Patent Application
20130113857
This invention generally relates to a digital printing system for web media and more particularly relates to a media transport system of the printing system that includes an arrangement of components for feeding a continuous web of media from a media supply section through one or more media operation zones in which an operation is performed on the media and to a media take-up section.
Continuous web printing allows economical, high-speed, high-volume print reproduction. In this type of printing, a continuous web of paper or other print media material is fed past one or more printing subsystems that form images by applying one or more colorants onto the print media surface. Proper registration of the print media to the printing device is of considerable importance in print reproduction, particularly where multiple colors are used in four-color printing and similar applications.
The problem of maintaining precise and repeatable web registration and transport becomes even more acute with the development of high-resolution non-contact printing, such as high volume inkjet printing. With this type of printing system, finely controlled dots of ink are rapidly and accurately propelled from the printhead onto the surface of a moving print media, with the web of print media often coursing past the printhead at speeds measured in hundreds of feet per minute. Synchronization and timing are employed to determine the sequencing of colorant application to the moving media. With dot resolution of 600 dots-per-inch (DPI) and better, a high degree of registration accuracy is needed. During printing, variable amounts of ink may be applied to different portions of the rapidly moving print media web, with drying mechanisms typically employed after each printhead or bank of printheads. Variability in ink or other liquid amounts and types or variability in drying times can cause print media stiffness and tension characteristics to vary dynamically for different types of print media, contributing to the overall complexity of print media handling and print media dot registration.
Some digital printing systems including, for example, high volume inkjet printing systems and processes introduce significant moisture content during operation, particularly when the system is used to print multiple colors on a single side of print media or print single or multiple colors on a first side (a front side) of the print media and a second side (a back side) of the print media. Due to changes in its moisture content, the print media expands and contracts (in a cross track direction, an in-track direction, or both) in a non-isotropic manner often with significant hysteresis, a phenomena known as hygroexpansivity. The continual change of dimensional characteristics of the print media often adversely affects dot registration on the print media or adversely affects the alignment of the print media relative to the media transport system of the printing system. The occurrence of either condition may ultimately result in a reduction in print or image quality. While dryers are frequently used to remove the added moisture from the print media, which reverses the moisture-driven expansion of the print media, drying can also cause changes in the dimensional characteristics of the print media that often adversely affects image quality. This is due in part to the drying process removing moisture from the portions of the print media that were not printed on, and also due to the hysteresis inherent in the hygroexpansivity process.
As such, there is an ongoing need to improve the dot registration of patterns printed by these types of digital printing systems. There is also an ongoing need to enhance the print media handling capabilities of these types of printing systems.
According to one aspect of the invention, a digital printing system, for printing on a continuous web of print media, includes a media operation zone in which an operation is performed on the print media. A support structure guides a continuous web of print media under tension through the media operation zone. The support structure includes a first mechanism and a second mechanism. The first mechanism, located upstream relative to the media operation zone, includes structure that positions the print media in a cross track direction so as to establish center justification of the print media as the print media enters the media operation zone. The second mechanism, located downstream relative to the media operation zone, includes structure that positions the print media in a cross track direction so as to maintain center justification of the print media as the print media travels through the media operation zone.
According to another aspect of the invention, a method of printing on a continuous web of print media includes providing a digital printing system. The digital printing system includes a media operation zone in which an operation is performed on the print media, and a support structure that guides a continuous web of print media under tension through the media operation zone. The support structure includes a first mechanism and a second mechanism. The first mechanism, located upstream relative to the media operation zone, includes structure that positions the print media in a cross track direction so as to establish center justification of the print media as the print media enters the media operation zone. The second mechanism, located downstream relative to the media operation zone, includes structure that positions the print media in a cross track direction so as to maintain center justification of the print media as the print media travels through the media operation zone. After a print media has been provided, center justification of the print media is established as the print media enters the media operation zone by positioning the print media in a cross track direction using the structure of the first mechanism. Center justification of the print media is maintained as the print media travels through the media operation zone by positioning the print media in a cross track direction using the structure of the second mechanism.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
The apparatus and method of the present invention are particularly well suited for printing systems that provide non-contact application of ink or other colorant onto a continuously moving medium, for example, a web of print media. The printhead of the present invention selectively moistens at least some portion of the media as it courses through the printing system, but without the need to make contact with the print media.
In the context of the present invention, the term “continuous web of print media” relates to a print media that is in the form of a continuous strip of media as it passes through the printing system from an entrance to an exit thereof. The continuous web of print media itself serves as the receiving print medium to which one or more printing ink or inks or other coating liquids are applied in non-contact fashion. This is distinguished from various types of “continuous webs” or “belts” that are actually transport system components (as compared to the print receiving media) which are typically used to transport a cut sheet medium in an electrophotographic or other printing system. The terms “upstream” and “downstream” are terms of art referring to relative positions along the transport path of a moving web; points on the web move from upstream to downstream.
Additionally, as described herein, the example embodiments of the present invention provide a printing system or printing system components typically used in inkjet printing systems. However, many other applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid,” “ink,” “print,” and “printing” refer to any material that can be ejected by the liquid ejector, the liquid ejection system, or the liquid ejection system components described below.
Kinematic web handling is provided not only within each module of the system described below, but also at the interconnections between modules, as the continuously moving web medium passes from one module to another. Unlike a number of conventional continuous web imaging systems, the apparatus described below does not require a slack loop between modules, but typically uses a slack loop only for media that has been just removed from the supply roll at the input end. Removing the need for a slack loop between modules or within a module allows the addition of a module at any position along the continuously moving web, taking advantage of the self-positioning and self-correcting design of media path components. The system described below adapts a number of exact constraint principles to the problem of web handling. As part of this adaptation, techniques have been identified to allow the moving web to maintain proper cross-track registration in a “passive” manner. Steering of the web is avoided; instead, the web's lateral and angular positions in the plane of transport are exactly constrained. Moreover, other web support devices used in transporting the web, other than non-rotating surfaces or those devices purposefully used to exactly constrain the web, are allowed to self-align with the web.
In one example embodiment of the present invention, however, an active steering mechanism is used to determine lateral constraint in order to align or re-align the web span relative to a desired reference point as the web of print media enters and leaves the media operation zone that typically includes one or more printheads for printing on the print media and one or more dryers to dry the ink printed on the print media.
It has been determined that the application of an additional constraint helps maintain registration of the image planes printed by multiple printheads at an acceptable level. Accordingly, one example embodiment of the present invention steers the continuously moving media web, when it is necessary, in order to facilitate acceptable levels of image registration at high transport speeds while reducing the likelihood of damage to the media web or misregistration of liquid, for example, ink or other colorant, applied to the media web.
Referring to the schematic side view of
A second module 40, positioned downstream from first module 20 along the path of the continuous web media 60, also has a support structure 48, similar to the support structure 28 for first module 20. Affixed to the support structure 28, 48 of either or both the first or second module 20 or 40 is a kinematic connection mechanism that maintains the kinematic dynamics of the continuous web of print media 60 in traveling from the first module 20 into the second module 40. Also affixed to the support structure 28, 48 of either the first or second module 20 or 40 are one or more angular constraint structures 26 for setting an angular trajectory of the web media 60.
Printing system 10 optionally also includes a turnover mechanism 30 that is configured to turn the media 60 over, flipping it backside-up in order to allow printing on the reverse side as the print media 60 travels through second module 40. When printing is complete, the print media 60 leaves the digital printing system 10 and travels to a media receiving unit, in this case a take-up roller 18. A roll of printed media is then formed, rewound from the printed web of media 60. The digital printing system 10 can include a number of other components, including, for example, multiple print heads and dryers, as described in more detail below. Other examples of digital printing system components include web cleaners, web tension sensors, or quality control sensors.
Referring to the schematic side view of
Table 1, presented below, identifies the lettered components used for web media transport and shown in
The first angular constraint is provided by in-feed drive roller B. This is a fixed roller that cooperates with a drive roller in the turnover section TB and with an out-feed drive roller N in second module 40 in order to move the web through the printing system with suitable tension in the direction of print media movement or travel (from left to right as shown in
The media transport system of the example embodiment shown in
In one example embodiment of the present invention, cross track position of the print media is center justified as it enters the media operating zone. This is done at transport element E either by a passive centering web guide (for example, by a web guide such as is described in commonly-assigned U.S. Pat. No. 5,360,152 entitled “WEB GUIDANCE MECHANISM FOR AUTOMATICALLY CENTERING A WEB DURING MOVEMENT OF THE WEB ALONG A CURVED PATH” by Matoushek, the disclose of which is incorporated by reference herein in its entirety) or by an active centering web guide such as a steered angular constraint with hinge (Servo-Caster with Gimbaled Roller), which is described in more detail below. Fixed rollers at F and L precede printhead(s) 16 in each module 20 and 40, providing the desired angular constraint to the web in each print zone 54. These rollers provide a suitable location for mounting an encoder for monitoring the motion of the media 60 through the printing system 10. Under printheads 16, the print media 60 is supported by fixed non-rotating supports 32, for example, brush bars. Alternatively, fixed rollers can support the paper under the printheads, if the print media has minimal wrap around the rollers. Supports 32 provide minimal constraint to the web.
Printhead 16 prints in response to supplied print data on the print media 60 in the span between roller F and G, which includes the media operation zone. Water-based inks add moisture to the print media, which can cause the print media to expand, especially in the crosstrack direction. The added moisture also lowers the stiffness of the print media. A dryer 14 following the printhead dries the ink, typically by a directing heat and a flow of air at the print media. The dryer drives moisture out of the print media, causing the print media to shrink and its stiffness to change. These changes to the print media in the media operation zone can cause the print media to drift in the crosstrack direction as it passes through the media operation zone. The width of the print media as it leaves the media operation zone can also differ from the width of the print media as it entered the media operation zone. To accommodate these effects, one example embodiment of the present invention includes a steered angular constraint with hinge (a Servo-Caster with Gimbaled Roller) at roller G to center justify the print media as it leaves the media operation zone. Because of the relative length to width ratio of the media 60 in the segment between F and G, the continuous web in that segment is considered to be non-stiff, showing some degree of compliance in the cross-track direction. As a result, the additional constraint provided by the steered angular constrain can be included without over constraining that web segment.
A similar configuration is used in module 40. Accordingly, in one example embodiment of the present invention a steered angular constraint with hinge (a Servo-Caster with Gimbaled Roller) is included at roller M to center justify the print media as it leaves the media operation zone. Roller K includes either a passive web centering guide (for example, the centering guide of U.S. Pat. No. 5,360,152) or an active mechanism such as a steered angular constraint with hinge (Servo-Caster with Gimbaled Roller) to center justify the print media as it enters the media operation zone.
The angular orientation of the print media 60 in the print zone containing one or more printheads and possibly one or more dryers is controlled by a roller placed immediately before or immediately after the print zone. This is critical for ensuring registration of the print from multiple printheads. It is also critical that the web not be over constrained in the print zone. As a result of the transit time of the print drops from the jetting module to the print media 60, variations in spacing of the printhead to the print media 60 from one side of the printhead to the other, it is desirable to orient the printheads parallel to the print media 60. To maintain the uniformity of this spacing between the printhead and the print media 60, preferably the constraint relieving roller placed at one end of the print zone is not free to pivot in a manner that will alter the printhead to print media 60 spacing. Therefore, the castered roller following the print zone should preferably not include a gimbal pivot. However, the use of non-rotating supports 32 under the media 60 in the print zone as shown in
A digital printing system 10 shown schematically in
For the embodiments shown in
Load cells are provided in order to sense web tension at one or more points in the system. In the embodiments shown in
The configuration shown in
An entrance module 70 is the first module in sequence, following the media supply roll, as was shown earlier with reference to
An end feed module 74 provides an angular constraint to the incoming media 60 from printhead module 72 by means of gimbaled roller H. Turnover module TB accepts the incoming media 60 from end feed module 74 and provides an angular constraint with its drive roller, as described above. Optionally, digital printing system 10 can also include other components within any of the modules described above. Examples of these types of system components include components for inspection of the print media, for example, components to monitor and control print quality.
A forward feed module 76 provides a web span corresponding to each of its gimbaled rollers 3 and K. These rollers again provide angular constraint only. The lateral constraint for web spans in module 76 is obtained from the edge of the incoming media 60 itself. Roller K includes either a lateral constraint (for example, an additional edge guide like the one included at roller A) or a steered angular constraint with hinge (Servo-Caster with Gimbaled Roller) in order to maintain the cross-track position of the print media web.
A second printhead module 78 accepts the web media 60 from forward feed module 76, with the given edge constraint, and applies an angular constraint with fixed roller L. A series of stationary fixed non-rotating supports 32, for example, brush bars or, optionally, minimum-wrap rollers then feed the web along past a second series of printheads 16 with their supporting dryers and other components, while providing little or no lateral constraint on the print media. One example embodiment of the present invention includes a steered angular constraint with hinge (a Servo-Caster with Gimbaled Roller) at roller M to center justify the web of print media as it leaves the media operation zone that is located between rollers L and M. Here again, because of considerable web length in the web segment (that is, extending the distance between rollers L and M), that segment can exhibit flexibility in the cross track direction which is an additional degree of freedom enabling the use of the steered angular constraint without over constraining the print media in that span.
An out feed module 80 provides an out-feed drive roller N that serves as angular constraint for the incoming web and cooperates with other drive rollers and sensors along the web media path that maintain the desired web peed and tension. Optional rollers O and P (not shown in
Each module in this sequence provides a support structure and an input and an output interface for kinematic connection with upstream or downstream modules. With the exception of the first module in sequence, which provides the edge guide at A, each module utilizes one edge of the incoming web media 60 as its “given” lateral constraint. The module then provides the needed angular constraint for the incoming media 60 in order to provide the needed exact constraint or kinematic connection of the web media transport. It can be seen from this example that a number of modules can be linked together using the apparatus and methods of the present invention. For example, an additional module could alternately be added between any other of these modules in order to provide a useful function for the printing process.
When multiple modules are used, as was described with reference to the embodiment shown in
As noted earlier, slack loops are not required between or within the modules described with reference to
The servo-caster with gimbaled roller example embodiments of the present invention will now be described in more detail with reference to
Referring to
In some example embodiments of the invention, printing system 10 also includes an edge guide that sets an initial cross track position of the print media 60. This edge guide is located upstream relative to first mechanism 102. This edge guide is conventional. One example of a suitable edge guide is described in commonly-assigned U.S. Patent Application Publication No. US 2011/0129278 A1, published on Jun. 2, 2011, entitled “EDGE GUIDE FOR MEDIA TRANSPORT SYSTEM”, by Muir et al., the disclose of which is incorporated by reference herein in its entirety. This edge guide is designed to expand and contract to accommodate different widths of print media in a manner that the centerline of the media doesn't shift significantly in the cross track direction, approximately center justifying the print media. As a result, the print media typically undergoes only minor shifts in crosstrack position when it is center justified by the first mechanism.
The print media 60 includes a structural characteristic that changes, at least temporarily, when the print media 60 is in the media operation zone 100. The print media structural characteristics include, for example, a dimensional characteristic of the print media or a stiffness characteristic of the print media. Typically, the change in the structural characteristic(s) of the print media 60 occurs due to one or a plurality of devices positioned in the media operation zone that change the structural characteristic(s) of the print media 60, at least temporarily, while the print media 60 is in the media operation zone 100. For example, when a portion of the print media 60 is selectively moistened by the device(s), for example, one or a plurality of printheads, the moistened portions of the print media tend to expand, in particular in the crosstrack direction as the print media passes through the media operation zone 100. The selective moistening of portions of the print media also tends to lower the tension in the in-track direction in those portions of the print media. This can cause the print media 60 to drift laterally as it passes through the media operation zone 100. When the device(s) includes a dryer that dries the print media, portions of the print media contract, in particular in the cross track direction, as the print media passes through the media operation zone 100. As the print media is dried by the device(s), portions of the print media that had been selectively moistened contract which tend to increase tension in the in-track direction in these portions of the print media. Additionally, drying of the print media causes the print media to become stiffer in both the in-track and cross track directions, in particular in areas of the print media that had been selectively moistened by, for example, one or a plurality of printheads. This can cause the print media 60 to drift laterally as it passes through the media operation zone 100. Accordingly, the media operation zone begins at the location of the first device that alters, at least temporarily, the structural characteristic(s) of the print media 60 and ends at the location of the last device that alters, at least temporarily, the structural characteristic(s) of the print media 60.
First mechanism 102 and second mechanism 106 help to center justify the print media 60 while the print media 60 is in the media operation zone 100. In this sense, the center line of the print media web is maintained within acceptable tolerances by controlling the cross track position or location of the print media web. Typically, the center line of the print media web is maintained within acceptable tolerances relative to a device that is performing an operation on the print media while the print media is traveling through (located in) the media operation zone 100. In one example embodiment of the present invention, the print media 60 is center justified, rather than edge justified, as it has been found that when the width of the print media changes and the print media is edge justified the registration errors tend to increase from a low level near the edge justification edge to, in some situations, significant registration errors near the print media edge that is opposite the edge of the edge justification. Center justification, by reducing the distance from the line of justification to the distant edge of the print media, produces lower peak levels of registration errors when compared to edge justification. Accordingly, center justification of the print media 60 represents a significant improvement when compared to conventional edge justification of the print media.
Referring back to
Referring back to
First mechanism 102 additionally includes a sensor 110 that senses the cross track position of the print media 60 and communicates with a control system 112 that controls structure 104 to position the print media 60 in a cross track direction based on information received from sensor 110. Sensor 110 is located between structure 104 of first mechanism 102 and media operation zone 100 to provide an accurate measurement of the print media as it enters the media operation zone. Preferably the sensor 110 includes sensing elements positioned on both the first and the second edge of the print media. By means of the sensing elements along both sides (edges) of the print media, the sensor 110 can determine the width of the print media 60 and the crosstrack position of the centerline of the print media. In some embodiments the determination of the width of the print media and the cross track position of the centerline of the print media is carried out within the sensor 110, which sends that information to the control system 120. In other embodiments, the sensor 110 send the position of the first edge and the position of the second edge of the print media to the control system 120, which uses that data to determine of the width of the print media and the cross track position of the centerline of the print media.
In one example embodiment of structure 104 of first mechanism 102, structure 104 actively positions the print media 60 in a cross track direction so as to establish center justification of the print media 60 as the print media 60 enters the media operation zone 100. To accomplish this, structure 104 includes, for example, a steered caster roller 114 that is rotatable about a caster roller axis. Steering of the caster roller 114 is accomplished by adjustment of an angle of the caster roller about caster axis using, for example, a servo motor 116, shown in more detail in
Optionally, control system 112 includes a low pass filter that filters out localized imperfections in an edge of the print media 60. In some example embodiments of the invention, the low pass filter includes a cut off frequency that is dependent, for example, on the speed of the print media 60 as the print media 60 travels through media operation zone 100 to enable the low pass filter system to filter out localized imperfections having a spatial period down the edge of the print media of less than some critical length, independent of the speed of the print media through the media operation zone.
Alternatively, structure 104 of first mechanism 102 can include a media centering guide to establish center justification of the print media 60 as the print media 60 enters the media operation zone 100. A suitable media centering guide is described in commonly assigned U.S. Pat. No. 5,360,152 entitled “WEB GUIDANCE MECHANISM FOR AUTOMATICALLY CENTERING A WEB DURING MOVEMENT OF THE WEB ALONG A CURVED PATH” by Matoushek, the disclose of which is incorporated by reference herein in its entirety.
Second mechanism 106 additionally includes a sensor 118 that senses the cross track position of the print media 60 and communicates with a control system 120 that controls structure 108 to actively position the print media 60 in a cross track direction based on information received from sensor 118. Sensor 118 is located between structure 108 of second mechanism 106 and media operation zone 100.
In one example embodiment of structure 108, structure 108 includes a steered caster roller 122 that is rotatable about a caster roller axis. Steering of the caster roller 122 is accomplished by adjustment of an angle of the caster roller relative to the caster roller axis using, for example, a servo motor 124, shown in more detail in
Control system 112 of first mechanism 102 and control system 120 of second mechanism 106 can be included in the same control system, for example, controller 126 shown in
Control system 112 of first mechanism 102 and control system 120 of second mechanism 106 can also be maintained as separate and distinct computers or processors. In this configuration, sensor 110 of first mechanism 102 is a first sensor and control system 112 of first mechanism 102 is a first control system. Sensor 118 of second mechanism 106 is a second sensor and control system 120 of second mechanism 106 is a second control system that controls the structure that positions the print media in a cross track direction based on information received from the second sensor. In certain embodiments, at least one of the first control system and the second control system is responsive to information received from both the first sensor and the second sensor so as to maintain the cross track position of the print media 60 while the print media 60 is traveling through (or located in) the media operation zone 100.
Referring to
Sensor 110 senses the cross track position of the print media 60 and sends this information to control system 112. Depending on the information received by control system 112, if it is necessary control system 112 steers caster roller 114 using servo motor 116 to adjust a location of caster roller 114 through linkage connected to an arm that is responsive to servo motor 116 to adjust the position the print media 60 in a cross track direction. Sensor 110 is located between structure 104 of first mechanism 102 and media operation zone 100. Referring additionally back to
When structure 104 includes the edge guide described above, sensor 110 is not needed in all example embodiments of the present invention because the edge guide component of the media transport system is aligned (for example, center justified) with the media operation zone 100 of the printing system.
An example embodiment of second mechanism 106 is configured in the same manner as that of the example embodiment of first mechanism 102 shown in
Sensor 118 is located between structure 108 of second mechanism 104 and media operation zone 100 to provide an accurate measurement of the crosstrack position of the print media as it leaves the media operation zone 100. In an alternate embodiment, the sensor is located between the final device that acts on the print media in the media operation zone and the structure 108. Referring additionally back to
Depending on the information received by control system 120, if it is necessary, control system 120 steers caster roller 122 using servo motor 124 to adjust a location of caster roller 122 through linkage connected to an arm that is responsive to servo motor 116 to adjust the position the print media 60 in a cross track direction. In this manner, the second mechanism 106 controls the crosstrack position of the print media 60 in such a way that the crosstrack position of the centerline of the print media doesn't drift, even when the width of the print media varies as a result of the operation of one or more device on the print media as the print media passes through the media operation zone 100 As such the second mechanism center justifies the print media, maintaining the centerline of the print media at a fixed position in the cross track direction in spite of changes in the print media width.
Center justifying the print media at each end of the media operation zone by means of the first mechanism and the second mechanism of the invention helps to improve the color to color registration of images or documents printed by printheads located within the media operation zone. As mentioned earlier, the print media can change width and can also drift in the crosstrack direction as a result of the action of one or more devices within the media operation zone. In prior art digital printing systems, having multiple printheads in a print zone, a drift in the crosstrack position of the print media as it moves from the beginning to the end of the print zone can cause the print of the latter printheads in the print zone to be misregistered relative to the print of the first printhead in the print zone. The invention by controlling the crosstrack position of the print media at the beginning and end of the media operation zone reduces these registration errors.
The invention furthermore center justifies the print media by means of the first mechanism and the second mechanism. As a result, the centerline of the print media doesn't drift in the crosstrack direction as it passes through the media operation zone, even if the print media expands or shrinks in the crosstrack direction. The expansion or shrinkage of the print media in the crosstrack direction can still produce varying amounts of crosstrack registration errors of the image planes across the width of the print media. As the invention reduces or eliminates the drift in the crosstrack position of the centerline of the print media, the crosstrack registration errors produced by the crosstrack expansion or shrinkage of the print media invention are near zero at or near to the centerline of the print media and they get progressively larger on both sides of the centerline. Compared to a system that keeps an edge of the print media from drifting in the crosstrack direction rather than the centerline, the invention cuts the peak misregistration errors by approximately 50%.
Referring to
It has been found that web transports systems as described above maintain effective control of the print media 60 in the context of a digital print system where the selected portions of the print media 60 are moistened in the printing process. This is true even when the print media 60 is prone to expanding in length and width and to becoming less stiff when it is moistened, for example, for cellulose based print media 60 moistened by water based ink. This enables the individual color planes of a multi-colored document to be printed with good registration to each other. Accordingly, the web transport arrangements described above provide acceptable registration and repeatable performance at high speeds commensurate with the requirements of high-speed color inkjet printing. As has also been described above, multiple modules can be integrated to form printing system 10, without the requirement for painstaking alignment of rollers or other media handling components at the interface between two modules.
An example embodiment of printing on a continuous web of print media using the present invention will now be described. A digital printing system is provided which includes a media operation zone in which an operation is performed on the print media, and a support structure that guides a continuous web of print media under tension through the media operation zone. The support structure includes a first mechanism and a second mechanism. The first mechanism, located upstream relative to the media operation zone, includes structure that positions the print media in a cross track direction so as to establish center justification of the print media as the print media enters the media operation zone. The second mechanism, located downstream relative to the media operation zone, includes structure that positions the print media in a cross track direction so as to maintain center justification of the print media as the print media travels through the media operation zone. After a print media has been provided, center justification of the print media is established as the print media enters the media operation zone by positioning the print media in a cross track direction using the structure of the first mechanism. Center justification of the print media is maintained as the print media travels through the media operation zone by positioning the print media in a cross track direction using the structure of the second mechanism.
The print media includes a structural characteristic and during printing an operation is performed on the print media while the print media is in the media operation zone using a device that at least temporarily changes the structural characteristic of the print media. When the device includes a printhead, the operation includes selectively moistening of portions of the print media using the printhead. When the device includes a dryer, the operation includes drying the portions of the print media that have been moistened using the dryer.
While the invention has been described in the context of a digital printing having a media transport with exact constraints for guiding the print media to and from the media operation zone, the invention can also be effectively used in digital printing systems having conventional media transports. The invention can also be effectively employed in the digital printing module of a larger printing system that can include digital printing portions and analog printing (such as offset, gravure, or flexographic) portions.
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 scope of the invention.
