Abstract:
An image forming apparatus discharging a printed medium at a stable speed. A image developer affixes an image to a printing medium to form a printed medium and a transporting roller moves the printed medium toward a discharge roller. A one-way clutch driving the transport roller permits the discharge roller to assert control over the printed medium while the printed medium is in contact with the transport roller. The discharge roller is controllable to accelerate and decelerate the printed medium so that printed media are orderly stacked. The one way clutch permits the discharge roller and the transport roller to be spaced apart less than a length of the printed medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 2005-42064, filed on May 19, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     An aspect of the present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus discharging a printing paper at a stable speed.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, an image forming apparatus includes a paper providing unit, a developing unit, a fixing unit and a paper discharging unit. The paper providing unit provides a printing paper to the developing unit, which selectively applies developer to the printing paper, thereby forming an image. The fixing unit fixes the applied developer to the printing paper. The paper discharging unit receives the printing paper on which the image is formed and discharges the paper having the formed image to the outside of the image forming apparatus. Although the term “printing paper” is used as a convenience in describing aspects of the present invention, the present invention is applicable to printable media other than paper, such as for example, plastic sheets.  
         [0006]     The developing unit includes a photosensitive body, a light scanning unit, a developing roller and a transferring roller. When the light scanning unit transfers light containing printing image information to the photosensitive body, an electrostatic latent image is formed by a potential difference on the photosensitive body. The developing roller provides the developer to the electrostatic latent image on the photosensitive body and develops the electrostatic latent image, and the transferring roller transfers a development image formed on the photosensitive body to the printing paper.  
         [0007]     In order to improve printing speed, the printing paper is transported in the apparatus at high speed. All of the paper providing unit, the developing unit, the fixing unit and the paper discharging unit transport the printing paper at high speed. However, the printing speed should decelerate to a predetermined speed or less at the moment the printing paper is last discharged to the outside of the apparatus. Therefore, the paper discharging unit transports the printing paper at variable speed.  
         [0008]      FIG. 1  is a schematic view of a conventional image forming apparatus. The image forming apparatus  100  includes a paper providing roller part  160 , a developing part  110 , a fixing roller part  120 , a transporting roller part  140  and a paper discharging roller part  130 . The paper providing roller part  160  includes a pickup roller  162  picking up a printing paper (P) from a paper providing tray (not shown) and a feeding roller  164  feeding the printing paper (P) to the developing part  110 .  
         [0009]     The developing part  110  selectively applies developer to the printing paper (P) according to a developing process. The fixing roller part  120  includes a pair of fixing rollers and receives the printing paper (P) to which the developer is applied from the developing part  110  and fixes the developer to the printing paper (P), thereby forming an image.  
         [0010]     The transporting roller part  130  includes a transporting roller  142  receiving the printing paper (P) from the fixing roller part  120  and transporting the printing paper (P) to the paper discharging roller part  130  and a transporting roller driving part  144  driving the transporting roller  142 . The transporting roller driving part  144  drives the transporting roller  142  in order to transport the printing paper (P) at the same speed as the fixing roller part  120  transports the printing paper (P), using a same driving motor as the fixing roller part  120  so as not to influence the speed at which the fixing roller part  120  fixes the printing paper (P).  
         [0011]     The paper discharging roller part  130  includes a paper discharging roller  132  discharging the printing paper (P) to a paper storing part  150  and a paper discharging roller driving part  134  driving the paper discharging roller  132 . The printing paper (P) is orderly transported by the paper providing roller part  160 , the developing part  110 , the fixing roller part  120  and the transporting roller part  140  so as to be printed at high speed.  
         [0012]     When the paper discharging roller part  130  and the transporting roller part discharge the printing paper (P) to the paper storing part  150  at high speed, a following printing paper (P) is stacked before a former printing paper (P) is settled and the printing papers (P) may not be properly stacked in the paper storing part  150 . Therefore, after receiving the printing paper (P) from the transporting roller part  140  at high speed, the paper discharging roller part  130  discharges the printing paper (P) at a predetermined decelerated speed before discharging the printing paper (P) to the paper storing part  150 , and then transports the following printing paper (P) at the original high speed.  
         [0013]      FIG. 2  is a graph showing a transporting speed pattern of the paper discharging roller part in  FIG. 1 . A horizontal axis shows time and a vertical axis shows a transporting speed of the printing paper (P) of the paper discharging roller part  130 . Time ‘a’ shows a time at which a lower part of the printing paper (P) leaves the fixing roller part  120 , time ‘b’ shows a time at which the lower part of the printing paper (P) leaves the transporting roller part  140 , and time ‘c’ shows a time at which the lower part of the printing paper leaves the paper discharging roller part  130 . Line Vp shows the transporting speed pattern of the image forming apparatus  100 .  
         [0014]     The fixing roller part  120  and the transporting roller part  140  regularly transport the printing paper P at a high fixing speed V 1 . The paper discharging roller part  130  continues transporting the printing paper (P) at V 1 , the same speed as the fixing speed V 1 , until the time ‘b’ so as not to disturb the fixing roller part  120  in fixing the printing paper. The paper discharging roller part  130  decelerates down to a discharging speed V 3  at the time ‘c’ and discharges the printing paper (P), and then returns the discharging speed to a fixing speed V 1 . In order to increase an interval between the printing papers (P) so that the former printing paper is not contacted with the following printing paper when the printing paper is deceleratedly transported between time ‘b’ and time ‘c’, the paper discharging roller part  130  acceleratedly transports the printing paper (P) up to a predetermined accelerated speed V 2  after time ‘b’, and thereafter deceleratedly transports the printing paper (P) down to the discharging speed V 3 .  
         [0015]     However, the conventional image forming apparatus  100  may not correctly discharge the printing paper (P) since the printing speed decelerates at a sufficiently stable speed as the printing speed becomes higher-speed. Since the fixing speed V 1  becomes an even higher-speed as the printing speed becomes high-speed, a difference in transporting speed at which the paper discharging roller part  130  should decelerate from time ‘b’ to time ‘c’ becomes large, and a time interval between time ‘b’ and the time ‘c’ may become short. Therefore, the paper discharging roller part  130  accelerates the transporting speed between the time ‘b’ and the time ‘c’, and then may not decelerate the transporting speed back to stable speed. Accordingly, the printing paper (P) is discharged and transported at a speed which is not sufficiently decelerated to be stable, thereby the printing paper is incorrectly stacked.  
         [0016]     To discharge the printing paper at stable speed, the transporting roller part  140  may be spaced from the paper discharging roller part  130  in order to extend the interval between the time ‘b’ and the time ‘c’. However, the distance between the transporting roller part  140  and the paper discharging roller part  130  may not be more than the maximum length of the printing paper (P). Otherwise, the printing paper (P) may not be stably transported. Increasing a transporting interval between the printing papers may obtain time to decelerate the transporting speed, however, increasing the transporting interval makes the printing speed slower.  
       SUMMARY OF THE INVENTION  
       [0017]     Accordingly, an aspect of the present invention is to provide an image forming apparatus and a paper transporting apparatus capable of discharging printing papers at stable speed.  
         [0018]     The foregoing and/or other aspects of the present invention are achieved by providing an image forming apparatus including a developing part applying a developer to a printing paper, the developing part including a fixing roller part receiving the printing paper from the developing part and fixing the developer to the printing paper; a paper discharging roller part receiving the printing paper from the fixing roller part and discharging it at a transporting speed pattern; and a transporting roller part including a transporting roller interposed between the fixing roller part and the paper discharging roller part and transporting the printing paper from the fixing roller part to the paper discharging roller part, a transporting roller driving part driving the transporting roller in a transporting-rotating direction so that the transporting roller transports the printing paper at a first speed, and a one-way clutch interposed between the transporting roller and the transporting roller driving part and transmitting driving force of the transporting roller driving part to the transporting roller only in the transporting-rotating direction.  
         [0019]     According to an embodiment of the present invention, the paper discharging roller part starts to accelerate the transporting speed of the printing paper at least after the printing paper leaves the fixing roller part, and accelerates the printing paper up to a second speed at least exceeding the first speed, and then decelerates the printing paper down to a third speed less than the first speed when the printing paper leaves the paper discharging roller part.  
         [0020]     According to the embodiment of the present invention, the fixing roller part and the paper discharging roller part are disposed at an interval within at least the length of the printing paper along the progress path of the printing paper.  
         [0021]     The foregoing and/or other aspects of the present invention are also achieved by providing a paper transporting apparatus interposed between a fixing roller part fixing a developer to a printing paper and a paper discharging roller part discharging the printing paper and transporting the printing paper from the fixing roller part to the paper discharging roller part, the paper transporting apparatus including a transporting roller receiving the printing paper from the fixing roller part and transporting the printing paper to the paper discharging roller part; a transporting roller driving part driving the transporting roller at a predetermined angular velocity in a transporting-rotating direction; and a one-way clutch interposed between the transporting roller and the transporting roller driving part and transmitting driving force of the transporting roller driving part to the transporting roller only in the transporting-rotating direction.  
         [0022]     Additional aspects and/or advantages 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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which:  
         [0024]      FIG. 1  is a schematic view of a conventional image forming apparatus;  
         [0025]      FIG. 2  is graph showing a transporting speed pattern of a paper discharging roller part shown in  FIG. 1 ;  
         [0026]      FIG. 3  is a schematic view of an image forming apparatus according to an embodiment of the present invention;  
         [0027]      FIG. 4  is a schematic view of a transporting roller part in  FIG. 3 ;  
         [0028]      FIG. 5  is a graph showing a transporting speed pattern of a paper discharging roller part in  FIG. 3 ; and  
         [0029]      FIGS. 6A-6D  are schematic views to illustrate transporting a printing paper by the paper discharging roller part in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0030]     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0031]      FIG. 3  is a schematic view of an image forming apparatus according to an embodiment of the present invention and  FIG. 4  is a schematic view of a transporting roller part schematically shown in  FIG. 3 .  
         [0032]     Referring to  FIG. 3 , an image forming apparatus  1  includes a paper providing roller part  60 , a developing part  10 , a fixing roller part  20 , a transporting roller part  40  and a paper discharging roller part  30 . A printing paper (P) orderly passes through the paper providing roller part  60 , the developing part  10 , the fixing roller part  20 , the transporting roller part  40  and the paper discharging roller part  30 , thereby forming printing images.  
         [0033]     The paper providing roller part  60  receives the printing paper (P) from a paper providing tray (not shown) and provides the printing paper (P) to the developing part  10 . The paper providing roller part  60  includes a pickup roller  62  and a feeding roller  64 . The pickup roller  62  picks up the printing papers (P) by a sheet stacked in the paper providing tray. The feeding roller  64  receives the printing paper (P) from the pickup roller  62  and feeds the printing paper (P) to the developing part  10 .  
         [0034]     The developing part  10  selectively applies a developer in order to form images on the printing paper (P) provided by the paper providing roller part  60 . The developing part  10  includes a photosensitive body  12  and a transferring roller  14 . A light scanning unit (not shown) scans light, based on printing image information, thereby forming an electrostatic latent image on the photosensitive body  12 . The developing roller (not shown) is provided with the developer from a developer providing part (not shown) and provides the developer to the electrostatic latent image of the photosensitive body  12 , thereby developing the image. The transferring roller  14 , using a potential difference, transfers the developer applied to the photosensitive body  12  to the printing paper (P) passing between the photosensitive body  12  and the transferring roller  14 .  
         [0035]     The fixing roller part  20  fixes the developer applied on the printing paper (P) while receiving the printing paper from the developing part  10  and transporting the printing paper (P) to the transporting roller part  40 , thereby completing the image. The fixing roller part  20  includes a fixing roller  22  and a fixing roller driving part  24 . The fixing roller  22  may include a pair of rollers respectively heating and pressurizing the printing paper passing between the pair of rollers. The fixing roller driving part  24  drives the fixing roller  22  at a predetermined speed so that the fixing roller  22  fixes the developer on the printing paper (P) as well as transports the printing paper (P) at the predetermined speed.  
         [0036]     The transporting roller part  40 , which is interposed between the fixing roller part  20  and the paper discharging roller part  30 , receives the printing paper (P) from the fixing roller part  20  and transports the printing paper (P) to the paper discharging roller part  30 . The transporting roller part  40  includes a transporting roller  42 , a transporting roller driving part  44  and a one-way clutch  46 .  
         [0037]     The transporting roller  42  transports the printing paper (P) from the fixing roller part  20  to the paper discharging roller part  30 . The transporting roller driving part  44  is provided with a driving force from a driving motor  45  and rotates the transporting roller  42  at a predetermined angular velocity so that the transporting roller  42  transports the printing paper (P) at a first speed U 1 , as shown in  FIG. 5 . The transporting roller driving part  44  may be an electric-powered device such as a gear, a pulley, etc.  
         [0038]     The first speed U 1  at which the transporting roller  42  transports the printing paper (P) may be the same speed as at which the fixing roller part  20  transports the printing paper (P) so as not to disturb the fixing roller part  20  in fixing the printing paper (P). For maintaining the transporting speed, the fixing roller  22  may also be provided with rotary force from the driving motor  45  providing rotary force to the transporting roller  42 . As long as the first speed U 1  is made to be the same speed as the fixing roller part  20  transports the printing paper (P), the transporting roller  42  and the fixing roller  22  may be driven by separate motors.  
         [0039]     The one-way clutch  46  is interposed between the transporting roller  42  and the transporting roller driving part  44  and transmits the driving force of the transporting roller driving part  44  to the transporting roller  42  only in a same transporting-rotating direction as the transporting roller  42  transports the printing paper (P) from the fixing roller part  20  to the paper discharging roller part  30 . The one-way clutch  46  does not transmit the driving force of the transporting roller driving part  44  to the transporting roller  42  in the opposite transporting-rotating direction.  
         [0040]     Accordingly, when the transporting roller  42  is applied with a force causing an angular velocity more than an angular velocity at which the transporting roller driving part  44  rotates the transporting roller  42  in the transporting-rotating direction, the transporting roller  42  is idle-rotated. Therefore, the transporting roller  42  may not only transport the printing paper (P) in the direction of the paper discharging roller part  30  at the first speed U 1  by the transporting roller driving part  44 , but the transporting roller  42  may also be rotated in the direction of the paper discharging roller part  30  without being restricted by the transporting roller driving part  44 , so the printing paper (P) may stably be transported to the paper discharging roller part  30  at the first speed U 1  or more. The well-known one-way clutch  46  is used in the embodiment, which is disclosed in the Korean First Publication No. 2004-77442.  
         [0041]     The paper discharging roller part  30  receives the printing paper(P) from the fixing roller part  20  and discharges the printing paper (P) at a predetermined transporting speed pattern. The image forming apparatus  1  includes a paper storing part  50  where the printing papers (P) on which the image is formed are stacked. The paper discharging roller part  30  discharges the printing paper (P) on which the image is formed to the paper storing part  50 .  
         [0042]     The paper discharging roller part  30  includes a paper discharging roller  32  and a paper discharging roller driving part  34 . The paper discharging roller driving part  34  drives the paper discharging roller  32  so that the paper discharging roller  32  transports the printing paper (P) according to the transporting speed pattern. The paper discharging roller driving part  34  may have a separate driving motor from the transporting roller driving part  44 . The paper discharging roller driving part  34  may drive the paper discharging roller  32  at the transporting speed pattern by varying the paper discharging roller&#39;s  32  transporting speed by a well-known controller.  
         [0043]     The paper discharging roller part  30  starts to accelerate the transporting speed of the printing paper (P), at least after the printing paper (P) leaves the fixing roller part  20 , and keeps accelerating the speed up to a second speed U 2  exceeding the first speed U 1 . Thereafter, the paper discharging roller part  30  decelerates the transporting speed of the printing paper (P) down to a third speed U 3  less than the first speed U 1  when the printing paper (P) leaves the paper discharging roller part  30 .  
         [0044]     The paper discharging roller part  30  starts to accelerate the transporting speed immediately after the printing paper (P) leaves the fixing roller part  20  and increases the speed to the second speed U 2 . Accordingly, the transporting interval between the printing paper (P) in the middle of transporting and the following printing paper (P) becomes longer, thereby providing time to decelerate the speed. The paper discharging roller part  30  may also accelerate the transporting speed after the printing paper (P) leaves the fixing roller part  20 . The second speed U 2  is at least exceeding the first speed U 1  and may be enough to space the transporting interval between the printing papers (P) at a predetermined interval.  
         [0045]     The transporting roller  42  is not restricted by the transporting roller driving part  44  driving due to the one-way clutch  46  and is operated at the transporting speed exceeding the first speed U 1  by tension the paper discharging roller part  30  gives to the printing paper (P), thereby transporting the printing paper (P) at the second speed U 2 . Therefore, the transporting roller  42  may become free from the accelerating start point limitation that the transporting speed cannot start to be accelerated until the printing paper (P) leaves the transporting roller  42  which is gear driven along with the fixing roller  22  so as not to prevent the fixing roller part  20  from fixing the printing paper (P). Since the paper discharging roller part  30  may accelerate the transporting speed as soon as the printing paper (P) leaves the fixing roller part  20 , additional time may be obtained to accelerate or decelerate the transporting speed of the paper discharging roller part  30  as much as the interval between the point the printing paper (P) leaves the fixing roller part  20  and the point the printing paper (P) leaves the transporting roller part  40 .  
         [0046]     The paper discharging roller part  30  accelerates the transporting speed up to the second speed U 2 , and thereafter decelerates the transporting speed down to the third speed U 3  before the printing paper (P) is discharged to the paper storing part  50 . The third speed U 3  is at least less than the first speed U 1  and is preferably low enough that the printing paper (P) may stably be stacked in the paper storing part  50 . The paper discharging roller part  30  decelerates a discharging speed of the printing paper (P) to the third speed U 3 , which is stably low, and discharges the printing paper (P) to the paper storing part  50 , thereby discharging at the stably low speed when finally discharging the printing paper (P) transported through the developing part  10 , the fixing roller part  20 , etc., at high speed.  
         [0047]     The fixing roller part  20  and the paper discharging roller part  30  may be disposed in the course of the printing paper (P) at the interval within the length of the printing paper (P). The printing paper (P) is transported by at least two of the fixing roller part  20 , the transporting roller part  40  or the paper discharging roller part  30 , not a single roller part, at any location, thereby improving transporting stability.  
         [0048]     When the fixing roller part  20  and the paper discharging roller part  30  are disposed in the course of the printing paper (P) at the interval more than the length of the printing paper (P), the printing paper (P) may be transported by only the transporting roller part  40  before the printing paper (P) is received to the paper discharging roller part  30 , although the printing paper (P) leaves the fixing roller part  20 . However, the paper discharging roller part  30  starts to accelerate immediately after the printing paper (P) leaves the fixing roller part  20 , receives the printing paper (P) at the predetermined accelerated speed and transports the printing paper (P).  
         [0049]     Further, the paper discharging roller part  30  may start to accelerate after the printing paper (P) is received by the discharging roller  30 .  
         [0050]     Hereinafter, functions of the image forming apparatus will be described by reference to  FIGS. 5, 6A ,  6 B,  6 C and  6 D.  FIG. 5  is a graph showing a transporting speed pattern of the paper discharging roller part  30 ; and  FIGS. 6A-6D  are schematic views to illustrate transporting the printing paper by the paper discharging roller part. A horizontal axis shows time and a vertical axis shows a transporting speed of the printing paper (P) of the paper discharging roller part  30 . Referring to  FIG. 5 , a time ‘A’ shows the time at which a lower part of the printing paper (P) leaves the fixing roller part  20 , a time ‘B’ shows the time at which the lower part of the printing paper (P) leaves the transporting roller part  40 , a time ‘C’ shows the time at which the lower part of the printing paper leaves the paper discharging roller part  30 , and a time ‘D’ shows the time at which the paper discharging roller part  30  starts to decelerate the transporting speed. Line ‘Up’ shows the transporting speed pattern of the paper discharging roller part  30  according to the embodiment of the present invention and line ‘Vp’ shows the transporting speed pattern of the conventional image forming apparatus.  FIG. 6A  shows a fixing condition of the printing paper (P),  FIG. 6B  corresponds to the time ‘A’ in  FIG. 5 ,  FIG. 6C  corresponds to the time ‘D’ in  FIG. 5 , and  FIG. 6D  corresponds to a time before the time ‘C’ in  FIG. 5 .  
         [0051]     When the printing paper (P) is in the fixing condition, the upper part of the printing paper (P) is received by the paper discharging roller part  30  due to the fixing roller part  20  transporting the printing paper (P) at a first speed U 1 . At this point, the paper discharging roller part  30  transports the printing paper (P) at the first speed U 1  so as not to disturb the fixing roller part  20  in its function. (See  FIG. 6A .)  
         [0052]     Immediately after the lower part of the printing paper (P) leaves the fixing roller part  20  (the time ‘A’), the paper discharging roller part  30  starts to accelerate, then transports the printing paper (P) at a second speed U 2  until the time ‘D’ where the printing paper (P) starts to decelerate. At the point where the printing paper (P) starts to decelerate, the transporting roller  42  exceeds the speed by the first speed U 1  by the one-way clutch  46  and may transport the printing paper (P) at the same speed as the paper discharging roller part  30 . Accordingly, the interval between the printing papers (P 1 , P 2 ) may be sufficient. (See  FIGS. 6B and 6C )  
         [0053]     At the time D, when the paper discharging roller part  30  starts to decelerate the transporting speed, the transporting speed should be at least the first speed U 1  when the lower part of the printing paper (P) leaves the transporting roller part  40  while being deceleratedly transported.  
         [0054]     The paper discharging roller part  30  transports the printing paper (P) at a third speed U 3  at the moment when the lower part of the printing paper (P) leaves the paper discharging roller part  30  (time ‘C’). Accordingly, the printing paper (P) is discharged at the sufficiently stable speed, thereby well being stacked in the paper storing part  50 . The paper discharging roller part  30 , after discharging the printing paper P 1 , accelerates and prepares to receive the next printing paper P 2  at the first speed U 1 . The paper discharging roller part  30  transports the printing papers (P) at the transporting speed pattern.  
         [0055]     The image forming apparatus  1  includes the transporting roller part  40  equipped with the one-way clutch  46 , thereby extending an available time that the paper discharging roller part  30  may start as much as the interval between time ‘A’ and time ‘B’. Therefore, the image forming apparatus  1  may obtain an additional time to accelerate or decelerate the transporting speed of the paper discharging roller part  30  without extending the interval between the printing papers (P) or the interval of disposition between the fixing roller part  20  and the paper discharging roller part  30 .  
         [0056]     Accordingly, the printing paper (P) may be discharged at the third speed U 3  lower than the conventional discharging speed V 3  at time ‘C’.  
         [0057]     A paper transporting apparatus according to the embodiment of the present invention will be described with reference to  FIGS. 3 and 4 . The paper transporting apparatus  40  is interposed between the fixing roller part  20  fixing the printing paper (P) and the paper discharging roller part  30  discharging the printing paper (P), thereby transporting the printing paper (P) from the fixing roller part  20  to the paper discharging roller part  30 .  
         [0058]     The paper transporting apparatus  40  includes the transporting roller  42 , the transporting roller driving part  44 , and the one-way clutch  46 . The transporting roller  42  receives the printing paper P from the fixing roller part  20  and transports the printing paper to the paper discharging roller part  30 . The transporting roller driving part  44  drives the transporting roller  42  at a predetermined angular velocity in the transporting-rotating direction. Accordingly, the transporting roller  42  may transport the printing paper (P) from the fixing roller part  20  to the paper discharging roller part  30  at the predetermined transporting speed.  
         [0059]     The one-way clutch  46  is interposed between the transporting roller  42  and the transporting roller driving part  44  and transmits driving force of the transporting roller driving part  44  to the transporting roller  42  only in the transporting-rotating direction. Therefore, the transporting roller  42  may be idle-rotated at the predetermined angular velocity or more by the transporting roller driving part  44 .  
         [0060]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.