identify to the machine which of the nozzles are non-functioning. For instance, if the printer does not include nozzle detectors, the printbar could print a test pattern including nozzle identifiers, such as a number, which is printed by each of the functioning nozzles and which identifies a nozzle. The printer might print a test pattern responsive to a user selecting the image mend selector 86. The missing number or numbers would indicate to the user which of the nozzles is non-functioning. The user would then input the nozzle number or numbers into the printer controller through, a user input device, such as a keypad 93, of the user interface 80.
Once the defective nozzle(s) have been identified, the information is accessed by the controller 54 and is used by a nozzle control circuit 94. The nozzle control circuit 94 provides a plurality of functions, which include enabling the storage of the identity of one or more defective nozzles as well as the direction of the storage of image data corresponding to a defective nozzle in a defective nozzle data RAM 96. RAM 96 can be included in the RAM 76 or separately embodied. The nozzle control circuit 94, upon receipt of the identity of the defective nozzle, would cause the defective data RAM to store appropriate data, which cannot be printed during printing of the image due to the defective nozzle. For instance, if there are two defective nozzles, then the image data, which is not printed by the first defective nozzle is stored in a plurality of registers 97. This data, for example, corresponds to a single column of information wherein the image data for every pixel location of the column is stored for each of the lines of the missing column of the printed image. The second defective nozzle data is stored in a register 98.
During image processing, the controller 54 and the nozzle control circuit 94 transmits the stored image data from the RAM 96 to a suitable selected replacement nozzle for printing. The selected replacement nozzle could be determined as a function of the moving capabilities provided by the positioning device 440 or may be selected as a function of a distance measured in nozzle spacing from the defective nozzles. For instance, if a single nozzle is determined to be defective, the replacement printhead module 500 may be moved by a predetermined distance under control of the positioning device control circuit 95 of the controller 54. The positioning device control circuit 95 transmits a signal representative of the desired nozzle spacing or the movement thereof to a printer control circuit 99 that is coupled to the positioning device 440. After the positioning device control circuit 95 has transmitted a signal over the bus 71 to cause the positioning device 440 to move a predetermined distance from the defective nozzle, the controller 54 retrieves the defective nozzle data from the RAM 96 such that the data is printed by the replacement printhead module 500.
In this particular example, printbar 100 is for a single color, such as black, and includes two serially oriented printbar arrays 200 and 300. The first printbar array 200 has four individual printhead modules (200A, 200B, 200C, and 200D), each having a length L that collectively provide a full width array extending the length of the printer (e.g., 4×L) and have a uniform nozzle spacing of S. The second printbar array 300 also has four individual printhead modules (300A, 300B, 300C, and 300D) that collectively provide a full width array extending the length of the printer and has a uniform nozzle spacing of S. However, because second printbar 300 is offset from the first printbar 200 by a distance of S/2, the individual nozzles 210 of the first array do not overlap with corresponding nozzles 310 of the second array. Thus, for example, if the spacing S corresponds to 300 dpi (dots per inch), the combination of printbars 200 and 300 will result in an effective doubling of the resolution to 600 dpi. While shown to have four modules in each array, this is a non-limiting example. Any number of modules may be present in each array.
Various methods of printer operation will be described with reference to
If however, all defective jets are determined to be within length L in step S5060, the process advances to step S5090 where the image data is extracted for the defective jet(s). Flow then advances to step S5100 where the temporary replacement printhead module is positioned in line with the missing jet(s). Flow then advances to step S5110 where the extracted data from the defective jet(s) is sent to predetermined nozzles of the replacement module. Flow then advances to step S5120 where a temporary print mode operation is performed. During this temporary operation, properly functioning jets are printed as normal and the missing or defective jet(s) are printed by aligned nozzles in the temporary replacement printhead module through suitable timing and control of the image printing process. From step S5120, flow advances to step S5050 where the process stops.
Thus, during the method of
A second method of operation will be described with reference to
This embodiment provides a mechanism in which a single replacement printhead module 500 can be used and aligned to either array 200 or 300 and may even be adjusted to compensate one or more defective jets on each of two non-aligned modules 200 and 300. This is possible through a slight roll of the printhead module 500 about a roll axis in a direction R as shown. Thus, besides the ability to translate in the X-axis, the replacement module can be rotated slightly about a roll axis in direction R (which may be counterclockwise as shown or clockwise) to adjust the effective spacing between replacement nozzles to other than an even pitch spacing of S and to better align the replacement module with a defective jet.
For example, in
For example, when the replacement printhead module has nozzles arranged in a known sawtooth layout arranged on a diagonal, a nozzle spacing S that results in 300 dpi, and a module length of about 3 inches, a printhead module roll in axis R of at little as 10 m radians can cause a shift in spacing between a far left nozzle and a far right nozzle of a sawtooth of 42 μm, which corresponds to 1/600 dpi. In the illustrated example of a spacing S that corresponds to 300 dpi nozzle spacing, results in the ability to accommodate alignment with a spacing that is a multiple of S/2 as illustrated in
An example of a method of correction using this structure will be described with reference to
If however, all defective jets are determined to be within length L in step S8060, the process advances to step S8090 where the image data is extracted for the defective jet(s). Flow then advances to step S8100 where the temporary replacement printhead module is positioned in line with the missing jet(s). Flow then advances to step S8110 where it is determined whether all defective jets are aligned with corresponding nozzles of the replacement printhead module. If they are, flow advances to step S8130 where the extracted data from the defective jets is sent to predetermined nozzles of the replacement module. Flow then advances to step S8140 where a temporary print mode operation is performed. During this temporary operation, properly functioning jets are printed as normal and the missing or defective jets are printed by aligned nozzles in the temporary replacement printhead module through suitable timing and control of the image printing process. From step S8140, flow advances to step S8050 where the process stops.
However, if it is determined at step S8110 that all defective jets are not aligned, flow advances to step S8120 where replacement module 500 is slightly rotated about axis R until defective nozzle(s) are properly aligned with a replacement nozzle of module 500. From step S8120, flow advances to step S8130. Alignment can be achieved through use of adjustment tables, known mathematical geometric relationships, or through automated or manual visual inspection and subsequent calibration or adjustment. Thus, with only a single replacement module having nozzles with a spacing S, defective nozzles on two different modules that have non-uniformly aligned nozzles can be compensated for.
Although printing could proceed indefinitely through use of the spare replacement module 500, the defective printhead module (200 or 300) may be replaced at an appropriate time, such as after completion of a production run or when service can be scheduled. At this time, it may not be necessary to purchase or install a new printhead module in the array. Rather, because the temporary spare module only needs to have at least one jet that fires, the first time the “replacement” printhead module 500 is used, it can itself be used to replace the defective printhead module (200 or 300) having one or more defective nozzles. Then, the defective printhead module (200 or 300) can be mounted as the new “replacement” temporary spare printhead module 500. This “replacement” module can theoretically be used for the life of the product, since it only needs to have one operational jet to serve its purpose as a temporary spare. All that is required is knowledge of the location of defective jet(s) so that the replacement module can be suitably positioned to have an operable jet aligned with defective jet(s) in the main printbar array.
While the various described circuits 85, 94, and 95 have been identified as part of the controller 54, these circuits can be separate from the controller. In addition, the controller 54 as well as the described circuits 85, 94, and 95 can be embodied as hardware, software, or firmware. It is known and commonplace to program and execute imaging, printing, document, and/or paper handling control functions and logic with software instructions for conventional or general purpose microprocessors. This is taught by various prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, or prior knowledge of functions which are conventional, together with general knowledge in the software and computer arts. That can include object oriented software development environments, such as C++. Alternatively, the disclosed system or method may be implemented partially or fully in hardware, using standard logic circuits or a single chip using VLSI designs.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
