Abstract:
A recording device includes: a first suction unit which has a support member for supporting a recording medium and a plurality of suction holes provided in the support member to support the recording medium under control that a second suction force of the suction holes not covered by the recording medium is restricted to be smaller than a first suction force of the suction holes covered by the recording medium; a recording head which performs recording on the recording medium supported by the first suction unit.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a recording device, and more particularly, to a recording device which performs recording by ejecting ink onto a recording medium sucked and transported on a transport member. 
     2. Related Art 
     There has been known a recording device using an ink jet recording head (see JP-A-10-315551). In the recording device, a recording medium is sucked onto a transport belt by a suction force of through holes formed in the transport belt to be transported to a recording area. In this manner, floating of the recording medium from the transport belt is suppressed. 
     However, in the recording device, airflow is generated by the suction force of the through holes not blocked by the recording medium in the recording area of the recording head. The air flow affects a flight state of ink droplets. When the suction force of the through holes is decreased to stabilize the flight state of ink droplets, the floating of the recording medium from the transport belt cannot be sufficiently suppressed. Particularly, since the suction of the recording medium onto the transport belt is started on the upstream side of the recording area in a transport direction, the floating of the recording medium from the transport belt easily occurs. 
     SUMMARY 
     According to an aspect of the invention, there is provided a recording device including: a first suction unit which has a support member for supporting a recording medium and a plurality of suction holes provided in the support member to support the recording medium under control that a second suction force of the suction holes not covered by the recording medium is restricted to be smaller than a first suction force of the suction holes covered by the recording medium; a recording head which performs recording on the recording medium supported by the first suction unit; and a second suction unit which has a support member for supporting a recording medium and a plurality of suction holes provided in the support member and is disposed near the first suction unit in a transport direction of the recording medium and in which a third suction force of the suction holes not covered by the recording medium is set to be larger than the second suction force. Accordingly, an effect of airflow on a flight state of ink droplets can be suppressed and floating of a recording medium from the support member can be sufficiently suppressed. 
     In the recording device, the second suction unit may be disposed on the upstream side of the first suction unit in the transport direction to feed a recording medium to the first suction unit. In the recording device, the second suction unit may be disposed on the downstream side of the first suction unit in the transport direction to transport a recording medium on which recording has been performed by the recording head. 
     In the recording device, each of the first suction unit and the second suction unit may have a plurality of communication channels communicating a suction force generating section which generates a suction force for sucking air with the suction holes, and a suction force adjusting section provided to correspond to the suction holes and restricting the first suction force to be smaller than the second suction force, the communication channel may have: a hole-side channel section which is closer to the suction hole than the suction force adjusting section; and a suction-side channel section which is closer to the suction force generating section than the suction force adjusting section, the suction force adjusting section may have: a diaphragm which is arranged between the hole-side channel section and the suction-side channel section and is displaced toward the hole-side channel section or the suction-side channel section by a differential pressure between the hole-side channel section and the suction-side channel section; an open-close communication hole which is formed in the diaphragm, is opened and closed by the displacement of the diaphragm and communicates the hole-side channel section with the suction-side channel section in an opened state; and an open communication hole which is formed in the diaphragm, is opened regardless of the position of the diaphragm and communicates the hole-side channel section with the suction-side channel section, and a hole diameter of the open communication hole disposed in the recording area may be smaller than a hole diameter of the open communication hole disposed on the upstream side of the recording area in the transport direction. Accordingly, a channel cross-sectional area of some of the communication channels communicating with the suction holes opened in the recording area can be made narrower than that on the upstream side or the downstream side of the recording area in the transport direction. As a result, a recording medium on the upstream side or the downstream side in the transport direction can be sufficiently sucked onto the support member to sufficiently suppress floating of the recording medium from the support member, and airflow generated in the recording area can be weakened to suppress an effect of the airflow on a flight state of ink droplets. 
     In the recording device, each of the first suction unit and the second suction unit may have a plurality of communication channels communicating a suction force generating section which generates a suction force for sucking air with the suction holes, and suction force adjusting sections provided to correspond to the suction holes and restricting the first suction force to be smaller than the second suction force, and the number of the suction force adjusting sections of the first suction unit may be larger than the number of the suction force adjusting sections of the second suction unit. Accordingly, the number of the suction holes, the suction force of which is decreased by the suction force adjusting sections, among the opened suction holes is larger in the recording area than on the upstream side or the downstream side of the recording area in the transport direction. Therefore, airflow generated in the recording area can be made weaker than airflow generated on the upstream side or the downstream side of the recording area in the transport direction. 
     The recording device may further include a suction force generating section which generates a suction force for sucking air, each of the first suction unit and the second suction unit may have a plurality of communication channels communicating the suction force generating section with the suction holes, and a suction force adjusting section provided to correspond to the suction holes and restricting the first suction force to be smaller than the second suction force, the first suction unit may have a first chamber in which the communication channels communicating with the suction holes are disposed, the second suction unit may have a second chamber in which the communication channels communicating with the suction holes are disposed, and the suction force generating sections may be provided to correspond to the first chamber and the second chamber, respectively. Accordingly, a suction force generated in the suction holes blocked by a recording medium can be made stronger than in the case where a suction force is generated in the first chamber and the second chamber by one suction force generating section, and thus the recording medium can be stably sucked onto the transport member. 
     According to another aspect of the invention, there is provided a recording device including: a recording head which performs recording by ejecting ink on a recording medium; a transport member which has a plurality through holes formed therein to transport the recording medium to a recording area of the recording head; a suction unit which has a suction force generating section which generates a suction force for sucking air and a plurality of communication channels which communicate the suction force generating section with the through holes, and sucks the recording medium onto the transport member by generating a suction force in the through holes; and a suction force adjusting section which is provided to correspond to at least the through holes positioned in the recording area and restricts a suction force of the through holes opened to be smaller than a suction force of the through holes blocked by the recording medium, and by the suction force adjusting section, the suction force generated in the opened through holes positioned in the recording area can be made weaker than the suction force generated in the opened through holes positioned on the upstream side or the downstream side of the recording area in the transport direction. Accordingly, airflow generated in the recording area can be weakened to suppress an effect of the airflow on a flight state of ink droplets, and a suction force between a recording medium and the transport member on the upstream side or the downstream side of the recording area in the transport direction can be sufficiently ensured to sufficiently suppress floating of the recording medium at the stage where suction is started or after recording from the transport member. 
     In the recording device, when the through holes are blocked by a recording medium, the suction force adjusting section may increase a channel cross-sectional area of the communication channels communicating with the through holes, and when the through holes are opened, the suction force adjusting section may decrease a channel cross-sectional area of the communication channels communicating with the through holes. Accordingly, without controlling a drive force of the suction force generating section, the suction force of the through holes can be increased when the through holes are blocked by the recording medium, and the suction force of the through holes can be decreased when the through holes are opened. 
     In the recording device, by the suction force adjusting section, a channel cross-sectional area of the communication channels communicating with the opened through holes positioned in the recording area may be made narrower than a channel cross-sectional area of the communication channels communicating with the opened through holes positioned on the upstream side of the recording area in the transport direction. Accordingly, the suction force generated in the opened through holes in the recording area can be made weaker than that on the upstream side of the recording area in the transport direction. 
     In the recording device, some of the suction force adjusting sections may be disposed on the upstream side of the recording area in the transport direction. Accordingly, on the upstream side of the recording area in the transport direction, suction amounts from the opened through holes can be decreased without decreasing the suction force of the through holes blocked by the recording medium. Thus, on the upstream side of the recording area in the transport direction, floating of the recording medium from the transport member can be sufficiently suppressed and airflow generated in the opened through holes can be weakened to suppress an effect of the airflow on a flight state of ink droplets. 
     The above description of the invention does not include all the features of the invention and subcombinations of the features can construct the invention. 
    
    
     
       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 side view illustrating the schematic structure of a recording device. 
         FIG. 2  is a perspective view illustrating the inner structure of the recording device. 
         FIG. 3  is an exploded perspective view illustrating a fan and a recording area chamber in a sheet sucking device. 
         FIG. 4  is an enlarged perspective view illustrating a transport belt and a belt receiving plate. 
         FIG. 5  is a perspective view illustrating a valve. 
         FIG. 6  is a partial sectional view illustrating the sheet sucking device. 
         FIG. 7  is a schematic sectional side view illustrating the operation of the valve and air flows in a communication channel. 
         FIG. 8  is a perspective view illustrating valve plates disposed in an upstream chamber, a recording area chamber and a downstream chamber. 
         FIGS. 9A to 9C  are partial sectional side views illustrating the upstream chamber, the recording area chamber and the downstream chamber. 
         FIG. 10  is a perspective view illustrating a valve plate and a spacer plate disposed in a recording area chamber and spacer plates disposed in an upstream chamber and a downstream chamber. 
         FIGS. 11A to 11C  are partial sectional side views illustrating the upstream chamber, the recording area chamber and the downstream chamber. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described and the following embodiments do not limit the invention, which is defined in the claims. In addition, all the combinations of features described in the embodiments are not essential to the invention. 
       FIG. 1  is a side view illustrating the schematic structure of an ink jet recording device  100  according to this embodiment. As illustrated in the drawing, the recording device  100  has a transport unit  120  which transports a sheet P as a recording medium and plural recording heads  110  which eject ink onto the sheet P to perform a recording operation. 
     The transport unit  120  has a drive roller  124 , driven rollers  125  and  126  and an endless transport belt  140  as a transport member extended over the rollers. The drive roller  124  and the driven roller  125  are substantially horizontally arranged. The driven roller  126  is arranged below a middle position in-between the drive roller  124  and the driven roller  125 . That is, the transport belt  140  is made to extend in a substantially triangular shape by the drive roller  124  and the driven rollers  125  and  126  and a part of the transport belt  140  (hereinafter, referred to as “upper face  141 ”) is made to substantially horizontally extend by the drive roller  124  and the driven roller  125 . A transport drum can be also applied as the transport member. 
     The plural recording heads  110  are arranged to be opposed to the upper face  141  of the transport belt  140 . On the upstream side of the transport unit  120  in a transport direction, a feed roller  121 , a gate roller  122  and a sheet pressing roller  123  are sequentially arranged from the upstream side in the transport direction. The sheet P is transported to the transport unit  120  by the rollers. 
     The transport unit  120  has a sheet sucking device  130  as a suction unit. The sheet sucking device  130  has fans  148 ,  150  and  149  as a suction force generating section, an upstream chamber  158 , a recording area chamber  160  and a downstream chamber  159 . The fans  148 ,  150  and  149  are sequentially arranged in the transport direction on an inner circumferential side of the transport belt  140 . The upstream chamber  158  is arranged between the upper face  141  and the fan  148 . Similarly, the recording area chamber  160  is arranged between the upper face  141  and the fan  150 , and the downstream chamber  159  is arranged between the upper face  141  and the fan  149 . 
     The upstream chamber  158  and the fan  148  are arranged in an upstream area  201  on the upstream side of a recording area  202  of the recording heads  110 . The recording area chamber  160  and the fan  150  are arranged to be opposed to the recording area  202  of the recording heads  110 . The downstream chamber  159  and the fan  149  are arranged in a downstream area  203  on the downstream side of the recording area  202  of the recording heads  110 . 
       FIG. 2  is a perspective view illustrating the inner structure of the recording device  100 . As illustrated in the drawing, each of the recording heads  110  is shorter than a width of the sheet P and they are vertically and horizontally arranged in a direction perpendicular to the transport direction (hereinafter, referred to as “sheet width direction”) and the transport direction. The plural recording heads  110  are arranged in a zigzag manner in the transport direction. 
     Plural through holes  142  are vertically and horizontally arranged in the sheet width direction and the transport direction over the entire area of the transport belt  140 . The plural through holes  142  are arranged in a zigzag manner in the transport direction. 
       FIG. 3  is an exploded perspective view illustrating the fan  150  and the recording area chamber  160  in the sheet sucking device  130 . Since the fans  148  and  149  and the upstream and downstream chambers  158  and  159  have the same structure as the fan  150  and the recording area chamber  160 , respectively, a description thereof will be omitted. 
     As illustrated in the drawing, the fan  150  has a housing  152  and a blade arranged in the housing  152 . A circular intake port  154  is formed in a face of the housing  152  on the side of the recording area chamber  160 . An exhaust port  156  is formed in a side face of the housing  152 . Other than the fan  150 , a blower, a pump or the like can be applied as the suction force generating section. 
     The recording area chamber  160  has a belt receiving plate  161 , a valve plate  162 , a spacer plate  163 , a body  164  and a sealing plate  165 . The belt receiving plate  161 , the valve plate  162 , the spacer plate  163 , the body  164  and the sealing plate  165  are sequentially laminated in a direction from the upper face  141  toward the fan  150 . 
     In the belt receiving plate  161 , plural elliptical grooves  261 , the longitudinal direction of which is the transport direction, are vertically and horizontally arranged in the transport direction and the sheet width direction. The plural grooves  261  are arranged in a zigzag manner in the sheet width direction. 
     A hole-side channel section  262  is formed at the bottom of the groove  261 . The hole-side channel section  262  is formed of a circular through hole. In this embodiment, each groove  261  is provided with one hole-side channel section  262 . However, each groove  261  may be provided with plural hole-side channel sections  262 . 
     In the valve plate  162 , plural circular valves  263  are formed. The valves  263  are arranged so as to overlap the hole-side channel sections  262 . In the spacer plate  163 , plural valve chambers  264  are formed. The valve chambers  264  are formed of circular through holes. The hole-side channel sections  262  and the valves  263  are arranged so as to overlap each other. A diameter of the hole-side channel section  262  is equal to a diameter of the valve  263 . 
     The body  164  is provided with plural suction-side channel sections  265 . The suction-side channel sections  265  are formed of circular through holes. The suction-side channel sections  265  and the valves  263  are arranged so as to overlap each other. A diameter of the suction-side channel section  265  is smaller than a diameter of the valve  263 . A lower portion of the body  164  is provided with a channel  266  which communicates the plural suction-side channel sections  265  with each other. 
     In the sealing plate  165 , a circular through hole  267  is formed so as to overlap the intake port  154  of the fan  150 . A diameter of the through hole  267  is equal to a diameter of the intake port  154 . The intake port  154  and the channel  266  communicate with each other via the through hole  267 . 
       FIG. 4  is an enlarged perspective view illustrating the transport belt  140  and the belt receiving plate  161 . As illustrated in the drawing, the grooves  261  are arranged so as to overlap the arrays of the through holes  142  arranged in the transport direction. A length of the groove  261  in the transport direction is equal to an interval between the through holes  142  aligned in the transport direction. Accordingly, the groove  261  is provided so as to overlap any through hole  142  when the transport belt  140  moves. 
       FIG. 5  is a perspective view illustrating the valve  263 . As illustrated in the drawing, the valve  263  has a diaphragm  271 , a support section  272 , a pair of arms  273 , a pair of arms  274 , a pair of slits  275  as an open-close communication hole and an open communication hole  276 . The diaphragm  271  is formed in a circular shape. The pair of slits  275  having a semicircular shape is formed around the diaphragm  271  to be symmetrical to each other with respect to the center of the diaphragm  271 . The open communication hole  276  is formed at the center of the diaphragm  271 . 
     The support section  272  having a circular shape is arranged around the pair of slits  275 . The diaphragm  271  is supported at both sides by the pair of arms  273  provided between the opposite ends of the pair of slits  275 . A pair of semicircular slits  277  is formed around the support section  272  to be symmetrical to each other with respect to the open communication hole  276 . The support section  272  is supported at the valve plate  162  at both sides by the pair of arms  274  provided between the opposite ends of the pair of slits  277 . 
     Herein, the opposite ends of the slit  275  and the opposite ends of the slit  277  are arranged around the open communication hole  276  with their phases shifted by 90°. Moreover, the arms  273  and  274  are arranged around the open communication hole  276  with their phases shifted by 90°. That is, the valve  263  has a so-called gimbal structure. The valve plate  162  is made of an elastically deformable metal material or a resin material. The valve  263  is formed by etching or punching of metal or molding or punching of resin. 
       FIG. 6  is a partial sectional view illustrating the sheet sucking device  130 . As illustrated in the drawing, the hole-side channel section  262 , the open communication hole  276 , the valve chamber  264  and the suction-side channel section  265  are arranged so that axial centers thereof are aligned on the same straight line indicated by the dashed line in the drawing. Accordingly, a communication channel  180  communicating the through hole  142  with the fan  150  is formed. 
     A diameter of the diaphragm  271  is larger than a diameter of the hole-side channel section  262  and a diameter of the suction-side channel section  265 . Thus, the slit  275  is positioned closer to the outer diameter side than the hole-side channel section  262  and the suction-side channel section  265 . Accordingly, as illustrated in the drawing, when the diaphragm  271  is flush with the valve plate  162 , the slit  275  is blocked by the belt receiving plate  161 . 
       FIG. 7  is a schematic sectional side view illustrating the operation of the valve  263  and air flows in the communication channel  180 . As indicated by the chain double-dashed lines in the drawing, when the suction-side channel section  265  has a negative pressure lower than that of the hole-side channel section  262  due to driving of the fan  150 , the diaphragm  271  elastically deforms the arm  273  toward the suction side to displace the arm  273  toward the suction side. 
     When the through hole  142  is not blocked by the sheet P, the pressure in the hole-side channel section  262  is approximately atmosphere pressure and the suction-side channel section  265  has a negative pressure. Therefore, a differential pressure between the sections increases. In this pressure state, the diaphragm  271  moves downward up to the lowest position of the valve chamber  264  to be brought into contact with an upper face of the body  164 . Accordingly, the slit  275  is blocked by the upper face of the body  164  and thus all of the air flows in the communication channel  180  pass through the open communication hole  276 . 
     On the other hand, when the through hole  142  is blocked by the sheet P, the pressure in the hole-side channel section  262  becomes a negative pressure and thus a differential pressure between the hole-side channel section  262  and the suction-side channel section  265  decreases. In this pressure state, the diaphragm  271  is stopped at a position in which a restoring force caused by the elasticity of the arms  273  and  274  is balanced with a force of the air flows in the communication channel  180  pressing the diaphragm  271 . 
     Herein, the position at which the diaphragm  271  is stopped is an intermediate position between the highest position and the lowest position of the valve chamber  264  and the slit  275  is opened. Accordingly, the air flows in the communication channel  180  pass through the open communication hole  276  and the slit  275 . 
     That is, when the through hole  142  is opened, a channel cross-sectional area of the valve chamber  264  decreases, and when the through hole  142  is blocked, the channel cross-sectional area of the valve chamber  264  increases. Accordingly, when the through hole  142  is opened, a suction force generated in the through hole  142  decreases. However, when the through hole  142  is blocked, a suction force generated in the through hole  142  increases. 
     When the open communication hole  276  is not formed in the diaphragm  271 , the diaphragm  271  completely blocks the communication channel  180  in a state in which the through hole  142  is not blocked by the sheet P. Accordingly, even when the through hole  142  is subsequently opened, the pressure in the hole-side channel section  262  is not lowered from the atmosphere pressure, and thus the suction from the through hole  142  does not occur and the sheet P is not sucked onto the transport belt  140 . 
       FIG. 8  is a perspective view illustrating the valve plates  162  disposed in the upstream chamber  158 , the recording area chamber  160  and the downstream chamber  159 . As illustrated in the drawing, the valve plate  162  disposed in the recording area  202  is provided with the open communication holes  276 . The valve plate  162  disposed in the upstream area  201  is provided with open communication holes  376 , and the valve plate  162  disposed in the downstream area  203  is provided with open communication holes  476 . 
       FIGS. 9A to 9C  are partial sectional side views illustrating the upstream chamber  158 , the recording area chamber  160  and the downstream chamber  159 . As illustrated in  FIGS. 9A and 9C , hole diameters of the open communication holes  376  and  476  formed in the valve plate  162  disposed in the upstream chamber  158  and the downstream chamber  159  are D 1 . As illustrated in  FIG. 9B , a hole diameter of the open communication hole  276  formed in the valve plate  162  disposed in the recording area chamber  160  is D 2 , which is smaller than D 1 . 
     Next, actions of the embodiment will be described. In the recording device  100 , when a print job is started, the sheet P is transported to a nip section between the driven roller  125  and the sheet pressing roller  123  by the feed roller  121  and the gate roller  122 . The sheet P is pressed onto the transport belt  140  while passing through the nip section. 
     In the upstream area  201 , the sheet P pressed onto the transport belt  140  is sucked onto the upper face  141  of the transport belt  140  by a suction force generated in the through holes  142  by the fan  148 , and is transported to the recording area  202  by the rotation of the transport belt  140 . In the recording area  202 , the sheet P is sucked onto the upper face  141  of the transport belt  140  by a suction force generated in the through holes  142  by the fan  150 , and is transported by the transport belt  140 . At this time, recording is performed on the sheet P by ejecting ink from the recording heads  110 . The sheet P on which the recording operation has been performed is sucked onto the upper face  141  of the transport belt  140  by a suction force generated in the through holes  142  by the fan  149  in the downstream area  203 , and is transported to the downstream side of the transport belt  140  to be discharged from the recording device  100 . 
     Herein, while the sheet P is transported to the upstream area  201 , the recording area  202  and then the downstream area  203 , the through holes  142  of the areas are opened. Thus, each of the diaphragms  271  blocks the slit  275  at the lowest position of the valve chamber  264 . Accordingly, the air channel for the valve chamber  264  becomes a first channel passing through the open communication hole  276  and a channel cross-sectional area of the valve chamber  264  becomes minimum in a changeable range. 
     When the sheet P is transported to the areas, the through holes  142  positioned outside of the transport areas for the sheet P in the areas are opened, so the channel cross-sectional area of the valve chambers  264  communicating with the through holes  142  does not change. On the other hand, the through holes  142  positioned in the transport areas for the sheet P in the areas are blocked by the sheet P, so inner pressures in the hole-side channel sections  262  communicating with the through holes  142  are lowered and thus a differential pressure between the hole-side channel section  262  and the suction-side channel section  265  decreases. Accordingly, the diaphragm  271  is displaced toward the hole-side channel section  262  and the slit  275  is opened. Thus, the air channel for the valve chamber  264  becomes a second channel passing through the open communication hole  276  and the slit  275  and the channel cross-sectional area of the valve chambers  264  increases. 
     As hole diameters of the open communication holes  276 ,  376  and  476  increase, air suction amounts from the open communication holes  276 ,  376  and  476  when the through holes  142  are blocked by the sheet P and opened increase. Accordingly, promptness of the change in inner pressure of the hole-side channel section  262  increases and thus responsiveness of the diaphragm  271  is improved. In addition, since the air suction amounts from the open communication holes  276 ,  376  and  476  increase, airflow generated outside the opened open communication holes  276 ,  376  and  476  becomes strong and thus has an effect on a flight state of the ink. 
     Herein, the hole diameter of the open communication hole  276  arranged in the recording area  202  is D 2  and the hole diameters of the open communication holes  376  and  476  arranged in the upstream area  201  and the downstream area  203  are D 1 , which is larger than D 2 . Accordingly, the responsiveness of the diaphragms  271  when the through holes  142  are blocked by the sheet P is more rapid in the upstream area  201  and the downstream area  203  than in the recording area  202 . Accordingly, when the sheet P is transported to the vicinity of the through holes  142 , the negative pressures of the hole-side channel sections  262  communicating with the through holes  142  are more rapidly generated in the upstream area  201  and the downstream area  203  than in the recording area  202 . 
     Since the channel cross-sectional area of the valve chambers  264  communicating with the opened through holes  142  are narrower in the recording area  202  than in the upstream area  201  and the downstream area  203 , the air suction amounts from the opened through holes  142  become smaller in the recording area  202  than in the upstream area  201  and the downstream area  203 . Accordingly, airflow generated around the opened through holes  142  in the recording area  202  is weaker than airflow generated around the opened through holes  142  in the upstream area  201  and the downstream area  203 . 
     As described above, the air suction amounts from the through holes  142  which are opened in the recording area  202  can be decreased without decreasing the suction force of the through holes  142  which are blocked by the sheet P in the upstream area  201  and the downstream area  203 . Accordingly, the suction force between the transport belt  140  and the sheet P in the upstream area  201  and the downstream area  203  can be sufficiently ensured to sufficiently suppress floating of the sheet P from the transport belt  140  and weaken airflow generated in the recording area  202 , and thus an effect of the airflow on a flight state of ink droplets can be suppressed. This is particularly effective when borderless printing is performed for the front end or back end of the sheet P. Moreover, in the upstream area  201 , this is effective from the viewpoint that the sheet P at the stage where the suction onto the transport belt  140  is started can be sucked onto the transport belt  140  in a short time. 
     In addition, in the downstream area  203 , when the sheet P swollen by ink blocks the through holes  142 , the sheet P can be sucked onto the transport belt  140  by a sufficient suction force. Accordingly, cockling of the sheet P swollen by ink and floating of the sheet P from the transport belt  140  can be suppressed. Variation in behavior caused in the sheet P by detachment of the sheet P from the transport belt  140  also can be suppressed. 
     In addition, in this embodiment, a channel cross-sectional area of some of the communication channels  180  is increased or decreased by the displacement of the diaphragms  271  by the differential pressure between the hole-side channel sections  262  and the suction-side channel sections  265 . Accordingly, without the change in drive forces for the fans  148 ,  149  and  150 , the suction force of the through holes  142  can be increased when the through holes  142  are blocked by the sheet P, and the suction force of the through holes  142  can be decreased when the through holes  142  are opened. 
     In this embodiment, a channel cross-sectional area of some of the communication channels  180  communicating with the opened through holes  142  is narrower in the recording area  202  than in the upstream area  201  and the downstream area  203 . Accordingly, the suction force generated in the opened through holes  142  in the recording area  202  can be made weaker than that in the upstream area  201  and the downstream area  203 . 
     In this embodiment, the hole diameters of the open communication holes  276  and  376  formed in the diaphragms  271  are smaller in the recording area  202  than in the upstream area  201  and the downstream area  203 . Accordingly, a channel cross-sectional area of some of the communication channels  180  communicating with the opened through holes  142  in the recording area  202  can be made narrower than those in the upstream area  201  and the downstream area  203 . 
     In this embodiment, some of the valves  263  are arranged in the upstream area  201  and the downstream area  203 . Accordingly, in the upstream area  201  and the downstream area  203 , the suction amounts from the opened through holes  142  can be decreased without decreasing the suction force of the through holes  142  blocked by the sheet P. Accordingly, in the upstream area  201  and the downstream area  203 , the floating of the sheet P from the transport belt  140  can be sufficiently suppressed and airflow generated in the opened through holes  142  can be weakened to suppress an effect of the airflow on a flight state of ink droplets. 
     In this embodiment, the upstream chamber  158  and the recording area chamber  160  are arranged in the upstream area  201  and the recording area  202 , respectively, and the fans  148  and  150  are provided to correspond to the chambers, respectively. Accordingly, a suction force generated in the through holes  142  blocked by the sheet P can be made stronger than in the case where a suction force is generated in the recording area chamber  160  and the upstream chamber  158  by one fan and thus the sheet P can be stably sucked onto the transport belt  140 . 
     Similarly, the downstream chamber  159  and the recording area chamber  160  are arranged in the downstream area  203  and the recording area  202 , respectively, and the fans  149  and  150  are provided to correspond to the chambers, respectively. Accordingly, a suction force generated in the through holes  142  blocked by the sheet P can be made stronger than in the case where a suction force is generated in the recording area chamber  160  and the downstream chamber  159  by one fan and thus the sheet P can be stably sucked onto the transport belt  140 . 
     The transport belt  140  is an example of a support member. The through hole  142  is an example of a suction hole. A suction force of the through holes  142  not covered by the sheet P in the recording area  202  is an example of a second suction force. A suction force of the through holes  142  covered by the sheet P in the recording area  202  is an example of a first suction force. A portion supporting the sheet P in the recording area  202  of the transport belt  140  is an example of a first suction unit. 
     Suction forces of the through holes  142  not covered by the sheet P in the upstream area  201  and the downstream area  203  are an example of a third suction force. Portions supporting the sheet P in the upstream area  201  and the downstream area  203  of the transport belt  140  are an example of a second suction unit. 
     Next, other embodiments will be described. The same components as in the above embodiment will be denoted by the same reference signs and a description thereof will be omitted.  FIG. 10  is a perspective view illustrating the valve plate  162  and the spacer plate  163  disposed in the recording area chamber  160  and the spacer plates  163  disposed in the upstream chamber  158  and the downstream chamber  159 . As illustrated in the drawing, the valve plate  162  is arranged in the recording area  202  and the valve plate  162  is not arranged in the upstream area  201  and the downstream area  203 . 
       FIGS. 11A to 11C  are partial sectional side views illustrating the upstream chamber  158 , the recording area chamber  160  and the downstream chamber  159 . As illustrated in  FIGS. 9A and 9C , in the upstream chamber  158  and the downstream chamber  159 , the valve plate  162  is not present between the belt receiving plate  161  and the spacer plate  163 , so the valve chambers  264  have no valve  263 . Accordingly, a channel cross-sectional area of the valve chambers  264  is constant regardless of whether the sheet P blocking the through holes  142  is present. 
     As illustrated in  FIG. 11B , in the recording area  160 , the valve plate  162  is present between the belt receiving plate  161  and the spacer plate  163 , so the valves  263  are present in the valve chambers  264 , respectively. Accordingly, a channel cross-sectional area of the valve chambers  264  increases when the through holes  142  are blocked by the sheet P and the channel cross-sectional area decreases when the through holes  142  are opened. 
     Accordingly, in the recording area  202 , when the through holes  142  are opened, the suction amounts from the through holes  142  are decreased by the valves  263 . On the other hand, in the upstream area  201 , the suction force generated in the through holes  142  when the sheet P is transported to the vicinity of the through holes  142  is not decreased. Accordingly, airflow generated in the recording area  202  can be made weaker than airflow generated in the upstream area  201 . In addition, in the upstream area  201 , the suction force generated in the through holes  142  when the sheet P is transported to the vicinity of the through holes  142  can be made stronger than that in the recording area  202 . Similarly, the airflow generated in the recording area  202  can be made weaker than the airflow generated in the downstream area  203 . In the downstream area  203 , the suction force generated in the through holes  142  when the sheet P is transported to the vicinity of the through holes  142  can be made stronger than that in the recording area  202 . 
     In this embodiment, the valves  263  are not arranged in the upstream area  201  and the downstream area  203 . However, the recording area  202  may be provided with a larger number of the valves  263  than in the upstream area  201  and the downstream area  203  and the valves  263  may be arranged in the upstream area  201  and the downstream chamber  203 . In this case, the valves  263  may be arranged so that the number of the valves  263  gradually increases from the upstream side to the downstream side in the transport direction in the upstream area  201 . Similarly, the valves  263  may be arranged so that the number of the valves  263  gradually decreases from the upstream side to the downstream side in the transport direction in the downstream area  203 . 
     As described above, the embodiments of the invention have been described. However, the technical scope of the invention is not limited to the above description. It is obvious to those skilled in the art that various changes or modifications may be made to the embodiments. It is obvious from the claims that configurations to which such changes or modifications are made can be also included in the technical scope of the invention.