Sheet feeding device and image forming device

Abstract

To provide a sheet feeding device that can realize proper sheet transport by keeping constant an entry position of sheets with respect to a separation transport part which separates and transports sheets one by one.SOLUTION: A sheet feeding device 20 includes a lift plate 23, a swinging mechanism 24, a pickup roller 251, and a separation transport section 25S. The swinging mechanism 24 swings a downstream section of the lift plate 23 in a sheet transport direction Dc in an up-down direction. The separation transport section 25S is disposed downstream of the pickup roller 251 in the sheet transport direction Dc, and separates and transports sheets S one by one. A control section controls the swinging mechanism 24 based on a remaining amount of sheets S stacked on the lift plate 23 to change a feeding position P1 of the lift plate 23 in the up-down direction, thereby adjusting an entry position of the sheets S with respect to the separation transport section 25S.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a sheet feeding device and an image forming apparatus. [Background technology]

[0002] Image forming apparatuses such as copiers and printers are equipped with a sheet feeding device that separates and transports sheets, which are recording media used for printing (recording) images, one by one from a sheet storage unit that stores the stacked sheets toward an image forming unit.

[0003] For example, the conventional automatic feeder disclosed in Patent Document 1 includes a paper feed roller that feeds out paper and a separation roller that separates paper one by one, which come into contact to form a nip. In this automatic feeder, the angle at which the paper enters the separation roller is 45 degrees or less with respect to the tangent line that passes through the contact point between the separation roller and the leading edge of the paper. This reduces the angle at which the paper enters the nip. As a result, jams and non-feeding due to paper thickness are prevented, and paper can be fed smoothly. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-338065 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art, the angle at which the paper enters the nip between the paper feed roller and the separation roller changes depending on the amount of paper remaining in the paper stack, which can cause the paper's entry position relative to the nip to change. The prior art also had a problem in that it did not consider maintaining a consistent entry position for the paper relative to the nip between the paper feed roller and the separation roller. If the entry position of the paper relative to the nip is inconsistent and inappropriate, there are concerns that problems such as damage to the roller surface due to the leading edge of the paper coming into contact with the roller, adhesion of paper dust to the roller surface, and double-feeding of paper may occur.

[0006] The present invention has been made in consideration of the above points, and aims to provide a sheet feeding device and an image forming device that can maintain a constant entry position of a sheet into a separation conveying section that separates and conveys sheets one by one, thereby achieving proper sheet conveyance. [Means for solving the problem]

[0007] To solve the above problems, the sheet feeding device of the present invention includes a sheet storage unit, a lift plate, a swing mechanism, a pickup roller, a separation conveyance unit, and a control unit. Sheets are stacked in the sheet storage unit. The lift plate is disposed within the sheet storage unit, and its downstream portion swings up and down around its upstream portion in the sheet conveyance direction, moving the sheets stacked on top of it between a feeding position and a retracted position. The swing mechanism swings the downstream portion of the lift plate in the sheet conveyance direction up and down. The pickup roller contacts the topmost sheet stacked on the lift plate from above and sends the sheet downstream in the sheet conveyance direction. The separation conveyance unit includes a feed roller disposed downstream of the pickup roller in the sheet conveyance direction and a separating member contacting the feed roller, and separates and conveys the sheets one by one. The control unit controls the operation of the swing mechanism and the pickup roller. The control unit adjusts the entry position of the sheet relative to the separation conveying unit by controlling the swing mechanism to change the feeding position of the lift plate in the vertical direction based on the remaining amount of sheets loaded on the lift plate. [Effects of the Invention]

[0008] According to the configuration of the present invention, the feeding position can be determined appropriately and arbitrarily depending on the amount of sheets remaining on the lift plate, which makes it possible to keep the sheet entry position into the separation conveyance section constant and realize proper sheet conveyance. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional front view of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing the configuration of the image forming apparatus of FIG. 1. [Figure 3] 2 is a schematic cross-sectional front view of a sheet feeding device of the image forming apparatus of FIG. 1. [Figure 4] FIG. 4 is a partial cross-sectional front view of the sheet feeding device of FIG. 3. [Figure 5]5 is a partial cross-sectional front view showing the vicinity of a supply unit of the sheet feeding device of FIG. 4. [Figure 6] 2 is an explanatory diagram illustrating an example of the configuration of a sheet remaining amount detection unit in FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following.

[0011] Fig. 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. Fig. 2 is a block diagram showing the configuration of the image forming apparatus 1 shown in Fig. 1. An example of the image forming apparatus 1 according to this embodiment may be a so-called multifunction peripheral capable of monochrome printing and equipped with functions such as printing, scanning (image reading), and facsimile transmission. Note that the image forming apparatus 1 may be, for example, a copying machine, a printer, or a color printing machine.

[0012] 1 and 2, the image forming apparatus 1 includes a document transport unit 3 and an image reading unit 4. The document transport unit 3 is placed on the top surface of a main body 2 of the image forming apparatus 1. The image reading unit 4 is disposed inside the main body 2 below the document transport unit 3. An image of a document loaded on the document transport unit 3 or an image of a document placed on a contact glass (not shown) on the top surface of the image reading unit 4 is read by the image reading unit 4.

[0013] The image forming apparatus 1 further includes a sheet feeding device 20, a sheet conveying section 5, an exposure section 6, an image forming section 7, a transfer section 8, a fixing section 9, a sheet discharge section 10, a control section 11, and a memory section 12, which are provided in the main body 2.

[0014] The sheet feeding device 20 is disposed at the bottom of the main body 2. The sheet feeding device 20 includes a sheet storage cassette 21 and a cassette storage section 22. The sheet storage cassette 21 stores a plurality of sheets (recording media) S before an image is printed thereon. The sheet storage cassette 21 is inserted into the cassette storage section 22. During printing, the sheet feeding device 20 separates and feeds out the sheets S one by one from the sheet storage cassette 21. The detailed configuration of the sheet feeding device 20 will be described later.

[0015] The sheet conveying unit 5 extends vertically along the side wall of the main body 2. The sheet conveying unit 5 conveys the sheet S sent out from the sheet feeding device 20 to the transfer unit 8 and the fixing unit 9, and then discharges the sheet S after fixing to the sheet discharge unit 10. The exposure unit 6 irradiates the image forming unit 7 with laser light controlled based on image data.

[0016] The image forming unit 7 is disposed above the sheet feeding device 20. The image forming unit 7 includes a photosensitive drum 71 and a developing device 72. In the image forming unit 7, an electrostatic latent image of the document image is formed on the outer peripheral surface of the photosensitive drum 71 by laser light irradiated from the exposure unit 6. The developing device 72 supplies toner to the electrostatic latent image on the outer peripheral surface of the photosensitive drum 71 to develop it and form a toner image. The transfer unit 8 transfers the toner image formed on the outer peripheral surface of the photosensitive drum 71 onto the sheet S.

[0017] The fixing unit 9 is disposed above the transfer unit 8. The fixing unit 9 fixes the toner image to the sheet S by applying heat and pressure to the sheet S onto which the toner image has been transferred.

[0018] The sheet discharge section 10 is disposed below the image reading section 4. The sheet S on which the toner image has been fixed and printing has been completed is transported to the sheet discharge section 10. The sheet discharge section 10 has an opening on the front side, and the printed sheet (printed material) is taken out from the front side.

[0019] The control unit 11 includes a CPU, an image processing unit, and other electronic circuits and electronic components (none of which are shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in the storage unit 12, and performs processing related to the functions of the image forming apparatus 1. The sheet feeding device 20, the sheet conveying unit 5, the exposure unit 6, the image forming unit 7, the transfer unit 8, and the fixing unit 9 each receive individual commands from the control unit 11 and work together to print on the sheet S.

[0020] Regarding the control of the operation of the sheet feeding device 20, the function of the control section 11 may be provided in the sheet feeding device 20.

[0021] The storage unit 12 is configured by combining a non-volatile storage device (not shown) such as a program ROM (Read Only Memory) or a data ROM, and a volatile storage device (not shown) such as a RAM (Random Access Memory).

[0022] Next, the configuration of sheet feeding device 20 will be described using Figures 3, 4, and 5 in addition to Figures 1 and 2. Figure 3 is a schematic cross-sectional front view of sheet feeding device 20 of image forming apparatus 1 in Figure 1. Figure 4 is a partial cross-sectional front view of sheet feeding device 20 in Figure 3. Figure 5 is a partial cross-sectional front view showing the periphery of a supply unit of sheet feeding device 20 in Figure 4.

[0023] The sheet feeding device 20 includes a sheet storage cassette (sheet storage section) 21, a cassette storage section 22, a lift plate 23, a swinging mechanism 24, and a feeding section 25.

[0024] The sheet storage cassette 21 is housed in the cassette housing section 22. The sheet storage cassette 21 is a sheet housing section that can house a plurality of sheets S, which are recording media such as unprinted cut paper. The sheet storage cassette 21 is formed in the shape of a flat box with an open top, and the sheets S are stacked inside from above. The sheets S in the sheet storage cassette 21 are sent out to the right in FIGS. 1 and 2 (sheet conveying direction Dc) by the operation of the feeding section 25.

[0025] A pair of width restriction cursors 211 are also arranged in the sheet storage cassette 21. The pair of width restriction cursors 211 are capable of reciprocating movement in the sheet width direction perpendicular to the sheet conveying direction Dc, and position the sheet S stored in the sheet storage cassette 21 in the sheet width direction.

[0026] The cassette accommodating section 22 is formed in a recessed shape that is open at the front and recessed toward the rear side of the main body 2. The sheet storage cassette 21 is inserted into the cassette accommodating section 22. A pair of slide rails (not shown) are arranged between the inner surface of the cassette accommodating section 22 and the outer surface of the sheet storage cassette 21.

[0027] The pair of slide rails are arranged laterally opposite each other with the sheet storage cassette 21 in between, and extend parallel to the front-to-rear direction of the image forming apparatus 1. The sheet storage cassette 21 is supported via the slide rails so that it can be inserted into and extracted from the cassette storage section 22. The sheets S in the sheet storage cassette 21 are transported along a sheet transport direction Dc that is perpendicular to the direction in which the sheet storage cassette 21 is pulled out and inserted.

[0028] The lift plate 23 is disposed on the inner bottom of the sheet storage cassette 21. The sheets S in the sheet storage cassette 21 are stacked on the lift plate 23. The lift plate 23 is supported by the sheet storage cassette 21 via a support shaft 23x that is provided at the upstream end in the sheet conveying direction Dc and extends in the sheet width direction.

[0029] The lift plate 23 can swing around the axis of the support shaft 23x, with the downstream end in the sheet conveying direction Dc as the swing end. In other words, the lift plate 23 swings up and down with the upstream portion as the center in the sheet conveying direction Dc, and the downstream portion swings up and down. The inclination angle of the lift plate 23 with respect to the horizontal direction changes depending on the amount of sheets S loaded. As a result, the lift plate 23 moves the sheets S loaded on its upper surface between the feeding position and the retracted position.

[0030] The swing mechanism 24 is disposed below the downstream portion of the lift plate 23 in the sheet conveying direction Dc, between the inner bottom surface of the sheet storage cassette 21 and the lift plate 23. The swing mechanism 24 includes a rotation shaft 241, a lift lever 242, and a lift motor 24m.

[0031] The rotating shaft 241 is disposed on the inner bottom surface of the sheet storage cassette 21 and extends in the front-rear direction (sheet width direction). A lift lever 242 is fixed to the front end of the rotating shaft 241. The rear end of the rotating shaft 241 protrudes further rearward from the rear surface of the sheet storage cassette 21 into the main body 2.

[0032] The lift lever 242 is disposed at the center of the lift plate 23 in the front-rear direction (sheet width direction). One end of the lift lever 242 in the sheet conveying direction Dc is fixed to the rotary shaft 241, and extends radially outward from the rotary shaft 241. The other end of the lift lever 242 in the sheet conveying direction Dc is a swing end, and comes into contact with the lower surface of the downstream part of the lift plate 23 in the sheet conveying direction Dc.

[0033] The lift motor 24m is disposed within the main body 2 of the image forming apparatus 1, behind the sheet storage cassette 21. When the sheet storage cassette 21 is inserted into the cassette storage unit 22, the rear end of a rotation shaft 241 protruding from the rear surface of the sheet storage cassette 21 is connected to the lift motor 24m. When the lift motor 24m is driven, the lift lever 242 rotates around the axis of the rotation shaft 241 via the rotation shaft 241. The lift plate 23 is pushed up by the lift lever 242 as a result of the rotation of the lift lever 242. As a result, the downstream portion of the lift plate 23 in the sheet conveying direction Dc rises, and the lift plate 23 is displaced to a sheet S feeding position P1 (see FIG. 5) where the top layer of the sheets S contacts a pickup roller 251 (described later).

[0034] Furthermore, the lift plate 23 is released from the lift lever 242, causing the downstream portion in the sheet conveying direction Dc to descend. As a result, the uppermost sheet S separates from the pickup roller 251, and the lift plate 23 is displaced to a retracted position P2 (see FIG. 5) where it lies flat against the inner bottom of the sheet storage cassette 21. When the sheet storage cassette 21 is pulled out of the cassette storage unit 22, the connection between the rotation shaft 241 and the drive unit is released, i.e., the force of the lift lever 242 to push up the lift plate 23 is lost, and the lift plate 23 lies flat against the inner bottom of the sheet storage cassette 21 and is displaced to the retracted position P2. In this way, the swing mechanism 24 swings the downstream portion of the lift plate 23 in the sheet conveying direction Dc up and down.

[0035] The feeding unit 25 is disposed above the downstream portion of the sheet storage cassette 21 in the sheet conveying direction Dc. The feeding unit 25 includes a pickup roller 251, a separation conveying unit 25S including a feeding roller 252 and a separation roller 253, a pickup holder 254, and a feeding position sensor (feeding position detection unit) 255.

[0036] The rotation axes of the pickup roller 251, the feeding roller 252, and the separation roller 253 extend along the front-rear direction (sheet width direction) of the sheet storage cassette 21. The sheets S stored in the sheet storage cassette 21 are separated one by one by the feeding unit 25 and sent out toward the sheet conveying unit 5 on the downstream side in the sheet conveying direction Dc.

[0037] The pickup roller 251 is disposed above the downstream portion of the lift plate 23 in the sheet conveying direction Dc. When the downstream portion of the sheets S stacked on the lift plate 23 is pushed up by the lift plate 23, the uppermost sheet of the sheets S stacked on the lift plate 23 presses against and contacts the pickup roller 251 from below. The pickup roller 251 sends out the sheet S downstream in the sheet conveying direction Dc. The sheet S in the sheet storage cassette 21 is handed over to the feed roller 252 by the pickup roller 251, and is sent out to the sheet conveying unit 5 by the feed roller 252.

[0038] The feed roller 252 is disposed downstream of the pickup roller 251 in the sheet conveying direction Dc. The feed roller 252 is provided so that a lower portion of its surface protrudes into a sheet conveying path that extends from the sheet storage cassette 21 to the downstream side in the sheet conveying direction Dc. The feed roller 252 is connected to and rotated by a feed motor 25m provided in the main body 2.

[0039] A drive mechanism (not shown) for the pickup roller 251 is disposed between the feed roller 252 and the pickup roller 251. The drive mechanism has multiple gears connected to each other, and rotatably connects the feed roller 252 and the pickup roller 251. When the feed roller 252 is rotated by the feed motor 25m, the drive mechanism also rotates the pickup roller 251 in the same direction and at the same speed as the feed roller 252.

[0040] Separation roller 253 is disposed below feed roller 252 across the sheet transport path in feed section 25. Separation roller 253 presses against and contacts feed roller 252 due to the action of a biasing member (not shown). Sheet S is inserted into nip N formed by contact between separation roller 253 and feed roller 252. Separation roller 253 is not connected to a motor, and rotates in accordance with the rotation of feed roller 252 by coming into contact with feed roller 252.

[0041] A torque limiter 253t, for example, is provided on a shaft 253x of the separation roller 253. When no sheet S is present in the nip N or when only one sheet S has entered, a torque equal to or greater than the set torque of the torque limiter 253t is applied to the separation roller 253, and the separation roller 253 rotates in the direction of feeding the sheet S following the feed roller 252. In this way, the separation and conveyance unit 25S separates and conveys the sheets one by one.

[0042] On the other hand, when multiple overlapping sheets S enter the nip portion N, the torque applied to the separation roller 253 becomes less than the set torque of the torque limiter 253t, and the separation roller 253 stops rotating. This prevents the lower overlapping sheet S from being fed, thereby preventing the problem of double feeding, in which overlapping sheets S are fed.

[0043] Pickup holder 254 rotatably supports shaft 251x of pickup roller 251 and shaft 252x of feed roller 252. Pickup holder 254 is attached to main body 2 so as to be swingable in a vertical plane around shaft 252x of feed roller 252. This allows the pickup roller 251 portion of pickup holder 254, which is a downstream portion of pickup holder 254 in the sheet conveying direction Dc, to swing in a vertical plane around shaft 252x of feed roller 252. Note that the pickup roller 251 portion of pickup holder 254 is biased downward by, for example, gravity.

[0044] The pickup holder 254 has a shielding plate 254h at the upstream end in the sheet conveying direction Dc. The shielding plate 254h is a plate-like member that protrudes toward the upstream side of the pickup holder 254 in the sheet conveying direction Dc and extends in the vertical direction.

[0045] The feeding position sensor 255 is disposed close to the shielding plate 254h of the pickup holder 254. The feeding position sensor 255 is configured, for example, as a transmission-type optical sensor, and the shielding plate 254h passes on its optical path. The optical sensor outputs signals of different levels depending on whether the optical path is in a transmission state or a shielding state. The feeding position sensor 255 detects that the shielding plate 254h, which is displaced upward together with the pickup roller 251 that has come into contact with the top layer of sheets S as the lift plate 23 rises, blocks the optical path of the optical sensor.

[0046] That is, the feeding position sensor 255 detects that the uppermost layer of the sheets S stacked on the lift plate 23 pushed up by the swinging mechanism 24 comes into contact with the pickup roller 251. An output signal of the feeding position sensor 255 is input to the control unit 11.

[0047] In the lift-up process of the lift plate 23, the control unit 11 stops the lifting of the lift plate 23 by the swing mechanism 24 after a predetermined time has elapsed since the feeding position sensor 255 detected that the uppermost layer of the sheets S has come into contact with the pickup roller 251. As a result, the lift plate 23 is positioned at a predetermined feeding position P1 (see FIG. 5) where the sheets S on the lift plate 23 are sent downstream in the sheet conveyance direction Dc. That is, more specifically, the feeding position sensor 255 detects the movement of the lift plate 23 to a feeding approaching position P3 (see FIG. 5) which is located between the feeding position P1 and the retracted position P2 of the sheets S.

[0048] Then, in the process of feeding the sheets S stored in the sheet feeding device 20 to the transfer unit 8, the control unit 11 controls the swing mechanism 24 to change the feeding position P1 of the lift plate 23 in the vertical direction based on the remaining number of sheets S stacked on the lift plate 23. In this way, the control unit 11 adjusts the entry position of the sheets S with respect to the separation and conveyance unit 25S.

[0049] According to the above configuration, the feeding position P1 can be determined appropriately and arbitrarily depending on the remaining number of sheets on the lift plate 23. This makes it possible to keep the entry position of the sheet S into the separation conveying section 25S constant, thereby realizing appropriate sheet conveyance.

[0050] Here, in order to avoid problems such as damage to the roller surface due to contact of the leading edge of the sheet with the separation conveying section 25S, adhesion of paper dust to the roller surface, and double feeding of sheets S, it is preferable to set the entry position of the sheet S at a predetermined position below the nip section N. The fewer the remaining sheets on the lift plate 23, the greater the inclination angle of the lift plate 23 becomes, and there is a risk that the entry position of the sheet S with respect to the separation conveying section 25S will rise.

[0051] Therefore, to be more specific about the feeding process, the control unit 11 lowers the feeding position P1 of the lift plate 23 as the remaining amount of sheets on the lift plate 23 decreases. In this case, a data table is created in advance based on experiments or the like to determine the relationship between the remaining amount of sheets on the lift plate 23 and the lowering amount of the feeding position P1, and is stored in the storage unit 12 or the like.

[0052] According to the above configuration, it is possible to prevent the entry position of the sheet S with respect to the separating and conveying section 25S from rising, and to keep the entry position of the sheet S constant depending on the remaining number of sheets.

[0053] More specifically, when adjusting the entry position of the sheet S with respect to the separation and conveyance unit 25S, the control unit 11, when further moving the lift plate 23 that has moved to the feeding approach position P3 to the feeding position P1, shortens the movement time of the lift plate 23 from the feeding approach position P3 to the feeding position P1 as the number of remaining sheets on the lift plate 23 decreases. In this case, a data table is created in advance based on experiments or the like to store in the storage unit 12 or the like regarding the relationship between the number of remaining sheets on the lift plate 23 and the movement time of the lift plate 23 from the feeding approach position P3 to the feeding position P1.

[0054] According to the above configuration, the smaller the remaining amount of sheets on the lift plate 23, the lower the feeding position P1 of the lift plate 23 can be. Therefore, it is possible to prevent the entry position of the sheet S into the separation conveying section 25S from rising.

[0055] Next, detection of the remaining amount of sheets on the lift plate 23 will be described. The control unit 11 detects the movement time of the lift plate 23 from the retracted position P2 to the feed approach position P3 using the feeding position sensor 255. Then, the control unit 11 detects the remaining amount of sheets on the lift plate 23 based on the movement time of the lift plate 23. In this case, a data table regarding the relationship between the remaining amount of sheets on the lift plate 23 and the movement time of the lift plate 23 from the retracted position P2 to the feed approach position P3 is created in advance based on experiments or the like and stored in the storage unit 12 or the like.

[0056] According to the above configuration, the amount of remaining sheets on the lift plate 23 can be detected by utilizing the feeding position sensor 255 used to move the sheets S on the lift plate 23 to a predetermined feeding position. This makes it possible to detect the amount of remaining sheets on the lift plate 23 without providing a dedicated sensor or detection mechanism for detecting the amount of remaining sheets on the lift plate 23. Therefore, it is possible to reduce the cost, size and weight of the sheet feeding device 20, i.e., the image forming apparatus 1.

[0057] Note that a dedicated sheet remaining amount detection unit 30 (see FIG. 2) may be provided in the sheet feeding device 20 to detect the amount of sheets remaining on the lift plate 23. FIG. 6 is an explanatory diagram showing an example of the configuration of the sheet remaining amount detection unit 30 in FIG. 1. The sheet remaining amount detection unit 30 detects the remaining amount level (thickness level of the stack of sheets) in the sheet storage cassette 21, i.e., the sheets stacked on the lift plate 23. As shown in FIG. 6, the sheet remaining amount detection unit 30 includes a shielding plate 31 and a lift position detection unit 32 including a first sensor 321 and a second sensor 322.

[0058] The shielding plate 31 is fixed to the rotating shaft 241 of the swing mechanism 24, and extends radially outward from the rotating shaft 241. The shielding plate 31 is a fan-shaped plate that extends around the axis of the rotating shaft 241 (in the circumferential direction). The rotation angle of the shielding plate 31 changes depending on the rotation angle of the rotating shaft 241. The fan-shaped shielding plate 31 rotates around the axis of the rotating shaft 241 (in the circumferential direction).

[0059] The first sensor 321 and the second sensor 322 of the lift position detection unit 32 are arranged on the movement path of the fan-shaped shielding plate 31. The first sensor 321 and the second sensor 322 are each composed of, for example, a transmission-type optical sensor, and the shielding plate 31 passes on its optical path. The optical sensor outputs signals of different levels depending on whether the optical path is in a transmission state or a shielded state. The output signals of the first sensor 321 and the second sensor 322 are input to the control unit 11. The control unit 11 detects the remaining level of the sheets S on the lift plate 23 based on a combination of the input output signals.

[0060] The number of sensors shielded by the shielding plate 31 changes according to the amount of rotation of the rotating shaft 241. FIG. 6 shows an example of the state when the sheet remaining amount is 100% (the lift amount of the lift plate 23 is small). When the pick-up roller 251 contacts the uppermost layer of the sheet S on the lift plate 23, the control unit 11 rotates the rotating shaft 241. The smaller the remaining amount of the sheet on the lift plate 23, the larger the rotation angle of the shielding plate 31 (rotating shaft 241) to the feeding proximity position P3 (see FIG. 5).

[0061] When the ratio Rr of the remaining amount of the sheet to the sheet loading capacity at full capacity of the sheet storage cassette 21 is 75% < Rr ≤ 100%, the first sensor 321 and the second sensor 322 are arranged at positions not shielded by the shielding plate 31. Also, when the ratio Rr of the remaining amount of the sheet to the sheet loading capacity at full capacity of the sheet storage cassette 21 is 50% < Rr ≤ 75%, the first sensor 321 is arranged at a position shielded by the shielding plate 31, and the second sensor 322 is arranged at a position not shielded by the shielding plate 31.

[0062] Also, when the ratio Rr of the remaining amount of the sheet to the sheet loading capacity at full capacity of the sheet storage cassette 21 is 25% < Rr ≤ 50%, the first sensor 321 and the second sensor 322 are arranged at positions shielded by the shielding plate 31. Also, when the ratio Rr of the remaining amount of the sheet to the sheet loading capacity at full capacity of the sheet storage cassette 21 is 0% < Rr ≤ 25%, the first sensor 321 is arranged at a position not shielded by the shielding plate 31. The second sensor 322 is arranged at a position shielded by the shielding plate 31. <00>

[0063] When the output levels of the first sensor 321 and the second sensor 322 are in the transmission state, the control unit 11 recognizes the remaining amount level 4 of the sheet S (remaining amount 75% < Rr ≤ 100%). When the output level of the first sensor 321 is in the light-shielding state and the output level of the second sensor 322 is in the transmission state, the control unit 11 recognizes the remaining amount level 3 of the sheet S (remaining amount 50% < Rr ≤ 75%). When the output levels of the first sensor 321 and the second sensor 322 are in the light-shielding state, the control unit 11 recognizes the remaining amount level 2 of the sheet S (remaining amount 25% < Rr ≤ 50%). When the output level of the first sensor 321 is in the transmission state and the output level of the second sensor 322 is in the light-shielding state, the control unit 11 recognizes the remaining amount level 1 of the sheet S (remaining amount 0% < Rr ≤ 25%).

[0064] In this way, the lift position detection unit 32 changes the output level of the output signal according to the degree of the rise of the lift plate 23 (rotation of the rotary shaft 241). That is, the lift position detection unit 32 detects the vertical position which is the vertical direction position of the swing end of the lift plate 23. The control unit 11 detects the vertical position of the lift plate 23 by the lift position detection unit 32, and detects the remaining amount of the sheet on the lift plate 23 based on the vertical position.

[0065] According to the above configuration, the remaining amount of the sheet on the lift plate 23 can be suitably detected by using a dedicated sensor or detection mechanism for detecting the remaining amount of the sheet on the lift plate 23. That is, by using the lift position detection unit 32, it becomes possible to recognize the remaining amount of the sheet more accurately.

[0066] And, calibration using the lift position detection unit 32 may be performed for the method of detecting the remaining amount of the sheet on the lift plate 23 using the feed position sensor 255. In this case, the control unit 11 adjusts the movement time of the lift plate 23 from the retreat position P2 to the feed proximity position P3 and the movement time of the lift plate 23 from the feed proximity position P3 to the feed position P1 by using the vertical position of the lift plate 23 detected by the lift position detection unit 32.

[0067] Specifically, the control unit 11 adjusts the movement time of the lift plate 23 from the retracted position P2 to the feeding proximity position P3 corresponding to each of the remaining sheet S levels 1, 2, 3, and 4, using the up / down position of the lift plate 23 corresponding to each of the remaining sheet S levels 1, 2, 3, and 4 detected by the lift position detection unit 32. Furthermore, the control unit 11 adjusts the movement time of the lift plate 23 from the feeding proximity position P3 to the feeding position P1 using the adjusted movement time of the lift plate 23 from the retracted position P2 to the feeding proximity position P3.

[0068] According to the above configuration, it is possible to improve the detection accuracy when detecting the remaining amount of sheets on the lift plate 23 using the feeding position sensor 255. That is, the feeding position sensor 255 makes it possible to recognize the remaining amount of sheets more accurately.

[0069] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention.

[0070] For example, in the above embodiment, the image forming apparatus 1 is an image forming apparatus for monochrome printing, but is not limited to such a model. The image forming apparatus may be, for example, an image forming apparatus for color printing. [Industrial Applicability]

[0071] The present invention can be used in a sheet feeding apparatus and an image forming apparatus. [Explanation of symbols]

[0072] 1. Image forming device 2 Main unit 11 Control section 12 Storage section 20 Sheet feeding device 21-sheet cassette 22 Cassette storage section 23 Lift Board 24 Swing mechanism 25 Feeding section 25S Separation and conveyance section 30 Sheet remaining amount detection unit 31 Shielding plate 32 Lift position detector 241 Rotating shaft 242 Lift lever 251 Pickup roller 252 Feeding roller 253 Separation Roller 255 Feeding position sensor 321 First Sensor 322 Second Sensor Dc Sheet transport direction N Nip P1 feeding position P2 Evacuation position P3 Feeding proximity position S seat

Claims

1. a sheet storage section in which sheets are stacked; a lift plate that is disposed in the sheet storage section and that moves the sheets stacked on an upper surface of the lift plate between a feeding position and a retracted position by vertically swinging a downstream portion of the lift plate around an upstream portion of the lift plate with respect to a sheet conveying direction; a swing mechanism for swinging a downstream portion of the lift plate in the sheet conveying direction in a vertical direction; a pickup roller that contacts the uppermost layer of the sheets stacked on the lift plate from above and sends the sheet downstream in the sheet conveying direction; a separation and conveyance unit including a feed roller disposed downstream of the pickup roller in the sheet conveying direction and a separation member in contact with the feed roller, the separation and conveyance unit separating and conveying the sheets one by one; A control unit that controls operations of the swing mechanism, the pick-up roller, and the separation and transport unit; Equipped with The control unit is A sheet feeding device characterized by controlling the swing mechanism to change the feeding position of the lift plate in the vertical direction based on the remaining amount of sheets loaded on the lift plate, thereby adjusting the entry position of the sheets relative to the separation conveying section.

2. The sheet feeding device according to claim 1 , wherein the control unit lowers the feeding position of the lift plate as the remaining amount of the sheets on the lift plate decreases.

3. a feed position detection unit that detects movement of the lift plate to a feed approach position that is located between the feed position and the retracted position, The sheet feeding device according to claim 1 , wherein the control unit detects the movement time of the lift plate from the retracted position to the feeding approach position using the feeding position detection unit, and detects the remaining amount of sheets on the lift plate based on the movement time.

4. The sheet feeding device according to claim 3, characterized in that when the control unit further moves the lift plate, which has moved to the feeding approach position, to the feeding position, the smaller the amount of sheets remaining on the lift plate, the shorter the movement time of the lift plate from the feeding approach position to the feeding position.

5. A lift position detection unit is provided to detect the vertical position of the swing end of the lift plate, 2 . The sheet feeding device according to claim 1 , wherein the control unit detects the vertical position of the lift plate by the lift position detection unit, and detects the remaining amount of sheets on the lift plate based on the vertical position.

6. a feed position detection unit that detects movement of the lift plate to a feed approach position that is located between the feed position and the retracted position, The sheet feeding device according to claim 5, characterized in that the control unit adjusts the movement time of the lift plate from the retracted position to the feeding approach position and the movement time of the lift plate from the feeding approach position to the feeding position using the vertical position of the lift plate detected by the lift position detection unit.

7. 7. An image forming apparatus comprising the sheet feeding device according to claim 1.

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