Sheet feeding device and image forming device equipped with the same

Abstract

To provide a sheet feeding device capable of extending a feeding possible distance with a simple configuration when using a sheet feeding roller having a half-moon feeding surface, and an image forming device equipped with the same.SOLUTION: A sheet feeding device includes: a sheet stacking tray; a sheet abutment part; a sheet feeding roller; a separation member; a first energizing member; an eccentric cam; a cam follower; a sheet detection mechanism; and a holding mechanism. The holding mechanism holds the separation member at a position spaced apart from the sheet feeding roller after a half-moon feeding surface passes through the separation member due to rotation of the sheet feeding roller. The sheet stacking tray is made to wait at a waiting position radially inward from the outer diameter of the feeding surface immediately before starting a sheet feeding, so that a feeding possible distance which is the distance between a feeding start position and the sheet abutment part, is made larger than a detection possible distance which is the maximum distance between the detection possible position where the sheet can be detected by the sheet detection mechanism and the sheet abutment part.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a sheet feeding device that feeds sheets such as paper, and an image forming apparatus equipped with the same. [Background technology]

[0002] A sheet feeding device that feeds sheets such as cut paper is known in image forming devices such as copiers and printers. A sheet feeding device generally feeds a stack of sheets by pressing the top surface of the stack of sheets against a pickup roller.

[0003] One example of a sheet feeding device is one that has a paper feed roller (half-moon roller) that is formed in a circular cross section with a portion cut out and feeds paper (sheets), and a pressure plate that is biased toward the paper feed roller by a biasing means and presses the loaded paper against the paper feed roller in synchronization with one rotation of the paper feed roller using a cam, clutch, etc.

[0004] For example, Patent Document 1 discloses a paper feeder in which a half-moon roller (paper feed roller) has a low-friction coefficient section that covers the area from the contact start point of a full stack of paper on a pressure plate to the contact start point of a single sheet of paper. The low-friction coefficient section is an arc-shaped area that does not have a paper-feeding function and is connected to the circumferential area of ​​the high-friction coefficient section.

[0005] According to the configuration of Patent Document 1, whether a full stack of paper or a single sheet is being fed, paper is not fed in the circumferential region of the low friction coefficient part of the half-moon roller, and the paper feed operation begins when the paper contacts the high friction coefficient part. Therefore, the position at which the paper feed operation by the high friction coefficient part begins is the same. Therefore, regardless of the amount of paper loaded on the pressure plate, instability at the start of contact between the paper feed roller and the loaded paper can be eliminated, and variations in the distance between the sheets can be suppressed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-124084 Summary of the Invention [Problem to be solved by the invention]

[0007] In the sheet feeding device described above, a photointerrupter (PI) sensor is sometimes used as a paper detection sensor to detect the presence or absence of paper on the sheet stack tray. If the area in which this paper detection sensor can detect paper is larger than the area in which the paper feed roller can feed paper, a situation occurs in which paper is detected but cannot be fed, resulting in a poor usability.

[0008] In view of the above problems, the present invention aims to provide a sheet feeding device that can extend the sheet feeding distance with a simple configuration when using a sheet feeding roller with a crescent-shaped feeding surface, and an image forming apparatus equipped with the same. [Means for solving the problem]

[0009] In order to achieve the above object, a first configuration of the present invention is a sheet feeding device including a sheet stacking tray, a sheet abutment portion, a sheet feed roller, a separation member, a first biasing member, an eccentric cam, a cam follower, a sheet detection mechanism, and a holding mechanism. The sheet stacking tray is movable up and down and has sheets stacked thereon. The sheet abutment portion abuts the leading edges of sheets stacked on the sheet stacking tray to align them. The sheet feed roller has a crescent-shaped feed surface that is pressed against the upper surfaces of the sheets stacked on the sheet stacking tray and sends the sheets in the feed direction. The separation member contacts the feed surface of the sheet feed roller to form a feed nip. The first biasing member biases the sheet stacking tray in a direction approaching the sheet feed roller. The eccentric cam is fixed to the rotation shaft of the sheet feed roller and has a maximum eccentric radius greater than the radius of the sheet feed roller. The cam follower is positioned to contact the eccentric cam of the sheet stack tray, and the contact point moves from the large diameter portion of the eccentric cam to the small diameter portion of the eccentric cam as the eccentric cam rotates, thereby lifting the sheet stack tray.The sheet detection mechanism has a sheet detection sensor equipped with a detection unit having a light-emitting portion and a light-receiving portion, and a detection member that comes into contact with the sheets stacked on the sheet stack tray and swings to form a light-blocking portion that blocks or opens the light path of the detection unit, and detects the sheets stacked on the sheet stack tray.The holding mechanism holds the separation member in a position separated from the sheet feed roller after the feeding surface passes the separation member due to the rotation of the sheet feed roller. By making the sheet stacking tray wait at a standby position radially inward of the outer diameter of the feeding surface immediately before starting to feed the sheets, the feedable distance, which is the distance between the feeding start position where the feeding surface and the sheet stacking tray come into contact and the sheet abutting part, is made larger than the detectable distance, which is the maximum distance between the sheet abutting part and the detectable position where the sheet can be detected by a sheet detection mechanism when the leading edge of the sheet is separated from the sheet abutting part. [Effects of the Invention]

[0010] According to the first aspect of the present invention, by having the sheet stacking tray wait at a standby position radially inward from the outer diameter of the feeding surface immediately before starting sheet feeding, the feeding distance of the sheet feeding roller is made greater than the detectable distance of the sheet detection mechanism. This prevents the occurrence of a problem in which a sheet is not fed even though it is detected. Furthermore, by providing a holding mechanism that holds the separating member at a position separated from the sheet feeding roller, it is possible to suppress positional fluctuations of the separating member after the feeding surface has passed and the resulting sheet feeding problems. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 equipped with a manual paper feed unit 26 according to an embodiment of the present invention. [Figure 2] 1 is a perspective view of a manual paper feed unit 26 according to a first embodiment of the present invention; [Figure 3] FIG. 1 is a front view of the manual paper feed unit 26 according to the first embodiment, viewed from the upstream side in the sheet feeding direction; [Figure 4] 1 is a side cross-sectional view of a manual paper feed unit 26 according to a first embodiment; [Figure 5] 5 is an enlarged view of the vicinity of the sheet detection sensor 57 in FIG. 4 as viewed from the axial direction of the shaft 50. [Figure 6] FIG. 10 is an explanatory diagram of a sheet feeding operation in the conventional manual sheet feed unit 26, showing a state in which the MPF tray 27 is separated from the sheet feeding roller 41. [Figure 7] 7 is a diagram showing a state immediately before the sheet feeding roller 41 and the eccentric cam 53 rotate a predetermined amount from the state of FIG. 6 and the MPF tray 27 comes into contact with the feeding surface 41a of the sheet feeding roller 41. FIG. [Figure 8] 8 is a diagram showing a state in which the sheet feeding roller 41 and the eccentric cam 53 have rotated a predetermined amount from the state in FIG. 7, and the MPF tray 27 has come into contact with the feeding surface 41a of the sheet feeding roller 41. [Figure 9] FIG. 10 is a side cross-sectional view of the vicinity of the eccentric cam 53 in the manual paper feed unit 26 according to the first embodiment, showing a state in which the MPF tray 27 has been lowered to the lowest position. [Figure 10] FIG. 10 is a side cross-sectional view of the vicinity of the sheet feed roller 41 in the state of FIG. 9, showing the positional relationship between the sheet feed roller 41 and the MPF tray 27. [Figure 11] FIG. 10 is a side cross-sectional view showing a positioning mechanism for the separation pad 51 in the manual paper feed unit 26 according to the first embodiment. [Figure 12] FIG. 10 is an enlarged side view of the vicinity of the eccentric cam 53 in the manual paper feed unit 26 according to the first embodiment, showing a state in which the MPF tray 27 has been raised from the state shown in FIG. [Figure 13] FIG. 13 is a side cross-sectional view of the vicinity of the sheet feed roller 41 in the state of FIG. 12, showing the positional relationship between the sheet feed roller 41 and the MPF tray 27. [Figure 14] 12 is an enlarged side view of the vicinity of the eccentric cam 53 in the manual paper feed unit 26 according to the first embodiment, showing a state in which the MPF tray 27 is further raised from the state shown in FIG. 11. [Figure 15] FIG. 15 is a side cross-sectional view of the vicinity of the sheet feed roller 41 in the state of FIG. 14, showing the positional relationship between the sheet feed roller 41 and the MPF tray 27. [Figure 16] FIG. 10 is a side cross-sectional view of the vicinity of a sheet feed roller 41 in a manual paper feed unit 26 according to a second embodiment of the present invention, illustrating the positional relationship between the sheet feed roller 41 and an MPF ​​tray 27. DETAILED DESCRIPTION OF THE INVENTION

[0012] [1. Configuration of image forming device] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 equipped with a manual paper feed unit 26 according to an embodiment of the present invention. The image forming apparatus 100 shown in Fig. 1 is a so-called tandem color printer.

[0013] Image forming units Pa to Pd are arranged horizontally inside the device body 7 of the image forming apparatus 100. The image forming units Pa to Pd sequentially form images of yellow, magenta, cyan, and black through the processes of charging, exposure, development, and transfer, respectively. The image forming units Pa to Pd are provided corresponding to the images of each color. Only the image forming unit Pa will be described below, but the image forming units Pb to Pd will not be described as they are basically configured in the same way.

[0014] The image forming unit Pa is provided with a photosensitive drum 1a that carries a visible image (toner image). An exposure device 5 is disposed above the image forming unit Pa. The exposure device 5 emits a light beam toward the surfaces of the photosensitive drums 1a to 1d to draw an electrostatic latent image. Around the photosensitive drum 1a, a charging device 2a, a developing device 3a, and a rubbing roller 23a are disposed in the drum rotation direction (clockwise in FIG. 1).

[0015] The charging device 2a is disposed opposite the photosensitive drum 1a and is capable of charging the surface of the photosensitive drum 1a. The developing device 3a has a developing container 4a, a developing roller 21a, and a supply roller 24a. The developing container 4a is filled with a predetermined amount of toner. The toner filled in the developing containers 4a to 4d for each of the developing devices 3a to 3d is either yellow, magenta, cyan, or black. The developing roller 21a is disposed opposite the photosensitive drum 1a. The supply roller 24a supplies the toner in the developing container 4a to the outer peripheral surface of the developing roller 21a. The developing roller 21a is capable of supplying the toner supplied to its outer peripheral surface to the photosensitive drum 1a.

[0016] Below the photosensitive drums 1a to 1d, an intermediate transfer unit 31 is provided. The intermediate transfer unit 31 includes a frame 30, a drive roller 10, a tension roller 11, an intermediate transfer belt 8, and primary transfer rollers 6a to 6d.

[0017] The frame 30 extends in the width direction (the left-right direction in FIG. 1) of the image forming apparatus 100. The drive roller 10 and the tension roller 11 are rotatably supported on both ends of the frame 30 in the longitudinal direction.

[0018] The intermediate transfer belt 8 is an endless belt (preferably a seamless belt having no joints). The intermediate transfer belt 8 is wound around a tension roller 11 and a drive roller 10 so as to be rotatable in the circumferential direction.

[0019] The drive roller 10 is connected to a belt drive motor (not shown). When the drive roller 10 is rotated by the rotational drive force of the belt drive motor, the rotational drive force is transmitted to the intermediate transfer belt 8 by frictional force. As a result, the intermediate transfer belt 8 rotates in the same direction as the rotational direction of the drive roller 10.

[0020] The primary transfer rollers 6a to 6d are rotatably and movably supported by a frame 30 at positions facing the photosensitive drums 1a to 1d with the intermediate transfer belt 8 sandwiched therebetween.

[0021] A secondary transfer roller 9 is provided opposite the drive roller 10 with the intermediate transfer belt 8 sandwiched therebetween. The secondary transfer roller 9 is pressed against the intermediate transfer belt 8 to form a secondary transfer nip N. The secondary transfer roller 9 performs a second transfer of the toner image formed on the intermediate transfer belt 8 onto the sheets S1 and S2 passing through the secondary transfer nip N.

[0022] Inside the image forming apparatus 100, at positions to the side of the image forming sections Pa to Pd and the intermediate transfer belt 8, there are arranged a sheet conveying path 20, a pair of resist rollers 12, a sheet cassette 16, a sheet feeding section 25, and a manual paper feeding section 26.

[0023] The sheet transport path 20 is configured to include a main transport path 28 and a duplex transport path 18. The main transport path 28 extends in the vertical direction. A registration roller pair 12, a secondary transfer roller 9, and a fixing device 13 are arranged in a position midway along the main transport path 28. The main transport path 28 transports the sheet S1 or the sheet S2 from a manual paper feed unit 26 and a sheet cassette 16 (described later) so that the sheet S1 or the sheet S2 passes through the registration roller pair 12, the secondary transfer nip N, and the fixing device 13 in this order.

[0024] The pair of registration rollers 12 aligns the conveying direction of the sheets S1 and S2 so that the leading edges (downstream edges in the sheet conveying direction) of the sheets S1 and S2 are perpendicular to the sheet conveying direction, thereby correcting skew.

[0025] A sheet discharge port 15 leading to the outside of the image forming apparatus 100 is provided at the downstream end of the main transport path 28 in the sheet transport direction. A discharge roller pair 22 is provided at the sheet discharge port 15.

[0026] A branching section 14 is provided between the discharge roller pair 22 and the fixing device 13 in the sheet conveying direction. The duplex conveying path 18 branches off from the main conveying path 28 at a position overlapping with the branching section 14 of the main conveying path 28 in the sheet conveying direction, and rejoins the main conveying path 28 at a position upstream of the registration roller pair 12. The branching section 14 can distribute the sheets S1 and S2 that have passed through the fixing device 13 to the sheet discharge outlet 15 or the duplex conveying path 18.

[0027] The sheet cassette 16 and the manual feed unit 26 are provided upstream of the main transport path 28 in the sheet transport direction. The sheet cassette 16 can hold sheets S1, and the manual feed unit 26 can hold sheets S2. The sheet feed unit 25 is disposed between the main transport path 28 and the sheet cassette 16 and manual feed unit 26, and feeds the sheets S1 and S2 to the main transport path 28.

[0028] The sheet cassette 16 is detachable from the device main body 7. Specifically, it can be pulled out from the device main body 7 after being inserted to the deepest part of the cassette accommodating section in the horizontal direction (attached state).

[0029] Manual paper feed unit 26 is attached to the side of device body 7, at a position between entrance 38 and the edge of the opening of cassette storage unit 29 in the vertical direction. Manual paper feed unit 26 is capable of feeding sheets S2 (sheets serving as recording media including special-sized paper, cardboard, envelopes, transparencies, etc.) onto its upper surface.

[0030] The carry-in entrance 38 is provided with a pair of carry-in rollers 40 and a sheet feed roller 41. The sheet feed roller 41 abuts against the downstream end of the sheet S2 in the sheet conveyance direction. The sheet feed roller 41 and the carry-in roller pair 40 rotate to carry the sheet S2 into the manual feed path 39. The feeding of the sheet S2 from the manual feed unit 26 will be described in detail later.

[0031] A plurality of transport roller pairs 47 are arranged at predetermined intervals in the sheet transport direction along the manual feed path 39. The transport roller pairs 47 are a pair of roller bodies that face each other above and below with the manual feed path 39 in between. The sheet S2 transported into the manual feed path 39 is transported by each transport roller pair 47 toward the pickup roller 42.

[0032] The sheet feeding section 25 includes a pickup roller 42 and a pair of feeding rollers 43. The pickup roller 42 is rotatably supported by a roller holder 44 (see FIG. 2) and rotates by the rotational driving force of a driving device (not shown). The pickup roller 42 rotates while contacting the upper surface of the sheet S1 stacked on the sheet stacking plate 37 in the sheet cassette 16 and the sheet S2 transported from the manual paper feed section 26 to the manual feed path 39. As a result, the sheets S1 and S2 are sent in the feeding direction and handed over to the pair of feeding rollers 43.

[0033] An operation panel 101 is disposed in front of the image forming apparatus 100. The operation panel 101 is an operation unit for receiving various setting inputs. For example, a user can operate the operation panel 101 to input information about the type of sheet. The user can also operate the operation panel 101 to input the number of sheets to be printed and to instruct the start of a print job. The control unit 102 supervises the overall operation of the image forming apparatus 100 and controls each unit of the image forming apparatus 100.

[0034] Next, we will explain the image formation procedure in the image forming apparatus 100. When a user inputs a command to start image formation, first, the photosensitive drum 1a is rotated while the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates the surfaces of the photosensitive drums 1a to 1d with light, and electrostatic latent images corresponding to the image signals are formed on the photosensitive drums 1a to 1d.

[0035] The toner in the developer in the developing devices 3a to 3d is supplied onto the photosensitive drums 1a to 1d by the developing rollers 21a to 21d and electrostatically adheres to the photosensitive drums 1a to 1d, thereby forming toner images on the photosensitive drums 1a to 1d corresponding to the electrostatic latent images.

[0036] In this state, the drive roller 10 is rotated to start the counterclockwise rotation of the intermediate transfer belt 8. Then, the toner images of each color formed on the photosensitive drums 1a to 1d are sequentially transferred (primary transfer) onto the intermediate transfer belt 8.

[0037] Thereafter, at a predetermined timing, sheets S1 and S2 are fed from sheet cassette 16 or manual paper feed unit 26 to main transport path 28, pass through registration roller pair 12, and are transported to secondary transfer nip N. Then, the toner images on intermediate transfer belt 8 are secondarily transferred onto sheets S1 and S2. Then, sheets S1 and S2 are transported to fixing device 13, where they are heated and pressed by fixing roller pair 13a of fixing device 13, and the toner images are fixed to the surfaces of sheets S1 and S2.

[0038] When single-sided printing is performed on sheets S1 and S2, branching unit 14 distributes sheets S1 and S2 that have passed through fixing device 13 to sheet discharge outlet 15. Sheets S1 and S2 that have reached sheet discharge outlet 15 are discharged onto sheet discharge tray 17 by discharge roller pair 22.

[0039] When double-sided printing is performed on sheets S1 and S2, branching unit 14 distributes sheets S1 and S2 that have passed through fixing device 13 to double-sided conveying path 18. Double-sided conveying path 18 conveys sheets S1 and S2 again to registration roller pair 12 while turning them over. Sheets S1 and S2 then pass through secondary transfer nip N and fixing device 13 again, and after the toner image is fixed on the back side, they are distributed by branching unit 14 to sheet discharge outlet 15.

[0040] [2. Manual feed unit configuration] Fig. 2 is a perspective view of manual paper feed unit 26 according to the first embodiment of the present invention. Fig. 3 is a front view of manual paper feed unit 26 according to the first embodiment, as seen from the upstream side in the sheet feeding direction. Fig. 4 is a side cross-sectional view of manual paper feed unit 26 according to the first embodiment (cross-sectional view taken along arrow XX' in Fig. 3). As shown in Fig. 2, manual paper feed unit 26 includes an MPF ​​tray 27, a tray support cover 28, a sheet feed roller 41, a separation pad 51, and a sheet detection sensor 57.

[0041] The MPF tray 27 is swingably supported by a tray support cover 28 at a swing fulcrum 27a on the upstream side in the sheet feeding direction (from left to right in FIG. 4), and the end portion on the downstream side in the sheet feeding direction moves up and down. The tray support cover 28 is openably and closably supported by the device main body 7 at a support shaft 28a on the upstream side in the sheet feeding direction. Support arms 29 are connected to both widthwise ends of the tray support cover 28. The support arms 29 regulate the opening angle of the tray support cover 28.

[0042] A biasing spring 58 is disposed between the MPF tray 27 and the tray support cover 28. The MPF tray 27 is biased by the biasing spring 58 in a direction away from the tray support cover 28 (upward).

[0043] A shaft 50 is disposed near the downstream end of the MPF tray 27 in the sheet feeding direction. The shaft 50 is rotatably supported by a bearing (not shown) of the main body frame of the image forming apparatus 100. A sheet feeding roller 41 that feeds sheets S2 (not shown in FIGS. 2 to 4) stacked on the MPF tray 27 is fixed to approximately the center of the shaft 50 in the axial direction. The sheet feeding roller 41 has a rubber feeding surface 41a (see FIG. 5) that is crescent-shaped in cross section.

[0044] A separation pad 51 is disposed at the upstream end of the manual feed path 39 in the sheet feeding direction, facing the sheet feed roller 41. The surface of the separation pad 51 is formed of a material with high friction. The separation pad 51 comes into contact with the feed surface 41a of the sheet feed roller 41 to form a feed nip. The feed surface 41a of the sheet feed roller 41 rotates while abutting against the stack of sheets S2 stacked on the MPF tray 27, so that only the uppermost sheet S2 is separated between the separation pad 51 and the sheet S2 and fed.

[0045] Fixed to both ends of the shaft 50 are eccentric cams 53 in the shape of a comma-shaped bead, the maximum eccentric radius of which is greater than the radius of the sheet feed roller 41. Furthermore, attached to one end of the shaft 50 is a drive input gear 54, the peripheral surface of which is partially missing teeth. The drive input gear 54 is engaged with a drive output gear (neither of which is shown) that is rotationally driven by a drive motor.

[0046] When feeding sheet S2, the control unit 102 (see FIG. 1) transmits the driving force of the drive motor to the drive input gear 54 at a predetermined timing, and the rotation of the shaft 50 causes the sheet feeding roller 41 and the eccentric cam 53 to make one rotation in the direction of arrow A. In addition, cam followers 55 that can come into contact with the eccentric cam 53 are provided to protrude upward at positions facing the eccentric cam 53 on both side ends of the MPF tray 27.

[0047] A sheet detection sensor 57 is disposed above the shaft 50. The following describes the configuration for detecting the presence or absence of the sheet S2 by the sheet detection sensor 57.

[0048] Fig. 5 is an enlarged view of the vicinity of the sheet detection sensor 57 in Fig. 4 as viewed from the axial direction of the shaft 50. As shown in Fig. 5, the sheet detection sensor 57 is a PI (photointerrupter) sensor equipped with a detection unit 57a in which a light receiving unit and a light emitting unit are arranged opposite each other.

[0049] A detection member 60 is disposed on the shaft 50 at a position facing the sheet detection sensor 57. The detection member 60 has a light-shielding portion 60a and a contact portion 60b. The detection member 60 is rotatable relative to the shaft 50, and its movement in the axial direction is restricted. The sheet detection sensor 57 and the detection member 60 constitute a sheet detection mechanism that detects the presence or absence of a sheet S2 on the MPF tray 27.

[0050] A sheet abutment portion 39a is formed at the upstream end of the manual feed path 39. When the sheet S2 is stacked on the MPF tray 27, the leading edge of the sheet S2 is abutted against the sheet abutment portion 39a and aligned, whereby the sheet S2 is positioned at the feed position.

[0051] When no sheets S2 are stacked on the MPF tray 27, the contact portion 60b hangs down to the lowest position due to its own weight. In this state, the light-shielding portion 60a is not inserted between the light-receiving portion and the light-emitting portion of the detection portion 57a, and the detection signal of the detection portion 57a ​​is in a HIGH state (light-transmitting state).

[0052] When sheet S2 is stacked on the MPF tray 27, contact portion 60b is lifted by sheet S2, and detection member 60 rotates clockwise in FIG. 5. As a result, light-shielding portion 60a is inserted between the light-receiving portion and light-emitting portion of detection unit 57a, and the detection signal of detection unit 57a becomes LOW (light-shielding state). This change in detection signal allows control unit 102 to detect the presence or absence of sheet S2 on the MPF tray 27.

[0053] Here, the larger the area of ​​the detection unit 57a in the movement direction of the light-shielding unit 60a (left-right direction in FIG. 5), the larger the distance (detectable distance) d1 from the position (detection start position) P1 where the light-shielding unit 60a starts to shield the detection unit 57a to the sheet abutment unit 39a. The detectable distance d1 is the maximum distance between the sheet abutment unit 39a and the position (detectable position) where the sheet detection mechanism can detect the sheet when the leading edge of the sheet S2 is separated from the sheet abutment unit 39a. For example, if the detection unit 57a of the sheet detection sensor 57 is arranged horizontally as shown in FIG. 5 to make the configuration around the MPF tray 27 more compact (lower in height), the detectable distance d1 increases. That is, the sheet S2 can be detected even when the leading edge of the sheet S2 is separated from the sheet abutment unit 39a by the detectable distance d1.

[0054] [3. Sheet feeding operation in conventional configuration] 6 to 8 are explanatory diagrams of the sheet feeding operation in the conventional manual paper feed unit 26. In the conventional configuration, the sheet feeding roller 41 has a crescent-shaped feeding surface 41a and a pair of pulleys 41b arranged on both sides of the feeding surface 41a in the axial direction. The pulleys 41b have a radius slightly smaller than the radius of the feeding surface 41a. The separation pad 51 is fixed to a separation pad holder 70. The separation pad holder 70 is biased upward by a coil spring (not shown).

[0055] Pulley 41b regulates the height position of sheet S2 that has risen to the feeding position due to the rise of MPF tray 27, and also regulates the position of separation pad 51 in the pressing direction by rotating while in contact with separation pad 51 after feeding surface 41a has passed separation pad 51. The configuration of other parts of manual sheet feed unit 26 is the same as that of the first embodiment shown in FIG.

[0056] When the rotation of the shaft 50 causes the crescent-shaped feeding surface 41a of the sheet feeding roller 41 to move out of the feeding position, the sheet S2 is sandwiched between the separation pad 51 and the pulley 41b. In order to reduce the transport load of the sheet S2 at this time, the pulley 41b is rotatably supported on the shaft 50.

[0057] 6 shows a state in which the MPF tray 27 is separated from the sheet feed roller 41. When feeding a sheet S2 from the manual sheet feed unit 26, the shaft 50 is rotated based on a control signal from the control unit 102 (see FIG. 1). As a result, the sheet feed roller 41 and the eccentric cam 53 rotate a predetermined amount from the state in FIG. 6, and the MPF tray 27 rises.

[0058] 6, when the sheet feed roller 41 and the eccentric cam 53 rotate a predetermined amount, the MPF tray 27 rises and comes into contact with the pulley 41b, and the eccentric cam 53 and the cam follower 55 (see FIG. 2) are separated from each other, as shown in FIG. 7. In this state, the feed surface 41a of the sheet feed roller 41 is not yet in contact with the MPF tray 27.

[0059] When the sheet feeding roller 41 and the eccentric cam 53 further rotate a predetermined amount from the state in Fig. 7, the feeding surface 41a rotates and comes into contact with the MPF tray 27, feeding the sheet S2, as shown in Fig. 8. If the leading edge of the sheet S2 is within the range of the distance (feedable distance) d2 from the contact position (feed start position) P2 between the feeding surface 41a and the MPF tray 27 to the sheet abutment portion 39a, feeding of the sheet S2 becomes possible.

[0060] As mentioned above, if the detectable distance d1 (see Figure 5) of the sheet detection sensor 57 becomes greater than the feedable distance d2, there is a risk that a problem will occur in which sheet S2 cannot be fed even though it is detected that sheet S2 is stacked on the MPF tray 27.

[0061] 6 to 8, it is conceivable to increase the possible feeding distance d2 by positioning the MPF tray 27 just before it comes into contact with the feeding surface 41a of the sheet feeding roller 41 at a deeper position (inside the outer circumferential surface of the feeding surface 41a) so that the feeding surface 41a comes into contact with the MPF tray 27 from further upstream of the feeding start position P2 in Fig. 8. One possible means for achieving this is to reduce the outer diameter of the pulley 41b.

[0062] However, in the conventional configuration, the pulley 41b also plays a role in contacting the separation pad 51 after the feeding surface 41a has passed, thereby regulating the position of the separation pad 51. Therefore, if the outer diameter of the pulley 41b is reduced, the position of the separation pad 51 changes after the feeding surface 41a has passed, which causes a problem of poor feeding of the sheet S2.

[0063] 3. Sheet Feeding Operation in the Configuration of the Present Embodiment Fig. 9 is an enlarged side view of the vicinity of eccentric cam 53 in manual paper feed unit 26 of the first embodiment, showing a state in which MPF tray 27 has lowered to the lowest position. Fig. 10 is a side cross-sectional view showing the positional relationship between sheet feed roller 41 and MPF tray 27 in the state shown in Fig. 9. Fig. 11 is a view showing a positioning mechanism for separation pad 51 in manual paper feed unit 26 of the first embodiment.

[0064] 9 and later-described Figures 12 and 14 are enlarged perspective views of the eccentric cam 53 and cam follower 55 located on the front side of Figure 2, as viewed from the outside. The eccentric cam 53 and cam follower 55 located on the back side of Figure 2 have the same configuration, so a description thereof will be omitted.

[0065] As shown in Fig. 10, in this embodiment, pulley 41b (see Fig. 4) is not provided, and sheet feed roller 41 is configured only with crescent-shaped feed surface 41a. Therefore, the position of MPF tray 27 is determined only by the outer diameter of eccentric cam 53 at the position where cam follower 55 comes into contact. As shown in Fig. 9, the large diameter portion of eccentric cam 53 comes into contact with cam followers 55 provided at both ends of MPF tray 27 in the width direction. Therefore, in Fig. 10, MPF tray 27 is spaced radially outward from the outer circumferential surface of sheet feed roller 41 (feed surface 41a).

[0066] In addition, in this embodiment, since the pulley 41b is eliminated, the position of the separation pad 51 after the feeding surface 41a has passed cannot be regulated by the pulley 41b. Therefore, the position of the separation pad 51 after the feeding surface 41a has passed is determined by another positioning shape.

[0067] Specifically, as shown in Fig. 11, guide grooves 70a extending in the vertical direction are provided at both ends in the longitudinal direction (direction perpendicular to the plane of Fig. 11) of the separation pad holder 70 to which the separation pad 51 is fixed. A support rib 71 formed on the manual feed path 39 is slidably engaged with the guide grooves 70a. The separation pad holder 70 is biased upward by a coil spring 73.

[0068] 11, the lower end of the guide groove 70a comes into contact with the support rib 71, thereby restricting the upper limit position of the separation pad 51 after the feeding surface 41a has passed. This restricts a significant rise in the separation pad 51 after the feeding surface 41a has passed, thereby preventing poor feeding of the sheet S2.

[0069] Next, the feeding operation of sheet S2 in manual paper feed unit 26 of the first embodiment will be described. Fig. 12 is an enlarged side view of the vicinity of eccentric cam 53 in manual paper feed unit 26 of the first embodiment, showing a state in which MPF tray 27 has been raised from the state in Fig. 9. Fig. 13 is a side cross-sectional view of the vicinity of sheet feed roller 41 in the state in Fig. 12, showing the positional relationship between sheet feed roller 41 and MPF tray 27.

[0070] 9, when the shaft 50 rotates a predetermined amount in the counterclockwise direction (sheet feeding direction), the eccentric cam 53 rotates a predetermined amount, and the contact position between the eccentric cam 53 and the cam follower 55 moves from the large diameter portion of the eccentric cam 53 to the small diameter portion. Because the sheet feeding roller 41 is not provided with a pulley 41b, the MPF tray 27 rises to the position shown in FIG. 12 while maintaining the contact state between the eccentric cam 53 and the cam follower 55. In other words, the raised position of the MPF tray 27 is determined only by the contact position between the eccentric cam 53 and the cam follower 55.

[0071] 13, the MPF tray 27 can be placed on standby at a standby position (inner than the outer circumferential surface of the feeding surface 41a) that is closer to the sheet feeding roller 41 in the radial direction than in the conventional configuration (see FIG. 7). In the state shown in FIG. 13, the feeding surface 41a has not yet come into contact with the upper surface of the MPF tray 27.

[0072] Fig. 14 is an enlarged side view of the vicinity of eccentric cam 53 in manual paper feed unit 26 of the first embodiment, showing a state in which MPF tray 27 has been raised from the state in Fig. 12. Fig. 15 is a side cross-sectional view of the vicinity of sheet feed roller 41 in the state in Fig. 14, showing the positional relationship between sheet feed roller 41 and MPF tray 27.

[0073] 12, when the shaft 50 further rotates counterclockwise (sheet feeding direction) by a predetermined amount, the eccentric cam 53 rotates by a predetermined amount, and the cam follower 55 moves away from the eccentric cam 53 as shown in FIG. 14. Meanwhile, as shown in FIG. 15, the feeding surface 41a further rotates counterclockwise from the position shown in FIG. 13 and comes into contact with the upper surface of the MPF tray 27. This enables the feeding of the sheet S2.

[0074] At this time, the contact position (feed start position) P3 between the feeding surface 41a and the MPF tray 27 is located further inward in the radial direction of the sheet feeding roller 41 than the contact position (feed start position) P2 in the conventional configuration (see FIG. 8). Therefore, the distance d2 (feedable distance) from the feeding start position P3 to the sheet abutment portion 39a is longer than in the conventional configuration.

[0075] With the configuration of this embodiment, the feedable distance d2 when feeding sheet S2 from MPF tray 27 can be made longer than the detectable distance d1 by sheet detection sensor 57. As a result, it is possible to prevent a situation in which sheet S2 is not fed even though it is detected by sheet detection sensor 57, causing discomfort to the user.

[0076] Furthermore, even if the detection portion 57a ​​of the sheet detection sensor 57 is installed horizontally (so that the detectable distance d1 is large) from the standpoint of space saving, the feedable distance d2 can be made longer than the detectable distance d1, and the configuration around the MPF tray 27 can be made space-saving (low-profile).

[0077] Furthermore, in the configuration of this embodiment, the upper limit position of the separation pad 51 is restricted by the lower end of the guide groove 70a formed in the separation pad holder 70 coming into contact with the support rib 71. This makes it possible to restrict the upper limit position of the separation pad 51 after it has passed the feeding surface 41a without providing the pulley 41b, thereby preventing poor feeding of the sheet S2 due to a change in the position of the separation pad 51.

[0078] 16 is a side cross-sectional view of the vicinity of sheet feed roller 41 in manual feed unit 26 according to the second embodiment of the present invention, illustrating the positional relationship between sheet feed roller 41 and MPF tray 27. In this embodiment, sheet feed roller 41 has a crescent-shaped feed surface 41a and pulley 41b. The configuration of other parts of manual feed unit 26 is the same as in the first embodiment. As shown in FIG. 16, pulley 41b regulates the position of MPF tray 27 that has risen to the feed position by rotation of eccentric cam 53 (see FIG. 2).

[0079] In this embodiment, the outer diameter of pulley 41b is smaller than that of the conventional configuration (see FIG. 6). More specifically, the outer diameter of pulley 41b is sufficiently smaller than the outer diameter of feed surface 41a so that the standby position of MPF tray 27, just before it rises to the feed position and comes into contact with feed surface 41a, is located radially inward of the outer circumferential surface of sheet feed roller 41.

[0080] Furthermore, since the outer diameter of the pulley 41b is reduced, if the upper limit position of the separation pad 51 is regulated by the pulley 41b as in the conventional configuration, the position of the separation pad 51 will change after passing the feeding surface 41a, causing feeding problems for the sheet S2. Therefore, in this embodiment, as in the first embodiment, the upper limit position of the separation pad 51 is regulated by the guide groove 70a and the support rib 71 formed in the separation pad holder 70 (see FIG. 11).

[0081] By adopting the configuration of this embodiment, similarly to the first embodiment, the feedable distance d2 when feeding the sheet S2 from the manual paper feed unit 26 can be made longer than the detectable distance d1 by the sheet detection sensor 57. Also, the upper limit position of the separation pad 51 after it has passed the feeding surface 41a can be regulated without the separation pad 51 coming into contact with the pulley 41b.

[0082] The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiments, a PI (photointerrupter) sensor having a detection unit 57a in which a light receiving unit and a light emitting unit are arranged opposite each other is used as the sheet detection sensor 57. However, a reflective optical sensor in which a light receiving unit and a light emitting unit are arranged on the same side can also be used as the sheet detection sensor 57. In this case, a reflecting unit is provided instead of the light-shielding unit 60a of the detection member 60, and the detection light emitted from the light emitting unit is reflected by the reflecting unit and detected by the light receiving unit, thereby detecting the sheet S2 on the MPF tray 27.

[0083] Even when a reflective optical sensor is used, the detectable distance d1 may be increased depending on the location and size of the light receiving section. Therefore, it is effective to apply the present invention to such a sensor, just as when a PI (photointerrupter) sensor is used.

[0084] Furthermore, in the above embodiments, an electrophotographic color printer is exemplified as the image forming apparatus 100, but the image forming apparatus 100 can also be a monochrome printer, a color and monochrome copier, or an inkjet recording printer. [Industrial Applicability]

[0085] The present invention can be used in a sheet feeding device that feeds sheets such as paper. By using the present invention, it is possible to provide a sheet feeding device that can extend the sheet feeding distance with a simple configuration when using a sheet feeding roller with a crescent-shaped feeding surface, and an image forming apparatus equipped with the same. [Explanation of symbols]

[0086] 7. Device body 26 Manual paper feed unit (sheet feeder) 27 MPF tray (sheet stacking tray) 28 Tray support cover 39 Manual feed path 39a Sheet abutment 41 Sheet feeding roller 41a Feeding surface 41b Pulley 50 Shaft (rotating axis) 51 Separation pad (separation member) 53 Eccentric cam 55 Cam follower 57 Sheet detection sensor (sheet detection mechanism) 57a Detection unit 58 biasing spring (first biasing member) 60 Detection member (sheet detection mechanism) 70 Separation Pad Holder 70a Guide groove (retention mechanism) 71 Support rib (retention mechanism) 73 Coil spring (second biasing member) 100 Image forming device 102 Control section Pa~Pd Image forming section S1, S2 seats

Claims

1. a sheet stacking tray that can be raised and lowered up and down on which sheets are stacked; a sheet abutment portion that abuts against and aligns the leading edge of the sheets stacked on the sheet stacking tray; a sheet feeding roller having a crescent-shaped feeding surface that is in pressure contact with the upper surface of the sheet stacked on the sheet stacking tray and feeds the sheet in a feeding direction; a separating member that contacts the feeding surface of the sheet feeding roller to form a feeding nip; a first biasing member that biases the sheet stacking tray in a direction approaching the sheet feeding roller; an eccentric cam fixed to a rotation shaft of the sheet feeding roller and having a maximum eccentric radius larger than the radius of the sheet feeding roller; a cam follower provided at a position of the sheet stacking tray where the cam comes into contact with the eccentric cam, the cam follower moving a contact point from a large diameter portion to a small diameter portion of the eccentric cam in response to rotation of the eccentric cam, thereby lifting the sheet stacking tray; a sheet detection sensor including a detection unit having a light emitting unit and a light receiving unit; a detection member having a light-shielding portion that comes into contact with the sheets stacked on the sheet stacking tray and swings to block or open the light path of the detection portion; a sheet detection mechanism for detecting the sheets stacked on the sheet stacking tray; In a sheet feeding device comprising: a holding mechanism that holds the separating member at a position separated from the sheet feeding roller after the feeding surface has passed the separating member due to rotation of the sheet feeding roller; By making the sheet stacking tray wait at a waiting position radially inward from the outer diameter of the sheet feeding surface immediately before starting to feed the sheets, A feedable distance, which is the distance between a feed start position where the feed surface and the sheet stacking tray abut and the sheet abutment portion, is defined as: A sheet feeding device characterized in that a detectable position at which the sheet can be detected by the sheet detection mechanism when the leading edge of the sheet is separated from the sheet abutment portion is larger than a detectable distance, which is the maximum distance from the sheet abutment portion.

2. the sheet feeding roller has only the feeding surface; 2. The sheet feeding device according to claim 1, wherein the sheet stacking tray rises to the standby position while maintaining a contact state between the eccentric cam and the cam follower.

3. The sheet feeding roller the feeding surface; pulleys arranged on both sides of the feed surface in the axial direction and having an outer diameter smaller than that of the feed surface; 2. The sheet feeding device according to claim 1, wherein the sheet stacking tray is disposed at the standby position in contact with an outer peripheral surface of the pulley.

4. a holder that holds the separating member and is movable in a direction toward or away from the sheet feeding roller; a second biasing member that biases the holder in a direction approaching the sheet feeding roller; and The holding mechanism includes: a guide groove formed along the moving direction of the holder; a support rib slidably engaged with the guide groove; and 2. The sheet feeding device according to claim 1, wherein the separating member is held at a position spaced apart from the sheet feeding roller by an end of the guide groove coming into contact with the support rib.

5. 2. The sheet feeding device according to claim 1, wherein the sheet detection sensor is disposed in a direction in which the area of ​​the detection portion becomes larger in the moving direction of the light blocking portion.

6. an image forming unit that forms an image on a sheet; a sheet feeding device according to any one of claims 1 to 5, which feeds the sheet to the image forming unit; An image forming apparatus comprising:

Images