JP4739085B2 - Sheet feeding apparatus and image forming apparatus - Google Patents

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 conveys (see Patent Document 1).

  FIG. 12 shows an example of such an air feeding type sheet feeding apparatus. As shown in FIG. 12, the storage 11 which is a sheet storage unit in which a plurality of sheets S are stored has a sheet. A tray 12 on which S is loaded is provided so as to be movable up and down. In addition, on the upper portion of the storage 11, the suction conveyance unit 50A that sucks and conveys the sheet S, and air is blown to the end of the sheet bundle on the tray to float a plurality of sheets S and separate them one by one. The air spraying part 30 for this is provided.

  Here, the suction conveyance unit 50A is stretched over the belt driving roller 41 and sucks and conveys the sheet S in the right direction in the drawing, and the negative conveyance for adsorbing the sheet S to the suction conveyance belt 21. An adsorption fan 136 that generates pressure is provided. A suction duct 51 is provided inside the suction conveyance belt 21 and sucks air through a suction hole formed in the suction belt 21. Further, a suction shutter 37 is provided between the suction fan 136 and the suction duct 51 in order to turn ON / OFF the suction operation by the suction fan 136.

  Further, the air blowing unit 30 is a separation nozzle 33 and a separation nozzle 34 for blowing air onto the upper portion of the stored sheet bundle, a separation fan 31, and a separation that sends air from the separation fan 31 to the nozzles 33 and 34. A duct 32 is provided.

  A part of the air sucked in the direction of arrow C by the separation fan 31 passes through the separation duct 32 and is blown in the direction of arrow D by the firing nozzle 33, and the upper part of the sheet bundle loaded on the tray 12 is blown. Raise several sheets. Other air is blown in the direction of arrow E by the separation nozzle 34, and the uppermost sheet is separated one by one from the several sheets floated by the separation nozzle 33, and is sucked onto the suction conveyance belt 21.

  By the way, such a conventional air sheet feeding type sheet feeding apparatus includes a sheet presence / absence detection unit for detecting the presence / absence of the sheets S stacked on the tray 12.

  FIG. 13 is a diagram illustrating a configuration of such a sheet presence / absence detection unit. The sheet presence / absence detection unit 60A is rotatably mounted on the support shaft 53 and turned on / off by the rotation of the sheet presence / absence detection sensor flag 62 and the sheet presence / absence detection sensor flag 62 that can contact the upper surface of the sheet S. The sheet presence / absence detection sensor 65 is provided.

  The sheet presence / absence detection sensor flag 62 includes a contact portion 62A that contacts the upper surface of the uppermost sheet Sa, a detection portion 62B that shields the light receiving portion of the sheet presence / absence detection sensor 65, and a stopper portion 62c. Here, when the sheet presence / absence detection sensor flag 62 is rotated in the direction of the tray 12, the stopper portion 62c comes into contact with the end portion 43a of the frame body 43 of the sheet feeding device, whereby the sheet presence / absence detection sensor flag 62 is rotated. Movement is regulated.

  When the rotation is thus restricted by the stopper portion 62c, the contact portion 62A of the sheet presence / absence detection sensor flag 62 is at the lowest position shown in FIG.

  Next, the sheet presence / absence detection operation of the sheet presence / absence detection unit 60A having the above configuration will be described.

  When the tray 12 on which the sheets are stacked for feeding the sheets rises, as shown in FIG. 14A, the contact portion 62A of the sheet presence / absence detection sensor flag 62 contacts the upper surface of the uppermost sheet Sa. In contact therewith, the sheet presence / absence detection sensor flag 62 rotates upward.

  Thereafter, the tray 12 is further raised, and the sheet presence / absence detection sensor flag 62 is also raised accordingly. Eventually, when the distance between the suction conveyance belt 21 and the upper surface of the uppermost sheet Sa reaches S1, a sheet surface detection sensor (not shown) detects the upper surface of the sheet and stops the tray 12.

  In this state, the detection unit 62B shields the light receiving unit of the sheet presence / absence detection sensor 65 from light. As a result, the sheet presence / absence detection sensor 65 outputs an ON signal. When the sheet presence / absence detection sensor 65 outputs an ON signal in this way, the control device (not shown) has a sheet S on the tray based on the ON signal. Is detected.

  Then, when a feeding signal for starting the sheet feeding operation is detected, air is blown from the firing nozzle 33 to the end of the sheet S as shown in FIG. Among the stacked sheets, a plurality of upper sheets float up. At this time, a plurality of sheets positioned below the lower end of the air outlet 33a of the rolling nozzle 33 are also raised.

  As a result, when the floating state of the sheet is stabilized, the distance from the suction surface of the suction conveyance belt 21 to the upper surface of the sheet Sc below the lower end of the air blowing port 33a that has not floated becomes S2, and FIG. It becomes larger than the distance S1 before ascent shown in FIG. This tendency becomes more conspicuous for light and small sheets that are likely to float.

  At this time, the sheet surface detection sensor (not shown) detects that the uppermost position of the sheet reaches a predetermined upper limit position or lower limit position so that the sheet floated by air falls within a predetermined range in the height direction. Detect. When air is blown and the uppermost position of the sheet exceeds the upper limit position, the tray 12 is lowered to lower the uppermost position. When the uppermost position of the sheet exceeds the lower limit position, the tray 12 is Control to raise and raise the top position.

  Next, after the sheet floating state is stabilized in this way, the suction operation is started, and the uppermost sheet Sa is sucked onto the suction conveyance belt 21 as shown in FIG. Thereafter, the suction conveyance belt 21 rotates, and thereby the sheet is conveyed toward an image forming unit (not shown).

  When the sheet Sa is attracted to the suction conveyance belt 21 in this way, the sheet Sa is pressed by the sheet Sa and retreats while rotating, and is retracted and stored near the suction conveyance belt 21. . Here, when the sheets are stored in this way, the distance between the sheet presence / absence detection flag 62 and the suction conveyance belt 21 is the shortest, but the distance G1 is also secured at that time. Thus, the sheet presence / absence detection flag 62 is retracted and stored without being obstructed by the suction conveyance belt 21.

  On the other hand, after this, the sheet continues to be conveyed, and when there is no sheet S on the tray, the contact portion 62A of the sheet presence / absence detection sensor flag 62 enters a hole (not shown) formed in the tray 12. Become. As a result, the sheet presence / absence detection sensor flag 62 moves to the lowest position shown in FIG.

  When the sheet presence / absence detection sensor flag 62 moves in this manner, the detection unit 62B does not shield the light receiving portion of the sheet presence / absence detection sensor 65, so that the sheet presence / absence detection sensor 65 is turned off. When the sheet presence / absence detection sensor 65 is turned off in this way, a control device (not shown) detects that there is no sheet S on the tray, and stops the subsequent sheet conveyance operation.

JP-A-7-196187 (page 9, FIG. 6)

  By the way, in the conventional sheet feeding apparatus and image forming apparatus provided with such a sheet presence / absence detection unit, when the sheet feeding operation is finished, the sheet that has floated as shown in FIG. Descend. At this time, as shown in FIG. 15, when the sheet Sb that has been lifted up to this point is stacked on the sheet Sc that has not been lifted at a distance S <b> 2 from the suction transport belt 21, the suction transport belt of the sheet Sb is stacked. The distance to 21 is S3 (S2 + S4).

  At this time, in the case of a light and small sheet, the air is blown higher by the blown air and often exceeds the upper limit position. When the upper limit position is exceeded, the tray 12 is controlled to descend. Then, the position of the tray 12 may be greatly lowered from the initial position, and the distance S3 may become extremely large.

  In this case, the position of the sheet Sb is lower by S5 (S3-S1) than the lowest position of the contact portion 62A of the sheet presence / absence detection sensor flag 62. Therefore, in this state, the detection unit 62B of the sheet presence / absence detection sensor flag 62 does not shield the light receiving unit of the sheet presence / absence detection sensor 65. For this reason, the control device erroneously detects that there is no sheet S on the tray 12 despite the presence of the sheet S on the tray 12.

  In order to solve such a false detection, the tray 12 may always be raised after the feeding operation is completed to detect the presence or absence of a sheet. However, the control is not only complicated. The determination takes time and productivity may be reduced.

  Further, the floating sheet surface during the sheet feeding operation is not always stable, and may be greatly waved up and down. When the sheet is waved greatly in this way, the sheet presence / absence detection sensor flag 62 is accompanied by this. In some cases, the abutting portion 62A reaches the lowest lowered position.

  When the contact portion 62A reaches the lowest position in this way, the sheet presence / absence detection unit 60A detects the absence of a sheet. As a result, despite the presence of the sheet, the operation of the apparatus is stopped and productivity is lowered.

  Accordingly, the present invention has been made in view of such a situation, and provides a sheet feeding apparatus and an image forming apparatus capable of reliably detecting the presence or absence of a sheet with a simple configuration in an air feeding method. The purpose is to do.

The present invention provides a tray that supports a sheet and that can freely move up and down, an air spraying section that blows air from an air outlet to an end of the sheet to float the sheet supported by the tray, and a spray by the air spraying section An adsorbing and conveying unit that adsorbs and conveys the sheet that has floated by the air that has been conveyed, and a sheet presence / absence detecting unit that detects the presence / absence of a sheet supported by the tray, and the sheet presence / absence detecting unit is provided on the tray. A sensor flag that rotates in contact with the upper surface of the supported sheet, and a sensor that is turned ON / OFF in accordance with the rotation of the sensor flag, and that is in contact with the upper surface of the sheet of the sensor flag a possible detecting the presence or absence of the sheet at the position of the sheet without also floats air is blown from the air blowing portion, prior to the air blowing portion Is characterized in that arranged projecting below the lower end of the air outlet.

  As in the present invention, the contact portion of the sensor flag that turns the sensor ON / OFF with the sheet can protrude downward from the lower end of the air blowing port of the air blowing unit, so that the sheet can be formed with a simple configuration. Presence / absence can be reliably detected.

  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 includes a photosensitive drum 112, a developing device 113, a laser scanner unit 111, and the like. In addition, the sheet feeding apparatus 103 is an example of a plurality of sheet storage units 115 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 115. 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 (not shown) 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 supplied from the sheet storage unit 115. 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. 13 described above indicate the same or corresponding parts.

  The storage 11 has a tray 12, a rear end regulating plate 13 that regulates the upstream side (rear side) of the sheet S in the feeding direction, and a side end regulation that regulates the position in the width direction orthogonal to the sheet conveying direction of the sheet S. 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. Further, the storage 11 can be pulled out from the printer main body 101 by the slide rail 15.

  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 in the upper part of the storage 11. The air feeding mechanism 150 floats the upper portion of the sheet bundle on the tray, and the air for separating the sheets S one by one while sucking and conveying the sheets S stacked on the tray 12. And a spraying part 30.

  Here, the suction conveyance unit 50A is stretched over the belt driving roller 41 and sucks and conveys the sheet S in the right direction in the drawing, and the negative conveyance for adsorbing the sheet S to the suction conveyance belt 21. An adsorption fan 36 that generates pressure is provided. In addition, a suction duct 51 is provided inside the suction conveyance belt 21 and sucks air through a suction hole (not shown) formed in the suction belt 21.

  In addition, a suction shutter 37 that is disposed between the suction fan 36 and the suction duct 51 and that turns ON / OFF the suction operation of the suction 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 31 for blowing air onto the upper portion 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 is part of the upper part of the sheet 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.

  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 storage 11 and sets the sheet S, and then stores the sheet S in a predetermined position as shown in FIG. 2, the tray 12 is first moved to an arrow A by driving means (not shown) as shown in FIG. Begins to rise in the direction. Eventually, when reaching the feedable position where the distance from the suction conveyance belt 21 becomes B, the control device (not shown) 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 activates the separation fan 31 and sucks air in the direction of arrow C, and this air passes through the separation duct 32 from the nozzle 33 and the separation nozzle 34, respectively. The sheet bundle is sprayed from the E direction. As a result, the upper several sheets of the sheet bundle rise. Further, the control device 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, when a predetermined time elapses after the feeding signal is detected and the upper sheet SA is stably lifted as shown in FIG. 4, the control device rotates the suction shutter 37 in the direction of the arrow G to perform suction transport. A suction force in the direction of arrow H is generated from a suction hole provided in the 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, by rotating the belt drive roller 41 in the arrow J direction in FIG. 5, the uppermost sheet Sa is conveyed in the arrow K direction while being adsorbed by the adsorption conveyance belt 21, and thereafter, the arrows L and M The sheet is fed toward the image forming unit by a pair of drawing rollers 42 rotating in the direction.

  By the way, in order to attract the sheet S to the suction conveyance belt 21 in this way, the position of the uppermost sheet Sa of the sheet bundle stored in the storage 11 is set to a predetermined sheet feeding position where the suction belt 21 can suck. Need to be maintained. For this reason, a paper surface detection mechanism 49 for controlling the position of the uppermost sheet Sa of the sheet bundle is provided.

  Next, the paper surface detection mechanism 49 will be described.

  As shown in FIG. 6, the paper surface detection mechanism 49 includes a sheet surface detection sensor flag 52, a first sheet surface sensor 54, a second sheet surface sensor 55, and a sensor flag mechanism 50. The first and second sheet surface sensors 54 and 55 are provided at positions away from the suction conveyance region (belt surface on the sheet suction side) of the suction conveyance belt 21 on the upstream side in the sheet feeding direction.

  By arranging the first and second sheet surface sensors 54 and 55 in such a position instead of in the suction duct 51 as described above, the above-described increase in the size of the suction duct 51 can be prevented. The size of 101 can be reduced.

  Here, the sheet surface detection sensor flag 52 is swingably supported by the support shaft 53 as shown in FIG. 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.

  Further, as shown in FIG. 6, the sensor flag mechanism 50 includes a support member 60 in which one end 60a is rotatably held inside the suction duct 51, a rotation end 60b of the support member 60, and a sheet surface detection sensor flag. And a sheet surface detection member 61 supported by the support portion 52D.

  Here, the sheet surface detection member 61 is provided below the suction conveyance area of the suction conveyance unit 50A 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 that is rotatably supported in the suction duct is attached to a suction conveyance region of the suction conveyance belt 21 from a retraction hole (not shown) formed in a gap in the sheet width direction of the plurality of suction conveyance belts 21. Protrudes underneath.

  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.

  The sheet stored in the storage 11 is lifted by the raising of the tray 12, and the upper surface of the uppermost sheet Sa contacts the sheet surface detection member 61. Thereafter, when the tray 12 further rises, the sheet surface detection member 61 rises, and as the sheet surface detection member 61 rises, the sheet surface detection sensor flag 52 moves upward with the support portion 52D centered on the support shaft 53. Rocks in the direction toward.

  Then, as shown in FIG. 8, when 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 is S1, the sheet surface detection sensor flag 52 is set. The first sheet surface sensor 54 is shielded from light by the first detector 52B.

  As a result, the first sheet surface sensor 54 outputs an ON signal. When the first sheet surface sensor 54 outputs the ON signal in this way, the control device stops raising the tray 12 based on the ON signal. Here, this position is set as the lower limit of the flying region, and thereafter, the control device starts air blowing and floats the sheet.

  Next, after the sheet is lifted in this way, the control device raises the tray 12 and determines that it is “too low” until an ON signal of the second sheet surface sensor 55 is obtained, and an ON signal is obtained. Raise the tray 12 until.

  As shown in FIG. 9, when the distance between the belt surface of the suction conveyance belt 21 and the upper surface of the uppermost sheet Sa becomes SL, the second sheet surface is detected by the second detection unit 52B of the sheet surface detection sensor flag 52. The sensor 55 is shielded from light. Thereby, the second sheet surface sensor 55 outputs an ON signal, and when the ON signals are output from the first sheet surface sensor 54 and the second sheet surface sensor 55 in this way, the control device stops the raising of the tray 12. .

  Here, this position is defined as the upper limit of the flying region. 10, the tray 12 may exceed this upper limit, and the distance between the belt surface of the suction conveyance belt 21 and the upper surface of the uppermost sheet Sa may be SH. In this case, the shielding of the first sheet surface sensor 54 by the first detection unit 52B of the sheet surface detection sensor flag 52 is released, and thereby the first sheet surface sensor 54 is turned off. In this case, it is determined that it is “too high”, and then the tray 12 is lowered until the ON signal of the first sheet surface sensor 54 is obtained.

  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 control device can position the tray 12 so that only the uppermost sheet Sa can be separated and conveyed. Can be controlled. 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.

  By the way, such a sheet feeding apparatus includes a sheet presence / absence detection unit for detecting the presence / absence of the sheets S stacked on the tray 12.

  FIG. 11 is a diagram illustrating the configuration of such a sheet presence / absence detection unit 70A. The sheet presence / absence detection unit 70A includes a sheet presence / absence detection sensor flag 72 that is rotatably supported by a support shaft 53 that supports the sheet surface detection sensor flag 52 and that can contact the upper surface of the sheet S. . Further, a sheet presence / absence detection sensor 65 that is turned ON / OFF by rotation of the sheet presence / absence detection sensor flag 72 is provided.

  Here, the sheet presence / absence detection sensor flag 72 includes a contact portion 72A that contacts the upper surface of the uppermost sheet Sa and a detection portion 72B that shields the light receiving portion of the sheet presence / absence detection sensor 65. When the tray 12 is lifted and comes into contact with the upper surface of the uppermost sheet Sa stacked on the tray 12, the sheet presence / absence detection sensor flag 72 rotates, and the detection unit 72B causes the sheet presence / absence detection sensor 65 to rotate. The light receiving unit is shielded from light.

  Accordingly, the sheet presence / absence detection sensor 65 outputs an ON signal. When the ON signal is output from the sheet presence / absence detection sensor 655 in this way, the control device detects that the sheet S is present on the tray 12.

  When there is no sheet S on the tray 12, the sheet presence / absence detection sensor flag 62 rotates so that the contact portion 62 </ b> A enters a hole (not shown) formed in the tray 12. The light shielding of the light receiving part of the sheet presence / absence detection sensor 65 by the detection part 62B is released. As a result, the sheet presence / absence detection sensor 65 is turned off, and the control device detects that there is no sheet S on the tray.

  Incidentally, a stopper 72c is formed at the end of the sheet presence / absence detection sensor flag 72, and the stopper 72c abuts on the end 43a of the frame 43 of the sheet feeding device, thereby rotating the sheet presence / absence detection sensor flag 72. Movement is regulated. And when it is in the state where rotation is controlled in this way, the position of the contact portion 72A is the lowest lowered position indicated by a two-dot chain line 72A-1.

  The contact portion 72 </ b> A is at the lowest position when the tray 12 has no sheet and the contact portion 72 </ b> A enters a hole (not shown) formed in the tray 12.

  Here, when a light and small sheet is fed, if the sheet is blown higher by the air blown and exceeds the above-described upper limit position, the tray 12 is controlled to descend. If the position of the tray 12 is greatly lowered from the initial position, there is a risk of erroneously detecting the absence of sheets in the conventional configuration.

  On the other hand, in the present embodiment, when the contact portion 72A is in the lowest lowered position, the position of the tip (lower end) of the contact portion 72A is a distance from the lower end 33L of the air outlet 33a of the firing nozzle 33. It is located on the lower side by α.

  Here, when air is blown from the firing nozzle 33, the sheet Sc below the lower end 33L is not blown up. For this reason, the position of the final sheet among the stacked sheets is not positioned below this, and the upper surface of the tray 12 when the final sheet is sent out is also below the lower end 33L. Never become.

  Therefore, if the presence / absence of a sheet can be detected even at the position of the lower end 33L, the presence / absence of a sheet on the tray 12 can be reliably detected without erroneous detection as in the prior art. That is, in the present embodiment, the presence or absence of the sheet S on the tray 12 is reliably detected by detecting the presence or absence of the sheet at the position of the sheet that does not float even when air is blown. .

  Actually, the contact portion 72A of the sheet presence / absence detection sensor flag 72 is located at a position lower than the lower end 33L of the air outlet 33a so that the presence / absence of the sheet can be detected at the position of the sheet that does not rise even when air is blown. The margin is projected downward by a distance α to allow for a margin. Thereby, during the sheet feeding operation, the presence or absence of the sheet S can be reliably detected without interruption after the operation.

  Here, the length of the sheet presence / absence detection sensor flag 72 between the rotation shaft 53 and the contact portion 72A is set so as to satisfy the following condition. In FIG. 11, a dotted line 72A-2 indicates a storage state in which the contact portion 72A of the sheet presence / absence detection sensor flag 72 is retracted and stored when the suction conveyance belt 21 sucks and conveys the sheet.

  (1) When the contact portion 72A of the sheet presence / absence detection sensor flag 72 is at the lowest position, the sheet presence / absence detection sensor flag 72 is positioned below the lower end 33L of the blow-out port 33a that blows air from the firing nozzle 33.

  (2) When the sheet presence / absence detection sensor flag 72 is in the retracted state, the contact portion 72A can be stored so as not to interfere with the suction conveyance portion 50A. That is, when the sheet presence / absence detection sensor flag 72 is stored, the distance G2 between the tip of the contact portion 72A and the transport belt 21 is secured.

  (3) The contact portion 72A of the sheet presence / absence detection sensor flag 72 is located upstream of the suction surface of the suction conveyance belt 21 and downstream of the rear end of the smallest size sheet SS that can be stored in the storage 11. It is possible to contact the upper surface of the upper sheet Sa.

  As described above, by making the contact portion 72A of the sheet presence / absence detection sensor flag 72 protrude below the lower end of the air outlet 33a, erroneous detection can be prevented with a simple configuration. The presence or absence of a sheet can be reliably detected.

  Note that the setting condition (3) of the length of the contact portion 72A of the sheet presence / absence detection sensor flag 72 is a condition for reducing the size of the sheet feeding apparatus 103, and is not necessarily an essential condition. . Therefore, a sheet presence / absence detection unit such as the sheet presence / absence detection sensor flag 72 and the sheet presence / absence detection sensor 65 may be provided in the suction duct 51.

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. 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 figure explaining the structure of the sheet surface detection sensor flag provided in the said paper surface detection mechanism. FIG. 4 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. FIG. 3 illustrates a sheet surface control operation of the sheet feeding apparatus. The figure explaining the structure of the sheet presence or absence detection part provided in the said sheet feeding apparatus. FIG. 10 is a diagram illustrating an operation of a conventional sheet feeding apparatus. The figure explaining the structure of the sheet presence detection part of the conventional sheet feeding apparatus. The figure explaining the sheet presence detection operation | movement of the sheet presence detection part of the conventional sheet feeding apparatus. The figure explaining the misdetection of the presence or absence of a sheet | seat by the sheet presence or absence detection part of the conventional sheet feeding apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Storage 12 Tray 21 Adsorption conveyance belt 30 Air blowing part 33 Firing nozzle 33a Air blower outlet 34 Separation nozzle 36 Adsorption fan 50A Adsorption conveyance part 51 Suction duct 65 Sheet presence detection sensor 70A Sheet presence detection sensor 72 Sheet presence detection sensor flag 72A Contact unit 100 Printer 101 Printer main body 102 Image forming unit 103 Sheet feeding device 150 Air feeding mechanism S Sheet

Claims (5)

A tray that supports the seat and can be raised and lowered;
An air blowing section for blowing air from an air blowing port to an end portion of the sheet to float the sheet supported by the tray;
An adsorbing and conveying unit that adsorbs and conveys a sheet levitated by the air blown by the air blowing unit;
A sheet presence / absence detection unit that detects the presence / absence of a sheet supported by the tray,
The sheet presence / absence detection unit includes a sensor flag that rotates in contact with an upper surface of a sheet supported by the tray, and a sensor that is turned ON / OFF according to the rotation of the sensor flag,
The abutment portion that abuts the upper surface of the sheet of the sensor flag is configured to detect the presence or absence of a sheet at a position of the sheet that does not float even when air is blown from the air blowing portion. A sheet feeding apparatus, characterized in that it is provided so as to protrude downward from the lower end of the outlet.   The adsorbing and conveying unit includes an adsorbing and conveying belt that adsorbs and conveys the sheet, and the sensor flag is retracted while being rotated by being pressed by the adsorbed sheet when the sheet is adsorbed to the adsorbing and conveying belt. The sheet feeding apparatus according to claim 1, wherein   The sheet presence / absence detection unit is disposed at a position off the upstream side of the suction conveyance unit in the sheet conveyance direction. 2. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus is set to a length that does not interfere with the suction conveyance unit when the sheet is pressed and retracted.   2. The sheet feeding device according to claim 1, wherein the sheet presence / absence detection unit is arranged so that the contact portion of the sensor flag can contact a minimum size sheet that can be supported by the tray. apparatus. The sheet feeding device according to any one of claims 1 to 4,
An image forming unit that forms an image on the sheet fed from the sheet feeding device;
An image forming apparatus comprising:

Images