Abstract:
A printer apparatus and method for sequentially withdrawing sheets loaded into a cassette and printing images on the sheets is provided. The printer includes: a pickup roller for picking up a sheet from a plurality of sheets in the cassette; a resistance member for contacting a front end of the sheets such that the top sheet is separated based on stiffness and picked up from the cassette; and an angle change unit for changing a tilt angle of the resistance member about the front end of the sheets from a first tilt angle to a second tilt angle in a process of picking up the top sheet, and allowing the tilt angle to return to the first tilt angle when the top sheet has been completely picked up.

Description:
BACKGROUND OF THE INVENTION 
     This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2003-56008, filed on Aug. 13, 2003, in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a printer and a method for feeding sheets in the printer. More particularly, the present invention relates to a printer for separating and feeding loaded sheets in accordance with stiffness of the sheets and a corresponding method of feeding the sheets in the printer. 
     DESCRIPTION OF THE RELATED ART 
     Printers allow a large number of sheets to be loaded onto a cassette, and to be withdrawn and fed sequentially from the cassette. Examples of a method of sequentially separating the sheets typically include a frictional separation method that uses a frictional plate, and a resistance method that uses stiffness of sheets. 
       FIG. 1  is a diagram illustrating a conventional arrangement for separating sheets using a resistance method. 
     Referring to  FIG. 1 , a large number of sheets are loaded onto a cassette  51 . A pickup roller  52  comes into contact with the loaded sheets P. A resistance member  53  having a predetermined tilt angle A is provided on a front end of the sheets P. When the pickup roller  52  rotates, the sheets P are fed. Two or more sheets P are fed via frictional force between the sheets P and reach the resistance member  53 . The frictional force between the pickup roller  52  and the sheets P is larger than the frictional force between the sheets P. Therefore, as the pickup roller  52  rotates, only the top sheet P 1  in contact with the pickup roller  52  is slipped from the underlying sheets P and fed. The front end of the sheet P 1  becomes curved, thereby forming a curl as indicated by a reference numeral C 1  in  FIG. 1 . Due to the rotation of the pickup roller  52 , the curl grows as indicated by a reference numeral C 2 , the curl then gets unfolded instantaneously as indicated by a reference numeral C 3  by the stiffness of the sheet P 1 . Only the sheet P 1  is separated and fed. 
     A tilt angle A of the resistance member  53  is chosen to be suitable for standard size sheets. Therefore, when using thick sheets having a large stiffness, the separation processes C 1 , C 2 , and C 3  in  FIG. 1  are not performed or are improperly performed after the front end of the sheet P reaches the resistance member  53 , so that a jam may occur or a pickup error where the sheet P is not fed may occur. Further, overload may be applied to a drive motor (not shown) that drives the pickup roller  52 . 
     In order to solve these problems, if thick sheets are used, the resistance member  53  needs to have a large tilt angle A. Referring to  FIG. 2 , the resistance member  53  is able to rotate and is elastically biased by a spring  54 . Then, when thick sheets P having a large stiffness are fed, the resistance member  53  rotates as indicated by a reference numeral B so as to reduce a load applied to the drive motor (not shown), and the separation processes C 1  through C 3  are performed. However, in such a construction the tilt angle A may be changed even when using standard size sheets, thereby causing a paper jam. 
     SUMMARY OF THE INVENTION 
     Accordingly, embodiments of the present invention provide a printer that can change a tilt angle of a resistance member so as to stably separate and feed standard size sheets and thick sheets having a relatively large stiffness, and a method of feeding sheets in the printer. 
     According to an aspect of the present invention, there is provided a printer comprising a pickup roller that picks up a sheet from a cassette; a resistance member that comes in contact with a front end of the sheets such that a top sheet is separated by stiffness and picked up from the cassette; and an angle change unit that changes a tilt angle of the resistance member about the front end of the sheets from a first tilt angle to a second tilt angle in the process of picking up the top sheet, and allows the resistance member to return to the first tilt angle when the top sheet has been picked up. The angle change unit may keep the resistance member at the first tilt angle at least for a time required for separating a standard size sheet, and then change the tilt angle of the resistance member to the second tilt angle. 
     According to another aspect of the present invention, there is provided a method of feeding sheets in a printer comprising a cassette that sheets are loaded into, a pickup roller that comes in contact with a top sheet of the loaded sheets and rotates, and a resistance member that comes in contact with a front end of the sheets such that the top sheet is separated by stiffness and picked up from the cassette. The method comprises changing a tilt angle of the resistance member about the front end of the sheets from a first tilt angle to a second tilt angle in the process of picking up the top sheet; and returning the resistance member to the first tilt angle when the pickup of the top sheet is completed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings in which: 
         FIG. 1  is a cross-sectional diagram illustrating a conventional arrangement for separating sheets using a resistance method; 
         FIG. 2  is a cross-sectional diagram illustrating another example of a resistance arrangement; 
         FIG. 3  is a schematic structural diagram of a printer according to an embodiment of the present invention; 
         FIG. 4  is a perspective view schematically illustrating a sheet feed system of the embodiment shown in  FIG. 3 ; 
         FIG. 5  is a diagram illustrating a first gear train in detail; 
         FIG. 6  is a diagram illustrating a second gear train in detail; 
         FIG. 7  is a diagram illustrating a third gear train in detail; 
         FIG. 8  is a diagram illustrating a first tilt angle and a second tilt angle; 
         FIG. 9  is a perspective view illustrating an example of an angle change unit that changes a tilt angle of a resistance member; 
         FIGS. 10 and 11  are graphs illustrating drive currents of a drive motor that drives a pickup roller when separating a standard size sheet and a thick sheet in a state where the resistance member is fixed to the first tilt angle; 
         FIG. 12  is a perspective view illustrating another example of the angle change unit; 
         FIG. 13  is a schematic side view of the angle change unit of  FIG. 12 ; and 
         FIG. 14  is a diagram illustrating an operation of the angle change unit shown in  FIGS. 12 and 13 . 
     
    
    
     Throughout the drawings, it should be noted that the same or similar elements are denoted by like reference numerals. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIG. 3  is a schematic structure diagram of a printer according to an embodiment of the present invention. For convenience of explanation, the printer of  FIG. 3  is described as an inkjet printer that prints images on sheets by ejecting ink droplets, however, the embodiments of the present invention are not limited to this example. 
       FIG. 3  illustrates a cassette  110  whereon a number of sheets P are loaded, and a pickup roller  120  and a drive roller  130  that pick up the sheets P from the cassette  110  and supply the sheets P to a feed roller  140  that feeds the sheets P at a predetermined speed. The pickup roller  120  comes in contact with the sheets P loaded on the cassette  110  and rotates when picking up the sheets P, and is separated from the sheets P when the pickup is completed. A driven roller  141  comes in contact with the feed roller  140 . A driven roller  131  comes in contact with the drive roller  130 . A reference numeral  170  indicates a resistance member that separates the sheets P one by one using a resistance method. A reference numeral  150  indicates a printer head that ejects ink droplets on a sheet and prints images thereon. The print head  150  is mounted on a carriage  151  which is reciprocated in a direction perpendicular to a feed direction of the sheets by means of a carriage motor  160 . 
       FIG. 4  is a perspective view schematically illustrating a sheet feed system in accordance with the embodiment of the invention shown in  FIG. 3 . 
     Referring to  FIG. 4 , a first gear  1  is coupled to an end of a shaft  142  of the feed roller  140 . A drive motor  180  is connected to the first gear  1  through a belt  181  and a pulley  182  and makes the feed roller  140  rotate. A gear  2  is coupled to the other end of the shaft  141  of the feed roller  140 . The gear  2  is connected to a gear  4  coupled to a pickup shaft  200  through a gear  3 . 
     A first gear train  210  for driving the drive roller  130  is provided to an outside  191  of a bracket  190 . A pickup arm  240  is rotatably installed at the pickup shaft  200 . The pickup roller  120  and a second gear train  220  as shown in  FIG. 6  are provided in the pickup arm  240 . A third gear train  230  for driving cam members  310 ,  380  to be described later is provided in an inside  192  of the bracket  190 , as shown in  FIG. 7 . 
       FIG. 5  illustrates the first gear train  210  in detail. Referring to  FIG. 5 , a swing bracket  250  having a first arm  251  and a second arm  252  is rotatably coupled to the pickup shaft  200 . A gear  5  is coupled to the first arm  251 . A gear  6  and a gear  7  connected to each other are coupled to the second arm  252 . The gear  5  and the gear  6  are connected to the gear  4 , respectively. When the feed roller  140  rotates in an F 1  direction that is opposite to a feed direction of the sheets P, the swing bracket  250  rotates in a G 1  direction, and thus the gear  5  is connected to the gear  8 . When the feed roller  140  rotates in an F 2  direction that is the feed direction of the sheets P, the swing bracket  250  rotates in a G 2  direction, and thus the gear  7  is connected to the gear  8 . The gear  8  is connected to a gear  9  coupled to one end of the drive roller  130 . 
       FIG. 6  illustrates a second gear train  220  in detail. Referring to  FIG. 6 , a gear  10  is coupled to the pickup shaft  200 . A rotatable pickup arm  240  is provided in the pickup shaft  200 . The pickup roller  120  is provided at an end of the pickup arm  240 . A gear  13  coupled to the pickup roller  120  is connected to the gear  10  through the gear  11  and the gear  12 . When the feed roller  140  rotates in the F 1  direction, the pickup arm  240  rotates in an H 1  direction, and thus the pickup roller  120  comes in contact with the sheet P and feeds the sheet P. When the feed roller  140  rotates in the F 2  direction, the pickup arm  240  rotates in an H 2  direction, and thus the pickup roller  120  is separated from the sheet P. 
       FIG. 7  illustrates a third gear train  230  in detail. Referring to  FIG. 7 , a gear  14  is coupled to the pickup shaft  200 . Gears  15 ,  16 , and  17  are connected in turn to the gear  14 . A third arm  260  is provided rotatably in a rotational axis  270  of the gear  16 . The gear  17  is provided in the third arm  270 . When the feed roller  140  rotates in the F 1  direction, the third arm  260  rotates in a J 1  direction, the gear  17  is connected to a gear portion  18  of the cam member  310 , and thus the cam member  310  rotates in a first direction K 1 . When the feed roller  140  rotates in the F 2  direction, the third arm  260  rotates in a J 2  direction, the gear  17  is separated from the gear portion  18 , and a rotational force of the drive motor  180  is not transferred to the cam member  310 . 
     As shown in  FIG. 8 , the printer according to an embodiment of the present invention is characterized, in that in the process of picking up the sheet P, a tilt angle of the resistance member  170  about the front end of the sheet P is changed from a first tilt angle A 1  for separating a standard size sheet to a second tilt angle A 2  for separating a thick sheet. In this embodiment of the present invention, by providing the resistance member  170  in a support member  330  and rotating the support member  330 , the tilt angle of the resistance member  170  is changed. The first tilt angle A 1  is a tilt angle for separating a standard size sheet having an exemplary thickness of about 100 μm or less, and the second tilt angle A 2  is a tilt angle for separating a thick sheet having an exemplary thickness of about 100 μm or more having a relatively large stiffness. It is preferable that the second tilt angle A 2  is larger than the first tilt angle A 1 . 
       FIG. 9  illustrates one example of an angle change unit for changing the tilt angle of the resistance member  170 . 
     Referring to  FIG. 9 , the cam member  310 , the sliding member  320 , and the support member  330  are illustrated. The cam member  310  is provided in the inside  192  of the bracket  190 . A cam profile  311  and the gear portion  18  are provided in the cam member  310 . The cam profile  311  is provided with a first section  312  and a second section  313  corresponding to the first tilt angle A 1  and the second tilt angle A 2  of the resistance member  170 , respectively. One end of a compression spring  340  is supported by the bracket  190 , and the other end is supported by the cam member  310 . The compression spring  340  is elastically biased to allow the cam member  310  to rotate in the second direction K 2 . A slant portion  321  is provided in the sliding member  320 . One end portion  322  of the sliding member  320  is in contact with the cam profile  311 . The sliding member  320  slides in a third direction M 1  with rotation of the cam member  310  in the first direction K 1 . A compression spring  350  is provided in the other end  323  of the sliding member  320 . The compression spring  350  elastically biases the sliding member  320  to slide in the fourth direction M 2 . A plurality of resistance members  170  may be provided in the support member  330 . An interference portion  331  interfering with the slant portion  321  is provided in the support member  330 . A plurality of slant portions  321  and a plurality of interference portions  331  may be provided with the sliding member  320  and the support member  330 , respectively. A plurality of tension springs  360  are provided on a back surface of the support member  330 . The tension springs  360  elastically biases the support member  330  to rotate to the second tilt angle A 2 . 
     A sheet feed method performed in the printer according to an embodiment of the present invention will now be described with reference to  FIGS. 3 through 9 , and  FIG. 1  showing a resistance method. 
     When a print command is issued by a host (not shown), in order to pick up the sheets P from the cassette  110 , the drive motor  180  allows the feed roller  140  to rotate in the F 1  direction. Then, as shown in  FIG. 6 , the pickup arm  240  rotates in the H 1  direction, and the pickup roller  120  comes in contact with the sheets P loaded on the cassette  110  and rotates. At this time, as shown in  FIG. 5 , the swing bracket  250  rotates in the G 1  direction, and thus the gear  5  is connected to the gear  8 , whereby the drive roller  130  rotates in a direction  21  of  FIG. 5 . Further, as shown in  FIG. 7 , the third arm  260  rotates in the J 1  direction, and thus the gear  17  is connected to the gear portion  18 . The cam member  310  rotates in the first direction K 1 . Due to the rotation of the pickup roller  120 , the sheet P 1  loaded on the top of the cassette  110  is separated from the sheets P through the processes C 1 , C 2 , and C 3  of  FIG. 1 , picked up from the cassette  110 , and drawn into the feed roller  140  by means of the drive roller  130 . 
     In this process, the tilt angle of the resistance member  170  is changed from the first tilt angle A 1  to the second tilt angle A 2 . Referring to  FIG. 9 , the end portion  322  of the sliding member  320  is in contact with the first section  312  of the cam profile  311 . When the cam member  310  rotates in the first direction K 1 , the sliding member  320  slides in the third direction M 1  as indicated by dotted lines in  FIG. 9  in a state where the second section  313  of the cam profile  311  is in contact with the end portion  322  of the sliding member  320 . The support member  330  is elastically biased to rotate to the second tilt angle A 2  by means of the tension spring  360 . When the sliding member  320  slides in the third direction M 1 , the support member  330  naturally rotates to the second tilt angle A 2  by means of the elastic force of the tension spring  360 . In this way, the tilt angle of the resistance member  170  is changed from the first tilt angle A 1  to the second tilt angle A 2 . It is preferable that the resistance member  170  is kept at the first tilt angle A 1  for a predetermined time and is changed to the second tilt angle A 2 . 
       FIGS. 10 and 11  are graphs illustrating drive currents of the drive motor  180  that drives the pickup roller  120  when separating the standard size sheet and the thick sheet in a state where the resistance member  170  is fixed to the first tilt angle A 1 . 
     Referring to  FIG. 10 , when separating the standard size sheet, the amount of drive current is increased instantaneously as indicated by a reference numeral D 1 . At this time, the separation processes C 1  through C 3  of  FIG. 1  are performed. Referring to  FIG. 11 , when separating the thick sheet, as indicated by a reference numeral D 2 , the drive current is increased for a longer time period than that for separating the standard size sheet, is maintained for a time, and is decreased again. The drive current is decreased when separation of the sheet P is completed. 
     A time required for separating the sheet P is about 0.01 second in the case of the standard size sheet, and is about 0.13 second in a case of the thick sheet, although it was not illustrated in detail in  FIGS. 10 and 11 . In other words, a time interval for keeping the tilt angle of the resistance member  170  to the first tilt angle A 1  for separating the standard size sheet is about 0.1-0.2 seconds. This time interval can be determined by experimentation by considering various variables such as a friction coefficient of the pickup roller  120 , a contact pressure between the pickup roller  120  and the sheet P, and so on. In consideration of the time interval, a length of the first section  312  of the cam profile  311  is determined. 
     The pickup process is completed by aligning the front end of the sheet P to the feed roller  140  after the front end of the sheet P is detected by a detection sensor ( 91  of  FIG. 3 ). Then, the drive motor  180  allows the feed roller  140  to rotate in the F 2  direction. Then, the sheet P passes between the feed roller  140  and the driven roller  141 , the print head  150  ejects ink droplets to the sheet P, thereby forming images on the sheet P. At this time, as shown in  FIG. 5 , the swing bracket  250  rotates in the G 2  direction, the gear  5  is separated from the gear  8 , and the gear  7  is connected to the gear  8 . Therefore, the drive roller  130  rotates continuously in the direction  21  of  FIG. 5 . Further, referring to  FIG. 6 , the pickup arm  240  rotates in the H 2  direction, and the pickup roller  120  is separated from the sheet P. In this way, by separating the pickup roller  120  from the sheet P after pickup of the sheet P is completed, a load applied to the drive motor  180  can be reduced. Furthermore, referring to  FIGS. 7 and 9 , since the third arm  260  rotates in the J 2  direction, the gear  17  is separated from the gear portion  18  of the cam member  310 , and the cam member  310  rotates in the second directions K 2  by means of the elastic force of the compression spring  340 . The compression spring  350  pushes the sliding member  320  in the fourth direction M 2 . The slant portion  321  pushes the interference portion  331 , thereby allowing the support member  330  to rotate to the first tilt angle A 1 . Therefore, the tilt angle of the resistance member  170  about the front end of the sheet P returns to the first tilt angle A 1  from the second tilt angle A 2 . 
     Conventionally, as mentioned above, since the tilt angle of the resistance member  170  has been fixed to an angle suitable for separating the standard size sheet, the thick sheet having a large stiffness has not been separated well, and thus jams may occur, or since the resistance is too large, pickup errors that the sheets P has not been fed may occur. However, in the printer and the sheet feed method according to an embodiment of the present invention, at the initial stage of the process of picking up the sheet P, the tilt angle of the resistance member  170  about the front end of the sheet P is kept at the first tilt angle A 1  suitable for separating the standard size sheet, and by changing the tilt angle to the second tilt angle A 2  suitable for separating the thick sheet after a predetermined time, both of the standard size sheet and the thick sheet P can be stably separated and fed. 
       FIG. 12  is a perspective view illustrating another example of the angle change unit.  FIG. 13  is a schematic side view of the angle change unit of  FIG. 12 .  FIG. 14  is a diagram illustrating an operation of the angle change unit shown in  FIGS. 12 and 13 . 
     In  FIGS. 12 and 13 , the support member  370  and the cam member  380  are illustrated. The resistance member  170  is provided in the support member  370 . A projected portion  371  is provided at one side of the support member  370 . A reference numeral  390  indicates a tension spring for elastically biasing the support member  370  toward the first tilt angle A 1 . The gear portion  18 , which is connected to the gear  17  when the feed roller  140  rotates in the F 1  direction, is provided in the cam member  380 . The cam member  380  rotates in the first direction K 1  when the feed roller  140  rotates in the F 1  direction. A reference numeral  340  indicates a compression spring that elastically biases the cam member  380  to rotate in the second directions K 2 . A cam profile  381  recessed in an arc shape is provided in the cam member  380 . The projected portion  371  is inserted into the cam profile  381 . 
     At the initial stage, as shown in  FIG. 13 , the support member  370  has the first tilt angle A 1 . For this purpose, although not shown, the support member  370  is supported by the compression spring  390  to be pushed no more from the position where the support member  370  has the first tilt angle A 1 . Referring to  FIG. 13 , the projected portion  371  is in contact with the first end portion  382  of the cam profile  381 . When the feed roller  140  rotates in the F 1  direction, the cam member  380  rotates in the first direction K 1 . At this time, until the first end portion  383  of the cam profile  381  comes in contact with the projected portion  371 , the support member  370  keeps the first tilt angle A 1 . If the first tilt angle A 1  is maintained, that is, a distance from the first end portion  382  to the second end portion  383  can be determined as shown in  FIGS. 10 and 11 . When the second end portion  383  of the cam profile  381  comes in contact with the projected portion  371 , the support member  370  rotates to the second tilt angle A 2 , as shown in  FIG. 14 , with rotation of the cam member  380  in the first direction K 1 . When the pickup of a sheet is completed and the feed roller  140  rotates in the F 2  direction, the gear  17  is separated from the gear portion  18 , and the cam member  380  rotates in the second directions K 2  by means of the compression spring  340 . The support member  370  rotates to the first tilt angle A 1  by means of the compression spring  390 . 
     The printer and the sheet feed method according to embodiments of the present invention can be applied regardless of the type of the printer used as long as the printer separates sheets using a resistance method. 
     As described above, in the printer and the sheet feed method according to embodiments of the present invention, it is possible to stably separate and feed both standard size sheets and thick sheets having a relatively large stiffness, so that jams or a pickup errors can be eliminated or reduced. 
     While the present invention has been particularly shown and described with reference to the exemplary embodiments thereof, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.