Sheet feeding apparatus and image forming apparatus

Provided is a sheet feeding apparatus capable of reliably feeding thin sheets in a separated state and an image forming apparatus including the same.A floating preventing member which regulates an upward movement of an uppermost sheet floated by air is provided so as to be lifted and lowered between a tail end regulating plate regulating the position of the sheet above a tray and an adsorbing and conveying portion which conveys the uppermost sheet floated by the air blowing from a downstream air blowing portion. The adsorbing and conveying portion is moved to a predetermined regulating position higher than the height position of the uppermost sheet and lower than the feeding surface of the adsorbing and conveying portion before the sheet is floated, which suppresses the movement of the sheet toward the tail end side caused by the curling of the sheet due to the air.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus and an image forming apparatus, and particularly, to a sheet feeding apparatus capable of conveying sheets in a separated state by blowing air to the sheets and an image forming apparatus including the same.

2. Description of the Related Art

Hitherto, an image forming apparatus such as a printer and a copying machine includes a sheet feeding apparatus which feeds sheets one by one from a sheet accommodating portion that accommodates a plurality of sheets. As the sheet feeding apparatus, there is known an air feeding type sheet feeding apparatus which blows air to an upper portion of a sheet bundle stacked on a tray so as to feed the sheets in a sorted state or in a floated state while being adsorbed onto an adsorbing and conveying belt disposed above the sheet.

The sheet feeding apparatus includes a tail end regulating member which regulates the tail end of the sheet bundle stacked on the tray and a tail end pressing member which is provided in the tail end regulating member so as to be movable in the vertical direction. The tail end pressing member is used to press the tail end portion of the sheet by a certain force, of which the tail end position is regulated by the tail end regulating member while being floated by the blown air, from the upper side of the sheet.

Here, since the tail end pressing member is provided, even when the uppermost sheet is floated by the air blowing from a leading end separating duct which is positioned at the sheet front end side, the tail end portion of the sheet may be pressed by the tail end pressing member from the upper side of the sheet. As a result, only the center portion of the uppermost sheet in the width direction is separated from a second sheet, and for example, when the separated uppermost sheet is adsorbed onto the adsorbing and conveying belt by a negative pressure, a gap is formed between the uppermost sheet and the second sheet so that the gap is blocked by the tail end portions of the sheets.

Then, since the gap is formed, air which flows along the gap flows throughout the entire area between the uppermost sheet and the second sheet. As a result, the uppermost sheet and the second sheet may be effectively separated from the leading ends of the sheet to the tail end thereof, which improves the sheet separating performance (see U.S. Patent Application Publication No. 2008/0088078 A1).

Incidentally, in the sheet feeding apparatus of the related art, when sorting air blows from the leading end of the sheet, the sheet is pressed toward the downstream side in the blowing direction, but the tail end portion is regulated by the tail end regulating plate and is pressed by the tail end pressing member from the upper side of the sheet. For this reason, when the sorting air blows from a leading end of a sheet having a small stiffness (stiffness degree), for example, a thin sheet called an ultrathin sheet having a basis weight of 50 g/m2or less, the sheet is floated and the leading end is pressed so as to be deviated backward.

This is because the center portion of the sheet rises when the leading end of the sheet is pressed by air while the tail end is regulated due to the small stiffness of the sheet. The state is illustrated inFIG. 14. Sheets S which are stacked on a tray12are regulated by a tail end pressing member17which is provided in a tail end regulating plate13. When sorting air and separating air blow in the directions C and D by an air blowing portion152to the leading ends of the sheets S stacked on the tray12, the center portion of the floating upper sheet rises due to the small stiffness of the sheet.

Here, when the center portion rises in this way, the upper sheet is deviated backward. At this time, when the backward deviation amount of the next sheet Sb of the uppermost sheet Sa is smaller than that of the uppermost sheet Sa, the leading end of the next sheet Sb is exposed to the adsorbing portion of the adsorbing and conveying belt21. When the adsorbing and conveying belt21adsorbs and conveys the sheet in this state, the adsorbing and conveying belt21also adsorbs the next sheet Sb together with the uppermost sheet Sa, which causes double-feeding of the sheet.

Then, when the double-feeding of the sheet occurs, a feeding failure such as skew-feeding or curling occurs on the sheet. Also, when the double-fed sheets are sent to the image forming portion, a defective image occurs. That is, when air blows to particularly thin sheets so as to feed the sheets in a separated state, there is a concern that the sheets may not be reliably fed in a separated state. Furthermore, such drawbacks also occur in a sheet feeding apparatus which sorts sheets by blowing air to a sheet bundle from the side portion thereof and feeds the sheet by a feeding roller.

Therefore, the invention is made in view of such circumstances, and provides a sheet feeding apparatus capable of feeding even thin sheets in a separated state and an image forming apparatus including the same.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a sheet feeding apparatus including a tray that supports sheets thereon and is able to be lifted and lowered, an air blowing portion provided on a downstream of the tray in a sheet feeding direction that blows air from downstream end portions of the sheets supported on the tray, and a sheet feeding portion that conveys an uppermost sheet of the sheets, supported on the tray, to which air blows. In the sheet feeding apparatus, a tail end regulating portion that comes into contact with upstream end portions of the sheets supported on the tray in the sheet feeding direction so as to regulate the positions of the sheets, a rising regulating portion that is installed above the tray so as to be able to be lifted and lowered between the tail end regulating portion and the sheet feeding portion and regulates upward rising of the uppermost sheet, a lifting and lowering portion that lifts and lowers the rising regulating portion, and a controller that controls the lifting and lowering portion and moves the rising regulating portion to a predetermined regulating position higher than the height position of the uppermost sheet and lower than a feeding surface of the sheet feeding portion before the air blowing from the air blowing portion.

According to the aspect of the invention, the rising regulating member which moves to a predetermined regulating position higher than the height position of the uppermost sheet and lower than the feeding conveying surface of the feeding portion suppresses the movement of the sheet toward the tail end side which is caused by the curling of the sheet due to the blowing air. Accordingly, even the thin sheets may be reliably fed in a separated state.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described in detail by referring to the drawings.FIG. 1is a schematic configuration diagram illustrating an image forming apparatus that includes a sheet feeding apparatus according to a first embodiment of the invention. InFIG. 1, an image forming apparatus300A is provided, and the image forming apparatus300A includes an image forming apparatus body (hereinafter, referred to as an apparatus body)300, a sheet feeding unit301, and a sheet processing apparatus304. Then, various processes such as a sheet feeding and conveying operation, an image forming operation, and a stapling operation are performed based on a sheet process setting set by a user through an operation portion4or an external host PC (not illustrated) and image information transmitted from a reader portion303or the external host PC.

The sheet feeding unit301includes a sheet feeding apparatus311which is disposed in the vertical direction. The sheet feeding apparatus311is provided with a sheet storage case11which is a sheet accommodating portion accommodating a sheet bundle and an adsorbing and conveying portion50which is a sheet feeding portion feeding the sheets accommodated in the sheet storage case11. Here, in the embodiment, the adsorbing and conveying portion50is of an air feeding type, and feeds the sheet while adsorbing the sheet on an endless belt during a sheet feeding operation.

Here, the sheet feeding unit301sequentially conveys the sheets of the respective sheet storage cases11in accordance with the sheet request information transmitted from the apparatus body300, and notifies the completion of the sheet preparation to the apparatus body300after the sheet preparation is completed. The apparatus body300receives the completion of the sheet preparation from the sheet feeding unit301, and notifies a delivery request. In accordance with each notification of the delivery request, the sheet feeding unit301sequentially feeds the sheets one by one in a separated state to the apparatus body300, ends the sheet feeding operation after the sheets are fed by the number of required sheets, and becomes a standby state.

Furthermore, the sheet which is conveyed by the adsorbing and conveying portion50of the upper sheet feeding apparatus311is fed to the apparatus body300through an upper conveying portion317and a merging and conveying portion319. Further, the sheet which is conveyed by the adsorbing and conveying portion50of the lower sheet feeding apparatus311is fed to the apparatus body300through a lower conveying portion318and the merging and conveying portion319. Furthermore, the respective conveying portions317to319are provided with conveying stepping motors (not illustrated), and these motors are controlled so as to rotate the conveying rollers of the respective portions, thereby feeding the sheets.

The upper surface of the sheet feeding unit301is provided with an escape tray101which compulsorily discharges an abnormal sheet caused by double-feeding or jamming. A full loaded state detecting sensor102is provided so as to detect a full loaded state of the sheets discharged to the escape tray101. Further, the respective conveying paths of the sheet feeding units301are provided with a plurality of conveying sensors (not illustrated), and the conveying sensors detect whether the sheets pass along the respective conveying paths.

The apparatus body300is used to form an image on the sheet fed by the sheet feeding unit301, the upper surface thereof is provided with the operation portion4through which the user sets an operation setting mode, and the upper portion thereof is provided with the reader portion303which reads out an original image. Further, the apparatus body300includes an image creating portion307which is an image forming portion including a photosensitive drum353, a laser scanner unit354, a developing portion352, an intermediate transfer belt355, and the like, a fixing portion308, a reverse conveying portion309, and the like.

Then, the apparatus body300receives the sheet from the sheet feeding unit301, and performs a sheet conveying operation by controlling the respective conveying portions provided in a conveying path391which guides the sheet to the image creating portion307. Then, an image forming operation is performed based on the image data received in the image creating portion307at the time point when the sheet is detected in an image reference sensor305. Furthermore, when a jam sensor503detects the abnormal sheet, a switching member310is switched so as to guide the sheet to an escape path390in front of the image creating portion307and to discharge the abnormal sheet to the escape tray101as a discharge portion.

Here, when the image reference sensor305detects the sheet during the image forming operation, a semiconductor laser (not illustrated) constituting the laser scanner unit354is turned on and the light quantity thereof is controlled. At the same time, a scanner motor which rotationally controls a polygon mirror (not illustrated) is controlled. Accordingly, the laser beam based on the image data is irradiated to the photosensitive drum353, and a latent image is formed on the photosensitive drum353.

Next, in the developing portion352, the latent image on the photosensitive drum353is developed by feeding a toner from a toner bottle351thereto, and the developed toner image is primarily transferred to the intermediate transfer belt355. Subsequently, by secondarily transferring the toner image transferred onto the intermediate transfer belt355to the sheet, a toner image is formed on the sheet. Furthermore, a register controller306is provided at a position directly before the secondary transfer position. Then, by using the register controller306, the correction of the skew-feeding of the sheet or the sheet conveying control of minutely adjusting the toner image formed on the intermediate transfer belt355and the sheet leading end position so as to match them each other is performed on the sheet at a position directly before the transfer position without stopping the sheet.

Next, the secondarily transferred sheet is conveyed to the fixing portion308, the toner is melted by the application of a heat and a pressure to the sheet in the fixing portion308, and hence the toner is fixed onto the sheet. Furthermore, in a case where an image is printed (formed) on the rear surface of the fixed sheet or the front and rear surfaces of the sheet are reversed, the fixed sheet is conveyed to the reverse conveying portion309. In a case where the printing operation ends, the fixed sheet is conveyed to the sheet processing apparatus304at the downstream side. Then, the sheet processing apparatus304performs a desired process (folding, stapling, and perforating) set by the user in the operation portion4on the sheet which is discharged from the apparatus body300and has an image formed thereon, and sequentially outputs the sheets as a result to a discharge tray360.

FIG. 2is a diagram illustrating a configuration of the sheet feeding apparatus311which is provided in the sheet feeding unit301. The sheet storage case11includes a tray12which places the plurality of sheets S thereon in a supported state and is able to be lifted and lowered and a tail end regulating plate13which constitutes a tail end regulating portion coming into contact with the tail end of the sheet as the upstream end in the sheet feeding direction and regulating the tail end position. The sheet storage case11further includes a leading end regulating plate11awhich regulates the leading end of the sheet as the downstream end in the sheet feeding direction and side end regulating plates14and16which regulate the position of the sheet S in the width direction as a direction perpendicular to the sheet feeding direction.

Furthermore, a slide rail15is provided so as to guide the sheet storage case11when the sheet storage case is drawn out, and the sheet storage case11may be drawn out from the sheet feeding unit301by the slide rail15. Then, the sheet may be supplemented or replaced by lowering the tray12to a predetermined position when the sheet storage case11is drawn out from the sheet feeding unit301.

Further, on the upper portion of the sheet storage case11, an air feeding type sheet feeding mechanism (hereinafter, referred to as an air feeding mechanism)150is disposed so as to feed the sheets one by one in a separated state. The air feeding mechanism150includes an adsorbing and conveying portion50which adsorbs and conveys the sheets S stacked on the tray12and a downstream air blowing portion152which sorts the sheets by floating the upper portion of the sheet bundle on the tray and separates the sheets S one by one.

Here, the adsorbing and conveying portion50includes an adsorbing and conveying belt21which is suspended on belt driving rollers41and adsorbs and conveys the sheet S in the horizontal direction in the drawing and a suctioning fan36which generates a negative pressure used to adsorb the sheet S onto the adsorbing and conveying belt21. Further, the adsorbing and conveying portion50includes a suctioning duct34which is disposed inside the adsorbing and conveying belt21and suctions air through a suctioning hole (not illustrated) formed in the adsorbing and conveying belt21. In addition, the adsorbing and conveying portion50includes a suctioning shutter37which is disposed inside the suctioning duct34and enables or disables the adsorbing operation of the adsorbing and conveying belt21.

Further, the downstream air blowing portion152includes a sorting nozzle33aand a separating nozzle33bwhich blows air from leading ends to the upper portion of the sheet bundle, a sorting fan32, and a separating duct33which sends air from the sorting fan32to the respective nozzles33aand33b. Then, the air which is suctioned by the sorting fan32passes through the separating duct33, and is blown in the direction indicated by the arrow C by the sorting nozzle33aso as to float several sheets of the upper portion of the sheets S stacked on the tray12. Further, the air which is suctioned by the sorting fan32is blown in the direction indicated by the arrow D by the separating nozzle33b, and separates the uppermost sheet Sa floated by the sorting nozzle33aso as to adsorb the uppermost sheet Sa onto the adsorbing and conveying belt21.

Furthermore, a sheet surface detecting sensor18is a sheet detector which detects the sheet surface height position when the sheet is floated by the sorting fan32and detects that the sheet reaches a position where the sheet may be fed. The sheet surface detecting sensor18has three detection levels, and the sheet surface height increases as the level advances from a first level to a third level. Here, in the embodiment, the sheet surface detecting sensor18includes, for example, two detectors (not illustrated), and detects the sheet surface height position by the combination of the on and off states of two detectors.

Then, the case where the sheet surface detection is performed at the second level indicates that the sheet surface height of the floated sheet is at a position where the sheet may be appropriately adsorbed by the adsorbing and conveying belt21. Thus, in a case where the sheet surface detecting sensor18performs the sheet surface detection at the first level, the tray12needs to be controlled so that it is lifted. In a case where the sheet surface detecting sensor18performs the sheet surface detection at the third level, the tray12needs to be controlled so that it is lowered. Then, when the tray12is lifted and lowered in response to the detection level of the sheet surface detecting sensor18and the detection level of the sheet surface detecting sensor18becomes the second level, it may be determined that the sheet surface of the uppermost sheet Sa reaches an appropriate height position.

Next, the sheet feeding operation of the sheet feeding apparatus311(air feeding mechanism150) with such a configuration will be described. First, when the user extracts the sheet storage case11, sets the sheets S therein, and accommodates the sheet storage case11, the tray12starts to be lifted in the direction indicated by the arrow A illustrated inFIG. 2by a lifter motor19illustrated inFIG. 4to be described later. Then, when the distance between the sheet surface of the uppermost sheet Sa and the adsorbing and conveying belt21reaches a feeding enabled position B, a CPU1illustrated inFIG. 4to be described later stops the tray12at that position, and then prepares a sheet feeding signal that starts a feeding operation.

Next, when the sheet feeding signal is detected, the CPU1operates the sorting fan32so that air is blown by the sorting nozzle33aand the separating nozzle33bin the respective directions C and D, that is, a direction from the downstream end of the sheet bundle in the sheet feeding direction toward the upstream in the sheet feeding direction. Accordingly, several upper sheets of the sheet bundle are blown up. Further, the CPU1operates the suctioning fan36, so that air starts to blow in the direction indicated by the arrow F. At this time, since the suctioning shutter37is still closed, the uppermost sheet Sa is not adsorbed onto the adsorbing and conveying belt21.

Next, when several upper sheets are stably floated after a predetermined time elapses from the detection of the sheet feeding signal, the CPU1drives an suctioning solenoid38to be described later so as to rotate the suctioning shutter37in the direction indicated by the arrow G. Accordingly, air is suctioned from the suctioning hole provided in the adsorbing and conveying belt21, thereby generating an adsorbing force. Then, the uppermost sheet Sa is adsorbed onto the adsorbing and conveying belt21by the adsorbing force and the separating air from the separating nozzle33b.

Subsequently, the CPU1drives a feeding motor44illustrated inFIG. 4to be described later so as to rotate a belt driving roller41in the direction indicated by the arrow J. Accordingly, the uppermost sheet Sa is fed in the direction indicated by the arrow K while being adsorbed onto the adsorbing and conveying belt21, and then is sent toward the image forming portion by a pair of drawing rollers42rotating in the directions indicated by the arrows P and M. Furthermore, a pass sensor43is provided at the downstream side of the pair of drawing rollers42, and the CPU1monitors the passage of the sheet Sa through the pass sensor43.

Incidentally, in some cases, a sheet called an ultrathin sheet may be fed of which the length in the sheet feeding direction is long, the basis weight is 50 g/m2or less, and the stiffness is small. In a case where such a sheet is fed, as illustrated inFIG. 14, the leading end of the uppermost sheet Sa is pressed to the downstream side in the blowing direction by the sorting air so that the center portion rises and the leading end is deviated backward from the leading end regulating plate11adue to the low stiffness of the sheet.

Therefore, in the embodiment, a floating preventing member30which constitutes a rising regulating portion regulating the upper rising portion of the uppermost sheet is disposed in parallel to the sheet surface from the upstream end surface of the adsorbing and conveying portion50in the sheet feeding direction to the downstream end surface of the tail end regulating plate13. Furthermore, the length of the floating preventing member30in the sheet main scanning direction is set to the minimum length of the sheet to be conveyed, and is a length corresponding to A5R in the embodiment.

Further, the floating preventing member30is provided so as to be lifted and lowered in the direction indicated by the arrow E illustrated inFIG. 2by a preventing motor31rotatable forward and backward as the lifting and lowering portion, and moves to a retracting position which does not interfere with the sheet storage case11illustrated inFIG. 2when the sheet storage case11is drawn out. Further, when the sheet storage case11is accommodated, the floating preventing member30is lowered to a predetermined height position X as illustrated inFIG. 3by the forward rotation of the preventing motor31. Here, the predetermined height position X as a predetermined regulating position is controlled by the reference surface as the sheet facing surface of the floating preventing member30, and is a position where the reference surface is present between the initial sheet surface position of the uppermost sheet Sa indicated by B ofFIG. 2before the air sortation and the adsorbing surface of the adsorbing and conveying belt21.

FIG. 4is a control block diagram illustrating the sheet feeding apparatus311according to the embodiment. InFIG. 4, the CPU1is a controller which controls the sheet feeding apparatus311, and in the embodiment, the CPU1is provided in the apparatus body300. The CPU1is connected with an exclusive ASIC2which drives various loads by outputting a driving start command to a driving circuit driving various loads of the sheet feeding apparatus311such as a motor or a fan.

Further, the CPU1is connected with an operation portion (DISP)4as a sheet information setting portion through which sheet information on the size of the sheet, the basis weight thereof, the surface property thereof, and the like may be input. Further, the CPU1is connected with a storage unit (memory)3which stores a target value or a PWM value used to adjust the fan and various data input through the operation portion4.

Then, the CPU1adjusts the distance B between the adsorbing and conveying belt21and the uppermost sheet Sa of the sheet storage case11in response to the sheet information input by the user from the operation portion4by referring to the data stored inside the storage unit3. Furthermore, instead of the operation portion4, a detection portion (not illustrated) may be provided which detects at least one of the sheet size information, the basis weight information, and the surface property information as the sheet information, and the sheet information may be input to the CPU1from the detection portion as the input portion.

The ASIC2is connected with a sheet accommodating portion opening and closing sensor48which detects the opening and closing state of the sheet storage case11and lower and upper position detecting sensors55and57which detect the position of the tray12inside the sheet storage case11. Further, the ASIC2is connected with the sheet surface detecting sensor18which detects the upper surface of the sheet stacked on the tray12and a sheet presence detecting sensor56which detects the presence of the sheet on the tray12.

Further, the ASIC2is connected with the pass sensor43and an adsorbing completing sensor58which monitors a negative pressure state inside the suctioning duct when the sheet is adsorbed by the suctioning fan36and detects that the adsorption of the sheet is completed. Then, the ASIC2outputs a driving start command to the driving circuit driving the respective loads of the sheet feeding apparatus311, and also performs a PWM control so that the fans rotate at the target number of rotations by receiving the rotation number signals (FG) of the sorting fan32and the suctioning fan36.

Furthermore, inFIG. 4, a sorting fan driving circuit (driver)22transmits a PWM signal output from the ASIC2to the sorting fan32and supplies power thereto. A suctioning fan driving circuit (driver)40transmits a PWM signal output from the ASIC2to the suctioning fan36and supplies power thereto. A preventing motor driving circuit (driver)29transmits a PWM signal output from the ASIC2to the preventing motor31and supplies power thereto.

A driving circuit (driver)39is provided for the suctioning solenoid38which opens and closes the suctioning shutter37inside the suctioning duct34, and a driving circuit (driver)46drives the feeding motor44which drives the belt driving roller41. A driving circuit (driver)47drives a drawing motor45which drives the pair of drawing rollers42.

The feeding motor44, the drawing motor45, and the preventing motor31are pulse motors, and control pulses are given from the ASIC2to the respective driving circuits20,46, and47, so that the motor rotation amounts thereof are controlled by the number of pulses. A driving circuit (driver)20drives the lifter motor19as the tray lifting and lowering portion which lifts and lowers the tray12. The lifter motor19is a DC motor, and the driving state is controlled in the on and off states.

Furthermore, in the embodiment, various loads of the sheet feeding apparatus311such as the motor, the fan, and the sensor are controlled through the exclusive ASIC2from the CPU1, but may be directly controlled by the CPU1. Further, in the embodiment, the operation portion4is provided as the setting portion through which the sheet information such as the size of the sheet, the basis weight thereof, and the surface property thereof may be input, and the storage unit3which stores a target value or a PWM value used for adjusting the fan and various data items input through the operation portion4is directly connected to the CPU1. However, the different device of the image forming apparatus300A, for example, the operation portion4may be used as the storage unit so as to input and store the sheet information.

Incidentally, when the sorting air is blown to the sheet bundle, a force is generated which presses the upper sheet toward the sheet tail end by the sorting air. At this time, in the case of the sheet having a small stiffness, as illustrated inFIG. 14, the center portion of the sheet rises, which may cause a double-feeding of the sheet.

Therefore, in the embodiment, when the sheet is fed, the CPU1as the controller drives the preventing motor31through the ASIC2, so that the floating preventing member30is lowered to the predetermined height position X illustrated inFIG. 3. Accordingly, even when a sheet having a very low stiffness is fed, the floating preventing member30which is disposed above the tray12may suppress the movement of the upper sheet toward the tail end which is caused when the sheet rises upward due to the sorting air.

Next, the sheet conveying operation of the sheet feeding apparatus311with such a configuration will be described by referring to the flowchart illustrated inFIG. 5. Furthermore, the flowchart starts from a state where the tray12is lifted in the direction indicated by the arrow A ofFIG. 2by the lifter motor19and stops at a position where the distance between the adsorbing and conveying belt21and the uppermost sheet Sa becomes B so as to wait for a feeding signal.

When the CPU1receives the feeding signal in this state, the CPU1inputs a control signal to the suctioning fan driving circuit40so as to drive (turn on) the suctioning fan36(S101). In the same way, the CPU1inputs a control signal to the preventing motor driving circuit29so as to drive the preventing motor31at a predetermined number of pulses, whereby the floating preventing member30is dropped so as to be installed at the predetermined height position X illustrated inFIG. 3(S103). Subsequently, the CPU1inputs a control signal to the sorting fan driving circuit22so as to drive (turn on) the sorting fan32, whereby the air sortation starts (S104). Here, since the floating preventing member30is disposed at the predetermined height position at the time point at which the air sortation starts, even when the sheet is pressed toward the sheet tail end, it is possible to prevent the sheet from rising.

Subsequently, the position of the sheet surface of the uppermost sheet Sa becomes the position in which the distance between the adsorbing and conveying belt21and the sheet surface becomes B′ illustrated inFIG. 3by the air sortation, and the CPU1waits until the sheet surface detection using the sheet surface detecting sensor18becomes stable (S105). Here, the sheet surface detecting sensor18has three detection levels as described above, and when the sheet surface detection at the second level is detected, the CPU1determines that the sheet surface detection is stable (Y in S105). That is, the CPU determines that the sheet surface of the uppermost sheet Sa reaches an appropriate height position.

Then, the CPU1inputs a control signal to the suctioning solenoid driving circuit39so as to drive the suctioning solenoid38based on the determination, whereby the suctioning shutter37inside the suctioning duct34is opened (S106). Accordingly, air is suctioned from the suctioning hole provided in the adsorbing and conveying belt21, whereby a suctioning force is generated. Then, the uppermost sheet Sa is adsorbed to the adsorbing and conveying belt21by the suctioning force and the separating air from the separating nozzle33b.

Next, when the CPU1monitors the output from the adsorbing completing sensor58and determines that the adsorption of the uppermost sheet Sa is completed (Y in S107), the CPU1inputs a control signal to the feeding motor driving circuit46so as to drive the feeding motor44, whereby the rotation of the adsorbing and conveying belt21starts (S108). In addition, the CPU1inputs a control signal to the drawing motor driving circuit47so as to drive the drawing motor45, whereby the rotation of the pair of drawing rollers42starts (S109). Accordingly, the sheet is discharged onto the sheet conveying path.

Subsequently, when the CPU1monitors the output from the pass sensor43and determines that the sheet discharged onto the sheet conveying path passes by the pass sensor43(Y in S110), the rotation of the adsorbing and conveying belt21stops (S111). In addition, the CPU1stops the rotation of the pair of drawing rollers42(S112), and finally closes the suctioning shutter37inside the suctioning duct34(S113). Accordingly, the feeding of the uppermost sheet Sa ends.

Next, when there are plural sheets to be fed and the next sheet is fed, that is, the next sheet is present (Y in S114), the routine returns to S106so as to perform the same process. When the next sheet is not present (N in S114), that is, the feeding operation ends in this state, the CPU1inputs a control signal to the suctioning fan driving circuit40so as to stop (turn off) the suctioning fan36(S115). In the same way, the CPU1inputs a control signal to the sorting fan driving circuit so as to stop the sorting fan32, whereby the air sortation ends (S116). In addition, the CPU1inputs a control signal to the preventing motor driving circuit29so as to drive the preventing motor31in the reverse rotation direction at a predetermined number of pulses, whereby the floating preventing member30moves to the retracting position (S117) and the sheet feeding operation ends.

On the other hand, when the sheet surface detection is not stable (N in S105), that is, the sheet surface of the uppermost sheet Sa does not reach an appropriate height position, the CPU1performs a movement control (a height position control) on the tray12so that the tray12is lifted and lowered based on the detection result of the sheet surface detecting sensor18(S201). Here, when the lifter motor19is driven so that the tray12is lifted and lowered, for example, only the tray12is lifted, the sheet on the tray12collides with the floating preventing member30. Further, when only the tray12is lowered, the gap between the floating preventing member30and the sheet on the tray12is widened, so that the movement of the upper sheet toward the tail end may not be suppressed.

Therefore, when the tray12is lifted and lowered, the driving amount equal to the driving amount of the lifter motor19is given to the preventing motor31so that the floating preventing member30and the tray12are simultaneously lifted and lowered, whereby the gap between the floating preventing member30and the sheet on the tray12is maintained to be constant. Furthermore, when the floating preventing member30and the tray12are simultaneously lifted, that is, the floating preventing member30is lifted so as to be synchronized with the tray12in this way, the floating preventing member30may be lifted so as to be higher than the adsorbing surface of the adsorbing and conveying belt21as the maximum upper limit position of the predetermined height position X.

Here, when the floating preventing member30is lifted in this way, the sheet on the lifted tray comes into contact with the adsorbing and conveying belt21so that the sheet may be deviated therefrom. For this reason, in the embodiment, it is determined whether the floating preventing member30is out of the range of the predetermined height position X by giving the driving amount equal to the driving amount of the lifter motor19to the preventing motor31during the movement control of the tray12. Furthermore, as described above, the predetermined height position X indicates a position from the initial sheet surface position of the uppermost sheet Sa before the air sortation to the adsorbing surface of the adsorbing and conveying belt21, where the sheet facing surface of the floating preventing member30is used as the reference surface. Then, when the position of the floating preventing member30which moves together with the tray12is present in the position range (the installation range) (Y in S202), a synchronous movement control is performed which moves the floating preventing member30in the same direction by the same movement amount as that of the tray12at the same time (S203), and the routine returns to S105.

On the other hand, when it is assumed that the position of the floating preventing member30which moves together with the tray12is present out of the installation range (N in S202), a floating preventing member upper limit relating movement control is performed (S204). That is, when it is assumed that the position of the floating preventing member30is present out of the installation range, the tray12is lifted, and the floating preventing member30reaches the adsorbing surface of the adsorbing and conveying belt21as the maximum upper limit position of the predetermined height position X. Then, the CPU1stops the floating preventing member30so as to wait at the position. Accordingly, even when the height of the sheet which is floated by the sorting air becomes higher due to the lifting of the tray12, the sheet facing surface of the floating preventing member30is positioned so as to be lower than the adsorbing surface of the adsorbing and conveying belt21, whereby the sheet S may be prevented from being caught.

Further, when the movement direction of the tray12is the lowering direction, the floating preventing member30is also lowered by the same amount in accordance with the movement amount of the lifter motor19. Then, when the sheet height position is lowered in this way, the floating preventing member30is controlled so that it is lowered in accordance with the sheet height position, whereby the floating preventing member30is disposed so that the gap between the floating preventing member and the sheet surface is constant at all times. For this reason, it is possible to prevent the sheet from rising, and hence to reliably adsorb and convey even the thin sheets in a separated state.

As described above, in the embodiment, when the sheet is fed, the floating preventing member30is moved to a position higher than the height position of the uppermost sheet and lower than the adsorbing surface of the adsorbing and conveying belt21. Then, if the floating preventing member30is moved in this way, even when a sheet having a very low stiffness is fed, it is possible to suppress the movement of the upper sheet toward the tail end which is generated when the sheet rises due to the sorting air by using the floating preventing member30. Accordingly, even in a case of a sheet having a very low stiffness such as an ultrathin sheet, double-feeding of the upper sheet and the lower sheet is not performed, thereby preventing a feeding failure such as skew-feeding, curling, and an adsorbing failure from occurring in the sheet.

Next, a second embodiment of the invention will be described.FIG. 6is a diagram illustrating a configuration of a sheet feeding apparatus according to the embodiment. Furthermore, inFIG. 6, the same reference numeral as that ofFIG. 2indicates the same or corresponding portion.

InFIG. 6, a floating preventing member30A is provided, and the bottom surface of the floating preventing member30A includes a surface which is parallel to the sheet upper surface and a sloped surface which is disposed on the downstream side of the sheet feeding direction so as to be inclined toward the adsorbing and conveying portion50. Further, the floating preventing member30A is provided so as to be lowered to a predetermined height position when the sheet storage case11is accommodated.

Here, the predetermined height position is set so that the height position of the downstream end of the sloped surface of the bottom surface in the sheet feeding direction becomes a predetermined height position Y which is present in the range of the distance B′ between the position of the sheet surface of the uppermost sheet Sa floated by the air sortation and the adsorbing surface of the adsorbing and conveying belt21. Further, the position of the parallel surface of the bottom surface is set to a predetermined height position Z so that the distance between the position of the sheet surface of the uppermost sheet Sa before the air sortation and the adsorbing surface of the adsorbing and conveying belt21is present in the range B illustrated inFIG. 2.

Then, when the floating preventing member30A is configured in this way, even when a force is generated which presses the upper sheet toward the sheet tail end by the sorting air, it is possible to suppress the upper sheet from moving toward the sheet tail end portion by using the floating preventing member30A. Further, as in the embodiment, it is possible to sufficiently widen the air which is blown from the sheet leading end portion toward the sheet tail end by forming the sloped surface which is inclined toward the sheet feeding portion in the bottom surface of the floating preventing member30A. Accordingly, even in a case of an ultrathin sheet, double-feeding of the upper sheet and the lower sheet is not performed, thereby preventing a feeding failure such as skew-feeding, curling, and an adsorbing failure from occurring in the sheet.

Next, a third embodiment of the invention will be described. In the embodiment, the floating preventing member is selectively lifted and lowered in response to the basis weight of the sheet and the size of the sheet. That is, only in the case of the sheet which has a very thin thickness and a low stiffness and moves in the direction opposite to the sheet feeding direction due to the blowing air, the floating preventing member is installed at a predetermined height position.

Next, the sheet feeding operation of the sheet feeding apparatus according to the embodiment will be described by referring to the flowchart illustrated inFIG. 7. Furthermore, the control starts from a state where the tray12is lifted in a direction indicated by the arrow A ofFIG. 2by the lifter motor19, stops at a position where the distance between the adsorbing and conveying belt21and the uppermost sheet becomes B, and waits for a feeding signal.

When the CPU1receives the feeding signal in this state, the CPU1inputs a control signal to the suctioning fan driving circuit40so as to drive (turn on) the suctioning fan36(S101). Next, the CPU1refers to the storage unit3which stores the sheet information such as the size of the sheet, the basis weight thereof, and the surface property thereof input through the operation portion4(S102a). Then, the CPU1determines whether the basis weight of the sheet to be fed is equal to or smaller than 64 g/m2and the sheet size is larger than the size A4 based on the sheet information (S102b). Then, when the basis weight of the sheet to be fed is equal to or smaller than 64 g/m2and the size thereof is larger than the size A4 (Y in S102b), the CPU1installs the floating preventing member30at a predetermined height position (S103).

Further, when the basis weight of the sheet to be fed is equal to or smaller than 64 g/m2and the size thereof is other than the size A4 (N in S102b), the CPU1waits the floating preventing member30at the retracting position. Furthermore, since the following process is controlled in the same way as that of the flowchart illustrated inFIG. 5, the description thereof will not be repeated. However, in S117, the retracting operation is performed only when the floating preventing member30is installed in S103.

In this way, it is possible to prevent the unnecessary setting operation of the floating preventing member30by installing the floating preventing member30only for the sheet which has a size larger than the size A4, has a basis weight equal to or smaller than 64 g/m2, has a very thin thickness, and a low stiffness. Furthermore, in the embodiment, the floating preventing member30which has the shape of the first embodiment is used, but the floating preventing member30which has the shape of the second embodiment may be used.

Further, instead of the operation portion4, a detection portion (not illustrated) may be provided which detects one of the sheet size information, the basis weight information, and the surface property information as the sheet information, and the sheet information may be input to the CPU1from the detection portion as the input portion. Then, the CPU1automatically determines the size of the sheet, the basis weight thereof, and the surface property thereof based on the sheet information.

Next, a fourth embodiment of the invention will be described.FIG. 8is a diagram illustrating a configuration of a sheet feeding apparatus according to the embodiment. Furthermore, inFIG. 8, the same reference numeral as that ofFIG. 2indicates the same or corresponding portion.

InFIG. 8, a floating preventing portion30B is provided, and the floating preventing portion30B includes a first floating preventing member30aand a second floating preventing member30bas two (plural) rising regulating members. Furthermore, the first floating preventing member30awhich is positioned at the downstream side in the sheet conveying direction may be selectively moved by a first preventing motor31ain the direction indicated by the arrow E, and the second floating preventing member30bwhich is positioned at the upstream side in the sheet conveying direction may be selectively moved by a second preventing motor52in the direction indicated by the arrow E.

Further, the bottom surface of the first floating preventing member30ais inclined toward the adsorbing and conveying portion50, and the bottom surface of the second floating preventing member30bis parallel to the sheet upper surface. In addition, the first floating preventing member30ais disposed above the tail end of the sheet which has a sheet size larger than A4 and smaller than A3, and the second floating preventing member30bis disposed above the tail end of the sheet which has a sheet size larger than A3. Then, the first and second floating preventing members30aand30brespectively move to the upper retracting positions which do not interfere with the sheet storage case11when the sheet storage case11is drawn out, and are respectively lowered to the predetermined height positions Y and Z in a state where the sheet storage case11is accommodated.

Furthermore, the predetermined height position Y is set to a position in which the height position of the downstream end of the sloped surface of the bottom surface of the first floating preventing member30ain the sheet feeding direction is in the range of the distance B′ between the position of the sheet surface of the uppermost sheet Sa floated by the air sortation and the adsorbing surface of the adsorbing and conveying belt21. Further, the predetermined height position Z is set so that the position of the parallel surface of the bottom surface of the second floating preventing member30bbecomes a predetermined height position in which the distance between the position of the sheet surface of the uppermost sheet Sa before the air sortation and the adsorbing surface of the adsorbing and conveying belt21is in the range of B illustrated inFIG. 2.

FIG. 9is a control block diagram illustrating a sheet feeding apparatus according to the embodiment. Furthermore, inFIG. 9, the same reference numeral as that ofFIG. 4indicates the same or corresponding portion. InFIG. 9, a first driving circuit29is provided which drives the first preventing motor31adriving the first floating preventing member30aso as to be moved. A second driving circuit53is provided which drives the second preventing motor52driving the second floating preventing member30bso as to be moved. The first and second preventing motors31aand52are plus motors, and a control pulse is given from the ASIC2to the driving circuits29and53respectively so that the rotation amount of the motor is controlled by the number of pulses.

Next, the sheet feeding operation of the sheet feeding apparatus according to the embodiment will be described by referring to the flowchart illustrated inFIG. 10. Furthermore, the control starts from a state where the tray12is lifted in the direction indicated by the arrow A ofFIG. 2by the lifter motor19, stops at a position where the distance between the adsorbing and conveying belt21and the uppermost sheet becomes B, and waits for a feeding signal.

When the CPU1receives the feeding signal in this state, the CPU1inputs a control signal to the suctioning fan driving circuit40so as to drive (turn on) the suctioning fan36(S101). Next, the CPU1refers to the storage unit3which stores the sheet information such as the size of the sheet, the basis weight thereof, and the surface property thereof input through the operation portion4(S1021). Then, the CPU1determines whether the basis weight of the sheet to be fed is equal to or smaller than 64 g/m2and the sheet size is larger than the size A4 based on the sheet information (S1022).

Here, when the basis weight of the sheet to be fed is equal to or smaller than 64 g/m2and the size thereof is larger than the size A4 (Y in S1022), the CPU1determines whether the size of the next sheet is equal to or larger than A3 which is larger than A4 (S1023). Then, when the size of the sheet is smaller than A3 (Y in S1023), only the first floating preventing member30ais installed at a predetermined height position (S1024). Furthermore, as described above, the first floating preventing member30ais disposed above the tail end of the sheet which is larger than A4 and is smaller than A3. Accordingly, when the first floating preventing member30ais installed at the predetermined height position Y, it is possible to prevent the sheet which is larger than A4 and is smaller than A3 from rising upward, and hence reliably adsorb and convey even the thin sheets in a separated state.

Further, when the size of the sheet is A3 or is larger than A3 (N in S1023), the first and second floating preventing members30aand30bare installed at the predetermined height positions Y and Z (S1025). Here, as described above, the second floating preventing member30bis disposed above the tail end of the sheet which is larger than A3. Accordingly, when the first and second floating preventing members30aand30bare installed at the predetermined height positions, it is possible to prevent the sheet which is larger than A3 from rising upward, and hence reliably adsorb and convey even the thin sheets in a separated state.

Further, when the basis weight of the sheet to be fed is equal to or smaller than 64 g/m2and the size thereof is other than the size A4 (N in S1022), the first and second floating preventing members30aand30bare waited at the retracting positions. Further, since the following process is controlled in the same way as that of the flowchart illustrated inFIG. 5, the description thereof will not be repeated. However, in S202and S203, the floating preventing member indicates all floating preventing members which are installed in the processes of S1021to S1025. Further, in S117, the retracting operation is performed only when at least one of the floating preventing members30aand30bis installed in the processes of S1021to S1025.

In this way, according to the embodiment, the first and second floating preventing members30aand30bare selectively moved to a position higher than the height position of the uppermost sheet and lower than the adsorbing surface of the adsorbing and conveying belt21in response to the sheet size. Then, it is possible to prevent the movement of the upper sheet toward the tail end which is generated when the sheet rises upward due to the sorting air by selectively moving the first and second floating preventing members30aand30bin this way. Further, since the floating preventing portion30B includes the first and second floating preventing members30aand30b, the motor to be used may be decreased in size and may be decreased in cost.

Incidentally, in the description so far, the sheet feeding apparatus which includes the adsorbing and conveying portion50adsorbing and conveying the sheet has been mentioned, but the invention is not limited thereto. That is, the invention may be also applied to a sheet feeding apparatus which sorts the sheets by blowing air to the upper portion of the sheet bundle and feeds the sheets by the feeding roller.

Next, a fifth embodiment of the invention will be described.FIG. 11is a diagram illustrating a configuration of a sheet feeding apparatus in which air is blown to the upper portion of the sheet bundle according to the embodiment so as to sort the sheets and the sheets are fed by the feeding roller. Furthermore, inFIG. 11, the same reference numeral as that ofFIG. 2indicates the same or corresponding portion.

InFIG. 11, a feeding unit1300is provided, and the feeding unit1300includes a pickup roller1301as a feeding roller, a sheet feeding roller1302, a separating roller1303pressing the sheet feeding roller1302, and a pair of drawing rollers42.

Here, the pickup roller1301is rotatably supported by a front end portion of a pickup arm1304which is rotatable in the direction indicated by H in the drawing, and is lowered with the downward rotation of the pickup arm1304during the sheet feeding operation so as to come into contact with the sheet surface. Then, the uppermost sheet Sa which is sent out by the pickup roller1301from the sheet storage case11is conveyed to a nip portion between the sheet feeding roller1302and the separating roller1303, is separated from the lower sheet, and is sent to the pair of drawing rollers42. Furthermore, the pickup arm1304is rotated in the vertical direction by turning on or off a pickup solenoid1403to be described later illustrated inFIG. 12.

Furthermore, in the embodiment, the downstream air blowing portion152includes the sorting nozzle33awhich blows air from the leading end to the upper portion of the sheet bundle, the sorting fan32, and the separating duct33which sends air from the sorting fan32to the sorting nozzle33a. Then, the air which is suctioned by the sorting fan32passes through the separating duct33, and is blown in the direction indicated by the arrow C by the sorting nozzle33a, so that several sheets of the upper portion of the sheets S stacked on the tray12are sorted.

Further, inFIG. 11, a floating preventing member30C is provided, and the floating preventing member30C is disposed in parallel to the sheet surface from the upstream end surface of the feeding unit1300in the sheet conveying direction to the downstream end surface of the tail end regulating plate13. Further, the length of the floating preventing member30C in the sheet main scanning direction is set to the minimum length of the sheet to be conveyed, and is set to the length corresponding to A5R in the embodiment.

In addition, the floating preventing member30C is configured to be movable in the direction indicated by E in the drawing by the preventing motor31. Then, the floating preventing member30C is moved to the upper retracting position which does not interfere with the sheet storage case11when the sheet storage case11is drawn out, and is lowered so as to be installed at the predetermined height position X which does not contact the uppermost sheet Sa in a state where the sheet storage case11is accommodated.

Furthermore, the predetermined height position X is a position in which the position of the sheet facing surface of the floating preventing member30C is present in a gap between the position of the sheet surface of the uppermost sheet Sa before the air sortation and the lower surface of the roller when the pickup roller1301indicated by the solid line and serving as the feeding and conveying surface is present at the retracting position during a non-feeding operation, where the gap is indicated by G.

FIG. 12is a control block diagram illustrating a sheet feeding apparatus according to the embodiment. Furthermore, inFIG. 12, the same reference numeral as that ofFIG. 4indicates the same or corresponding portion. InFIG. 12, a solenoid driving circuit1404is provided which drives the pickup solenoid1403lifting and lowering the pickup roller1301through the pickup arm1304. A driving circuit1402is provided which drives the feeding motor1401driving the pickup roller1301, the sheet feeding roller1302, and the separating roller1303. Furthermore, the CPU1adjusts the distance G between the pickup roller1301and the uppermost sheet Sa of the sheet storage case11in response to the sheet information which is input by the user from the operation portion4by referring to the data stored in the storage unit3.

Next, the sheet feeding operation of the sheet feeding apparatus according to the embodiment will be described by referring to the flowchart illustrated inFIG. 13. Furthermore, the control starts from a state where the tray12is lifted in the direction indicated by the arrow A ofFIG. 11by the lifter motor19, stops at a position where the distance between the pickup roller1301and the uppermost sheet Sa becomes G, and waits for a feeding signal.

When the CPU1receives the feeding signal in this state, the CPU1inputs a control signal to the preventing motor driving circuit29so as to drive (turn on) the preventing motor31at a predetermined number of pulses, whereby the floating preventing member30C is dropped and is installed at the predetermined height position X illustrated inFIG. 11(S1501). Subsequently, the CPU1inputs a control signal to the sorting fan driving circuit22so as to drive (turn on) the sorting fan32, whereby the air sortation starts (S1502). Here, when the air sortation stars, since the floating preventing member30C is disposed at the predetermined height position X, it is possible to prevent the sheet from rising due to the pressing of the sheet toward the sheet tail end. Furthermore, the air sortation is performed for a predetermined time which is determined in advance depending on the type of sheet.

Then, when a predetermined time elapses (Y in S1503), the CPU1inputs a control signal to the feeding motor driving circuit1402so as to start the driving of the feeding motor1401(S1504), whereby the pickup roller1301, the sheet feeding roller1302, and the separating roller1303are rotated at a predetermined speed. Next, the CPU1inputs a control signal to the drawing motor driving circuit47so as to start the driving of the drawing motor45(S1505), whereby the pair of drawing rollers42is rotated at a predetermined speed.

Next, the CPU1inputs a control signal to the solenoid driving circuit1404so as to drive (turn on) the pickup solenoid1403(S1506), whereby the pickup roller1301is brought into contact with the uppermost sheet Sa. Accordingly, the uppermost sheet Sa is fed by the pickup roller1301, is separated from the lower sheet by the separating portion including the sheet feeding roller1302and the separating roller1303, and is conveyed to the pair of drawing rollers42so as to be discharged to the sheet conveying path.

Subsequently, when the CPU1monitors the output from the pass sensor43and determines that the sheet discharged onto the sheet conveying path passes by the pass sensor43(Y in S1507), the CPU1turns off the pickup solenoid1403(S1508). Accordingly, the pickup roller1301is separated from the uppermost sheet Sa. Next, the CPU1stops the driving of the feeding motor1401(S1509), whereby the rotation of the pickup roller1301, the sheet feeding roller1302, and the separating roller1303stops. In addition, the CPU1stops the drawing motor45(S1510), whereby the rotation of the pair of drawing rollers42stops.

Next, when there are plural sheets to be fed and the next sheet is fed, that is, the next sheet is present (Y in S1511), the routine returns to S1504so as to perform the same process. Further, when the next sheet is not present and the feeding operation directly ends in this state, the CPU1inputs a control signal to the sorting fan driving circuit so as to stop the sorting fan32, whereby the air sortation ends (S1512). Further, the CPU1inputs a control signal to the preventing motor driving circuit29so as to drive the preventing motor31so that it rotates in the reverse rotation direction at a predetermined number of pulses, whereby the floating preventing member30C is retracted to the retracting position (S1513). Accordingly, the sheet feeding operation ends.

As described above, even when the sheets are sorted and are fed by the pickup roller1301, the floating preventing member30may suppress the movement of the sheet toward the tail end side caused by the curling of the sheet, whereby even thin sheets may be reliably fed in a separated state. That is, since the floating preventing member30moves so as to be disposed on the upper surface of the sheet, even the thin sheets may be reliably fed in a separated state regardless of the type of the sheet feeding structure.

Furthermore, in the respective embodiments described so far, an example has been described in which the invention is applied to the sheet feeding apparatus configured to feed the sheet to the image forming portion, but the invention is not limited thereto. For example, the invention may be applied to an inserter which supplies a sheet having an image formed thereon to a post-processing portion as a sheet processing portion or is disposed between an image forming portion and a post-processing portion so as to supply another sheet between the conveyed sheets having an image formed thereon in the image forming portion.

This application claims the benefit of Japanese Patent Application No. 2011-182340, filed Aug. 24, 2011, which is hereby incorporated by reference herein in its entirety.