Abstract:
A sheet feeding apparatus including a stacking portion for stacking a plurality of sheets thereon, a sheet feeding portion for feeding the sheets stacked on the stacking portion, a fan for sending air to the sheets to loosen the sheets stacked on the stacking portion, a heater for warming the air sent by the fan, a temperature detecting portion for detecting the temperature of the heater, and a control portion for starting the driving of the fan in conformity with the temperature detecting portion having detected a predetermined temperature after temperature control for adjusting the heater to a target temperature has been started.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a sheet feeding apparatus for sending warm air to a sheet to be fed.  
         [0003]     1. Related Background Art  
         [0004]     There has been proposed a construction for flowing warm air against paper in a sheet feeding paper deck mounted on an image forming apparatus such as a copying machine to thereby loosen the paper (for example, Japanese Patent Application Laid-Open No. 2001-048366).  
         [0005]     In this example of the prior art, basically the temperature controlling operation of an air heater and a sheet loosening operation (for example, the start of fan rotation and the start of swing shutter motor rotation) are started at a time. That is, the fan starts rotation simultaneously with the start of the temperature control of the air heater.  
         [0006]     Therefore, much time is required until the air heater temperature, i.e., warm air temperature assumes a predetermined value, and this leads to the disadvantage that the time until the loosening operation is terminated and the sheet feeding operation becomes possible is slow with a result that the performance of the entire apparatus is lowered.  
         [0007]     Also, in order to avoid the above-noted disadvantage peculiar to the above-described example of the prior art, there is conceivable a construction for starting the loosening operation before the air heater temperature reaches the predetermined value, but in this case, the loosening operation (air assisting operation) is started before the warm air temperature rises sufficiently, and this leads to the disadvantage that loosening becomes insufficient.  
         [0008]     Generally, in an air assisting construction wherein warm air is blown against the sheets in the paper deck to thereby loosen the sheets to reliably loosen the sheets, it is necessary to flow warm air of a predetermined temperature or higher for a predetermined value of time or longer, and flowing air of a temperature lower than the predetermined temperature is little effective for the loosening of the paper. Also, in case of blowing an air of low temperature against the sheets of paper, the sheets of paper may get damp. As a result, this may affect the loosening operation, and deteriorate quality of images to be formed on the sheets of paper.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide a sheet feeding apparatus which has eliminated the above-noted inconveniences and a controlling method therefor.  
         [0010]     It is another object of the present invention to provide a sheet feeding apparatus which can quickly and reliably effect the loosening of sheets and can accurately convey the sheets and a controlling method therefor.  
         [0011]     Other objects of the present invention will become apparent from the following description based on the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  shows a paper deck according to a first embodiment of the present invention.  
         [0013]      FIG. 2A  shows heater temperature and warm air temperature in a case not according to the first embodiment.  
         [0014]      FIG. 2B  shows heater temperature and warm air temperature in a case according to the first embodiment.  
         [0015]      FIG. 3  shows a paper deck according to a second embodiment of the present invention.  
         [0016]      FIG. 4A  shows heater temperature and warm air temperature in a case not according to the second embodiment.  
         [0017]      FIG. 4B  shows heater temperature and warm air temperature in a case according to the second embodiment.  
         [0018]      FIG. 5A  shows a chart for determining the target temperature of an air heater  14  in the case of coat paper.  
         [0019]      FIG. 5B  shows a chart for determining the target temperature of the air heater  14  in the case of non-coat paper.  
         [0020]      FIG. 6  is a control flow chart of a controller  16 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [heading-0021]     (First Embodiment)  
         [0022]     In  FIG. 1 , an image forming apparatus  1  effects image forming on a sheet  7  supplied from a paper deck  4 . A pickup roller  5  is rotated to thereby feed the uppermost one of a plurality of sheets  7  stacked on the paper deck  4  toward the image forming apparatus  1 .  
         [0023]     A sheet detecting sensor  8  detects the thickness, density (basis weight) and size of the sheet  7  and sends information to a controller  16 . Besides the detection by the sheet detecting sensor  8 , a user can also input information regarding the sheet from the operating portion or the like of the image forming apparatus  1 .  
         [0024]     A temperature detecting sensor  9  and a humidity detecting sensor  10  detect the temperature and humidity of the interior of the paper deck  4 , and send this information to the controller  16 .  
         [0025]     A fan  11  blows warm air against the vicinity of the uppermost one of the stacked sheets and loosens the sheet  7  to thereby prevent the double feeding of the sheets. A swing shutter  19  is reciprocally moved, for example, in a vertical direction, and partly intercepts or passes the warm air from the fan  11  to thereby loosen the sheet  7 . The swing shutter  19  is driven by a swing motor (not shown).  
         [0026]     A duct  13  has an air heater  14  therein. In this embodiment, air is taken in from the lower portion of the duct  13 , and the air warmed by the air heater  14  is exhausted by the fan  11 .  
         [0027]     An AC voltage  18  is supplied to the air heater  14  by the controller  16  through the ON/OFF control of a solid state relay (SSR)  17 , and for example, a resistor included in the air heater  14  generates heat to thereby warm the air taken in from the lower portion of the duct  13 .  
         [0028]     An air heater temperature detecting sensor  15  is in contact with the air heater  14  and sends information regarding the temperature of the air heater  14  to the controller  16 . The controller  16  effects temperature control through the AC voltage  18  and the ON/OFF control of the SSR  17  on the basis of the information from the air heater temperature detecting sensor  15  so that the temperature of the air heater  14  may assume a predetermined value.  
         [0029]     Description will hereinafter be made of the operation until in the above-described construction, the air heater  14  starts temperature control to thereby loosen the sheets  7  and the pickup roller  5  starts sheet feeding.  FIG. 6  shows a control flow chart of the controller  16 .  
         [0030]     First, information regarding the kind, thickness, density and size of the sheet is obtained from the sheet detecting sensor  8  or the operating portion (step S 61 ). An optimum target air heater temperature is determined on the basis of the temperature information and humidity information sent form the temperature detecting sensor  9  and the humidity detecting sensor  10 , respectively, to the controller  16 , and the information regarding the kind, thickness, density and size of the sheet sent from the sheet detecting sensor  8  or the operating portion to the controller  16 . The controller  16  determines the target air heater temperature on the basis of a program for executing a judgment flow corresponding to charts shown in  FIGS. 5A and 5B  (step S 62 ).  
         [0031]     For example, let it be assumed that the sheet detecting sensor  8  has detected that the kind of the sheet is coat paper, the temperature detecting sensor  9  has detected 25° C. and the humidity detecting sensor  10  has indicated 70%. In that case, the controller  16  determines the optimum target air heater temperature to be 90° C.  
         [0032]     In a case where the controller  16  temperature-controls the air heater  14 , when the information from the air heater temperature detecting sensor  15  indicates a temperature less than 90° C., the SSR  17  is switched on to thereby electrically energize the air heater  14  and raises the temperature of the air heater, and when the aforementioned information indicates 90° C. or higher, the SSR  17  is switched off and the air heater  14  is not electrically energized.  
         [0033]     In the case of non-coat paper, the heater is always turned off.  
         [0034]     The subsequent operation will be described with reference to  FIGS. 2A and 2B .  FIG. 2B  shows the operation of the present embodiment. The axis of abscissas indicates time, and the axis of ordinates indicates temperature, and the graph shows the temperature of the air heater  14  (the output of the air heater temperature detecting sensor  15 ) and the warm air temperature. The arrows in  FIGS. 2A and 2B  indicate a trigger relation.  
         [0035]     The warm air temperature is the temperature of the air at a point A in  FIG. 1 . Although in present embodiment, the temperature detecting sensor is not provided at the point A, there is shown the state of the warm air temperature at the point A when the temperature of the air heater  14  is such a curve as shown in  FIG. 2B .  
         [0036]     First, the controller  16  starts the temperature control of the air heater  14  at the timing of T=0. At this point of time, the fan  11  is not rotated, nor the swing shutter  19  is operated.  
         [0037]     Thereby, the temperature of the air heater  14  rises and reaches an air heater target temperature at timing T1.  
         [0038]     In  FIG. 6 , whether the temperature of the air heater has reached the target temperature is judged (step S 63 ), and when it reaches the target temperature, the controller  16  starts the rotation of the fan  11  (step S 64 ). At this point of time, however, the swing shutter  19  is not operated.  
         [0039]     Thereby, the warm air temperature rises and reaches a warm air final temperature at timing T2. Here, for the first time, the controller  16  operates the swing shutter  19 , and the air of the warm air final temperature is flown against the vicinity of the uppermost one of the sheets  7  whereby the sheets are loosened. During the time between T1 and T2, the heater temperature overshoots undershoots, but actually the time from T1 till T2 is short and therefore, there is little or no influence upon the warm air temperature.  
         [0040]     Accordingly, the sheet loosening operation is started from the timing T2. The warm air temperature at this time has reached the warm air final temperature and the warm air has become warm air of a predetermined temperature from the beginning of the loosening operation.  
         [0041]     The time necessary for loosening when this warm air of the predetermined temperature is flown is TS. That is, the loosening operation is completed at timing T3 whereat the time TS has elapsed from the timing T2, and it is possible to start the sheet feeding operation (to rotate the pickup roller  5 ) from the timing T3.  
         [0042]     In air assist wherein warm air as flown against the sheets in the paper deck to thereby loosen the sheets, to loosen the sheets reliably, it is necessary to flow warm air of a predetermined temperature or higher for the predetermined time TS or longer, and flowing air of a temperature lower than the predetermined temperature is little effective for the loosening of the sheets.  
         [0043]     Here, the state when unlike the present embodiment, the rotation of the fan  11  has been started with the start of the temperature control of the air heater  14  will be described with reference to  FIG. 2A . At the timing of T=0, the temperature control of the air heater  14  is started and simultaneously therewith, the rotation of the fan  11  is started. It is to be understood that at this time, the swing shutter  19  is not operated.  
         [0044]     Thereupon, the air of a low temperature from the lower portion of the duct  13  introduced by the rotation of the fan  11  hampers the temperature rise of the air heater  14  and therefore, the rising speeds of the heater temperature and warm air temperature are lower than in the present embodiment ( FIG. 2B ), and it is after timing T4 later than T2 that the heater temperature reaches the air heater target temperature.  
         [0045]     Then, the swing shutter  19  is operated from the timing T4 and barely the original loosening operation becomes possible and therefore, it is at timing T5 whereat a time TS has elapsed from the timing T4 that the loosening operation is completed. For the first time at the timing T5, the sheet feeding operation becomes possible and therefore, as compared with the present embodiment, the time when sheet feeding becomes possible is late, and an improvement in the productivity of the entire apparatus cannot be expected.  
         [0046]     Also, there is conceivable a method of starting the loosening operation before the heater temperature reaches a target temperature, i.e., a method of operating the swing shutter  19  from T=0 (or somewhere between T=0 to T=4, instead of operating the swing shutter  19  from the timing T4, but in this method, the loosening operation is started before the warm air temperature rises sufficiently and therefore, loosening becomes insufficient.  
         [0047]     As previously described, generally, in the air assist wherein warm air is blown against the sheets in the paper deck to thereby loosen the sheets, to loosen the sheets reliably, it is necessary to flow warm air of the predetermined temperature or higher for the predetermined time TS, and flowing air of a temperature lower than the predetermined temperature is little effective for the loosening of the sheets. Also, in case of blowing an air of low temperature against the sheets of paper, the sheets of paper may get damp. As a result, this may affect the loosening operation, and deteriorate quality of images to be formed on the sheets of paper.  
         [0048]     Accordingly, by controlling as in the present embodiment as previously described, it becomes possible to effect reliable loosening of the sheets within the shortest time.  
         [0049]     That is, the air assisting operation (the rotation of the fan and the rotation of the swing shutter motor) is started, after the air heater has assumed a predetermined temperature or higher, or after a predetermined time has elapsed after the air heater has assumed the predetermined temperature or higher and therefore, warm air of a predetermined temperature can be made more quickly, and the loosening operation can be terminated earlier to thereby bring about a state in which sheet feeding is possible.  
         [heading-0050]     (Second Embodiment)  
         [0051]     A second embodiment is shown in  FIG. 3 . Chiefly the differences of this embodiment from the first embodiment will hereinafter be described. In the second embodiment, a warm air temperature detecting sensor  12  is provided at the point A of  FIG. 1  in the first embodiment. The warm air temperature detecting sensor  12  sends information regarding the temperature of the warm air to the controller  16 . While in the first embodiment, the timing for the start of the loosening operation has been effected by the detection of the heater temperature, in the second embodiment, it is effected by a value from the warm air temperature detecting sensor  12 .  
         [0052]     The time description of the above-described operation is shown in  FIGS. 4A and 4B . Basically, it is the same as the operation shown in  FIGS. 2A and 2B , but the trigger of the start of the loosening operation is not the heater temperature detected by the air heater temperature detecting sensor  15 , but the warm air temperature detected by the warm air temperature detecting sensor  12 . Thereby, the accuracy of the temperature of the air blown against the uppermost one of the sheets  7 , and the control or the like of the loosening time can be effected accurately, and it is possible to further improve the loosening performance of the whole.  
         [0053]     The present invention is not restricted to the above-described embodiments, but various modifications one possible within the scope of the invention shown in the appended claims.  
         [0054]     This application claims priority from Japanese Patent Application No. 2003-308783 filed on Sep. 1, 2003, which is hereby incorporated be reference herein.