Abstract:
A paper-feeding apparatus is used for feeding print medium from a paper cassette. The paper cassette holds a stack of print paper therein. The feeding roller is disposed close to a forward end of the paper cassette. The feeding roller engages a top page of the stack of print paper to feed the top page from the paper cassette to a printing area. The paper separator engages the feeding roller to cooperate with the feeding roller to separate the top page from the stack of print paper. The paper-positioning member is, for example, an arm. When the feeding roller is not feeding the print medium, the arm pushes back the forward ends of pages of print medium toward the rear end of the paper cassette, thereby aligning the forward ends of the pages of the stack of print paper. The paper feeding apparatus may further have an urging member, e.g., a spring, which urges the paper separator against the feeding roller, and an urging-force-changing member, e.g., a cam that changes an urging force of the urging member. When the cam rotates to a high-pressure position, the cam pushes the spring to cause the spring to urge the medium separator against the feeding roller with a larger force. When the cam rotates to a low-pressure position, the cam pushes the spring to cause the spring to urge the medium separator against the feeding roller with a smaller force.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a paper-feeding apparatus and a method of feeding paper. 
     2. Description of the Related Art 
     Conventional paper-feeding apparatuses are of a construction where a platform or sheet guide frame is pushed upward by the urging force of a pressure spring so that the print medium placed on the platform is pressed against a feeding roller. A controller provides an instruction to a paper-feeding motor and the paper-feeding motor drives the feeding roller into rotation to advance the print medium from the platform. 
     When feeding the print medium from the platform, a plurality of pages of print medium may be advanced simultaneously by chance from the platform. In order to prevent such a simultaneous advancement of pages, a separator wall is provided which is formed of a film and located at the forward end of the platform. The separator wall obstructs the plurality of pages and allows only the top page to be fed. There is also provided a brake shoe formed of a foamed material that opposes the feeding roller, and the forward end of the print medium is allowed to abut the brake shoe. The top page of the print medium is advanced by a frictional force between the feeding roller and the print medium and the following pages are trapped by the rough surface of the brake shoe. 
     One conventional paper-feeding apparatus is provided with a cam mechanism provided at each longitudinal end of a shaft of the feeding roller. The platform is moved upward and downward as the feeding roller rotates. When not feeding the print medium, the platform is moved away from the feeding roller so that a user can easily place a stack of print medium into the platform. The platform does not exert any load on the print medium when the print medium is being advanced by a main feeding roller once the print medium has been fed by the feeding roller. 
     Another conventional paper feeding apparatus is provided with a feeding roller having a D-shaped cross-section. In other words, the feeding roller is generally a deformed cylinder that has been partially cut away in a plane parallel to a longitudinal axis of the cylinder. When not feeding the print medium, the flat surface of the feeding roller opposes the brake shoe, creating a gap between the flat surface and the brake shoe. Thus, the feeding roller is not in contact with the print medium and does not interfere with the print medium being advanced from the platform. 
     The feeding roller has idle rollers that have a smaller diameter smaller than the feeding roller and freely rotate on the shaft of the feeding roller. When the flat surface of the feeding roller opposes the brake shoe, the idle rollers are brought into contact with the brake shoe, thereby preventing the print medium placed on the platform from being advanced inadvertently. 
     However, the aforementioned conventional paper-feeding apparatuses cannot ensure that print medium of various kinds such as thin paper, thick paper, envelopes and so on is advanced one page at a time. In general, a plurality of pages tend to be advanced simultaneously when thin print medium is fed while paper feeding often fails when thick print medium is fed. 
     Pressing the brake shoe against the feeding roller with a larger force in an attempt to prevent multi-page feeding will cause failure of a paper feeding operation if the print medium is thick. Pressing the brake shoe against the feeding roller with a smaller force in an attempt to prevent failure of a paper feeding operation will cause multi-page feeding. 
     SUMMARY OF THE INVENTION 
     The present invention was made in view of the aforementioned drawbacks of the prior art paper-feeding apparatus. 
     An object of the invention is to provide a paper feeding apparatus for a printer and a method of feeding print medium paper feeding. 
     A paper-feeding apparatus includes a medium-container, a medium-feeding member, a medium separator, and a medium-positioning member. 
     The medium-container is, for example, a paper cassette that accommodates a stack of print medium therein. The medium-feeding member is, for example in the form of a feeding roller disposed close to a forward end of the paper cassette. The feeding roller engages a top page of the stack of print medium to feed the top page from the stack of print medium to a printing area. The medium-separator is disposed to oppose the feeding roller to engage the feeding roller, thereby cooperating with the feeding roller to separate the top page from the stack of print medium. The medium-positioning member is in the shape of, for example, an arm. When the feeding roller is not feeding the print medium, the arm pushes back the forward ends of pages of print medium toward the rear end of the paper cassette, thereby aligning the forward ends of the pages of the stack of print medium. 
     The paper feeding apparatus may further have an urging member in the form of, for example, a spring that urges the medium-separator against the medium-feeding member, and an urging-force-changing member that changes an urging force of the urging member. The urging-force-changing member is, for example, a cam mounted on a shaft rotated by operating a lever radially extending from the shaft. When the lever is moved to a high-pressure position, the cam engages a holder on which the spring is mounted and pushes, causing the spring to further urge the medium separator against the feeding roller. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a general construction of a paper-feeding apparatus according to a first embodiment; 
     FIG. 2A is a perspective view of a paper feeding apparatus according to the first embodiment; 
     FIG. 2B is a partial cross-sectional view taken along lines  2 B— 2 B of FIG. 2A; 
     FIG. 3 is a side view of the paper-feeding apparatus; 
     FIG. 4 is an expanded view of a relevant portion of the first embodiment; 
     FIG. 5 is a perspective view of the paper positioner according to the first embodiment; 
     FIGS. 6 and 7 illustrate the operation of the paper-feeding apparatus according to the first embodiment; 
     FIG. 8 illustrates an arm according to the first embodiment; 
     FIG. 9 illustrates a gear cam; and 
     FIG. 10 illustrates a gear train; 
     FIG. 11 is a timing chart illustrating the operation of the paper-feeding apparatus of the first embodiment; 
     FIGS. 12 and 13 illustrate a brake shoe spring according to a second embodiment; and 
     FIG. 14 illustrates a gear train according to the second embodiment. 
    
    
     DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     FIRST EMBODIMENT 
     Construction 
     FIG. 1 illustrates a general construction of a paper-feeding apparatus according to a first embodiment. 
     Referring to FIG. 1, a carriage  13  runs on two parallel guide shafts  14   a  and  14   b . The carriage  13  supports a print head  12  thereon. A paper feeding apparatus  15  includes a base frame  16 , platform  17 , pressure spring  18 , feeding roller  20 , and brake shoe  22 . A stack of print medium  11  such as thin paper, thick paper, and envelopes is accommodated in the base frame  16  inclined at an angle with the horizontal. The base frame  16  supports the platform  17  thereon. The platform  17  supports the stack of print medium  11  thereon and is pivotal about a pin  17   b  relative to the base frame  16 . The platform  17  is urged upward by the pressure spring  18  disposed on the bottom of the base frame  16 , so that the top page of the print medium  11  is pressed against the feeding roller  20 . 
     The feeding roller  20  rotates on a shaft  19  disposed near the forward end of the base frame  16 . The feeding roller  20  is generally a deformed cylinder that has been partially cut away in a plane parallel to the longitudinal axis of the cylinder. 
     FIG. 2A is a perspective view of a paper feeding apparatus according to the first embodiment. 
     FIG. 2B is a partial cross-sectional view taken along lines  2 B— 2 B of FIG.  2 A. 
     A motor  30  (FIG. 10) drives the feeding roller  20  in rotation in a direction shown by arrow G, thereby advancing the print medium  11 . Idle rollers  21  are also mounted on the shaft  19  such that the feeding roller  20  is between the idle rollers  21 . The idle rollers  21  have a smaller diameter than the feeding roller  20  and freely rotate. 
     A cam  19   a  is eccentrically formed in one-piece construction with the shaft  19  and engages a slide portion  17   a  of the platform  17 . When the shaft  19  rotates, the cam  19   a  cams the platform  17  so that the platform  17  pivots about a pin  17   b  upward and downward. 
     The brake shoe  22  is made of rubber or a foamed rubber and is disposed to oppose the feeding roller  20  and idle rollers  21 . The brake shoe  22  serves as a separator that cooperates with the feeding roller  20  to separate the top page from the following pages of the print medium  11 . The foamed rubber is advantageous in that even if its surface wears out, the surfaces of new foams are exposed, thereby maintaining the same frictional force. The rubber brake shoe  22  may have a roughened surface for increased friction. 
     FIG. 3 is a cross-sectional view of the paper-feeding apparatus  15 . 
     FIG. 4 is an enlarged view of a relevant portion of FIG.  3 . 
     The base frame  16  has a front wall  16   a  at its forward end. A separator wall  23  is provided beside the front wall  16   a  inside the base frame  16  and is formed of a film. The front wall  16   a  is disposed to oppose the feeding roller  20  and serves as a separator. A holder  25  is pivotally mounted to the upper end portion of the front wall  16   a  by means of a pin  25   a . The holder  25  is positioned outside of the base frame  16  and under the feeding roller  20 . Disposed under the holder  25  is a spring  24  that urges the holder  25  so that the brake shoe  22  is pressed against the round surface of the feeding roller  20  when the feeding roller  20  rotates. 
     When the feeding roller  20  rotates in the direction shown by arrow G, the print medium  11  accommodated in the platform  17  is advanced to main feed rollers  37 , one top page at a time, with the aid of the separator wall  23  and the brake shoe  22 . The print medium  11  is then transported by the main feed rollers  37  to a print area P 1  of the printer where the printhead  12  opposes the print medium  11  and prints information on the print medium  11 . 
     FIG. 5 is a perspective view of a paper positioner and surroundings according to the first embodiment. 
     FIGS. 6 and 7 are side views of the paper feeding apparatus of the first embodiment. 
     Referring to the figures, arms  28  are pivotally disposed with the holder  25  positioned therebetween. The arm  28  is pivotal about a shaft  29  supported on the base frame  16 . The arm  28  has a hub  28   a  on which a cam  27  is mounted. The cam  27  opposes an arm  26  of the holder  25 . When the feeding roller  20  is not operating to feed the top page of the print medium  11  from the platform  17 , the arm  28  pushes back the forward ends of the upper pages of print medium  11  toward a rearward end of the base frame  16  as shown in FIG. 7, thereby aligning the forward ends of the pages evenly. When the feeding roller  20  is operating to feed the print medium  11 , the arm  28  pivots away from the forward ends of the print medium  11  as shown in FIG.  6 . 
     FIG. 8 illustrates the arm according to the first embodiment. 
     FIG. 9 illustrates a gear cam  32 . 
     The shaft  29  has a radially extending lever  34  mounted at its one end. The lever  34  has a roller  34   a  attached to its free end portion. The roller  34   a  is urged by a tension spring  35  against the cam  33 . The cam  33  has a constant-radius surface  33   a  that is the same distance or radius R from the shaft  29  and a varying-radius surface  33   b  that is at distances, shorter than R, from the shaft  29 . The lever  34  pivots in directions shown by arrows B and C as the gear cam  32  is rotated in a direction shown by arrow A. 
     FIG. 10 illustrates a gear train  32 . 
     The feeding roller  20  is driven by the motor  30  in rotation. There is provided an idle gear train  31  between the motor  30  and the gear cam  32 . The gear cam  32  includes a cam  33  and gear  82  that rotates together with the cam  33 . 
     The gear  82  is cut away over a predetermined length of arc to form a cutout  82   a . The cutout  82   a  is at the same angular position as the varying-radius surface  33   b  with respect to the shaft back  29  and is radially outward than the varying-radius surface  33   b  (FIG.  9 ). 
     As shown in FIG. 10, a final gear  31   a  of the idle gear train  31  is always in mesh with the gear cam  32  but the feed roller gear  36  does not mesh with the gear  82  at the cutout  82   a.    
     Operation 
     The operation of the paper feeding apparatus  15  of the aforementioned construction will be described with reference to FIGS. 5-8 and FIG.  11 . 
     FIG. 11 is a timing chart illustrating the operation of the paper-feeding apparatus. 
     Initially, the feeding roller  20  is at its standby position (FIG. 6) from where one complete rotation of the feeding roller  20  will start. With the feeding roller  20  is at the standby position, the arm  28  is at the position shown in FIG.  6  and the roller  34   a  is at the arc  33   a  while the feed roller gear  36  opposes the cutout  82   a  but does not mesh with the gear  82 . 
     At the standby position, the user places a stack of print medium  11  in the paper guide frame  17 . When a controller, not shown, provides a paper feed instruction to the motor  30 , the motor  30  rotates. The rotation of the motor  30  is transmitted via the idle gear train  31  to the gear cam  32  and causes the gear cam  32  to rotate. As the gear cam  32  rotates, the roller  34   a  moves along the shape of the cam  33 , moving into engagement with the varying-radius surface  33   b  at timing t1 so that the lever  34  and shaft  29  are rotated in the direction shown by arrow C. 
     Thus, as shown in FIG. 7, the arm  28  on the shaft  29  is rotated in the direction shown by arrow C, thereby aligning the forward ends of pages of the print medium  11  evenly. The cam  27  is also rotated in the direction shown by arrow C (FIG.  8 ), pushing the arm  26  so that the holder  25  is pivoted about the pin  25   a  away from the feeding roller  20  and idle roller  21  in the direction shown by arrow F. 
     At timing t2, the roller  34   a  is moved from the varying-radius surface  33   b  to the constant-radius surface  33   a  so that the lever  34  and shaft  29  are rotated in the direction shown by arrow B (Fig.  8 ). Accordingly, the arm  28  is rotated in the direction shown by arrow B (FIG.  8 ), leaving the forward ends of the pages of the print medium  11 . The cam  27  is rotated away from the arm  26  with the result that the holder  25  is pivoted in such a direction as to approach the feeding roller  20  and idle roller  21 , i.e., a direction opposite to the F direction (FIG.  7 ). 
     During the period from the beginning (t1) of the rotation of the gear cam  32  to timing t2, the feed roller gear  36  does not mesh with the gear  82 . Therefore, the rotation of the motor  30  is not transmitted to the feed roller gear  36  so that the feed roller  20  is not rotated. 
     As the gear cam  32  further rotates, the feed roller gear  36  is brought into meshing engagement with the gear  82  so that the shaft  19  and feeding roller  20  are driven into rotation. As the shaft  19  rotates, the platform  17 , which has been depressed at a portion  17   a  by the cam  19   a  (FIG.  2 ), is moved upward by the pressure spring  18  at timing t4 so that the top page of the print medium  11  abuts the feeding roller  20 . 
     Subsequently, the round surface  20   b  of the feeding roller  20  abuts the brake shoe  22  at timing t5. Since the idle rollers  21  have a smaller diameter than the feeding roller  20 , the idle rollers  21  disengage from the brake shoe  22  when the round surface  20   b  abuts the brake shoe  22 . The mechanism may be modified so that the idle rollers  21  are brought into contact with the brake shoe  22  due only to its own weight. 
     When the platform  17  is moved upward at t4, the upper pages of the print medium  11  abutting the feeding roller  20  is advanced by the rotation of the feeding roller  20  to the brake shoe side. The separator wall  23  separates upper several pages including the top page from the stack of the print medium  11 . The separated first several pages abut the brake shoe  22  which in turn separates the first page from the several pages so that only the top page is fed to the print area P 1  (FIG.  1 ). This mechanism prevents multi-page feeding. 
     At timing t6, the forward end of the top page arrives at the main feed roller  37 , and the main feed roller  37  begins to transport the print medium  11 . A flat surface  20   a  of the feeding roller  20  now opposes the brake shoe  22  and the idle rollers  21  are now in contact with the brake shoe  22 . Since the flat surface  20   a  opposes the brake shoe  22  when not feeding the print medium  11 , only the idle rollers  21  exert a small load on the print medium  11  while the print medium  11  is passing between the feeding roller  20  and the brake shoe  22 . 
     As the shaft  19  further rotates, the cam  19   a  abuts the platform  17  at timing t7, causing the platform  17  to move downward against the urging force of the pressure spring  18 . Thus, the platform  17  is set free from its paper-supplying task. As a result, only idle rollers  21  exert a small load on the print medium  11  while the print medium  11  is being advanced by the main feed roller  37 . No load is exerted on the print medium  11  by the platform  17 . 
     At timing t8, the platform  17  completes its downward movement and the feed roller gear  36  opposes the cutout  82   a  again. The feeding roller  20  is moved out of meshing engagement with the gear  82  and comes to a stop. 
     Even if some pages including the second page are advanced together over a short distance beyond the separator wall  23  during the last paper-feeding operation, the brake shoe  22  is moved out of engagement with the feeding roller  20  and idle rollers  21 , and the arm  28  aligns the forward ends of the pages of print medium  11  evenly. This operation prevents multi-page feeding during the feeding of the second page. 
     Thus, less urging force is needed in pressing the brake shoe  22  against the idle rollers  21  and decreases chance of malfunction of the paper feeding operation. 
     The motor  30  is only necessary to be driven in one direction, when bringing the brake shoe  22  into and out of contact engagement with the feeding roller  20  and idle rollers  21 , moving the platform  17  upward and downward, advancing the print medium  11  from the paper guide frame  17 , and separating the top page from the stack of print medium  11 . Thus, the construction and control of the paper feeding apparatus of the printer can be simplified. 
     SECOND EMBODIMENT 
     Construction 
     Elements of the same construction as those of the first embodiment have been given the same reference numerals and description thereof is omitted. 
     FIG. 12 is a side view of the paper feeding apparatus when it is at a “low pressure position.” 
     FIG. 13 is a side view of the paper feeding apparatus when it is at a “high pressure position.” 
     Referring to FIGS. 12 and 13, the compression  24  urges the brake shoe  22  against the feeding roller  20 . The spring  24  is substantially vertically mounted between the holders  40  and  42 . The holder  40  is pivotally mounted to the base frame  16  by means of a pin  40   a  in the similar manner that the holder  25  is mounted to the base frame  16  as shown in FIG.  1 . The holder  42  is also pivotally mounted to the base frame  16  by means of a pin  42   a.    
     A cam shaft  43  is rotatably supported by the base frame  16  and has a cam  43   a  fixedly mounted to the cam shaft  43 . The cam  43   a  is located under the holder  42 . When the cam shaft  43  is rotated in a direction shown by arrow D, the cam  43   a  is brought into engagement with a bottom surface of the holder  42  as shown in FIG.  13 . 
     FIG. 14 illustrates a gear train according to the second embodiment. 
     As shown in FIG. 14, the cam shaft  43  has a radially extending handle lever  44  secured at one end thereof. 
     When the user operates the handle lever  44  either in a direction shown by arrow D or in a direction shown by arrow E, the cam shaft  43  rotates to cause the cam  43   a  to engage or disengage from the bottom surface of the holder  42 , so that the holder  42  pivots about the pin  42   a  relative to the base frame  16  between the “low pressure position” (FIG. 12) and the “high pressure position (FIG.  13 ).” 
     Operation 
     The operation of the aforementioned structure will now be described. 
     The user places a stack of print medium  11  on the platform  17  and operates the handle lever  44  for adjustment of the urging force of the spring  24 . 
     If the print medium  11  is relatively thin, the handle lever  44  is shifted in the direction shown by arrow D to the high pressure position where the brake shoe  22  is pressed against the feeding roller  20  to develop more force that separates the top page from the rest. The larger force prevents multi-page feeding and does not cause malfunction of paper feeding operation of a thick print medium. 
     If the print medium  11  is relatively thick, the handle lever  44  is shifted in the direction shown by arrow E to the low pressure position as shown in FIG. 12 where the brake shoe  22  is not pressed strongly against the feeding roller  20  to develop less force that separates the top page of print medium  11  from the rest. The smaller force between the brake shoe  22  and the feeding roller  20  prevents malfunction of the paper feeding operation and does not cause multi-page feeding of a thin print medium. 
     When the motor  30  is driven in accordance with an instruction from the controller, not shown, the idle gear train  31  transmits the rotation of the motor  30  to the gear  36  so that the feeding roller  20  is driven into rotation. The operation of the second embodiment at timing t3 onward is the same as that of the first embodiment. 
     In the second embodiment, the user operates the handle lever  44  between the high-pressure position and the low-pressure position to change the pressure that the brake shoe  22  applies to the feeding roller  20 . Alternatively, the shaft cam  43  may be rotated by a drive means such as a motor, not shown. 
     While the handle lever  44  is switched between two positions, i.e., the high pressure position and the low pressure position, the handle lever  44  may also be switched among three or more positions for smaller increments of pressure according to the kinds of print medium. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art intended to be included within the scope of the following claims.