Abstract:
The image forming apparatus comprises: a line type recording head which is arranged so that a longitudinal direction thereof is substantially orthogonal to a conveyance direction of a recording medium; a suction pipe which is disposed in parallel with the recording head and connected to a suctioning device; a rotating body which is supported rotatably on an outer circumference of the suction pipe and has a first opening section and a second opening section; a platen which is arranged in the first opening section of the rotating body movably in parallel with the conveyance direction of the recording medium; and a cap member which is arranged in the second opening section of the rotating body and adapted to cap nozzles of the recording head, wherein the recording medium is suctioned onto the platen and parallelly moved along a conveyance path in a state where the first opening section of the rotating body is connected to the suction pipe.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an image forming apparatus and more particularly, to an image forming apparatus provided with a nozzle recovery unit on the side thereof opposing the nozzle surface of a recording head.  
         [0003]     2. Description of the Related Art  
         [0004]     An image forming apparatus based on an inkjet method forms images on recording paper by discharging ink onto recording paper from a recording head. In an image forming apparatus of this kind, in order to clean the nozzles of the recording head and prevent the nozzles from drying out, nozzle recovery processing is carried out whereby, for example, ink is discharged from the nozzles at prescribed time intervals (preliminary discharge), of the nozzles are cleaned by wiping the nozzles with a blade, or the like. This nozzle recovery processing is problematic in that, if the recording head is withdrawn until a region outside the image forming region, then the overall size of the apparatus becomes very large, the time taken to perform maintenance becomes long, and the efficiency of image forming declines. In order to resolve this, technology is known wherein a platen unit and a maintenance unit are provided on a rotating body disposed opposing the recording head (see Japanese Patent Application Publication No. 2001-71521).  
         [0005]     More specifically, in the image forming apparatus disclosed in Japanese Patent Application Publication No. 2001-71521, a cap for covering the discharging surface of the recording head, and a blade, or the like, for wiping the nozzles are provided on a rotating body, on the opposite side to a platen unit, and maintenance of the recording had is carried out by causing the rotating body to rotate and making the cap and blade contact the recording head.  
         [0006]     However, in the case of full-surface marginless printing for forming an image on the entire surface of the recording paper, ink falling beyond the sides of the recording paper may land on the platen unit, and hence there is a risk that the rear surface of the subsequently conveyed recording paper may become soiled. In order to resolve this situation, technology is known whereby recording is performed by causing a platen made from a plurality of holding plates disposed at prescribed intervals to rotate in synchronization with the conveyance of the recording paper (see Japanese Patent Application Publication No. 2001-80145). In this image forming apparatus, since the platen is hidden on the rear side of the recording paper, full-surface marginless printing can be carried out without causing soiling of the platen by means of ink beyond the edges of the recording paper.  
         [0007]     In the image forming apparatus described in Japanese Patent Application Publication No. 2001-80145, however, since the platen is provided on the circumferential face of the rotating body, close contact between the recording paper and the platen cannot be achieved, and waves may arise in the paper, in addition to which, since the surface of the platen supporting the recording paper, which makes contact with the recording paper, is a curved surface, then the distance of flight of the ink ejected from the nozzles of the recording head is not uniform, and hence image quality will decline.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is contrived in view of such circumstances, and an object thereof is to provide an image forming apparatus whereby the clearance between the nozzles and the recording paper can be maintained at a uniform value, and good image quality can be obtained.  
         [0009]     In order to attain the aforementioned object, the present invention is directed to an image forming apparatus, comprising: a line type recording head which is arranged so that a longitudinal direction thereof is substantially orthogonal to a conveyance direction of a recording medium; a suction pipe which is disposed in parallel with the recording head and connected to a suctioning device; a rotating body which is supported rotatably on an outer circumference of the suction pipe and has a first opening section and a second opening section; a platen which is arranged in the first opening section of the rotating body movably in parallel with the conveyance direction of the recording medium; and a cap member which is arranged in the second opening section of the rotating body and adapted to cap nozzles of the recording head, wherein the recording medium is suctioned onto the platen and parallelly moved along a conveyance path in a state where the first opening section of the rotating body is connected to the suction pipe.  
         [0010]     According to the present invention, since the recording medium is suctioned in a state where the first opening section is connected to the suction pipe, and the recording medium is conveyed over the platen which moves horizontally in the direction of conveyance, it is possible to prevent occurrence of waves in the recording medium, and hence the clearance between the nozzles and the recording medium is uniform and the flight distance of the ink is maintained at a uniform distance. Thereby, it is possible to improve the accuracy of the landing position of the ink and hence good image quality can be obtained. A platen is used which is provided with suction holes connected to a suction pipe, through which air is sucked out, and the recording medium is suctioned onto the platen by means of these suction holes.  
         [0011]     Preferably, the nozzles are suctioned in a state where the cap member caps the nozzles and the second opening section of the rotating body is connected to the suction pipe. According to this, since the cap member caps and suctions the nozzles in a state where the second opening section of the rotating body is connected to the suction pipe, then it is possible to prevent blockages in the nozzles.  
         [0012]     Preferably, the image forming apparatus further comprises: a blade which is arranged at the platen and advanced and withdrawn with respect to the nozzles of the recording head, wherein the platen is moved in a state where the blade is abutting against the nozzles, whereby the nozzles are wiped by the blade. According to this, since a blade advanced and withdrawn with respect to the nozzles of the recording head is provided in the platen, and the platen is moved in a state where the blade is abutting against the nozzles, whereby the nozzles are wiped by the blade, then it is possible to remove foreign material, and the like, adhering to the nozzles.  
         [0013]     Preferably, the rotating body and the platen are respectively divided in the direction orthogonal to the conveyance direction of the recording medium into divided portions independently drivable. According to this, since the rotating body and the platen are divided respectively in the longitudinal direction thereof orthogonal to the conveyance direction of the recording medium, and each divided portion thereof is drivable independently, then it is possible to drive a platen that corresponds to the paper size.  
         [0014]     Preferably, the platen comprises first and second platens independently movable in the conveyance direction of the recording medium. According to this, since the platen is constituted by the first platen and the second platen, that move independently in the conveyance direction of the recording medium, then conveyance of the recording medium is facilitated.  
         [0015]     In the present specification, the term “recording” indicates the concept of forming images in a broad sense, including text. Moreover, “recording medium” indicates a medium on which an image is formed by means of a recording head (this medium may be called an image forming medium, recording medium, image receiving medium, recording paper, or the like), and this term includes various types of media, irrespective of material and size, such as continuous paper, cut paper, sealed paper, resin sheets, such as OHP sheets, film, cloth, and other materials.  
         [0016]     A “full line type recording head” is usually disposed following a direction that is orthogonal to the relative direction of conveyance of the recording medium (for example, the conveyance direction of the recording medium), but modes may also be adopted wherein the recording head is disposed following an oblique direction that forms a prescribed angle with respect to the direction orthogonal to the relative direction of movement. Furthermore, the arrangement of the nozzles in the recording head is not limited to being a single line type arrangement, and a matrix arrangement comprising a plurality of rows may also be adopted. Moreover, a mode may also be adopted wherein a row of nozzles corresponding to the entire width of the recording medium is constituted by combining a plurality of short dimension recording head units having nozzle rows which do not reach a length corresponding to the entire width of the recording medium.  
         [0017]     According to the present invention, since a platen which moves horizontally is provided on a rotating body for performing nozzle recovery, it is possible to carry out nozzle recovery processing while at the same time maintaining a uniform clearance between the nozzles of the recording head and the recording paper, and hence obtaining good image quality. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein:  
         [0019]      FIG. 1  is a side view showing an image forming apparatus according to the first embodiment of the present invention;  
         [0020]      FIG. 2  is an oblique view of a nozzle recovery unit in the image forming apparatus;  
         [0021]      FIG. 3  is an oblique view of the structure of a blade of the nozzle recovery unit;  
         [0022]      FIG. 4  is a side view of the image forming apparatus in the stationary state prior to the start of image recording;  
         [0023]      FIG. 5  is a principal block diagram showing the system composition of the image forming apparatus;  
         [0024]      FIGS. 6A  to  6 H are descriptive diagrams showing the positional relationship between a platen and recording paper, in the image forming apparatus according to the first embodiment;  
         [0025]      FIG. 7  is a side view showing an image forming apparatus according to the second embodiment of the present invention; and  
         [0026]      FIGS. 8A  to  8 I are descriptive diagrams showing the positional relationship between a platen and recording paper, in the image forming apparatus according to the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Below, a first embodiment of an image forming apparatus according to the present invention is described with reference to the accompanying drawings.  FIG. 1  is a side view showing the composition of an image forming apparatus  10  according to the first embodiment, and  FIG. 2  is an oblique view showing the composition of a nozzle recovery unit  14  used in the image forming apparatus  10 .  
         [0028]     The image forming apparatus  10  comprises: a nozzle head  12 ; a nozzle recovery unit  14  for the recording head  12 , disposed in a position opposing the recording head  12 ; fixed guide plates  18 A and  18 B for guiding recording paper  16  while holding the recording paper  16  in a flat state; a paper supply unit  20  whereby the recording paper  16  is supplied; and a paper output unit  22  for externally outputting the recording paper  16  on which an image has been formed.  
         [0029]     The recording head  12  is constituted by a so-called line type recording head, wherein a line type head having a length corresponding to the width of the recording paper  16  is disposed in a direction that is orthogonal to the conveyance direction of the recording paper, (i.e., in the main scanning direction, which is the direction perpendicular to the sheet of  FIG. 1 ). In the recording head  12 , heads corresponding to respective ink colors are disposed in the order, black (K), cyan (C), magenta (M) and yellow (Y), from the upstream side, following the direction of conveyance of the recording paper  16  (arrow A).  
         [0030]     Conveyance rollers  24  and fixed guide plates  18 A are disposed on the upstream side of the recording head  12  in the conveyance direction of the recording paper  16  (the right-hand side in  FIG. 1 ), and a paper supply unit  20  is provided further on the upstream side of the conveyance rollers  24 . A cassette  21  in which the recording paper (cut paper)  16  is stacked and loaded is installed detachably in the paper supply unit  20 . A composition may also be adopted wherein a plurality of cassettes loaded with recording paper  16  of different sizes are provided in a parallel fashion. The cut paper is conveyed and supplied from the cassette  21  to the conveyance roller  24  by a supply roller  27 .  
         [0031]     A fixed guide plate  18 B is provided on the downstream side (the left-hand side in  FIG. 1 ) of the recording head  12  in the conveyance direction, and the paper output unit  22  having paper output rollers  23  is provided further on the downstream side of the fixed guide plate  18 B. A paper output tray (not shown) on which sheets of recording paper whereon images have been formed are stacked is provided in the paper output unit  22 .  
         [0032]     The drive force of the motor  109  (see  FIG. 5 ) described hereinafter is transmitted to at least one of the conveyance rollers  24 , and the recording paper  16  supplied from the paper supply unit  20  is guided by the conveyance rollers  24 , conveyed from right to left in  FIG. 1 , and an image is formed thereon by the recording head  12 , whereupon the recording paper  16  is outputted via the paper output unit  22 .  
         [0033]     The nozzle recovery unit  14  is provided in a substantially parallel fashion to the recording head  12 , in a position opposing the nozzle surface of the recording head  12 , below the conveyance path of the recording paper  16 . As shown in  FIG. 2 , the nozzle recovery unit  14  comprises rotating bodies  30  and  32 , platens  34  and  36 , and one liquid receiving pipe  38  disposed in a substantially parallel to the recording heads  12 .  
         [0034]     As shown in  FIG. 2 , the rotating bodies  30  and  32  have an approximately tubular shape, and are supported axially in a rotatable fashion about the fixed liquid receiving pipe  38 , which is disposed in a parallel direction to the main scanning direction of the recording head  12 , and is connected to a pump P. The rotating bodies  30  and  32  are disposed in a coaxial fashion, and each of the rotating bodies  30  and  32  is able to rotate independently. Furthermore, gears  44 A and  44 B which mesh with drive gears  42 A and  42 B of motors  40  and  41  are formed on either end portion of the rotating bodies  30  and  32 , in the main scanning direction, by means of which the rotating bodies  30  and  32  are driven in rotation independently by the motors  40  and  41 . A portion of the liquid receiving pipe  38  is cutaway to form a cutaway section  46 , and when the pump P is operated, waste liquid can be introduced into and suctioned via this cutaway section  46 . Furthermore, the inner wall of the liquid receiving pipe  38  receives a liquid-repelling treatment, in such a manner that fluid attached to the inner wall flows away readily. In this manner, recovery of ink is facilitated. In the present embodiment, one nozzle recovery unit  14  is provided for an integrated head comprising the respective heads of the colors, but if there are a plurality of independent heads for the colors, then it is possible to reuse the inks by having a plurality of recovery units on the side opposing the heads.  
         [0035]     A portion of the circumferential surface of each of the rotating bodies  30  and  32  is cutaway to form elongated holes  48  and  50 .  
         [0036]     As shown in  FIG. 1 , the elongated holes  48  and  50  connect with the cutaway section  46  in the aforementioned liquid receiving pipe  38 , when the rotating bodies  30  and  32  are rotated and the elongated holes  48  and  50  are positioned facing towards the upper side, and air can be suctioned inside the rotating bodies  30  and  32  through the elongated holes  48  and  50 . Moreover, the platens  34  and  36  for supporting the recording paper  16  are provided in the rotating bodies  30  and  32  in such a manner that the platens  34  and  36  cover a portion of the elongated holes  48  and  50 . Suction holes  34   a  and  36   a  are formed in the platens  34  and  36 , and when the pressure in the interior of the elongated holes  48  and  50  is reduced by means of the pump P, the recording paper can be suctioned by the suction holes  34   a  and  36   a . The platens  34  and  36  are formed in such a manner that the dimension L 1  of the platen  34  on the left-hand side in  FIG. 2  is shorter than the dimension L 2  of the platen  36  on the right-hand side.  
         [0037]     Each of the platens  34  and  36  screws together with a screw shaft  58 , which is a drive shaft of a motor  56  installed in the vicinity of each of the elongated holes  48  and  50 . By driving each screw shaft  58 , each of the platens  34  and  36  is driven along the direction of conveyance of the recording paper  16 , in other words, following the sub-scanning direction (the direction indicated by arrow B). Furthermore, the platens  34  and  36  are provided with a blade  60  which wipes the nozzle surface of the recording head  12 , as shown in  FIG. 1 . As shown in  FIG. 3 , the blade  60  is coupled to an oval-shaped cam  64  that is coupled directly to the output shaft of a motor  62  provided on the platens  34  and  36 , and it is raised and lowered along guide grooves  66  formed in the platens  34  and  36 , thereby causing the blade  60  to project from the elongated holes  48  and  50 , in such a manner that the top end of the blade  60  can abut against the nozzle surface of the recording head  12 . In this state, if the platens  34  and  36  are driven along the sub-scanning direction, then the blade  60  moves in the sub-scanning direction and the nozzle surface is wiped by the top end of the blade  60 . Although only a portion of the blade  60  is illustrated in  FIG. 3  in order to simply the description, the blade  60  is in fact disposed along the platens  34  and  36  in such a manner that the blade  60  can wipe the entire area of the nozzle surface of the recording head  12 .  
         [0038]     As shown in  FIG. 1 , opening sections  67 A and  67 B are formed in the circumferential surface of the rotating bodies  30  and  32 , in positions opposing by 180° the positions of the elongated holes  48  and  50 . Caps  68 A and  68 B for covering the nozzle surface of the recording head  12  when images are not being formed, are installed in the opening sections  67 A and  67 B. As shown in  FIG. 4 , when the rotating bodies  30  and  32  are rotated and the caps  68 A and  68 B are positioned facing towards the upper side, the opening sections  67 A and  67 B connect to the cutaway section  46  of the liquid receiving pipe  38  in such a manner that air can be suctioned with the caps  68 A and  68 B. Furthermore, the nozzle surface of the recording head  12  can be sealed (capped) by means of the caps  68 A and  68 B. The caps  68 A and  68 B are constituted by elastic members made of rubber, or the like. By means of this embodiment, it is possible to restrict drying of the ink.  
         [0039]     As shown in  FIG. 1 , a recording paper detection unit  70  is provided in the vicinity of the fixed guide plate  18 A. The recording paper detection unit  70  reads in the position and size of the recording paper, and determines the timing of ink discharge onto the recording paper  16 . Phase detection units  72  and  73 , which are provided in the vicinity of the nozzle recovery unit  14 , determine the rotational phase of the rotating bodies  30  and  32 , respectively. Platen detection units  74  and  75 , which are disposed in the vicinity of the platens  34  and  36 , detect the positions of the platens  34  and  36 , respectively.  
         [0040]      FIG. 5  is a principal block diagram showing the system composition of the image forming apparatus  10 . The image forming apparatus  10  comprises a communication interface  100 , a system controller  102 , a print control unit  110 , a head driver  112 , a sensor unit  114 , and the like.  
         [0041]     The communication interface  100  is an interface unit for receiving image data transmitted by a host computer  120 . Image data sent from the host computer  120  is read into the image forming apparatus  10  through the communication interface  100 , and it is stored temporarily in an image memory  104 .  
         [0042]     The system controller  102  is a control unit for controlling the various sections, such as the communication interface  100 , the image memory  104 , the motor driver  106 , and the like. The system controller  102  is constituted by a central processing unit (CPU), peripheral devices relating to therefor, and the like. The system controller  102  controls communications with the host computer  120  and writing to and reading from the image memory  104 . Moreover, the system controller  102  generates control signals for controlling various operations, such as the rotational commands for the rotating bodies  30  and  32  supplied to the motors  40  and  41 , determines the positions of the platens  34  and  36  according to the motors  56 , drives the blade  60  by means of the motor  62 , and conveys the recording paper  16  by means of the motor  109 , and so on.  
         [0043]     The motor driver  106  is a driver (drive circuit) which drives the motors  40  and  41 ,  56 ,  62  and  109  in accordance with control signals from the system controller  102 .  
         [0044]     The print control unit  110  is a control unit for controlling various sections, such as the head driver  112 , and the like, according to the detection results outputted from the sensor unit  114 . In accordance with the control implemented by the system controller  102 , the print control unit  110  performs various processes, and the like, in order to generate signals for controlling image formation, from the image data in the image memory  104 , and the print control unit  110  supplies the image formation control signals (image data) thus generated to the head driver  112 . The head driver  112  drives the recording heads corresponding to various colors (K, C, M, Y) in the recording head  12 , according to the image data supplied from the print control unit  110 .  
         [0045]     The sensor unit  114  provided in the print control unit  110  is a block comprising the aforementioned recording paper detection unit  70 , the phase detection units  72  and  73 , the plate detection units  74  and  75 , and the like, and the detection results obtained by these various detection units are supplied to the print control unit  110 . In the print control unit  110 , prescribed calculational processes are carried out according to the detection results obtained by the respective detection units, and these detection results are supplied to the system controller  102 . More specifically, the ink discharge timing, and the like, is determined according to the detection results in the recording paper detection unit  70 , and the drive positions of the rotating bodies  30  and  32  are detected according to the detection results from the phase detection units  72  and  73 . Furthermore, the positions of the platens  34  and  36  are detected according to the detection results of the platen detection units  74  and  75 . Apart from this, an operation for cleaning the nozzles of the recording head  12 , as described hereinafter, is carried out at time intervals previously determined by the print control unit  104 , or after a certain number of recording operations.  
         [0046]     Next, the action of the image forming apparatus  10  having the foregoing composition will be described.  
         [0047]     In the stationary state prior to the start of image recording shown in  FIG. 4 , the rotating bodies  30  and  32  are positioned in such a manner that the opening sections  67 A and  67 B oppose the nozzle surface of the recording head  12 . In this state, the opening sections  67 A and  67 B are connected to the cutaway section  46  of the liquid receiving pipe  38 .  
         [0048]     The nozzle of the recording head  12  is capped by the caps  68 A and  68 B, so that the nozzles of the recording head  12  are shielded from the air, and the ink in the nozzles is prevented from drying out. Moreover, if suctioning force is applied while the nozzles are capped by the caps  68 A and  68 B, then ink can be suctioned from the nozzles, and hence nozzle blockages can be prevented. More specifically, when the power supply to the image forming apparatus  10  is switched on, or the like, the system controller  102  (see  FIG. 5 ) drives the pump P and air is suctioned out through the opening section  67 . Thereby, the pressure inside the caps  68 A and  68 B is reduced, and ink is sucked out from the nozzles of the recording head  12 . Thereupon, the system controller  102  drives the motors  40  and  41  though the motor driver  106 , thereby causing the rotating bodies  30  and  32  to rotate so that the caps  68 A and  68 B are detached from the nozzles of the recording head  12 , thereby releasing the sealed state of the nozzles. A raising and lowering device (not shown) is provided in the recording head  12 , and the recording head  12  is moved in the upwards direction indicated by arrow C in  FIG. 4 , in conjunction with the rotation of the rotating bodies  30  and  32 , whereby the base end edges of the caps  68 A and  68 B are prevented from making contact with the nozzles in the recording head  12 .  
         [0049]     The rotating bodies  30  and  32  can rotate to halt in the position in  FIG. 1 , which represents a rotation of approximately 180° from the capping position (see  FIG. 4 ). Thereby, the elongated holes  48  and  50  are brought to positions opposing the nozzle surface of the recording head  12 , and the elongated holes  48  and  50  are connected to the cutaway section  46  of the liquid receiving pipe  38 . Moreover, the platens  34  and  36  are positioned in line with the conveyance path of the recording paper  16  as shown in  FIG. 1  and an image forming position is assumed wherein the platens  34  and  36  and the recording head  12  are mutually opposing.  
         [0050]     In  FIG. 5 , the image data to be printed is inputted from the host computer  120  through the communication interface  100 , and the image data is stored in the image memory.  104 . The system controller  102  drives the motor  109  through the motor driver  106  so that the recording paper  16  is picked up from the paper supply unit  20  shown in  FIG. 1  and is conveyed through the fixed guide plate  18  to the recording head  12 .  
         [0051]     When the recording paper  16  arrives at the recording head  12 , recording onto the recording paper  16  is carried out. More specifically, the image data stored in the image memory  104  in  FIG. 5  is supplied to the print control unit  110 , and the image data is converted into data for dots of the respective ink colors, by means of the head driver  112 . The head driver  112  reads in the dot data, and generates drive control signals for the recording head  12 . By supplying the drive control signals generated by the head driver  112  to the nozzles of the recording head  12 , ink is discharged from the nozzles onto the recording surface of the recording paper  16 . The ink discharge timing from the recording head  12  is controlled in synchronism with the conveyance speed of the recording paper  16 , according to the-detection results outputted from the recording paper detection unit  70  of the sensor unit  114 , and hence the recording head  12  is able to form an image on the recording paper  16  without halting the conveyance of the recording paper  16 .  
         [0052]      FIGS. 6A  to  6 H are side views showing the relationship between the platens  34  and  36  of the nozzle recovery unit  14  and the conveyance position of the recording paper  16 , during image formation. In the following description, the platen  36  provided to the rear side of the platen  34  performs similar actions to those of the platen  34 , and hence description of the platen  36  is omitted here.  
         [0053]     While the recording paper  16  is conveyed on the fixed guide plate  18 A to the platen  34  by the conveyance rollers  24 , the recording paper  16  is suctioned onto the platen  34  by air suction through the suction holes  34   a  in the platen  34  as shown in  FIG. 6A . When the platen  34  is positioned to the rear surface of the recording paper  16  and assumes a position whereby the platen  34  is covered by the recording paper  16  as shown in  FIG. 6B , the motor  56  (see  FIG. 5 ) is driven so that the platen  34  is moved in the direction of conveyance of the recording paper  16  (the direction indicated by the arrow D) as shown in  FIG. 6C . The positional relationship between the platen  34  and the recording paper  16  in this case is recognized by the system controller  102 , through the recording paper detection unit  70  and the platen detection units  74  and  75 . In this state, the recording paper  16  is conveyed while being maintained in a flat position as shown in  FIG. 6D . Here, in the case of full-surface marginless printing, ink is discharged from the nozzles of the recording head  12  in such a manner that the discharged ink extends beyond the leading edge portion of the recording paper  16  as shown in  FIG. 6D , but since the platen  34  is positioned at the rear face of the recording paper  16  and is covered by the recording paper  16 , then ink does not adhere to the platen  34 .  
         [0054]     Thereupon, as shown in  FIGS. 6E and 6F , the platen  34  is moved in a position opposing the recording head  12 , and an image is formed on the recording paper  16 . Thus, it is possible to form an image on the recording paper  16  while maintaining the recording paper  16  in a flat state by means of the platen  34 .  
         [0055]     In the case of full-surface marginless printing, ink is discharged from the recording head  12  onto a position extending beyond the trailing edge portion of the recording paper  16  as shown in  FIGS. 6G and 6H , but this surplus ink is suctioned up through the elongated hole  48  and the suction pipe  38 , and is thus removed. Moreover, since the platen is narrower than the paper width, the ink extending beyond either side of the paper can also be recovered. In  FIGS. 6E and 6F , the platen  34  is halted and the recording paper  16  is caused to slide over the platen  34  by means of the conveyance force of the conveyance rollers  24 .  
         [0056]     Here, a case where either one of the platens  34  and  36  is used, according to the size of the recording paper, is described.  
         [0057]     The system controller  102  determines the size of the recording paper conveyed from the cassette  21  in  FIG. 1 , by means of the recording paper detection unit  70 , and the system controller  102  drives one of the motors  40  and  41  in accordance with the size (see  FIG. 2 ). More specifically, if it is judged by the system controller  102  that the conveyed recording paper  16  is a size corresponding to the platen  36 , then the system controller  102  drives the motor  40  from the state shown in  FIG. 1  to rotate the rotating body  30  so that the elongated hole  48  is moved to a position rotated by approximately 180° from a position opposing the nozzle surface of the recording head  12 . Thereby, the connection between the elongated hole  48  of the rotating body  30  and the cutaway section  46  of the liquid receiving pipe  38  is released, and the elongated hole  48  of the platen  34  becomes sealed. In this state, the recording paper  16  of the size corresponding to the platen  36  is conveyed to the side corresponding to the rotating body  32 , the recording paper  16  is conveyed while being suctioned by the platen  36 , and image forming onto the recording paper  16  is carried out. Since only the elongated hole  50  of the rotating body  32  is connected to the cutaway section  46  of the liquid receiving pipe  38 , it is possible to seal the cutaway section  46  on the side corresponding to the rotating body  30 , where the recording paper  16  is not conveyed, thereby preventing a decline in the air suction pressure at the suction holes  36   a  in the platen  36 , and thus maintaining the suction force for the recording paper  16  onto the platen  36 .  
         [0058]     On the other hand, if it is judged by the system controller  102  that the recording paper conveyed from the cassette  21  is a size corresponding to the platen  34 , then the system controller  102  drives the motor  41  from the state shown in  FIG. 1  to rotate the rotating body  32  so that the elongated hole  50  is moved to a position rotated by approximately 180° from a position opposing the nozzle surface of the recording head  12 . Thereby, the connection between the elongated hole  50  of the rotating body  32  and the cutaway section  46  of the liquid receiving pipe  38  is released, and the cutaway section  46  on the side of the platen  36  is sealed. In this state, the recording paper  16  is conveyed on the side corresponding to the rotating body  30 , guided while being suctioned by the platen  34 , and image forming onto the recording paper  16  is carried out. Consequently, only the elongated hole  48  of the rotating body  30  is connected to the cutaway section  46  of the liquid receiving pipe  38 , and air suction on the side corresponding to the platen  36 , where the recording paper  16  is not conveyed, can be halted, thereby making it possible to prevent a decline in the air suction pressure at the suction holes  34   a  of the platen  34 .  
         [0059]     In this way, the suctioning of the recording paper by the platen in a region other than that where the recording paper  16  is conveyed can be halted by rotating the rotating body, and thereby, it is possible to prevent decline in the suction force of the platen in the region where the recording paper  16  is conveyed. After forming an image on the recording paper  16 , the motors  40  and  41  are driven by the system controller  102 , and the rotating bodies  30  and  32  are driven to positions wherein the platens  34  and  36  are opposing the recording head  12  as illustrated in  FIG. 1 , thereby reverting to the image formation standby state.  
         [0060]     At prescribed time intervals, or after a certain number of recording operations have been performed, or alternatively, if a discharge error in the recording head  12  has been detected by means of a discharge error detection device, then maintenance of the recording head  12  is performed as described below.  
         [0061]     More specifically, if recording operations are carried out in a continuous fashion until a prescribed period of time or a prescribed number of recording operations is reached, or if the existence of a discharge error in the nozzles has been detected by the discharge error detection device (not illustrated), then the system controller  102  detects by the recording paper detection unit  70  the leading edge of the recording paper  16  that is to be conveyed next, and when the trailing edge of the recording paper  16  that is currently being conveyed has passed a position opposing the recording head  12 , ink which does not contribute to printing is discharged (blank discharge) from at least the nozzles detected to be defective in the recording head  12 , by means of the head driver  112 . More specifically, the conveyance interval between the trailing edge of the recording paper  16  currently being conveyed and the leading edge of the recording paper  16  that is to be conveyed subsequently is used in order to discharge ink that does not contribute to printing, from the nozzles of the recording head  12 , in the gap between the paper sheets, when the interval (gap) between the respective sheets of recording paper  16  is situated in a position opposing the recording head  12 . The ink thus discharged is suctioned up via the elongated holes  48  and  50  and is removed.  
         [0062]     Furthermore, the print control unit  110  drives the motor  62  through the motor driver  106  and causes the blade  60  provided on the platen  34  in  FIG. 1  to advance from the elongated holes  48  and  50 . Moreover, the print control unit  110  drives the motor  56 , thereby driving the platen  34  in the sub-scanning direction (the direction indicated by arrow B), so that the blade  60  wipes the nozzle surface of the recording head  12 . By this means, ink that has dried out due to lack of use, or defective ink whose viscosity has changed, can be removed from the nozzles of the recording head  12 , and since wiping is performed in parallel with the nozzle surface, no removal failures occur. When the nozzles have been cleaned, the motor  62  is driven by the motor driver  106 , and the blade  60  is withdrawn from the nozzle surface of the recording head  12 .  
         [0063]     In this way, according to the image forming apparatus  10  of the present embodiment, since it is possible to switch between four states, namely, nozzle suction, nozzle wiping, nozzle dry-out prevention (capping), and recording paper conveyance, by means of the nozzle recovery unit  14 , and since, including blank discharge, a total of five types of operation can be carried out, then it is possible to dispense with maintenance members which are complicated and bulky, and with movement mechanisms for same, and the maintenance time can also be shortened significantly. In particular, since it is possible to prevent the occurrence of waves in the recording medium by means of the platen  34  which moves horizontally while suctioning the recording paper  16 , then the accuracy of the landing positions of the ink can be improved and hence good image quality can be obtained. Moreover, since the movement of the platen  34  is controlled while the platen  34  is in a covered stated in a position at the rear face of the recording paper  16 , then ink which falls beyond the edges of the recording paper  16  in the case of full-surface marginless printing will not land on the platen, and hence soiling of the rear face of the recording paper can be prevented.  
         [0064]     Next, a second embodiment of an image forming apparatus according to the present invention is described.  
         [0065]     The image forming apparatus according to the second embodiment involves a different composition of the platens, apart from which, the composition thereof is virtually the same as that of the image forming apparatus  10  according to the first embodiment described above, and hence the same reference numerals are used and detailed description thereof is omitted.  
         [0066]     As shown in  FIG. 7 , the maintenance unit  152  used in the image forming apparatus  150  according to the second embodiment comprises platens  154  and  156  situated on the downstream side of the elongated holes  48  and  50  of the rotating bodies  30  and  32  in the conveyance direction of the recording paper  16 . The platens  154  and  156  oppose the platens  34  and  36  provided on the upstream side of the elongated holes  48  and  50  in the conveyance direction of the recording paper  16 . The platens  154  and  156  are formed with suction holes  154   a  and  156   a  and are disposed in such a manner that the platens  154  and  156  seal off the elongated holes  48  and  50 . Each of the platens  154  and  156  screws together with a screw shaft  160  forming the drive shaft of a motor  158  installed in the vicinity of each of the elongated holes  48  and  50 . Therefore, by driving each screw shaft  160 , each of the platens  154  and  156  can be driven along the conveyance direction of the recording paper  16 , in other words, the sub-scanning direction (the direction indicated by arrow B). The platen  156  is installed on the rotating body  32  to the rear side of the platen  154  in  FIG. 7 , and therefore it is not seen in  FIG. 7 . A platen detection unit  162  detects the position of the platen  156 .  
         [0067]     Next, the action of the image forming apparatus  150  having the foregoing composition will be described.  
         [0068]      FIGS. 8A  to  8 I are side views showing the relationship between the platens  34  and  154  of the maintenance unit  152  and the conveyance position of the recording paper  16 , during image formation. In the following description, the platen  36  and the platen  156 , which are provided on the rear sides of the platens  34  and  154  in  FIG. 8 , are not illustrated, but the platen  36  and the platen  156  perform a similar operation to the platen  34  and the platen  154 .  
         [0069]     While the recording paper  16  is conveyed on the fixed guide plate  18 A to the platen  34  by the conveyance rollers  24 , the recording paper  16  is suctioned onto the platen  34  by air suction through the suction holes  34   a  in the platen.  34  as shown in  FIG. 8A . When the platen  34  is positioned to the rear surface of the recording paper  16  and assumes a position whereby the platen  34  is covered by the recording paper  16  as shown in  FIG. 8B , the motor  56  (see  FIG. 5 ) is driven so that the platen  34  is moved in the direction of conveyance of the recording paper  16  (the direction indicated by the arrow D) as shown in  FIG. 8C . In this state, the recording paper  16  is conveyed while being maintained in a flat position as shown in  FIG. 8D . Here, in the case of full-surface marginless printing, ink is discharged from the nozzles of the recording head  12  in such a manner that the discharged ink extends beyond the leading edge portion of the recording paper  16  as shown in  FIG. 8D , but since the platen  34  is positioned at the rear face of the recording paper  16  and is also narrower than the width of the recording paper  16 , then the platen  34  is not soiled with ink. When the recording paper  16  is conveyed to the platen  154  as shown in  FIG. 8E , then the motors  56  and  158  are driven so that the platens  34  and  154  are moved towards the right-hand side in  FIG. 8F .  
         [0070]     Next, when the platen  154  suctions the recording paper  16  as shown in  FIG. 8G , the platen  34  moves to the right-hand side as shown in  FIG. 8H , and reverts to the position shown in  FIG. 8A . The platen  154  moves in the direction of conveyance together with the recording paper  16  as shown in  FIG. 8H . In the case of full-surface marginless printing, ink is discharged from the recording head  12  in such a manner that the discharged ink falls beyond the trailing edge section of the recording paper  16  as shown in  FIG. 81 , but since the platen  154  is positioned at the rear face of the recording paper  16 , the platen  154  does not become soiled by the ink. The ink falling beyond the edge of the recording paper  16  is suctioned up via the elongated holes  48  and  50  and is removed. Thereupon, the recording paper  16  on which an image has been formed is conveyed to the paper output unit  22  and is outputted, and the platen  154  returns to the position indicated in  FIG. 8A , whereupon image forming of a full-surface marginless print ends. In  FIG. 8E , the platen is halted and in  FIGS. 8F and 8G , the recording paper  16  slides over the platen by means of the conveyance force of the conveyance rollers  24 .  
         [0071]     After an image has been formed, the motors  56  and  158  are driven by the system controller  102 , and the platens  34  and  154  are driven back to their positions illustrated in  FIG. 8A , thereby returning the apparatus to an image formation standby state.  
         [0072]     In the second embodiment, since the recording paper is transferred by means of two platens  34  and  154 , the conveyance of the recording paper become smoother, and productivity improves.  
         [0073]     The composition of the image forming apparatus illustrated in the embodiments described above is not limited to an inkjet printer. For example, although the present embodiment described an example applied to an image forming apparatus which forms images on recording paper  16  by discharging ink onto the recording paper  16 , the present invention is not limited to this and may also be applied to a processing apparatus, or the like, for applying a coat of developing process solution, or the like.  
         [0074]     It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.