Patent Publication Number: US-7591459-B2

Title: Sheet feeding apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus equipped with a sheet feeding apparatus that feeds a sheet. 
     2. Description of the Related Art 
     Conventionally the image forming apparatus such as a copying machine and a printer is equipped with the sheet feeding apparatus. The sheet feeding apparatus feeds the sheet cut into a predetermined size to a transfer position one by one in order to transfer a toner image, formed on a photosensitive member, onto the sheet at the transfer position. 
     For example, Japanese Patent Application Laid-Open No. 7-196187 discloses a sheet feeding apparatus having a configuration in which air is blown to the sheet from one end side in a conveyance direction of the sheets loaded in an accommodation box using a separating fan and the floating sheet is adsorbed to and conveyed by a conveyance belt. 
     However, a floatation amount depends on a material (thickness or weight) of the sheet. Therefore, there is proposed a configuration in which lifting and lowering of the tray on which the sheets are loaded are controlled such that the sheet floatation by the air blow is positioned within a predetermined range. For example, in a configuration disclosed in USP 200506068A1, position detecting unit determines whether or not the sheet floatation position is located within a predetermined range, and the tray is lifted and lowered such that the floating sheet is located within the predetermined range when the sheet floatation position is located out of the predetermined range. 
     There is also proposed a configuration in which a rotating speed of the separating fan is controlled such that the sheet becomes the optimum floatation amount irrespective of the material. When the sheet is thin, or when sheet is made of a light material, the control is performed such that the rotating speed of the separating fan is decreased. When the sheet is thick, or when sheet is made of a heavy material, the control is performed such that the rotating speed of the separating fan is increased. Specifically, in a configuration disclosed in Japanese Patent Application Laid Open No. 7-89625, a distance measuring sensor measures a distance from a belt surface of the conveyance belt to the floating sheet, and the air blowing quantity is controlled based on the measured distance by controlling the rotating speed of the separating fan. 
     There is also proposed a configuration in which the material (thickness and weight) of the sheet on the tray is inputted from an operation portion of the image forming apparatus and the air blowing quantity is uniquely determined according to the inputted material of the sheet. 
     In the technique disclosed in USP 200506068A1, even if the materials (thicknesses and weights) of the sheets differ from one another, the sheet is positioned within a predetermined range by the lifting and lowering of the tray. However, it cannot be determined whether or not the sheet positioned within the predetermined range becomes an optimum dealing state. As disclosed in Japanese Patent Application Laid-Open No. 7-89625, in order to obtain the optimum dealing state irrespective of the material of the sheet, the rotating speed of the separating fan is changed in each time the material (thickness and weight) of the sheet loaded on the tray is changed. However, even if the rotating speed of the separating fan is set in each sheet material to obtain the proper air blowing quantity, sometimes the proper rotating speed is not stably obtained due to a fluctuation of the fan itself, aged deterioration of fan characteristics, and voltage drop caused by bundle conductors. In this case, for example, when the sheet is thin, or when sheet is made of the light material, the rotating speed of the separating fan is faster than the target value, the sheet dealing state is not stabilized, which possibly results in a trouble such as sheet jam, skew feeding, position shift, a flaw, folded sheet, and dirt. When the sheet is thick, or when sheet is made of the heavy material, the rotating speed of the separating fan is slower than the target value, the proper air does not flow between the sheets, which possibly results in a trouble such as conveyance of overlapped sheets. 
     In the configuration in which the sheet material (thickness and weight) is inputted from the operation portion of the image forming apparatus, sometimes sheet material (thickness and weight) which is inputted from the operation portion differs from the material of the sheet which is actually loaded on the tray. In such cases, the rotating speed of the separating fan becomes improper value, which possibly results in the trouble such as the conveyance of overlapped sheets, the skew feeding, the position shift, the flaw, the folded sheet, and the dirt. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the invention is to provide an image forming apparatus, in which the rotating speed of the fan can be set so as to become the optimum air quantity irrespective of the fluctuation of the fan itself, the aged deterioration of the fan characteristics, and the like and the fan can be stabilized at an optimum rotating speed. 
     An aspect according to the invention provides an image forming apparatus that has a sheet feeding apparatus which separates and feeds a sheet one by one, the image forming apparatus comprising: a tray which supports a plurality of sheets; an air blowing portion which loosens the sheet by blowing air to an end portion of the sheet supported by the tray; and wherein an amount of blowing air from the air blowing portion is adjusted while the sheet supported by the tray moves away from a position at where the sheets are loosened by the air blowing portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view illustrating a schematic configuration in which a sheet feeding apparatus according to an embodiment is arranged on an input side of an image forming apparatus; 
         FIG. 2  is a sectional view illustrating an example of a sheet separating and feeding portion of the sheet feeding apparatus of the embodiment; 
         FIG. 3  illustrates a control block diagram of the sheet feeding apparatus of the embodiment; 
         FIG. 4  is a block diagram illustrating configurations of a control unit of a printer body of the embodiment and a control unit of the sheet feeding apparatus of the embodiment; 
         FIG. 5  is a sectional view illustrating a schematic configuration in which the sheet insertion apparatus according to an embodiment is arranged on an output side of the image forming apparatus; 
         FIG. 6  illustrates a schematic configuration of an operation portion of the sheet feeding apparatus of the embodiment; 
         FIG. 7  illustrates a screen in which sheet conditions are inputted on an operation screen; 
         FIG. 8  illustrates a coefficient for an adjustment value with respect to the sheet condition; 
         FIG. 9  is a sectional view illustrating an example of a sheet separating and feeding portion of the sheet feeding apparatus according to the embodiment; 
         FIG. 10  illustrates detectable lower limits of a sheet floatation upper-limit sensor and a sheet floatation lower-limit sensor; 
         FIG. 11A  illustrates logic of the sheet floatation upper-limit sensor and the sheet floatation lower-limit sensor in a standby state; 
         FIG. 11B  illustrates logic of the sheet floatation upper-limit sensor and the sheet floatation lower-limit sensor after a loosening fan is operated; 
         FIGS. 12A to 12C  illustrate control of an uppermost sheet surface in the normal case; 
         FIGS. 13A to 13C  illustrate cases where a fan rotating speed can be adjusted; 
         FIGS. 14A to 14C  illustrate cases where the fan rotating speed cannot be adjusted; 
         FIG. 15  illustrates a range of a target value when the fan rotating speed is adjusted; 
         FIG. 16  illustrates selection whether or not an air quantity is adjusted from an operation screen; 
         FIG. 17  is a flowchart illustrating adjustment of fan air quantity according to the embodiment; 
         FIG. 18  illustrates warning on the operation screen before the fan rotating speed is adjusted; 
         FIG. 19  illustrates warning on the operation screen when the adjustment of the fan rotating speed fails; 
         FIGS. 20A and 20B  illustrate operation after the adjustment of the fan rotating speed is normally ended; 
         FIG. 21  illustrates a timing chart from start of the adjustment of the fan rotating speed to the normal end; 
         FIG. 22  illustrates a timing chart when the fan rotating speed is not adjusted; 
         FIG. 23  illustrates a timing chart from start of the adjustment of the fan rotating speed to the normal end after a sheet is removed; and 
         FIG. 24  illustrates a timing chart explaining control after the adjustment of the fan rotating speed fails. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the invention will be described in detail with reference to the drawings. However, in the following embodiments, dimensions, materials, and shapes of components and a relative arrangement of the components should appropriately be changed depending on a configuration of an apparatus to which the invention is applied and various conditions. Accordingly, unless otherwise specifically described, the scope of the invention is not limited to the embodiments. 
     (Image Forming Apparatus) 
     A schematic configuration of an image forming apparatus shown in  FIG. 1  will be described below.  FIG. 1  is a sectional view illustrating a schematic configuration of the image forming apparatus having a sheet feeding apparatus; 
     Referring to  FIG. 1 , an image forming apparatus  1  includes a printer body  1000  and a scanner  2000  arrange on an upper surface of the printer body  1000 . The image forming apparatus  1  also includes a sheet feeding apparatus  3000  which feeds the sheet to the printer body  1000 . The sheet feeding apparatus  3000  includes an air separating and feeding mechanism which is of a sheet separating and feeding portion in order to stably separate and feed various sheets. The sheet feeding apparatus  3000  will be described later. 
     First the image forming apparatus  1  will be described in detail. The scanner  2000  which reads an original includes a scanning optics light source  201 , a platen glass  202 , an openable original platen  203 , a lens  204 , a light receiving element (photoelectric conversion)  205 , an image processing portion  206 , and a memory portion  208 . An image processing signal processed by the image processing portion  206  is stored in the memory portion  208 . 
     In reading the original, the original placed on the platen glass  202  is irradiated with light by the scanning optics light source  201  to read the original. The read original image is processed by the image processing portion  206  and converted into an electrically-coded electric signal  207 , and the electric signal  207  is transmitted to a laser scanner  111  which is of image forming unit. Alternatively, the coded image information processed by the image processing portion  206  is temporarily stored in the memory portion  208 , and the image information may be transmitted to the laser scanner  111  by a signal from a control unit  130  if needed. 
     The printer body  1000  includes a sheet conveyance portion  1004  and the control unit  130 . The sheet conveyance portion  1004  conveys the sheet fed by the sheet feeding apparatus  3000 , to an image forming portion  1005 . The control unit  130  controls the printer  1000 . 
     The sheet conveyance portion  1004  includes a registration roller portion which has a pre-registration roller pair  122  and a registration roller pair  123 . The sheet fed from the sheet feeding apparatus  3000  is guided by a sheet conveyance path  121  formed by a guide plate, and the sheet is led to the registration roller pair  123  after passing through the pre-registration roller pair  122 . Then, the sheet once abuts on the registration roller pair  123  to correct skew feeding generated in feeding and conveying the sheet, and the sheet is conveyed to the forming portion  1005 . 
     The image forming portion  1005  includes a photosensitive drum  112 , a laser scanner  111 , a development device  114 , a transfer charger  115 , and a separation charger  116 . Informing the image, a laser beam from the laser scanner  111  is folded by a mirror  113 , and an exposure position  112   a  on the photosensitive drum  112  is irradiated with the laser beam. The photosensitive drum  112  is rotated in a clockwise direction of  FIG. 1 . Therefore, a latent image is formed on the photosensitive drum  112 . Then, the latent image formed on the photosensitive drum  112  is visualized as a toner image by the development device  114 . The position irradiated with the laser beam can be changed through a laser writing position control circuit by a control signal from the control unit  130 , and thereby the position where the latent image is formed on the photosensitive drum  112  can be changed in a longitudinal direction, that is, in a so-called main scanning direction. 
     The toner image on the photosensitive drum  112  is transferred to the sheet in a transfer portion  112   b  by the transfer charger  115 . The sheet to which the toner image is transferred is electrostatically separated from the photosensitive drum  112  by the separation charger  116 . Then, the sheet is conveyed to a fixing device  118  by a conveyance belt  117 , and the toner image is fixed to the sheet by the fixing device  118 . The sheet to which the toner image is fixed is discharged to the outside of the apparatus by a discharge roller  119 . A discharge sensor  120  is provided in a conveyance path between the fixing device  118  and the discharge roller  119  to be able to detect the passage of the sheet. 
     In the embodiment, the printer body  1000  and the scanner  2000  are separately formed. Alternatively, the printer body  1000  and the scanner  2000  are integrally formed. In either case, the printer body  1000  functions as the copying machine when the signal processed by the scanner  2000  is inputted to the laser scanner  111 , and the printer body  1000  functions as the facsimile when a facsimile transmission signal is inputted. The printer body  1000  also functions as the printer when an output signal of a personal computer is inputted. 
     On the contrary, the printer body  1000  functions as the facsimile when the signal processed by the image processing portion  206  of the scanner  2000  is transmitted to the above facsimile. In the scanner  2000 , the original can automatically be read, when an automatic original feeding apparatus  250  shown by an alternate long and two short dashes line is attached in place of the platen  203 . 
     (Sheet Feeding Apparatus) 
     Then, the sheet feeding apparatus  3000  in the image forming apparatus  1  of  FIG. 1  will be described. 
     The sheet feeding apparatus  3000  includes a sheet feeding portion  331  located in a lower portion of the sheet feeding apparatus  3000  and a sheet feeding portion  322  located in an upper portion. The sheet feeding portions  331  and  332  include sheet accommodation portions  301  and  311  in which plural sheets S can be accommodated respectively. A tray  302  and a rear-end regulating plate  303  are provided in the sheet accommodation portion  301 , and a tray  312  and the rear-end regulating plate  303  are provided in the sheet accommodation portion  311 . The accommodated sheets S are loaded on each of the trays  302  and  312  which can be lifted and lowered. The rear-end regulating plate  303  regulates a rear end of the sheet S in the conveyance direction (direction of arrow A). The rear-end regulating plate  303  is movable according to the size in the conveyance direction of the sheet S, and the rear-end regulating plate  303  regulates the rear end of the sheet conveyance direction such that the front end in the sheet conveyance direction is aligned with the front-end side in the conveyance direction of the sheet accommodation portion  302 . Although the sheet feeding portion  331  and  332  have the same configuration, the rear-end regulating plate is not shown on the side of the sheet feeding portion  332 . 
     The sheet separating and feeding portion (air separating and feeding mechanism) in the sheet feeding apparatus will be described below with reference to  FIG. 2 .  FIG. 2  is an enlarged view illustrating a main part of the sheet separating and feeding portion in the sheet feeding apparatus shown in  FIG. 1 . 
     With regard to sheets in the sheet accommodation portion  301 , a loosening fan F 151  is rotated as a pre-feeding operation, and thereby the air is blown from a loosening nozzle  151  which is of an air outlet to loosen with a periphery in the upper portion of the loaded sheets S in the sheet separating and feeding portion  304 . When a feeding start signal is transmitted from the control unit  300 , a negative pressure (suction force) is generated in a suction belt  305  by a suction fan F 150 , and the suction of the sheet is started. After a predetermined suction time elapses since the suction is started, only the uppermost sheet S 1  in the loaded sheets S is adsorbed by the suction belt  305 . After a predetermined time, in the suction belt  305 , rotation is started by a suction belt motor M 102  while the sheet S 1  is adsorbed, and the sheet S 1  is conveyed in the direction of the arrow A. When the front end of the sheet reaches a belt pulley portion, the front end portion of the sheet is released from the suction force generated by the suction fan F 150 , and the sheet is separated from the suction belt  305  and transferred to a drawing roller pair  10 .  FIG. 2  illustrates a configuration in which a separating fan F 152  is provided. The separating fan F 152  blows the air from a separating nozzle  152  to separate the front end portion of the sheet from the suction belt  305 . When the front end of the sheet S 1  reaches the drawing roller pair  10 , the negative pressure generated by the suction fan F 150  is released to release the sheet from the suction force to the suction belt  305 , and the sheet is conveyed only by conveyance force of the drawing roller pair  10 . When the feeding start signal is transmitted again by the control unit  300  after the rear end of the sheet passes through the suction belt portion, the feeding operation is started and the subsequent sheet S 2  is separated and fed. 
     In this case, the loosening fan F 151  is operated as the pre-feeding operation before the feeding start signal is transmitted. Alternatively, the loosening fan F 151  may be operated after the feeding start signal is transmitted. 
     Although only the sheet separating and feeding portion  304  on the side of the sheet accommodation portion  301  is described, the sheet separating and feeding portion  314  is similarly provided on the side of the sheet accommodation portion  311  to perform the similar separation and feeding. 
     As shown in  FIG. 3 , the drawing roller pairs  10  and  20  are connected to drawing motors M 10  and M 20  respectively. Conveyance roller pairs  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  21 ,  22 , and  23  are connected to conveyance motors M 11 , M 12 , M 13 , M 14 , M 15 , M 16 , M 21 , M 22 , and M 23  respectively. In the sheet feeding apparatus, each roller pair can independently be driven. 
     In  FIG. 3 , lifter motors M 5  and M 205  which are of lifter driving unit lift and lower the trays  302  and  312  in the sheet feeding portion  331  and  332  respectively. Suction belt motors M 102  and M 202  rotate the suction belts in the sheet feeding portion  331  and  332  respectively. Suction fans F 150  and F 250  suck the sheets to the suction belt in the sheet feeding portions  331  and  332  respectively. Sheet loosening fans F 151  and F 251  are located in the sheet feeding portions  331  and  332  respectively, and separating fans F 152  and F 252  are located in the sheet feeding portions  331  and  332  respectively. These operation portions are controlled by the control unit  300  which is of control unit. 
     In  FIG. 3 , a rotating-speed detecting sensor  604 , which is of rotating-speed detecting unit, detects a rotating speed of the loosening fan. A tray lower-position detecting sensor  605 , which is of lower-position detecting unit, detects a lower position of the tray. As used herein the lower position shall mean the lowest position where each of the trays  302  and  312  is lowered in the normal operation. A sheet existence detecting sensor  606 , which is of sheet existence detection unit, detects the presence or absence of the sheet loaded on each of the trays  302  and  312 . A sheet floatation lower-limit sensor  607  and a sheet floatation upper-limit sensor  608  are sensors which detect a position of the sheet floated by the air blown from the loosening fan F 151 . A sheet loading position detecting sensor  609  is provided in the lifting and lowering range of the tray to stop the sheet at the position higher than the lower position. The control unit  300  controls the operations of the sheet feeding apparatus based on pieces of information from various sensors. 
     Pieces of information such as a size, a type, and a basis weight of the sheet accommodated in the sheet accommodation portions  301  and  311  can be set from an operation portion of the image forming apparatus. 
     (Sheet Insertion Apparatus) 
     Then, a schematic configuration of an image forming apparatus shown in  FIG. 5  will be described below.  FIG. 5  is a sectional view illustrating a schematic configuration of the image forming apparatus having the sheet feeding apparatus. In the image forming apparatus of  FIG. 5 , the member having the same function as the image forming apparatus of  FIG. 1  is designated by the same numeral and the detailed description is neglected. 
     Referring to  FIG. 5 , the image forming apparatus  1  includes the printer body  1000  and the scanner  2000  arranged on the upper surface of the printer body  1000 . The image forming apparatus  1  shown in  FIG. 1  also includes a sheet insertion apparatus  4000  which is of the sheet feeding apparatus. The sheet insertion apparatus  4000  is connected to the sheet discharge side of the printer body  1000  to feed the sheet to the printer body  1000 . The image forming apparatus  1  also includes a finisher  5000  which is of sheet processing apparatus. The finisher  5000  is provided on the sheet discharge side of the sheet insertion apparatus  4000 . 
     In the image forming apparatus  1  of  FIG. 5 , the sheet s discharged from the printer body  1000  is led to a sheet conveyance portion  430  of the sheet insertion apparatus  4000 . The sheet insertion apparatus  4000  includes the sheet feeding portion  331  located in the lower portion of the sheet feeding apparatus  4000  and the sheet feeding portion  322  located in the upper portion. The sheet conveyance portion  430  is connected to a convergent portion  333  of the sheet feeding portions  331  and  332 . Because the configurations of the sheet feeding portions  331  and  332  of the sheet insertion apparatus  4000  are similar to those of the sheet feeding portions  331  and  332  of the sheet feeding apparatus  3000 , the member having the same function is designated by the same numeral and the description is neglected. Each of the sheet feeding portions  331  and  332  of the sheet insertion apparatus  4000  accommodates interleaving paper, a cover, a back-side cover, and a divider of a sheet stack and sheets in which the image is already formed. The sheet separated one by one by each of the sheet feeding portions  331  and  332  is conveyed to the finisher  5000  so as to be inserted between the sheets conveyed from the printer body  1000  at the convergent portion of the midpoint of the sheet conveyance portion  430 . 
     As described above, because the sheet feeding portions  331  and  332  have the same configuration, the sheet can be fed by selecting the necessary feeding portion as needed according to the sheet accommodated in the feeding portion. In the sheet feeding, both the sheet feeding portions  331  and  332  may be alternately be used, or one of the sheet feeding portions  331  and  332  may be continuously used. 
     The finisher  5000  sequentially loads and aligns the sheets conveyed through the sheet insertion apparatus  4000 . Although the detailed description of the operation is neglected, the control unit  130  of the printer body  1000  and a control unit  131  of the finisher  5000  conduct communication with each other to obtain optimum conditions from pieces of information on the sheet size, the number of sheets, the type, and the like. Various processing methods can be selected in the finisher  5000 . For example, a staple device (not shown) performs a binding process to each stack to be bound, or the binding process is not performed but only the sheets are loaded. 
     The production of the sheet stack with the image forming apparatus  1  of  FIG. 5  will be described below. The case where the sheet stack including 13 sheets S 1  to S 13  is produced will be described by way of example. The 10 sheets S 2  to S 6  and S 8  to S 12  for text body are produced with the printer body, the previously-printed cover S 1  and back-side cover S 13  are added by the sheet insertion apparatus, and the divider S 7  is inserted between the fifth sheet S 6  for text body and the sixth sheet S 8  for text body to complete the sheet stack. 
     The printer body  1000  of  FIG. 5  includes two sheet feeding portions  1002  and  1003  in the lower portion thereof. The sheet feeding portions  1002  and  1003  have the same configuration. In the sheet feeding portions  1002  and  1003 , the sheets accommodated in sheet accommodation portions  100  and  104  are selectively drawn by pickup rollers  101  and  105 , the sheets are separated one by one by feed rollers  102  and  106  and retard rollers  103  and  107 , and the sheet is conveyed to a sheet conveyance portion  1004 . 
     The sheets for producing the text body are accommodated in the sheet accommodation portions  100  and  104  of the printer body  1000 . The divider sheets are accommodated in the sheet accommodation portion  311  in the upper stage of the sheet insertion apparatus  4000 , and the sheet stack in which the previously-printed covers and back-side covers are alternately loaded are accommodated in the sheet accommodation portion  301  in the lower stage. 
     Since the control unit  130  of the printer body  1000  controls not only the single printer but also the whole of the image forming apparatus, the control unit  130  of the printer body  1000  first receives a signal for producing the sheet stack when the signal for producing the sheet stack is inputted. For the signal input method, the signal may be inputted from the operation portion of the image forming apparatus  1  or the signal may be inputted from a remote computer. 
     When the signal for producing the sheet stack is inputted, the control unit  130  transmits the pieces of information on the number of sheets in one stack, sheet insertion timing, and the like to a control unit  300  of the sheet insertion apparatus  4000  and a control unit  131  of the finisher  5000 . An operating preparation is started in each apparatus. 
     Specifically, in the sheet insertion apparatus  4000 , the divider sheet S 7  is separated and fed from the upper-stage sheet feeding portion  332 , and the divider sheet S 7  stands by at a standby position before the divider sheet S 7  reaches the convergent portion  333  of the sheet conveyance portion  430 . The cover S 1  is separated and fed from the lower-stage sheet feeding portion  331 , and the cover S 1  stands by at a standby position before the cover S 1  reaches the convergent portion  333  of the sheet conveyance portion  430 . 
     When the operating preparation is completed in each apparatus, the cover S 1  of a first set is conveyed from the standby position in the sheet insertion apparatus  4000  and, at the same time, the sheets S 2  to S 6  (first to fifth sheets) for text body are separated and fed at equal intervals in the printer body  1000 . After a time necessary to insert the divider sheet S 7  of the sheet insertion apparatus  4000 , that is, after a time necessary to convey the one sheet, the sheets S 8  to S 12  (sixth to tenth sheets) for text body are separated and fed in the printer body  1000 . After a space of the two-sheet interval of the back-side cover S 13  of the first set and the cover of the second set is kept, the first to fifth sheets for text body of the second set are separated and fed in the printer body. 
     Thus, the images are formed while the space of the sheet inserted by the sheet insertion apparatus is kept. In the sheet insertion apparatus  4000 , the sheets S 2  to S 6  in which the images are already formed is conveyed at a conveyance speed higher than that of the printer body. That is, the front end of each sheet passes through the discharge sensor  120 , and the sheet is conveyed into the sheet insertion apparatus  4000 . After the rear end of each sheet passes through the discharge roller  119 , the conveyance speed is enhanced to a second conveyance speed V 1  higher than a first conveyance speed V 0  which is of an image forming speed. 
     The cover S 1  which stands by in the sheet insertion apparatus  4000  is started in motion from the standby position before the first sheet S 2  for text body is discharged from the printer body  1000 , and the conveyance is started at the second conveyance speed V 1 . The speed of the conveyance roller  13  located near the convergent portion  333  in the sheet insertion apparatus  4000  is enhanced to the second conveyance speed V 1  during the conveyance of the cover S 1 . When the rear end of the cover S 1  passes through the conveyance roller  13 , the sheet insertion apparatus  4000  reduces the conveyance speed to the first conveyance speed V 0  which is of the discharge speed of the printer body  1000  in order to prepare the transfer of the sheet for text body from the printer body  100 . 
     As described above, in the sheet insertion apparatus  4000 , the sheets S 2  to S 6  for text body are conveyed while the speed is enhanced. The enhancement of the sheet conveyance speed is ended before the rear end of the sheet for text body reaches the convergent portion  333  of the conveyance path. Therefore, the divider S 7  which stands by at the standby position in the sheet insertion apparatus  4000  is started in conveyance at the second conveyance speed V 1  after the rear end of the sheet S 6  for text body passes through the convergent portion  333 , and the divider S 7  is inserted between the sheet S 6  and the next sheet S 7  discharged from the printer body. Thus, the sheet passing through the convergent portion  333  in the sheet insertion apparatus  4000  is conveyed at the second conveyance speed V 1 . Although the sheet is conveyed at the second conveyance speed V 1  in the sheet insertion apparatus  4000 , the speed of the sheet is reduced to the first conveyance speed V 0  when the front end of the sheet passes through the discharge sensor  319  of the sheet insertion apparatus  4000 , and the sheet is transferred to the finisher  5000 . That is, the sheet insertion apparatus  4000  reduces the conveyance speed again to the first conveyance speed V 0  which is of the image forming speed in order to prepare the transfer of the sheet from the printer body  1000 . 
     After the divider S 7  is conveyed, in the sheet insertion apparatus, the sheets S 8  to S 12  for text body are conveyed in the same manner as the sheets S 2  to S 6 . As with the divider S 7 , the back-side cover S 13  which is stands by at the standby position in the sheet insertion apparatus  4000  is started in conveyance at the second conveyance speed V 1  after the rear end of the sheet S 12  for text body passes through the convergent portion  333 . The back-side cover S 13  is separated and fed from the sheet accommodation portion  301  until the sheet S 12  is delivered to the sheet insertion apparatus  4000  since the sheet S 1  is conveyed, and the back-side cover S 13  stands by at the standby position in front of the convergent portion. 
     Then, in the case where the next sheet stack is similarly processed, unless the back-side cover S 13  is conveyed, the rear end of the back-side cover S 13  blocks the cover S 14  of the next stack, and the suction of the cover S 14  cannot be started in the sheet separating and feeding portion. Therefore, after the time (suction time) when the rear end of the back-side cover S 13  is separated from the belt elapses since the conveyance of the back-side cover S 13  is started, the suction and conveyance of the cover S 14  is started. 
     (Control Block) 
       FIG. 4  is a block diagram illustrating configurations of the control unit  130  of the printer body  1000  and the control unit  300  of the sheet feeding apparatus  3000  shown in  FIG. 1 . In  FIG. 5 , the configurations of the control unit  130  in the printer body  1000  and the control unit  300  in the sheet insertion apparatus  4000  are similar to those of  FIG. 4 . 
     The control unit  130  in the printer body  1000  includes CPU  211 , ROM  212 , RAM  213 , a communication interface (I/F)  214 , an input and output port  215 , an operation portion  216 , an image processing portion  206 , and an image memory portion  208 . 
     CPU  211  performs basic control of the printer body  1000 . CPU  211  is connected to ROM  212  in which a control program is written, a working RAM  213  which is used to perform the processing, and the input and output port  215  through an address bus and a data bus. A part of the region of RAM  213  is used as a backup RAM in which data is not erased even if the power is turned off. Various load devices such as motors and clutches which are controlled by the printer body  1000  and various inputs devices such as a sensor for detecting the position of the sheet are connected to the input and output port  215 . 
     CPU  211  sequentially controls input and output through the input and output port  215  to perform the image forming process according to contents of the control program stored in ROM  212 . The operation portion  216  is connected to CPU  211  such that CPU  211  controls a display portion and a key input portion of the operation portion  216 . A user provides an instruction of an image forming operating mode or display exchange to CPU  211  through the key input portion, and CPU  211  causes the display portion of the operation portion  216  to display an operating status of the printer body  1000  or an operating mode set by key input. The image processing portion  206  and the image memory portion  208  are connected to CPU  211 . The image processing portion  206  processes the signal which is converted into the electric signal by the image sensor portion (light receiving element)  205 . The processed image is stored in the image memory portion  208 . 
     In order to realize the operation described with reference to  FIG. 1 , the control unit  300  of the sheet feeding apparatus  3000  includes CPU  351 , ROM  352 , RAM  353 , a communication interface (I/F)  354 , an input and output port  355 , and an operation portion  356 . Detection results are inputted to CPU  351  through the input and output port  355  from a floatation upper-limit sensor  608  and a floatation lower-limit sensor  607  which will be described later, the rotating-speed detecting sensor  604 , the tray lower-position detecting sensor  605 , and the sheet existence detecting sensor  606 . On the basis of the detection results, CPU  351  outputs a drive command to lifter motor M 5  and M 205 , the loosening fan F 151  and F 251 , and the suction fans F 150  and F 250 . The floatation upper-limit sensor  608  is arranged above the floatation lower-limit sensor  607 . A distance measuring sensor (not shown) which can measure a distance may be used in place of the floatation upper-limit sensor and the floatation lower-limit sensor. 
     (Operation Portion) 
       FIG. 6  is a schematic view illustrating a configuration of an operation portion in the image forming apparatus of the embodiment. 
     Referring to  FIG. 6 , a display portion  221  displays various messages such as the operating status of the apparatus and a working instruction to a user and a working procedure. A surface of the display portion  221  is formed by a touch panel which acts as a selection key by touching the surface. A ten key  222  is used to input a figure. A start key  223  is used to start the copy action when the start key  223  is pressed. An application mode selection key  224  is used to input sheet conditions such as a material of the sheet surface, the basis weight, and surface smoothness. 
     For example, the sheet material accommodated in the sheet feeding apparatus  3000  is selected from the display portion (operation screen)  225  shown in  FIG. 7 . In this case, thin paper  231 , plain paper  232 , thick paper  233 , and thickest paper  234  are illustrated as specific materials of the sheet. The material may be automatically set (the numeral  235  in  FIG. 7 ). The sheet conditions such as the material of the sheet surface, the basis weight, and the surface smoothness may be set in detail (the numeral  236  in  FIG. 7 ). 
     The control unit  300  of the sheet feeding apparatus  3000  has a table. The table is used to change the rotating speeds of the loosening fans F 151  and F 251  to obtain the optimum sheet loosening air according to the setting of the sheet material conditions (basis weight, surface roughness, and the like) through the display portion  225  of  FIG. 7 . When the setting is not performed, the plain paper  232  is usually used. Additionally, detailed setting may be added in addition to the setting items of the display portion shown in  FIG. 7 . 
     (Sheet Separating and Feeding Portion) 
     The configuration of the sheet separating and feeding portion (air separating and feeding mechanism) included in the sheet feeding portion will be described below. 
       FIG. 9  is a sectional view illustrating a configuration of the sheet separating and feeding portion in the sheet feeding apparatus and a peripheral portion of the sheet accommodation portion. Although  FIG. 2  illustrates the configuration in which the suction fan F 150  is arranged in the suction belt  305 , the suction fan F 150  may be arranged outside the suction belt  305  as shown in  FIG. 9 . 
       FIG. 9  illustrates the sheet separating and feeding portion  304  of the sheet feeding portion  331  in the sheet feeding apparatus  3000  of  FIG. 1 , and the sheet feeding portion  332  in the sheet feeding apparatus  3000  and the sheet feeding portion in the sheet insertion apparatus  4000  have the similar configurations. The sheet feeding portion  1002  and  1003  in the printer body  1000  of  FIG. 5  is an example of retard type separating and feeding mechanism. Alternatively, an air separating and feeding mechanism with an adsorption conveyance belt may be used. 
     In  FIG. 9 , the tray  302  which lifts and lowers the sheet stack including the loaded sheets S can vertically be moved through a pulley  603  by driving the lifter motor M 5 . An encoder is attached to the lifter motor M 5 , and the amount of drive of the lifter motor M 5 , that is, the amount of movement of the tray  302  can be detected by the encoder. The moving direction of the tray  302  can be detected by the rotational direction of the encoder or the control signal of the motor. 
     The tray lower-position detecting sensor  605  is arranged to detect the lower position of the tray  302 . On the other hand, the sheet existence detecting sensor  606 , the sheet floatation lower-limit sensor  607 , and the sheet floatation upper-limit sensor  608  are arranged in the upper portion of the sheet separating and feeding portion  304  to detect a height of the sheet. The sheet existence detecting sensor  606  is a flag sensor for detecting the sheet, and the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  are an optical sensor for detecting the sheet. The sheet existence detecting sensor  606  is arranged below the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608 . When the sheets S loaded on the tray  302  is lifted to the feeding start position, the sheet existence detecting sensor  606  can detect the upper surface of the sheet stack prior to the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608 . 
     The sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  detect the position of the sheet floatation by the air from the loosening fan F 151 . In the sheet floatation lower-limit sensor  607 , sensitivity is adjusted so as to detect the floating sheet located below the sheet floatation upper-limit sensor  608 . Therefore, using the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608 , it is possible to detect whether or not the floating sheet is located within a predetermined range. A relationship between the detection states of the sheet floatation lower-limit sensor  607  and sheet floatation upper-limit sensor  608  and the sheet state will be described later. 
     The loosening fan F 151  and a loosening fan duct  610  are provided to loosen with the sheet S accommodated in the sheet accommodation portion  301  in advance of the feeding operation. A wind pressure in a discharge direction generated by the rotation of the loosening fan F 151  is imparted to the periphery of the uppermost sheet of the sheet stack S through the loosening fan duct  610 , which prevents the plural sheets from being fed at once (overlap feeding) during the sheet feeding operation. 
     The suction belt  305 , the suction fan F 150  and a suction fan duct  613  are provided as the sheet feeding mechanism. The wind pressure in a suction direction generated by the rotation of the loosening fan F 150  is imparted to the suction belt  305  through the suction fan duct  613 , which adsorbs the uppermost sheet of the sheet stack S. The sheet adsorbed to the suction belt  305  is conveyed onto the sides of a feeding retry sensor  620  and the drawing roller pair  10  by the rotation of the suction belt  305  in the direction of the arrow of  FIG. 9 . 
       FIG. 9  illustrates the state in which the sheet is adsorbed by the suction fan F 150 . The sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  detect the sheet floatation position while the loosening fan F 151  is operated. As shown in  FIG. 10 , the lifting and lowering of the tray  302  are controlled based on the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  while the suction fan F 150  is not operated but the loosening fan F 151  is operated. In the state in which both the suction fan F 150  and the loosening fan F 151  are not operated, the standby position of the sheet stack S may be set to on-edge (detecting position) of the sheet floatation lower-limit sensor  607  (detecting position) or to on-edge of the sheet existence detecting sensor  606 . 
     In  FIG. 9 , the sheet existence detecting sensor  606  detects the presence or absence of the sheet on the tray  302 , and the on-edge (shown by a dotted line of  FIG. 9 ) of the sheet existence detecting sensor  606  is arranged below the loosening nozzle  151  which is of the air outlet of the loosening fan duct  610 . When the loosening fan F 151  is not operated, the stop position (standby position) of the tray  302  is located at the on-edge of the sheet existence detecting sensor  606 . The sheet loading sensor  609  is arranged in the mid point of the lifting and lowering range of the tray  302 . In the case where the sheet existence detecting sensor  606  detects the absence of the sheet, the sheet loading position detecting sensor  609  detects the tray  302  to output a signal for stopping the tray  302  when the tray  302  is lowered to the lower position. Thus, the tray  302  is not lowered to the lower position but the tray  302  is stopped to be able to load the sheets, which improves the workability in loading the sheets. When the sheets of one package (500 sheets) are loaded on the tray  302 , the tray  302  is controlled so as to be lowered until the sheet loading position detecting sensor  609  detects the uppermost surface of the loaded sheets, and thereby the upper surface position of the sheets is always kept constant. Therefore, the workability is improved because the sheets can always be loaded at the same height position. 
       FIGS. 11A and 11B  show logic of the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608 . In the non-operating states of both the suction fan F 150  and the loosening fan F 151 , assuming that the standby position of the sheet stack S is the on-edge of the sheet floatation lower-limit sensor  607 , this state becomes the standby state of the sheet stack S. In this state of things, when the loosening fan F 151  is driven, several sheets in the upper portion of the sheet stack S are loosened with, and the uppermost sheet of the sheet stack S floats. Then, the lifting and lowering of the tray  302  are controlled such that the floating sheet is located between the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608 . 
       FIG. 10  illustrates the detectable lower limits of the sheet floatation lower-limit sensor  607  and sheet floatation upper-limit sensor  608 . In  FIGS. 9 and 10 , the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  are arrayed in the sheet feeding direction. However, the correct detection can be achieved by arraying the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  in the direction perpendicular to the sheet feeding direction. 
     When the sheet conditions such as the surface material, the basis weight, and the surface smoothness of the sheet loaded on the tray  302  are inputted from the operation screen  225  of  FIG. 7 , the rotating speed of the loosening fan F 151  is set such that an air quantity of the loosening fan F 151  becomes optimum. When the loosening fan F 151  is operated under the inputted sheet conditions, obviously the uppermost sheet of the sheet stack S is moved between the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  without performing the lifting and lowering operation of the tray  302 . Alternatively, the uppermost sheet of the sheet stack S is moved above the sheet floatation upper-limit sensor  608 . Thus, the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  are arranged at the position where the sheet floatation lower-limit sensor  607  and the sheet floatation upper-limit sensor  608  can detect the floating sheet without performing the lifting and lowering operation of the tray  302  when the loosening fan F 151  is operated at the optimum rotating speed according to the sheet material. As shown in  FIG. 12 , when the sheet conditions set on the operation screen correspond to the conditions of the sheet loaded on the tray  302 , the tray  302  is controlled so as to be finally lowered by ΔL 1 . 
     (Adjustment Mode of Loosening Fan) 
     An adjustment mode in which the rotating speed of the loosening fan F 151  is stabilized will be described below with reference to  FIGS. 9 and 13 . The control is performed such that the loosening fan F 151  transfers to the adjustment mode after the power is turned on, after predetermined number of sheets are conveyed by the sheet feeding apparatus  3000 , or after a predetermined time elapses. The predetermined number of sheets may be the previously-set number of sheets or the number of sheets inputted from the operation screen. In the case where job operation is continued after the predetermined number of sheets are conveyed by the sheet feeding apparatus  3000 , the control may be performed such that the loosening fan F 151  transfers to the adjustment mode after the job is ended, or before the job is started. Although the one loosening fan F 151  is used in the embodiment, the plural loosening fans F 151  may be used. In the suction fan F 150 , the control may be performed such that the suction fan F 150  transfers to the adjustment mode. A counter (measuring unit, not shown) which counts a rise edge or a fall edge of the signal output from the retry sensor  620  is provided in the control unit  300  (CPU  351 ) for the number of sheets fed by the sheet feeding apparatus  3000 . 
     Referring to  FIG. 13 , when an adjustment mode transfer signal is detected after the power is turned on, after predetermined number of sheets are conveyed by the sheet feeding apparatus  3000 , or after a predetermined time elapses, the lifter motor M 5  (lifter drive unit) starts the lowering operation of the tray  302  (see  FIG. 13A ). When the lower-position detecting sensor  605  detects the tray  302 , the lifter motor M 5  is controlled so as to be stopped to stop the tray  302  (see  FIG. 13B ). At this point, unless the sheet existence detecting sensor  606  detects the sheet, the loosening fan F 151  is driven, and the adjustment of the fan rotating speed is started after a predetermined time elapses (see  FIG. 13C ). In order to correctly adjust the rotating speed of the loosening fan F 151 , it is necessary that the obstacles (shielding object) be removed in front (on the extended line in the air blowing direction) of the air outlet (loosening nozzle  151 ) of the loosening fan F 151 . For example, the sheet stack S loaded on the tray  302  is located on an extended line of the air outlet of the loosening nozzle  151  of the loosening fan F 151 , because air flow passage of the loosening fan F 151  is interrupted, the rotating speed, the air quantity, and the wind pressure cannot correctly be obtained. Therefore, the lifter motor M 5  lowers the tray  302 , and the lifter motor M 5  is stopped when the lower-position detecting sensor  605  detects the tray  302 . At this point, unless the sheet existence detecting sensor  606  detects the sheet, it is possible to make a determination that the obstacle does not exist in front of the loosening nozzle  151  (on the extended line of the air outlet), so that the rotating speed of the loosening fan F 151  can be adjusted. 
     The adjustment of the rotating speed of the loosening fan F 151  will be described with reference to  FIG. 15 . In a fan whose rotating speed can be monitored, a target value is required to adjust the rotating speed of the fan. When the fan is rotated in the setting of predetermined PWM (Pulse Width Modulation), it is previously found that a predetermined rotating speed (FG) output and a predetermined wind pressure are obtained from fan characteristics. For example, when a fan is operated at PWM of 100%, the rotating speed (FG) output of 600 Hz is obtained, and the wind pressure of 1000 Pa is obtained. When the wind pressure of 840 Pa is necessary for the adjustment of the fan rotating speed, the target fan rotating speed is set to 500 Hz, and a range of the target value is set such that a target upper-limit value is set to 502 Hz while a target lower-limit value is set to 498 Hz. The control is performed such that the fan rotating speed is adjusted after a predetermined time elapses since the fan operation is started, which results in PWM of 90% after the fan adjustment is normally ended, for example. The reason why the after predetermined time elapses since the fan operation is started is that the fan rotating speed is stabilized, as described above. After the fan rotating speed is stabilized, the rotating speed is adjusted, and the PWM value of the fan is changed such that the fan rotating speed (FG) becomes a predetermined value. Examples of the fan rotating-speed adjustment method includes a method of decreasing the PWM value in each predetermined value after the fan is rotated at the PWM value of 100% and a method of increasing and decreasing the PWM value by a value in which a difference between the target value and the actual rotating speed is multiplied by a coefficient. In adjusting the fan rotating speed, the control may be performed such that the fan is not rotated at 100% of the PWM value but the fan is rotated at predetermined PWM setting value. 
     The state in which the PWM value of the loosening fan is changed depending on the sheet conditions after the adjustment of the rotating speed of the loosening fan is normally ended will be described with reference to  FIG. 8 .  FIG. 8  illustrates the coefficients only by way of example, and the coefficient can be changed according to the sheet conditions. As described above, when the PWM value of 90% is obtained to satisfy the wind pressure of 840 Pa necessary for the adjustment value of the loosening fan, the thickest sheet can be loosened with. That is, when the thickest sheet is selected, the PWM value of the loosening fan is set to 90%×1.0=90%. When the thick paper is selected, the PWM value of the loosening fan is set to 90%×0.75=67.5%. When the plain paper is selected, the PWM value of the loosening fan is set to 90%×0.5=45%. When the thin paper is selected, the PWM value of the loosening fan is set to 90%×0.25=22.5%. 
     Then, the case in which the fan rotating speed cannot be adjusted will be described with reference to  FIG. 14 . When the adjustment mode transfer signal is detected after the power is turned on, after predetermined number of sheets are conveyed by the sheet feeding apparatus  3000 , or after the predetermined time elapses, the lifter motor M 5  starts the lowering operation of the tray  302  (see  FIG. 14A ). When the lower-position detecting sensor  605  detects the tray  302 , the lifter motor M 5  is controlled so as to be stopped to stop the tray  302  (see  FIG. 14B ). At this point, when the sheet existence detecting sensor  606  detects the sheet (see  FIG. 14C ), a warning shown in  FIG. 18  is displayed on the operation screen. Then, the sheet accommodation portion is opened to remove the several sheets loaded on the tray  302 , and the sheet accommodation portion is closed again, which starts the lowering operation of the tray  302  again. When the lower-position detecting sensor  605  detects the tray  302 , the lifter motor M 5  is stopped to stop the tray  302 . At this point, unless the sheet existence detecting sensor  606  detects the sheet, the loosening fan F 151  is driven, and the adjustment of the fan rotating speed is started after the predetermined time elapses. 
     For the adjustment mode in which the fan rotating speed is stabilized, the adjustment mode may be selected from the operation screen as shown in  FIG. 16 . 
     Then, the operation after the adjustment of the air quantity of the loosening fan F 151  is started will be described with reference to  FIG. 20 . In the case where the air quantity falls within the range of the target value shown in  FIG. 15  within a predetermined time since the adjustment of the air quantity of the loosening fan F 151  is started, the adjustment of the air quantity of the loosening fan F 151  is ended, and the fan operation is stopped. At the same time, the lifter motor M 5  lifts the tray  302 , and the lifter motor M 5  is stopped when the floatation lower-limit sensor  607  detects the upper surface of the sheets loaded on the tray  302 . 
     On the other hand, in the case where the air quantity does not fall within the range of the target value shown in  FIG. 15  within a predetermined time since the adjustment of the air quantity of the loosening fan F 151  is started, the rotating speed adjustment of the loosening fan F 151  is ended, and the operation of the loosening fan F 151  is stopped. Then, as shown in  FIG. 19 , a warning indicating that the rotating speed adjustment of the fan fails is displayed. In  FIG. 19 , the rotating speed of the fan is adjusted again. Alternatively, an error message may be displayed. The warning indicating that the rotating speed adjustment fails may be displayed before operation stop timing of the loosening fan F 151 . 
     When the sheets are loaded on the tray  302  during the air quantity adjustment of the loosing fan F 151  as described above, the sheet may be blown up by the air running around to the back of the sheet, even if the sheets are not located in front of the air blown from the loosing fan F 151 . Particularly, for the light-weight sheet, the small sheet, and the sheet whose end portion is curled upward, the air invades between the sheets to blow high up the sheet. Accordingly, sometimes the adjustment cannot accurately be performed. 
     Therefore, a control portion  300  may adjust the loosing fan F 151  while the sheets are not loaded on the tray  302 . 
     With reference to the specific adjusting method, the sheet accommodation portion is opened to take out all the sheets loaded on the tray  302 . Then, tray  102  is lifted when the sheet accommodation portion is closed again. Because the sheet existence detecting sensor  606  detects no sheet, the tray  302  is lowered until the sheet loading position detecting sensor  609  detects the tray  302 . In this state of things, the rotating speed of the loosing fan F 151  can be adjusted because the tray  302  is not located in front of the loosing nozzle  151 . 
     Alternatively, the rotating speed of the loosing fan F 151  may be adjusted when the tray  302  runs out of sheets. When the tray  302  runs out of sheets, the tray  102  is lifted, and the sheet existence detecting sensor  606  detects no sheet. Therefore, the tray  302  is lowered until the sheet loading position detecting sensor  609  detects the tray  302 . Similarly, in this state of things, the rotating speed of the loosing fan F 151  is adjusted. In this case, the frequency of the rotating speed adjustment is not a sort of thing that the adjustment is performed in each time the tray  302  runs out of sheets. Therefore, for example, a status of use (such as time and the number of sheets) is counted, and the rotating speed may be adjusted when the number of times of the sheet absence reaches the predetermined number of times. 
     The rotating speed of the loosing fan F 151  may be adjusted when the apparatus is turned on to recognize that the tray  302  runs out of sheets. For example, in the case where the remaining amount of sheet is detected by the position of the tray (specifically, an encoder is attached to the drive motor to count the pulses), in order to reset a counter to perform initialization, it is necessary that the tray be lowered once to the lowest position. Then, the tray  302  is lifted, and the sheet existence detecting sensor  606  detects no sheet. Therefore, the tray  302  is lowered until the sheet loading position detecting sensor  609  detects the tray  302 . Similarly, in this state of things, the rotating speed of the loosing fan F 151  is adjusted. 
     Thus, the rotating speed of the loosing fan F 151  is surely adjusted, when the rotating speed of the loosing fan F 151  is adjusted while the sheets are not loaded on the tray  302 . 
     (Timing Chart of Adjustment Mode) 
     Then, the operation timing concerning the adjustment mode will be described with reference to a timing chart of  FIG. 21   
     The operations of the sheet feeding apparatus  3000  and loosening fan F 151  after the loosening fan F 151  is transferred to the adjustment mode after the power is turned on, after predetermined number of sheets are conveyed by the sheet feeding apparatus  3000 , or after a predetermined time elapses, will mainly be described. 
     In  FIG. 21 , all the devices are activated by the H (high) active signal (detected by H signal, operated by H signal, and enabled by H signal). However, the devices may be activated by the L (low) active signal (detected by L signal, operated by L signal, and enabled by L signal). 
     When the adjustment signal becomes H (active) to enter the rotating-speed adjustment mode of the loosening fan F 151 , the lifter motor M 5  is controlled to start the lifting and lowering operation of the tray  302 . When the lift motor M 5  is stopped and the tray  302  reaches the lower-position detecting sensor  605 , the lifter motor M 5  is stopped. When the sheet existence detecting sensor  606  detects the absence of the sheet, the loosening fan F 151  is driven. The rotating speed adjustment of the loosening fan F 151  is started after a predetermined time T 1  elapses since the operation of the loosening fan F 151  is started. The rotating speed adjustment of the loosening fan F 151  is performed for a predetermined time T 2 . In the case where the rotating speed of the loosening fan F 151  falls within the predetermined range of the target value within the predetermined time T 2 , the rotating speed adjustment of the loosening fan F 151  is ended, and the operation of the loosening fan F 151  is stopped. The determination whether or not the rotating speed of the loosening fan F 151  falls within the predetermined range of the target value can be made based on the state of an adjustment mode normal termination signal. In  FIG. 21 , the rotating speed adjustment is ended after the H level of the adjustment mode normal termination signal is continued for a time T 4 . Alternatively, the determination that the adjustment mode is normally ended may be made when the H level of the adjustment mode normal termination signal is continued by the predetermined number of times for a predetermined interval.  FIG. 21  illustrates the state in which the rotating speed adjustment is ended within the predetermined time T 2 . Then, the tray  302  is lifted, and the lifter motor M 5  is stopped to stop the tray  302  when the sheet existence detecting sensor  606  detects the presence of the sheet, which transfers to the standby state. Therefore, the feeding can be started in response to the feeding start signal. In  FIG. 21 , the raising start timing of the tray  302  may be set at any point of the interval (T 3 ) between the turn-on of the adjustment mode normal termination signal and the turn-off of the fan drive signal. In  FIG. 21 , a transfer state shown by an arrow may be generated at the same time or with delay. 
     The case in which the rotating speed adjustment mode of the fan is not transferred will be described with reference to  FIG. 22 . When the adjustment signal becomes H (active) to enter the rotating-speed adjustment mode of the loosening fan F 151 , the lifter motor M 5  which lifts and lowers the tray  302  is controlled to start the lowering operation of the tray  302 . When the tray  302  reaches the lower-position detecting sensor  605 , the lifter motor M 5  is stopped. When the lifter motor M 5  is stopped and the sheet existence detecting sensor  606  detects the presence of the sheet, an alarm display signal is turned on to display the warning shown in  FIG. 18  on the operation screen. 
     The state in which the fan rotating speed is adjusted after the several sheets in the upper portion of the sheets loaded on the tray  302  are removed will be described below with reference to a timing chart of  FIG. 23 . In order to remove the sheets loaded on the tray  302 , it is necessary that the sheet accommodation portion be drawn from the apparatus body, and it is necessary that the sheet accommodation portion be accommodated in the apparatus body after the sheets are removed. However, the operations are neglected here. After the several sheets in the upper portion of the sheets loaded on the tray  302  are removed, the loosening fan F 151  is driven when the sheet existence detecting sensor  606  detects the absence of the sheet. After a predetermined time elapses since the operation of the loosening fan F 151  is started, the rotating speed adjustment of the loosening fan F 151  is started. In the case where the rotating speed of the loosening fan F 151  falls within the predetermined rotating speed range within the predetermined time, the rotating speed adjustment of the loosening fan F 151  is ended, and the operation of the loosening fan F 151  is stopped. Then, the tray  302  is lifted, and the lifter motor M 5  is stopped to stop the tray  302  when the sheet existence detecting sensor  606  detects the presence of the sheet, which transfers to the standby state. Therefore, the feeding can be started in response to the feeding start signal. 
     The case in which the adjustment of the fan rotating speed fails will be described with reference to  FIG. 24 . When the adjustment signal becomes H (active) to enter the rotating-speed adjustment mode of the loosening fan F 151 , the lifter motor M 5  is controlled to start the lowering operation of the tray  302 . When the tray  302  reaches the lower-position detecting sensor  605 , the lifter motor M 5  is stopped. When the lifter motor M 5  is stopped and the sheet existence detecting sensor  606  detects the absence of the sheet, the loosening fan F 151  is driven. The rotating speed adjustment of the loosening fan F 151  is started after the predetermined time T 1  elapses since the operation of the loosening fan F 151  is started. The rotating speed adjustment of the loosening fan F 151  is performed for the predetermined time T 2 . In the case where the rotating speed of the loosening fan F 151  does not fall within the predetermined range of the target value within the predetermined time T 2 , the rotating speed adjustment of the loosening fan F 151  is ended, and the warning indicating that the rotating speed adjustment fails is displayed as shown in  FIG. 19 . Then, the operation of the loosening fan F 151  is stopped. 
     After the raising operation of the tray  302  is performed by the lifter motor M 5 , the sheet existence detecting sensor  606  outputs the stop signal. Alternatively, the floatation lower-limit sensor  607  or the floatation upper-limit sensor  608  may be used to output the stop signal. 
     (Flowchart of Adjustment Mode) 
     The operation concerning the adjustment mode will be described with reference to a flowchart of  FIG. 17 . 
     The operations of the sheet feeding apparatus  3000  and loosening fan F 151  after the loosening fan F 151  is transferred to the adjustment mode after the power is turned on, after predetermined number of sheets are conveyed by the sheet feeding apparatus  3000 , or after a predetermined time elapses will mainly be described. 
     In the rotating-speed adjustment mode of the loosening fan F 151 , the lifter motor M 5  controlling the tray  302  starts the lowering operation of the tray  302  (S 101 ). When the tray  302  reaches the lower-position detecting sensor  605  (S 102 ), the lifter motor M 5  is stopped. The sheet existence detecting sensor  606  detects the presence or absence of the sheet (S 103 ). When the sheet existence detecting sensor  606  detects the presence of the sheet, the warning is displayed on the operation screen as shown in  FIG. 18  (S 116 ). The sheet accommodation portion is opened to remove the several sheets loaded on the tray  302 , and the sheet accommodation portion is closed, which starts a series of the processes from the step S 101 . 
     On the other hand, when the sheet existence detecting sensor  606  detects the absence of the sheet, the loosening fan F 151  is driven. In the case where the plural loosening fans are continuously connected, the plural loosening fans are controlled so as to be simultaneously operated (S 104 ). After the predetermined time elapses since the operation of the loosening fan F 151  is started (S 105 ), the rotating speed adjustment of the loosening fan F 151  is started (S 106 ). After the rotating speed adjustment of the loosening fan F 151  is started, it is determined whether or not the rotating speed of the loosening fan F 151  falls within the predetermined range of the target value within the predetermined time (S 107 ). When the rotating speed of the loosening fan F 151  does not fall within the predetermined range of the target value within the predetermined time (S 112 ), the rotating speed adjustment of the loosening fan F 151  is ended, and the operation of the loosening fan F 151  is stopped (S 113 ). Then, as shown in  FIG. 19 , the warning indicating that the rotating speed adjustment of the loosening fan F 151  fails is displayed (S 114 ). In  FIG. 19 , the rotating speed of the fan is adjusted again. Alternatively, an error message may be displayed. The warning indicating that the rotating speed adjustment fails may be displayed before operation stop timing of the loosening fan F 151 . 
     On the other hand, when the rotating speed of the loosening fan F 151  falls within the predetermined range of the target value within the predetermined time (S 107 ), the rotating speed adjustment of the loosening fan F 151  is ended, and the operation of the loosening fan F 151  is stopped (S 108 ). Then, the tray is lifted (S 109 ). When the sheet existence detecting sensor  606  detects the presence of the sheet (S 110 ), the lifter motor M 5  is stopped to stop the tray  302  (S 111 ), which transfers to the standby state. Therefore, the feeding can be started in response to the feeding start signal. 
     Thus, the rotating speed can be adjusted such that the wind pressure necessary for the fan is obtained by including the rotating speed adjustment mode of the loosening fan. Therefore, the rotating speed can be set such that the loosening fan becomes the optimum air quantity (wind pressure) irrespective of the fluctuation of the fan, the aged deterioration of the fan characteristics, and the voltage drop caused by the bundle conductors. The loosening fan can be stabilized at the optimum rotating speed. In the configuration in which plural fans are continuously connected, the range of the target value is set to adjust the rotating speed in each fan based on the relationship between the fan rotating speed and the fan wind pressure, which allows the optimum wind pressure to be set in each fan. 
     In the above embodiment, the tray  302  is lowered to the lower position in the rotating speed adjustment mode, and the rotating speed adjustment of the loosening fan F 151  is started when the sheet existence detecting sensor  606  detects the absence of the sheet. Alternatively, following may be applicable. That is, the tray  302  is lowered in the rotating speed adjustment mode, the rotating speed adjustment may be started when the sheet loading position detecting sensor  609  detects the uppermost surface of the sheet stack S supported by the tray  302 . In this case, because the uppermost surface of the sheet stack S is already located below the detection position of the sheet existence detecting sensor  606 , it is not necessary that the rotating speed be adjusted based on the detection of the sheet existence detecting sensor  606 . That is, when the sheet loading position detecting sensor  609  detects the position of the uppermost surface of the sheet stack S supported by the tray  302 , the sheet stack S is not located in front of the air outlet of the loosening nozzle  151  of the loosening fan F 151 . In this case, when the lower-position detecting sensor  605  detects the tray  302  before the sheet loading position detecting sensor  609  detects the uppermost surface of the sheet stack S, the control is performed based on the detection of the sheet existence detecting sensor  606  in the above embodiment. 
     The rotating speed adjustment of the loosening fan F 151  may be started as follows. The lifting and lowering of the tray  203  are counted with a counter to detect the position in the height direction of the tray  203 . That is, the position in the height direction of the tray  203  can be detected in the form of the number of counts using the encoder provided in the lifter motor M 5  or a stepping motor which is of the lifter motor. The number of counts is set to zero at the lower position, and the number of counts is incremented as the tray  203  is lifted. In the rotating speed adjustment mode, the tray  302  is lowered at the predetermined number of counts. At this point, the number of counts is a value when the sheet stack S loaded on the tray  302  is eliminated in front of the air outlet of the loosening nozzle  151  of the loosening fan F 151 , the number of counts can previously be set. In this case, when the lower-position detecting sensor  605  detects the tray  302  before the number of counts reaches the predetermined value, the control is performed based on the detection of the sheet existence detecting sensor  606  of the above embodiment. 
     In the above embodiment, the sheet feeding apparatus or the sheet insertion apparatus includes two sheet feeding portions having the air separating and feeding mechanisms. The number of sheet feeding portions having the air separating and feeding mechanisms is not limited to two, but any number of sheet feeding portions may be used as needed. 
     In the embodiment, the sheet feeding apparatus provided on the upstream side in the sheet conveyance direction of the image forming apparatus body and the sheet insertion apparatus provided on the downstream side in the sheet conveyance direction are shown as an example of the sheet feeding apparatus having the sheet loosening fan (air separating and feeding mechanism). However, the invention is not limited to the above embodiment. For example, the invention can be applied to the sheet feeding apparatus which is integral with the image forming apparatus body. 
     In the embodiment, the sheet feeding apparatus separates and feeds the sheet of the recording target one by one. However, the invention is not limited to the above embodiment, but the invention can effectively be applied to the sheet feeding apparatus which separates and feeds the sheet of the reading target one by one. 
     This application claims the benefit of Japanese Patent Applications No. 2006-101824, filed Apr. 3, 2006 and 2007-076661 filed Mar. 23, 2007 which are hereby incorporated by reference herein in their entirety.