Sheet feeding apparatus and image forming apparatus having the same

Abstract

A sheet feeding apparatus for feeding sheets supported by sheet stacking means capable of ascending and descending by sheet feeding means is provided. The sheet feeding apparatus includes sheet position detection means for detecting that an upper surface of a sheet stack supported by said sheet stacking means reaches a position whereat it can be fed by said sheet feeding means, blowing means for blowing air on an end portion of sheets stacked on said sheet stacking means, and control means for controlling said blowing means, wherein at least, either when it has been detected by said sheet position detection means that the sheets reach a position whereat they can be fed, or before a sheet feeding operation by said sheet feeding means is started, said control means performs a blowing operation by said blowing means during predetermined time.

1 . A sheet feeding apparatus for feeding sheets supported by liftable sheet stacking means, comprising: 
 sheet feeding means for feeding a sheet supported on said sheet stacking means;    sheet position detection means for detecting that an upper surface of a sheet stack supported by said sheet stacking means reaches a feeding position whereat it can be fed by said sheet feeding means;    blowing means for blowing air on an end portion of sheets stacked on said sheet stacking means; and    control means for controlling said blowing means, wherein    at least, either when it has been detected by said sheet position detection means that the upper surface of the sheet stack reach the feeding position, or before a sheet feeding operation by said sheet feeding means is started, said control means performs a blowing operation by said blowing means during a predetermined time.    
   
   
       2 . The sheet feeding apparatus according to  claim 1 , wherein in a case where blowing is performed by said blowing means when it has been detected by said sheet position detection means that the upper surface of the sheet stack reach the feeding position, the blowing operation is performed during first predetermined time, and in a case where blowing is performed by said blowing means before said sheet feeding operation is started, said blowing operation is performed during second predetermined time.  
   
   
       3 . The sheet feeding apparatus according to  claim 2 , comprising: 
 temperature and humidity detection means for detecting temperature and humidity in the neighborhood of said sheet stacking means; and    a control table of blowing time in which data of said blowing time corresponding to the temperature and humidity has been stored, wherein    said control means calls out said first predetermined time or second predetermined time from said control table of blowing time on the basis of temperature and humidity information from said temperature and humidity detection means to operate said blowing means on the basis of these predetermined time.    
   
   
       4 . The sheet feeding apparatus according to  claim 3 , comprising: 
 heating means for heating air before blown from said blowing means; and    a control table of heating temperature in which temperature of said air to be blown corresponding to temperature and humidity has been stored, wherein    said control means calls out temperature of air to be blown from said control table of heating temperature on the basis of temperature and humidity information from said temperature and humidity detection means to control a heating operation of said heating means on the basis thereof.    
   
   
       5 . A sheet feeding apparatus for feeding sheets, comprising: 
 sheet stacking means for supporting sheets;    sheet feeding means for feeding sheets stacked on said sheet stacking means;    blowing means for blowing air on an end portion of a sheet stack supported on said sheet stacking means; and    control means for controlling said blowing means, wherein    said control means causes said blowing means to perform a blowing operation before a sheet feeding operation is started by said sheet feeding means.    
   
   
       6 . The sheet feeding apparatus according to  claim 5 , provided with said sheet stacking means so as to be liftable, further comprising sheet position detection means for detecting that an upper surface of a sheet stack supported by said sheet stacking means reaches a feeding position whereat it can be fed by said sheet feeding means, wherein 
 when it has been detected by said sheet position detection means that the sheet stack reaches the feeding position, the blowing operation is caused to be performed by said blowing means during first predetermined time.    
   
   
       7 . The sheet feeding apparatus according to  claim 6 , further comprising: 
 temperature and humidity detection means for detecting temperature and humidity in the neighborhood of said sheet stacking means; and    a control table of blowing time in which data of said first predetermined blowing time corresponding to the temperature and humidity has been stored, wherein    said control means calls out data of said first predetermined blowing time from said control table of blowing time on the basis of temperature and humidity information from said temperature and humidity detection means to control said blowing means on the basis of this data.    
   
   
       8 . The sheet feeding apparatus according to  claim 5 , further comprising: 
 job starting signal generating means for generating a job starting signal for starting a job, wherein    when a job starting signal has been generated by said job starting signal generating means, the blowing operation is caused to be performed by said blowing means during second predetermined blowing time.    
   
   
       9 . The sheet feeding apparatus according to  claim 8 , further comprising: 
 temperature and humidity detection means for detecting temperature and humidity in the neighborhood of said sheet stacking means; and    a control table of blowing time in which data of second predetermined blowing time corresponding to the temperature and humidity has been stored, wherein    said control means calls out data of second predetermined blowing time from said control table of blowing time on the basis of temperature and humidity information from said temperature and humidity detection means to control said blowing means on the basis of this data.    
   
   
       10 . The sheet feeding apparatus according to  claim 7 , further comprising: 
 heating means for heating air before blown from said blowing means; and    a control table of heating temperature in which data of temperature of said air to be blown corresponding to temperature and humidity has been stored, wherein    said control means calls out data of heating temperature from said control table of heating temperature on the basis of temperature and humidity information from said temperature and humidity detection means to control a heating operation of said heating means on the basis of this data.    
   
   
       11 . The sheet feeding apparatus according to  claim 9 , further comprising: 
 heating means for heating air before blown from said blowing means; and    a control table of heating temperature in which data of temperature of said air to be blown corresponding to temperature and humidity has been stored, wherein    said control means calls out data of heating temperature from said control table of heating temperature on the basis of temperature and humidity information from said temperature and humidity detection means to control a heating operation of said heating means on the basis of this data.    
   
   
       12 . A sheet feeding apparatus for feeding sheets, comprising: 
 a lifter base on which a sheet stack has been stacked; a pickup roller for sending out sheets from said lifter base;    an air duct port arranged to oppose to an end portion of the sheet stack on said lifter base;    a fan for blowing air through said air duct port;    a sheet surface position detection sensor for detecting, by raising said lifter base, that an upper surface of the sheet stack reaches a feeding position whereat it can be fed; and    a controller for controlling an operation of said fan, wherein    at least either when it has been detected by said sheet surface position detection sensor that the sheet stack reaches the feeding position whereat, or before a sheet feeding operation by said pickup roller is started, said fan is caused to perform a blowing operation.    
   
   
       13 . The sheet feeding apparatus according to  claim 12 , comprising: 
 a humidity sensor for detecting humidity in the neighborhood of said lifter base; and    a control table of time in which data of said stand-by time correspondingly to humidity has been stored, wherein    said controller calls out data of said first predetermined blowing time from said control table of blowing time on the basis of temperature and humidity information from said temperature and humidity detection means to control said blowing means on the basis of this data.    
   
   
       14 . The sheet feeding apparatus according to  claim 12 , comprising: 
 a humidity sensor for detecting humidity in the neighborhood of said lifter base; and    a control table of time in which data of said blowing time correspondingly to humidity has been stored, wherein    said controller calls out data of blowing time from said control table of time on the basis of humidity information from said humidity sensor to operate said fan on the basis of this data of blowing time.    
   
   
       15 . An image forming apparatus comprising: an image forming portion for forming an image on a sheet; and a sheet feeding apparatus for feeding the sheet to said image forming portion according to any one of said  claims 1  to  14 .