This invention relates generally to the field of digital printing systems, and more particularly to a web transport design for improved registration of printed patterns from different printing stations in a roll-to-roll printing system.
In a digitally controlled printing system, for example an inkjet printing system, a print media is directed through a series of components. The print media can be a cut sheet or a continuous web. A web or cut sheet transport system physically moves the print media through the printing system. As the print media moves through the printing system, marks are controllably made on the print media by one or more printheads, which are typically not in contact with the print media, to form the desired image or pattern.
For printing a color image, the printing system can have a plurality of printing stations, each having a printhead for printing one of the color channels (e.g., cyan, magenta, yellow and black) that make up the color image. If suitable color-to-color registration is not maintained in the printing system, print defects such as color halos at the edges of multicolor features can be seen.
Similarly, functional printing of devices can be done in multiple successive steps using a plurality of printing stations. If suitable registration is not maintained between printing stations, the performance of the printed device can be degraded. In fact, the desired registration tolerances for functional printing can be tighter than what is required for color image printing.
One approach for achieving registration of patterns printed by different printheads on a web of media is to use in-situ measurement techniques on the printed web such that the registration can be monitored and controlled to be within a required tolerance. Registration marks can be printed on the web of media at the same time as each color layer of the image is printed. The registration marks can be monitored by a control system and appropriate adjustments can be made to the printing process. For example, registering a pattern along the web motion direction (also called the in-track direction) that is being printed by a second digital printhead to a pattern that was printed previously by first digital printhead can be done by controlling the timing of the marking process of the second digital printhead. For example, for inkjet printheads the timing of the jetting of the ink drops by the second printhead can be advanced or delayed as needed.
Although methods exist for registering portions of the print that are successively printed by different printheads, what is needed for precision printing is to design the web transport for a roll-to-roll digital printing system in such a way that the size of registration errors introduced in the printing system is reduced.
The present invention represents a printing system for printing on a web of media traveling along a web transport path, comprising:
a plurality of printheads for printing on the web of media, each of the printheads being configured to print at one or more corresponding print locations along the web transport path, wherein at least one of the printheads includes:
a plurality of web transport rollers to guide the web of media along the web transport path, including:
a span extension member disposed along the web transport path between the first print line roller and the second print line roller of the particular printhead for increasing the span of the web of media along the web transport path between the first print line and the second print line of the particular printhead;
wherein at least some of the web transport rollers are constrained web transport rollers that are constrained to have a roller circumference that is substantially equal to an integer fraction of a span of the web of media along the web transport path between two successive print locations in successive printheads; and
wherein the span extension member is configured such that the increased span of the web of media along the web transport path between the first print line and the second print line of the particular printhead is an integer multiple of the roller circumferences of the constrained web transport rollers.
This invention has the advantage that disturbances in the motion of the web of media caused by any run-out or other imperfections in the web-transport rollers are made more consistent by keeping the rollers all in phase with each other.
It has the additional advantage that registration errors between image data printed by the different print stations are reduced.
It has the further advantage that the span expansion member enables larger diameter web transport rollers to be used while still satisfying the constraint that the roller circumference is substantially equal to an integer fraction of a span of the web of media along the web transport path between two successive print locations in the same printhead.
It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale.
The present description will be directed in particular to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present invention. It is to be understood that elements not specifically shown, labeled, or described can take various forms well known to those skilled in the art. In the following description and drawings, similar or identical reference numerals have been used, where possible, to designate identical elements. It is to be understood that elements and components can be referred to in singular or plural form, as appropriate, without limiting the scope of the invention.
The invention is inclusive of combinations of the embodiments described herein. References to “a particular embodiment” and the like refer to features that are present in at least one embodiment of the invention. Separate references to “an embodiment” or “particular embodiments” or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. It should be noted that, unless otherwise explicitly noted or required by context, the word “or” is used in this disclosure in a non-exclusive sense.
The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention.
As described herein, the exemplary embodiments of the present invention provide a printhead or printhead components typically used in digital printing systems such as inkjet printing systems. However, many other applications are emerging which use digital printheads to make marks of various types on print media (sometimes called receiver media). For example, inkjet printheads can be used to emit liquids that need to be finely metered and deposited with high spatial precision. Such liquids include inks, both water-based and solvent-based, that include one or more dyes or pigments. These liquids also include various substrate coatings and treatments, various medicinal materials, and functional materials useful for forming, for example, various circuitry components or structural components. As such, as described herein, the terms “liquid” and “ink” refer to any material that is ejected by inkjet printheads or inkjet printhead components described below.
Inkjet printing is commonly used for printing on paper, however, there are numerous other materials in which inkjet is appropriate. For example, the print media can be vinyl sheets, plastic sheets, textiles, paperboard, or corrugated cardboard. Additionally, although the term inkjet is often used to describe the printing process, the term jetting is also appropriate wherever ink or other liquids is applied in a consistent, metered fashion, particularly if the desired result is a thin layer or coating.
Inkjet printing is a non-contact application of a liquid such as an ink to a print media. Typically, one of two types of ink jetting mechanisms are used and are categorized by technology as either drop on demand ink jet (DOD) or continuous ink jet (CIJ).
The first technology, “drop-on-demand” (DOD) ink jet printing, provides ink drops that impact upon a recording surface using a pressurization actuator, for example, a thermal, piezoelectric, or electrostatic actuator. One commonly practiced drop-on-demand inkjet type uses thermal energy to eject ink drops from a nozzle. A heater, located at or near the nozzle, heats the ink sufficiently to form a vapor bubble that creates enough internal pressure to eject an ink drop. This form of inkjet is commonly termed “thermal ink jet.” A second commonly practiced drop-on-demand inkjet type uses piezoelectric actuators to change the volume of an ink chamber to eject an ink drop.
The second technology, commonly referred to as “continuous” ink jet (CIJ) printing, uses a pressurized ink source to produce a continuous stream of ink by forcing ink, under pressure, through a nozzle. The stream of ink is perturbed using a drop forming mechanism such that the stream of ink breaks up into drops of ink in a predictable manner. One continuous inkjet printing type uses thermal stimulation of the stream of ink with a heater to form drops that eventually become print drops and non-print drops. Printing occurs by selectively deflecting either the print drops or the non-print drops and catching the non-print drops. Various approaches for selectively deflecting drops have been developed including electrostatic deflection, air deflection, and thermal deflection.
More generally, digital printing systems can include printheads having arrays of marking elements that are controlled to make marks on a print media as the printheads and print media are moved relative to one another in order to form a desired pattern.
The invention described herein is applicable to both drop on demand and continuous inkjet printing technologies, as well as other digital printing technologies employing a printhead including an array of marking elements. As such, the term printhead, as used herein, is intended to be generic and not specific to a particular technology.
Referring to
Web transport rollers guide the web of media 110 from upstream to downstream along a web transport path 115 through the printing module 150. (The terms “upstream” and “downstream” are terms of art referring to relative positions along the web transport path 115; points on the web of media 110 move from upstream to downstream.) In this example, below each printhead 120a, 120b, 120c, 120d is a corresponding print line roller 131 that guides the web of media 110 in the media advance direction 104 past a corresponding print line 121a, 121b, 121c, 121d as the web of media 110 is advanced along the web transport path 115 through printing module 150. Below each dryer 140 is at least one dryer roller 141 for controlling the position of the web of media 110 near the dryers 140. Various other support rollers 133 also support and guide the web of media 110 as it moves along the web transport path 115 through printing module 150.
The web of media 110 originates from a supply roll 111 of unprinted print media and ends up on a take-up roll 112 of printed print media. Other details of printing system are not shown in
Embodiments of the invention provide design criteria for a printing system 100 that prints on a continuous web of media 110 traveling along a web transport path 115, where the printing system 100 has a plurality of printheads 120a, 120b, 120c, 120d for printing on the web of media 110, each of the printheads 120a, 120b, 120c, 120d being configured to print at one or more corresponding print locations (e.g., at print lines 121a, 121b, 121c, 121d) along the web transport path 115. The design criteria are intended to reduce disturbances in the motion of the web of media 110 as it is conveyed through the printing system 100. By reducing such disturbances there is greater reproducibility and registration precision in the composite printed patterns that are formed by the plurality of printheads at the various print locations.
In particular it is observed that the web-transport rollers, including print line rollers 131, dryer rollers 141 and support rollers 133 tend not to be perfectly uniform. A roller can be out of round or eccentrically mounted for example. Such non-uniformities in rollers supporting the web of media 110 can result in non-uniformity in the motion of the web of media 110. This can adversely affect registration between successive printed patterns along media advance direction 104. In order to reduce the overall non-uniformity in the motion of the web of media 110, it is beneficial for the individual non-uniformities of the various web-transport rollers to remain in phase from one print location to the next print location. It is therefore advantageous for each web transport roller in a printing module 150 to complete an integer number of revolutions as the web of media 110 is advanced from one print location (e.g. print line 121a) to the next downstream print location (e.g. print line 121b). This design criterion can equivalently be stated as each of the plurality of web transport rollers (including print line rollers 131, dryer rollers 141 and support rollers 133) has a roller circumference CR that is substantially equal to an integer fraction of a span L of the web of media 110 between two successive print locations. That is, the roller circumference CR of each web-transport roller satisfies the design criterion that:
CR=L/N (1)
where N is a positive integer. By substantially equal it is meant that the roller circumference CR of each of the web transport rollers is equal to an integer fraction of the span of the web of media 110 between successive print locations to within 1.0%, and more preferably to within 0.1%.
It is not required that the web transport rollers all have the same roller circumference as each other, only that each web transport roller has a circumference that is an integer fraction of the span L of the web of media 110 between successive print locations. However, the case where all web transport rollers have the same circumference can be advantageous from the standpoint of commonality of parts.
Where the web of media 110 follows a substantially straight path (as is the case between successive print lines 121a and 121b in the example shown in
In the example shown in
CR=Lab/N1=Lbc/N2=Lcd/N3 (2)
where N1, N2 and N3 are positive integers. Positioning the various components of the printing system to satisfy this design criterion will have the effect that each of the web-transport rollers will be in the same angular orientation (i.e., have the same phase) whenever a particular location on the web of media 110 is passing by each of the print lines 121a, 121b, 121c, 121d. As a result, any non-uniformities in the motion of the web of media 110 caused by irregularities in the web-transport rollers will be consistent at each print location, thereby reducing relative registration errors between the image content printed by the different printheads 120a, 120b, 120c, 120d (e.g., color-to-color registration errors). Furthermore, the registration errors for the image content printed by a particular 120a, 120b, 120c, 120d will be much more consistent and predictable from one frame to another since the rollers will all be in consistent angular orientations for a given location within the frame. As a result, the registration errors can be characterized as a function of position within the image frame (for example by using the quality control sensor 145 to sense the position of registration marks printed in the margin of the printed image), and can be compensated for by providing a correction function which specifies compensating shifts to be applied during the process of printing the image data. For example, if a particular image line at a particular location within the image frame is found to be consistently shifted by a certain displacement from its nominal position, then the controller 160 can control the timing of when the printheads 120a, 120b, 120c, 120d print the image data for that print line accordingly (e.g., the timing can be advanced or delayed).
Although the printhead shown in
In the exemplary embodiment of
Referring to
Registration considerations for inkjet printing system 200 of
CR=W/M (3)
where M is a positive integer. In a preferred embodiment, both this design criterion and the design criterion discussed earlier with respect to Eqs. (1)-(2) are satisfied simultaneously. However, a partial benefit can be obtained if even one of these design criteria is satisfied.
Other design considerations for web transport rollers include strength and stability, which are related to the size and weight of media to be used in the printing system, as well as the intended web tension and the wrap angle of the media around the web transport rollers. If the diameter of a web transport roller is too small, it will have insufficient strength to support the web of media 110 without flexing and causing conveyance non-uniformity. As indicated above with reference to
Since the span extension roller 135 in the configuration of
Alternately, the span extension member can be an air shoe where the web of media 110 rides around the air shoe on a cushion of air so that the printed surface of the web of media 110 does not contact the surface of the air shoe. Air shoes are well-known in the media-guiding art and generally include a fixed media guide surface with holes or grooves through which a stream of air is blown to lift the media away from the media guide surface. In some embodiments, the air shoe can be of the type described in commonly-assigned, co-pending U.S. patent application Ser. No. 14/190,146 to Cornell et al., entitled “Air shoe with roller providing lateral constraint,” which is incorporated herein by reference.
For the embodiment illustrated in
Referring to
Transport roller size has previously been considered in different ways for web transport in a printing system. For example, Kodak's NexPress line of color electrophotographic printers has a seamed transport web for advancing cut sheets of paper past a series of electrophotographic print modules. All rollers used in this assembly, including the main drive roller, tension roller, steering roller, detack roller, touch down roller, guide rollers, and paper transfer rollers are designed in a way that their circumference matches an integer fraction of the print module-to-module spacing. So, for example, the main drive roller rotates exactly 3 times while the transport web moves from one print module to the next, while the receiver is firmly attached to the transport web. In consequence, all periodic variations due to roller run-out or unbalance that might cause an in-track timing problem stay in phase between the print modules and do not show up as a print registration problem. Line spacing might vary from the ideal pitch (e.g., 600 lines per inch), but registration is not affected because the variation occurs in the same way in all print modules. Although the motivation of precision registration is similar in the present invention, the design criterion is different for printing systems using a continuous web of media 110 rather than cut sheets as in the NexPress printers. Rather than the transfer rollers having a circumference that is equal to an integer fraction of the print module-to-module spacing as in the cut sheet system, the web transport rollers have a circumference that is equal to an integer fraction of a span of the web of media 110 between two successive print locations. The design criterion for web transport systems allows for web transport paths that are not straight lines between successive print locations.
Other differences in design criteria in embodiments of the invention result from a roll-to-roll printing system architecture. With reference to
Inkjet printing system 400 includes a media guiding subsystem 460 downstream of supply roll 111. The media guiding subsystem 460 can move side-to-side and helps to guide the web of media 110 to start down the web transport path 115 as it unwinds from supply roll 111, and generally includes one or more web-transport rollers 461 and other components such as edge guides and control systems. An out-of-round supply roll 111 will cause disturbances on the motion of the web of media 110 at increasing frequency as the web is unwound. A front-end motion isolation mechanism, such as an S-wrap tensioning subsystem 470 is commonly provided to buffer such disturbances and allow a steady motion of the continuous web of media 110 at controlled tension throughout the inkjet printing system 400. The S-wrap tensioning subsystem 470 generally includes two or more web-transport rollers 462 which define an S-shaped media path. In alternate embodiments, other types of motion isolation mechanism can be used such as slack loops or festoons. Additional web transport rollers 471 are located along the web transport path 115 between the supply roll 111 and the first print location associated with the first print line 221 of first printhead 220a.
On the output side of inkjet printing system 400, a main drive roller 480 driven by a motor 483 is used to pull the web of media 110 at a predetermined tension measured with a load cell roller 475. The main drive roller 480 also serves the function of a back-end motion isolation mechanism to isolates the printheads 220a, 220b from the take-up roll 112. In alternate embodiments, other types of motion isolation mechanism can be used such as slack loops or festoons. Additional web transport rollers 481 are also located along the web transport path 115 between the last print location (corresponding to the second print line 222 of the second printhead 220b) and the take-up roll 112.
The design criterion described above constraining the circumference of each of the web transport rollers, is preferably also applied to some or all of the web transport rollers 471, 481, 482, the load cell roller 475, the main drive roller 480, and any rollers associated with the media-guiding subsystem 460 and the S-wrap subsystem 470. In some embodiments one or more of the constrained web-transport rollers can include encoders or tachometers that are used to characterize web motion. There is particular benefit to constraining the web-transport rollers 471 between the S-wrap tensioning subsystem 470 and the first printhead 220a, as well as the web-transport rollers 462, 475 in the S-wrap tensioning subsystem 470, to be selected according to the aforementioned design criteria. Since the S-wrap tensioning subsystem 470 serves to effectively isolate the supply roll 111 and media guiding subsystem 460 from the printheads 220a, 220b, the benefit of constraining any web-transport rollers 461 upstream of the S-wrap tensioning subsystem 470 to conform to the design criteria is reduced. Likewise, it is preferable that the main drive roller 480, as well as any web-transport rollers 481 between the last printhead 220b and the main drive roller 480, be constrained to satisfy the aforementioned design criteria. Since the main drive roller 480 effectively isolates the printheads 220a, 220b from the take-up roll 112, the benefit of constraining the web-transport rollers 482 downstream of the main drive roller 480 to conform to the design rule is reduced.
In some embodiments, the main drive roller 480 is driven by the motor 483 using a direct servo drive. In other embodiments, as illustrated in
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
100 printing system
104 media advance direction
106 marking element array direction
110 web of media
111 supply roll
112 take-up roll
115 web transport path
116 first side
117 second side
120 printhead
120
a printhead
120
b printhead
120
c printhead
120
d printhead
121 print line
121
a print line
121
b print line
121
c print line
121
d print line
123 printhead module
124 marking element array
130 support structure
131 print line roller
133 support roller
135 span extension roller
139 surface
140 dryer
141 dryer roller
145 quality control sensor
150 printing module
151 first zone
152 second zone
160 controller
200 inkjet printing system
205 inkjet printing system
220 printhead
220
a printhead
220
b printhead
220
c printhead
220
d printhead
221 print line
222 print line
223 printhead module
224 nozzles
225
a inkjet nozzle array
225
b inkjet nozzle array
225
c inkjet nozzle array
226
a inkjet nozzle array
226
b inkjet nozzle array
226
c inkjet nozzle array
230 support structure
239 surface
240
a printhead
240
b printhead
240
c printhead
240
d printhead
250 printing module
300 inkjet printing system
309 exit direction
355 first printing module
360 turnover mechanism
365 second printing module
366 drive roller
367 nip roller
368 drive roller
369 nip roller
400 inkjet printing system
460 media-guiding subsystem
461 web transport roller
462 web transport roller
470 S-wrap tensioning subsystem
471 web transport roller
475 load cell roller
480 main drive roller
481 web transport roller
482 web transport roller
483 motor
485 driven gear
486 drive gear
CR roller circumference
L span
Lab span
Lbc span
Lcd span
M integer
N integer
N1 integer
N2 integer
N3 integer
R non-printing region
S speed
V overlap region
W spacing distance
We extended spacing distance
Δt timing delay
This is a continuation of U.S. application Ser. No. 14/280,718 filed May 19, 2014, which is incorporated herein by reference in its entirety. Reference is made to commonly assigned, co-pending U.S. patent application Ser. No. 14/280,707, entitled “Precision registration in printing cylinder systems” by K. Peter et al; to commonly assigned, co-pending U.S. patent application Ser. No. 14/280,714, entitled “Drive gears providing improved registration in printing cylinder systems” by K. Peter et al; and to commonly assigned, co-pending U.S. patent application Ser. No. 14/280,724, entitled “Drive gears providing improved registration in digital printing systems” by K. Peter et al, each of which is incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
4534288 | Brovman | Aug 1985 | A |
4658723 | Tokuno | Apr 1987 | A |
5440328 | Nardone | Aug 1995 | A |
6493012 | Buch et al. | Dec 2002 | B2 |
6739688 | Kniazzeh et al. | May 2004 | B2 |
20040189783 | Mogi | Sep 2004 | A1 |
20090283002 | Schultze | Nov 2009 | A1 |
20110128337 | Muir | Jun 2011 | A1 |
20130321544 | Vandagriff | Dec 2013 | A1 |
Number | Date | Country |
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2013063188 | May 2013 | WO |
Number | Date | Country | |
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20150328907 A1 | Nov 2015 | US |
Number | Date | Country | |
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Parent | 14280718 | May 2014 | US |
Child | 14811888 | US |