Sheet Supplier

Abstract

A sheet supplier includes: a tray having a support surface; a roller that supplies a sheet supported on the support surface; an arm pivotable about a pivot shaft, extending in a supply direction and toward the support surface, and supports the roller at its pivotal distal end portion; a motor; and a driving-force transmitting mechanism supported by the arm and configured to transmit a driving force supplied from the motor, to the roller. The driving-force transmitting mechanism includes: a rotating member supported by the pivot shaft and configured to be rotated by the driving force supplied from the motor; and a speed changer configured to determine a rotational speed of the roller to a speed different from a rotational speed of the rotating member.

What is claimed is: 
     
         1 . A sheet supplier, comprising:
 a tray comprising a support surface configured to support a plurality of sheets stacked on the support surface;   a roller located above the support surface and configured to supply a sheet supported on the support surface, in a supply direction;   an arm pivotable about a pivot shaft, the arm extending such that a portion of the arm nearer to the support surface than to the pivot shaft is located downstream, in the supply direction, of a portion of the arm nearer to the pivot shaft than to the support surface, the arm comprising a pivotal distal end portion supporting the roller such that the roller is rotatable;   a motor; and   a driving-force transmitting mechanism supported by the arm and configured to transmit a driving force supplied from the motor, to the roller,   wherein the driving-force transmitting mechanism comprises:
 a rotating member supported by the pivot shaft and configured to be rotated by the driving force supplied from the motor; and 
 a speed changer configured to determine a rotational speed of the roller to a speed different from a rotational speed of the rotating member, the rotational speed of the roller being the number of rotations of the roller rotated by the driving force transmitted from the rotating member for a unit time, the rotational speed of the rotating member being the number of rotations of the rotating member for the unit time. 
   
     
     
         2 . The sheet supplier according to  claim 1 ,
 wherein a normal reaction force N (in newton) is a reaction force against a force by which the roller being rotated at the rotational speed determined by the speed changer and different from the rotational speed of the rotating member pushes one of the support surface and the sheet supported by the support surface, and   wherein a value obtained by dividing a roller radius of the roller by a speed reduction ratio of the roller to the rotating member is set to a value within a range in which the normal reaction force N satisfies the following Expression 1 and Expression 2: N>f/μ r  and N<f/(2μ p1 −μ p2 ), where   f is a force by which the roller supplies the sheet in the supply direction;   μ r  is a static friction coefficient of the roller against an uppermost one of the plurality of sheets supported by the support surface;   μ p1  is a dynamic friction coefficient of the uppermost one of the plurality of sheets against a second one of the plurality of sheets supported by the support surface from a top of the plurality of sheets; and   μ p2  is a dynamic friction coefficient of the second one of the plurality of sheets against a third one of the plurality of sheets supported by the support surface from the top of the plurality of sheets.   
     
     
         3 . The sheet supplier according to  claim 1 , wherein, in a case where the speed changer is in a first state in which the rotational speed of the roller is greater than the rotational speed of the rotating member, a value obtained by dividing a roller radius of the roller by a speed reduction ratio of the roller to the rotating member is set to a value greater than or equal to eleven. 
     
     
         4 . The sheet supplier according to  claim 1 , wherein, in a case where the speed changer is in a second state in which the rotational speed of the roller is less than the rotational speed of the rotating member, a value obtained by dividing a roller radius of the roller by a speed reduction ratio of the roller to the rotating member is set to a value less than or equal to four. 
     
     
         5 . The sheet supplier according to  claim 1 , wherein a state of the speed changer is switchable between a first state in which the rotational speed of the roller is greater than the rotational speed of the rotating member and a second state in which the rotational speed of the roller is less than the rotational speed of the rotating member. 
     
     
         6 . The sheet supplier according to  claim 5 , wherein the speed changer comprises:
 a slide gear slidable to a first position and a second position along an axial direction of the pivot shaft;   a first gear train engaged with the slide gear located at the first position to transmit a driving force transmitted from the slide gear, to the roller such that the rotational speed of the roller becomes greater than a rotational speed of the slide gear; and   a second gear train engaged with the slide gear located at the second position to transmit the driving force transmitted from the slide gear, to the roller such that the rotational speed of the roller becomes less than the rotational speed of the slide gear.   
     
     
         7 . The sheet supplier according to  claim 6 , wherein the slide gear is the rotating member. 
     
     
         8 . The sheet supplier according to  claim 6 ,
 wherein the slide gear is located at the first position when an angle of an imaginary plane with respect to the support surface is less than a particular angle, and the imaginary plane is directed toward the support surface and extends through the pivot shaft and a contact position at which the roller contacts one of the support surface and the sheet supported by the support surface, and   wherein the slide gear is located at the second position when the angle of the imaginary plane with respect to the support surface is greater than the particular angle.   
     
     
         9 . The sheet supplier according to  claim 8 , wherein the particular angle is half a sum of (i) a first angle that is an angle of the imaginary plane with respect to the support surface in a state in which a maximum number of sheets storable in the tray are stored in the tray and (ii) a second angle that is an angle of the imaginary plane with respect to the support surface in a state in which no sheet is supported by the tray. 
     
     
         10 . The sheet supplier according to  claim 6 , further comprising:
 a third gear engaged with the slide gear located at the first position to transmit the driving force supplied from the motor, to the slide gear; and   a fourth gear engaged with the slide gear located at the second position to transmit the driving force supplied from the motor, to the slide gear,   wherein the rotational speed of the slide gear being rotated when the slide gear is located at the first position and engaged with the third gear is less than the rotational speed of the slide gear being rotated when the slide gear is located at the second position and engaged with the fourth gear, and   wherein the rotational speed of the roller being rotated by the driving force transmitted from the slide gear by the first gear train when the slide gear is located at the first position is equal to the rotational speed of the roller being rotated by the driving force transmitted from the slide gear by the second gear train when the slide gear is located at the second position.   
     
     
         11 . The sheet supplier according to  claim 1 , further comprising:
 a plurality of trays each as the tray;   a plurality of rollers, each as the roller, provided respectively for the plurality of trays;   a plurality of arms, each as the arm, provided respectively for the plurality of trays; and   a plurality of driving-force transmitting mechanisms, each as the driving-force transmitting mechanism, provided respectively for the plurality of trays,   wherein a ratio between (i) a value obtained by dividing a roller radius of the roller by a speed reduction ratio of the roller to the rotating member and (ii) a length of the arm is identical among the plurality of arms, and   wherein the length of the arm is a length from a contact position at which the roller contacts the support surface, to the pivot shaft in a direction in which the arm extends.