Patent Publication Number: US-9884484-B2

Title: Printing apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a printing apparatus that is provided with a recovery device which recovers mist arising from a liquid discharged from a printing unit. 
     2. Related Art 
     In the related art, a printing apparatus  100  illustrated in  FIG. 17  is known as an example of this type of printing apparatus. 
     In the printing apparatus  100 , a recovery device  130  is disposed in the vicinity of a printing unit  120  and the recovery device  130  suctions mist by means of a fan  131  after the mist is generated from a liquid (ink) that is discharged from the printing unit  120  to a medium PR transported by a transport drum  110 . A recovery container  132  of the recovery device  130  accommodates the fan  131  and a filter  133  placed upstream of the fan  131 . The recovery device  130  suctions the mist from a suction port  134  formed in the recovery container  132  and recovers the mist by means of the filter  133  by driving the fan  131 . 
     In this recovery device  130 , the mist is likely to adhere to the filter  133 , and thus the filter  133  is likely to be subjected to clogging and the mist suction force of the fan  131  is likely to decline. 
     A recovery device in which mist is unlikely to adhere to a filter is conceivable in solving this problem (refer to, for example, JP-A-2013-180539). As an example thereof, a recovery device  230  of a printing apparatus  200  illustrated in  FIG. 18  is provided with a suction unit  231  that suctions mist arising from ink discharged from a printing unit  220  to a medium PR transported by a transport drum  210 , a recovery unit  232  that recovers the mist, and a hose-shaped outlet portion  233  that allows the suction unit  231  and the recovery unit  232  to communicate with each other. A fan  234  is disposed in the recovery unit  232 . A filter  235  is disposed upstream of the fan  234  in the recovery unit  232 , and a recovery container  236  to which the outlet portion  233  is connected is disposed upstream of the filter  235 . A plurality of vertical walls  237  alternating with each other and an absorbing material  238  absorbing the mist are disposed in the recovery container  236 . 
     As the fan  234  is driven in the recovery device  230 , a suction force is generated to the suction unit  231  via the outlet portion  233 . Accordingly, the mist between the printing unit  220  and the transport drum  210  is suctioned by the suction unit  231  and is recovered by the recovery unit  232  through the outlet portion  233 . 
     In the printing apparatus  200  that is illustrated in  FIG. 18 , the recovery container  236  and the vertical walls  237  are placed upstream of the filter  235  along a flow path of the mist, and thus the mist recovered from the outlet portion  233  to the recovery container  236  adheres to the vertical walls  237  and the inner wall of the recovery container  236  before reaching the filter  235 . As a result, the mist is unlikely to adhere to the filter  235 , and thus a decline in mist recovery performance is more suppressed than in the printing apparatus  100  that is illustrated in  FIG. 17 . 
     Because the distances between the adjacent vertical walls  237  are equal to each other as illustrated in  FIG. 18 , however, the passage cross-sectional areas of the flow paths are equal to each other and the mist has a constant speed during its movement in the recovery container  236 . Accordingly, a deviation in terms of mist adhesion amount increases between the plurality of vertical walls  237  and the inner wall of the recovery container  236 , and mist adhesion is less likely to occur on the inner wall of the recovery container  236  and the vertical walls  237  where the amount of mist adhesion is large. As a result, the mist is likely to reach the filter  235 , and there is room for improvement in this regard. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a printing apparatus that is capable of further suppressing a decline in mist recovery performance. 
     Hereinafter, means of the invention and operation effects thereof will be described. 
     A printing apparatus for solving the above problem includes a printing unit performing printing by discharging a liquid to a transported medium, a recovery unit recovering mist arising from the liquid discharged from the printing unit, and an airflow generation source moving the mist into the recovery unit, in which the recovery unit has a recovery path recovering the mist in an inner portion, the recovery path has walls and ribs disposed on the walls, the walls have a first wall and a second wall placed to face the first wall, the ribs have two first ribs disposed toward the second wall from the first wall and having gaps between the second wall and themselves and one second rib disposed toward the first wall from the second wall and having a gap between the first wall and itself, the second rib is disposed between the two first ribs, the first ribs and the second rib have overlapping parts in a direction intersecting with a direction in which the ribs extend, and a gap between the second rib and one of the two first ribs positioned downstream with respect to a direction in which the mist moves is narrower than a gap between the second rib and the other one of the two first ribs positioned upstream with respect to the direction in which the mist moves. 
     Various types of airflow generation sources are conceivable as the airflow generation source, and the airflow generation source may be a fan performing suctioning from the downstream side of the flow path (recovery path for mist recovery) or may be a pressurization mechanism performing pressurization from the upstream side of the flow path. The placement of the airflow generation source can be performed at any position. In other words, the mist may be caused to flow (move) by the suction force of the fan being transferred to the flow path and an airflow from the upstream side toward the downstream side of the flow path being generated with the fan being placed on the upstream side of the flow path and the fan being connected to the downstream side of the flow path (such as the notches  58   a ) by means of a tube-shaped member. In a case where the airflow generation source is the fan, for example, the driving energy of the airflow generation source is the rotation speed of the fan. When the airflow generation source is the pressurization mechanism, the driving energy is pressure generated per unit area. 
     The first wall is, for example, the supporting member  56  that is illustrated in  FIG. 7 . The second wall is, for example, the bottom wall  53   a  that is illustrated in  FIG. 7 . The first rib is, for example, the drooping rib  57  that is illustrated in  FIG. 7 . The second rib is, for example, the standing rib  58  that is illustrated in  FIG. 7 . 
     A printing apparatus for solving the above problem includes a printing unit performing printing by discharging a liquid to a transported medium, a recovery unit recovering mist arising from the liquid discharged from the printing unit, and an airflow generation source moving the mist into the recovery unit, in which the recovery unit has a recovery path recovering the mist in an inner portion, the recovery path has walls and ribs disposed on the walls, the walls have a first wall and a second wall placed to face the first wall, the ribs have one first rib disposed toward the second wall from the first wall and having a gap between the second wall and itself and one second rib disposed toward the first wall from the second wall and having a gap between the first wall and itself, the first rib and the second rib have overlapping parts in a direction intersecting with a direction in which the ribs extend, the first rib is disposed upstream of the second rib with respect to a direction in which the mist moves, and a gap between a tip of the second rib and the first wall is narrower than a gap between a tip of the first rib and the second wall. 
     The tips of the ribs are, for example, end portions of the drooping rib  57  and the standing rib  58  that are illustrated in  FIG. 7 . 
     In the apparatus described above, it is preferable that the gap between the first rib and the second rib be narrower on the downstream side than on the upstream side in the direction in which the mist moves. 
     According to this configuration, the passage cross-sectional area of the flow path is smaller on the downstream side than on the upstream side of the mist flow path in the recovery unit, and thus the flow rate of the mist increases from the upstream side toward the downstream side in the flow path. As a result, on the upstream side of the flow path, the mist with a large particle diameter, that is, heavy mist is likely to adhere to the rib, the wall, and the like without turning a curve in the flow path even at the low flow rate of the mist. On the downstream side of the flow path, the mist with a small particle diameter, that is, light mist is likely to adhere to the rib, the wall, and the like without turning a curve in the flow path because of the high flow rate of the mist. The mist is evenly recovered on each of the upstream side and the downstream side of the flow path as described above, and thus a decline in mist recovery performance can be suppressed. 
     In the apparatus described above, it is preferable that the first wall be a plate-shaped member having a first surface on which the rib is disposed and a second surface on a side opposite to the first surface and the first wall be disposed such that the second surface faces a suction port in the recovery unit suctioning the mist through a gap and is inclined toward an upstream side of the flow path. 
     According to this configuration, the mist passing through the suction port of the recovery unit is moved in the direction away from the downstream side of the flow path by the first wall forming the flow path and then passes through the flow path formed by the rib and the wall, and thus the mist flow path can be lengthened by the internal space of the recovery unit being effectively used. Accordingly, the amount of mist recovery can be larger than in a case where the flow path is short. 
     The plate-shaped member mentioned above is, for example, the supporting member  56  that is illustrated in  FIG. 7  and is a member whose front and back surfaces have a planar shape alike. The first surface refers to the surface of the supporting member  56  on the bottom wall  53   a  side. The second surface refers to the surface of the supporting member  56  on the suction port  55   a  side. 
     In the apparatus described above, it is preferable that the recovery unit be connected to a lower part of a support base supporting the medium, a hole communicating with the suction port in the recovery unit suctioning the mist be formed in the support base, the printing unit discharge the liquid toward the support base in a state where a part of the medium is not positioned in the hole during flushing, and driving energy of the airflow generation source during the movement of the mist can be variably controlled. 
     In the apparatus described above, it is preferable that the airflow generation source be controlled such that the driving energy of the airflow generation source for recovering the mist after printing termination in a case where a share of the liquid in the medium is equal to or higher than a threshold exceeds the driving energy of the airflow generation source for recovering the mist after printing termination in a case where the share is lower than the threshold. 
     In the apparatus described above, it is preferable that the airflow generation source be driven during the flushing and the printing by the printing unit and the airflow generation source be controlled such that the driving energy at a time when the printing unit performs the flushing in a period following termination of the printing on one surface of the medium and initiation of the printing on the other surface of the medium by the printing unit exceeds the driving energy of the airflow generation source at a time when the printing unit performs the printing on the medium. 
     In the apparatus described above, it is preferable that the airflow generation source be driven during the flushing and the printing by the printing unit, the printing unit be provided with a nozzle capable of discharging the liquid and a cap capable of covering the nozzle, and the airflow generation source be controlled such that the driving energy at a time when the printing unit performs the flushing after a predetermined period of time in which the printing unit does not discharge the liquid and the nozzle is not covered by the cap exceeds the driving energy of the airflow generation source at a time when the printing unit performs the printing on the medium. 
     In the apparatus described above, the airflow generation source is a fan and the driving energy is a rotation speed of the fan. 
     In the apparatus described above, it is preferable that the fan be placed on a downstream side of the flow path. 
     In the apparatus described above, it is preferable that an absorbing material absorbing the mist be disposed in at least a part of a part constituting the flow path in the recovery unit and a density inside the absorbing material be higher than a density on a surface side of the absorbing material. 
     Insofar as a printing apparatus for solving the above problem includes a printing unit performing printing by discharging a liquid to a transported medium, a recovery unit recovering mist arising from the liquid discharged from the printing unit, and an airflow generation source moving the mist into the recovery unit, in which the recovery unit has a recovery path along which the mist is moved by an airflow generated by the airflow generation source, and a speed of the mist movement along the recovery path is higher downstream than upstream with respect to a direction of the mist movement, the printing apparatus is not limited to a specific mechanism in solving the above problem. 
     Hereinafter, the means for solving the above problem and the effects thereof will be described by means of an expression differing from the means for solving the above problem described above. It is a matter of course that the effects described herein apply the same to the means for solving the above problem described above. 
     The printing apparatus for solving the above problem includes the printing unit performing the printing by discharging the liquid to the transported medium, and a recovery device recovering the mist arising from the liquid discharged from the printing unit, the recovery device has a recovery container in which the mist flows, the fan suctioning the mist into the recovery container, and a filter recovering the mist and disposed upstream of the fan in the flow direction of the mist in the recovery container, the recovery container is provided with a plurality of vertical walls forming the mist flow path by being disposed in an alternating manner, and at least one of the gap between the vertical walls adjacent to each other to form the flow path in the recovery container and the gap between the tip portions of the vertical walls facing each other to form the flow path and a component facing the tip portions becomes gradually narrower toward the downstream side of the flow path that is closer to the fan. 
     According to this configuration, the passage cross-sectional area of the flow path is smaller on the downstream side than on the upstream side of the mist flow path in the recovery container, and thus the flow rate of the mist increases from the upstream side toward the downstream side in the flow path. As a result, on the upstream side of the flow path, the mist with a large particle diameter, that is, heavy mist is likely to adhere to the vertical wall, the wall of the recovery container, and the like without turning a curve in the flow path even at the low flow rate of the mist. On the downstream side of the flow path, the mist with a small particle diameter, that is, light mist is likely to adhere to the vertical wall, the wall of the recovery container, and the like without turning a curve in the flow path because of the high flow rate of the mist. The mist is evenly recovered on each of the upstream side and the downstream side of the flow path as described above, and thus the amount of the mist adhering to the filter can be reduced and a decline in filter performance is unlikely to occur. Accordingly, a decline in mist recovery performance that is attributable to a decline in the performance of the filter can be suppressed. 
     In the printing apparatus described above, it is preferable that the supporting member be further provided that faces the mist suction port in the recovery container through a gap and is disposed such that the mist passing through the suction port hits against the supporting member and its flow direction is changed sideways (that is, the upstream side of the flow path), drooping ribs drooping from the supporting member be disposed beneath the supporting member, standing ribs standing toward the supporting member be disposed at parts of the recovery container facing the supporting member from the side opposite to the suction port, and the plurality of vertical walls be configured by the drooping ribs and the standing ribs being disposed in an alternating manner. 
     According to this configuration, the mist passing through the suction port of the recovery container is moved in the direction away from the fan by the supporting member without moving at the shortest distance toward the fan (filter), and then reaches the filter through the flow path formed by the drooping ribs and the standing ribs. Accordingly, the mist flow path can be lengthened by the internal space of the recovery container being effectively used. 
     In the printing apparatus described above, it is preferable that an absorbing material absorbing the mist be disposed in at least a part of a part constituting the flow path in the recovery container and a density inside the absorbing material be higher than a density on a surface side of the absorbing material. 
     According to this configuration, the absorbing material facilitates the recovery of the mist in the recovery container upstream of the filter in the mist flow path. In addition, the mist adhering to the surface of the absorbing material is likely to permeate the absorbing material because of a change in the density of the absorbing material. Accordingly, ink pool formation in the surface of the absorbing material can be suppressed. 
     In the printing apparatus described above, it is preferable that the recovery container be connected to a lower part of a support base supporting the medium, a hole communicating with the suction port in the recovery container suctioning the mist be formed in the support base, the printing unit discharge the liquid toward the support base in a state where the medium is not transported onto the support base during flushing, and the rotation speed of the fan during the suctioning of the mist can be variably controlled. 
     It is a matter of course that the flushing may be performed in a state where a part of the medium is not at a position covering the hole in the support base. In addition, it is a matter of course that the rotation speed of the fan can be variably controlled in a state where a part of the medium is not at a position covering the hole in the support base. 
     According to this configuration, the mist suction force can be changed by the rotation speed of the fan being variably controlled. Accordingly, the mist suction force (fan rotation speed) is appropriately set in accordance with, for example, the amount of the mist afloat between the support base and the printing unit, and then mist adhesion to a part of the support base supporting the medium is unlikely to occur. 
     In the printing apparatus described above, it is preferable that the fan be driven during the flushing and the printing by the printing unit, the printing unit be provided with a nozzle capable of discharging the liquid and a cap capable of covering the nozzle, and the fan be controlled such that the rotation speed at a time when the printing unit performs the flushing after a predetermined period of time in which the printing unit does not discharge the liquid and the nozzle is not covered by the cap is higher than the rotation speed of the fan at a time when the printing unit performs the printing on the medium. 
     In a case where the nozzle is not covered by the cap for a long period of time and the liquid in the nozzle is likely to be thickened, it is preferable that the amount of liquid discharge during the execution of the flushing by the printing unit exceed the amount of liquid discharge during the execution of the flushing in a state preceding the thickening of the liquid. However, an increase in the liquid discharge amount leads to an increase in the amount of the mist afloat between the printing unit and the support base. 
     According to this configuration, the mist suction force is increased by the rotation speed of the fan being increased in a case where the liquid discharge amount during the execution of the flushing by the printing unit is large, and thus the mist afloat between the printing unit and the support base is likely to be suctioned into the recovery container. Accordingly, mist adhesion to the part of the support base supporting the medium can be suppressed. 
     In the printing apparatus described above, it is preferable that the fan be driven during the flushing and the printing by the printing unit and the fan be controlled such that the rotation speed at a time when the printing unit performs the flushing in a period following termination of the printing on one surface of the medium and initiation of the printing on the other surface of the medium by the printing unit is higher than the rotation speed of the fan at a time when the printing unit performs the printing on the medium. 
     As is already known, the length of time that is required for so-called switchback in a case where duplex printing is performed on the medium by the printing unit, in which printing on one surface of the medium is terminated and then the medium is transported onto the support base with the medium reversed to the other surface, exceeds the length of time taken for the next medium to be transported onto the support base after the printing on a single surface of the medium by the printing unit is terminated. The printing unit executes the flushing during the switchback in some cases. 
     A certain period of time is required for an effect in the form of the suctioning of the mist into the recovery container being further facilitated by means of an increase in the rotation speed of the fan to be achieved. Accordingly, the printing unit is not capable of achieving the effect in the form of the suctioning of the mist into the recovery container being further facilitated to a sufficient extent, even if the rotation speed of the fan is increased, within a short period of time such as the length of time taken for the next medium to be transported onto the support base after the printing on the single surface of the medium is terminated. 
     According to this configuration, the rotation speed of the fan is increased when the printing on the medium is not performed for a long period of time, examples of which include the switchback during execution of a printing job, in this regard. Accordingly, the effect in the form of the suctioning of the mist afloat between the printing unit and the support base into the recovery container being further facilitated can be achieved and mist adhesion to the part of the support base supporting the medium can be suppressed. 
     In the printing apparatus described above, it is preferable that the fan be controlled such that the rotation speed of the fan for recovering the mist after printing termination in a case where a printing ratio is equal to or higher than a threshold is higher than the rotation speed of the fan for recovering the mist after printing termination in a case where the printing ratio is lower than the threshold. 
     The total amount of the liquid that the printing unit discharges to the medium when the printing ratio is high exceeds the total amount of the liquid that the printing unit discharges to the medium when the printing ratio is low, and thus the amount of the mist afloat between the printing unit and the support base increases after the printing termination. 
     According to this configuration, the rotation speed of the fan for suctioning the mist after the printing termination is increased in the case of a high printing ratio in this regard, and thus the mist afloat between the printing unit and the support base is likely to be suctioned into the recovery container. Accordingly, mist adhesion to the part of the support base supporting the medium can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic front view of a first embodiment of a printing apparatus. 
         FIG. 2  is a block diagram illustrating an electrical configuration of the printing apparatus. 
         FIG. 3  is a schematic plan view of a discharge head. 
         FIG. 4  is a schematic plan view of a support base. 
         FIG. 5  is a schematic sectional view of the discharge head and the support base. 
         FIG. 6  is a perspective view of the support base, the discharge head, and a recovery device. 
         FIG. 7  is a schematic sectional view in which the recovery device and the support base illustrated in  FIG. 6  are cut along a plane along a sheet transport direction and a vertical direction. 
         FIG. 8  is a schematic sectional view of the recovery device and the support base for showing an operation. 
         FIG. 9  is a schematic sectional view of the recovery device and the support base for showing an operation. 
         FIG. 10  is a flowchart showing fan rotation speed setting processing at a time of flushing preceding printing initiation with regard to a second embodiment of the printing apparatus. 
         FIG. 11  is a flowchart showing fan rotation speed setting processing at a time of duplex printing execution. 
         FIG. 12  is a flowchart showing fan rotation speed setting processing following printing job termination. 
         FIG. 13  is a schematic sectional view of a recovery device and a support base of a printing apparatus according to a modification example. 
         FIG. 14  is a schematic sectional view of a recovery device and a support base of a printing apparatus according to a modification example. 
         FIG. 15  is a schematic sectional view of a recovery device and a support base of a printing apparatus according to a modification example. 
         FIG. 16  is a schematic sectional view of a recovery device and a support base of a printing apparatus according to a modification example. 
         FIG. 17  is a schematic sectional view of a part of a printing apparatus according to the related art. 
         FIG. 18  is a schematic front view of a part of another printing apparatus according to the related art. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, first and second embodiments of a printing apparatus will be described with reference to accompanying drawings. In each of the embodiments, the printing apparatus is an ink jet printer that forms a character or an image on a sheet by discharging ink as an example of a liquid to the sheet as an example of a medium. 
     First Embodiment 
     As illustrated in  FIG. 1 , a printing apparatus  10  is provided with a sheet cassette  11  that is capable of accommodating stacked sheets P, a support base  20  that supports the sheet P, a printing unit  30  that performs printing by discharging the ink to the sheet P transported onto the support base  20 , and a transport unit  40  that transports the sheet P onto the support base  20 . In addition, the printing apparatus  10  is provided with a recovery device  50  that recovers mist arising from the ink discharged from the printing unit  30  and a control device  60  that controls the printing unit  30 , the transport unit  40 , and the recovery device  50 . In the following description, the width direction of the sheet P will be defined as a “width direction X” and a direction in which the sheet P is transported will be defined as a “transport direction Y”. The width direction X, which is an example of directions intersecting with the transport direction Y, is orthogonal to the transport direction Y. 
     The printing unit  30  is provided with a discharge head  31  that has multiple nozzles  31   a  which are capable of discharging the ink to the sheet P passing on the support base  20  and a cap  32  that is capable of covering each of the nozzles  31   a  in order to prevent the multiple nozzles  31   a  from drying. The discharge head  31 , which is placed at a position that faces the support base  20  through a gap above the support base  20 , is a so-called line head that is capable of simultaneously discharging the ink across the width direction X. The discharge head  31  executes so-called flushing, which is forced ink discharge from the nozzle  31   a  at a time when the ink at the nozzle  31   a  has dried and hardened or the viscosity of the ink has increased. The discharge head  31  is provided with piezoelectric elements  33  that discharge the ink from the nozzles  31   a . The piezoelectric element  33  is disposed for each of the nozzles  31   a.    
     The printing unit  30  is also provided with a head moving motor  34  that moves the discharge head  31  between a printing position and a withdrawal position, the printing position being a position of the discharge head  31  where the printing is performed on the sheet P and the withdrawal position being a position where the discharge head  31  is withdrawn from the printing position and the cap  32  is mounted on the nozzle  31   a.    
     The support base  20  is a metallic base (such as an aluminum base). The support base  20  has an internal space  21 , through which the ink discharged from the nozzle  31   a  as a result of the flushing and the mist arising from the ink are capable of passing. The recovery device  50  is disposed below the support base  20 . As a fan  51  of the recovery device  50  is driven, the mist afloat between the printing unit  30  and the support base  20  is recovered via the internal space  21  of the support base  20 . The fan  51  according to the present embodiment is an axial fan. The fan  51  may also be another type of fan such as a centrifugal fan. 
     The transport unit  40  is provided with a pickup roller  41  that sends the uppermost one of the sheets P in the sheet cassette  11 , a transport roller pair  42  that transports the sheet P sent by the pickup roller  41  toward the support base  20 , and a sheet discharge roller pair  43  that discharges the sheet P after the passage of the sheet P on the support base  20 . In addition, the transport unit  40  is provided with a relay roller pair  44  that is disposed in the middle of a transport path of the pickup roller  41  and the transport roller pair  42  (one-dot chain line) and transports the sheet P to the transport roller pair  42 . 
     The pickup roller  41  is rotated by a pickup motor  45  with the width direction X being its axial direction. The transport roller pair  42  is provided with a driving roller  42   a  that is rotated by a transport motor  46  with the width direction X being its axial direction and a driven roller  42   b  that is driven to rotate with the width direction X being its axial direction. As illustrated in  FIG. 1 , the driven roller  42   b  is positioned above the driving roller  42   a  and downstream of the driving roller  42   a  in the transport direction Y. As a result, the sheet P is pressed on the support base  20 . The sheet discharge roller pair  43  is provided with a driving roller  43   a  that is rotated by a sheet discharge motor  47  with the width direction X being its axial direction and a driven roller  43   b  that is driven to rotate with the width direction X being its axial direction. 
     As illustrated in  FIG. 2 , the control device  60  is provided with a printing control unit  61  that controls the printing unit  30 , a transport control unit  62  that controls the transport unit  40 , and a fan control unit  63  that controls the fan  51  of the recovery device  50 . A printing job is transmitted to the control device  60  from an external device (such as a personal computer). Based on the printing job, the control device  60  controls the piezoelectric element  33  and the head moving motor  34  by means of the printing control unit  61 , controls the pickup motor  45 , the transport motor  46 , and the sheet discharge motor  47  by means of the transport control unit  62 , and controls the fan  51  by means of the fan control unit  63 . The fan control unit  63  controls the fan  51  by means of, for example, pulse width modulation (PWM) control. 
     According to the above-described configuration of the printing apparatus  10  that is illustrated in  FIGS. 1 and 2 , the sheet P in the sheet cassette  11  is sent by the pickup roller  41 , is transported toward the relay roller pair  44  by a guide unit  48  disposed in the middle of the transport path, and is transported onto the support base  20  by the transport roller pair  42 . The printing on the sheet P on the support base  20  is performed by the ink being discharged from the discharge head  31 . After the printing is performed, the sheet discharge roller pair  43  transports the sheet P downstream in the transport direction Y from the support base  20 . 
     Configurations of the discharge head  31  and the support base  20  will be described in detail with reference to  FIGS. 3 to 5 . 
     As illustrated in  FIG. 3 , nozzle columns  31   b , each of which is divided into the plurality of nozzles  31   a , are formed on a surface of the discharge head  31  that faces the support base  20  (refer to  FIG. 1 ). The nozzle columns  31   b  extend in a direction intersecting with the transport direction Y (in a direction diagonally intersecting with the transport direction Y in  FIG. 3 ). The nozzle columns  31   b  according to the present embodiment extend to one side in the width direction X (right side in the drawing) downstream in the transport direction Y. The nozzle columns  31   b  are parallel to one another and are arranged in the width direction X. Parts of the nozzle columns  31   b  that are adjacent to each other in the width direction X overlap with each other in the transport direction Y. 
     As illustrated in  FIG. 4 , a plurality of ribs  23  for supporting the sheet P and a plurality of discarding portions  24 , which allow the passage of the ink discharged from the discharge head  31  during the flushing into the internal space  21  (refer to  FIG. 1 ), are disposed in a supporting portion  22  of the support base  20  that supports the sheet P (refer to  FIG. 1 ). The plurality of discarding portions  24  are illustrated by hatching in the drawing to be clearly distinguished from the plurality of ribs  23 . 
     The plurality of ribs  23  are formed integrally with the supporting portion  22 . Each of the plurality of ribs  23  extends along the transport direction Y. Each of the plurality of ribs  23  is subjected to a water-repellent treatment, a treatment for suppressing static electricity generation, and an anti-wear treatment. Fluorine coating is an example of the water-repellent treatment. Chrome plating is an example of the treatment for suppressing static electricity generation and the anti-wear treatment. Because of these treatments, the ink discharged from the discharge head  31  during the flushing and the mist arising from the ink are unlikely to adhere to the plurality of ribs  23 . The ink adhering to the parts of the plurality of ribs  23  that are adjacent to the discarding portions  24  flows to the discarding portions  24 . By the fan  51  being driven during the flushing, in particular, the ink adhering to the plurality of ribs  23  is suctioned toward the discarding portions  24 . In addition, charging of the ink is suppressed since static electricity generation in the plurality of ribs  23  is suppressed. Furthermore, an increase in the distance between the sheet P supported by the ribs  23  and the discharge head  31  is suppressed since wear of the plurality of ribs  23  attributable to the transport of the sheet P is reduced. The plurality of ribs  23  may be attached to the supporting portion  22  after being formed separately from the supporting portion  22  and one or more of the three treatments described above may be omitted. The three treatments described above may be performed at least on parts of the ribs  23  that are brought into contact with the sheet P. 
     As illustrated in  FIG. 5 , the plurality of discarding portions  24  penetrate the supporting portion  22 , at positions of the supporting portion  22  that face the respective nozzle columns  31   b , to communicate with the internal space  21 . As illustrated in  FIG. 4 , the discarding portions  24  are elongated holes that extend to one side in the width direction X (right side in the drawing) downstream in the transport direction Y as is the case with the nozzle columns  31   b . Accordingly, when the fan  51  (refer to  FIG. 1 ) is driven during the flushing, the ink discharged from the discharge head  31  and the mist arising from the ink pass through the respective discarding portions  24  and are suctioned into the internal space  21  of the support base  20 . 
     The discarding portion  24  extends across the rib  23  in the width direction X. Accordingly, the rib  23  is divided into a plurality of parts in the transport direction Y by intersecting with the discarding portion  24 . As illustrated by the one-dot chain lines in  FIG. 4 , division positions Dv, which are positions resulting from the division in the transport direction Y by the plurality of discarding portions  24 , have different positions in the transport direction Y. 
     Hereinafter, a configuration of the recovery device  50  will be described in detail with reference to  FIGS. 6 and 7 . 
     As illustrated in  FIG. 6 , the dimension of the recovery device  50  in the width direction X is almost equal to the dimension of the support base  20  in the width direction X and the dimension of the recovery device  50  in the transport direction Y exceeds the dimension of the support base  20  in the transport direction Y. The support base  20  is placed at the center of the recovery device  50  in the transport direction Y. 
     The recovery device  50  is provided with a recovery container  52  that accommodates the ink and the mist passing through the support base  20  and causes the mist to flow therein. A box-shaped container main body  53  that has an open upper portion and a cover  54  that covers the opening of the container main body  53  are assembled with each other and constitute the recovery container  52 . The fan  51  is attached to an outside wall of the container main body  53  on the upstream side in the transport direction Y and suctions the mist in the recovery container  52 . 
     As illustrated in  FIG. 7 , an attachment portion  55  is disposed at the center of the cover  54  in the transport direction Y and the support base  20  is attached to the attachment portion  55 . In this manner, the recovery container  52  is connected to a lower part of the support base  20 . A suction port  55   a  is formed in the attachment portion  55 , and the suction port  55   a  allows the internal space  21  of the support base  20  to communicate with the inside of the container main body  53 . The dimension of the suction port  55   a  in the width direction X is almost equal to the dimension of the support base  20  in the width direction X and the dimension of the suction port  55   a  in the transport direction Y is almost equal to the dimension of the support base  20  in the transport direction Y. The discarding portion  24  of the support base  20  is an example of a hole that communicates with the mist suction port  55   a  of the recovery container  52 . 
     A supporting member  56  is disposed in an upstream end portion of the attachment portion  55  in the transport direction Y, and the supporting member  56  extends to be inclined downwards toward the downstream side in the transport direction Y. The supporting member  56  faces the suction port  55   a  through a gap below the suction port  55   a  of the recovery container  52  and is disposed such that the ink and the mist passing through the suction port  55   a  hit against the supporting member  56  and their flow direction is changed sideways (to the downstream side in the transport direction Y that is illustrated by the bold arrow Y 1  in  FIG. 7 ). The supporting member  56  has a dimension in the width direction X that is almost equal to the dimension of the support base  20  in the width direction X and extends to the downstream side in the transport direction Y more than the support base  20  does. A plurality of drooping ribs  57  are disposed beneath the supporting member  56  with gaps in the transport direction Y and the drooping ribs  57  are an example of a vertical wall drooping toward a bottom wall  53   a  of the container main body  53 , which is a part of the container main body  53  facing the supporting member  56  from the side opposite to the suction port  55   a . The drooping ribs  57  are formed integrally with the supporting member  56 . The dimension of the drooping rib  57  in the width direction X is equal to the dimension of the supporting member  56  in the width direction X. The drooping ribs  57  have the same lower end portion positions. Accordingly, gaps GZ1 between the respective lower end portions (tip portions) of the drooping ribs  57  and the bottom wall  53   a  facing the lower end portions (tip portions) are equal to one another. The drooping rib  57  may be fixed to the supporting member  56  after being formed separately from the supporting member  56 . In addition, the bottom wall  53   a  of the container main body  53  is an example of components that face the tip portion (lower end portion) of the vertical wall (drooping rib  57 ). 
     A plurality of standing ribs  58 , which are an example of a vertical wall standing toward the supporting member  56 , are disposed on the bottom wall  53   a  of the container main body  53 , which is an example of a part of the recovery container  52  facing the supporting member  56  from the side opposite to the suction port  55   a . The standing ribs  58  are formed integrally with the bottom wall  53   a . The standing ribs  58  are disposed with gaps such that the standing ribs  58  alternate with the drooping ribs  57  in the transport direction Y. In other words, the drooping ribs  57  and the standing ribs  58  disposed to alternate with each other constitute the plurality of vertical walls. The dimension of the standing rib  58  in the width direction X is equal to the dimension of the supporting member  56  (drooping rib  57 ) in the width direction X. The dimensions of the standing ribs  58  in a vertical direction Z gradually increase from the downstream side toward the upstream side in the transport direction Y. At this time, gaps GZ2 between respective upper end portions (tip portions) of the standing ribs  58  and the supporting member  56  facing the upper end portions (tip portions) are equal to one another. The gap GZ2 is narrower than the gap GZ1. 
     One of the plurality of standing ribs  58  that is on the most upstream side in the transport direction Y is in contact with a lower surface of the cover  54 . As a result, the inside of the recovery container  52  is partitioned into two spaces, one being a first recovery space  52   a  in which the supporting member  56 , the drooping ribs  57 , and the standing ribs  58  are disposed and the other one being a second recovery space  52   b  allowing the first recovery space  52   a  and the fan  51  (refer to  FIG. 6 ) to communicate with each other. A filter  59 , which is illustrated by the two-dot chain lines in  FIG. 7 , is disposed in the second recovery space  52   b . The filter  59 , which recovers the mist in the recovery container  52 , is disposed at a position upstream of the fan  51  in the flow direction of the mist in the recovery container  52  and with a gap from the fan  51 . 
     A plurality of notches  58   a  are formed, with gaps in the width direction X, on the standing rib  58  on the most upstream side in the transport direction Y. The notches  58   a  have the shape of a recess that is recessed downward from the upper end portion of the standing rib  58 . As a result, the first recovery space  52   a  and the second recovery space  52   b  communicate with each other. 
     A flow path RM is formed in the first recovery space  52   a  as illustrated in  FIG. 7 , and the flow path RM is a mist-flowing space partitioned by the supporting member  56 , the drooping ribs  57 , the bottom wall  53   a  of the container main body  53 , and the standing ribs  58 . As illustrated by the bold arrow Y 1  in  FIG. 7 , the flow path RM is formed by the supporting member  56  and in a direction away from the fan  51  (refer to  FIG. 6 ) in the transport direction Y, that is, in a direction away from the second recovery space  52   b  in the transport direction Y. The supporting member  56 , the drooping ribs  57 , the bottom wall  53   a  of the container main body  53 , and the standing ribs  58  constitute the flow path RM below the supporting member  56 . In this manner, the recovery container  52  is provided with the plurality of vertical walls that form the mist flow path RM by being disposed in an alternating manner. The flow path RM below the supporting member  56  has a passage cross-sectional area gradually decreasing toward the downstream side, which is closer to the fan  51 . Specifically, a gap GY2 in the transport direction Y between the second drooping rib  57  from the upstream side of the flow path RM and the second standing rib  58  from the upstream side of the flow path RM is narrower than a gap GY1 in the transport direction Y between the first and second drooping ribs  57  from the upstream side of the flow path RM and the first standing rib  58  from the upstream side of the flow path RM. A gap GY3 in the transport direction Y between the third and fourth drooping ribs  57  from the upstream side of the flow path RM and the third standing rib  58  from the upstream side of the flow path RM is narrower than the gap GY2. In this manner, the gaps GY1 to GY3 between the drooping ribs  57  and the standing ribs  58  become gradually narrower toward the downstream side in the flow path RM, which is closer to the fan  51 . 
     In the following description, the flow path RM that has the passage cross-sectional area which the gap GY1 forms will be defined as an “upstream region RM1”, the flow path RM that has the passage cross-sectional area which the gap GY2 forms will be defined as a “midstream region RM2”, and the flow path RM that has the passage cross-sectional area which the gap GY3 forms will be defined as a “downstream region RM3”. 
     An operation of the printing apparatus  10  will be described with reference to  FIGS. 8 and 9 .  FIG. 8  shows a simulation result illustrating how mist (black circles) with a large particle diameter flows through the flow path RM and  FIG. 9  shows a simulation result illustrating how mist (black circles) with a small particle diameter flows through the flow path RM. The rotation speeds of the fan  51  ( FIG. 6 ) in these simulations are equal to each other. 
     As illustrated in  FIG. 8 , the passage cross-sectional area of the upstream region RM1 exceeds the passage cross-sectional areas of the midstream region RM2 and the downstream region RM3, and thus the flow rate of the mist in the upstream region RM1 is lower than the flow rates of the mist in the midstream region RM2 and the downstream region RM3. However, the large particle diameter of the mist, that is, the large weight of the mist, leads to adhesion of the mist to the bottom wall  53   a  of the container main body  53 , the supporting member  56 , the standing rib  58 , and the drooping rib  57  during the mist turning the curve in the upstream region RM1 that is attributable to the centrifugal force resulting from the turning. Although the flow rate of the mist in the midstream region RM2 is lower than the flow rate of the mist in the downstream region RM3, the large particle diameter of the mist similarly leads to adhesion of the mist to the bottom wall  53   a  of the container main body  53 , the supporting member  56 , the standing rib  58 , and the drooping rib  57  during the mist turning the curve in the midstream region RM2. As illustrated in  FIG. 8 , the mist with the large particle diameter rarely reaches the downstream region RM3. 
     Meanwhile, the mist with the small particle diameter moves into the downstream region RM3, with a small amount of the mist adhering to the bottom wall  53   a  of the container main body  53 , the supporting member  56 , the standing ribs  58 , and the drooping ribs  57  as illustrated in  FIG. 9 , after turning the curves in the upstream region RM1 and the midstream region RM2 in the flow path RM. Since the flow rate of the mist is high in the downstream region RM3, the mist adheres to the standing rib  58  and the drooping rib  57  when turning the curve in the downstream region RM3 in the flow path RM as a result of the centrifugal force attributable to the turning. 
     Once the flow rate of the mist is controlled by the gaps GY1 to GY3 being regulated as described above, mists with different particle diameters evenly adhere to the upstream region RM1, the midstream region RM2, and the downstream region RM3. Then, a deviation in terms of mist adhesion amount among the upstream region RM1, the midstream region RM2, and the downstream region RM3 is reduced during the recovery of the mist by the recovery device  50 . 
     The following effects can be achieved from the present embodiment. 
     (1) The gaps GY1 to GY3 between the drooping ribs  57  and the standing ribs  58  that are adjacent to each other to form the mist flow path RM become gradually narrower toward the downstream side of the flow path RM closer to the fan  51 , and thus the passage cross-sectional area of the flow path RM decreases from the upstream side toward the downstream side of the flow path RM in the recovery container  52 . As a result, the flow rate of the mist increases from the upstream side toward the downstream side of the flow path RM, the mists with the different particle diameters evenly adhere in the flow path RM, and thus the amount of the mist adhering to the filter  59  can be reduced. Accordingly, the performance of the filter  59  is unlikely to decline and a decline in mist recovery performance that is attributable to a decline in the performance of the filter  59  can be suppressed. 
     (2) The mist recovered by the recovery container  52  hits against the supporting member  56 , is moved in the direction away from the fan  51 , and then reaches the filter  59  through the flow path RM formed by the drooping ribs  57  and the standing ribs  58 . The flow path RM can be lengthened by the internal space of the recovery container  52  being effectively used in this manner. Accordingly, the probability of the mist adhering to the drooping ribs  57  and the like in the middle of the flow path RM increases, and thus the mist becomes less likely to adhere to the filter  59 . Accordingly, the filter  59  can be used without having to be replaced for an extended period of time and the service life of the recovery device  50  can be extended. 
     (3) In the recovery container  52 , the supporting member  56  extends to the downstream side in the transport direction Y more than the suction port  55   a  does, and thus the mist passing through the suction port  55   a  is likely to hit against the supporting member  56 . Accordingly, the mist is moved in the direction away from the fan  51  after hitting against the supporting member  56 , and thus the mist is unlikely to reach the filter  59 . 
     (4) One of the plurality of standing ribs  58  that is on the most downstream side of the flow path RM is in contact with the cover  54  and has the notches  58   a  formed in the upper end portion. Accordingly, the probability of the mist coming into contact with the standing rib  58  increases, and thus the amount of the mist adhering to the filter  59  can be reduced. 
     (5) Since the plurality of discarding portions  24  are formed on the support base  20 , the ink discharged from the discharge head  31  is recovered into the recovery container  52  via the discarding portions  24  during the flushing by the discharge head  31 . Accordingly, the discharge head  31  does not have to be moved during the flushing by the discharge head  31  and the length of time taken for the printing job to be terminated after the printing job is initiated can be shortened in a case where, for example, the flushing is executed in the middle of the execution of the printing job. 
     (6) Even if the sheet P subjected to the printing cockles and droops between the plurality of ribs  23  (refer to  FIG. 5 ), the cockling region does not ride on the plurality of ribs  23  since the plurality of ribs  23  on the support base  20  extend along the transport direction Y. Accordingly, the region of the sheet P other than the cockling region coming into contact with the nozzle column  31   b  of the discharge head  31  can be suppressed during the passage of the sheet P subjected to the printing on the plurality of ribs  23 . 
     (7) Since the respective division positions Dv of the plurality of ribs  23  are at different positions in the transport direction Y, the sheet P is transported in a state where a tip portion of the sheet P in the transport direction Y is in the division positions Dv over the entire width direction X and coming into contact in the transport direction Y with those of the plurality of ribs  23  that are on the downstream side in the transport direction Y is suppressed. Accordingly, curling of the tip portion of the sheet P in the transport direction Y is suppressed, and thus the posture of the sheet P on the plurality of ribs  23  can be stabilized and a decline in printing quality can be suppressed. 
     Second Embodiment 
     A printing apparatus  10  according to the second embodiment will be described with reference to  FIGS. 10 to 12 . The printing apparatus  10  according to the present embodiment differs from the printing apparatus  10  according to the first embodiment in that the rotation speed of the fan  51  (refer to  FIG. 1 ) of the recovery device  50  can be variably controlled. In the following description, components of the printing apparatus  10  to which signs are attached represent the respective components of the printing apparatus  10  illustrated in  FIGS. 1 to 7 . 
     The control device  60  drives the fan  51  throughout, for example, a driving period following the termination of the printing job after the printing job is received. In other words, the fan  51  is driven during the flushing and the printing by the printing unit  30 . In some cases, the flushing is executed before the initiation of the printing on the sheet P following the reception of the printing job and in the middle of the printing on the sheet P. In some cases, the printing unit  30  discharges the ink toward the support base  20  in a state where the sheet P has yet to be transported onto the support base  20  during the flushing. The driving period mentioned above is a period in which the fan  51  is driven for mist suctioning after the termination of the printing job. This driving period is set in advance through an experiment or the like. 
     The ink discharged from the multiple nozzles  31   a  during, for example, the flushing is accommodated in the recovery container  52  via the plurality of discarding portions  24  of the support base  20 . Since the ribs  23  are divided by the discarding portions  24  intersecting with the ribs  23 , it is preferable that the discarding portion  24  have a small width dimension for the sheet P to be stably supported on the ribs  23 . However, since the ink (mist) discharged from the nozzles  31   a  is moved toward the support base  20  while spreading in a fan shape, a small width dimension of the discarding portion  24  might result in adhesion to the supporting portion  22  or the rib  23  other than the discarding portion  24 . As a result, the sheet P is contaminated due to ink transfer onto the sheet P when the sheet P is transported onto, for example, the ink-adhering rib  23 . 
     An increase in the suction force with which the mist is suctioned by the recovery device  50  is conceivable in view of this problem. Once the suction force is increased, the mist is suctioned into the discarding portion  24 , even if the ink (mist) discharged from the nozzle  31   a  spreads in a fan shape, since the suction force generated via the discarding portion  24  by the driving of the fan  51  is large. When a large mist suction force is maintained at all times, that is, when a high rotation speed of the fan  51  is maintained at all times, however, the ink discharged from the nozzle  31   a  during the printing on the sheet P is affected as well. As a result, an image or the like that is printed on the sheet P is disturbed. 
     Accordingly, it is not preferable that a high rotation speed of the fan  51  be maintained at all times and it is preferable that the rotation speed of the fan  51  be increased in a case where the mist is afloat between the printing unit  30  and the support base  20  and the mist might adhere to the rib  23  and the supporting portion  22 , examples of which include a moment during the flushing and a moment following the termination of the printing. 
     In this regard, the control device  60  variably controls the rotation speed of the fan  51  when the recovery device  50  suctions the mist in a state where the mist is afloat between the discharge head  31  and the support base  20 , examples of which include a moment during the flushing and a moment following the termination of the printing job. The fan control unit  63  of the control device  60  changes the rotation speed of the fan  51  by changing the duty ratio of a PWM driving circuit (not illustrated) of the fan  51 . The rotation speed of the fan  51  increases as, for example, the duty ratio increases. In a case where the rotation speed of the fan  51  does not have to be variably controlled, the rotation speed of the fan  51  is set to the rotation speed of the fan  51  during the printing on the sheet P (hereinafter, referred to as a “reference rotation speed”). 
     Examples of a case where the rotation speed of the fan  51  is variably controlled include a moment during the flushing preceding the initiation of the printing on the sheet P, a moment in the middle of the execution of duplex printing on the sheet P, and the driving period following the termination of the printing job. Hereinafter, processing for setting the rotation speed of the fan  51  for each of the occasions will be described. 
     The processing for setting the rotation speed of the fan  51  during the flushing preceding the initiation of the printing on the sheet P will be described first with reference to  FIG. 10 . This setting processing is repeatedly executed at predetermined time intervals until the elapse of a set period of time after the termination of the previous printing job. The set period of time, which is set in advance through an experiment or the like, is a period of time leading to a determination that the cap  32  needs to be mounted on the nozzle  31   a . Examples of the set period of time include a period of time starting at the termination of the printing job and ending at the moment immediately preceding the possibility of the printing quality being affected by the drying of the ink and an excessive increase in its viscosity attributable to the exposure of the nozzle  31   a  to air. 
     The control device  60  determines whether or not a predetermined period of time shorter than the set period of time has elapsed (Step S 11 ). This predetermined period of time, which is set in advance through an experiment or the like, is a period of time during which the exposure of the nozzle  31   a  to the air, the drying of the ink, and an increase in its viscosity are regarded as occurring after the termination of the printing job. Once it is determined that the predetermined period of time has elapsed (Step S 11 : YES), the control device  60  determines whether or not the set period of time has elapsed (Step S 12 ). 
     In a case where it is determined that the set period of time has elapsed (Step S 12 : YES), the control device  60  mounts the cap  32  on the nozzle  31   a  (Step S 13 ). In this case, the control device  60  maintains the rotation speed of the fan  51  at the reference rotation speed (Step S 14 ). The control device  60  temporarily terminates the processing in a case where it is determined that the predetermined period of time has not elapsed (Step S 11 : NO). 
     In a case where it is determined that the set period of time has not elapsed (Step S 12 : NO), the control device  60  determines whether or not the next printing job has been received (Step S 15 ). Once it is determined that the next printing job has not been received (Step S 15 : NO), the control device  60  returns to the determination of Step S 12 . Once it is determined that the next printing job has been received (Step S 15 : YES), the control device  60  determines whether or not a flushing execution period is in progress (Step S 16 ). The flushing execution period is a period starting at the execution of the flushing by the printing unit  30  and ending at the termination of the recovery of the mist afloat between the printing unit  30  and the support base  20  by the recovery device  50 . The flushing execution period is set in advance through an experiment or the like. 
     Once it is determined that the flushing execution period is in progress (Step S 16 : YES), the control device  60  sets the rotation speed of the fan  51  to a rotation speed higher than the reference rotation speed (Step S 17 ). The rotation speed higher than the reference rotation speed is set in advance through an experiment or the like. The amount of suctioning per unit time of the mist afloat between the printing unit  30  and the support base  20  during the driving of the fan  51  at the rotation speed higher than the reference rotation speed may exceed the amount of suctioning per unit time of the mist afloat between the printing unit  30  and the support base  20  during the driving of the fan  51  at the reference rotation speed. The rotation speed higher than the reference rotation speed can be changed at will. Once it is determined that the flushing execution period is not in progress (Step S 16 : NO), the control device  60  temporarily terminates the processing. 
     The processing for setting the rotation speed of the fan  51  in the middle of the execution of the duplex printing on the sheet P will be described below with reference to  FIG. 11 . This setting processing is repeatedly executed during the printing on the sheet P and is terminated at the termination of the printing on the sheet P. This setting processing is not executed in the case of simplex printing on the sheet P. 
     The control device  60  determines whether or not to execute the flushing (Step S 21 ). The flushing is executed during so-called switchback, during which the sheet P is transported onto the support base  20  in a state where the sheet P is reversed for the other surface of the sheet P to be directed toward the discharge head  31  after the termination of the printing on one surface of the sheet P. In the case of printing on the plurality of sheets P, the flushing is executed after the printing on a certain number of the sheets P without the flushing being executed for the switchback of each of the sheets P. In a case where the printing according to the printing job is to be performed on the single sheet P, the flushing is executed during the switchback when the ink at the nozzle  31   a  has a high viscosity and the flushing is not executed during the switchback when the ink at the nozzle  31   a  has a low viscosity. For example, the viscosity of the ink to trigger the execution of the flushing is set in advance and the flushing is executed during the switchback when a viscosity higher than the set ink viscosity is anticipated. 
     Accordingly, the determination of Step S 21  is performed based on whether or not a period is in progress in which the switchback during the execution of the flushing is in progress. 
     Once it is determined that the execution of the flushing is in progress (Step S 21 : YES), the control device  60  sets the rotation speed of the fan  51  to a rotation speed higher than the reference rotation speed (Step S 22 ). Once it is determined that the execution of the flushing is not in progress (Step S 21 : NO), the control device  60  maintains the rotation speed of the fan  51  at the reference rotation speed (Step S 23 ). The rotation speed higher than the reference rotation speed may be equal to or different from the rotation speed higher than the reference rotation speed according to the setting processing illustrated in  FIG. 10 . The rotation speed higher than the reference rotation speed can be changed at will. 
     The processing for setting the rotation speed of the fan  51  during the driving period following the termination of the printing job will be described below with reference to  FIG. 12 . 
     The control device  60  determines whether or not a printing ratio is equal to or higher than a threshold (Step S 31 ). The printing ratio is the share of an image, a character, or the like in the sheet P and is calculated from information on the image, the character, or the like that is included in the printing job. The threshold, which is set in advance through an experiment or the like, is a lower limit value of the printing ratio at which the amount of the mist afloat between the discharge head  31  and the support base  20  is predicted to become excessively large after the termination of the printing job. 
     Once it is determined that the printing ratio is equal to or higher than the threshold (Step S 31 : YES), the control device  60  sets the rotation speed of the fan  51  to a rotation speed higher than the reference rotation speed (Step S 32 ). Once it is determined that the printing ratio is lower than the threshold (Step S 31 : NO), the control device  60  maintains the rotation speed of the fan  51  at the reference rotation speed (Step S 33 ). The rotation speed higher than the reference rotation speed may be equal to or different from the rotation speed higher than the reference rotation speed according to the setting processing illustrated in  FIGS. 10 and 11 . The rotation speed higher than the reference rotation speed can be changed at will. 
     The following effects as well as the effects of the first embodiment are achieved from the present embodiment. 
     (8) If the cap  32  is mounted on the nozzle  31   a  when the next printing job is quickly received after the termination of the printing job, an operation for removing the cap  32  again from the nozzle  31   a  will be included when the printing is performed on the sheet P based on the next printing job, and thus the length of time until the initiation of the printing will increase. Accordingly, it is preferable that the printing on the sheet P based on the next printing job be initiated in a state where the cap  32  is not mounted on the nozzle  31   a . The length of time during which the nozzle  31   a  is exposed to the air increases at this time, and thus the viscosity of the ink in the nozzle  31   a  increases in some cases. During the flushing preceding the printing initiation, the amount of the ink discharged from the nozzles  31   a  is increased. Accordingly, the amount of the mist afloat between the discharge head  31  and the support base  20  increases and the possibility of adhesion to the ribs  23  of the support base  20  increases. 
     In the present embodiment, the rotation speed of the fan  51  during the execution of the flushing preceding the initiation of the printing on the sheet P is controlled to become higher than the reference rotation speed in a case where the next printing job is received after the termination of the printing job and before the elapse of the set period of time in this regard. As a result, the mist suction force increases, and thus the mist afloat between the discharge head  31  and the support base  20  can be suctioned in quantity into the recovery container  52 . Accordingly, mist adhesion to the plurality of ribs  23  of the support base  20  can be suppressed. 
     (9) As is already known, the length of time that is required for the switchback when the duplex printing is performed on the sheet P exceeds the length of time taken for the next sheet P to be transported onto the support base  20  after the printing on one surface of the sheet P is terminated. The printing unit  30  executes the flushing during the switchback in some cases. 
     A certain period of time is required for an effect in the form of the suctioning of the mist into the recovery container  52  being further facilitated by means of an increase in the rotation speed of the fan  51  to be achieved. Accordingly, the printing unit  30  is not capable of achieving the effect in the form of the suctioning of the mist into the recovery container  52  being further facilitated to a sufficient extent, even if the rotation speed of the fan  51  is increased, within a short period of time such as the length of time taken for the next sheet P to be transported onto the support base  20  after the printing on one surface of the sheet P is terminated. 
     In the present embodiment, the rotation speed of the fan  51  is increased when the printing on the sheet P is not performed for a long period of time, examples of which include the switchback during the duplex printing on the sheet P, in this regard. Accordingly, the effect in the form of the suctioning of the mist afloat between the printing unit  30  and the support base  20  into the recovery container  52  being further facilitated can be achieved and mist adhesion to the plurality of ribs  23  of the support base  20  can be suppressed. 
     (10) The total amount of the ink that the printing unit  30  discharges to the sheet P when the printing ratio is high exceeds the total amount of the ink that the printing unit  30  discharges to the sheet P when the printing ratio is low, and thus the amount of the mist afloat between the printing unit  30  and the support base  20  increases after the printing termination. 
     In the present embodiment, the rotation speed of the fan  51  after the printing termination is increased in the case of a high printing ratio in this regard, and thus the mist afloat between the printing unit  30  and the support base  20  is likely to be suctioned into the recovery container  52 . Accordingly, mist adhesion to the plurality of ribs  23  of the support base  20  can be suppressed. 
     Modification Example 
     Each of the embodiments described above may be modified in the form of another embodiment as follows.
         In the second embodiment, one or more of the setting processing regarding the rotation speed of the fan  51  illustrated in  FIGS. 10 to 12  may be omitted. In a case where the entire setting processing regarding the rotation speed of the fan  51  illustrated in  FIGS. 10 to 12  is omitted, for example, control may be performed such that the fan  51  has a constant rotation speed (such as the reference rotation speed).   In the second embodiment, the rotation speed of the fan  51  is allowed to be higher than the reference rotation speed in a case where the printing ratio is equal to or higher than the threshold. The driving period may be lengthened instead in that case. Alternatively, the driving period may be lengthened after the rotation speed of the fan  51  is allowed to be higher than the reference rotation speed.   In each of the embodiments, any length can be set as the lengths of the drooping ribs  57  and the standing ribs  58  in the vertical direction Z. For example, the drooping ribs  57  may have a length in the vertical direction Z that exceeds the lengths of the drooping ribs  57  in the vertical direction Z according to each of the embodiments (refer to  FIG. 7 ) as illustrated in  FIG. 13 . In this case, the gap GZ1 in the vertical direction Z between the lower end portions of the drooping ribs  57  and the bottom wall  53   a  of the recovery container  52  is narrower than the gap GZ1 in the vertical direction Z between the lower end portions of the drooping ribs  57  according to each of the embodiments and the bottom wall  53   a  of the recovery container  52  (refer to  FIG. 7 ). In addition, the lengths of the standing ribs  58  in the vertical direction Z may be exceeded by the lengths of the standing ribs  58  in the vertical direction Z according to each of the embodiments (refer to  FIG. 7 ) as illustrated in  FIG. 13 . In this case, the gap GZ2 in the vertical direction Z between the upper end portions of the standing ribs  58  and the supporting member  56  is wider than the gap GZ2 in the vertical direction Z between the upper end portions of the standing ribs  58  according to each of the embodiments and the supporting member  56  (refer to  FIG. 7 ). The gap GZ1 and the gap GZ2 are equal to each other in the recovery device  50  that is illustrated in  FIG. 13 .       

     Furthermore, the gap GZ1 in the vertical direction Z between the lower end portions of the drooping ribs  57  and the bottom wall  53   a  of the recovery container  52  and the gap GZ2 in the vertical direction Z between the upper end portions of the standing ribs  58  and the supporting member  56  may differ from each other by the length of the drooping rib  57  in the vertical direction Z being exceeded by the length of the drooping rib  57  in the vertical direction Z illustrated in  FIG. 13  as illustrated in  FIG. 14 . The gap GZ1 is wider than the gap GZ2 in the recovery device  50  that is illustrated in  FIG. 14 . The length of the drooping rib  57  in the vertical direction Z that is illustrated in  FIG. 14  is exceeded by the length of the drooping rib  57  in the vertical direction Z according to each of the embodiments, but the length of the drooping rib  57  in the vertical direction Z that is illustrated in  FIG. 14  may be equal to the length of the drooping rib  57  in the vertical direction Z according to each of the embodiments as well. 
     Although not illustrated herein, the gap GZ1 in the vertical direction Z between the lower end portions of the drooping ribs  57  and the bottom wall  53   a  of the recovery container  52  and the gap GZ2 in the vertical direction Z between the upper end portions of the standing ribs  58  and the supporting member  56  may differ from each other by the length of the standing rib  58  in the vertical direction Z being reduced in the recovery device  50  that is illustrated in  FIG. 13 . According to these configurations, the flow rate of the mist can be regulated based on a change in the passage cross-sectional area of a part of the mist flow path.
         In each of the embodiments, an absorbing material  70  may be disposed on the bottom wall  53   a  of the container main body  53 , which is an example of a part constituting the mist flow path RM in the recovery container  52 , as illustrated in  FIG. 15 . Examples of the absorbing material  70  include sponge. It is preferable that the density inside the absorbing material  70  be higher than the density on the surface side of the absorbing material. According to this configuration, the absorbing material  70  facilitates the recovery of the mist in the recovery container  52  upstream of the filter  59  in the flow path RM. In addition, the mist adhering to the surface of the absorbing material  70  is likely to permeate the absorbing material  70  because of a change in the density of the absorbing material  70 . Accordingly, ink pool formation in the surface of the absorbing material  70  can be suppressed. The absorbing material  70  may be disposed on a part of the bottom wall  53   a  and may be disposed on at least one of the supporting member  56 , the drooping rib  57 , and the standing rib  58  that constitute the flow path RM. The absorbing material  70  can also be similarly applied to the recovery device  50  illustrated in  FIGS. 13 and 14 . The absorbing material  70  disposed on the bottom wall  53   a  is an example of components that face the tip portion (lower end portion) of the vertical wall (drooping rib  82 ).   In the recovery device  50  according to each of the embodiments and those illustrated in  FIGS. 13 to 15 , the gap GZ1 in the vertical direction Z between the lower end portions of the drooping ribs  57  and the bottom wall  53   a  of the recovery container  52  may become gradually narrower in the flow path RM as the downstream side closer to the fan  51  is approached.   In the recovery device  50  according to each of the embodiments and those illustrated in  FIGS. 13 to 15 , the gap GZ2 in the vertical direction Z between the upper end portions of the standing ribs  58  and the supporting member  56  may become gradually narrower in the flow path RM as the downstream side closer to the fan  51  is approached.   The supporting member  56  according to each of the embodiments may be omitted. The configuration of the recovery device  50  that is illustrated in  FIG. 16  will be described as an example thereof. The recovery device  50  is provided with a cover  80  instead of the cover  54 . An attachment portion  81 , where a mist-suctioning suction port  81   a  is formed, is disposed on the downstream side of the cover  80  in the transport direction Y. The support base  20  is attached to the attachment portion  81  for communication between the suction port  81   a  and the internal space  21 . A plurality of the drooping ribs  82  are disposed with gaps in the transport direction Y beneath the cover  80  and upstream of the attachment portion  81  in the transport direction Y. The plurality of drooping ribs  82  and the standing ribs  58  are disposed to alternate with each other.       

     As illustrated in  FIG. 16 , the gaps GY1 to GY3 between the drooping ribs  82  and the standing ribs  58  that are adjacent to each other to form the mist flow path RM become gradually narrower toward the downstream side in the flow path RM that is closer to the fan  51  (refer to  FIG. 6 ). In addition, the lengths of the drooping ribs  82  in the vertical direction Z increase from the upstream side toward the downstream side of the flow path RM. Accordingly, the gap GZ1 between the lower end portions of the drooping ribs  82  forming the flow path RM and the bottom wall  53   a  of the recovery container  52  facing the lower end portions becomes gradually narrower toward the downstream side in the flow path RM that is closer to the fan  51 . Furthermore, the lengths of the standing ribs  58  in the vertical direction Z increase from the upstream side toward the downstream side of the flow path RM. Accordingly, the gap GZ2 between the upper end portions of the standing ribs  58  forming the flow path RM and the cover  80  facing the upper end portions becomes gradually narrower toward the downstream side in the flow path RM that is closer to the fan  51 . In an alternative configuration, the gaps GY1 to GY3 may have the same size and the gaps GZ1 and GZ2 may become gradually narrower toward the downstream side in the flow path RM that is closer to the fan  51 . 
     In each of the embodiments, two of the upstream region RM1, the midstream region RM2, and the downstream region RM3 may be combined with each other to constitute the flow path RM. In addition, four or more regions that have different passage cross-sectional areas may constitute the flow path RM. In other words, the number of partitioned regions in the flow path RM is not limited insofar as the flow path RM that is formed by alternating vertical walls such as the drooping ribs  57  and the standing ribs  58  becomes gradually narrower.
         In each of the embodiments, the placement and shape of the plurality of nozzle columns  31   b  of the discharge head  31  can be set at will. The placement and shape of the plurality of discarding portions  24  of the support base  20  are changed similarly to the nozzle columns  31   b  along with a change in the placement and shape of the plurality of nozzle columns  31   b . In other words, the number, placement, and shape of the discarding portions  24  are not limited to the number, placement, and shape of the discarding portions  24  according to each of the embodiments described above insofar as the ink discharged from the discharge head  31  is recovered into the recovery container  52  via the plurality of discarding portions  24  during the flushing by the discharge head  31 .   In each of the embodiments, the plurality of ribs  23  of the support base  20  may extend in a direction intersecting with the transport direction Y. For example, the direction in which the rib  23  extends may be parallel to the direction in which the discarding portion  24  extends. In this case, the ribs  23  and the discarding portions  24  may be alternately placed in the width direction X.   In each of the embodiments, the printing apparatus  10  may be provided with a cap moving motor for moving the cap  32  to the discharge head  31  instead of the head moving motor  34  moving the discharge head  31  to the cap  32 . In this case, the discharge head  31  is fixedly placed at a position facing the support base  20 .   In each of the embodiments, the printing apparatus  10  may also be a multifunction printer without having to be limited to a configuration provided only with a printing function.   The medium is not limited to the sheet P and may be continuous paper, a resin film, a metal foil, a metallic film, a resin-metal composite film (laminate film), a fabric, a nonwoven fabric, a ceramic sheet, and so on.   In each of the embodiments, the printing apparatus  10  is embodied in the form of the ink jet printer. However, the printing apparatus is not limited thereto and may be a liquid discharge device discharging a fluid other than ink (such as a liquid, a liquid body in which functional material particles are dispersed in or mixed with a liquid, and a flowing body such as gel). Examples thereof may include a liquid discharge device discharging a liquid body containing a material such as an electrode material and a color material (pixel material) in the form of dispersion or dissolution and used for liquid crystal display manufacturing, electroluminescence (EL) display manufacturing, surface-emitting display manufacturing, and so on. The examples may also include a liquid discharge device discharging bioorganic matter used for biochip manufacturing and a liquid discharge device discharging a liquid as a sample and used as a precision pipette. The examples may also include a liquid discharge device discharging a lubricant by means of a pin point to precision machinery such as watches and cameras, a liquid discharge device discharging a transparent resin liquid such as a UV curable resin onto a substrate in order to form a micro hemispherical lens (optical lens) or the like used in an optical communication element or the like, and a liquid discharge device discharging an acidic etchant, an alkaline etchant, or the like for etching on a substrate and so on. The examples may also include a liquid discharge device manufacturing 3D models by means of liquid discharge.       

     The entire disclosure of Japanese Patent Application No.: 2016-000401, filed Jan. 5, 2016 is expressly incorporated by reference herein.