SHEET FEEDING DEVICE AND IMAGE FORMING APPARATUS INCLUDING THE SAME

Abstract

To provide a sheet supply device and an image forming device capable of suppressing inconvenience by inviting image defect such as missing image even if the transmission of a rotary driving force to the supply roller is interrupted at the timing when the rear edge of the minimum size sheet in a supply direction on which the image is formed in an image forming part passes the supply roller.SOLUTION: A sheet supply device including a supply roller and a conveyance roller transmits a predetermined first rotary driving force to the supply roller when supplying sheet, performs first cutoff operation to cut off transmission of a second rotary driving force to the supply roller, after the second rotary driving force smaller than the first rotary driving force is transmitted to the supply roller at the timing when rear edge of the minimum size sheet in a supply direction in which an image is formed in an image forming part passes the supply roller, regardless of the size of the sheets stacked on a sheet stacking tray while the sheet is conveyed by the conveyance roller.SELECTED DRAWING: Figure 8A

Description

[Technical field]

[0001] The present invention relates to a sheet supplying device and an image forming apparatus including the same, such as a copying machine, a multifunction machine, a printer, or a facsimile machine. [Background technology]

[0002] A sheet supply device provided in an image forming apparatus typically includes a supply roller that supplies multiple sheets of recording paper, documents, etc., loaded on a sheet stacking tray one by one, and a transport roller (e.g., a registration roller) that transports the sheets supplied from the supply roller to an image forming section.

[0003] Among such sheet supplying devices, there are those that transmit a rotational driving force to the conveying roller, and when the sheet being driven and conveyed by the conveying roller passes through the supply roller, transmit a rotational driving force to the supply roller as well, so that the sheet is driven and conveyed by both the conveying roller and the supply roller (see, for example, Patent Document 1 (particularly step S315 in Figure 5)).

[0004] In a conventional sheet feeder, when continuously feeding sheets, in order to prevent the next sheet from being continuously fed by the feed roller and causing double feeding, the transmission of the rotational driving force to the feed roller is usually cut off when the trailing end of the sheet passes the feed roller. However, when there is no detection unit that detects that the sheet has passed the feed roller, the timing when the trailing end of the sheet passes the feed roller is determined based on a set size in a preset feed direction to be loaded on the sheet stacking tray, and the transmission of the rotational driving force to the feed roller is cut off. Here, the set size is a size, and examples of the size include a size set by a size detection unit provided on the sheet stacking tray and a size set by a user through an input operation on an operation unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-154682 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, if for some reason sheets smaller than the set size (e.g., A3 portrait size) (e.g., A4 landscape size or A5 landscape size) are loaded on the sheet stacking tray, the rotational drive force is transmitted to the supply roller even after the smaller size sheet has passed through the supply roller, causing the next sheet to be continuously fed by the supply roller, resulting in double feeding.

[0007] From this perspective, regardless of the size of the sheets loaded on the sheet stacking tray (e.g., A3 portrait, A4 landscape, or A5 landscape), it is possible to cut off the transmission of the rotational driving force to the supply roller when the rear end of a sheet of the smallest size in the supply direction (e.g., A5 landscape) on which an image is formed in the image forming unit passes through the supply roller.

[0008] By doing so, regardless of the size of the sheets loaded on the sheet stacking tray, when the trailing edge of the sheet passes through the supply roller, the transmission of the rotational driving force to the supply roller is interrupted, so that it is possible to effectively prevent the next sheet from being continuously fed by the supply roller and causing double feeding. However, on the other hand, in the case of a sheet that is larger in size (e.g., A3 portrait size or A4 landscape size) than the minimum size in the supply direction (e.g., A5 landscape size), when the transmission of the rotational driving force to the supply roller is interrupted while the sheet is passing through the supply roller, it is subjected to an impact when the transmission of the rotational driving force to the supply roller is interrupted while passing through the supply roller (the sheet is tensed). In this case, vibrations caused by the impact are transmitted from the supply roller or the conveying roller to the photoconductor or the image writing system, which causes inconveniences such as image defects such as missing images.

[0009] Therefore, the present invention aims to provide a sheet supplying device and an image forming apparatus that can suppress inconveniences such as image defects such as missing images even if the transmission of rotational driving force to the supply roller is cut off at the timing when the rear end of a sheet of the smallest size in the supply direction on which an image is formed in the image forming unit passes the supply roller. [Means for solving the problem]

[0010] In order to solve the above problem, a sheet supplying device according to the present invention is a sheet supplying device including a supply roller that supplies a plurality of sheets stacked on a sheet stacking tray one by one, and a transport roller that transports the sheets supplied from the supply roller to an image forming unit, and when supplying the sheets, a predetermined first rotational driving force is transmitted to the supply roller, and in a state in which the sheets are transported by the transport roller, regardless of the size of the sheets stacked on the sheet stacking tray, a second rotational driving force smaller than the first rotational driving force is transmitted to the supply roller at a timing when the rear end of the sheet of a minimum size in a supply direction on which an image is formed by the image forming unit passes the supply roller, and then a first cut-off operation is performed to cut off the transmission of the second rotational driving force to the supply roller. Also, an image forming apparatus according to the present invention includes the sheet supplying device according to the present invention. Effect of the Invention

[0011] According to the present invention, even if the transmission of rotational driving force to the supply roller is cut off at the timing when the rear end of a sheet of the smallest size in the supply direction on which an image is formed in the image forming section passes the supply roller, it is possible to suppress inconveniences such as image defects such as missing images. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus including a sheet feeding device according to an embodiment of the present invention, as viewed from the front. [Diagram 2] FIG. 2 is a perspective view showing a drive system portion of the sheet feeding device according to the embodiment of the present invention. [Diagram 3] 2 is a system block diagram of a drive system of the sheet feeding device according to the embodiment of the present invention. [Figure 4] 5 is a flowchart showing a flow of a sheet supplying operation by the sheet supplying device. [Figure 5A] 11 is a timing chart showing a flow of a sheet supply operation for a minimum size sheet. [Figure 5B] 11 is a timing chart showing a flow of a sheet supply operation for a minimum size sheet. [Figure 5C] 11 is a timing chart showing a flow of a sheet supply operation for a minimum size sheet. [Figure 6A] 11 is a timing chart showing a flow of a sheet supply operation for a sheet having a size larger than the minimum size. [Figure 6B] 11 is a timing chart showing a flow of a sheet supply operation for a sheet having a size larger than the minimum size. [Figure 6C] 11 is a timing chart showing a flow of a sheet supply operation for a sheet having a size larger than the minimum size. [Figure 7] 11 is a timing chart for explaining inconveniences that occur when the first interruption operation is not performed. [Figure 8A] 5 is a timing chart showing an example of pulse width modulation control performed on the first electromagnetic clutch. [Figure 8B] 6 is a timing chart showing another example of performing pulse width modulation control on the first electromagnetic clutch. [Figure 9A] 5 is a timing chart showing an example of power control for the first electromagnetic clutch. [Figure 9B] 6 is a timing chart showing another example of power control for the first electromagnetic clutch. [Figure 10A] 10 is a timing chart showing an example of pulse width modulation control performed on a first electromagnetic clutch to explain suppression of an impact on a sheet when the trailing edge of the sheet passes through a supply roller. [Figure 10B]10 is a timing chart showing an example of power control for a first electromagnetic clutch to explain suppression of an impact on a sheet when the trailing edge of the sheet passes through a supply roller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed description thereof will not be repeated.

[0014] [Image forming equipment] 1 is a schematic cross-sectional view of an image forming apparatus 100 equipped with a sheet feeding device 200 according to an embodiment of the present invention, viewed from the front. The image forming apparatus 100 is a monochrome image forming apparatus. However, the image forming apparatus 100 may be a color image forming apparatus. In the figure, the symbol X represents the left-right direction when viewed from the front. The symbol Y represents the depth direction perpendicular to the left-right direction X. The symbol Z represents the up-down direction, or vertical direction.

[0015] The image forming apparatus 100 performs image formation processing according to image data read by the image reading device 106 or image data transmitted from an external source. Note that the image forming apparatus 100 may be a color image forming apparatus that forms multi-color and monochrome images on a sheet P such as a recording paper.

[0016] An image forming apparatus main body 110 of the image forming apparatus 100 is provided with an image forming section 102 and a sheet transport system 103 .

[0017] The image forming section 102 includes an exposure device 1 (exposure unit), a development device 2 (development unit), a toner storage container 21, a photoconductor drum 3 acting as an electrostatic latent image carrier, a cleaning section 4, a charging device 5, and a fixing device 7 (fixing unit). The sheet transport system 103 includes a sheet supply device 200, a sheet stacking tray 81 (80) (paper feed tray) on the main body side, a sheet stacking tray 82 (80) (manual feed tray) on the manual feed side, a discharge roller 31, and a discharge tray 14.

[0018] An image reading device 106 for reading an image of an original G is provided on the upper part of the image forming apparatus main body 110. The image reading device 106 includes an original placement table 107 on which the original G is placed. The original placement table 107 is a rectangular member made of transparent reinforced glass. In the image forming apparatus 100, the image of the original G read by the image reading device 106 is sent to the image forming apparatus main body 110 as image data, and the image is recorded on a sheet P.

[0019] The image forming apparatus main body 110 is provided with a sheet transport path W1. The sheet supply device 200 supplies the uppermost sheet P of the sheets P to P stacked on the sheet stacking trays 81, 82 (80) to the sheet transport path W1. The sheet transport path W1 guides the sheet P to the discharge tray 14 via the transfer roller 10 and the fixing device 7. The fixing device 7 heats and fixes the toner image formed on the sheet P to the sheet P. Near the sheet transport path W1, a supply roller 220a (220) on the main body side, a supply roller 220b (220) on the manual feed side, a transport roller 12a, a registration roller 230, a transfer roller 10, a fixing roller 71 and a pressure roller 72 in the fixing device 7, and a discharge roller 31 are arranged. In the image forming apparatus 100 of this embodiment, there is no pick-up roller (pickup roller) for picking up the sheets P-P one by one stacked on the sheet stacking trays 81, 82 (80), and the supply rollers 220a, 220b (220) (feed rollers) also serve as the pick-up rollers. In addition, separation members 222a, 222b (222) are provided at positions facing the supply rollers 220a, 220b (220). The separation members 222a, 222b (222) regulate the supply of the second and subsequent sheets P among the sheets P-P stacked on the sheet stacking trays 81, 82 (80). Representative examples of the separation member 222 include a separation roller and a separation pad, and in this embodiment, the separation member 222 is a separation roller.

[0020] In the image forming apparatus 100, the top sheet P of the sheets P to P stacked on the sheet stacking trays 81, 82 (80) in the sheet supply device 200 is conveyed to the registration rollers 230. Next, the sheet P is conveyed to the transfer rollers 10 at a timing when the registration rollers 230 align the sheet P with the toner image on the photosensitive drum 3. The toner image on the photosensitive drum 3 is transferred onto the sheet P by the transfer rollers 10. Thereafter, the sheet P passes through the fixing rollers 71 and the pressure rollers 72 in the fixing device 7, and is discharged onto the discharge tray 14 via the conveying rollers 12a and the discharge rollers 31. When an image is formed on the back side of the sheet P as well as the front side, the sheet P is conveyed in the opposite direction from the discharge rollers 31 to the inverted sheet conveying path W2. The sheet P passes through the inverted conveying rollers 12b and is inverted and guided to the registration rollers 230 again. Then, the sheet P is discharged toward the discharge tray 14 after a toner image is formed and fixed on the back side of the sheet P in the same manner as the front side.

[0021] [Sheet feeding device] Next, a sheet feeding device 200 according to an embodiment of the present invention will be described below with reference to FIGS. 2A to 10B.

[0022] Fig. 2 is a perspective view showing a drive system portion of sheet supplying device 200 according to an embodiment of the present invention. Note that supply roller 220b on the manual feed side is omitted in Fig. 2. Fig. 3 is a system block diagram of the drive system of sheet supplying device 200 according to an embodiment of the present invention.

[0023] As shown in FIG. 2, the sheet supply device 200 includes a drive unit 210 (drive motor), a main body side supply roller 220a (220), a first electromagnetic clutch 221a (221) (electromagnetic clutch) for the main body side supply roller, a manual feed side supply roller 220b (220), a first electromagnetic clutch 221b (221) (electromagnetic clutch) for the manual feed side supply roller, a registration roller 230 (an example of a conveying roller), a second electromagnetic clutch 231 for the registration roller, a first drive transmission mechanism 240, a second drive transmission mechanism 250, and a sheet detection unit 260.

[0024] The driving unit 210 is a driving source that generates a rotational driving force, and is electrically connected to an output system of the control unit 120 (see FIG. 3). The driving unit 210 is coupled to a first driving transmission mechanism 240 and a second driving transmission mechanism 250. This allows the driving unit 210 to transmit the rotational driving force to the first driving transmission mechanism 240 and the second driving transmission mechanism 250 under the command of the control unit 120.

[0025] The main body side supply roller 220a supplies the uppermost sheet P of the multiple sheets P to P stacked on the main body side sheet stacking tray 81 to the registration rollers 230 one by one. The rotational driving force from the first drive transmission mechanism 240 is transmitted to the supply roller 220a via a first electromagnetic clutch 221a for the main body side supply roller. The manual feed side supply roller 220b supplies the uppermost sheet P of the multiple sheets P to P stacked on the manual feed side sheet stacking tray 82 to the registration rollers 230 one by one. The rotational driving force from the first drive transmission mechanism 240 is transmitted to the supply roller 220b via a first electromagnetic clutch 221b for the manual feed side supply roller.

[0026] The first electromagnetic clutch 221a for the main body side supply roller and the first electromagnetic clutch 221b for the manual feed side supply roller are provided on the supply rollers 220a and 220b, respectively, and are electrically connected to the output system of the control unit 120 (see FIG. 3). This allows the first electromagnetic clutches 221a and 221b to transmit the rotational driving force from the first drive transmission mechanism 240 to the supply rollers 220a and 220b under the command of the control unit 120.

[0027] The supply rollers 220a and 220b are supported in a state in which they can rotate when an external force acts on them when the first electromagnetic clutches 221a and 221b are not transmitting the rotational driving force from the first drive transmission mechanism 240 to the supply rollers 220a and 220b. Therefore, as described below, when the sheet P is being transported by the registration rollers 230 and the downstream side in the transport direction of the transported sheet P is in contact with the supply rollers 220a and 220b, the supply rollers 220a and 220b rotate (rotate together) while in contact with the transported sheet P. In this state, the supply rollers 220a and 220b are in contact with the sheet P with a predetermined load, so the transport load of the sheet P increases by the amount of the transport of the supply rollers 220a and 220b.

[0028] The registration rollers 230 transport the sheet P supplied from the supply rollers 220a and 220b to the image forming unit 102. The registration rollers 230 transport the sheet P, which is stopped with its leading edge in contact with the registration rollers 230, at a predetermined timing (timing to align with the image on the photosensitive drum 3). The distance between the supply rollers 220a and 220b and the registration rollers 230 is smaller than the length of the minimum size sheet P (A5 landscape size in this example).

[0029] The second electromagnetic clutch 231 is provided on the registration roller 230 and is electrically connected to an output system of the control unit 120 (see FIG. 3). This allows the second electromagnetic clutch 231 to transmit the rotational driving force from the first drive transmission mechanism 240 to the registration roller 230 under the command of the control unit 120.

[0030] As shown in FIG. 2, the first drive transmission mechanism 240 transmits the rotational drive force from the drive unit 210 to the first electromagnetic clutches 221a, 221b (221) and the second electromagnetic clutch 231. The first drive transmission mechanism 240 includes a plurality of gears (a first gear 241 to a fifth gear 245). The first electromagnetic clutch 221a receives the rotational drive force from the drive unit 210 via the first gear 241 and the second gear 242. The first electromagnetic clutch 221b receives the rotational drive force from the drive unit 210 via the first gear 241 to the fifth gear 245. The second electromagnetic clutch 231 receives the rotational drive force from the drive unit 210 via the first gear 241 to the third gear 243. Further, the rotational driving force from the driving unit 210 is transmitted to the photosensitive drum 3 via a plurality of gears (a first gear 251 and a second gear 252) of a second driving transmission mechanism 250.

[0031] The sheet detection unit 260 detects the presence or absence of a sheet P conveyed between the supply rollers 220a, 220b (220) and the registration rollers 230. In other words, the sheet detection unit 260 can detect that the sheet P has passed through the registration rollers 230. The sheet detection unit 260 is provided between the supply rollers 220a, 220b (220) and the registration rollers 230, and is electrically connected to an input system of the control unit 120 (see FIG. 3). This enables the sheet detection unit 260 to transmit a detection signal to the control unit 120.

[0032] 3, the image forming apparatus 100 includes a control unit 120. The control unit 120 includes a processing unit 121 including a microcomputer such as a CPU, and a storage unit 122 including a non-volatile memory such as a ROM and a volatile memory such as a RAM. The control unit 120 controls the operation of various components by the processing unit 121 loading a control program stored in advance in the ROM of the storage unit 122 onto the RAM of the storage unit 122 and executing the program. Note that the sheet supplying device 200 may also include the control unit 120.

[0033] Fig. 4 is a flowchart showing the flow of the sheet supplying operation by the sheet supplying device 200. Fig. 5A to Fig. 5C are timing charts showing the flow of the sheet supplying operation for a sheet P of the minimum size.

[0034] 5A to 5C, the flow of the sheet supply operation for a sheet P of the minimum size (A5 landscape in this example) to be loaded on the sheet stacking tray 80 will be described while explaining the flowchart shown in Fig. 4. Note that the dimension Lm (148 mm in this example) in the supply direction H of the sheet P of the minimum size (A5 landscape in this example) in the supply direction H on which an image is formed by the image forming unit 102 is stored in advance in the storage unit 122.

[0035] 4, when supplying sheet P, control unit 120 first turns on first electromagnetic clutch 221 (S1, see S1 in FIG. 5A) and transmits a predetermined first rotational driving force to supply rollers 220 (220a, 220b). Next, control unit 120 waits until sheet detection unit 260 detects the leading edge of sheet P (S2: No), and when the leading edge of sheet P is detected (S2: Yes, see S2 in FIG. 5A), control unit 120 turns off first electromagnetic clutch 221 at the timing when the leading edge of sheet P abuts against registration rollers 230 (S3, see S3 in FIG. 5A).

[0036] Next, the control unit 120 waits until a conveyance start signal for the sheet P is sent (a predetermined waiting time after the sheet P reaches the registration rollers 230) (S4: No), and if it is determined that a conveyance start signal for the sheet P has been sent (S4: Yes), it determines whether the sheet P is the first sheet of the job (S5). Next, if the control unit 120 determines that the sheet P is the first sheet of the job (S5: Yes), it turns on the first electromagnetic clutch 221 and the second electromagnetic clutch 231 at a timing when the sheet P is aligned with the image on the photosensitive drum 3. At this time, the control unit 120 performs a first cutoff operation (S6, see S6 in FIG. 5A) because the detected size (actual size) of the sheet P in the supply direction H is unknown. In the first cut-off operation, in a state where the sheet P is conveyed to the registration rollers 230, a second rotational driving force smaller than the first rotational driving force is transmitted to the supply rollers 220 at the timing when the rear end of the sheet P of the minimum size stored in the memory unit 122 passes the supply rollers 220, and then the transmission of the second rotational driving force to the supply rollers 220 is cut off. Here, in this example, the timing when the rear end of the sheet P of the minimum size passes the supply rollers 220 is the timing after the first time t1 has elapsed (after passing the first distance L1) from the start of rotation of the registration rollers 230, and is calculated from the dimension Lm stored in the memory unit 122 and the length between the registration rollers 230 and the supply rollers 220 (the movement time of the first distance L1, which is the difference therebetween). In S6 of FIG. 5A, the size of the sheet P being transported is the minimum size (A5 landscape in this example), and the timing at which the rear end of the sheet P passes through the supply roller 220 is the minimum size (A5 landscape in this example), so there is no impact on the sheet P (the sheet P is pushed up) when the transmission of the rotational driving force to the supply roller 220 is cut off.

[0037] Next, the control unit 120 waits until the sheet detection unit 260 detects the rear end of the sheet P (S7: No), and when it is determined that the rear end of the sheet P has been detected (S7: Yes, see S7 in FIG. 5B), it detects the detection size of the sheet P in the supply direction H and stores the detected detection size in the storage unit 122. Here, the detection size is the size of the sheet P in the supply direction H that is actually loaded on the sheet stacking tray 80. In this example, the detection size is the sum of a second time t2 (second distance L2) from when the second electromagnetic clutch 231 is turned on to start the rotation of the registration roller 230 until the rear end of the sheet P is detected by the sheet detection unit 260, and a third time t3 (third distance L3) that is the time from when the leading edge of the sheet P passes through the sheet detection unit 260 until it reaches the registration roller 230 (=t2+t3) [distance (L2+L3)]. The detection size in the examples shown in FIGS. 5A to 5C is the minimum size, dimension Lm in the feeding direction H (A5 landscape size: 148 mm in this example).

[0038] Next, if the job is a single-sheet job (S8: No), the control unit 120 terminates the processing, whereas if the job is a multiple-sheet job (S8: Yes), the control unit 120 turns on the first electromagnetic clutch 221 (S9, see S9 in FIG. 5B), transmits the first rotational driving force to the supply roller 220, and transitions from S2 to S4 (see S2 to S4 in FIG. 5B).

[0039] Next, when the control unit 120 determines that the sheet P is the second or subsequent sheet of the job (S5: No) and that the number of sheets of the job is not the final number (S10: No), the control unit 120 turns on the first electromagnetic clutch 221 and the second electromagnetic clutch 231 at the timing when the sheet P is aligned with the image on the photosensitive drum 3, and performs a second cutoff operation (S11, see S11 in FIG. 5B). In the second cutoff operation, in a state in which the sheet P is conveyed to the registration roller 230, the transmission of the first rotational driving force to the supply roller 220 is cut off at the timing when the rear end of the sheet P of the detection size passes through the supply roller 220. In S11 in FIG. 5A, the timing when the rear end of the sheet P passes through the supply roller 220 is the timing of the detection size (actual size), so that no impact (stretching of the sheet P) is received by the sheet P when the transmission of the rotational driving force to the supply roller 220 is cut off regardless of the size of the sheet P.

[0040] Next, the control unit 120 turns on the first electromagnetic clutch 221 (S12, see S12 in FIG. 5C) after a predetermined fourth time t4 has elapsed since the third or subsequent sheet P passed through the supply roller 220 (after passing a fourth distance L4), transmits the first rotational driving force to the supply roller 220, and transitions from S2 to S4 (see S2 to S4 in FIG. 5C). Here, the fourth time t4 (fourth distance L4) is a time (distance) shorter than the time (distance) between the first sheet P and the second sheet P.

[0041] Next, when the control unit 120 determines that the sheet P is the second or subsequent sheet of the job (S5: No) and that the number of sheets of the job is the final number (S10: Yes), the control unit 120 proceeds to S13.

[0042] Next, the control unit 120 turns on the first electromagnetic clutch 221 and the second electromagnetic clutch 231 at the timing when the sheet P is aligned with the image on the photosensitive drum 3, and performs a second cut-off operation (S13). In S13, as in S11, the timing when the rear end of the sheet P passes the supply roller 220 is the timing of the detected size (actual size), so that the sheet P does not receive any impact (the sheet P is pushed up) when the transmission of the rotational driving force to the supply roller 220 is cut off, regardless of the size of the sheet P.

[0043] Next, the control unit 120 waits until the sheet detection unit 260 detects the rear end of the sheet P (S14: No), and when it is determined that the rear end of the sheet P has been detected (S14: Yes), ends the process.

[0044] 6A to 6C are timing charts showing the flow of a sheet supply operation for a sheet P that is larger than the minimum size.

[0045] Next, while explaining the flowchart shown in Figure 4, the flow of the sheet supply operation for sheets P of a size larger (in this example, A3 portrait size) than the minimum size (in this example, A5 landscape) that can be loaded on the sheet stacking tray 80 will be explained in Figures 6A to 6C.

[0046] The sheet supplying operation shown in FIGS. 6A to 6C is similar to the sheet supplying operation shown in FIGS. 5A to 5C except for S11, and the following description will focus on the points that are different from the sheet supplying operation shown in FIGS. 5A to 5C.

[0047] In S7, the detected size is the dimension Ln (in this example, the maximum size, A3 portrait size: 420 mm) of the size larger than the minimum size in the feeding direction H. The control unit 120 stores the detected size (in this example, A3 portrait size) larger than the minimum size in the memory unit 122.

[0048] In S11 and S13, the timing at which the rear end of sheet P passes through supply roller 220 is the timing of the detected size (actual size, in this example, A3 portrait size), so regardless of the size of sheet P, sheet P does not receive any impact (sheet P is pushed up) when the transmission of the rotational driving force to supply roller 220 is cut off.

[0049] On the other hand, in S5, when the control unit 120 determines that the sheet P is the first sheet of the job (S5: Yes), it performs a first cutoff operation (S6, see S6 in FIG. 6A). This will be described in detail below with reference to FIG.

[0050] FIG. 7 is a timing chart for explaining inconveniences that occur when the first cutoff operation is not performed.

[0051] As shown in FIG. 7, when the size of the sheet P is the minimum size (A5 landscape in this example), the transmission of the rotational driving force to the supply roller 220 is interrupted after the sheet P passes through the supply roller 220, so the sheet P is not subjected to an impact (the sheet P is not tensed). However, when the size of the sheet P is larger than the minimum size (A5 landscape in this example) (A3 portrait in this example), if the first interruption operation is not performed, the sheet P is subjected to an impact when the transmission of the rotational driving force to the supply roller 220 is interrupted while the sheet P is passing through the supply roller 220 (the supply roller 220 is switched to a state where there is no rotational driving force, so a load for rotating the supply roller 220 is applied to the sheet P during conveyance, causing momentary tensing of the sheet P). In this case, vibrations due to the impact are transmitted from the supply roller 220 or the registration roller 230 to the photosensitive member (3) or the image writing system (exposure device 1), which causes inconveniences such as image defects such as missing images.

[0052] (About this embodiment) In this regard, in the sheet supplying device 200 according to the present embodiment, when supplying a sheet P, the control unit 120 transmits a predetermined first rotational driving force to the supply rollers 220 (220a, 220b), and while the sheet P is being transported to the transport rollers (registration rollers 230), regardless of the size of the sheet P loaded on the sheet stacking tray 80 (81, 82), at the timing when the rear end of the smallest-sized sheet P in the supply direction H on which an image is formed by the image forming unit 102 passes the supply rollers 220, the control unit 120 transmits a second rotational driving force fk smaller than the first rotational driving force fp to the supply rollers 220, and then performs a first cut-off operation to cut off the transmission of the second rotational driving force fk to the supply rollers 220.

[0053] According to this embodiment, in the first cut-off operation, the second rotational driving force fk smaller than the first rotational driving force fp is transmitted to the supply roller 220, and then the transmission of the second rotational driving force fk to the supply roller 220 is cut off. Therefore, when the transmission of the rotational driving force to the supply roller 220 is cut off for a sheet P having a size (e.g., A3 portrait size or A4 landscape size) larger than the minimum size (e.g., A5 landscape size) in the supply direction H, even if the sheet P passes through the supply roller 220, the impact (stretching) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is cut off while the sheet P is passing through the supply roller 220 can be mitigated. This makes it possible to make it difficult for the vibration due to the impact to be transmitted from the supply roller 220 or the conveying roller (230) to the photosensitive member (3) or the image writing system (exposure device 1), and to suppress inconveniences such as image defects such as missing images.

[0054] Here, the second rotational driving force fk is a predetermined rotational driving force that can reduce the impact on the sheet P when the transmission of the rotational driving force to the supply roller 220 is cut off while the sheet P having a size larger than the minimum size is passing through the supply roller 220, and that prevents the supply roller 220 from supplying the next sheet P.

[0055] In addition, the timing at which the rear end of the smallest size sheet P passes through the supply roller 220 is a concept that includes not only the point at which the rear end of the sheet P passes, but also the point at which a predetermined time has elapsed from the point at which the rear end of the sheet P passes (for example, a time that allows for errors due to transport variations, etc.).

[0056] In the present embodiment, the control unit 120 performs the first blocking operation when supplying the first sheet P of the multiple sheets P to P.

[0057] This makes it possible to reduce the impact (stretching) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is cut off while the first sheet P is passing through the supply roller 220, thereby suppressing inconveniences such as image defects such as missing images on the first sheet P.

[0058] In this embodiment, the control unit 120 detects the detection size of the first sheet P in the supply direction H based on the detection result of the sheet detection unit 260. The storage unit 122 stores the detected size. The control unit 120 controls the rotation timing of the supply roller 220 and the conveying roller (230) at a timing according to the detected size stored in the storage unit 122.

[0059] In this way, the control unit 120 can recognize the size of the sheet P actually supplied in the supply direction H, and can thereby cut off the transmission of the rotational drive force to the supply roller 220 for the second and subsequent sheets P at the timing when the trailing edge of the sheet P actually passes the supply roller 220. Therefore, it is possible to effectively prevent the third and subsequent sheets P from being continuously supplied by the supply roller 220 without performing the first cut-off operation for the second and subsequent sheets P, resulting in double feeding.

[0060] In this embodiment, the conveying roller is a registration roller 230 that conveys the sheet P stopped with its leading edge in contact with the registration roller 230 at a predetermined timing. The control unit 120 detects the detection size from the time from when the registration roller 230 starts conveying the first sheet P to when the sheet detection unit 260 detects the trailing edge of the first sheet P.

[0061] In this way, the sheet detection unit 260 can also be used as a detection unit for detecting the timing at which the sheet P is stopped by contacting it with the registration rollers 230. In other words, the detection size can be detected by utilizing the detection unit for detecting the timing at which the sheet P is stopped by contacting it with the registration rollers 230.

[0062] In this embodiment, when supplying the second or subsequent sheet P of the multiple sheets P to P, the control unit 120 transmits a first rotational driving force fp to the supply roller 220, and when the sheet P is being transported by the transport rollers (230), the control unit 120 performs a second cut-off operation to cut off the transmission of the first rotational driving force fp to the supply roller 220 at the timing when the rear end of the sheet P of the detection size passes through the supply roller 220.

[0063] In this way, even if the second cut-off operation is performed on the second or subsequent sheets P of any size, it is possible to avoid the impact (stretching) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is cut off.

[0064] First Embodiment 8A and 8B are timing charts showing one example and another example of performing pulse width modulation control on first electromagnetic clutch 221, respectively.

[0065] In this embodiment, the control unit 120 transmits the second rotational driving force fk to the supply roller 220 by performing pulse width modulation control (PWM (Pulse Width Modulation) control) on the first electromagnetic clutch 221 (electromagnetic clutch), as shown in Figures 8A and 8B.

[0066] This makes it possible to realize switching of the rotational driving force from the first rotational driving force fp to the second rotational driving force fk with a simple control configuration.

[0067] In the example shown in FIG. 8A, in the first disconnecting operation, the control unit 120 performs pulse width modulation control so that the pulse width of the pulse signal supplied to the first electromagnetic clutch 221 becomes constant.

[0068] In this way, the impact (stretch) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is interrupted while the sheet P is passing through the supply roller 220 can be surely alleviated.

[0069] 8B, in the first cut-off operation, the control unit 120 gradually cuts off the transmission of the second rotational driving force fk to the supply roller 220. In particular, the control unit 120 performs pulse width modulation control so that the pulse width of the pulse signal supplied to the first electromagnetic clutch 221 gradually decreases. Note that the control unit 120 may also perform pulse width modulation control so that the pulse width of the pulse signal supplied to the first electromagnetic clutch 221 decreases in stages.

[0070] This makes it possible to further reduce the impact (stretch) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is interrupted while the sheet P is passing through the supply roller 220.

[0071] <Second embodiment> 9A and 9B are timing charts showing one example and another example of power control for first electromagnetic clutch 221. In Fig. 9A and Fig. 9B and Fig. 10A and Fig. 10B described later, Im represents the rated current of first electromagnetic clutch 221.

[0072] In this embodiment, control unit 120 transmits the second rotational driving force to supply roller 220 by performing power control (current control in this example) on first electromagnetic clutch 221 (electromagnetic clutch), as shown in FIGS. 9A and 9B.

[0073] This makes it possible to realize switching of the rotational driving force from the first rotational driving force fp to the second rotational driving force fk with a simple control configuration.

[0074] In the example shown in FIG. 9A, the control unit 120 performs power control in the first interrupting operation so that the current supplied to the first electromagnetic clutch 221 is constant.

[0075] In this way, the impact (stretch) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is interrupted while the sheet P is passing through the supply roller 220 can be surely alleviated.

[0076] 9B, in the first cut-off operation, the control unit 120 gradually cuts off the transmission of the second rotational driving force fk to the supply roller 220. In particular, the control unit 120 performs power control so that the current supplied to the first electromagnetic clutch 221 is gradually reduced. Note that the control unit 120 may also perform power control so that the current supplied to the first electromagnetic clutch 221 is reduced in stages.

[0077] This makes it possible to further reduce the impact (stretch) of the sheet P when the transmission of the rotational driving force to the supply roller 220 is interrupted while the sheet P is passing through the supply roller 220.

[0078] <Third embodiment> Incidentally, after the transmission of the rotational driving force to the supply roller 220 is cut off, the sheet P having a size larger than the minimum size in the supply direction H is transported only by the transport roller (registration roller 230), and is in a state in which a load is applied by the supply roller 220 in a state in which the transmission of the rotational driving force (second rotational driving force fk) is cut off. In this state, when the rear end of the sheet P passes through the supply roller 220, the sheet P is subjected to an impact when the rear end of the sheet P passes through the supply roller 220 (the tension of the sheet P is released). In this case, vibrations caused by the impact are transmitted from the supply roller 220 and the transport roller (registration roller 230) to the photoconductor (3) and the image writing system, which causes inconveniences such as image defects such as missing images.

[0079] 10A and 10B are timing charts showing an example of pulse width modulation control and power control for the first electromagnetic clutch 221 to illustrate the suppression of the impact that the sheet P receives when the trailing end of the sheet P passes through the supply roller 220.

[0080] In this embodiment, as shown in Figures 10A and 10B, in the first blocking operation, the control unit 120 blocks the transmission of the second rotational driving force fk to the supply roller 220 at the timing when the rear end of a sheet P of a set size in a predetermined supply direction H to be loaded on the sheet stacking tray 80, or a sheet P of the maximum size in the supply direction H on which an image is formed by the image forming unit 102 (A3 portrait size in this example) passes through the supply roller 220.

[0081] In detail, in the first blocking operation, the control unit 120 transmits the second rotational driving force fk to the supply roller 220 when the rear end of the minimum size sheet P (in this example, A5 landscape size) passes the supply roller 220, then continues to transmit the second rotational driving force fk to the supply roller 220 until the rear end of the set size sheet P or the maximum size sheet P (in this example, A3 portrait size) passes the supply roller 220, and blocks the transmission of the second rotational driving force fk to the supply roller 220 when the rear end of the set size sheet P or the maximum size sheet P passes the supply roller 220.

[0082] Here, the set size can be exemplified as a size set by a size detection unit provided in the sheet stacking tray 80 and / or a size set by a user through an input operation to the operation unit. The timing at which the rear end of the sheet P of the set size or the maximum size passes through the supply roller 220 is a concept that includes not only the point in time at which the rear end of the sheet P passes through, but also the point in time after a predetermined time (for example, a time that allows for an error due to conveyance variation, etc.) has elapsed since the point in time at which the rear end of the sheet P passes through.

[0083] By doing so, even if the rear end of the sheet P, which is larger than the minimum size in the supply direction H, passes through the supply roller 220, it is possible to reduce the impact (releasing tension) of the sheet P when the rear end of the sheet P passes through the supply roller 220. This makes it possible to make it difficult for vibrations caused by the impact to be transmitted from the supply roller 220 or the conveying roller (registration roller 230) to the photoconductor (3) or the image writing system, thereby suppressing inconveniences such as image defects, such as missing images.

[0084] (Other embodiments) In the above-described first to third embodiments, the sheet is a recording sheet such as paper, but it may be an original G. For example, although not shown in the figure in this example, the sheet supplying device according to the present embodiment may be applied to an original feeding device that conveys an original G to an original reading unit.

[0085] The present invention is not limited to the above-described embodiment, but can be embodied in various other forms. Therefore, the embodiment is merely illustrative in all respects and should not be interpreted as being restrictive. The scope of the present invention is defined by the claims, and is not limited in any way by the text of the specification. Furthermore, all modifications and changes within the scope of the claims are within the scope of the present invention. [Explanation of symbols]

[0086] 1 Exposure equipment 10 Transfer roller 100 Image forming device 102 Image forming section 120 Control section 121 Processing section 122 Storage section 200 Sheet Feeder 210 Drive unit 220 Supply roller 220a Main body side supply roller 220b Manual feed side supply roller 221 First electromagnetic clutch for supply roller 221a First electromagnetic clutch for main body side supply roller 221b First electromagnetic clutch for manual feed roller 230 Registration roller 231 Second electromagnetic clutch for registration roller 240 First drive transmission mechanism 250 Second drive transmission mechanism 260 Sheet detection unit 3 Photoconductor drum 80 sheet stacking tray 81 Sheet stacking tray on the main unit side 82 Manual feed sheet stacking tray H Supply direction P-sheet X Left / right direction Y Depth direction Z vertical direction fp 1st rotation driving force fk 2nd rotation driving force

Claims

1. A sheet supplying device including a supply roller that supplies a plurality of sheets stacked on a sheet stacking tray one by one, and a conveying roller that conveys the sheets supplied from the supply roller to an image forming unit, A sheet supplying device which, when supplying the sheet, transmits a predetermined first rotational driving force to the supply roller, and when the sheet is transported by the transport roller, regardless of the size of the sheets loaded on the sheet stacking tray, transmits a second rotational driving force smaller than the first rotational driving force to the supply roller at the timing when the rear end of the sheet of the smallest size in the supply direction on which an image is formed in the image forming unit passes the supply roller, and then performs a first cut-off operation to cut off the transmission of the second rotational driving force to the supply roller.

2. 2. The sheet feeding apparatus according to claim 1, The sheet supplying device performs the first blocking operation when supplying a first sheet of the plurality of sheets.

3. 3. The sheet feeding device according to claim 2, a sheet detection unit configured to detect the presence or absence of the sheet transported between the supply roller and the transport roller; a detection size of the first sheet in the supply direction based on a detection result of the sheet detection unit, and controls rotation timings of the supply roller and the transport roller at a timing according to the detected size.

4. 4. The sheet feeding apparatus according to claim 3, the conveying roller is a registration roller that conveys the sheet, the leading edge of which is in contact with the conveying roller and stops, at a predetermined timing; The sheet supplying device detects the detection size from a time period from when the registration roller starts conveying the first sheet to when the sheet detection unit detects the rear end of the first sheet.

5. 5. The sheet feeding device according to claim 3, further comprising: A sheet supplying device that, when supplying a second or subsequent sheet of the plurality of sheets, transmits the first rotational driving force to the supply roller, and, while the sheet is being transported by the transport roller, performs a second cut-off operation to cut off the transmission of the first rotational driving force to the supply roller at the timing when the rear end of a sheet of the detection size passes by the supply roller.

6. 6. The sheet feeding device according to claim 1, The supply roller receives a rotational driving force via an electromagnetic clutch, The sheet supplying device transmits the second rotational driving force to the supply roller by performing pulse width modulation control on the electromagnetic clutch.

7. 6. The sheet feeding device according to claim 1, The supply roller receives a rotational driving force via an electromagnetic clutch, The sheet supplying device transmits the second rotational driving force to the supply roller by performing power control on the electromagnetic clutch.

8. 8. The sheet feeding device according to claim 6, further comprising: In the first interrupting operation, the transmission of the second rotational driving force to the supply roller is gradually interrupted.

9. 9. The sheet feeding device according to claim 1, A sheet supplying device in which, in the first blocking operation, the transmission of the second rotational driving force to the supply roller is blocked at the timing when the rear end of the sheet of a set size larger than the predetermined minimum size in the supply direction to be loaded on the sheet stacking tray, or the sheet of a maximum size in the supply direction on which an image is formed in the image forming section, passes through the supply roller.

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

Images