JP2010173837A - Sheet feeder and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet feeder and an image forming device preventing double feeding of sheets regardless of the number of sheets on a tray. <P>SOLUTION: During an initial operation, when it is determined that an upper-most sheet Sa of floating sheets is positioned in an appropriate range even after predetermined time has elapsed from when air spray is started, the tray 12 is controlled to move down so that the upper-most sheet is moved out of the appropriate range and then to move up so that the upper-most sheet Sa is positioned in the appropriate range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly, to a sheet feeding and separating sheet by blowing air onto the sheet.

  2. Description of the Related Art Conventionally, image forming apparatuses such as printers and copiers include a sheet feeding device that feeds sheets one by one from a sheet storage unit that stores a plurality of sheets. As such a sheet feeding device, air is blown to the end of the sheet bundle stored in the sheet storage unit to float a plurality of sheets, and only one sheet is placed on the suction conveyance belt disposed above. There is an air feeding type that sucks and feeds (see Patent Document 1).

  FIG. 9 shows an example of such an air feeding type sheet feeding apparatus. As shown in FIG. 9, a sheet storage 11 that is a sheet storage unit in which a plurality of sheets S are stored is provided. A tray 12 on which the sheets S are stacked is provided so as to be movable up and down. In addition, on the upper portion of the sheet storage 11, a plurality of sheets are obtained by blowing air to an end portion of a bundle of sheets S on a tray, and an adsorption conveyance unit 20 including an adsorption conveyance belt 21 that adsorbs and feeds sheets S. An air blowing unit 30 is provided for floating S and separating the S one by one.

  Then, a part of the air sucked in the direction of the arrow C by the air blowing unit 30 is blown in the direction of the arrow D, so that the upper several sheets of the sheet bundle stacked on the tray 12 are floated. Further, by blowing other air in the direction of arrow E, the uppermost sheet is separated one by one from the several sheets that have floated, and is sucked onto the suction conveyance belt 21.

  Such a sheet feeding apparatus is employed in a highly productive apparatus capable of feeding 70 sheets of A4 or LTR size sheets per minute, and the tray 12 is maintained substantially horizontal by a driving means (not shown). It is often equipped with a mechanism that moves up and down in the vertical direction.

  By the way, in such a conventional air feeding type sheet feeding apparatus, there is one provided with a paper surface detection mechanism for controlling the position of the uppermost surface of the sheet stored in the sheet storage 11 (patent). Reference 2).

  FIGS. 10A and 10B are diagrams showing the configuration of such a conventional paper surface detection mechanism. As shown in FIG. 10, the sheet surface detection mechanism 49 includes a sheet surface detection sensor flag 52, a first sheet surface sensor 54 that is turned on / off (turned on / off) by rotation of the sheet surface detection sensor flag 52, and a second sheet surface detection sensor flag 52. A sheet surface sensor 55 and a sensor flag mechanism 50 are provided. The first sheet surface sensor 54 and the second sheet surface sensor 55 are photosensors and are connected to a control device (not shown).

  Here, the sheet surface detection sensor flag 52 is swingably supported by the support shaft 53. Then, a first detection unit 52B that shields the light receiving unit of the first sheet surface sensor 54, a second detection unit 52C that shields the light receiving unit of the second sheet surface sensor 55, and a sheet surface detection member 61 described later are provided. A support portion 52D that rotatably supports is provided.

  The sensor flag mechanism 50 includes a support member 60 whose one end 60 a is rotatably held inside the suction duct 22, a rotation end 60 b of the support member 60, and a support portion 52 D of the sheet surface detection sensor flag 52. And a supported sheet surface detection member 61.

  Here, the sheet surface detection member 61 is provided below the suction feeding area of the suction conveyance unit 20 so as to be movable in the vertical direction in parallel with the sheets S stacked on the tray 12. Further, the support member 60 rotatably supported in the suction duct is provided in the suction feeding area of the suction transport belt 21 from the retraction holes 51H1 formed in the gaps in the sheet width direction of the plurality of suction transport belts 21. Projects downward.

  The support member 60, the sheet surface detection sensor flag 52, and the sheet surface detection member 61 constitute a parallel link. As a result, the sheet surface detection member 61 maintains a parallel state (horizontal state) while swinging the sheet surface detection sensor flag 52 regardless of the position in the longitudinal direction of the sheet surface detection member 61. Can be moved up and down.

  Next, a paper surface control operation based on the detection by the paper surface detection mechanism 49 configured as described above will be described.

  When the sheet stored in the sheet storage case 11 is lifted by the raising of the tray 12, the upper surface of the uppermost sheet Sa contacts the sheet surface detection member 61. After that, when the tray 12 further rises, the sheet surface detection member 61 rises integrally with the uppermost sheet Sa, and the sheet surface detection sensor flag 52 is moved to the support shaft as the sheet surface detection member 61 rises. The support portion 52D swings in the upward direction around 53.

  Eventually, as shown in FIG. 11A, the distance between the upper surface of the uppermost sheet Sa raised while raising the sheet surface detection member 61 and the belt surface of the suction conveyance belt 21 becomes S1. In this state, the first sheet surface sensor 54 is shielded from light by the first detection unit 52B of the sheet surface detection sensor flag 52, and the second sheet surface sensor 55 is shielded from light by the second detection unit 52C. Output. Then, the control unit stops the tray 12 based on the ON signals from the first sheet surface sensor 54 and the second sheet surface sensor 55.

  Next, when the feeding start signal is received, the control means starts air blowing, and as shown in FIG. 11B, the upper portion SA of the sheet bundle is floated and the tray 12 is raised or lowered. Control is performed so that the uppermost sheet Sa floats in a specified area.

  Here, the position where the second sheet surface sensor 55 is shielded by the second detection unit 52B of the sheet surface detection sensor flag 52 and the second sheet surface sensor 55 is turned on is set as the lower limit of the floating region. Then, when the first sheet surface sensor 54 is ON and the ON signal of the second sheet surface sensor 55 cannot be obtained, that is, when the second sheet surface sensor 55 is OFF, it is determined as “too low” and the second The tray 12 is raised until the sheet surface sensor 55 is turned on.

  As shown in FIG. 12, when the distance between the belt surface of the suction conveyance belt 21 and the upper surface of the uppermost sheet Sa becomes smaller than SH, the light shielding by the first detection unit 52B is released, and the suction first sheet The surface sensor 54 is configured not to output an ON signal. If this position is set as the upper limit of the floating area, and the second sheet surface sensor 55 is ON and the ON signal of the first sheet surface sensor 54 cannot be obtained, it is determined that the position is too high, and the first sheet surface sensor 54 The tray 12 is lowered until becomes ON.

  The following table summarizes such a series of operations.

  Then, by raising and lowering the tray 12 based on the signals of the first and second sheet surface sensors 54 and 55 in this way, the position of the tray 12 is controlled to a position where only the uppermost sheet Sa can be separated and fed. can do. Accordingly, when the sheets are sucked by the suction conveyance belt 21, the sheets S can be separated one by one and fed toward the image forming unit, and stable sheet feeding can be performed.

JP-A-7-196187 JP 2007-276910 A

  By the way, in such a conventional sheet feeding apparatus and an image forming apparatus provided with the same, for example, as shown in FIG. 13, several sheets, for example, two sheets of the upper sheet Sa and the immediately lower sheet Sb are placed on the tray 12. May only set. Further, when the sheet feeding is finished, there are cases where only two sheets remain.

  As described above, when the number of sheets on the tray 12 is small, the position of the tray 12 becomes higher and is positioned to the side of the firing nozzle 33. Then, during the initial operation before starting the suction feeding of the sheet, if blowing air is blown by the blowing nozzle 33 in this state, a part of the blowing air comes into contact with the tray 12, and the amount of blowing air that hits the sheet decreases. . Here, when the amount of blown air hitting the sheet decreases in this way, the two sheets Sa and Sb remain in close contact with each other depending on the type, size, state, operating environment temperature, humidity, and the like of the sheet. May surface.

  In the conventional sheet feeding apparatus, in the initial operation, air is blown to temporarily float the sheet so that it exceeds the appropriate range of suction feeding by the suction conveyance unit, and then the uppermost sheet of the floating sheet Is lowered so as to be within an appropriate range.

  However, when the height of the upper sheet Sa is detected in a state where the two sheets Sa and Sb are in close contact with each other, the first and second sheet surface sensors 54 and 55 both output the ON signal, so that the tray No lowering operation of 12 is performed. In this case, since the height of the tray 12 is maintained as it is, the position of the tray 12 does not change.

  For this reason, the blowing state of blowing air by the blowing nozzle 33 does not change, and the floating state is maintained as it is. As a result, the close contact between the sheets is not eliminated, and the two sheets Sa and Sb are sucked and fed together by the suction conveyance belt 21 to cause double feeding of the sheets. As described above, conventionally, when the number of stacked sheets on the tray 12 is decreased, double feeding of sheets may occur.

  Therefore, the present invention has been made in view of such a situation, and provides a sheet feeding apparatus and an image forming apparatus that can prevent double feeding of sheets regardless of the number of sheets on the tray. It is the purpose.

  The present invention includes a tray that can move up and down to support a sheet, an air blowing unit that blows air onto the side surface of the sheet supported by the tray, and a suction conveyance that sucks and feeds the floated sheet And during the initial operation before starting the suction feeding of the sheet, after blowing the air by the air blowing unit, the sheet once floated so as to exceed the appropriate range of the suction feeding by the suction conveying unit, In a sheet feeding device that lowers the tray so that the uppermost sheet of the floating sheet is within an appropriate range, a paper surface detection mechanism that detects the upper surface of the uppermost sheet of the floating sheet, and the tray is moved up and down A lifting and lowering section that moves and floats even after a predetermined time has elapsed since the start of air blowing by a signal from the paper surface detection mechanism during the initial operation. The uppermost sheet is positioned in the appropriate range, once the tray is lowered and the uppermost sheet is moved out of the appropriate range, the tray is raised and again, The elevating part is controlled so that the uppermost sheet is positioned within an appropriate range.

  In the present invention, during the initial operation, if the uppermost sheet continues to be positioned within the proper range even after a predetermined time has elapsed since the start of air blowing, the tray is lowered once to remove the sheet on the tray. Can prevent double feeding of sheets regardless of the number of sheets

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of a printer which is an example of an image forming apparatus including a sheet feeding device according to an embodiment of the present invention.

  In FIG. 1, 100 is a printer, and 101 is a printer body. An image reading unit 130 for reading a document D placed on a platen glass 120a as a document placing table by an automatic document feeder 120 is provided on the upper portion of the printer main body 101. Below the image reading unit 130, an image forming unit 102 and a sheet feeding device 103 that feeds the sheet S to the image forming unit 102 are provided.

  Here, the image forming unit 102 is provided with a photosensitive drum 112, a developing unit 113, a laser scanner unit 111, and the like. The sheet feeding apparatus 103 is an example of a plurality of sheet storage units 11 that store sheets S such as OHT and are detachable from the apparatus main body 101 and a sheet feeding unit that sends out the sheets S stored in the sheet storage unit 11. And a suction conveyance belt 21 as a feeding belt.

  Next, an image forming operation of the printer 100 having such a configuration will be described.

  When an image reading signal is output to the image reading unit 130 from a control device shown in FIG. 3 (described later) provided in the apparatus main body 101, the image reading unit 130 reads an image. Thereafter, a laser beam corresponding to the electrical signal is emitted from the laser scanner unit 111 onto the photosensitive drum 112. At this time, the photosensitive drum 112 is charged in advance, and an electrostatic latent image is formed by irradiating light, and then the electrostatic latent image is developed by the developing device 113, thereby forming a toner image on the photosensitive drum. Is done.

  On the other hand, when a paper feed signal is output from the control device to the sheet feeding device 103, the sheet S is fed from the sheet storage unit 11. Thereafter, the fed sheet S is sent by a registration roller 117 to a transfer unit constituted by the photosensitive drum 112 and the transfer charger 118 in synchronization with the toner image on the photosensitive drum.

  Next, the toner image is transferred to the sheet sent to the transfer unit in this way, and then conveyed to the fixing unit 114. Thereafter, the unfixed transfer image is permanently fixed on the sheet S by being heated and pressed by the fixing unit 114. Then, the sheet on which the image is fixed in this manner is discharged from the apparatus main body 101 to the discharge tray 117 by the discharge roller 116.

  FIG. 2 is a diagram illustrating a configuration of the sheet feeding apparatus 103. In FIG. 2, the same reference numerals as those in FIG. 9 described above indicate the same or corresponding parts.

  The sheet storage 11 includes a tray 12 that can move up and down to support a sheet, a trailing edge regulating plate 13, a leading edge regulating plate 17, and a side edge regulation that regulates the position of the sheet S in the width direction orthogonal to the sheet feeding direction. A plate 14 is provided. The rear end regulating plate 13 and the side end regulating plate 14 are configured so that the positions can be arbitrarily changed according to the size of the stored sheet. In addition, the rear end regulating plate 13 is provided with a rear end separating portion 18 that regulates the position of the rear end portion that is the upstream end portion in the sheet feeding direction of the uppermost sheet Sa so as to be movable in the vertical direction.

  The sheet storage 11 can be pulled out from the printer main body 101 by a slide rail 15, and when the sheet storage 11 is pulled out from the printer main body, the tray 12 is lowered to a predetermined position to replenish or replace sheets. Etc. can be performed. The tray 12 is moved up and down by a stepping motor or a DC servo motor. When the tray 12 is lowered, the tray 12 can be lowered and lowered repeatedly for a predetermined time and then stopped for a predetermined time.

  Further, an air feeding type sheet feeding mechanism (hereinafter referred to as an air feeding mechanism 150) for separating and feeding the sheets one by one is disposed on the upper portion of the sheet storage case 11. The air feeding mechanism 150 floats the upper portion of the sheet bundle on the tray and the suction conveyance unit 20 that sucks and feeds the sheets S stacked on the tray 12 and separates the sheets S one by one. An air blowing unit 30.

  Here, the suction conveyance unit 20 is stretched over the belt driving roller 41 and sucks the sheet S and feeds the sheet S in the right direction in the figure, and the suction conveyance belt 21 sucks the sheet S to the suction conveyance belt 21. An adsorption fan 36 that generates negative pressure is provided. A suction duct 22 is provided inside the suction conveyance belt 21 and sucks air through a suction hole (not shown) formed in the suction conveyance belt 21.

  Further, an adsorption shutter 37 that is disposed between the adsorption fan 36 and the suction duct 22 and turns on / off the adsorption operation of the adsorption conveyance belt 21 is provided. In the present embodiment, a plurality of suction conveyance belts 21 are arranged with a predetermined interval in the width direction.

  Further, the air blowing unit 30 sends air from the separation fan 31 to the separating nozzle 31 and the separation nozzle 34 for blowing air to the upper side surface of the stored sheet S, the separation fan 31, and the nozzles 33 and 34. A separation duct 32 is provided.

  A part of the air sucked in the direction of the arrow C by the separation fan 31 passes through the separation duct 32 and is blown in the direction of the arrow D by the firing nozzle 33, and among the upper part of the sheets S stacked on the tray 12. Raise several sheets. Further, the other air is blown in the direction of arrow E by the separation nozzle 34, and the sheets floated by the separation nozzle 33 are separated one by one and adsorbed to the adsorption conveyance belt 21.

  FIG. 3 is a control block diagram of the sheet feeding apparatus. The control apparatus 200 includes a rear end sheet surface sensor that detects the rear end surface of the sheet, and a first sheet surface provided in a paper surface detection mechanism that will be described later. The sensor 54 and the second sheet surface sensor 55 are connected. Further, a tray lifting / lowering drive motor M1 that constitutes a lifting / lowering unit that lifts and lowers the tray 12, a suction conveyance belt drive motor M2 that drives the suction conveyance belt 21, and a suction shutter solenoid SL that rotates the suction shutter 37 are connected. Further, the control device 200 is connected to an adsorption fan 36 that generates a negative pressure for adsorbing the sheet to the adsorption conveyance belt 21 and a separation fan 31 that blows air onto the sheet.

  Next, the sheet feeding operation of the sheet feeding apparatus 103 (air feeding mechanism 150) configured as described above will be described.

  First, when the user pulls out the sheet storage 11 to set the sheet S and then stores it in a predetermined position as shown in FIG. 2, the tray elevating drive motor M1 is first driven by the control device 200 shown in FIG. 4, the tray 12 starts to rise in the direction of arrow A. Eventually, when reaching the feedable position where the distance from the suction conveyance belt 21 becomes B, the control device 200 stops the tray 12 at this position. Thereafter, the sheet feeding signal for starting feeding is prepared.

  Next, when the sheet feeding signal is detected, the control device 200 operates the separation fan 31 and sucks air in the direction of arrow C as shown in FIG. This air is blown to the sheet bundle from the firing nozzle 33 and the separation nozzle 34 through the separation duct 32 from the directions of arrows D and E, respectively. As a result, the upper several sheets of the sheet bundle rise. Further, the control device 200 operates the suction fan 36 and discharges air in the direction F in the drawing. At this time, the suction shutter 37 is still closed.

  Next, the feeding signal is detected to drive the suction shutter solenoid SL, and the suction shutter 37 is rotated in the direction of arrow G as shown in FIG. Thereby, a suction force in the direction of arrow H is generated from the suction hole provided in the suction conveyance belt 21. Only the uppermost sheet Sa is adsorbed to the adsorbing and conveying belt 21 by the adsorbing force and the separation air from the separation nozzle 34.

  Subsequently, the control device 200 drives the suction conveyance belt drive motor M2 shown in FIG. 3, and rotates the belt drive roller 41 in the arrow J direction in FIG. As a result, the uppermost sheet Sa is fed in the direction of the arrow K while being sucked by the suction conveyance belt 21, and is then fed toward the image forming unit by the drawing roller pair 42 that rotates in the directions of the arrows L and M. It is done.

  Here, in order to adsorb the sheet S to the adsorbing and conveying belt 21, a predetermined sheet feeding position range in which the adsorbing and conveying belt 21 can adsorb the position of the uppermost sheet Sa of the sheet bundle stored in the sheet storage case 11. (Hereinafter referred to as the appropriate range). Therefore, a paper surface detection mechanism 49 that is a paper surface detection unit that detects the position of the upper surface of the uppermost sheet is provided so as to keep the position of the uppermost surface of the sheets stacked on the tray 12 within an appropriate range.

  As shown in FIG. 7, the paper surface detection mechanism 49 includes a sheet surface detection sensor flag 52, first and second sheet surface sensors 54 and 55 that are turned on / off by the rotation of the sheet surface detection sensor flag 52, and a sensor flag mechanism. 50 etc. Then, by raising and lowering the tray 12 based on the signals of the first and second sheet surface sensors 54 and 55, the position of the tray 12 can be controlled to a position where only the uppermost sheet Sa can be separated and fed. . In the present embodiment, the first sheet surface sensor 54 detects that the position of the uppermost sheet is below the appropriate range, and the second sheet surface sensor 55 detects the position of the uppermost sheet. It detects that it is above the appropriate range.

  By the way, as described above, there are cases where several sheets, for example, only two sheets of the upper sheet Sa and the immediately lower sheet Sb are set on the tray 12. In this case, the position of the tray 12 becomes high, and the firing nozzle 33 It will be located on the side of. In this state, when the blowing air is blown by the firing nozzle 33 in the initial operation before starting the suction feeding of the sheet, a part of the blowing air comes into contact with the tray 12, and the amount of the blowing air that hits the sheet Decrease.

  When the amount of blowing air hitting the sheet decreases in this way, the two sheets Sa and Sb remain in close contact with each other depending on the type, size, state, usage environment temperature, humidity, and the like of the sheet, as if they were one sheet. May surface. That is, for example, when only two sheets are set, in the initial operation, the two sheets Sa and Sb may float as if they were one sheet as shown in FIG.

  When the height of the upper sheet Sa is detected in this state, when the second sheet surface sensor 55 is ON and the first sheet surface sensor 54 is OFF, the control device 200 is “too high as described above. And the tray 12 is lowered until the first sheet surface sensor 54 is turned on. By lowering the tray 12 in this way, the blowing air does not hit the tray 12, so the amount of blowing air that hits the sheet increases, thereby releasing the adhesion between the two sheets Sa and Sb.

  On the other hand, when both the first and second sheet surface sensors 54 and 55 are turned on, that is, when both the first and second sheet surface sensors 54 and 55 are turned on, the control unit 200 determines that the sheet is in an appropriate range. Therefore, the lowering operation of the tray 12 is not performed. If the lowering operation of the tray 12 is not performed as described above, the height of the tray 12 is maintained as it is, so that the tray 12 continues to be positioned beside the firing nozzle 33.

  For this reason, the blowing state of the blowing air to the two sheets Sa and Sb in close contact with the rolling nozzle 33 does not change, and the floating state is maintained as it is. In addition, when the tray 12 becomes high and comes to the side of the firing nozzle 33, the raising of the tray 12 is restricted. For this reason, the sheet does not exceed the appropriate range by raising the tray 12.

  Therefore, in the present embodiment, when the number of sheets on the tray 12 is small, if the sheet has floated in an appropriate range even after a predetermined time has elapsed since the start of the initial operation, the tray 12 is temporarily removed. The uppermost sheet is moved down to move out of the proper range. Then, by temporarily lowering the tray 12 in this way, the spraying state such as the amount of spraying air and the spraying direction of the sheet in close contact is changed.

  Next, the raising / lowering control of the tray when the number of sheets set (supported) on the tray 12 in this embodiment is small will be described with reference to the flowchart shown in FIG.

  First, upon receiving a feeding start signal, the control device 200 starts rotation of the separation fan 31 as an initial operation (S10), starts air blowing, and floats the sheet. As a result, the two sheets Sa and Sb shown in FIG. Then, the height of the surface of the upper sheet Sa is detected based on signals from the first sheet surface sensor 54 and the second sheet surface sensor 55.

  When the first sheet surface sensor 54 and the second sheet surface sensor 55 are ON (Y in S11), a predetermined time (for example, about 2 seconds) for which the rotation of the fan 31 is stabilized after the separation fan 31 starts to rotate next. Wait for the progress.

  Here, when the rotation of the fan 31 is stabilized after a predetermined time has elapsed, the amount of air blown also increases, so that the separated sheet usually floats greatly. Therefore, when the predetermined time has elapsed (Y in S12), the detection result of the sheet surface height is higher than that before the separation fan 31 rotates, and the second sheet surface sensor 55 is ON, and the first sheet surface The sensor 54 should be turned off. That is, the sheet to which air is blown should exceed the appropriate range for suction feeding.

  However, when the two sheets Sa and Sb are brought into close contact with each other, even if the rotation of the fan 31 is stabilized, the two sheets Sa and Sb in the close contact state do not rise greatly, and the first and first sheets The two sheet surface sensors 54 and 55 remain ON. In this case, since the height of the tray 12 is maintained as described above, the position of the tray 12 does not change.

  Therefore, when the predetermined time has passed with the first and second sheet surface sensors 54 and 55 being ON (Y in S12), the tray 12 is forcibly lowered (S13). This is continued until the detection result is “too low”, that is, until the first sheet surface sensor 54 is turned on and the second sheet surface sensor 55 is turned off (Y in S14). By lowering the tray 12 in this way, the spraying state such as the amount of blowing air and the spraying direction of the sheet in the close contact state changes, and the close contact state of the sheet is released.

  Next, when the tray 12 is forcibly lowered and the first sheet surface sensor 54 is turned on and the second sheet surface sensor 55 is turned off (Y in S14), the first and second sheet surface sensors 54 and 55 are turned on. The tray 12 is raised until it becomes (Y of S15) (S16). In addition, when the 1st sheet surface sensor 54 and the 2nd sheet surface sensor 55 are not ON (N of S11), the sheet | seat is over the appropriate range. Therefore, until the first sheet surface sensor 54 and the second sheet surface sensor 55 are turned on, the tray lifting / lowering drive motor M1 is driven to lower the tray 12 (S16).

  When the first and second sheet surface sensors 54 and 55 are turned on (Y in S15), that is, in the initial operation, when the upper sheet Sa falls within the proper range again, the tray 12 is stopped (S17). After the initial operation is finished and the sheet suction and feeding is started, the tray 12 is lowered even when the first sheet surface sensor 54 is OFF and the second sheet surface sensor 55 is ON. There is no control.

  Thus, by forcibly lowering the tray 12, not only the amount of blowing air by the tray blowing nozzle 33 but also the blowing state such as the blowing direction changes, so that the state of close contact as shown in FIG. The two sheets Sa and Sb can be appropriately separated. The reason why the tray 12 is not lowered until the rotation of the fan 31 is stabilized is to prevent the close contact between the sheets from being released due to insufficient air blowing if the tray 12 is lowered in an unstable state. .

  As described above, when the uppermost sheet continues to be in the appropriate range during the initial operation, the tray is once lowered. Thereby, it is possible to prevent double feeding of sheets regardless of the sheet stacking amount. That is, even when a small number of sheets are set on the tray 12, the amount of air to be blown can be increased by forcibly lowering the tray 12, and the sheets can be reliably separated and fed.

1 is a diagram illustrating a schematic configuration of a printer that is an example of an image forming apparatus including a sheet feeding device according to an embodiment of the present invention. The figure which shows the structure of the said sheet feeding apparatus. The control block diagram of the said sheet feeding apparatus. FIG. 6 is a first diagram illustrating a sheet feeding operation of the sheet feeding apparatus. FIG. 9 is a second diagram illustrating a sheet feeding operation of the sheet feeding apparatus. FIG. 10 is a third diagram illustrating the sheet feeding operation of the sheet feeding apparatus. FIG. 4 is a diagram illustrating a configuration of a paper surface detection mechanism provided in the sheet feeding device. The flowchart explaining the raising / lowering control of the said tray. The figure explaining the structure of the conventional sheet feeding apparatus. The figure which shows the structure of the paper surface detection mechanism of the conventional sheet feeding apparatus. FIG. 1 is a first diagram illustrating a sheet surface control operation of the sheet feeding apparatus. FIG. 2 is a second diagram illustrating a sheet surface control operation of the sheet feeding apparatus. The figure explaining the state when feeding the 2 sheet | seat of the conventional sheet feeding apparatus.

DESCRIPTION OF SYMBOLS 11 Sheet storage 12 Tray 20 Adsorption conveyance part 21 Adsorption conveyance belt 30 Air blowing part 33 Firing nozzle 34 Separation nozzle 36 Adsorption fan 49 Paper surface detection mechanism 54 1st sheet surface sensor 55 2nd sheet surface sensor 65 Sheet presence or absence detection sensor 100 Printer DESCRIPTION OF SYMBOLS 101 Printer main body 102 Image forming part 103 Sheet feeding apparatus 150 Air paper feeding mechanism 200 Control apparatus M1 Tray raising / lowering drive motor S Sheet

Claims (4)

A tray that can be moved up and down to support the sheet, an air blowing unit that blows air onto a side surface of the sheet supported by the tray, and a suction conveyance unit that sucks and feeds the floated sheet. In the initial operation before starting the suction feeding of the sheet, the air is blown by the air blowing unit to float the sheet once so as to exceed the proper range of the suction feeding by the suction conveying unit. In the sheet feeding device that lowers the tray so that the uppermost sheet of the sheet is located within an appropriate range,
A paper surface detection mechanism for detecting the upper surface of the uppermost sheet of the floated sheet;
An elevating part for elevating the tray,
In the initial operation, when it is determined by the signal from the paper surface detection mechanism that the uppermost sheet of the flying sheet is located in the appropriate range even after a predetermined time has elapsed since the start of air blowing First, the tray is lowered to move the uppermost sheet out of the proper range, and then the tray is raised to control the elevating unit so that the uppermost sheet is positioned within the proper range again. A sheet feeding apparatus characterized by that. The sheet surface detection mechanism includes a first sheet surface sensor that detects that the position of the uppermost sheet is below the appropriate range, and a second sheet surface sensor that detects that the position is above the appropriate range. With
During the initial operation, the tray is raised when the first sheet surface sensor is ON and the second sheet surface sensor is OFF, and when both the first sheet surface sensor and the second sheet surface sensor are ON. 2. The sheet feeding device according to claim 1, wherein the sheet feeding device is controlled to stop and to move down when the first sheet surface sensor is OFF and the second sheet surface sensor is ON. 3.   After the initial operation is finished and the suction feeding of the sheet is started, the lowering control is not performed when the first sheet surface sensor is OFF and the second sheet surface sensor is ON. The sheet feeding apparatus according to claim 2. The sheet feeding device according to any one of claims 1 to 3,
An image forming unit that forms an image on a sheet fed from the sheet feeding device;
An image forming apparatus comprising:

Images