System and method for printing color images on substrates in inkjet printer

Abstract

To solve the problem in which, when coated substrates passes through a printhead at high speed, colored inks overlaid on different colored inks and are not readily absorbed by the coated substrates, so that the colored inks spread over a surface of the coated substrates before the substrates enter a dryer that removes water and solvents from the ink to fix the image to the coated substrates, and these unabsorbed inks produce an image defect known as overlay graininess.SOLUTION: A method of operating a printer comprises separating image content data for a sheet in a print job into multiple color separations, and operating a digital air curtain between printhead modules that print the multiple color separations. Image data of the printed color separations are used to adjust operating parameters for the digital air curtain.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to devices for generating ink images on a medium, and more particularly to the image quality of images generated by such devices.

Background Art

[0002] An inkjet imaging device, also known as an inkjet printer, sprays liquid ink from a print head to form an image on an image receiving surface. The print head includes a plurality of inkjets arranged in an array. Each inkjet has a thermal or piezoelectric actuator coupled to a print head controller. The print head controller generates a firing signal corresponding to digital data content corresponding to the image. The actuators within the print head respond to the firing signal by entering the ink chamber and ejecting ink droplets onto the image receiving member to form an ink image corresponding to the digital image content used to generate the firing signal. The image receiving member can be a continuous web of media material or a series of media sheets.

[0003] Inkjet printers used to produce color images typically include multiple printhead assemblies. Each printhead assembly typically contains one or more printheads that eject a single color of ink. In a typical inkjet color printer, four printhead assemblies are positioned in the process direction, with each printhead assembly ejecting a different color of ink. The four most frequently used ink colors are cyan, magenta, yellow, and black. The common name for such a printer is a CMYK color printer. Some CMYK printers have two printhead assemblies, each printing one color of ink. Printhead assemblies printing the same color of ink are offset from each other by half the distance between adjacent printheads in the cross-process direction, doubling the pixel density per inch of the color lines of ink ejected by the printheads in the two assemblies. As used in this document, the term “process direction” means the direction of movement of the image-receiving material as it passes through the printheads in the printer, and the term “cross-process direction” means the direction perpendicular to the process direction in the plane of the image-receiving material.

[0004] High-quality printing increasingly uses coated substrates for brochures, magazine covers, and other applications. These coated substrates present challenges to color ink image quality, particularly when passing through the print head at high speeds, as different colored inks overlap and are not readily absorbed by the coated substrate. As a result, these colored inks spread across the surface of the coated substrate before it enters a dryer, where water and solvents are removed from the inks to fix the image onto the substrate. These unabsorbed inks create image defects known as overlapping graininess. It would be beneficial to develop inkjet color printers that can produce ink images on coated substrates with little to no overlapping graininess. [Overview of the Initiative]

[0005] A color inkjet printer is configured to generate a color image on a coated substrate with little or no overlapping graininess. The color inkjet printer includes a first print head module configured to eject a first ink having a first color, and a second print head module configured to eject a second ink having a second color different from the first color, wherein the second print head module follows the first print head module in the process direction; a first heated air source positioned behind the first print head module and before the second print head module in the process direction; an optical sensor configured to generate image data of the substrate printed by the first and second print head modules, wherein the optical sensor is positioned behind the second print head module in the process direction; and a controller operably connected to the first print head module, the second print head module, the first heated air source, and the optical sensor. The controller is configured to receive image content data for a substrate in a print job, generate at least a first and a second color separation using the image content data for the substrate, operate a first print head module to print the first color separation onto the substrate, operate a first heated air source to direct heated air toward the substrate after the first color separation has been printed but before the second color separation has been printed, operate a second print head module to print the second color separation onto the substrate immediately after the substrate has passed the heated air source, and adjust the operating parameters of the first heated air source using image data of the printed first and second color separations generated by an optical sensor.

[0006] A method for operating a color inkjet printer generates a color image on a coated substrate with little or no overlapping graininess. The method includes receiving image content data for a substrate in a print job; generating at least a first color separation and a second color separation using the image content data for the substrate; operating a first print head module to print the first color separation onto the substrate; operating a first heated air source to direct heated air toward the substrate after the first color separation has been printed but before the second color separation has been printed on the substrate; operating a second print head module to print the second color separation onto the substrate immediately after the substrate has passed the first heated air source; and adjusting the operating parameters of the first heated air source using the image data of the printed first color separation and the printed second color separation. [Brief explanation of the drawing]

[0007] The aforementioned aspects and other features of a color inkjet printer and a method of operating a color inkjet printer that generate a color image on a coated substrate with little or no overlapping granularity are described in the following description in relation to the attached drawings. [Figure 1] This is a schematic diagram of a color inkjet printer that generates a color image on a coated substrate with little to no overlapping granularity. [Figure 2] Figure 1 shows a pair of digital air curtains inside the printer, which allows the printer to generate a color image on a coated substrate with little to no overlapping graininess. [Figure 3A] This is a graph showing the relationship between evaporation rate and temperature. [Figure 3B] This chart shows the drying time between color separation prints and the amount of water removed from the water-based inks that form the color separation. [Figure 4A] This is a graph showing the relationship between ink and substrate temperature and drying time. [Figure 4B] This is a graph showing the amount of water evaporated from water-based ink that forms color separation. [Figure 4C] This is a chart of three color separation printing scenarios. [Figure 5] Figure 1 is a flowchart of the process for operating the printer to generate a color image on a coated substrate with little to no overlapping graininess. [Figure 6] Figure 1 shows an alternative arrangement of the digital air curtain inside the printer. [Figure 7] This is a schematic diagram of a prior art color inkjet printer that is unable to generate a color image on a coated substrate with little or no overlapping granularity. [Figure 8] Figure 7 shows the printing zone inside the printer. [Modes for carrying out the invention]

[0008] Drawings are provided for a general understanding of the environment of the printers, printer operation methods, and printer configuration methods disclosed herein, as well as for details of the printers, printer operation methods, and printer configuration methods. In the drawings, similar reference numerals are used throughout to specify similar elements. As used herein, the word “printer” encompasses any device that sprays ink droplets onto different types of media to form an ink image.

[0009] Figure 7 shows a prior art high-speed color inkjet printer 10 that is unable to generate a color image on a coated substrate with little or no overlapping graininess. As illustrated, the printer 10 is a printer that directly forms an ink image on the surface of a media sheet taken from one of a media sheet supply unit S1 or S2, the sheet S being moved through the printer 10 by a controller 80 which operates one or more actuators 40 operably connected to rollers or to at least one drive roller of a conveyor 52 comprising a media transport unit 42. In one embodiment, each printhead module has only one printhead having a width corresponding to the widest media width in the cross-process direction that can be printed by the printer. In other embodiments, the printhead module has multiple printheads, each printhead having a width less than the widest media width in the cross-process direction that can be printed by the printer. In these modules, the printheads are arranged in an array of staggered printheads that allows for printing on media wider than a single printhead. Additionally, printheads within or between modules can also be combined such that the density of droplets ejected by the printheads in the cross-process direction is greater than the minimum spacing between inkjet printheads in the cross-process direction. Although printer 10 is shown to have only two media sheet feeders, the printer can consist of three or more sheet feeders, each containing a different type or size of media.

[0010] Figure 8 shows the print zone PZ in the prior art printer shown in Figure 7. The print zone PZ has a length in the process direction equal to the distance from the first inkjet through which the sheet passes in the process direction to the last inkjet through which the sheet passes in the process direction, and a width that is the maximum distance between the outermost inkjets on either side of the print zone that are directly opposite each other in the cross-process direction. Each print head module 34A, 34B, 34C, and 34D shown in Figure 8 has three print heads 204 mounted on print head carrier plates 316A, 316B, 316C, and 316D, respectively.

[0011] As shown in Figure 7, the printed image passes under the image dryer 30 after the ink image has been printed on the sheet S. The image dryer 30 may include an infrared heater, a heated air blower, an air return, or a combination of these components to heat the ink image and fix the image to the web at least partially. The infrared heater applies infrared heat to the printed image on the surface of the web to evaporate the water or solvent in the ink. The heated air blower, using a fan or other pressurized air source, directs heated air over the ink to supplement the evaporation of water or solvent from the ink. The air is then collected and exhausted by the air return to reduce interference of the dryer airflow with other components in the printer.

[0012] The dual path 72 is provided to receive the sheet from the transport system 42 after the substrate has been printed and to move the sheet by the rotation of rollers in the opposite direction to the direction of movement through the print head. At position 76 in the dual path 72, the substrate can be inverted so that it can join the job stream being carried by the media transport system 42. The controller 80 is configured to selectively flip the sheet. That is, the controller 80 can operate an actuator to flip the sheet so that the back side of the sheet can be printed, or it can operate an actuator so that the sheet is returned to the transport path without flipping the sheet so that the printed side of the sheet can be printed again. Access to the dual path 72 is provided by the movement of the pivot member 88. The rotation of the pivot member 88 is controlled by the controller 80 which selectively operates an actuator 40 operably connected to the pivot member 88. When the pivot member 88 is rotated counterclockwise as shown in Figure 7, the direction of the substrate from the media transport unit 42 is changed to the dual path 72. By rotating the pivot member 88 clockwise from its reversal position, access to the dual path 72 is closed, and as a result, the substrate on the media transport unit continues to move to the container 56. Another pivot member 86 is positioned between position 76 in the dual path 72 and the media transport unit 42. When the controller 80 operates the actuator to rotate the pivot member 86 counterclockwise, the substrate from the dual path 72 merges into the job stream on the media transport unit 42. By rotating the pivot member 86 clockwise, dual path access to the media transport unit 42 is closed.

[0013] As further shown in Figure 7, printed media sheets S that were not redirected to the dual path 72 are transported by the media transport unit to a sheet container 56 where these sheets are collected. Before the printed sheets reach the container 56, they pass through an optical sensor 84. The optical sensor 84 generates image data of the printed sheets, which is analyzed by the controller 80 to determine whether any inkjet that was intended to eject ink actually ejected ink, failed to eject ink droplets of sufficient mass, or landed irregularly on the sheet. Any inkjet operating in this manner is referred to in this document as a non-functioning inkjet. The controller can store data identifying non-functioning inkjets in a memory operably connected to the controller. The user can operate the user interface 50 to obtain a report displayed on the interface that identifies the number of non-functioning inkjets and the print heads where the non-functioning inkjets are located. The optical sensor can be a digital camera, an array of LEDs, and a photodetector, or other device configured to generate image data of the passing surface. As already mentioned, the media transport unit also includes a dual path that can invert the sheet and return it to the transport unit before the print head module, thereby allowing printing on the opposite side of the sheet. Figure 7 shows the printed sheets being collected in a sheet container, which can then be directed to other processing stations (not shown) that perform tasks such as folding, collating, binding, and stapling of the media sheets.

[0014] The operation and control of various subsystems, components, and functions of the machine or printer 10 are carried out with the help of a controller or electronic subsystem (ESS) 80. The ESS or controller 80' is operably connected to the components of the print head modules 34A-34D (and thus the print heads), the actuators 40, and the dryer 30. The ESS or controller 80 is, for example, a built-in dedicated minicomputer having a central processor unit (CPU) with electronic data storage and a display or user interface (UI) 50. The ESS or controller 80 includes, for example, sensor inputs and control circuits, as well as pixel arrangement and control circuits. In addition, the CPU reads, captures, prepares, and manages the flow of image data between the image input source, such as a scanning system or online or workstation connection (not shown), and the print head modules 34A-34D. Thus, the ESS or controller 80 is the main multitasking processor for operating and controlling all other machine subsystems and functions, including the printing process.

[0015] The controller 80 can be implemented using a general-purpose or dedicated programmable processor that executes programmed instructions. Instructions and data required to perform the programmed functions may be stored in memory associated with the processor or controller. The processor, its memory, and interface circuits constitute the controller to perform the operations described below. These components may be provided on a printed circuit card or as circuits within an application-specific integrated circuit (ASIC). Each circuit may be implemented on a separate processor, or multiple circuits may be implemented on the same processor. Alternatively, the circuits may be implemented as individual components or circuits provided within a very large-scale integrated (VLSI). Furthermore, the circuits described herein may be implemented in combination of processors, ASICs, individual components, or VLSI circuits.

[0016] During operation, the image content data of the generated images is transmitted to the controller 80 from either the scanning system or via an online or workstation connection for processing and generating print head control signals output to the print head modules 34A-34D. Along with the image content data, the controller receives print job parameters that identify the weight of the medium, the dimensions of the medium, the printing speed, the type of medium, the ink coverage of the areas to be generated on each surface of each sheet, the position of the images to be generated on each surface of each sheet, the color of the medium, the orientation of the media fibers in fibrous media, the temperature and humidity of the printing zone, the water content of the medium, and the manufacturer of the medium. As used in this document, the term "print job parameters" refers to non-image content data for a print job, and the term "image content data" refers to digital data that identifies the ink images to be printed on the media sheets.

[0017] Using similar reference numbers to identify similar components, Figure 1 shows a high-speed color inkjet printer 10' in which digital air curtains (DACs) 36 are installed between adjacent printhead modules in the process direction, and a controller 80' is configured to perform the process 500 described below to produce a color image on a coated substrate with little or no overlapping granularity. Figure 2 shows two of the DACs 36. A single DAC 36 is scattered between adjacent printheads in this configuration, but other arrangements of DACs are possible, as will be discussed below. Each DAC 36 includes a heater 202 that heats the airflow generated by a source of variable positive airflow 204. The DAC includes a housing configured to direct the heated air onto the top of the ink layer passing through the printhead. This heated airflow provides both a homogenizing force to the ink layer sprayed onto the substrate by the previous printhead, as well as a drying component for the ink layer. The heater 202 and the variable positive airflow 204 supply sources are connected to the controller 80', so that the controller can change the operation of the heater and airflow sources to adjust the temperature and flow rate of the airflow to control the spreading of ink dots within the printing zone. The vacuum unit 206 is also operably connected to the controller 80', so that the controller can operate the vacuum unit to remove moisture from the heated airflow on newly ejected ink droplets and mitigate their effects. The heater 202 may be an in-line cartridge heater, etc. In addition to controlling the airflow rate, the controller 80' is configured to digitally operate the airflow supply sources using the timing of the paper edge sensor 38 to pulse the airflow sources on and off to prevent the paper from separating from the conveyor belt.

[0018] As shown in FIGS. 1 and 2, a single DAC 36 is positioned between print head modules. Alternative arrangements of the DACs can be installed within a printer such as printer 10' of FIG. 1, such that multiple DACs 36 are stacked as an array between color modules. An example of an alternative arrangement is shown in FIG. 6. Such alternative arrangements can be useful in addressing issues arising from different viscosities of the inks being ejected by different print head modules, or pigments in the inks, or different types of media substrates being printed. Differences between the inks within the print head modules may require different numbers of DACs 36 to be positioned between the print head modules. For example, in the process direction, one DAC between a first print head module and an adjacent second print head module can be sufficient to control dot gain in a single color separation, while two DACs are installed between the second print head module and an adjacent third print head module in the process direction, and three DACs are installed between the third print head module and an adjacent fourth print head module in the process direction.

[0019] Experiments were conducted using a printer similar to that shown in FIG. 6. Each print head module ejected only one color of aqueous ink and printed a test pattern of lines extending in the process direction on a substrate passing through the print heads within the print head module. The time between printing of the substrate by one print head module and subsequent printing of it by the subsequent print head module was varied. The substrate was not heated above an ambient air temperature of 25°C. After printing the substrate, the printed lines were imaged and the image data was analyzed to measure overlap granularity. The measurements showed that the overlap granularity was within the image quality specifications when the time between printing by the print head modules was at least 3 seconds. The known evaporation rate of water at a substrate temperature of 25°C identified in the graph of FIG. 3A, the known mass of the ink ejected by each print head module, 10 W / m 2Using the heat transfer coefficient between air and substrate at -degK and a 3-second time interval, the amount of moisture evaporation required between printhead module prints to achieve acceptable image quality was determined. One such experiment yielded the chart shown in Figure 3C, which indicates that 35% of the water content of the aqueous ink sprayed onto the substrate by the printhead module needs to evaporate to achieve acceptable image quality.

[0020] Using this information, three scenarios were modeled in which the heated airflow is directed to the ink and paper between prints by each printhead module. The scenarios had different heat transfer coefficients and air temperatures for the heated air to collide with the ink. The heat transfer coefficient is a function of the airflow measured in cubic feet per minute (cfm), the dimensions of the airflow chute opening that directs the heated airflow towards the sheet, and the distance between the airflow opening and the sheet. For a fixed geometric shape of the airflow opening and the distance from the opening to the sheet, the heat transfer coefficient is adjusted by varying the airflow rate within a range that does not obstruct the ink image on the sheet. Standard heat transfer coefficients for laminar and turbulent flow scenarios are used for given flow rates and geometric shapes. Graphs of the ink temperature and the substrate area without ink are shown in Figure 4A. The graph in Figure 4B shows the corresponding grams (gsm) of water evaporated over time in the substrate per square meter. A chart of these results for the time interval shown in Figure 3B is shown in Figure 4C. These data indicate that the temperature of the heated air generated by the DAC36 and the flow rate of the heated air directed onto the substrate passing through the DAC36 are adjusted to achieve sufficient ink drying between color separations to reduce overlapping granularity. One constraint on the temperature of the unprinted areas of the substrate for this particular medium is that the temperature of these areas must be below 37°C, as temperatures above that level tend to dry out the inkjet and cause the inkjet to malfunction. As used in this document, the term "color separation" means the arrangement of multiple pixels of a single color that are printed or have been printed by the printhead module.

[0021] In the printer of FIG. 1, the optical sensor generates image data of the ink image printed on the substrate, while the DAC36 operates under the initial conditions of air temperature, air flow rate, and vacuum level. The controller 80' analyzes the image data to measure the size of ink droplets (dot gain) or ink lines (line growth) in the various color separations that form the ink image. Both dot gain and line growth indicate the amount of spread of the ink droplets that occurs during the printing of the ink image. If this is too large, overlapping granularity occurs. Instead of, or in addition to, using the ink image of the print job, a test pattern of ink droplets or ink lines can be printed within the ink image area or in the margins outside the ink image area for the purpose of dot gain and line growth measurements. Dot gain and line growth are measured for each color separation, as well as for the overlap of two or more of the color separations, to evaluate the interaction between the color separations. If the measured dot gain or line growth exceeds a predetermined threshold, one or more of the air temperature, flow rate, and vacuum level are increased. The image data of the subsequent ink image is then analyzed to determine whether the change or changes are appropriate to address the measured dot gain or line growth. If the change or changes do not result in a dot gain or line growth that is less than the predetermined threshold, a further increase in one or more of these parameters is made. The DAC36 is independently controlled because the ink ejected by the various print head modules differs in color (pigment) and viscosity. Therefore, the operating parameters of one or more DACs that direct air to the first color separation are likely to be different from the operating parameters of one or more DACs that process the combination of color separations. Similarly, in embodiments having multiple DACs between adjacent print head modules, each DAC among the multiple DACs can operate independently of each other and of the DACs between other adjacent print head modules.

[0022] Figure 5 shows a flowchart of process 500 for operating printer 10' to register the printing of a second color image using a previously printed color image on a media sheet. In the following discussion, references to process 500 performing a function or operation refer to the operation of the controller, such as controller 80 executing stored program instructions to perform a function or operation in relation to other components in the printer. For illustrative purposes, process 500 is described as being performed using printer 10' in Figure 1.

[0023] The process 500 for operating the printer 10' begins with the controller receiving print job parameters and image content data (block 504). The image content data for each sheet is divided into color separations for each print head module (block 508). The process prints each color separation and operates the DAC between the print head modules (block 512). The optical sensor generates image data of the ink image formed using the printed color separations (block 516) and measures the dot gain and line growth of ink droplets and lines in the image data of the ink image (block 520). If the measured dot gain or line growth for a color separation exceeds a predetermined threshold corresponding to an indication of overlapping granularity (block 524), the process increases the DAC that processes that color separation or one or more of the DAC's operating parameters (block 528). The process continues until the entire ink image is printed (block 532).

[0024] It will be understood that various variations of the above-disclosed features and functions, or substitutes thereof, may be desirablely combined with many other different systems or applications. Various currently unforeseen substitutes, modifications, variations, or improvements, which are also intended to be covered by the following "Claims," ​​may be subsequently made by those skilled in the art.

Claims

1. 1. A color inkjet printer, comprising: a first printhead module configured to eject a first ink having a first color; a second printhead module following the first printhead module in the process direction, the second printhead module configured to eject a second ink having a second color different from the first color; a first heated air source positioned after the first printhead module in the process direction and before the second printhead module in the process direction; an optical sensor positioned after the second printhead module in the process direction, the optical sensor configured to generate image data of a substrate printed by the first printhead module and the second printhead module; a controller operably connected to the first printhead module, the second printhead module, the first heated air source, and the optical sensor; wherein the controller: receiving image content data for a substrate in a print job; generating at least a first color separation and a second color separation using the image content data for the substrate; operating the first printhead module to print the first color separation onto the substrate; operating the first heated air source to direct heated air having a first temperature and a first air flow rate toward the substrate after the first color separation is printed on the substrate but before the second color separation is printed on the substrate; operating the second printhead module to print the second color separation onto the substrate immediately after the substrate has passed the first heated air source; measuring ink drop sizes in the image data of the printed first color separation and the printed second color separation with the optical sensor; changing operation of the first heated air source to adjust at least one of the temperature of the heated air and the air flow rate of the heated air when the measured size of at least some of the ink droplets in the image data of the printed first color separation and the printed second color separation exceeds a predetermined threshold; It is a color inkjet printer that is configured to do so.

2. a first vacuum source configured to draw the heated air away from the substrate after the heated air reaches the substrate; The color inkjet printer of claim 1 further comprising:

3. The controller: adjusting a level of vacuum drawn by the first vacuum source when the measured ink drop sizes of at least some of the ink drops in the printed first color separation and the printed second color separation exceed a predetermined threshold.

3. The color inkjet printer of claim 2, further configured as follows:

4. a third printhead module following the first printhead module and the second printhead module in the process direction, the third printhead module being configured to eject a third ink having a third color different from the first color and the second color; a second heated air source positioned after the second printhead module in the process direction and before the third printhead module in the process direction; Further provided with the controller is further operably connected to the third printhead module and the second heated air source, the controller: generating a third color separation using the image content data for the substrate; operating the second heated air source to direct heated air toward the substrate after the second color separation is printed on the substrate but before the third color separation is printed on the substrate; operating the third printhead module to print the third color separation onto the substrate immediately after the substrate has passed the second heated air source; adjusting operating parameters of the second heated air source using image data of the printed third color separation generated by the optical sensor; 4. The color ink jet printer of claim 3, further configured as follows:

5. the first heated air source comprising: further comprising a first plurality of heated air sources; The controller is further operably connected to each heated air source in the first plurality of heated air sources, the controller comprising: adjusting at least one operating parameter of at least one heated air source in the first plurality of heated air sources using the image data of the printed first color separation, the printed second color separation, and the printed third color separation generated by the optical sensor; 10. The color inkjet printer of claim 1, further configured as follows:

6. the second heated air source comprising: a second plurality of heated air sources; The controller is further operably connected to each heated air source in the second plurality of heated air sources, the controller comprising: adjusting at least one operating parameter of at least one heated air source in the second plurality of heated air sources using the image data of the printed first color separation, the printed second color separation, and the printed third color separation generated by the optical sensor; 6. The color inkjet printer of claim 5, further configured as follows:

7. 7. The color ink jet printer of claim 6, wherein the number of heated air sources in the first plurality of heated air sources is different from the number of heated air sources in the second plurality of air sources.

8. 8. The color ink jet printer of claim 7, wherein the controller is further configured to control the first plurality of heated air sources independently of the second plurality of heated air sources.

9. 9. The color inkjet printer of claim 8, wherein the controller is further configured to control each heated air source in the first plurality of heated air sources independently of other heated air sources in the first plurality of heated air sources.

10. 10. The color inkjet printer of claim 9, wherein the controller is further configured to adjust the temperature of the heated air generated by any heated air source in the first plurality of heating sources and the second plurality of heated air sources so as not to exceed a maximum temperature.

11. 11. The color inkjet printer of claim 10, wherein the maximum temperature is 37°C.

12. 1. A method for operating a printer, comprising: receiving image content data for a substrate in a print job; generating at least a first color separation and a second color separation using the image content data for the substrate; operating a first printhead module to print the first color separation onto the substrate; operating a first heated air source to direct heated air toward the substrate after the first color separation is printed on the substrate but before the second color separation is printed on the substrate; operating a second printhead module to print the second color separation onto the substrate immediately after the substrate has passed the first heated air source; generating image data for the printed first color separation and the printed second color separation; measuring ink drop sizes in the image data of the printed first color separation and the printed second color separation; adjusting an operating parameter of the first heated air source when ink droplet sizes of at least some of the ink droplets in the image data of the printed first color separation and the printed second color separation exceed a predetermined threshold; A method comprising:

13. The adjusting of the operating parameters of the first heated air source comprises: adjusting one of a temperature of the heated air directed at the substrate and an air flow rate of the heated air directed at the substrate; The method of claim 12 further comprising:

14. operating a first vacuum source to draw the heated air away from the substrate after the heated air reaches the substrate; The method of claim 13 further comprising:

15. adjusting a vacuum level drawn by the first vacuum source when the measured ink droplet sizes of at least some of the ink droplets in the image data of the first color separation and the second color separation exceed a predetermined threshold; The method of claim 14 further comprising:

16. generating a third color separation using the image content data for the substrate; and after the second color separation is printed on the substrate but before the third color separation is printed on the substrate, operating a second heated air source positioned after the second printhead module to direct heated air toward the substrate; operating a third printhead module to print the third color separation onto the substrate immediately after the substrate has passed the second heated air source; generating image data for the printed first color separation, the printed second color separation, and the printed third color separation; adjusting operating parameters of the second heated air source using the image data of the printed first color separation, the printed second color separation, and the printed third color separation; 16. The method of claim 15, further comprising:

17. said operating said second heated air source further comprising: operating a plurality of heated air sources; adjusting operating parameters of at least one heated air source in the plurality of heated air sources using the image data of the printed first color separation, the printed second color separation, and the printed third color separation; 17. The method of claim 16, further comprising:

Images