Paper-feeding apparatus and image-forming apparatus

Abstract

A paper-feeding apparatus includes a double paper feed prevention mechanism including a conveyance roller rotating forward in a paper feeding direction, and a handling roller rotating rearward in an opposite direction to the paper feeding direction through a torque limiter and being driven by the conveyance roller when the number of fed sheets of paper is one, a double paper feed detection sensor disposed at a downstream side of the double paper feed prevention mechanism to detect a physical quantity corresponding to the number of fed sheets of paper, and a control unit that determines a frequency of double paper feed events at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, and controls a speed of rearward rotation of the handling roller depending on the frequency of the double paper feed events.

1 . A paper-feeding apparatus comprising:
 a double paper feed prevention mechanism comprising a conveyance roller rotating forward in a paper feeding direction, and a handling roller rotating rearward in an opposite direction to the paper feeding direction through a torque limiter and being driven by the conveyance roller when the number of fed sheets of paper is one;   a double paper feed detection sensor disposed at a downstream side of the double paper feed prevention mechanism to detect a physical quantity corresponding to the number of fed sheets of paper; and   a control unit that determines a frequency of double paper feed events at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, and controls a speed of rearward rotation of the handling roller depending on the frequency of the double paper feed events.   
     
     
         2 . The paper-feeding apparatus of  claim 1 , wherein, upon detecting that a fed sheet of paper is in a double paper feed state at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, the control unit determines the number of paper feed events from a previous double paper feed detection to a current double paper feed detection as the frequency of double paper feed events. 
     
     
         3 . The paper-feeding apparatus of  claim 1 , wherein, upon detecting that a fed sheet of paper is in a double paper feed state at a downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, the control unit determines the total number of paper feed events from several double paper feed detections before to a current double paper feed detection as the frequency of double paper feed events. 
     
     
         4 . The paper-feeding apparatus of  claim 2 , wherein, when the number or the total number of paper feed events is smaller than a first preset value, the control unit determines that the frequency of the double paper feed events is high, and decreases the speed of rearward rotation of the handling roller. 
     
     
         5 . The paper-feeding apparatus of  claim 3 , wherein, when the number or the total number of paper feed events is smaller than a first preset value, the control unit determines that the frequency of the double paper feed events is high, and decreases the speed of rearward rotation of the handling roller. 
     
     
         6 . The paper-feeding apparatus of  claim 4 , wherein, when the number or the total number of paper feed events is equal to or larger than the first preset value and is larger than a second preset value, the control unit determines that the frequency of the double paper feed events is low, and increases the speed of rearward rotation of the handling roller. 
     
     
         7 . The paper-feeding apparatus of  claim 5 , wherein, when the number or the total number of paper feed events is equal to or larger than the first preset value and is larger than a second preset value, the control unit determines that the frequency of the double paper feed events is low, and increases the speed of rearward rotation of the handling roller. 
     
     
         8 . The paper-feeding apparatus of  claim 2 , wherein, upon detecting that the paper is in a double paper feed state, the control unit counts the number of double paper feed events and stores data indicating a corresponding relationship between the number of paper feed events and the number of double paper feed events in an embedded RAM. 
     
     
         9 . The paper-feeding apparatus of  claim 3 , wherein, upon detecting that the paper is in a double paper feed state, the control unit counts the number of double paper feed events and stores data indicating a corresponding relationship between the number of paper feed events and the number of double paper feed events in an embedded RAM. 
     
     
         10 . The paper-feeding apparatus of  claim 4 , wherein, whenever it is determined that the frequency of the double paper feed events is high, the control unit decreases the speed of rearward rotation of the handling roller step-by-step. 
     
     
         11 . The paper-feeding apparatus of  claim 5 , wherein, whenever it is determined that the frequency of the double paper feed events is high, the control unit decreases the speed of rearward rotation of the handling roller step-by-step. 
     
     
         12 . The paper-feeding apparatus of  claim 6 , wherein, whenever it is determined that the frequency of the double paper feed events is low, the control unit increases the speed of rearward rotation of the handling roller step-by-step. 
     
     
         13 . The paper-feeding apparatus of  claim 7 , wherein, whenever it is determined that the frequency of the double paper feed events is low, the control unit increases the speed of rearward rotation of the handling roller step-by-step. 
     
     
         14 . An image-forming apparatus comprising:
 the paper-feeding apparatus of  claim 1 ;   a toner image transfer unit that transfers a toner image on paper fed from the paper-feeding apparatus;   a fixing unit that fixes the toner image transferred onto the paper; and   a paper discharge unit that discharges the paper having the toner image fixed thereon to an outside.