Patent Application
20060044345
The present invention relates generally to printheads for incremental printers. More specifically, the present invention relates to a composite printhead for incremental printers that compensates for printhead malfunctions and which can act as a line-type printhead to print in a single pass printmode or as a serial-type printhead to print in a multipass printmode.
Incremental printing devices including inkjet printers of the thermal and piezoelectric varieties, dot matrix printers, impact printers, etc., provide an inexpensive and flexible solution to many printing problems. In particular, when used in a line-type configuration, these types of printing devices (hereinafter referred to as “printers) are capable of high printing throughputs at relatively low costs per page printed. However, the total cost of ownership of such a printer can be fairly high due to the fact that malfunctions in a line-type printing head typically necessitate replacement of the entire printing head. A number of prior art references describe attempts to ameliorate this problem.
U.S. Pat. No. 5,398,053 to Hirosawa, et al. describes the use of an ancillary printhead in addition to a primary, line-type printhead to compensate for printing errors due to malfunctions in the line type printhead. While a single auxiliary printhead allows for printing errors caused by malfunctions in the primary printhead to be corrected, at some point the number and/or position of the errors present in a primary line-type printhead will unduly reduce the rate of throughput and/or the quality of images being printed, thereby necessitating replacement or repair of the primary printhead.
U.S. Pat. No. 6,481,820 to Tamura, et al. discloses a printer having a redundant line-type printhead aligned directly behind a primary printhead for the purpose of compensating for printing errors in the primary printer. The redundant line-type printer will take over the printing functions of the entire primary printhead or selected portions thereof where there are malfunctions in the primary printhead. Tamura also describes a primary line-type printhead that can be moved laterally with respect to a sheet of recording media being printed so that functioning nozzles of the primary print head may print over the portion of the recording media missed due to malfunction in the printhead in a second or third pass. While Tamura's inventions describe means of correcting for at least some degree of malfunction in a print head, the described devices are limited at best. A redundant line-type printhead may also fail and where the failure of the redundant print head is aligned with that of the primary printhead, both printheads will have to be replaced. Malfunctions in a laterally moveable line-type printhead will greatly slow throughput of the printing process as correcting the resulting errors will necessarily require a multiple pass print mode and the limited range of motion of the printhead that results from the width of the printhead will also limit the nature of corrections that may be effected.
U.S. Pat. No. 6,270,187 to Murcia et al. describes a method of operating a malfunctioning line-type printhead so as to optimize the printing process. Murcia describes “cropping” the pen width, i.e. rendering that portion of the pen between the malfunction and the nearest edge inoperable, and then using the functional portion of the printhead to print images on recording media in a multipass printmode. Because the number of passes required is dictated by the location and magnitude of the malfunction in the printhead, it will often be the case that the printmode necessary to accomplish the printing process may not be particularly efficient, thereby resulting in higher costs per page.
Accordingly, there is a recognized need for a line-type print head that is capable of flexibly compensating for one or more malfunctions in a printhead in such a manner as to maintain maximal printing throughput. In addition, where malfunctions in a line-type print head obviate that printhead's ability to print in a single pass printmode, there is a need for a printhead and printing method that can maximize the “swath” with respect to the width of the recording media being printed upon. Such methods and/or mechanisms reduce the total cost of ownership of the printer by putting off the need to immediately replace the printhead or portions thereof, thereby reducing replacement costs of materials and costs arising from improper or interrupted operation of the printer.
The needs described above are met in a composite printhead constructed according to the principles of the present invention. Such a printhead generally has two or more printing heads, and preferably three, each having a plurality of printing mechanisms disposed on an operative surface thereof. The printing mechanisms of each of the printing heads are constructed and arranged such that when the printing mechanisms of the printing heads are addressed to a sheet of recording media and upon receiving a control signal from a controller, the printing mechanisms deposit colorant onto the recording media to form an image thereupon. The printing heads are mounted on respective movable guide rail assemblies. The guide rail assemblies render the printing heads independently moveable with respect to one another and are aligned in parallel with one another across the width of the sheet of recording media.
The printing heads are each narrower than the sheet of recording media as measured parallel to the guide rail assemblies, but are collectively wider than the recording media as measured along the guide rail assemblies. In addition, the printing heads are constructed such that there is at least some overlap between the respective printing heads when the printing heads are positioned on the guide rail assemblies in order to form an image on the sheet of recording media.
The printing heads of the printhead are of any type commonly used in incremental type printers, including, but not limited to, thermal and piezoelectric inkjet printers, dot matrix printers, and impact printers.
In use the printing heads may be arranged to print on the recording media in a single pass print mode or in a multipass print mode. When used in its single pass print mode, the printing heads are arranged to print a swath that is wider than a sheet of recording media. When used in its multipass print mode, the printing heads are arranged to print a swath that is narrower than the width of the sheet of recording media. What is more, when arranged in either of its single pass or multipass print modes, the respective printing heads may be arranged such that one or more functional printing mechanisms on one or more of the printing heads may be aligned with one or more nonfunctional printing mechanisms on another of the printing heads.
In the following detailed description of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and equivalents thereof.
While any form of incremental printer may embody the present invention, it will be hereinafter described as it applies to an inkjet style printer. Inkjet printing mechanisms may be used in a variety of different products, such as plotters, facsimile machines and inkjet printers (collectively referred to hereinafter as “printers”) to print images using colorants such inks, dyes, and pigments. These inkjet printing mechanisms use cartridges, often called “pens,” to shoot drops of ink onto a page or sheet of print media. Each pen has at least one printing surface or head that includes very small nozzles through which the ink drops are fired. Multi-color cartridges include several separate printing heads, each of the separate printing heads being connected to an ink reservoir of a different color.
The particular ink ejection mechanism within a printing head may take on a variety of different forms known to those skilled in the art, such as those using piezoelectric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company and hereby incorporated by reference. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
In a serial-type printer the pens are mounted on a carriage, which is arranged to scan across a scan axis relative to a sheet of print media as the pens print a series of individual drops of ink on the print media. The series of drops collectively form a band or “swath” of an image, such as a picture, chart or text. Between scans, the print medium is advanced relative to the scan axis.
Another type of printer, known as a line-type printer, utilizes elongate pens that extend across the entire width of a sheet of print media. Line-type pens are stationary and the sheets of print media are moved relative to the pens to effect printing. Using the terminology set forth above, a line-type printer ejects a series of drops that collectively forms a band or swath that is the width of the entire sheet of print media. Both serial- and line-type printing heads enable an image to be incrementally printed.
The pens of both serial- and line-type printers are typically formed of one or more dies, each die having one or more nozzles for ejecting ink formed thereon. Where one or more nozzles or an entire die of a pen malfunction, the quality of the images printed upon the print media may be degraded. As used herein, the term “malfunction” shall be construed to mean any type of operation that results in degraded print quality or in the complete inoperativeness of a nozzle, group of nozzles, or all of the nozzles on one or all of the dies of a pen or pens.
Referring first to
Note that the Figures illustrate printer carriages 14 as having only a single pen 12. It is to be understood however, that the printer carriages 14 may mount multiple pens 12 that are constructed and arranged so as to dispense multiple colors, shades, or hues of colorants. While not necessary, each of the printer carriages 14 may also be provided with two or more pens 12 to dispense the same colorant that act cooperatively to ensure that the selected colorant is dispensed when desired, i.e. a secondary pen (not shown) may be provided to take over printing duties for a primary pen 12, wholly or in part, where the primary pen 12 suffers a malfunction.
Though the preferred embodiment of the printhead 10 described herein includes three printer carriages 14, it is to be understood that the printhead 10 can be comprised of two, three, four, five, or more printer carriages and their respective pens. In all embodiments of the printhead 10, the respective widths of the pens 12 of the printheads 14 are narrower than the width of a sheet of recording media 18. However, the total width of the respective pens 12 is wider than the width of the sheet of recording media 18 being printed. In addition, the total width of the pens 12 of the printhead 10 will exceed the width of the sheet of recording media 18 so as to provide for a predetermined degree of overlap between the pens 12 of the printhead 10. While in one embodiment of the present invention each of the pens 12 are all of identical width, it is contemplated that the pens 12 may have varying widths.
The pens 12 are controlled by an electronic controller (not shown) of a type commonly known to the art. A typical electronic controller is a device capable of receiving, processing, storing and transmitting information from a computer or similar device to printer carriages 14 and pens 12 of the printhead 10. A suitable controller will communicate with a source device such as a desktop computer and will receive data therefrom regarding the nature of the images that are to be printed. Signals from the electronic controller dictate the position and operation of the pens 12 such that the pens 12 form an image on a sheet of recording media 18 as it is passed beneath the printhead 10.
Sheets of recording media 18 are passed beneath the printhead 10 by a media handling mechanism 20. Various types of media handling mechanisms 20 may be used in conjunction with the printhead 10 and it is to be understood that any mechanism capable of controlling recording media 18 so as to enable the printhead 10 to print an image on the recording media 18 will be found suitable. In general, a media handling mechanism 20 will include a media storage apparatus 22 such as a tray for individual sheets of recording media 18 or a roll support mechanism for continuous ribbons or rolls of recording media 18. Recording media 18 may be transferred from the media storage apparatus 22 and passed beneath the printhead 10 by various means known to the art.
In one embodiment of the present invention, the pens 12 of the printhead 10 are arranged so as to print an image on a sheet of recording media 18 in a single pass of the recording media 18 beneath the printhead 10, i.e. the swath of the printhead encompasses the entire width of the recording media 18 and hence the entire image that is to be printed. In this printing mode, referred to hereinafter as a single pass print mode, the printhead 10 acts as a typical line-type printhead.
In another embodiment of the present invention, the printhead 10 may be arranged so as to print an image on a sheet of recording media 18 in multiple passes. In this printing mode, hereinafter referred to as a multipass print mode, the recording media 18 is passed beneath the printhead 10 multiple times. During each pass of the recording media 18 beneath the printhead 10, the printhead 10 prints a swath of the image on the recording media 18. In its multipass print mode, the swath of the printhead 10 is narrower than the width of the entire image, thereby requiring multiple passes. Because the recording media 18 must be passed beneath the printhead 10 multiple times when printing in its multipass print mode, the media handling mechanism 20 must be constructed and arranged so as to accommodate moving the recording media 18 beneath the printhead 10 multiple times. Note that the embodiments of the media handling mechanism 20 illustrated in
The dies (not shown) of the pens 12 of the printhead 10 are arranged such that the nozzles thereof are aligned generally parallel with the guide rails 16 of the printer carriages 14. In a preferred embodiment, all the nozzles of each pen 12 are aligned parallel with the guide rail 16 of the printer carriage 14 in which the respective pen 12 is mounted. In an alternate embodiment, the nozzles of each pen 12 may be formed or positioned at an angle to the guide rail 16 of the printer carriage 14.
Each of the printer carriages 14 may have associated therewith a pen maintenance station (not shown). Where printer carriage 14 is provided with a pen maintenance station, the electronic controller will periodically address the pens 12 of the printer carriage 14 to the pen maintenance station to assure the proper operation of the pens 12. Pen maintenance stations are well known in the art and typically comprise a wiping mechanism for scraping deposits from the surface of the dies of each of the pens 12 and an ink reservoir for accepting ink that is ejected from the nozzles of the pens 12. A pen maintenance station may also include a vacuum device for applying a vacuum to the nozzles of the pen 12 for the purpose of removing blockages from the nozzles. See U.S. Pat. No. 6,238,112 to Girones et al., which is commonly assigned with the present invention and which is hereby incorporated by reference.
A nozzle function testing apparatus or method is used to analyze the function of the nozzles of the printhead 10. Any suitable apparatus or method designed to determine whether the nozzles of the printhead are functional may be used. One suitable example is disclosed in U.S. Pat. No. 6,238,112 to Girones et al., which was incorporated by referenced hereinabove. Other methods or mechanisms may also be used to identify and record the presence and location of malfunctioning nozzles in the pens 12 of the printhead 10.
Where a malfunctioning nozzle or group of nozzles is detected in one or more of the pens 12, the position of the malfunctioning nozzle(s) is noted and saved in the memory of the electronic controller. When a malfunction is detected, or where the number and/or arrangement of malfunctioning nozzles reaches a predetermined level that corresponds to an unacceptable print quality, the electronic controller will arrange the pens 12 of each of the printer carriages 14 so as to compensate for the malfunctioning nozzle(s).
The method of compensating for malfunctions in the pens 12 of the printhead 10 begins with the step of analyzing the performance of the nozzles of the pens 12 as indicated by reference numeral 30 in
Where one or more malfunctioning nozzles are detected, the next step in the method is to note the location of the malfunctioning nozzles (step 34). Should the printer carriages 14 be provided with pen maintenance stations, the printer carriages 14 having pens 12 with malfunctioning nozzles may be addressed to the pen maintenance stations to ameliorate the malfunction of the nozzles (step 36). Note that step 36 is optional and may be dispensed with or may be undertaken only infrequently, as the application demands. The pens 12 with malfunctioning nozzles will again be analyzed using the nozzle function testing apparatus or method to determine whether the repair attempt was successful. If the repair attempt was successful and there are no malfunctioning nozzles present, the electronic controller will elect to proceed with the printing of the image in a single pass print mode (step 32). Where the attempt to repair the malfunctioning nozzles is not successful, or where the printer carriages 14 are not provided with pen maintenance stations, the electronic controller will calculate an arrangement of the pens 12 of the printer carriages 14 that will compensate for the malfunctioning nozzle(s) (Step 38).
The parameters used to calculate the arrangement of the pens 12 of the printer carriages 14 will differ from application to application. However, two relevant parameters in determining the arrangement of the pens 12 are the rate at which images can be printed on the recording media 18 (hereinafter “throughput) and the print quality of the images printed on the recording media 18. As a single pass print mode will generally allow for the highest throughput, in one embodiment the electronic controller will arrange the pens 12 of the printhead 10 so as to enable a single pass print mode. In this embodiment the controller will determine whether an arrangement of the pens 12 exists that will be wider than the width of the recording media 18. Keep in mind that for a given set of pens 12 having a given arrangement of malfunctioning nozzles, there may be multiple arrangements of the pens 12 that will permit the use of a single pass print mode. The electronic controller may choose the appropriate arrangement of the pens 12 from a predetermined list of pen arrangements stored in the memory of the electronic controller, or may calculate the most efficient arrangement for the pens 12 based on the number and position of the malfunctioning nozzles of the pens 12 of the printhead 10. The term “arrangement” is to be construed so as to mean not only the positioning of the pens 12 of the printhead 10, but also the ordering of the movements of the printer carriages 14 in positioning the pens 12. Accordingly, in some circumstances it may turn out that the pens 12 must be moved in a complex pattern with respect to the recording media 18 to enable the printing of an image. In these circumstances, it is to be understood that the arrangement of the pens 12 also includes the pattern in which the pens 12 are moved.
By way of example only, and without limiting the scope of the present invention,
As can be seen in
Similarly,
Generally speaking, where an image to be printed upon a sheet of recording media 18 is narrower than the collective functional width of the pens 12 of the printhead 10, that image may be printed upon the recording media 18 in a single pass print mode even where the collective functional width of the pens 12 is less than the total width of the recording media 18. The width of the image to be printed on the recording media 18 is monitored by the electronic controller which will determine whether the image may be printed in a single pass print mode or in a multipass print mode (step 40 in
Under certain circumstances it may be possible for the pens 12 to print an image upon the recording media 18 (in either single or multipass print mode), but in a print quality that is unacceptable for the application to which the printhead 10 has been put. In these circumstances, it will be necessary to recalculate the positioning of the printer carriages 14 so as to improve the print quality. While it is possible to calculate the positions of the printer carriages 14 such that one or more functional nozzles on a pen 12 are aligned with a nonfunctional nozzle on a separate pen 12, thereby insuring that printing occurs across the entire functional width of the printhead 10, it is also the case that an acceptable print quality may be obtained without compensating for every single malfunctioning nozzle in the pens 12 of the printhead 10. Therefore, the arrangement of the printer carriages 14 will be such that in addition to maximizing the throughput of the printing operation, the print quality output by the printhead 10 will also be maximized. By way of example only, a single malfunctioning nozzle in a pen 12 may not give rise to an unacceptable print quality, whereas two or more adjacent malfunctioning nozzles will. In this case it would be acceptable align one or more functional nozzles with one, two or more of the malfunctioning nozzles to obtain an acceptable print quality. It would not be absolutely required in this example to align one or more functional nozzles with all of the malfunctioning nozzles to appropriately compensate for the malfunctioning nozzles.
Note that the degree to which either throughput or print quality may control of the arrangement of the printer carriages 14 may be varied from application to application. For example, where high-quality images are to be printed in a magazine or on photographic paper, the criteria of print quality may be paramount. Conversely, where single color label stock is to be printed, print quality may be discounted in favor of maximizing throughput of the printing operation.
In the embodiment illustrated in
Although specific embodiments of the present invention have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Many adaptations of the invention will be apparent to those of ordinary skill in the art. Accordingly, this application is intended to cover any adaptations or variations of the invention. It is manifestly intended that this invention be limited only by the following claims and equivalents thereof.
