This application claims the benefit of Korean Application No.  2001-68735, filed Nov. 6, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated hereby by reference. 
1.  Field of the Invention
The present invention relates to a paper-discharging system and a method in an inkjet printer, and more particularly to, a paper-discharging system of an inkjet printer which can prevent damage of printed contents, such as a smear of incompletely dried pictures or letters, of previously printed paper due to an overlap with current printed paper when the current printed paper is discharged to a paper-discharging tray to be stacked on the previously printed paper. 
2.  Description of the Related Art
Generally, an inkjet printer 10 as shown in FIGS.  1 and 2 includes a paper feeder 20 containing paper P, a paper transporter 30 transporting the paper P from the paper feeder 20, a printing part 40 printing data on the paper P transported by the paper transporter 30, and a paper-discharging system 60 discharging the paper P printed by the printing part 40 to an outside of the inkjet printer 10. 
In an operation of the inkjet printer 10, the paper P which is contained in the paper feeder 20 to be elastically supported by a lockup spring 21 is picked up by a pickup roller 22 and then moved to the paper transporter 30.  At the paper transporter 30, the paper P is transported to the printing part 40 by a rotation of a feed roller 31 and a friction roller 32.  Thus, when the paper P is transported from the paper transporter 30 to the printing part 40, a motor 45 driving a head carriage assembly is operated to drive a belt 43.  Consequently, a printing head 41 which is mounted in a head carriage 46 of the head carriage assembly of the printing part 45 is moved left and right along a carriage shaft 42, ejecting ink on the paper P transported by the paper transporter 30 to print a picture or letters thereon.  As the paper P is kept moving along a base frame 50 after printed by a nozzle 41a of the printing head 41, the paper P reaches the paper-discharging system 60.  At the paper-discharging system 60, the paper P is discharged to the outside through paper-discharging rollers 61 and star-shaped wheels 62. 
However, since the inkjet printer 10 uses a method of ejecting the ink on the paper P to print data thereon, it may produce damage of printed contents, such as a smear of printed images or letters, due to an overlap between previously printed paper and current printed paper when the current printed paper is dropped on the previously printed paper to be stacked thereon before the previously printed paper is completely dried.  Accordingly, the inkjet printer 10 needs a vexing post-process of drying the ink of the respective printed paper for a given time period in every printing operation. 
To solve the problem of producing the damage of printed contents and the vexing post-process, as shown in FIGS.  3A and 3B, there has been proposed another inkjet printer 10xe2x80x2 using a method of disposing an elongated guide 63 in the vicinity of a paper-discharging opening or port.  To prevent current printed paper P from being in contact with previously printed paper (not shown) already stacked on a paper-discharging tray 64, the inkjet printer 10xe2x80x2 supports the current printed paper P at an inclined state on the guide 63 until next printed paper is discharged.  The current printed paper P is dropped at the paper-discharging tray 64 by a pushing force generating when the next printed paper is discharged. 
Thus, the inkjet printer 10xe2x80x2 provides an advantage that prevents the smear of the printed letters or images of the previously printed paper when the current printed paper P is dropped on the previously printed paper at the paper-discharging tray 64 after the previous printed paper is almost dried.  However, since the inkjet printer 10xe2x80x2 has the elongated guide 63 which is longitudinally disposed in the paper-discharging tray 64, there was a problem that a volume of the inkjet printer 10xe2x80x2 increases due to an increase of the elongated guide 63xe2x80x2 in longitudinal and width directions thereof, thereby requiring a large space for the elongated guide 63. 
Therefore, it is an object of the present invention to provide an improved paper-discharging system of an inkjet printer which can provide a time period enough to dry ink on previously printed paper by controlling current printed paper to be planar by a stiffness of the current printed paper itself until a rear end of the current printed paper is completely discharged to an outside of the inkjet printer, thereby preventing damage, such as a smear, of printed letters or pictures of the previously printed paper due to an overlap between the current printed paper and the previously printed paper. 
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
These and other objects may be achieved according to an embodiment of the present invention, by providing a paper-discharging system discharging paper printed by a printing head to an outside of an inkjet printer.  The paper-discharging system includes a discharging unit discharging the printed paper upwardly and longitudinally bent from a discharging frame to ensure (control) the printed paper to be planar by a stiffness of the printed paper itself until a rear end of the printed paper is completely discharged to the outside.  The discharging unit includes a first roller part discharging the paper horizontally after the printed paper has been printed by the printing head, an upward-guiding part guiding the printed paper to be upwardly bent at a first given (tilt) angle with the base frame after the printed paper is passed through the first roller part, and a second roller part bending the printed paper longitudinally at a second given (tilt) angle and discharging the printed paper after the printed paper is passed through the upward-guiding part. 
The first roller part includes a shaft driven by a motor, a plurality of first paper-discharging rollers disposed at regular intervals on the shaft, and a plurality of first supporting rollers disposed over corresponding ones of the first paper-discharging rollers to transmit a rotation force of the first paper-discharging rollers to the printed paper. 
The upward-guiding part includes at least one inclined plate having an inclined surface in which is gradually slanted to the upstream of a paper-discharging direction.  Preferably, the tilt angle of the inclined surface is within the range of 10xc2x0 through 60xc2x0.  Alternatively, the upward-guiding part can include a plurality of inclined plates, each being disposed such that the first tilt angle of the inclined plates disposed at a center portion in width of the printed paper is smaller than that of the inclined plates disposed at a side portion in width of the printed paper. 
The second roller part includes at least one small roller portion disposed to be tilted at the second given angle with a plane of the printed paper discharged through the upward-guiding part.  The second tilt angle of the small roller portion is within the range of 5xc2x0 through 30xc2x0.  Also, the second roller part may have two small roller portions, each being disposed to be tilted at the second given angle upwardly from the horizontal plane of the printed paper discharged through the upward-guiding part with respect to the center in width of the printed paper.  Each of the small roller portions includes a shaft tilted by the second given (tilt) angles with the printed paper discharged through the first roller part, second paper-discharging rollers disposed in regular intervals on the shaft, and second supporting rollers disposed respectively over the corresponding second paper-discharging rollers to transmit the rotation force of the second paper-discharging rollers to the printed paper. 
The paper-discharging system includes a transmission transmitting the rotation force of the first roller part to the second roller part.  The transmission includes a first gear formed at the first roller part, an idle gear engaged with the idle gear, and a universal joint transmitting the rotation force of the idle gear to the second roller part by being engaged with the idle gear.  The universal joint includes a second gear engaged with the idle gear, T and ball-shaped ends formed respectively at the shafts of the small roller portions of the second roller part in the vicinity of the center in width of the printed paper, and a connecting part securing and interconnecting the T and ball-shaped ends at the second given angle to transmit the rotation force of the idle gear engaged with the second gear to the shafts of the small roller portions tilted at the second given angle. 
Alternatively, the transmission may have a first gear formed at one end of the first roller part, an idle gear engaged with the first gear, and a second gear engaged with the idle gear transmitting the rotation force of the idle gear to one of the small roller portions of the second roller part.  In this case, an universal joint is disposed between the small roller portions transmitting the rotation force from one to the other of the small roller portions.  The universal joint includes T and ball-shaped ends formed respectively at the shafts of the small roller portions of the second roller part in the vicinity of the center portion in the widthwise direction of the printed paper, and the connecting part secures and interconnects the T and ball-shaped ends at the second given angle to transmit the rotation force from one to the other of the shafts of the small roller portions tilted at the second given angle.