Patent Publication Number: US-11660888-B2

Title: Devices, systems, and methods for controlling airflow through vacuum platen of printing systems via airflow zones

Description:
FIELD 
     Aspects of this disclosure relate generally to inkjet printing, and more specifically to inkjet printing systems having a media transport device utilizing vacuum suction to hold and transport print media. Related devices, systems, and methods also are disclosed. 
     INTRODUCTION 
     In some applications, inkjet printing systems use an ink deposition assembly with one or more printheads, and a media transport device to move print media (e.g., a substrate such as sheets of paper, envelopes, or other substrate suitable for being printed with ink) through an ink deposition region of the ink deposition assembly (e.g., a region under the printheads). The inkjet printing system forms printed images on the print media by ejecting ink from the printheads onto the media as the media pass through the deposition region. In some inkjet printing systems, the media transport device utilizes vacuum suction to assist in holding the print media against a movable support surface (e.g., conveyor belt, rotating drum, etc.) of the transport device. Vacuum suction to hold the print media against the support surface can be achieved using a vacuum source (e.g., fans) and a vacuum plenum fluidically coupling the vacuum source to a side of the moving surface opposite from the side that supports the print media. The vacuum source creates a vacuum state in the vacuum plenum, causing vacuum suction through holes in the movable support surface that are fluidically coupled to the vacuum plenum. When a print medium is introduced onto the movable support surface, the vacuum suction generates suction forces that hold the print medium against the movable support surface. The media transport device utilizing vacuum suction may allow print media to be securely held in place without slippage while being transported through the ink deposition region under the ink deposition assembly, thereby helping to ensure correct locating of the print media relative to the printheads and thus more accurate printed images. The vacuum suction may also allow print media to be held flat as it passes through the ink deposition region, which may also help to increase accuracy of printed images, as well as helping to prevent part of the print medium from rising up and striking part of the ink deposition assembly and potentially causing a jam or damage. 
     One problem that may arise in inkjet printing systems that include a media transport device utilizing vacuum suction is unintended blurring of images resulting from air currents induced by the vacuum suction. In some systems, such blurring may occur in portions of the printed image that are near the edges of the print media. This blurring may occur due to uncovered holes in the media transport device adjacent to one or more of the edges of the print media. In particular, during a print job, the print media are spaced apart from one another on the movable support surface as they are transported through the deposition region of the ink deposition assembly, and therefore parts of the movable support surface between adjacent print media are not covered by any print media. This region between adjacent print media is referred to herein as the inter-media zone. Thus, adjacent to both the lead edge and the trail edge of each print medium in the inter-media zone there are uncovered holes in the movable support surface. Moreover, to ensure adequate hold down force is applied to all sizes of print media the system is designed to use, the holes for vacuum suction are generally distributed across a given region of the movable support surface that has a dimension in the cross-process direction that is close to a dimension in the cross-process direction of the largest size of print media that the system is designed to use. As a result of this, if the print medium currently being printed is smaller in the cross-process direction than the largest size, the print medium may not extend across the full width of the region containing the holes, and therefore a group of holes along and adjacent to the inboard edge of the print medium will be uncovered. (As described further below, the “inboard” edge of the print medium is defined herein as the edge that is opposite from the edge that is used to register the print media in the cross-process direction, which is defined as the “outboard” edge; registration schemes may vary from system to system, and therefore the edge that is the “inboard” edge, as used herein, may vary from system to system.) Because various holes near the lead, trail, and inboard edges are not covered, as described above, the vacuum of the vacuum plenum induces air to flow through those uncovered holes. This airflow around the lead, trail, and inboard edges may deflect ink droplets as they are traveling from a printhead to the substrate, and thus cause blurring of the images that are being printed near those edges. 
     A need exists to improve the accuracy of the placement of droplets in inkjet printing systems and to reduce the appearance of blur of the final printed media product. A need further exists to address the blurring issues in a reliable manner and while maintaining speeds of printing and transport to provide efficient inkjet printing systems. 
     SUMMARY 
     Embodiments of the present disclosure may solve one or more of the above-mentioned problems and/or may demonstrate one or more of the above-mentioned desirable features. Other features and/or advantages may become apparent from the description that follows. 
     In accordance with at least one embodiment of the present disclosure, a printing system comprises an ink deposition assembly, a media transport device, and an airflow control system. The ink deposition assembly comprises one or more printheads arranged to eject ink to a deposition region of the ink deposition assembly. The media transport device comprises a vacuum platen comprising a plurality of platen holes, and a movable support surface configured to support the print medium and movable along a process direction through the deposition region. The media transport device is configured to hold the print medium against the movable support surface by vacuum suction communicated to the movable support surface through the platen holes in the vacuum platen. The airflow control system comprises a plurality of airflow zones. Each of the airflow zones comprises a group of the platen holes, a duct, and a valve, the duct and the valve being arranged to selectively control vacuum suction through the group of the platen holes. For each of the printheads, at least one of the plurality of airflow zones is located under the respective printhead. 
     In accordance with at least one embodiment of the present disclosure, a method comprises transporting a print medium through a deposition region of a printhead of a printing system and ejecting print fluid from the printhead to deposit the ink to the print medium in the deposition region. The print medium is held during the transporting against a movable support surface of a media transport device via vacuum suction communicated to the movable support surface through platen holes in a vacuum platen. The printing system comprises airflow zones that each comprise a corresponding group of the platen holes. The method further comprises selectively controlling suction through a first group of airflow zones, comprising one or more of the airflow zones, based on the size of the print medium, and selectively controlling suction through a second group of airflow zones, comprising one or more of the airflow zones, based on the size of the print medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure can be understood from the following detailed description, either alone or together with the accompanying drawings. The drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments of the present teachings and together with the description explain certain principles and operation. In the drawings: 
         FIGS.  1 A- 1 L  schematically illustrate air flow patterns relative to a printhead assembly, transport device, and print media during differing stages of print media transport through an ink deposition region of a conventional inkjet printing system, and resulting blur effects in the printed media product. 
         FIG.  2    is a block diagram illustrating components of an embodiment of an inkjet printing system including an air flow control system. 
         FIG.  3    is a schematic illustration of a side view of components of an embodiment of an inkjet printing system. 
         FIG.  4    is a partial plan view of the inkjet printing system of  FIG.  3   , depicting a single inkjet printhead module. 
         FIGS.  5 A- 5 F  are cross-sectional views of the inkjet printing system of  FIG.  4   , with the cross-section taken along D in  FIG.  4   . 
         FIGS.  6 A- 6 C  are cross-sectional views of the inkjet printing system of  FIG.  4   , with the cross-section taken along E in  FIG.  4   . 
     
    
    
     DETAILED DESCRIPTION 
     In the Figures and the description herein, numerical indexes such as “_ 1 ”, “_ 2 ”, etc. are appended to the end of the reference numbers of some components. When there are multiple similar components and it is desired to refer to a specific one of those components, the same base reference number is used and different indexes are appended to it to distinguish individual components. However, when the components are being referred to generally or collectively without a need to distinguish between specific ones, the index may be omitted from the base reference number. Thus, as one example, a print medium  5  may be labeled and referred to as a first print medium  5 _ 1  when it is desired to identify a specific one of the print media  5 , as in  FIG.  1 A , but it may also be labeled and referred to as simply a print medium  5  in other cases in which it is not desired to distinguish between multiple print media  5 . 
     As described above, when an inter-media zone is near or under a printhead, the uncovered holes in the inter-media zone can create crossflows that can blow satellite droplets off course and cause image blur. Similarly, uncovered holes along an inboard or outboard side of the print media can also create crossflows that cause image blur. To better illustrate some of the phenomena occurring giving rise to the blurring issues, reference is made to  FIGS.  1 A- 1 F .  FIGS.  1 A,  1 D,  1 G, and  1 J  illustrate schematically printheads  10  printing on a print medium  5  near a trail edge TE, a lead edge LE, an inboard edge, and a middle, respectively, of the print medium  5 .  FIGS.  1 A,  1 D, and  1 J  are cross-sections taken through a printhead  10  along a process direction (y-axis direction in the figures), while  FIG.  1 G  is a cross-section taken through the same printhead  10  along a cross-process direction perpendicular to the process direction (x-axis direction in the figures), with the illustration in  FIG.  1 G  depicting an embodiment having three printheads in a series along the x-direction with one being offset from the other two.  FIGS.  1 B,  1 E,  1 H, and  1 K  illustrate enlarged views of the regions A, B, C, and D respectively in  FIGS.  1 A , AD,  1 B, and  1 J.  FIGS.  1 C,  1 F,  1 I and  1 L  illustrate enlarged pictures of printed images, the printed images comprising lines printed near the trail edge TE, lead edge LE, inboard edge, and middle, respectively, of a sheet of paper. 
     As shown in  FIGS.  1 A,  1 D,  1 G, and  1 J , the inkjet printing system comprises one or more printheads  10  to eject ink to print media  5  through printhead openings  19  in a carrier plate  11 . The inkjet printing system also comprises a movable support surface  20  to transport the print media  5  in a process direction P, which corresponds to a positive y-axis direction in the Figures. The movable support surface  20  slides along a top of a vacuum platen  26 , and a vacuum environment is provided on a bottom side of the platen  26 . The movable support surface  20  has holes  21  and the vacuum platen  26  has platen holes  27 . The holes  21  and  27  periodically align as the movable support surface  20  moves thereby exposing the region above the movable support surface  20  to the vacuum below the platen  26 . In regions where the print medium  5  covers the holes  21 , the vacuum suction through the aligned holes  21  and  27  generates a force that holds the print medium  5  against the movable support surface  20 . However, little or no air is drawn into these covered holes  21  and  27  from the environment above the movable support surface  20  since they are blocked by the print medium  5 . On the other hand, as shown in  FIGS.  1 A,  1 D, and  1 G  in the inter-media zone  22  (see  FIGS.  1 A and  1 D ) and in the uncovered region  24  near the inboard side IB of the platen  26  (see  FIG.  1 G ), the holes  21  and  27  are not covered by the print media  5 , and therefore the vacuum suction pulls air from above the movable support surface  20  to flow down through these holes  21  and  27 . This creates airflows, indicated by the dashed arrows in  FIGS.  1 A,  1 D, and  1 G  which flow from regions around the printhead  10  towards the uncovered holes  21  and  27  in the inter-media zone  22  and the uncovered region  24 , with some of the airflows passing under the printhead  10 . 
     In  FIG.  1 A , the print medium  5 _ 1  is being printed on near its trail edge TE, and therefore the region where ink is currently being ejected (“ink-ejection region”) (e.g., region A in  FIG.  1 A ) is located downstream of the inter-media zone  22  (upstream and downstream being defined with respect to the process direction P). Accordingly, some of the air being sucked towards the inter-media zone  22  will flow upstream through the ink-ejection region under the printhead  10 . More specifically, the vacuum suction from the inter-media zone  22  lowers the pressure in the region immediately above the inter-media zone  22 , e.g., region R 1  in  FIG.  1 A , while the region downstream of the printhead  10 , e.g., region R 2  in  FIG.  1 A , remains at a higher pressure. This pressure gradient causes air to flow in an upstream direction from the region R 2  to the region R 1 , with the airflows crossing through a portion of the ink-ejection region (e.g., region A in  FIG.  1 A ) which is between the regions R 1  and R 2 . Airflows such as these, which cross through the ink-ejection region, are referred to herein as crossflows  15 . In  FIG.  1 A , the crossflows  15  flow upstream, but in other situations the crossflows  15  may flow in different directions. 
     As shown in the enlarged view A′ in  FIG.  1 B , which comprises an enlarged view of the region A in  FIG.  1 A , as ink is ejected from the printhead  10  towards the medium  5 , main droplets  12  and satellite droplets  13  are formed. The satellite droplets  13  are much smaller than the main droplets  12  and have less mass and momentum, and thus the upstream crossflows  15  tend to affect the satellite droplets  13  more than the main droplets  12 . Thus, while the main droplets  12  may land on the print medium  5  near their intended deposition location  16  regardless of the crossflows  15 , the crossflows  15  may push the satellite droplets  13  away from the intended trajectory so that they land at an unintended location  17  on the medium  5 , the unintended location  17  being displaced from the intended location  16 . The result of such crossflows and consequent misplaced droplets can be seen in an actual printed image in  FIG.  1 C , in which a region  16 ′ of denser printed dots corresponding to the intended printed line is formed by droplets (e.g., generally the main droplets  12 ) which were deposited predominantly at their intended locations, whereas a region  17 ′ of sparser dots dispersed away from the line are formed by droplets (e.g., generally the satellite droplets  13 ) which were blown away from the intended locations to land in unintended locations. The resulting image has a blurred or smudged appearance for the printed line. Notably, the blurring in  FIG.  1 C  is asymmetrically biased towards the trail edge TE, which would be the expected result of the crossflows  15  near the trail edge TE blowing primarily in an upstream direction. The inter-media zone  22  may also induce other airflows flowing in other directions, such as downstream airflows from an upstream side of the printhead  10 , but these other airflows do not pass through the region where ink is currently being ejected in the illustrated scenario and thus do not contribute to image blur. Only those airflows that cross through the ink ejection region are referred to herein as crossflows. 
       FIGS.  1 D- 1 F  schematically illustrate another situation in which such blurring occurs, but this time near the lead edge LE of the print medium  5 _ 2 . The cause of blurring near the lead edge LE is similar to that described above in relation to the trail edge TE, except that in the case of printing near the lead edge LE the ink-ejection region is now located upstream of the inter-media zone  22 . As a result, the crossflows  15  that are crossing through the ink-ejection region now originate from the upstream side of the printhead  10 , e.g., from region R 3 , and flow downstream to region R 4 . Thus, as shown in the enlarged view B′ of  FIG.  1 E , which comprises an enlarged view of the region B of  FIG.  1 D , in the case of printing near the lead edge LE of the print medium  5 _ 2 , the satellite droplets  13  are blown downstream towards the lead edge LE of the print medium  5 _ 2  (positive y-axis direction) to land at unintended locations  17 , while the main droplets  12  tend to land at or near their intended locations  16 . As shown in  FIG.  1 F , such an effect results in asymmetric blurring that is biased towards the lead edge LE of the print medium (i.e., a denser region  16 ′ of printed dots corresponding to a line is formed with a sparser region  17 ′ of printed dots trailing away from the line toward the lead edge LE). 
       FIGS.  1 G- 1 I  illustrate yet another situation in which such blurring can occur, but this time near the inboard edge IE of the print medium  5  due to uncovered holes  21 ,  27  in that region. The cause of blurring near the inboard edge IE is similar to that described above in relation to the trail edge TE and lead edge LE, except that in the case of printing near the inboard edge IE the ink-ejection region is now located outboard of the uncovered region  24  of the holes  21  and  27  in the movable support surface  20  and platen  26 . As a result, the crossflows  15  that are crossing through the ink-ejection region now originate from the outboard side of the printhead  10 , e.g., from region R 5 , and flow in an inboard direction towards the region R 6 . Thus, as shown in the enlarged view C′ of  FIG.  1 H , which comprises an enlarged view of the region C of  FIG.  1 G , in the case of printing near the inboard edge IE, the satellite droplets  13  are blown inboard towards the inboard edge IE of the print medium  5  (positive y-axis direction) and land at unintended locations  17  rather than at the intended location  16  where main droplets  12  land. As shown in  FIG.  1 I , such a crossflow pattern is expected to result in asymmetric blurring that is biased towards the inboard edge IE (i.e., a denser region  16 ′ of printed dots corresponding to a line is formed with a sparser region  17 ′ of printed dots trailing away from the line toward the inboard edge IE). 
     In contrast, as shown in  FIG.  1 J  and the enlarged view D′ in  FIG.  1 K , which corresponds to an enlarged view of region D of  FIG.  1 J , when printing farther from the edges (trail, leading, or inboard) of the print medium  105  there may be little or no crossflows  15  because the inter-media zone  22  and the uncovered region  24  are too distant to induce much airflow. Because the crossflows  15  are absent or weak farther away from the edges of the print medium  5 , the satellite droplets  13  in this region are not as likely to be blown off course. Thus, as shown in  FIGS.  1 K and  1 L , when printing farther from the edges of the print medium  5 , the satellite droplets land at the intended location  16  or at locations  18  that are much closer to the intended locations  16  resulting in much less image blurring. The deposition locations  18  of the satellite droplets may still vary somewhat from the intended locations  16 , due to other factors affecting the satellite droplets  13 , but the deviation is smaller than it would be near the lead or trail edges.  FIG.  1 L  depicts a resulting image of a situation such as that in  FIGS.  1 J and  1 K , showing the printed line presenting droplets landing at intended locations  16 ′ in which and some droplets landing sufficiently close to the intended locations  16 ′ at locations  18 ′. The resulting image does not show a significantly noticeable blurring or smudged appearance of the line. 
     Embodiments disclosed herein may, among other things, reduce or eliminate such image blur by utilizing an airflow control system that reduces or eliminates the crossflows. With the crossflows reduced or eliminated, droplets, including satellite droplets, are more likely to land closer to or at their intended deposition locations, and therefore the amount of blur is reduced. Airflow control systems in accordance with various embodiments reduce or eliminate the crossflows by providing a number of discrete airflow zones in the vacuum plenum at locations near the printheads and selectively turning on and off the airflow zones. Each airflow zone comprises a group of the platen holes in the vacuum platen, a duct arranged to control airflow through the corresponding group of platen holes, and a valve to control airflow through the duct. The duct is arranged on the side of the vacuum platen that faces the interior of the vacuum plenum and defines a conduit or passageway to communicate the vacuum suction of the vacuum plenum to the corresponding group of platen holes. When a given airflow zone is “on,” as used herein, its valve is open such that the interior of the vacuum plenum is in fluidic communication with the corresponding group of holes via the duct, thus allowing vacuum suction through the corresponding group of holes. When the given airflow zone is “off,” as used herein, the associated valve is closed and the interior of the vacuum plenum is not in fluidic communication with the corresponding group of holes, thus preventing vacuum suction through the corresponding group of holes. Embodiments of the present disclosure contemplate selectively turning airflow zones on and off based on the location of the inter-media zone. More specifically, at any given time, any airflow zones that are currently under the inter-media zone are off, while other airflow zones are on. Because the airflow zones under the inter-media zone are off, vacuum suction through the uncovered holes of the inter-media zone does not occur. Thus, the inter-media zone is prevented from inducing crossflows, and therefore the edge blur that would otherwise be caused by these crossflows is reduced or eliminated. Because the other airflow zones (those under the print media and not under the inter-media zones) are on and the holes associated with those zones covered by a print medium, vacuum suction is communicated through the corresponding groups of holes to the print medium, thus applying hold down force to the print medium. In addition, airflow zones along an inboard edge of the media transport device that are not covered by the print media currently being used due to the size of the print media can be turned off. This prevents suction through the uncovered holes along the inboard edge. Thus, the uncovered region along the inboard side of the media transport device is prevented from inducing crossflows (or the crossflows are reduced), and therefore the image blur that would otherwise occur along the inboard edge due to these crossflows is reduced. 
     Turning now to  FIG.  2   , an embodiment of a printing system will be described in greater detail.  FIG.  2    is a block diagram which schematically illustrates a printing system  100  utilizing the above-described airflow control system. The printing system  100  comprises an ink deposition assembly  101  to deposit ink on print media, a media transport assembly  103  to transport print media through the ink deposition assembly  101 , and a control system  130  to control operations of the printing system  100 . These components of the printing system  100  are described in greater detail in turn below. In addition, various components of the printing system  100  participate in controlling airflow around the printheads, and thus these parts may be referred to collectively as an airflow control system  150 . 
     The ink deposition assembly  101  comprises one or more printhead modules  102 . One printhead module  102  is illustrated in  FIG.  2    for simplicity, but any number of printhead modules  102  may be included in the ink deposition assembly  101 . In some embodiments, each printhead module  102  may correspond to a specific ink color, such as cyan, magenta, yellow, and black. Each printhead module  102  comprises one or more printheads  110  configured to eject print fluid, such as ink, onto the print media to form an image. In  FIG.  2   , one printhead  110  is illustrated in the printhead module  102  for simplicity, but any number of printheads  110  may be included per printhead module  102 . The printhead modules  102  may comprise one or more walls, including a bottom wall which may be a carrier plate, as described in more detail below with regard to  FIG.  3   . The carrier plate may comprise printhead openings, and the printheads  110  are arranged to eject their ink through the printhead openings. In some embodiments, the carrier plate supports the printheads  110 . In other embodiments, the printheads  110  are supported by other structures. The printhead modules  102  may also include additional structures and devices to support and facilitate operation of the printheads  110 , such as, ink supply lines, ink reservoirs, electrical connections, and so on, as known in the art. 
     As shown in  FIG.  2   , the media transport device  103  comprises a movable support surface  120 , a vacuum plenum  125 , a vacuum source  128 , and a number of airflow zones  157  (e.g., airflow zones  157 _ 1 ,  157 _ 2 ). Each of the airflow zones  157  comprises a group of platen holes  127 , a duct  151  (e.g., ducts  151 _ 1  and  151 _ 2 ), and a valve  152  coupled to the duct  151  (e.g., valves  152 _ 1 ,  152 _ 2 ). In  FIG.  2    two airflow zones  157  are illustrated, but other numbers can be used depending on a variety of factors as will become apparent from the descriptions of the embodiments of  FIGS.  5  and  6    below. The movable support surface  120  transports the print media through a deposition region of the printing assembly  101 . The vacuum plenum  125  supplies vacuum suction to one side of the movable support surface  120  (e.g., a bottom side), and print media is supported on an opposite side of the movable support surface  120  (e.g., a top side). Air holes  121  through the movable support surface  120  communicate the vacuum suction through the surface  120 , such that the vacuum suction holds down the print media against the surface  120 . The movable support surface  120  is movable relative to the printing assembly  101 , and thus the print media held against the movable support surface  120  is transported relative to the printing assembly  101  as the movable support surface  120  moves. Specifically, the movable support surface  120  transports the print media through a deposition region of the printing assembly  101 , the deposition region being a region in which print fluid (e.g., ink) is ejected onto the print media, such as a region under the printhead(s)  110 . The movable support surface  120  can comprise any structure capable of being driven to move relative to the printing assembly  101  and which has holes  121  to allow the vacuum suction to be communicated to hold down the print media. Such structures of movable support surfaces that are contemplated as within the scope of the disclosure include, but are not limited to, for example a belt, one or more rotatable drums, etc. Those having ordinary skill in the art are familiar with various movable support structures used in printing systems to convey the print media. 
     The vacuum plenum  125  comprises baffles, walls, or any other structures arranged to enclose or define an environment in which a vacuum state (e.g., low pressure state) is maintained by the vacuum source  128 , with the plenum  125  fluidically coupling the vacuum source  128  to the movable support surface  120  such that the movable support surface  120  is exposed to the vacuum state within the vacuum plenum  125 . In some embodiments, the movable support surface  120  is supported by a vacuum platen  126 , which may be a top wall of the vacuum plenum  125 . In such an embodiment, the movable support surface  120  is fluidically coupled to the vacuum in the plenum  125  via platen holes  127  through the vacuum platen  126 . In some embodiments, the movable support surface  120  is itself one of the walls of the vacuum plenum  125  and thus is exposed directly to the vacuum in the plenum  125 . The vacuum source  128  may be any device configured to remove air from the plenum  125  to create the low-pressure state in the plenum  125 , such as a fan, a pump, etc. 
     As noted above, each airflow zone  157  comprises a duct  151 . The ducts  151  are provided within the vacuum plenum  125  on the side of the vacuum platen  126  and/or the movable support surface  120  that faces the interior of the vacuum plenum  125 . Each duct  151  comprises baffles or other structures that define a conduit or passageway to communicate the vacuum suction of the vacuum plenum  125  to a corresponding group of platen holes  127  in the vacuum platen  126 . Each duct  151  surrounds (fences in) a corresponding group of the platen holes  127 , such that the vacuum suction from the vacuum plenum  125  must be communicated through the respective duct  151  in order to be communicated to its corresponding group of platen holes  127 . Each duct  151  has an opening that can allow the coupling of the interior of the respective duct  151  with the rest of the vacuum plenum  125 . 
     As described above, each airflow zone  157  also has a valve  152 . Each valve  152  is positioned relative to the opening in the corresponding duct  151  such that when the respective valve  152  is open the interior of the corresponding duct  151  is communicably coupled to the rest of the vacuum plenum  125  and when the respective valve  152  is closed the interior of the corresponding duct  151  is not communicably coupled to (e.g., sealed off from) the rest of the vacuum plenum  125 . Thus, when a given valve  152  is open, the vacuum suction from the vacuum plenum  125  is communicated through the corresponding duct  151  to the corresponding group of platen holes  127 , and when the given valve  152  is closed the vacuum suction is not communicated through the corresponding duct  151  to the corresponding group of platen holes  127 . The state of an airflow zone  157  in which its corresponding valve  152  is open and vacuum suction is allowed through the corresponding platen holes  127  is referred to herein as the airflow zone  157  being “on.” The state of an airflow zone  157  in which its corresponding valve  152  is closed and vacuum suction is prevented through the corresponding platen holes  127  is referred to herein as the airflow zone  157  being “off.” 
     In an embodiment, the valves  152  comprise rotary valves movable between open and closed states by rotating a valve body of the valve  152 . The valves  152  may be operably coupled to one or more actuators (not illustrated) which actuate the valves  152  between the open and closed states. The actuator may be any device capable of imparting force/motion to the valves to actuate them between the open and closed states, such as an electronic motor, a pneumatic or hydraulic actuator, a solenoid, etc. The actuators may be part of the valves  152 , or they may be separate from the valves. In some embodiments, each valve  152  has its own actuator. In other embodiments, multiple valves  152  may share the same actuator. For example, multiple rotary valves  152  may be ganged to the same drive shaft, which is driven by a single actuator. Those having ordinary skill in the art are familiar with such rotary valves and actuators that can be used to actuate them between open and closed states. 
     The airflow zones  157  may be arranged at locations where it is desired to control airflow through the vacuum platen  126 . For example, in some embodiments at least some of the airflow zone  157  are provided at locations that are near (e.g., under) printheads  110 , to allow the airflow zones  157  to control suction around the printheads  110 . Such airflow zone  157  may be used to mitigate lead edge blur and trail edge blur as described above. In particular, such airflow zones  157  may be controlled to turn on and off based on the locations of print media (i.e., based on the locations of inter-media zones) relative to the respective airflow zones  157 . In some embodiments, the airflow zones  157  collectively cover at least all of the areas directly below all of the printheads  110 . When an airflow zone  157  is positioned (at least partially) below a printhead  110 , the airflow zone  157  may be referred to herein as corresponding to the printhead  110 . 
     As another example, in some embodiments at least some of the airflow zones  157  are positioned inboard of one or more of the printheads  110 . These airflow zones  157  may be sued to mitigate inboard edge blur, as described above. More specifically, in embodiments in which an edge of a print medium is registered to one side of the media transport device  103  (this form of registration is referred to herein as an “edge registration scheme”), an uncovered region appears inboard of the print media when smaller print media are used, as described above, and therefore in such embodiments some of the airflow zones  157  may be provided on an inboard side of the printheads  110  to mitigate the inboard edge blur that is caused by such uncovered regions. It is possible for other registration schemes to be used besides an edge registration scheme. For example, a print medium could be centered on the movable support surface. Thus, in embodiments in which an edge registration scheme is not used, airflow zones  157  may be provided at locations where the uncovered regions are expected to appear when smaller print media are used in view of the type of registration scheme that is used in that system. For example, in embodiments in which the print media is centered on the movable support surface, uncovered regions will appear adjacent to both lateral sides of the print media when smaller print media are used and therefore airflow zones  157  may be provided on both lateral sides of the media transport device  103 . Herein, it is assumed for convenience of discussion that an edge registration scheme is used, but it should be understood that everything said herein applies equally to systems in which other registration schemes are used, except that locations of some of the airflow zones  157  may be altered accordingly as described above. 
     In some embodiments, some of the airflow zones  157  that are located under a printhead  110  may be used both for mitigating lead/trail edge blur and also for mitigating inboard edge blur. For example, if the print medium being used is large enough to cover a particular airflow zones  157 , then the airflow zones  157  may be turned on and off based on the position of the inter-media zone to mitigate lead/trail edge blur. But if a smaller print medium were used such that the same airflow zones  157  is not covered by the print medium, then the airflow zone  157  may be turned off throughout printing of that smaller size print medium regardless of the location of the inter-media zone to mitigate inboard edge blur. 
     The sizes and locations of the airflow zones  157  may vary from one system to the next. In some embodiments, it may be beneficial for the airflow zones  157  to provide for controlling airflow independently around individual printheads, and thus in some embodiments airflow zones  157  that are positioned under printheads  110  have a width in the process direction that allows each printhead  110  to have its own corresponding set of airflow zones  157 , such as a width that is at most a little longer than a width of the printheads  110  in the process direction. The shorter the airflow zones  157  are in the process direction, the more fine-grained control may be had over airflow near the printheads  110 . However, the smaller the airflow zones  157  are, the more complicated and/or costly the system may become to manufacture and control, as smaller airflow zones  157  may require smaller valves  152  and actuators and also more numerous valves  152 . A person of ordinary skill in the art would understand that they can select a size for the airflow zones  157  for a particular printing system by balancing a desired granularity of control over airflow against other design goals and constraints for that system, such as the cost and availability of the valves  152  and actuators of various sizes. In some embodiments, each airflow zones  157  may have a width in the process direction corresponding to one row of holes  127 , such that suction through individual rows of holes  127  can be controlled independently by selectively turning on or off the corresponding airflow zones  157 . In some embodiments, each airflow zones  157  may have a width in the process direction corresponding to a group of multiple rows of platen holes  127 . In some embodiments, each airflow zones  157  may have a width in the process direction approximately equal to a width of a printhead. 
     The length of the airflow zones  157  in the cross-process direction may also vary from system to system, and also from airflow zone  157  to airflow zone  157  within the same system. For airflow zones  157  that are intended to mitigate lead/trail edge blur but are not intended to mitigate inboard edge blur, the length in the cross-process direction does not generally affect their ability to perform their intended function, and thus any length may be selected based on what is convenient in the given system. For example, the length of these airflow zones  157  may be selected based on the size of selected valves  152  and/or the number of holes  127  that can be supplied with sufficient suction given the impedance of the selected valve  152 . For example, if a given valve  152  has a particular impedance that would allow it to supply adequate suction to no more than n platen holes  127  (where n is an arbitrary integer number), then the lengths of the airflow zones  157  in the cross-process direction may be selected, in view of the length in the process direction, such that no more than n platen holes  127  are included in each airflow zone  157 . In some embodiments, a single airflow zone  157  may extend across a length of an entire printhead  110  in the cross-process direction. In some embodiments, the airflow zones  157  are shorter in the cross-process direction than a printhead  110  such that multiple airflow zones  157  cover one printhead  110  in the cross-process direction. In some embodiments, an individual airflow zone  157  may be provided with multiple valves  152  which are actuated together to reduce the impedance through the airflow zone  157 , which may allow the airflow zones  157  to be larger. 
     As noted above, in some circumstances the print medium may not fully cover the region of the movable support surface that contains the holes  121 , than thus may expose holes  121  and plate holes  127  adjacent to an inboard edge of the print medium. Thus, in some embodiments one or more airflow zones  157  are provided to mitigated inboard edge blur (either exclusively, or in conjunction with also mitigating lead/trail edge blur). For such airflow zones  157  that are intended to mitigate inboard edge blur, their lengths in the cross-process direction determine the relative location of the inboard edge IE of the print media with respect to the airflow zones  157 , which affects how well they can mitigate the inboard edge blur and provide hold down force. In particular, optimal blur mitigation and hold down force may be achieved, in some circumstances, when the inboard edge of the print medium is located (in the cross-process direction) at or near the boundary between two airflow zones  157 , while less optimal blur mitigation and/or hold down force may occur when the inboard edge is located in the middle of an airflow zone  157 . Thus, the airflow zone  157  that are intended to mitigate inboard edge blur may have lengths in the cross-process direction that are chosen to facilitate the mitigating of inboard edge blur, and they may have different lengths than the other airflow zones  157  which do not mitigate inboard edge blur. To maximize effectiveness at mitigating inboard edge blur while also not reducing the hold down force on the print media, the lengths of the airflow zones  157  in the cross-process direction may be set such that, for each size of print media the system is designed to use, the inboard edge of the print media falls along a boundary between two adjacent airflow zones  157 . This ensures that uncovered holes  127  inboard of the print media can be prevented from sucking in air (by turning off the airflow zone  157  that is immediately inboard of the inboard edge of the print media) while allowing suction through all of the holes  127  that are covered by the print media (by turning on the airflow zones  157  that are outboard of the inboard edge of the print media). Thus, in such a situation, crossflows along the inboard edge can be mitigated without reducing the hold down force on the print media. 
     In some embodiments, it may not be feasible or desired to have a perfect correspondence between the edges of the airflow zones  157  and each size of print media. For example, in some systems it might not be feasible to make airflow zones  157  that are short enough in the cross-process direction to perfectly match every size of print media, given the constraints and design goals of that printing system. Thus, in some embodiments, the airflow zones  157  may be sized to correspond to certain sizes of print media, such as frequently used sizes of print media, while not necessarily corresponding to all sizes of print media. In other embodiments, the airflow zones  157  may be provided with lengths in the cross-process direction that are not based on specific sizes of print media, such as each airflow zone  157  having a fixed length. In situations in which the inboard edge of the selected print media falls partway within an airflow zone  157 , rather than along the boundary between two airflow zones  157 , the system may decide whether to turn on or off that particular airflow zone  157  based on whether blur mitigation or hold down force is prioritized. If blur mitigation is prioritized, then the airflow zone  157  intersected by the edge of the print media may be turned off to ensure no crossflows are induced, at the cost of reducing the hold down force near the edge of the print media because some of the holes  127  corresponding to the airflow zone  157  are covered by the print media but are not provided with vacuum suction. If hold down force is prioritizes, then the airflow zone  157  intersected by the edge of the print media may be turned on to ensure all of the platen holes  127  thar are covered by the print media are provided with vacuum suction, at the cost of allowing some uncovered holes  127  to suction in air and thus induce some crossflows. The airflow control logic  155  may select between these priorities based on any of: a default programed priority, a user selection, the location of the inboard edge relative to the airflow zone  157  (e.g., if the print media covers a predetermined amount of the airflow zone  157  then the airflow zone  157  is turned on, while otherwise the airflow zone  157  is turned off), feedback of an amount of blur that is detected in printed images, of other detected conditions. 
     The determinations of which airflow zones  157  should be on or off and the timings for turning the airflow zones  157  on or off are described in greater detail below in relation to the control system  130 . 
     The control system  130  comprises processing circuitry to control operations of the printing system  100 . The processing circuitry may include one or more electronic circuits configured with logic for performing the various operations described herein. The electronic circuits may be configured with logic to perform the operations by virtue of including dedicated hardware configured to perform various operations, by virtue of including software instructions executable by the circuitry to perform various operations, or any combination thereof. In examples in which the logic comprises software instructions, the electronic circuits of the processing circuitry include a memory device that stores the software and a processor comprising one or more processing devices capable of executing the instructions, such as, for example, a processor, a processor core, a central processing unit (CPU), a controller, a microcontroller, a system-on-chip (SoC), a digital signal processor (DSP), a graphics processing unit (GPU), etc. In examples in which the logic of the processing circuitry comprises dedicated hardware, in addition to or in lieu of the processor, the dedicated hardware may include any electronic device that is configured to perform specific operations, such as an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Complex Programmable Logic Device (CPLD), discrete logic circuits, a hardware accelerator, a hardware encoder, etc. The processing circuitry may also include any combination of dedicated hardware and general-purpose processor with software. 
     The control system  130  also comprises a location tracking system  132 , which may be used to track the locations of the inter-media zones and/or print media as the print media are transported through the ink deposition assembly. As used herein, tracking the location of the inter-media zones or the print media refers to the system having knowledge, whether direct or inferred, of where the print media are located at various points as they are transported through the ink deposition assembly  101 . Direct knowledge of the locations of the inter-media zones or print media may comprise information obtained by directly observing the print media, for example via one or more sensors (e.g., an edge detection sensor). Inferred knowledge of the locations of the inter-media zones or print media may be obtained by inference from other known information, for example by calculating how far a print medium would have moved from a previously known location based on a known speed of the movable support surface  120 . In some embodiments, the location tracking system may explicitly track locations of the inter-media zones, the lead edges LE of print media, and/or the trail edges TE of print media. In other embodiments, the location tracking system may explicitly track the locations of some other parts of the print medium. Because the locations of the inter-media zones depend deterministically on the locations of the print media and on the dimensions of the print media (which are known to the control system  130 ), tracking the locations of some arbitrary part of the print media is functionally equivalent to tracking the locations of the inter-media zones  122 . 
     Most existing printing systems are already configured to track the locations of the print media as they are transported through the ink deposition assembly, as knowledge of the locations of the print media may be helpful to ensure accurate image formation on the print media. Thus, various systems for tracking the locations of print media are well known in the art. Because such location tracking systems are well known, they will not be described in detail herein. Any known location tracking system (or any new location tracking system) may be used as the location tracking system  132  in the embodiments disclosed herein to track the location of print media. 
     The processing circuitry of the control system  130  is also configured with airflow control logic  155 , among other things. The airflow control logic  155  controls which airflow zones  157  are on or off, as well as timings for turning the airflow zones  157  on and off. The airflow control logic  155  may receive information indicating the size of the print media currently being used or currently selected for upcoming use, and the locations of the inter-media zones as they move through the media transport device  103  (or the locations of the print media being transported through the media transport device, from which the locations of the inter-media zones can be deduced). The airflow control logic  155  also generates control signals to open or close the corresponding valves  152  at the determined timings. 
     Based on the size of the print media currently being used or selected for use, the airflow control logic  155  determines where the inboard edge of the print media will be located relative to the airflow zones  157 . Based on the location the inboard edge relative to the airflow zones  157 , the airflow control logic  155  can determine which ducts  155  to keep off throughout the printing process regardless of the location of the inter-media zone, and which airflow zones  157  can be allowed to remain on and be subjected to further control based on the location of the inter-media zone. Each airflow zone  157  that is fully inboard of the inboard edge may be turned off throughout printing, while each airflow zone  157  that is fully outboard of the inboard edge may be left on (and subjected to further control based on the location of the inter-media zone). If the inboard edge of the print media falls midway within any airflow zones  157 , then the intersected airflow zones  157  may be turned on or turned off based on whether blur mitigation or hold down force are prioritized, as described above. If the size of the print media being used changes, then the airflow control logic  155  repeats the process of determining which airflow zones  157  should be turned off based on the new size of print media and sends the appropriate control signals to adjust which airflow zones  157  are off as needed. 
     For the airflow zones  157  that are not turned off based on the size of the print media, the airflow control logic  155  determines the timings when these airflow zones  157  should be turned on/off based on the location of the inter-media zone  122 , or in other words based on the locations of the lead edges LE and trail edges TE of the print media. Specifically, airflow control logic  155  actuates the valves  152  at timings that correspond to particular positions of the inter-media zone  122 . In other words, particular positions of the inter-media zone  122  are used as triggers for closing and opening each valve  152 . In some embodiments, individual airflow zones  157  can be independently controlled, i.e., their respectively associated valves  152  can be independently actuated between open and closed states. In some embodiments, some ducts may be grouped together such that ducts in the same group are all turned on or off together, and the various groups of airflow zones  157  may be independently controlled. The positions used to trigger actuation of the valves  152  may be predetermined parameters which are programmed into a memory associated with the airflow control logic  155  and remain static during operation, or the positions may be dynamic parameters which can be automatically varied/updated during run-time. are turned off at timings that are determined based on the location of the inter-media zone. 
     Generally, the airflow control logic  155  may turn off a given airflow zone  157  when the inter-media zone is located over the airflow zone  157  and may turn the given airflow zone  157  back on once the inter-media zone has advanced past the duct. More specifically, in some embodiments, each airflow zone  157  is turned off when the downstream edge of the inter-media zone (which corresponds to the trail edge TE of a print medium) is at an upstream trigger location associated with the airflow zone  157 . Conversely, each airflow zone  157  is turned on the upstream edge of the inter-media zone (which corresponds to the lead edge LE of a print medium) is at a downstream trigger location associated with the airflow zone  157 . In some embodiments, the upstream trigger location associated with a given airflow zone  157  is an upstream edge of the airflow zone  157  and the downstream trigger location associated with the airflow zone  157  is a downstream edge of the airflow zone  157 . In some embodiments, the upstream trigger location associated with a given airflow zone  157  is any predetermined position on an upstream side of the airflow zone  157 , while the downstream trigger location associated with the given airflow zone  157  is any predetermined position on a downstream side of the airflow zone  157 . In some embodiments, upstream and downstream trigger location correspond to portions of other components of the printing system, such as an upstream or downstream face of the printhead  110 , an upstream or downstream edge of an ink deposition region of a printhead, etc. 
     Thus, by controlling the airflow zones  157  as described above, airflow may be blocked throughout the inter-media zone as the inter-media zone moves through the ink deposition assembly, thereby reducing crossflows near the lead and trail edges of the print media. Moreover, airflow is also blocked or reduced through the unblocked holes  127  on an inboard side of the print media, and therefore crossflows are reduced long the inboard edge of the print media. With crossflows reduced or eliminated near the lead, trail, and inboard edges, image blur near these edges is reduced. These phenomena are discussed in greater detail below with reference to  FIGS.  5 A- 6 C . 
     Although preventing suction through the holes  127  reduces crossflows, an issue associated with preventing suction through the holes  127  is that this can interfere with the hold down force being applied to the print media. For example, if the holes  127  near the printheads  110  were permanently blocked or eliminated entirely, this would permanently reduce or eliminate all hold down force in the vicinity of the printheads  110 , which might in some circumstances result in the leading edge of a print medium rising off the movable support surface  120 , potentially causing jams in the printing system and/or less accurate printing of images on the print medium. In contrast, in the approach described above, each airflow zone  157  is turned off only for a relatively brief period of time corresponding generally to the time it takes for the inter-media zone  122  to move past the airflow zone  157 . Moreover, at any given time the number of holes  127  that are covered by print media but prevented from providing suction to the print media is relatively low, since only a few airflow zones  157  are turned off at any given time and each airflow zone  157  corresponds to a relatively small number of holes. Thus, using the approaches described herein, there is generally sufficient hold down force applied to the print media at any given time to reduce the risk of the print media rising off the movable support surface  120  to an acceptably small level. In systems in which hold down force is of particular concern, the amount with which the airflow zones  157  reduce the hold down force can be tuned by adjusting the width and number of the airflow zones  157  in the process direction. Providing narrower and more numerous airflow zones  157  in the process direction may allow for more fine-grained control of turning the airflow zones  157  on and off following the movements of the inter-media zone, thus recuing the degree to which the airflow zones  157  interfere with the hold down force. 
       FIGS.  3 - 6 C  illustrate another embodiment of a printing system  300 , which may be used as the printing system  100  described above with reference to  FIG.  2   .  FIG.  3    comprises a schematic illustrating a portion of the printing system  300  from a side view.  FIG.  4    comprises a partial plan view from above a portion of the printing system  300  and depicting only a single printhead module  302 . In  FIG.  4   , some components that would not otherwise be visible in the view because they are positioned below other components are illustrated with dashed or dotted lines.  FIGS.  5 A- 5 F  comprise cross-sections of the printing system  300  with the section taken along line D-D in  FIG.  4   , with each of  FIGS.  5 A- 5 F  showing a sequence of states as the print media  305 _ 1  and  305 _ 2  are transported past one of the printhead modules  302 .  FIGS.  6 A- 6 C  comprise cross-sections of the printing system  300  with the section taken along line E-E in  FIG.  4   , with  FIGS.  6 A- 6 C  illustrating various different states. 
     As illustrated in  FIG.  3   , the printing system  300  comprises an ink deposition assembly  301 , a media transport device  303 , and an airflow control system  350 , which can be used as the ink deposition assembly  101 , media transport device  103 , and airflow control system  150 , respectively, which were described above with reference to  FIG.  2   . The printing system  300  may also comprise additional components not illustrated in  FIGS.  3 - 6 B , such as a control system (e.g., similar to control system  130 ) including airflow control logic (e.g., similar to airflow control logic  155 ). 
     In the printing system  300 , the ink deposition assembly  301  comprises four printhead modules  302  as shown in  FIG.  3   , with each module  302  having three printheads  310  (e.g., printheads  310 _ 1  through  310 _ 3 ) as shown in  FIG.  4   . As shown in  FIGS.  3  and  4   , the printhead models  302  are arranged in series along a process direction P above the media transport device  303 , such that the print media  305  is transported sequentially through an ink deposition region  323  of the ink deposition assembly, i.e., beneath each of the printhead modules  302 . The printheads  310  are arranged to eject print fluid (e.g., ink) through respectively corresponding openings  319  in a corresponding carrier plate  311  (shown in  FIG.  4   ), with a bottom end of the printhead  310  extending down partway into the opening  319 . In this embodiment, the printheads  310  are arranged in an offset manner with one of the printheads  310  being further upstream or downstream than the other two printheads  310  of the same printhead module  302 . Those having ordinary skill in the art would understand that other embodiments within the scope of the disclosure could have different numbers and/or arrangements of printheads  310  and/or printhead modules  302  are used, which may be selected based on a particular system or application. 
     In the printing system  300 , media transport device  303  comprises a flexible belt providing the movable support surface  320 . As shown in  FIG.  3   , the flexible belt comprising the movable support surface  320  is driven by rollers  329  (the number and arrangement of which in  FIG.  3    is nonlimiting as those of ordinary skill in the art would appreciate) to move along a looped path, with a portion of the path passing through the ink deposition region  323  of the ink deposition assembly  301 . Furthermore, in this embodiment, the vacuum plenum  325  comprises a vacuum platen  326 , which forms a top wall of the plenum  325  and supports the movable support surface  320 . The platen  326  comprises platen holes  327 , which allow fluidic communication between the interior of the plenum  325  and the underside of the movable support surface  320 . 
     In some embodiments, the platen holes  327  may include channels on a top side thereof, as seen in the expanded cutaway  3 A of  FIG.  3   , which may increase an area of the opening of the platen holes  327  on the top side thereof. Specifically, the platen holes  327  may include a bottom portion  327   a  which opens to a bottom side of the platen  326  and a top potion  327   b  which opens to a top side of the platen  326 , with the top portion  327   b  being differently sized and/or shaped than the bottom portion  327   a . For example,  FIGS.  3 - 6 C  illustrate an embodiment of the platen holes  327  in which the top portion  327   b  is a channel elongated in the process direction while the bottom portion  327   a  is a through-hole that is less-elongated and has a smaller sectional area (see the enlargement D in  FIG.  3    and the dashed-lines in  FIG.  4   ). In some embodiments, multiple platen holes  327  may share the same top portion  327   b , or in other words multiple bottom portions  327   a  may be coupled to the same top portion  327   b . References herein to the airflow zones  357  blocking a platen hole  327  refer to blocking at least the bottom portion  327   a  of the platen hole  327 . 
     The platen holes  327  are arranged in columns extending in the process direction P (y-direction shown in  FIGS.  3  and  4   ) and rows extending in a cross-process direction (the x-direction shown in the  FIGS.  3  and  4   ), with each column comprising a group of holes  327  that are aligned with one another in the process direction P and each row comprising a group of one or more holes  327  aligned with one another in a cross-process direction. In some embodiments, the columns and rows are arranged in a regular grid, but in other embodiments the columns and rows are arranged in another manner that does not form a regular grid. For example, in some embodiments, such as the embodiment of  FIG.  4   , the holes  327  (top portion  327   b , bottom portions  327   a , or both) of two adjacent columns may be offset or staggered from one another in the process direction P. In other words, a hole  327  in one column may not be aligned in the cross-process direction with any holes  327  in an adjacent column. Similarly, in some embodiments the holes  327  (top portion  327   b , bottom portion  327   a , or both) of two adjacent rows are offset or staggered from one another in the cross-process direction. In other words, a hole  327  in one row may not be totally aligned in the process direction with any holes  327  in an immediately adjacent row. In some embodiments, the holes  327  (top portion  327   b , bottom portion  327   a , or both) in each individual column are arranged with uniform spacing in the process direction, but in other embodiments some or all of the holes  327  in one or more columns may have non-uniform spacings. In some embodiments, the holes  327  (top portion  327   b , bottom portion  327   a , or both) in each individual row are arranged with uniform spacing in the cross-process direction, but in other embodiments some or all of the holes  327  in one or more rows may have non-uniform spacings. In some embodiments, each column has the same number of holes  327  as the other columns and/or each row has the same number of holes  327  as the other rows, but in some embodiments some or all of the columns and/or rows have differing numbers of holes  327 . In embodiments in which the holes  327  have bottom portions  327   a  and top portions  327   b  with different shapes/sizes, references herein to the holes  327  being aligned refer to the bottom portions  327   a  of the holes being  327  aligned. 
     The holes  321  of the movable support surface  320  are disposed such that each hole  321  is aligned in the process direction P (y-axis direction) with a collection of corresponding platen holes  327 . In other words, in the printing system  300 , each hole  321  is aligned in the with one of the columns of platen holes  327 . Thus, as the movable support surface  320  slides across the platen  326 , each hole  321  in the movable support surface  320  will periodically move over a corresponding platen hole  327 , resulting in the movable support surface hole  321  and the platen hole  327  being temporarily vertically aligned (i.e., aligned in a z-axis direction). When a hole  321  of the movable support surface  320  moves over a corresponding platen hole  327 , the holes  321  and  327  define an opening that fluidically couples the environment above the movable support surface  320  to the low-pressure state in the vacuum plenum  325 , thus generating vacuum suction through the holes  321  and  327 . This suction generates a vacuum hold down force on a print medium  305  if the print medium  305  is disposed above the hole  321 . 
     As shown in  FIGS.  3 - 6 B , the airflow control system  350  comprises airflow zones  357 , which may be used as the airflow zones  157  described above in relation to  FIG.  2   . The airflow zones  357  each comprise a group of the platen holes  327 , a duct  351  that surrounds outlet openings of the group of platen holes  327  to control airflow through the group of platen holes  327 , and a valve  352  to control airflow through the duct  351 . The ducts  351  and valves  352  of  FIGS.  3 - 6 B  may be used as the ducts  151  and valves  152  described above in relation to  FIG.  2   . An example arrangement of airflow zones  357  is illustrated in  FIGS.  3 - 6 C  with respect to one printhead module  302 . Similar arrangements of airflow zones  357  may be provided for the other printhead modules  302  of the printing system  300 . The arrangement illustrated in  FIGS.  3 - 6 C  is merely an example, and in other embodiments any number of airflow zones  357  may be provided and they may have different sizes, shapes, and locations than those illustrated. The description above of how the locations and sizes of airflow zones  157  may be selected is applicable to selecting locations and sizes for the airflow control zones  351 . 
     As shown in  FIGS.  3  and  5 A- 6 C , in the printing system  300 , the airflow zones  357  are created by the actuatable valving  352  and segregated ducts  351  disposed against a bottom surface of the platen  326  to provide selective communication with the vacuum plenum  325 . As shown in  FIGS.  4 - 6 C , a number of the airflow zones  357  are located directly under the printheads  310  (e.g., airflow zones  357 _ 1  through  351 _ 11  and  351 _ 13  through  351 _ 16 ). In this embodiment, the airflow zones  357  have a width in the process direction that is slightly longer than the openings  319  in the carrier plate  311  through which the printheads  310  eject ink. In other embodiments narrower airflow zones  357  may be used, for example, with two rows of airflow zones  357  being provided for each printhead  310 . 
     In addition, some airflow zones  357  may be provided that are not located under any printhead  310 , such as the airflow zone  357 _ 12 . Such airflow zones  357  may be provided, for example, to combat inboard edge blur. The number and location of such airflow zones  357  that are not located under a printhead  310  may vary from system to system based on the needs of the system, such as the sizes of print media that are to be used and the amount of image blur that is deemed acceptable. In the embodiment of  FIGS.  3 - 6 C , the airflow zone  357 _ 12  is provided inboard of the printhead  310 _ 3  to mitigate inboard edge blur resulting from ink ejected by the printhead  310 _ 3  in situations in which inboard edge IE of the print media is near the edge of the printhead  310 _ 3  (see  FIG.  4   ). In the embodiment of  FIGS.  3 - 6 C , just one airflow zone  357  is provided inboard of the printhead  310 _ 3 , but in other embodiments additional airflow zones  357  could be provided on the inboard side of the printhead  310 _ 3  along with the airflow zone  357 _ 12 . In some embodiments (not illustrated), airflow zones  357  that are not located under a printhead  310  may include airflow zones  357  disposed in the region between the printheads  310 _ 1  and  310 _ 2 . Such airflow zones  357  may be particularly useful, for example, in systems in which it is possible or likely for the inboard edge of the print media to fall between the printheads  310 _ 1  and  310 _ 2 . However, if desired the airflow zones  357  can also be omitted from the space between the printheads  310 _ 1  and  310 _ 2 , such as in the embodiment illustrated in  FIGS.  3 - 6 C . Omitting the airflow zones  357  between the printheads  310 _ 1  and  310 _ 2  may be particularly suitable, for example, in systems in which it is unlikely for the inboard edge IE of the print media to fall between the printheads  310 _ 1  and  310 _ 2 . 
     As shown in  FIGS.  5 A- 6 C , the ducts  351  comprise walls that define passageway or conduit having one end that opens to the bottom side of the platen  326  and another end that opens to the interior of the vacuum plenum  325 . A corresponding valve  352  is positioned at an opening of the duct  351  to control airflow through the duct  351  (and hence control airflow through the airflow zone  357 ). As shown in  FIGS.  5 A- 6 C , each of the valves  352  comprise an outer valve body  353  and an inner valve body  354  disposed within the outer valve body  353 . The inner valve body  354  has a passageway  356  extending diametrically through the body  354 . The inner valve body  354  is rotatable relative to the outer valve body  353  to an open state of the valve  352  in which the passageway  356  is aligned with openings in the outer valve body  353 , thus allowing airflow through the valve  352  via the passageway  356 . In the open state, the passageway  356  places the interior of the duct  351  in fluidic communication with the vacuum plenum  325  (see, e.g., the valve  352 _ 2  in  FIG.  6 A ). The inner valve body  354  is also rotatable relative to the outer valve body  353  to a closed state of the valve  352  in which the passageway  356  is not aligned with the openings in the outer valve body  353  and the inner and outer valve bodies  353  and  354  seal the interior of the duct  351  from the vacuum plenum  325  (see, e.g., the valve  352 _ 1  in  FIG.  6 A ). As shown in  FIGS.  6 A- 6 C , each valve  352  may be selectively actuated between the open and closed states by a drive shaft driven by an actuator  353 . Some valves  352  may have their own individual actuator  353 , such as the actuator  353 _ 1  which actuates the valve  352 _ 1  in  FIG.  6 A- 6 C . Other valves  352  may share an actuator  353  amongst multiple valves  352 , such as the valves  352  of the airflow zones  357 _ 6  to  357 _ 9  in  FIG.  6 A- 6 C  which all share the same actuator  353 _ 2  (i.e., the valves  352  are all coupled to the same drive shaft  354 , which is driven by the actuator  353 _ 2 ). 
     In some embodiments, individual control of valves  352  may be provided even without providing each valve  352  with its own actuator  353 . For example, a group of valves  352  could be ganged together on the same drive shaft  354  and share the same actuator  353 , similar to the valves  352  of the airflow zones  357 _ 6  to  357 _ 9  in  FIGS.  6 A- 6 C , but could be individually controlled by providing mechanisms at each of the valves  352  to allow selective coupling and decoupling of the valves from the drive shaft  354 . Thus, if a given airflow zone  357  is to be turned off due to the location of the inboard edge IE of the print media  305 , then the valve  352  of that airflow zone  357  can be moved to the closed stated and then it can be decoupled from the drive shaft  354  such that subsequent actuations of the shaft  354  to open the other ganged valves  352  (e.g., based on the location the inter-media zone  322 ) do not result in the decoupled valve  352  from opening. 
     As shown in  FIGS.  4  and  6 A , the lengths of the airflow zones  357  in the cross-process direction (x-axis direction) are not necessarily the same for each airflow zone  357 . For example, considering  FIG.  6 A , the airflow zones  357 _ 1  to  357 _ 5  are shorter in the cross-process direction than the airflow zones  357 _ 6  to  357 _ 9 . In this embodiment, the length of the airflow zones  357 _ 1  to  357 _ 5  in the cross-process direction is controlled such that edges of the airflow zones  357 _ 1  to  357 _ 5  correspond to locations of the inboard edges IE of different sizes of print medium  305 , such as the print mediums  305 _ 3  and  305 _ 4  illustrated in  FIGS.  6 A and  6 B . Moreover, by having the length of the airflow zones  357 _ 1  to  357 _ 5  in the cross-process direction be relatively short, in the event that the inboard edge IE of a print medium  305  falls in the middle of an airflow zone  357 , the area of overlap is kept relatively small and thus only a small region will be allowed to suction air if the overlapped airflow zone  357  is turned on or only a small region will have its hold down force reduced if the overlapped airflow zone  357  is turned off. The airflow zones  357 _ 6  to  357 _ 9 , on the other hand, are not intended to address inboard edge blur and do not need to align with the inboard edges of print media  305 , and thus they may be relatively long in the cross-process direction. Moreover, because the airflow zones  357 _ 6  to  357 _ 9  are aligned in the cross-process direction and because they are not intended to address inboard edge blur, the airflow zones  357 _ 6  to  357 _ 9  do not necessarily need to be individually controllable and thus can be configured to all be controlled to turn on or turn off together, as described above. 
     In the printing system  300 , the determination of which airflow zones  357  to turn on or off and the timings for doing so are similar to those described above with respect to the ducts  151 . In particular, a specific example of the timings for turning on and off airflow zones  357  based on the location of the inter-media zone  322  is described below with reference to  FIGS.  5 A- 5 F , which illustrate various positions of the inter-media zone  322  at which closing or opening of the airflow zones  357  are triggered. As noted above, each airflow zone  357  has a first (upstream) trigger location and a second (downstream) trigger location associated with it, and the airflow zone  357  is turned off (its valve  352  is closed) when the inter-media zone  322  reaches a position associated with the first trigger location and is turned back on (its valve  352  is opened) when the inter-media zone  322  reaches a position associated with the second trigger location.  FIGS.  5 A- 5 F  illustrate trigger locations of one embodiment, but in other embodiments different trigger locations are used. The first and second trigger locations may be any predetermined locations. 
     Note that, in practice, it takes a finite amount of time for the valves  352  to fully close or open, and during this time while a valve  352  is closing or opening the inter-media zone  322  continues to move. Thus, in some embodiments, to ensure that the airflow zone  357  is fully off or fully on when the inter-media zone  322  reaches a desired trigger location (“nominal trigger location”), the corresponding valve  352  may need to start closing or opening shortly before the inter-media zone  322  actually reaches the nominal trigger location. In other words, an actual trigger location that is used to trigger the closing or opening may be offset from the nominal trigger location by some fixed amount to account for the finite amount of time it takes the valves  352  to close or open. The known speed of the movable support surface  320  and a known actuation time for the valves  352  may be used to determine the offset. To simplify the description, only the nominal trigger locations are discussed below. 
     In the embodiment of  FIGS.  5 A- 5 F , the trigger locations for each airflow zone  357  correspond to upstream and downstream edges of the respective airflow zone  357 .  FIG.  5 A  illustrates the inter-media zone  322  in a first position. The first position corresponds to the downstream edge of the inter-media zone  322  (i.e., the trail edge TE of the print medium  305 _ 1 ) reaching a first trigger location associated with the airflow zone  357 _ 6 . Specifically, the inter-media zone  322  reaches the first trigger location when the trail edge TE of the print medium  305 _ 1  is at (i.e., vertically aligned with) the upstream edge of the airflow zone  357 _ 6 . Thus, at (or shortly before) the timing when the inter-media zone  322  reaches the first trigger location, the controller causes the valve  352 _ 6  to close, placing the airflow zone  357 _ 6  in the off state. In the state illustrated in  FIG.  5 A , the other airflow zones  357  associated with the same printhead module  302  are not closed because the inter-media zone  322  has not yet arrived at the trigger locations associated with those airflow zones  357 . 
       FIG.  5 B  illustrates the inter-media zone  322  at a second position in which the trail edge TE of the print medium  305 _ 1  is about midway under the printhead  310 _ 1 . This position is similar to the position of the inter-media zone  22  in  FIG.  1 A . As described above with respect to  FIG.  1 A , if countermeasures are not taken, then in this state the inter-media zone  322  is likely to pull air from the downstream side of the printhead  310 _ 1  through the ink deposition region  312  of the printhead  310 _ 1  and thus create crossflows that cause image blur. However, in contrast to the situation illustrated in  FIG.  1 A , in  FIG.  5 B  the airflow zone  357 _ 6  is turned off (i.e., the valve  352 _ 6  is in the closed state) and thus air cannot be suctioned through the holes  327  that are associated with the airflow zone  357 _ 6 . Thus, crossflows are prevented or reduced. In the state illustrated in  FIG.  5 B , a portion of the inter-media zone  322  is not blocked by the airflow zone  357 _ 6 , and thus some air is suctioned through the inter-media zone  322 , as indicated by the dash-lined arrow. However, the unblocked portion of the inter-media zone  322  is relatively distant from the downstream side of the printhead  310 _ 1  and has access to air from the upstream side of the printhead module  302 , and thus this portion of the inter-media zone  322  is unlikely to have much of an influence on the air underneath and/or downstream of the printhead  310 _ 1 . 
       FIG.  5 C  illustrates the inter-media zone  322  at a third position. The third position corresponds to the downstream edge of the inter-media zone  322  (i.e., the trail edge TE of the print medium  305 _ 1 ) reaching a first trigger location associated with the airflow zone  357 _ 16 . Specifically, the inter-media zone  322  reaches this trigger location when the trail edge TE of the print medium  305 _ 1  is at the upstream edge of the airflow zone  357 _ 16 . Thus, at (or shortly before) the timing when the inter-media zone  322  reaches the third position, the controller causes the valve  352 _ 16  associated with the airflow zone  357 _ 16  to close, placing the airflow zone  357 _ 16  in the off state. The airflow zone  357 _ 6  remains off in this state because the inter-media zone  322  has not yet fully passed it. 
     In the state illustrated in  FIG.  5 C , lead edge LE of the print media  305 _ 2  is under the printhead  310 _ 1 . This state is similar to the state illustrated in  FIG.  1 D . As described above with respect to  FIG.  1 D , if countermeasures are not taken, in this state the inter-media zone  322  is likely to suck air from the upstream side of the printhead  310 _ 1 , which will cross through the ink-deposition region  312  of the printhead  310 _ 1  and thus form a crossflow that can cause image blur. However, in contrast to the situation illustrated in  FIG.  1 D , in  FIG.  5 C  the airflow zone  357 _ 6  is turned off (i.e., by virtue of the valve  352 _ 6  being in the closed state) and thus air cannot be suctioned through the holes  327  that are associated with the airflow zone  357 _ 6 . Thus, the aforementioned crossflows are prevented or reduced. 
       FIG.  5 D  illustrates the inter-media zone  322  at a fourth position. The fourth position corresponds to the upstream edge of the inter-media zone  322  (i.e., the lead edge LE of the print medium  305 _ 2 ) reaching a second (downstream) trigger location associated with the first airflow zone  357 _ 6 . Specifically, the inter-media zone  322  reaches this trigger location when the lead edge LE of the print medium  305 _ 2  is at the downstream edge of the airflow zone  357 _ 6 . Thus, at (or shortly before) the timing when the inter-media zone  322  reaches the fourth position, the controller causes the valve  352  associated with the airflow zone  357 _ 6  to move to the open state, placing the airflow zone  357 _ 6  in the on state. Because the airflow zone  357 _ 6  is placed in the on state, vacuum suction resumes being applied to the print medium  305 _ 2  in that region. Thus, for a period of time while the lead edge LE moved over the airflow zone  357 _ 6 , the print medium  305 _ 2  is not subjected to hold down force in the vicinity of the airflow zone  357 _ 6 . However, because suction resumes through the airflow zone  357 _ 6  as soon as the lead edge LE of the print medium  305 _ 2  passes the airflow zone  357 _ 6 , the period in which the lead edge LE is subjected to reduced hold down force is relatively brief. Moreover, other portions of the print medium  305 _ 2  are also subjected to hold down suction while the lead edge LE is traversing the airflow zone  357 _ 6 , and between this and the relatively brief duration of the reduced suction, the print medium  305 _ 2  is unlikely to lift off of the movable support surface  320 . 
     In the state illustrated in  FIG.  5 D , the second airflow zone  357 _ 16  remains off because the inter-media zone  322  has not yet fully passed it. In particular, in this state the trail edge TE of the print medium  305 _ 1  is under the printhead  310 _ 3 . This position is similar to the position of the inter-media zone  22  in  FIG.  1 A , and in this position the inter-media zone  322  would normally create crossflows from the downstream side of the printhead  310 _ 3  to flow under the printhead  310 _ 3  toward the inter-media region  322 . However, because the airflow zone  357 _ 16  is off, such crossflows are prevented or reduced. Similarly, as shown in  FIG.  5 E , when the inter-media zone  322  advances further downstream to a fifth position at which the lead edge LE of the print medium  305 _ 2  is under the printhead  310 _ 3 , the airflow zone  357 _ 16  being off prevents the crossflows that might have otherwise been induced in this state (see discussion of  FIG.  1 D  above for how crossflows would otherwise be induced in this state). 
       FIG.  5 F  illustrates the inter-media zone  322  at a sixth position. The sixth position corresponds to the upstream edge of the inter-media zone  322  (i.e., the lead edge LE of the print medium  305 _ 2 ) reaching a second (downstream) trigger location associated with the second airflow zone  357 _ 16 . Specifically, the inter-media zone  322  reaches this trigger location when the lead edge LE of the print medium  305 _ 2  is at the downstream edge of the airflow zone  357 _ 16 . Thus, at (or shortly before) the timing when the inter-media zone  322  reaches the sixth position, the controller causes the valve  352 _ 16  associated with the airflow zone  357 _ 16  to open, placing the airflow zone  357 _ 16  in the on state. Because the airflow zone  357 _ 16  is placed in the on state, vacuum suction resumes being applied to the print medium  305 _ 2  in that region. 
     After the state illustrated in  FIG.  5 F , the airflow zones  357 _ 6  and  351 _ 16  are kept in the on state so that they can continue provide vacuum suction to hold down the print media  305 . The airflow zones  357 _ 6  and  351 _ 16  may be kept in the on state until a next inter-media zone  322  approaches the printhead module  302 , whereupon the cycle is repeated. 
     Although the actuation timings of just two airflow zones  357 _ 6  and  351 _ 16  are described above with reference to  FIGS.  5  and  6   , it should be understood that similar actuation timings apply to the other airflow zones  357  in the printing system  300 . Airflow zones  351  that are aligned in the cross-process direction may be actuated at the same timings as one another, except for those airflow zones  357  that are to be kept off throughout the printing process due to the size of the print media  305  to prevent crossflows due to exposed inboard edges as have been described. 
       FIGS.  6 A- 6 C  show cross-sections taken along E in  FIG.  4   , which illustrate various states of the printing system  300 . In  FIGS.  6 A- 6 C , airflow zones  357  are depicted in the off state and on state, with the off state being indicated in these figures by an X through the airflow zone  357 . The on state of an airflow zone  357  is indicated in these figures by the absence of the X and the presence of a dash-lined arrow indicating airflow through the airflow zone  357 . 
     In  FIG.  6 A , the print medium  305 _ 3  is being used, and the size of this print medium  305 _ 3  is such that its inboard edge IE lands between the first and second airflow zones  357 _ 1  and  351 _ 2 . Thus, the airflow control system  350  turns off each airflow zone  357  that is inboard of the inboard edge IE, namely the airflow zone  357 _ 1 , throughout printing regardless of the location of the inter-media zone  322 . The other the airflow zones  357  that are outboard of the inboard edge IE are allowed to remain on and are subjected to the above-described control related to the location of the inter-media zone  322 . Thus, suction through the uncovered platen holes  327  in the uncovered region  324  adjacent the inboard edge IE of the print medium  305 _ 3  is prevented, thereby eliminating or reducing the crossflows that would otherwise have been induced by the uncovered region  324 , while still maintaining full hold-down force along the print medium  305 _ 3  (see the discussion of  FIG.  1 G  above for how the crossflows would otherwise have been induced). 
     If a different size of print medium is used, then the airflow control system  350  determines anew which airflow zones  357  to turn off. For example, as illustrated in  FIG.  6 B , if a print medium  305 _ 4  is used that is sized such that its inboard edge IE lands between the airflow zones  357 _ 3  and  351 _ 4 , then the airflow zones  357 _ 1  through  351 _ 3  are turned off throughout printing regardless of the location of the inter-media zone  322 , while the remaining airflow zones  357  are allowed to remain on. Those having ordinary skill in the art would understand how to selectively turn on or off ducts depending on the size of the print medium and its relative positioning of inboard and outboard edges IE, OE, with the embodiments of  FIGS.  6 A- 6 C  being nonlimiting. 
       FIG.  6 C  illustrates a state in which the inter-media zone is directly above the airflow zones  357 _ 1  through  351 _ 9 . In this state, all of the airflow zones  357 _ 1  through  359 _ 9  are turned off. Some of the airflow zones  357  are only temporarily off in this state because of the current location of the inter-media zone  322 , and these will be returned to the on state when the inter-media zone  322  has moved on. Others of the airflow zones  357 , which are in the uncovered region  324 , will remain off even when the inter-media zone  322  moves on. 
     As described above, in each airflow zone, a duct (such as the ducts  151  or  351 ) and a corresponding valve (such as the valves  152  or  352 ) controls airflow between the interior of the vacuum plenum and a corresponding group of holes in the vacuum platen, and in an off state of the airflow zone airflow between the plenum and the group of holes is blocked. In this context, “blocking” or “preventing” air from flowing from the interior of the vacuum plenum to the group of holes means that the ducts and valves create a relatively high impedance state for such airflow between the plenum and the holes, and thus significantly reduce such airflow, as compared to a completely open state (e.g., impedance is increased by at least tenfold and/or airflow is decreased by at least 90%). Thus, references herein to the an airflow zone being off and/or preventing airflow does not necessarily require a hermetic seal or the strict elimination of all airflow. 
     Although the embodiments of the airflow control systems  350  described above are illustrated and described in the context of the specific ink deposition assemblies  301  and media transport device  303  of the printing system  300 , the same airflow control system  350  could be used in other embodiments of the printing system  300  having with differently configured ink deposition assemblies  301  and media transport devices  303 . For example, the various embodiments of the airflow control systems  350  could be used in printing systems  300  with different types of movable support surfaces  320 , printing systems  300  with different types of vacuum plenums  325 , printing systems  300  with different types of vacuum platens  326 , printing systems  300  with different numbers and/or types of printhead modules  302 , and so on. 
     This description and the accompanying drawings that illustrate aspects and embodiments of the present disclosure should not be taken as limiting. The claims define the scope of protection. Various mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known circuits, structures, and techniques have not been shown or described in detail in order not to obscure the invention. Like numbers in two or more figures represent the same or similar elements. 
     Further, the terminology used herein to describe aspects of the invention, such as spatial and relational terms, is chosen to aid the reader in understanding embodiments of the invention but is not intended to limit the invention. For example, spatially terms—such as “upstream”, “downstream”, “beneath”, “below”, “lower”, “above”, “upper”, “inboard”, “outboard”, “up”, “down”, and the like—may be used herein to describe directions or one element&#39;s or feature&#39;s spatial relationship to another element or feature as illustrated in the figures. These spatial terms are used relative to the poses illustrated in the figures, and are not limited to a particular reference frame in the real world. Thus, for example, the direction “up” in the figures does not necessarily have to correspond to an “up” in a world reference frame (e.g., away from the Earth&#39;s surface). Furthermore, if a different reference frame is considered than the one illustrated in the figures, then the spatial terms used herein may need to be interpreted differently in that different reference frame. For example, the direction referred to as “up” in relation to one of the figures may correspond to a direction that is called “down” in relation to a different reference frame that is rotated 180 degrees from the figure&#39;s reference frame. As another example, if a device is turned over 180 degrees in a world reference frame as compared to how it was illustrated in the figures, then an item described herein as being “above” or “over” a second item in relation to the Figures would be “below” or “beneath” the second item in relation to the world reference frame. Thus, the same spatial relationship or direction can be described using different spatial terms depending on which reference frame is being considered. Moreover, the poses of items illustrated in the figure are chosen for convenience of illustration and description, but in an implementation in practice the items may be posed differently. 
     The term “process direction” refers to a direction that is parallel to and pointed in the same direction as an axis along which the print media moves as is transported through the deposition region of the ink deposition assembly. Thus, the process direction is a direction parallel to the y-axis in the Figures and pointing in a positive y-axis direction. 
     The term “cross-process direction” refers to a direction perpendicular to the process direction and parallel to the movable support surface. At any given point, there are two cross-process directions pointing in opposite directions, i.e., an “inboard” cross-process direction and an “outboard” cross-process direction. Thus, considering the reference frames illustrated in the Figures, a cross-process direction is any direction parallel to the x-axis, including directions pointing in a positive or negative direction along the x-axis. References herein to a “cross-process direction” should be understood as referring generally to any of the cross-process directions, rather than to one specific cross-process direction, unless indicated otherwise by the context. Thus, for example, the statement “the valve is movable in a cross-process direction” means that the valve can move in an inboard direction, outboard direction, or both directions. 
     The terms “upstream” and “downstream” may refer to directions parallel to a process direction, with “downstream” referring to a direction pointing in the same direction as the process direction (i.e., the direction the print media are transported through the ink deposition assembly) and “upstream” referring to a direction pointing opposite the process direction. In the Figures, “upstream” corresponds to a negative y-axis direction, while “downstream” corresponds to a positive y-axis direction. The terms “upstream” and “downstream” may also be used to refer to a relative location of element, with an “upstream” element being displaced in an upstream direction relative to a reference point and a “downstream” element being displaced in a downstream direction relative to a reference point. In other words, an “upstream” element is closer to the beginning of the path the print media takes as it is transported through the ink deposition assembly (e.g., the location where the print media joins the movable support surface) than is some other reference element. Conversely, a “downstream” element is closer to the end of the path (e.g., the location where the print media leaves the support surface) than is some other reference element. The reference point of the other element to which the “upstream” or “downstream” element is compared may be explicitly stated (e.g., “an upstream side of a printhead”), or it may be inferred from the context. 
     The terms “inboard” and “outboard” refer to opposite sides of the media transport device along a cross-process direction. “Outboard” refers to the side of the media transport device closest to a registration location to which the edges of the print media are registered. “Inboard” refers to the side of the media transport device opposite from the outboard side. For example, in  FIGS.  6 A- 6 B  the outboard side of the media transport device is labeled OB and the inboard side of the media transport device is labeled IB. By extension, the “outboard” edge of a print medium is the edge that is closest to the outboard edge of the media transport device, or in other words the edge that is used to register the print medium in the cross-process direction, while the inboard edge of a print medium is the opposite edge of the print medium. There is no limitation to which side of the media transport device the print media are registered, and different systems may register the media different. Thus, if a first side (e.g., the left side, when facing in the process direction) of the media transport device is the outboard side in one system, the first side (e.g., left side) in another system that uses a different registration scheme may be the inboard side, or vice versa. Furthermore, if a given system changes which side the print media are registered to (e.g., between print jobs), then the side of the device that is considered the “outboard” side will change accordingly. The terms “inboard” and “outboard” are also used to refer to cross-process directions, with “inboard” referring to a cross-process direction that points from the outboard side to the inboard side and “outboard” referring to the cross-process direction that points from the inboard side to the outboard side. In the Figures, “inboard” corresponds to a positive x-axis direction, while “outboard” corresponds to a negative x-axis direction. The terms “inboard” and “outboard” also refer to relative locations, with an “inboard” element being displaced in an inboard direction relative to a reference point and with an “outboard” element being displaced in an outboard direction relative to a reference point. The reference point may be explicitly stated (e.g., “an inboard side of a printhead”), or it may be inferred from the context. Thus, for example, an “inboard side of a carrier plate” refers to a side of the carrier plate that is relatively further inboard than another side of the carrier plate. 
     The term “vertical” refers to a direction perpendicular to the movable support surface in the deposition region. At any given point, there are two vertical directions pointing in opposite directions, i.e., an “upward” direction and an “downward” direction. Thus, considering the reference frames illustrated in the Figures, a vertical direction is any direction parallel to the z-axis, including directions pointing in a positive z-axis direction (“up”) or negative z-axis direction (“down”). 
     The term “horizontal” refers to a direction parallel to the movable support surface in the deposition region (or tangent to the movable support surface in the deposition region, if the movable support surface is not flat in the deposition region). Horizontal directions include the process direction and cross-process directions. 
     The term “vacuum” has various meanings in various contexts, ranging from a strict meaning of a space devoid of all matter to a more generic meaning of a relatively low pressure state. Herein, the term “vacuum” is used in the generic sense, and should be understood as referring broadly to a state or environment in which the air pressure is lower than that of some reference pressure, such as ambient or atmospheric pressure. The amount by which the pressure of the vacuum environment should be lower than that of the reference pressure to be considered a “vacuum” is not limited and may be a small amount or a large amount. Thus, “vacuum” as used herein may include, but is not limited to, states that might be considered a “vacuum” under stricter senses of the term. 
     The term “air” has various meanings in various contexts, ranging from a strict meaning of the atmosphere of the Earth (or a mixture of gases whose composition is similar to that of the atmosphere of the Earth), to a more generic meaning of any gas or mixture of gases. Herein, the term “air” is used in the generic sense, and should be understood as referring broadly to any gas or mixture of gases. This may include, but is not limited to, the atmosphere of the Earth, an inert gas such as one of the Noble gases (e.g., Helium, Neon, Argon, etc.), Nitrogen (N 2 ) gas, or any other desired gas or mixture of gases. 
     In addition, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. And, the terms “comprises”, “comprising”, “includes”, and the like specify the presence of stated features, steps, operations, elements, and/or components but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups. Components described as coupled may be electrically or mechanically directly coupled, or they may be indirectly coupled via one or more intermediate components, unless specifically noted otherwise. Mathematical and geometric terms are not necessarily intended to be used in accordance with their strict definitions unless the context of the description indicates otherwise, because a person having ordinary skill in the art would understand that, for example, a substantially similar element that functions in a substantially similar way could easily fall within the scope of a descriptive term even though the term also has a strict definition. 
     Elements and their associated aspects that are described in detail with reference to one embodiment may, whenever practical, be included in other embodiments in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment.