Patent Publication Number: US-6217145-B1

Title: Ink-jet printer

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an ink-jet printer which prints an image onto a print medium held on a rotary drum with ink ejected from a print head, and particularly, to an ink-jet printer whose print head is constructed by a plurality of ink-jet nozzles disposed in the axial direction of the rotary drum. 
     Conventionally, serial-type ink-jet printers are widely spreading. In the serial-type ink-jet printer, a print head and an ink cassette of a relatively small capacity are integrally mounted on a carriage, and the carriage is movably attached to a guide bar extending across a paper sheet. The paper sheet is fed in a direction perpendicular to the guide bar at a constant pitch, and the carriage is moved along the guide bar each time the paper sheet is fed for one pitch. The print head ejects ink during the movement of the carriage. In the case where the printer is used for color printing, the print head includes a plurality of ink-jet nozzles which are respectively supplied with inks of different colors from ink tanks. In the structure as described above, for example, a color image of A4 size is printed out in ten minutes. Thus, the serial-type ink-jet printer operates at a slow print speed of 0.1 sheet per minute. 
     In recent years, a drum rotation type ink-jet printer has been developed to perform color printing at a higher speed. In this ink-jet printer, a paper sheet is held on a rotary drum rotating in only one direction, and a print head includes a plurality of nozzle units which are arranged along the peripheral surface of the rotary drum and eject inks of different colors other onto a paper sheet rotating together with the rotary drum. Each nozzle unit includes a plurality of ink-jet nozzles disposed across the paper sheet in the axial direction of the rotary drum. The pitch of the ink-jet nozzles is set to a value equal to a desired resolution or a value two to four times greater than the resolution. The print head is positioned such that the end surfaces of the ink-jet nozzles are close to the paper sheet on the rotary drum. The print head is set to a predetermined position in the case where the pitch of the ink-jet nozzles is equal to the desired resolution. The print head is set to be movable in the axial direction of the drum from the predetermined position in the case where the pitch of the ink-jet nozzles exceeds the desired resolution. When the print head is movable in the axial direction of the rotary drum, the print head is moved at a rate corresponding to the desired resolution, for each revolution of the rotary drum, and is returned to the predetermined position after the print head is moved for a distance equal to the pitch of the ink-jet nozzles. The rotation speed of the rotary drum is set to 120 rpm. In this structure, for example, a color image of A4 size can be printed out in about two or three seconds. Also, since the print head is not moved by a distance exceeding the nozzle pitch in the axial direction of the rotary drum, the number of prints to be obtained for each ink charge can be increased by setting large-capacity ink cassettes apart from the print head and supplying inks of different colors to the respective nozzle units of the print head. 
     In this ink-jet printer, the end surface of the print head corresponding to the end surfaces of all the ink-jet nozzles are close to a paper sheet with a gap of about 1 mm interposed therebetween. Therefore, during printing in which a paper sheet is rotated at a high speed by a rotary drum and moved relatively with respect to the ink-jet nozzles, paper particles scattered from the paper sheet easily adhere to the end surface of the print head. The paper particles are gradually accumulated and soak up ink on the end surfaces of the nozzles. If such paper particles drop on a paper sheet along with ink, the print quality is degraded. The degradation of the print quality is a more serious problem for a drum rotation type ink-jet printer in which the print head is used for a long period than for a serial type ink-jet printer in which the print head is replaced upon shortage of ink in an ink cassette of a small capacity. 
     However, since the gap between the end surface of the print head and a paper sheet is slight, it is difficult to remove safely and securely paper particles adhered to the end surface. Therefore, for example, a cleaning process may be performed at the non-printing time to remove the paper particles by moving the print head in the axial direction of the rotary drum from a printing position facing the peripheral surface of the rotary drum to a cleaning position not facing the peripheral surface of the rotary drum, and mechanically wiping the end surface of the print head with an elastic material such as rubber upon movement of the print head. In this case, the size of the drum rotation type ink-jet printer will be increased in accordance with the distance of moving the print head. Further, an increase of the print speed is hindered by time losses caused by moving the print head between the cleaning position and the printing position. In this respect, since the end surface of the print head is coated with a water repellent film so that ink is ejected from ink-jet nozzles through predetermined courses onto a paper sheet, the pressure to the elastic material and the moving speed of the print head must be appropriately restricted. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an ink-jet printer capable of quickly and safely removing paper particles adhered to an end surface of a print head without enlarging the size. 
     The present inventors paid attention to several points as follows. A water repellant film has a mechanically and thermally weak characteristic that the film is deformed or damaged when the film is rubbed with a blade made of hard rubber. Purging process such as prevention of clogging of nozzles and degassing can be carried out by ejecting ink from ink jet nozzles before starting printing and during printing halfway. Further, the present inventors have considered a technique of removing the paper particles by a flow of ink which is generated on the end surface of the print head by utilizing ink ejected for purge processing or a purge processing period. 
     According to the present invention, there is provided an ink-jet printer which comprises a rotary drum for carrying a print medium, a print head arranged above the rotary drum for printing an image by ejecting ink onto the print medium, a washing board facing the print head to wash an end surface of the print head with ink ejected from the print head, a control unit for controlling at a non-printing time the washing board to be set at a cleaning position located between the print head and the rotary drum and the print head to eject ink therefrom, wherein the washing board has a groove section which receives an entire end surface of the print head and a drain section for draining the ink ejected from the print head and flowing in contact with the end surface of the print head within the groove section. 
     The ink-jet printer ejects ink from the print head at the non-printing time to remove particles adhered to the end surface of the print head by a flow of ink generated between the end surface of the print head and the washing board. Thus,-the particles can be quickly, accurately and safely removed from the end surface of the print head. If the particles are removed as described above during the continuous printing, the printing quality would not be degraded due to ink soaked into the particles and dropped on the printing medium. In the washing board placed at the cleaning position, ink is drained through the drain section and not unnecessarily overflow from the groove section. Therefore, required amount of ink can be reduced and color mixture can be prevented if inks of different colors are ejected from the print head and partitioned in the groove section. The groove section is opened at the sides of the print head even while ink is ejected, and ink is maintained in the groove section. Therefore, it is not necessary that the print head and the washing board are combined to create a closed room for ensuring removal of particles by a flow of ink. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, ar may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a view schematically showing the internal structure of an ink-jet printer according to an embodiment of the present invention; 
     FIG. 2 is a view showing the structure around a print head shown in FIG. 1; 
     FIG. 3 is a perspective view showing a positional relationship between the print head and a rotary drum shown in FIG. 2; 
     FIGS. 4A and 4B are views showing cross-sectional structures of the washing board shown in FIG. 2, in the direction perpendicular to the axial direction of the rotary drum and in the axial direction of the rotary drum, respectively; 
     FIGS. 5A and 5B are views showing states of a dust cover for the washing board shown in FIG. 2; 
     FIG. 6 is a top view of one nozzle unit shown in FIG. 2; 
     FIG. 7 is a perspective view schematically showing the outer appearance of the nozzle unit shown in FIG. 6; 
     FIG. 8 is a view for explaining a structure which determines the positional relationship between the washing board and the nozzle unit shown in FIG. 2; 
     FIG. 9 is a perspective view schematically showing the outer appearance of the washing board shown in FIG. 2; and 
     FIGS. 10A to  10 D are views for explaining the motion of the washing board shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An ink-jet printer according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1 shows an internal structure of the ink-jet printer. The ink-jet printer is used to print a multicolor image on a paper sheet P cut as a printing medium. The paper sheet P may be a plain paper or OHP sheet. 
     The ink-jet printer includes a rotary drum  10  which holds a paper sheet P and rotates at a constant circumferential speed, and a print head  20  for printing a multicolor image on the paper sheet P rotating along with the rotary drum  10 . The ink-jet printer also includes a manual feed tray T 1  for a paper sheet P to be fed one by one, a paper cassette T 2  for containing a stack of paper sheets M, a sheet feed-in mechanism FM 1  for feeding a paper sheet P to the rotary drum  10  from the manual feed tray T 1  and paper cassette T 2 , a sheet feed-out mechanism FM 2  for feeding out the paper sheet P printed at the rotary drum  10 , and a control unit CNT for controlling the overall operation of the ink jet printer. As shown in FIG. 1, the rotary drum  10  is located near the central position within a housing  1 . The manual feed tray T 1  is located below the rotary drum  10  and projects externally from a front surface of the housing  1 , and the paper cassette T 2  is located under the rotary drum  10 . The sheet feed-in mechanism FM 1  is placed between the manual feed tray T 1  and the paper cassette T 2 . The print head  20  is located above the rotary drum  10 . The sheet feed-out mechanism FM 2  is located behind the rotary drum  10 . 
     The rotary drum  10  is supported so as to be ratable about the axis, and holds the paper sheet P wound around a peripheral surface  11  in accordance with its rotation. The rotational position of the rotary drum  10  is detected by a rotational position detector DT provided near the peripheral surface  11  of the rotary drum  10 . The print head  20  includes nozzle units  20 C,  20 Y,  20 M,  20 B which are arranged in series along the peripheral surface  11  of the rotary drum  10  from the upstream side to the down stream side so as to perform printing on the paper sheet P with inks of cyan, yellow, magenta and black. These nozzle units are supplied with inks of the corresponding colors from four ink supplying units SP remote therefrom. Each of the nozzle units  20 C,  20 Y,  20 M,  20 B has a plurality of ink-jet nozzles  23 , arranged at pitch PT of, for example, {fraction (1/75)} inch in the axial direction of the rotary drum  10 , for ejecting the corresponding color ink to the paper sheet P. The ink-jet nozzles  23  are arranged to have a span correspond to 210 mm, i.e., the width of the paper sheet P of A4 size. The sheet feed-in mechanism FM 1  includes a paper loader LD for loading the paper sheet P to the rotary drum  10  such that the width direction of the paper sheet P coincides with the axial direction of the rotary drum  10 , and feeds the paper sheet P taken out of either the manual feed tray T 1  or the paper cassette T 2 . The paper loader LD is controlled to feed the paper sheet P toward the rotary drum  10  when the position detector DT detects that the rotary drum  10  has arrived at a predetermined rotational position. The print head  20  prints a multicolor image on the paper sheet P as the rotary drum  10  rotates. 
     The paper sheet P is separated from the peripheral surface  11  of the rotary drum  10  by a paper separation unit PL and fed in a predetermined direction by the sheet feed-out mechanism FM 2 . The paper separation unit PL is a separation claw which is brought into contact with the rotary drum  10  at the time of separating the paper sheet. A discharge switch SEL guides the paper sheet P to a selected one of a rear discharge tray RT with the print surface facing upward, and an upper discharge tray UT with the print surface facing downward. 
     The print head  20  can be slightly and reciprocally shifted in a main scanning direction X parallel to the axis of the rotary drum  10 . The rotary drum  10  holds the paper sheet P wound around and held on the peripheral surface  11 , and rotates to move the paper sheet P in a sub-scanning direction Y perpendicular to the main scanning direction X, with the paper sheet P opposing to the nozzle units  20 C,  20 Y,  20 M,  20 B. To achieve a multicolor print of, for example, 20 PPM, the rotary drum  10  is maintained to be a constant rotation rate of 120 rpm; that is, it is rotated at one revolution per 0.5 second. In a printing operation, the print head  20  is shifted in the main scanning direction X at a constant rate of ¼ nozzle pitch PT every time the rotary drum makes one revolution, so that it moves by a distance equal to the nozzle pitch PT during four revolutions. With this structure, the printing of the entire surface of the paper sheet P is completed in 2 seconds (=0.5 second×4) required to make four revolutions of the rotary drum  10 . Even when a time required to make one revolution of the rotary drum  10  for winding the paper sheet P around the drum before printing and one revolution of the rotary drum  10  for separating the paper sheet after printing, a multicolor image can be printed on the paper sheet P of A4 size at a high speed of 3 (=2+1) seconds per sheet. Thus, printing can be consecutively performed on 20 paper sheets every minute. 
     The paper loader LD includes at least a pair of feed rollers R 1  and R 2  extending in the axial direction of the drum  10  so as to load the paper sheet P supplied from the feeder T 1  or T 2  to the rotary drum  10  at a predetermined timing. The feed rate of the paper sheet P is set to the circumferential speed of the rotary drum  10 . Since the diameter of the rotary drum  10  is 130 mm, a circumferential speed of 816 mm/sec can be obtained. The peripheral surface  11  of the rotary drum  10  is about 220 mm wide in the axial direction and 408 mm long in the rotational direction. Therefore, the rotary drum  10  can fully hold the A4 size paper sheet P having a length of 297 mm and a width of 210 mm. 
     In the ink-jet printer, the rotary drum  10  and the print head  20  are positioned as shown in FIGS. 2 and 3, and a washing board  30  can be inserted between the print head  20  and the rotary drum  10 . The washing board  30  is used to remove paper particles adhered to the end surface  24  with ink ejected from the ink-jet nozzles  23  of the nozzle units  20 C,  20 Y,  20 M,  20 B in a state where the washing board  30  faces the end surface  24  of the print head  20 . 
     The nozzle units  20 C,  20 Y,  20 M and  20 B are constructed to have the same structure. For example, the nozzle unit  20 C has a joint plate  21  and four nozzle segments  20 CA,  20 CB,  20 CC, and  20 CD as shown in FIGS. 6 and 7. The joint plate  21  is set so as to extend in the axial direction X of the rotary drum  20  which coincides with the widthwise direction of a paper sheet P shown in FIG.  2 . The nozzle segments  20 CA,  20 CB,  20 CC, and  20 CD are provided in a zigzag arrangement on the joint plate  21 , shifted from each other in the rotation direction R of the rotary drum  10 . Specifically, the nozzle segments  20 CA and  20 CC are fixed to the front surface of the joint plate while the nozzle segments  20 CB and  20 CD are fixed to the back surface of the joint plate. Pairs of adjacent nozzle segments  20 CA and  20 CB,  20 CB and  20 CC, and  20 CC and  20 CD are arranged so as to overlap each other slightly. The end surfaces of the ink-jet nozzles  23  of the nozzle segments  20 CA,  20 CB,  20 CC, and  20 CD are aligned to a height equal to the end surface  24  of the print head  20 . 
     The height of the print head  20  is automatically adjustable by a lift  90 . By the adjustment of the height, the print head  20  is set to a lower limit position shown in FIG. 10A at the printing time, and the print head  20  is set to an upper limit position shown in FIGS. 10B and 10C at the non-printing time. The print head  20  is set to a cleaning position shown in FIG. 10D at the purging time. 
     As shown in FIG. 2, the lift  90  is comprised of a pair of guide rails  91 , a slider  92 , and a lift drive section  93 . The pair of guide rails  91  stand on one side of and in parallel to a vertical axis J passing through the axis Z of the rotary drum  10  and arranged in the axial direction X of the rotary drum  10 . The slider  92  is slidably mounted on the guide rails  91 , and supports the nozzle units  20 C,  20 Y,  20 M, and  20 B by a head support member  29 . The lift drive section  93  elevates up and down the slider  92  by an electric power. 
     The pair of guide rails  91  stand on both ends of a fixed frame  99 F in the axial direction X of the rotary drum  10 . The slider  92  is supported by both of the guide rails  91 . The lift drive section  93  is comprised of a motor  94 , a power converter  95  for converting the rotation torque of the motor  94  into a force for lifting the slider  92 , a rack-pinion mechanism  96  formed of a rack  97  and a pinion  98 , and a power transmission gear mechanism  99 . 
     The washing board  30  is rotatable around the axis Z of the rotary drum  10  as a center by a rotation position determination section  70 , so that the washing board  30  can be selectively removably inserted between the print head  20  and the peripheral surface  11  of the rotary drum  10 . 
     The rotation position determination section  70  includes a support frame  71 , a power transmission gear mechanism  76 , a drive motor  75 , and position detection sensors  77  and  78 . The section  70  is arranged to automatically determine the position of the washing board  30  at a selected one of a rest position where the section  70  is inclined by 45 degrees to the left side as shown in FIG.  10 A and at a cleaning position shown in FIGS. 10C and 10D. 
     The support frame  71  is formed to be rotatable around the axis Z of the rotary drum  10  via a support shaft  72  while supporting the washing board  30  as shown in FIG.  2 . The support flame  72  has a slave gear  73  of an arc-like shape attached thereto. The slave gear  73  is connected through the power transmission gear mechanism  76  to a drive gear  74  on the axis of the drive motor  75  mounted on a stationary member like the housing  1 . The position detection sensor  77  is provided to detect that the washing board  30  is positioned at the rest position, and the position detection sensor  78  is provided to detect that the washing board  30  is positioned at the cleaning position. 
     The washing board  30  is formed to be used in common by the nozzle units  20 C,  20 Y,  20 M, and  20 B, as shown in FIG.  9 . That is, the washing board  30  includes four lines of grooves GR 1  to GR 4  for the nozzle units  20 C,  20 Y,  20 M, and  20 B. The grooves GR 1  to GR 4  extend in the axial direction of the rotary drum  10  along lines of the ink-jet nozzles  23 , and partitioned by ink stopper walls  32 . These grooves GR 1  to GR 4  are respectively associated with the nozzle units  20 C,  20 Y,  20 M, and  20 B to create four ink flow generation chambers  30 S. The ink flow generation chambers  30 S are defined as spaces surrounded by ink reception plates  31  serving as the bottoms of the grooves GR 1  to GR 4 , the end surfaces  24  of the nozzle units  20 C,  20 Y,  20 M, and  20 B, and the ink stopper walls  32 . Each ink reception plate  31  has a pair of drain holes  35  formed in non-opposed areas  31 E located on the both sides of the end surface  24  in the axial direction of the rotary drum  10  and not opposed to the end surface  24  as shown in FIGS. 4B and 9. An ink drain section  50  is connected through the drain holes  35  to the ink flow generation chambers  30 S so as to commonly drain inks ejected from the nozzle units  20 C,  20 Y,  20 M, and  20 B. 
     The washing board  30  further includes a plurality of projections projected from the ink reception plates  31  and serving as position determination member  34  for determining a gap G between the end surfaces  24  and the ink reception plates  31  as shown in FIGS. 4A and 4B. The lift  90  stops elevating down the print head  20  when the lower surface of the joint plate  21  is brought into contact with the upper surface of the position determination member  34 , as shown in FIG.  8 . 
     The gap G is a very important factor which decides the ink flow ability, the paper particle removal ability, and the necessary amount of ink. If the gap G is a value larger than 0.5 mm, for example, the necessary amount of ink is increased. Otherwise, if the gap G is a value smaller than 0.1 mm, for example, a smooth flow of ink cannot be guaranteed and it is difficult to obtain an accurate gap G. Therefore, the gap G of 0.3 mm is selected, which has led to the most desirable result in an experiment using a value within a range of 0.1 to 0.5 mm. 
     As shown in FIGS. 5A and 5B, the ink-jet printer includes a dust cover  80  for covering the ink reception plate  31  of the washing board  30  by utilizing the displacing motion of the washing board  30 . The dust cover  80  is constituted by a cover portion  81  and an actuator portion  85  which brings the cover portion  81  into contact with the washing board  30 . 
     The actuator portion  85  is constituted by a support member  87 , an urge spring (not shown), and a stopper  89 . The support member  87  is rotatably attached to a stationary member such as the housing  1  or the like via the support shaft  86 . The urge spring urges the support member  87  in the counterclockwise direction in FIG.  5 A. The cover portion  81  is attached to an upper portion  87   u  of the support member  87 , and a lower portion  87   d  of the support member  87  is formed as an engaging portion  87   e  capable of being engaged with the washing board  30 . 
     Therefore, when the washing board  30  is rotated toward the rest position as shown in FIG. 5B, the washing board  30  is engaged with the engaging portion  87   e  of the support member  87  to rotate the support member  87  in the counterclockwise direction. In this manner, the cover portion  81  is brought into tight contact with the washing board  30 , thereby covering the ink reception plate  31 . 
     The ink drain section  50  has a suction structure including a collection chamber  51  formed to be integral with the washing board  30 , a drain pipe  52 , a drain tube  53 , and a suction pump  54 . 
     The ink drain section  50  is driven by a controller (not shown) such that suction and drainage can be performed even while ink is ejected from the ink-jet nozzles  23 . Specifically, in FIGS. 4A and 4B, the suction pump  54  is driven to drain ink by suction after the ink flow generation chamber  31 S is filled with ink ejected from the nozzles  23  and the ink surface is brought into contact with the end surface  24 . This reduces the necessary amount of ink. 
     In this embodiment, waste ink from the ink drain section  50  is collected by a waste ink cassette  60 . The waste ink cassette  60  is detachably attached to the drain tube  53 . Thus, no troubles are caused by dealing with waste ink and the periphery is not soiled even when continuous printing is carried out for a great deal of 2000 sheets of paper. Simultaneously, simplification and downsizing of the entire printer can be achieved. In addition, the collection chamber  51  permits a suction force from a single drain tube to be applied commonly to the plural drain holes  35 . Therefore, the structure can be simplified while reducing the manufacturing cost. Further, the collection chamber  51  can prevents scattering of ink, which may be caused when the suction force from the drain tube  53  is directly applied to the drain holes  35 . 
     Next, a paper particle removing operation of the ink-jet printer will be described. The control unit CNT performs a control of removing paper particles at the non-printing time (e.g., after printing operation is finished or while printing operation is paused). With this control, the lift  90  elevates up the print head  20  from a position shown in FIG. 10A to an upper limit position shown in FIG. 10B, and thereafter or simultaneously, the rotation position determination section  70  rotates the washing board  30  to be positioned at a position shown in FIG.  10 C. In this state, the control unit CNT reverse the operation of the lift  90  to move down the print head  20  and stops it when the lower surface of the joint plate  21  is brought into contact with the position determination member  34  shown in FIG. 8 (shown in FIG.  10 D). In this manner, a predetermined gap G (0.3 mm) is obtained between the end surfaces of the nozzle units  20 Y,  20 M, and  20 B and the ink reception plates  31  of the washing board  30 . 
     In this state, ink is supplied via a press pump  41  and a supply tube  42  to the print head  20  and is ejected from the ink-jet nozzles  23  toward the ink reception plate  31  so as to remove paper particles on the end surface of the print head  20 . Prevention of clogging and degassing can be also achieved by this operation. 
     Ejected ink splashes from the ink reception plate  31  to contact with the end surface  24  of the print head  20 , and then fills the ink flow generation chambers  30 S while removing paper particles adhered to the end surface  24 . A part of the ink drops from the pair of drain holes  35  formed in the non-opposed areas  31 E shown in FIGS. 4A and 4B, and drained into the collection chamber  51 . 
     In this state, the suction pump  54  of the ink drain section  50  suctions ink in the collection chamber  51  to drain it outside. By this suction, a flow of ink is generated in the ink flow generation chamber  30 S and effectively removes paper particles adhered to the end surface  24 . In this case, the paper particles are drained together with ink. Thus, no particles would be scattered again. Since the amount of ink necessary for filling the gap G of 0.3 mm and removing the paper particles is very small, shortage of ink would not occur even if paper particles are removed by using an amount of ink ejected for a purge process such as prevention of clogging and degassing. 
     In the embodiment, after the ink flow generation chambers  30 S are filled with inks ejected (spitted) from the nozzles  23 , switching is made such that inks are ejected at a high frequency (e.g., 50 KHz) like in normal printing, by a control of the ink-jet control elements  25  indicated by a two-dot chain line in FIG.  4 A. This serves as a kind of ultrasonic cleaning function, so that paper particles adhered to the end surfaces  24  can be removed more securely. Further, clogging and gas can be also removed by this function. 
     The paper particle removing operation described above is simultaneously carried out for the nozzle units  20 C,  20 Y,  20 M, and  20 B, and completed within about 5 seconds. 
     After removal of paper particles, the print head  20  and the washing board  30  are quickly moved in the reverse order of FIGS. 10D,  10 C,  10 B, and  10 A by the lift  90  and the rotation positioning section  70 . Thus, a delay can be sufficiently suppressed when printing is restarted. 
     The washing board  30  is covered with the dust cover  80  which is responsive to the displacing motion of the washing board  30  directed to the rest position. The dust cover  80  protects the washing board  30  from paper particles and dusts at the printing time, and prevents the paper particles and dusts from being float up from the washing board  30  and adhered to the end surface  24  of the print head  20  by ink ejected for cleaning the end surface  24  of the print head  20  at the non-printing time. 
     As described above, the ink-jet printer of this embodiment ejects inks from the entire ink-jet nozzles  23  at the non-printing time to remove paper particles adhered to the end surface  24  by a flow of ink generated between the end surface  24  of the print head  20  and the washing board  30 . Therefore, the paper particles can be removed quickly, securely, and safely. If the particles are removed as described above during the continuous printing, the printing quality would not be degraded due to ink soaked into the particles and dropped on the paper sheet. Further, the paper particle removing operation is automatically performed, easy handling can be achieved. 
     Moreover, in the ink-jet printer, the print head  20  is movable between positions close to and remote from the peripheral surface  11  of the rotary drum  10 , and the washing board  30  is rotatable around the rotation center Z of the drum  10  to be set at a selected one of the rest position and the cleaning position. Therefore, the position of the washing board  30  can be more quickly and accurately changed, while reducing the space occupied for movement of the washing board  30 . Accordingly, it is possible to remove paper particles adhered to the end surface  24  of the print head  20  more quickly without increasing the size of the ink-jet printer. 
     Since the washing board  30  is covered with the dust cover  80  at the rest position, there is no paper particles and dusts which will be float up from the washing board  30  and adhered to the end surface  24  of the print head  20  by ink ejected in a state where the washing board  30  is placed at the cleaning position. Accordingly, an effective cleaning of removing paper particles from the end surface can be more effectively carried out by ejecting ink. 
     Also, the ink reception plate  31  corresponding to the print heads ( 20 C,  20 Y,  20 M and  20 B) is formed integrally, so that the ink reception plate  31  can be positioned at the paper particle removal position. Removal of paper particles from the entire print head unit  20 U can be performed in a much shorter period. 
     Further, since four lines of grooves GR 1  to GR 4  are integrally formed in the washing board  30  for the nozzle units  20 C,  20 Y,  20 M, and  20 B, removing operations of paper particles for the units can be simultaneously completed in a single process of setting the washing board  30  at the cleaning position and ejecting ink from all the nozzle units  20 C,  20 Y,  20 M, and  20 B. Therefore, the paper particles for the print head can be removed in a short period of time. 
     Ink is drained only through the drain holes  35 , and not unnecessarily flow into the outside of the grooves GR 1  to GR 4  over the ink stopper walls  32 . Therefore, required amount of ink can be reduced and color mixture can be prevented. The grooves GR 1  to GR 4  are opened at the sides of the print head even while ink is ejected, and ink is maintained in the grooves GR 1  to GR 4 . Accordingly, it is not necessary that the print head  20  and the washing board  30  are combined to create a closed room for ensuring removal of particles by a flow of ink. 
     Since the ink drain section  50  drains ink through the drain holes  35  while ink is ejected, the necessary amount of ink can be reduced much more while more improving the ink flow ability. 
     Since the pair of drain hales  35  are formed in the ink reception plate  31  and separated from each other on both sides of the nozzle unit to distribute ink toward two ends in the ink flow generation chambers  30 S. Therefore, it is possible to attain a smooth flow at a high speed while reducing the necessary amount of ink. 
     Since the gap G between the ink reception plate  31  of the washing board  30  and the end surface  24  is set to 0.3 mm, the effect of removing paper particles can be promoted much more and the necessary amount of ink thereby required can be reduced greatly. Also, automatic removal of paper particles can be facilitated much more while more downsizing the entire printer. 
     In each of the nozzle units  20 C,  20 Y,  20 M and  20 B, the nozzle segments  20 CA,  20 CB,  20 CC, and  20 CD are attached to the joint plate  21  such that the end surfaces of the ink-jet nozzles  23  thereof are aligned with each other, and the gap G is formed by bringing the lower surface of the joint plate  21  into contact with the upper surface of the position determination member  34 . Therefore, even if the gap G has a small value of 0.1 to 0.5 mm, the gap G can stably be formed without an error. 
     The washing board  30  is set at the cleaning position during the print standby period, irrespective of cleaning of the print head  30 . In this case, even if ink is leaked and dropped from the ink-jet nozzle  23 , it can be collected by the waste ink cassette  60  via the ink drain section  50 . Therefore, paper sheet is prevented from being contaminated by ink. Further, since the waste ink cassette  60  is detachable, it is possible to carry out continuous printing for a long period without increasing the size of the printer if waste ink is discarded at an appropriate interval. 
     Even when continuous printing is carried out for a great deal of 2000 sheets of paper, no troubles are caused by dealing with waste ink and the periphery is not soiled even when continuous printing is carried out for a great deal of 2000 sheets of paper. Simultaneously, simplification and downsizing of the entire printer can be achieved. In addition, the collection chamber  51  permits a suction force from a single drain tube to be applied commonly to the plural drain holes  35 . Therefore, the structure can be simplified while reducing the manufacturing cost. Further, the collection chamber  51  can prevents scattering of ink, which may be caused when the suction force from the drain tube  53  is directly applied to the drain holes  35 . 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.