JP2017111314A - Sheet conveying device and image forming apparatus including the same - Google Patents

Abstract

CONSTITUTION: A sheet conveying device (10) stops driving a paper feed roller 72 from when the leading end of the first sheet passes through a registration roller 68 until when the leading end reaches transfer roller 44, and drives the paper feed roller 72 again during a predetermined period before and after the rear end of the first sheet passes through the registration roller 68.EFFECT: A variation in load when the rear end of a sheet passes through a paper feed roller can be reduced to prevent the occurrence of image defects, such as displacement in transfer.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus including the same, and more particularly to a sheet conveying apparatus that conveys the sheet to a transfer unit that transfers a toner image on an image carrier onto the sheet and an image forming apparatus including the sheet conveying apparatus.

  An example of a background art image forming apparatus is disclosed in Japanese Patent Application Laid-Open No. H10-228707. In the image forming apparatus disclosed in Patent Document 1, the control unit starts driving the registration roller to convey the paper to the secondary transfer unit, and then, when the leading edge of the paper is between the registration roller and the secondary transfer unit. The paper feed roller is switched from the drive state to the non-drive state.

JP 2011-248176 A

  However, in the image forming apparatus according to the background art, when the rear end of the sheet passes through the sheet feeding roller, the sheet feeding roller is in a non-driven state, and thus a load fluctuation occurs. When the load fluctuates, there is a problem that the sheet vibrates or the driving rotation of the registration roller becomes unstable, resulting in transfer deviation at the transfer portion.

  SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a novel sheet conveying device and an image forming apparatus including the same.

  Another object of the present invention is to reduce the load fluctuation when the trailing edge of the paper passes the paper feed roller, and to prevent the occurrence of image defects such as transfer deviation and an image including the same. A forming apparatus is provided.

  A first invention is a paper transport device for transporting a paper to a transfer section for transferring a toner image on an image carrier onto the paper, and includes a paper feed roller, a registration roller, and a paper feed roller control means. The paper feed roller is provided upstream of the transfer unit in the paper transport direction, and transports the paper in the direction of the transfer unit. The registration roller is provided between the transfer unit and the paper feed roller, and adjusts the conveyance timing of the sheet so that the toner image is transferred to the sheet by the transfer unit. This registration roller is also called a paper stop roller (PS roller), and conveys the paper at a speed equal to the process speed at which the transfer roller 44 forms an image on the paper. The paper feed roller control means sets the paper feed roller from the drive state to the non-drive state at a timing before the leading edge of the paper passes the registration roller and reaches the transfer roller 44, and the rear edge of the paper is the paper feed roller. The paper feeding roller is again driven for a predetermined time before and after passing through.

  According to the first aspect of the invention, the paper feed roller is changed from the driven state to the non-driven state at the timing before the leading edge of the paper passes the registration roller and reaches the transfer roller 44, so that the paper passes the transfer roller 44. In this case, there is no load fluctuation when the paper feed roller is switched from the driving state to the non-driving state, and image defects such as transfer deviation can be prevented. In addition, since the paper feed roller is driven again for a predetermined time before and after the trailing edge of the paper passes the paper feeding roller, the load fluctuation when the trailing edge of the paper passes the paper feeding roller is reduced, and the transfer is performed. Occurrence of image defects such as displacement can be prevented.

  The second invention is dependent on the first invention, and a sheet joining point is provided between the sheet feeding roller and the registration roller, and the predetermined time is a period after the leading edge of the sheet passes through the sheet feeding roller. It is set to a time shorter than the paper conveyance time until it reaches.

  According to the second aspect of the invention, the predetermined time during which the paper feed roller is driven is set to a time shorter than the paper transport time from when the leading edge of the paper passes through the paper feed roller until it reaches the paper merge point. The As a result, even when the paper size is set to be small by mistake due to a user's operation error and the second sheet is fed, the leading edge of the second sheet is located upstream of the sheet merge point. Stop. Therefore, when performing double-sided printing or the like, it is possible to prevent a jam from occurring due to a collision between the first sheet passing through the junction and the second sheet.

  The third invention is dependent on the first or second invention, and the paper feed roller and the registration roller are driven by the same drive source.

  According to the third aspect of the invention, since the paper feed roller and the registration roller are driven by the same drive source, the number of parts can be reduced, and thus the manufacturing cost can be reduced.

  A fourth invention is dependent on any one of the first to third inventions, and is interposed between a driving force transmitting member for transmitting a driving force from a driving source, and between the driving force transmitting member and the paper feed roller. A clutch mechanism that is provided and switches between a driving state and a non-driving state of the paper feed roller is further provided.

  According to the fourth aspect, since the driving state and the non-driving state of the paper feed roller can be switched by the clutch mechanism, the vibration to the paper when the driving state and the non-driving state of the paper feeding roller are switched can be reduced. The occurrence of image defects such as transfer deviation can be prevented.

  A fifth invention is dependent on any one of the first to fourth inventions, and is provided in a paper conveyance path through which a paper is conveyed. A guide member for guiding paper is further provided, and the guide surface of the guide member in the vicinity of the downstream side of the paper feed roller in the paper transport direction is a smooth surface.

  According to the fifth aspect, since the guide surface of the guide member in the vicinity of the downstream side of the paper feed roller in the paper transport direction is a smooth surface, even when the paper is stopped in the vicinity of the downstream side of the paper feed roller. It is possible to prevent the paper from wobbling due to ribs or the like.

  A sixth aspect of the invention is an image forming apparatus provided with the paper transport device of any one of the first to fifth aspects of the invention.

  According to the sixth invention, the same effect as the first invention is achieved, the load fluctuation when the trailing edge of the paper passes the paper feed roller is reduced, and the occurrence of image defects such as transfer deviation is prevented. be able to.

  According to the present invention, it is possible to reduce the load fluctuation when the trailing edge of the paper passes the paper feed roller, and to prevent image defects such as transfer deviation.

FIG. 1 is an illustrative view showing an outline of an internal configuration of an image forming apparatus including a sheet conveying apparatus according to a first embodiment of the present invention. FIG. 2 is an illustrative view showing a configuration of the sheet conveying device of FIG. 1 and its peripheral members. FIG. 3 is a schematic diagram illustrating a configuration of a driving mechanism for the registration roller and the sheet feeding roller provided in the sheet conveying device illustrated in FIG. 1. FIG. 4 is a perspective view illustrating a configuration of a driving mechanism for the registration roller and the paper feed roller provided in the paper conveyance device shown in FIG. FIG. 5 is a perspective view showing the configuration of the registration roller and paper feed roller driving mechanism as seen from the opposite side of FIG. FIG. 6 is a block diagram illustrating an example of an electrical configuration of the image forming apparatus illustrated in FIG. 1. FIG. 7 is an illustrative view showing one example of a memory map of the RAM shown in FIG. FIG. 8 is a timing chart showing the operation of the paper feed roller and the registration roller when the first sheet is conveyed. FIG. 9 is a flowchart illustrating an example of sheet feeding processing of the image forming apparatus illustrated in FIG. FIG. 10 is a flowchart showing an example of the first sheet feed control process of FIG. FIG. 11 is a timing chart showing the operations of the paper feed roller and the registration roller when the first sheet is conveyed in the second embodiment. FIG. 12 is a schematic diagram showing the configuration of the drive mechanism for the registration roller and the paper feed roller in the third embodiment. FIG. 13A is a schematic diagram showing the configuration of a non-driven paper feed roller clutch in the third embodiment, and FIG. 13B is a drive paper feed roller clutch in the third embodiment. It is the schematic which shows the structure of these.

[First embodiment]
Hereinafter, a sheet conveying apparatus 10 according to a first embodiment of the present invention will be described with reference to the drawings as appropriate. FIG. 1 is an illustrative view schematically showing a cross section of an image forming apparatus 100 including a paper transport apparatus 10.

  Referring to FIG. 1, a sheet conveying apparatus 10 conveys a sheet to a transfer unit that transfers a toner image on an image carrier to the sheet, and includes a sheet feeding roller 72 and a registration roller 68. It is used in an image forming apparatus 100 such as a facsimile, a printer, and a multifunction machine thereof. In this embodiment, the image forming apparatus 100 is a multifunction peripheral (MFP) having a copying function, a printer function, a scanner function, a facsimile function, and the like.

  First, the configuration of the image forming apparatus 100 will be schematically described. As shown in FIG. 1, the image forming apparatus 100 includes an apparatus main body 12 and an image reading device 14 disposed above the apparatus main body 12. The image forming apparatus 100 converts image data read by the image reading device 14 or image data transmitted from an external computer. Based on this, a multicolor or monochromatic image is formed on a predetermined paper (recording paper).

  The image reading device 14 includes a document placing table 16 formed of a transparent material, and a document pressing cover 18 is attached above the document placing table 16 through a hinge or the like so as to be freely opened and closed. The document pressing cover 18 is provided with an ADF (automatic document feeder) 24 that automatically feeds documents placed on the document placing tray 20 one by one to the image reading position 22. Although not shown, an operation unit (operation panel) such as a touch panel and operation buttons for receiving an input operation by the user is provided on the front side of the document placing table 16.

  The image reading device 14 includes an image reading unit 26 including a light source, a plurality of mirrors, an imaging lens, a line sensor, and the like. The image reading unit 26 exposes the document surface with a light source, and guides the reflected light reflected from the document surface to the imaging lens by a plurality of mirrors. Then, the reflected light is imaged on the light receiving element of the line sensor by the imaging lens. The line sensor detects the luminance or chromaticity of the reflected light imaged on the light receiving element, and generates image data based on the image on the surface of the document.

  The apparatus main body 12 of the image forming apparatus 100 includes a control unit 28 and an image forming unit 30. The control unit 28 includes a CPU 110, a RAM 114, and the like (see FIG. 6). The control unit 28 transmits a control signal to each part of the image forming apparatus 100 in response to an input operation to an operation unit such as a touch panel, and the like. Various operations are executed.

  The image forming unit 30 includes an exposure unit 32, a developing device 34, a photosensitive drum 36, a cleaner unit 38, a charger 40, an intermediate transfer belt unit 42, a transfer roller (secondary transfer roller) 44, a fixing unit 46, and the like. An image is formed on paper fed (conveyed) from the paper feed cassette 48 or the manual paper feed cassette 50 and the paper on which the image has been formed is discharged to a paper discharge tray 52. As image data for forming an image on a sheet, as described above, image data read by the image reading unit 26, image data transmitted from an external computer, or the like is used.

  Note that image data handled in the image forming apparatus 100 corresponds to four color images of black (K), cyan (C), magenta (M), and yellow (Y). For this reason, each of the developing device 34, the photosensitive drum 36, the cleaner unit 38, and the charging device 40 is provided so as to form four types of latent images corresponding to the respective colors, thereby providing four image stations. Composed.

  The photosensitive drum 36 is an electrostatic latent image carrier having a photosensitive layer formed on the surface of a cylindrical substrate having conductivity. The charger 40 charges the surface of the photosensitive drum 36 to a predetermined potential. It is something to be made. Further, the exposure unit 32 is configured as a laser scanning unit (LSU) including a laser emitting portion and a reflection mirror, and exposes the surface of the charged photosensitive drum 36 so that an electrostatic latent image corresponding to image data is obtained. An image is formed on the surface of the photosensitive drum 36. The developing device 34 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 36 with toner of four colors (YMCK). The cleaner unit 38 removes and collects the toner remaining on the surface of the photosensitive drum 36 after development and image transfer.

  The intermediate transfer belt unit 42 includes an intermediate transfer belt 54, a drive roller 56, a driven roller 58, four intermediate transfer rollers 60, and the like, and is disposed above the photosensitive drum 36. The intermediate transfer belt 54 is provided so as to be in contact with each photosensitive drum 36, and the toner images of the respective colors formed on the respective photosensitive drums 36 are sequentially superimposed on the intermediate transfer belt 54 using the intermediate transfer roller 60. As a result, a multicolor toner image is formed on the intermediate transfer belt 54. Further, a transfer roller 44 is disposed in the vicinity of the driving roller 56, and the toner formed on the intermediate transfer belt 54 by passing the sheet through the nip area between the intermediate transfer belt 54 and the transfer roller 44. The image is transferred to the paper. That is, a portion where the transfer roller 44 and the driving roller 56 are provided becomes a transfer portion.

  The transfer roller 44 includes, for example, a core metal such as stainless steel or iron, and a conductive sponge elastic body layer is formed on the core metal from carbon, an ion conductive filler, or an ion conductive base polymer. . A foam layer (foamed cell) is formed on the surface layer of the sponge elastic body layer.

  The fixing unit 46 includes a heat roller 62 and a pressure roller 64 and is disposed above the transfer roller 44. The heat roller 62 is set to have a predetermined fixing temperature. When the paper passes through the nip area between the heat roller 62 and the pressure roller 64, the toner image transferred to the paper is melted. The toner image is heat-fixed on the sheet by mixing and pressing.

  Next, the configuration of the sheet conveying apparatus 10 and its peripheral members will be described with reference to FIG. FIG. 2 is an illustrative view showing a configuration of the sheet conveying device 10 of FIG. 1 and its peripheral members.

  As shown in FIGS. 1 and 2, the paper transport device 10 of the first embodiment is a device for transporting paper placed on a paper feed cassette 48 or a manual paper feed cassette 50 to a transfer unit. In the paper transport device 10, a pickup roller 70, a paper feed roller 72, a registration roller 68, a transfer unit, and the like are provided in this order in the paper transport direction. A fixing unit 46 and a plurality of transport rollers 66 are provided on the downstream side of the transfer unit in the paper transport direction. Accordingly, the sheet conveyed to the transfer unit by the sheet conveying apparatus 10 passes through the transfer unit, and is conveyed to the paper discharge tray 52 via the fixing unit 46 and the plurality of conveyance rollers.

  However, the image forming apparatus 100 of the first embodiment is provided with a plurality of paper feed cassettes 48 arranged in the vertical direction. For convenience of explanation, FIG. 2 shows two sheet feeding cassettes, that is, an upper sheet feeding cassette 48a and a lower sheet feeding cassette 48b provided below the upper sheet feeding cassette 48a. The upper paper feed cassette 48 a and the lower paper feed cassette 48 b are disposed below the image forming unit 30.

  The paper transport device 10 includes a paper transport path L11 through which paper is transported from the upper paper feed cassette 48a toward the transfer section, and a paper transport path L12 through which paper is transported from the lower paper feed cassette 48b toward the transfer section. And a paper transport path L13 through which the paper is transported from the manual paper feed cassette 50 toward the transfer section. A paper feed roller 72 is provided in each of the paper transport path L11, the paper transport path L12, and the paper transport path L13, and a pickup roller 70 is provided in each of the paper transport path L11 and the paper transport path L12.

  The sheet conveyance path L11, the sheet conveyance path L12, and the sheet conveyance path L13 merge on the upstream side of the registration roller 68 in the sheet conveyance direction, and become the first sheet conveyance path L1. Specifically, the sheet conveyance path L11 and the sheet conveyance path L12 merge at the merge point C1, and the sheet conveyance path L13 merges at the merge point C2 downstream in the sheet conveyance direction from the merge point C1.

  In addition, when performing duplex printing on a sheet, the sheet after completion of single-sided printing and passing through the fixing unit 46 is returned to the first sheet conveyance path L1 on the upstream side in the sheet conveyance direction of the transfer unit. A second paper transport path L2 is provided. The second paper conveyance path L2 merges with the first paper conveyance path L1 at a junction C2 provided between the junction C1 of the first paper conveyance path L1 and the registration roller 68. Further, the second paper transport path L2 joins the paper transport path L13 from the manual paper feed cassette 50 at a confluence section C3 upstream of the confluence section C2 in the paper transport direction. Hereinafter, when there is no need to distinguish between the upper sheet feeding cassette 48a and the lower sheet feeding cassette 48b, they are simply referred to as “sheet feeding cassette 48”.

  The pickup roller 70 picks up paper from the paper feed cassette 48 and sends it out to the paper feed roller 72. The paper feed roller 72 conveys the paper fed by the pickup roller 70 toward the registration roller 68.

  The first paper transport path L1 is provided with a plurality of guide members 84 for guiding the transported paper, and the first paper transport path L1 is curved at a position near the downstream side of the paper feed roller 72. The guide surface 84a of the guide member 84 disposed on the outer side of the guide member 84 is a smooth surface.

  The registration roller 68 is also called a paper stop roller (PS roller), and conveys the sheet at a speed equal to the process speed at which the image forming unit 30 forms an image of the sheet. The registration roller 68 is provided between the paper feed roller 72 and the transfer unit, and adjusts the sheet conveyance timing so that the toner image is transferred to the sheet at the transfer unit. For example, the registration roller 68 waits (temporarily stops) with the sheet conveyed by the sheet feeding roller 72 being held, and starts conveying the sheet in synchronization with the transfer unit. At this time, the registration roller 68 is rotated at a peripheral speed equal to the peripheral speed of the intermediate transfer belt 54.

  Further, a paper detection sensor 80 is provided in the first paper transport path L1 between the paper feed roller 72 and the registration roller 68. The sheet detection sensor 80 is turned on when a sheet is present at the position where the sheet detection sensor 80 is provided in the first sheet conveyance path L1, and outputs data indicating that the sheet detection sensor 80 is turned on to the CPU 110.

  In such an image forming apparatus 100, when performing single-sided printing in a print job, the sheets placed on the paper feed cassette 48 or the manual paper feed cassette 50 are fed one by one by the respective pickup rollers 70. L1 is guided to the transfer portion by the paper feed roller 72 and the registration roller 68, and the toner image is transferred onto the paper by the transfer portion. Thereafter, when the toner passes through the fixing unit 46, the unfixed toner on the paper is melted and fixed by heat, and the paper is discharged onto the paper discharge tray 52 via the transport roller 66.

  On the other hand, when performing double-sided printing, the trailing edge of the paper that has passed single-sided printing and has passed through the fixing unit 46 reaches the paper discharge roller 74 that is disposed closest to the paper discharge tray 52 in the first paper transport path L1. When the paper reaches, the paper is reversely rotated, whereby the paper runs backward and is guided to the second paper conveyance path L2. As shown in FIG. 2, the paper guided to the second paper transport path L <b> 2 is transported through the second paper transport path L <b> 2 by the plurality of transport rollers 66, and is provided upstream of the registration roller 68 in the paper transport direction. Then, it is guided to the first paper conveyance path L1 at the joining point C2. Thereafter, the sheet is conveyed to the transfer unit at a predetermined timing by the registration roller 68, but the front and back of the sheet are reversed at the stage where the second sheet conveyance path L2 merges with the first sheet conveyance path L1, so that the transfer unit Then, printing is performed on the back side of the paper.

  Next, the configuration of the drive mechanism of the registration roller 68 and the paper feed roller 72 provided in the paper transport device 10 will be described with reference to FIGS. FIG. 3 is a schematic diagram illustrating a configuration of a driving mechanism for the registration roller 68 and the sheet feeding roller 72 provided in the sheet conveying apparatus 10. FIG. 4 is a perspective view showing the configuration of the drive mechanism of the registration roller 68 and the paper feed roller 72 provided in the paper transport apparatus 10. FIG. 5 is a perspective view showing the configuration of the drive mechanism of the registration roller 68 and the paper feed roller 72 as viewed from the opposite side of FIG.

  As shown in FIGS. 3 to 5, the driving mechanism of the registration roller 68 and the paper feed roller 72 includes a motor 90, driven gears 92, 94, 96, 98, a registration roller clutch 680, a registration roller shaft 682, a paper feed roller clutch. 720, a paper feed roller shaft 722, and the like, and are provided inside the apparatus main body 12.

  Further, the registration roller 68 and the paper feed roller 72 are rotated by a rotational drive source (motor) provided in the apparatus main body 12. In the first embodiment, the registration roller 68 and the paper feed roller 72 are rotated by the same motor 90. The pickup roller 70 is rotationally driven together with the paper feed roller 72 when the drive from the motor 90 is transmitted through the drive gear 700 (see FIG. 5).

  The motor 90 is attached to a structural member 82 provided inside the apparatus main body 12. The motor 90 has a drive shaft 90a. The drive shaft 90a is a shaft member with a gear and transmits a driving force to the outside.

  The driven gears 92, 94, 96 and 98 are gears for transmitting the driving force applied from the drive shaft 90 a of the motor 90 to the registration roller clutch 680 and the paper feed roller clutch 720. These driven gears 92, 94, 96 and 98 are rotatably attached to the structural member 82. Specifically, the driven gear 92 meshes with the drive shaft 90 a and the driven gear 94, and transmits the driving force applied from the drive shaft 90 a of the motor 90 to the driven gear 94. The driven gear 94 meshes with the driven gear 96 and transmits the driving force transmitted from the driven gear 92 to the driven gear 96. The driven gear 96 meshes with the driven gear 98 and a paper feed roller clutch 720 (a driving node 720a described later), and transmits the driving force transmitted from the driven gear 94 to the driven gear 98 and the paper feed roller clutch 720. The driven gear 98 meshes with a registration roller clutch 680 (a driving node 680 a described later), and transmits the driving force transmitted from the driven gear 96 to the registration roller clutch 680.

  As described above, the driving force applied from the drive shaft 90 a of the motor 90 is transmitted to the registration roller clutch 680 and the paper feed roller clutch 720 via the driven gears 92, 94, 96 and 98. The number of driven gears is not limited to the above, and may be set as appropriate.

  The registration roller clutch 680 includes a driving node 680a to which driving force is transmitted first and a driven node 680b to which driving force is transmitted from the driving node 680a. The driving node 680a and the driven node 680b are rotatably provided. Further, the driving node 680a has a gear on the outer periphery. The gear of the driving node 680 a meshes with the driven gear 98. Further, the driven node 680 b is connected to the registration roller shaft 682. A registration roller 68 is provided on the registration roller shaft 682.

  The paper feed roller clutch 720 includes a driving node 720a and a driven node 720b, similar to the registration roller clutch 680. The driving node 720 a has a gear and meshes with the driven gear 98. The driven node 720 b is connected to the paper feed roller shaft 722. A paper feed roller 72 is provided on the paper feed roller shaft 722.

  The registration roller clutch 680 and the paper feed roller clutch 720 are electromagnetic clutches. For example, the paper feed roller clutch 720 excites an electromagnet (not shown) provided on one of the driving node 720a or the driven node 720b to attract or repel the other node.

  When the driving node 720a and the driven node 720b are brought into contact with each other, the driving force is transmitted from the driving node 720a to the driven node 720b, and the paper feed roller 72 is driven.

  On the other hand, when the driving node 720a and the driven node 720b are separated from each other, the driving force is not transmitted from the driving node 720a to the driven node 720b, and the sheet feeding roller 72 is in a non-driven state.

  Since the registration roller clutch 680 is the same as the paper feed roller clutch 720, the description thereof is omitted.

  The registration roller clutch 680 and the feed roller clutch 720 are not limited to electromagnetic clutches, and may be general-purpose clutches such as a disk clutch, a drum clutch, a conical clutch, and a meshing clutch.

  Further, in addition to the registration roller 68 and the paper feed roller 72, the conveyance roller 66 may be rotated by a motor 90. Further, the registration roller 68 and the paper feed roller 72 may be rotated by different motors.

  In the image forming apparatus 100 having such a configuration, after the sheet passes through the registration roller 68, the sheet feeding roller 72 is changed from the driving state to the non-driving state when the leading end of the sheet is between the registration roller 68 and the transfer unit. There is something to switch.

  However, when the trailing edge of the sheet passes through the sheet feeding roller 72, if the sheet feeding roller 72 is in a non-driven state, load fluctuation occurs. When the load fluctuates, the sheet vibrates, the driving rotation of the registration roller 68 becomes unstable, and there is a problem that a transfer deviation occurs when the toner image on the image carrier is transferred.

  Therefore, in the first embodiment, control is performed by the following method so that the toner image on the image carrier can be appropriately transferred onto the paper in the transfer unit. In brief, in the first embodiment, the paper feed roller 72 is brought into a non-driving state before the leading edge of the first sheet passes through the registration roller 68 and reaches the transfer section. The paper feed roller 72 is driven for a predetermined time before and after the trailing edge of the eye paper passes the registration roller 68.

  Hereinafter, the operations of the paper feed roller 72 and the registration roller 68 when the first sheet is conveyed in the image forming apparatus 100 of the first embodiment will be specifically described with reference to a timing chart. FIG. 8 is a timing chart showing the operation of the paper feed roller 72 and the registration roller 68 when the first sheet is conveyed.

  As shown in FIG. 8, when a print job is started in the image forming apparatus 100, first, the paper feed roller 72 (and the pickup roller 70) is driven. That is, the motor 90 is driven, the paper feed roller clutch 720 is brought into contact, and the driving force of the motor 90 is transmitted to the paper feed roller 72. By feeding the paper feed roller 72, feeding of the first sheet is started. However, at the time when feeding of the first sheet is started, the registration roller clutch 680 is in a separated state.

  When the leading edge of the sheet conveyed by the sheet feeding roller 72 reaches the registration roller 68, the registration roller clutch 680 is brought into contact at a predetermined timing, and the driving force of the motor 90 is transmitted to the registration roller 68. As a result, the registration roller 68 is driven, and the leading edge of the sheet passes through the registration roller 68. Here, the timing at which the registration roller 68 is driven is set to the reference time T0. The reference time T0 is a time serving as a reference for the transport timing. Note that the timing at which the registration roller 68 is driven is set to the reference time T0 because the registration roller 68 conveys the paper in synchronization with the image forming unit 30, so that the leading edge of the paper reaches the registration roller 68. This is because there is a case where it does not drive immediately.

  When the registration roller 68 is driven, the sheet is conveyed under the driving force of the paper supply roller 72 and the registration roller 68. Thereafter, the paper feed roller 72 is brought into a non-driven state at the first time T1. The first time T1 is the timing before the leading edge of the paper passes the registration roller 68 and before reaching the transfer portion (transfer roller 44), and is automatically set when the print job is started. That is, at the first time T1, the paper feed roller clutch 720 is brought into a separated state. Accordingly, the sheet is conveyed only by the driving force of the registration roller 68. However, since the paper feeding roller clutch 720 is in the separated state, the paper feeding roller 72 brought into the non-driven state can be driven and rotated by the paper conveyed by the driving force of the registration roller 68.

  When the leading edge of the paper passes through the transfer roller 44, the trailing edge of the paper passes through the paper feeding roller 72. The paper feed roller 72 is driven again at the second time T2 before and after the trailing edge of the paper passes through the paper feed roller 72, and then turned off again at the third time T3. That is, the paper feed roller 72 is driven for a predetermined time from the second time T2 to the third time T3. The second time T2 is the timing before the trailing edge of the paper passes the paper feed roller 72, and the third time T3 is the timing after the trailing edge of the paper passes the paper feed roller 72. The second time T2 and the third time T3 are automatically set when the print job is started. The second time T2 and the third time T3 are set according to the position of the rear end corresponding to the paper size set by the user, not the position of the rear end detected from the actually conveyed paper. This is because the paper detection sensor 80 is provided on the downstream side of the paper feed roller 72, so that when the rear edge of the first sheet passes through the paper feed roller 72, the rear edge of the actually conveyed paper This is because the position of cannot be detected.

  At the third time T3, the paper feed roller 72 is brought into a non-driven state, so that the paper is conveyed again by the driving force of the registration roller 68 and the transfer roller 44, and the trailing edge of the paper is the registration roller 68. Pass through. Thereafter, the sheet is conveyed to the sheet discharge tray 52 by receiving driving forces from the transfer roller 44 and the conveying roller 66.

  When the trailing edge of the first sheet passes the registration roller 68, feeding of the second sheet is started after a predetermined time. That is, the paper feed roller 72 is driven. Further, the registration roller 68 is brought into a non-driven state before the leading edge of the paper reaches the registration roller 68.

  Further, when the feeding of the second sheet is started, the size of the first sheet is calculated. Specifically, the CPU 110 calculates the passage time of the first sheet at the position where the sheet detection sensor 80 is provided according to the data transmitted from the sheet detection sensor 80, and determines the sheet size based on the passage time. calculate. However, in calculating the passage time of the first sheet, when the time when the registration roller 68 is stopped is included, the sheet size is calculated by the time obtained by subtracting the stop time of the registration roller 68. Accordingly, the second time T2 and the third time T3 when the second and subsequent sheets are conveyed are set according to the position of the trailing edge detected from the sheet that is actually conveyed.

  The reference time T0 is set according to the distance along the first sheet conveyance path L1 from the sheet detection sensor 80 to the registration roller 68 and the rotation speed of the sheet feed roller 72. The first time T1, the second time T2, and the third time T3 when the first and subsequent sheets are conveyed are the sheet size set by the user and the distance along the first sheet conveyance path L1 between the components. Also, it is set in advance according to the rotational speed (circumferential speed) of each roller (registration roller 68 or transfer roller 44).

  FIG. 6 is a block diagram illustrating an example of an electrical configuration of the image forming apparatus 100 illustrated in FIG. 1. As shown in FIG. 6, the image forming apparatus 100 includes a CPU 110, and a paper detection sensor 80, a RAM 114, a timer 116, and a motor driver 120 are connected to the CPU 110 via a bus 112. A motor 90 is connected to the motor driver 120. Among the components shown in FIG. 6, the control unit 28 shown in FIG. 1 includes a CPU 110, a bus 112, a RAM 114, a timer 116, and a motor driver 120.

  Although not shown, the image forming apparatus 100 includes the above-described paper transport device 10, the image reading unit 26, the image forming unit 30, an operation unit, a jam sensor, a flash memory, and the like. Connected to the CPU 110.

  The paper detection sensor 80 is a transmissive optical sensor, and is a sensor for detecting the presence / absence of paper at a position provided with the paper detection sensor 80. When the sheet detection sensor 80 detects a sheet, the sheet detection sensor 80 outputs data indicating that it is turned on to the CPU 110. On the other hand, when no paper is detected by the paper detection sensor 80, the paper detection sensor 80 outputs data indicating that the paper is off to the CPU 110.

  The CPU 110 governs overall control of the image forming apparatus 100, and comprehensively controls the operation of each part of the image forming apparatus 100 such as the image forming unit 30. Further, the CPU 110 comprehensively controls the operation of each part of the paper transport apparatus 10. The RAM 114 is used as a work area and a buffer area for the CPU 110.

  The timer 116 is a counter (timer) for counting time. In the first embodiment, the timer 116 starts counting when the leading edge of the paper passes through the position where the paper detection sensor 80 is provided, for example. The CPU 110 sets the reference time T0 according to the count of the timer 116, and then determines whether the first time T1, the second time T2, and the third time T3 have elapsed.

  The motor driver 120 controls driving and stopping of the motor 90 in accordance with instructions from the CPU 110. For example, the motor 90 is a DC motor and is driven by a voltage applied from the motor driver 120.

  FIG. 7 is an illustrative view showing one example of a memory map of the RAM 114 shown in FIG. As shown in FIG. 7, the RAM 114 includes a program storage area 302 and a data storage area 304. The program storage area 302 stores a control program for controlling the image forming apparatus 100. The control program includes an image forming program 310, a motor control program 312, and a roller control program (paper conveyance control program) 314.

  The image forming program 310 is a program for forming a multi-color or single-color image on a sheet based on image data read by the image reading unit 26 or image data transmitted from an external computer.

  The motor control program 312 is a program for controlling driving and stopping of the motor 90. The CPU 110 rotates the transport roller 66, the registration roller 68, the paper feed roller 72, and the pickup roller 70 according to the motor control program 312, or stops the rotation.

  The roller control program 314 is a program for controlling the driving state and non-driving state of the registration roller 68 and the paper feeding roller 72. In accordance with the roller control program 314, the CPU 110 excites an electromagnet provided on one of the driving node and the driven node of the registration roller clutch 680 and the paper feeding roller clutch 720 to attract or repel the other node. That is, the driving state and non-driving state of the registration roller 68 and the paper feed roller 72 are controlled according to the roller control program 314. Although detailed description is omitted, the roller control program 314 is also a program for controlling the driving state and the non-driving state of the transport roller 66.

  Although not shown, the program storage area 302 also stores other programs necessary for controlling the image forming apparatus 100.

  In the data storage area 304, time data 330 is stored. In the first embodiment, the time data 330 indicates that the leading edge or the trailing edge of the sheet passes between the components provided in the first sheet conveyance path L1 after the leading edge of the sheet has passed the registration roller 68. It is data about the time until.

  Although illustration is omitted, other data necessary for execution of the control program is also stored in the data storage area 304, and a counter or flag required for execution of the control program is also provided in the data storage area 304. For example, the other data is data on the paper size, the direction of the paper to be fed, and the rotation and stop time of the registration roller 68.

  FIG. 9 is a flowchart illustrating an example of paper feed processing of the image forming apparatus 100 illustrated in FIG. This paper feed process is executed when a print job is started in the image forming apparatus 100. Note that the paper feed process shown in FIG. 9 is referred to as the entire paper feed process in order to distinguish it from the paper feed control process for the first sheet, which will be described later.

  As shown in FIG. 9, when starting the entire paper feed process, the CPU 110 performs a paper feed control process for the first sheet in step S1, and proceeds to step S3. Details of the paper feed control process for the first sheet in step S1 will be described later.

  In step S3, the paper detection sensor 80 detected in step S1 is provided to calculate the first paper size according to the paper passage time at the position. In step S5, the paper size calculated in step S3 is stored. In step S7, paper feeding control for the second and subsequent sheets is performed according to the paper size stored in step S5. In step S9, it is determined whether the print job is completed. If “NO” in the step S9, the process returns to the step S7. On the other hand, if “YES” in the step S9, the motor 90 is stopped and the entire paper feeding process is ended.

  FIG. 10 is a flowchart showing an example of the first sheet feed control process of FIG. For example, the flow of paper feed control processing for the first sheet is a subroutine executed in step S1 of paper feed processing.

  As shown in FIG. 10, when the CPU 110 starts the first sheet feed control process, the CPU 110 starts driving the sheet feed roller 72 in step S31. That is, the motor 90 is driven, the paper feed roller clutch 720 is brought into contact, and the drive of the paper feed roller 72 is started.

  In step S33, the leading edge of the paper is detected by the paper detection sensor 80. At this time, the timer 116 starts counting. When the timer 116 starts counting, a reference time T0, a first time T1, a second time T2, and a third time T3 are set, and measurement of the passage time of the first sheet is started.

  In step S35, it is determined whether the first time T1 has elapsed since the leading edge of the sheet has passed the registration roller 68. That is, when the registration roller 68 is driven, it is determined that the leading edge of the sheet has passed the registration roller 68, and the reference time T0 is set. Further, the first time T1, the second time T2, and the third time T3 are set based on the reference time T0. Thereafter, it is determined whether or not the first time T1 has elapsed. If “NO” in the step S35, that is, if the first time T1 has not elapsed, the process returns to the same step S35. On the other hand, if “YES” in the step S35, that is, if the first time T1 has elapsed, the process proceeds to a step S37.

  In step S37, the paper feed roller 72 is switched to the non-driven state, and the process proceeds to step S39. In step S39, it is determined whether or not the trailing edge of the sheet has reached the vicinity (near) of the sheet feed roller 72. That is, it is determined whether the second time T2 has elapsed. If “NO” in the step S39, that is, if the second time T2 has not elapsed, the process returns to the same step S39. On the other hand, if “YES” in the step S39, that is, if the second time T2 has elapsed, the process proceeds to a step S41.

  In step S41, the paper feed roller 72 is switched to the non-driven state, and the process proceeds to step S43. In step S43, it is determined whether a predetermined time has elapsed. That is, it is determined whether the third time T3 has elapsed. If “NO” in the step S43, that is, if the third time T3 has not elapsed, the process returns to the same step S43. On the other hand, if “YES” in the step S43, that is, if the third time T3 has elapsed, the process proceeds to a step S45.

  In step S45, the paper feed roller 72 is switched to the driving state, and the process proceeds to step S47. In step S47, the trailing edge of the sheet is detected by the sheet detection sensor 80, and the process returns to the entire sheet feeding process.

  As described above, according to the first embodiment, since the leading edge of the first sheet passes through the registration roller 68 and stops before reaching the transfer roller 44, the sheet is transferred. When passing through the roller 44, there is no load fluctuation when the paper feed roller 72 is switched from the driving state to the non-driving state, and the occurrence of image defects such as transfer deviation can be prevented. Further, since the paper feed roller 72 is driven for a predetermined time before and after the trailing edge of the first sheet passes the registration roller 68, the load when the trailing edge of the sheet passes the feeding roller 72 Variations can be reduced and image defects such as transfer deviations can be prevented.

  Further, according to the first embodiment, since the paper feed roller 72 and the registration roller 68 are driven by the same motor 90, the number of parts can be reduced, and thus the manufacturing cost can be reduced.

  Furthermore, according to the first embodiment, since the driving state and the non-driving state of the paper feeding roller 72 can be switched by the paper feeding roller clutch 720, Vibration can be reduced, and image defects such as transfer deviation can be prevented. Furthermore, in the first embodiment, since the paper feed roller clutch 720 is an electromagnetic clutch, it is possible to reduce vibrations to the paper when the drive state and the non-drive state of the paper feed roller 72 are switched.

Furthermore, since the guide surface 84a of the guide member 84 at a position near the downstream side of the paper feed roller 72 in the paper transport direction is a smooth surface, even when the paper stops at a position near the downstream side of the paper feed roller 72 It is possible to prevent the sheet from wobbling due to ribs or the like.
[Second Embodiment]
The image forming apparatus 100 according to the second embodiment is the same as the image forming apparatus 100 according to the first embodiment except that the time setting method from the second time T2 to the third time T3 is different. Portions common to the embodiments are denoted by the same reference numerals, and redundant descriptions are omitted or simplified.

  In the image forming apparatus 100 configured as shown in the first embodiment, a detecting unit that detects the size of the paper placed in the paper feed cassette 48 or the manual paper feed cassette 50 may be provided. In this case, paper feeding control is performed according to the paper size detected by the detecting means. However, there are cases where the detection means as described above is not provided. In this case, as described above, the second time T2 and the third time T3 are set according to the paper size set by the user.

  However, the paper size may be set incorrectly due to a user operation error or the like. When the paper size actually transported is smaller than the set paper size, the second paper may be fed before the trailing edge of the first paper passes the registration roller 68. . In other words, when the paper feed roller 72 is driven for a predetermined time from the second time T2 to the third time T3, the rear end of the first sheet already has the paper feed roller 72 (and the pickup roller 70). If it passes, the second sheet is fed. In such a case, there is a problem that the second sheet is wasted or the second sheet stops at a halfway position and a jam occurs.

  Therefore, in the second embodiment, even if the second sheet is fed before the trailing edge of the first sheet passes the registration roller 68, the second sheet is wasted. The following method is used to prevent the second sheet from stopping at a halfway position and causing a jam. Briefly speaking, in the second embodiment, the time from the second time T2 to the third time T3 is the paper transport time from when the leading edge of the paper passes the paper feed roller 72 until it reaches the junction C1. The time is set to be shorter than W1.

  Hereinafter, the operations of the paper feed roller 72 and the registration roller 68 when the first sheet is conveyed in the image forming apparatus 100 of the second embodiment will be specifically described with reference to a timing chart. FIG. 11 is a timing chart showing the operations of the paper feed roller 72 and the registration roller 68 when the first sheet is conveyed in the second embodiment.

  As shown in FIG. 11, in the image forming apparatus 100 according to the second embodiment, the time from the second time T2 to the third time T3 reaches the joining point C1 after the leading edge of the paper passes the paper feed roller 72. It is set so as to be shorter than the paper conveyance time W1 until it is done.

  However, when the sheet is fed from the upper sheet feeding cassette 48a and the lower sheet feeding cassette 48b is not used, the leading edge of the sheet is from the second time T2 to the third time T3. The time is set to be shorter than the paper transport time W2 from when the paper passes through the paper feed roller 72 until it reaches the junction C2.

  When paper is fed from the manual paper feed cassette 50, the time from the second time T2 to the third time T3 reaches the junction C3 after the leading edge of the paper passes the paper feed roller 72. It is set so as to be shorter than the paper conveyance time W3 until it is done.

According to the second embodiment, the time from the second time T2 to the third time T3 is shorter than the paper transport time W1 from when the leading edge of the paper passes the paper feed roller 72 until it reaches the junction C1. Set to be time. In this way, even if the second sheet is fed before the trailing edge of the first sheet passes the registration roller 68, the leading edge of the second sheet is the junction C1. Stop upstream. Therefore, even when the second sheet is mistakenly fed, it is possible to prevent stopping at a halfway position. Also, since the leading edge of the second sheet stops upstream of the merge point C1, the first sheet and the second sheet passing through the merge point collide when performing double-sided printing. Jam can be prevented from occurring.
[Third embodiment]
The image forming apparatus 100 of the third embodiment has the same configuration as that of the first embodiment except that the structures of the registration roller clutch 680 and the paper feed roller clutch 720 are different. Are given the same reference numerals, and duplicate descriptions are omitted or simplified.

  Briefly, the registration roller clutch 680 and the paper feed roller clutch 720 of the third embodiment are clutches that combine a solenoid and a ratchet gear. Hereinafter, the structures of the registration roller clutch 680 and the paper feed roller clutch 720 will be described with reference to FIGS.

  FIG. 12 is a schematic diagram showing the configuration of the drive mechanism of the registration roller 68 and the paper feed roller 72 in the third embodiment. FIG. 13A is a schematic diagram showing the configuration of the non-driven state paper feed roller clutch 720 in the third embodiment, and FIG. 13B is the driven state feed roller in the third embodiment. FIG. 3 is a schematic diagram showing a configuration of a clutch 720.

  The paper feed roller clutch 720 will be described as an example. As shown in FIG. 12, FIG. 13 (A) and FIG. 13 (B), the paper feed roller clutch 720 includes a driving node 720a, a driven node 720b, a solenoid 720c, a spring 720d, a plunger 720e, a regulating plate 720f, and a rotating shaft 720g. , A latch 720h and a rotating shaft 720j.

  The solenoid 720 c is provided inside the apparatus main body 12 and reciprocally moves a plunger 720 e protruding in a direction toward the paper feed roller shaft 722 when energized. The solenoid 720c of the third embodiment is a two-position solenoid, and the amount of movement of the plunger 720e is set in advance.

  The restricting plate 720f is rotatably supported by the rotating shaft 720g and is pin-joined with the plunger 720e at one end. Thereby, the restricting plate 720f rotates around the rotation shaft 720g as the plunger 720e reciprocates.

  The restricting plate 720f is a member that restricts the movement of the latch 720h when the other end is displaced as the plunger 720e reciprocates and comes into contact with the latch 720h. The other end of the restricting plate 720f is displaced between a first position that contacts the latch 720h and a second position that does not contact the latch 720h. In the third embodiment, when the plunger 720e moves (protrudes) in the direction toward the paper feed roller shaft 722, the restriction plate 720f is positioned at the first position, and the plunger 720e moves away from the paper feed roller shaft 722. When moved (retracted), the restriction plate 720f is positioned at the second position.

  The latch 720h is rotatably provided on the driven node 720b by the rotation shaft 720j. Although not shown, the follower 720b is provided with a biasing member that biases the latch 720h in the clockwise direction. Therefore, the latch 720h rotates clockwise when the restriction plate 720f does not contact. As shown in FIG. 13B, when the latch 720h rotates clockwise, a part of the latch 720h is caught by the step formed on the driving node 720a, and the driving force is transmitted from the driving node 720a to the driven node 720b. Contact state. On the other hand, as shown in FIG. 13A, the latch 720h rotates counterclockwise when the restricting plate 720f contacts. When the latch 720h rotates counterclockwise, a part of the latch 720h is disengaged from the step of the driving node 720a, and the driving node 720a is idled. That is, a separated state is reached in which the driving force is not transmitted from the driving node 720a to the driven node 720b.

  With the configuration as described above, the solenoid 720c can be controlled to displace the position of the plunger 720e, and the contact state and the separation state of the paper feed roller clutch 720 can be switched. That is, the driving state and non-driving state of the paper feed roller 72 can be switched. The registration roller clutch 680 has the same structure as the paper feed roller clutch 720 described above, and a description thereof will be omitted.

  In the third embodiment, an example in which the registration roller clutch 680 and the paper feed roller clutch 720 are constituted by ratchet gears has been described. However, the present invention is not limited to this. For example, the registration roller clutch 680 and the paper feed roller clutch 720 can be configured by a mechanism combining a solenoid 720c and a spring clutch, a mechanism combining a solenoid 720c and a torque limiter, or the like.

  According to the third embodiment, similarly to the first embodiment, it is possible to reduce the load fluctuation when the trailing edge of the paper passes the paper feed roller 72 and to prevent the occurrence of image defects such as transfer deviation. .

  The aspect shown in the third embodiment can be employed in combination with the second embodiment.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example. Each of the specific examples given above is merely an example, and can be appropriately changed according to the necessity of product specifications and the like.

DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus 10 ... Paper conveying apparatus 12 ... Apparatus main body 14 ... Image reading apparatus 44 ... Transfer roller 68 ... Registration roller 70 ... Paper feed roller 80 ... Paper detection sensor 90 ... Motor

Claims (6)

A paper transport device that transports the paper to a transfer unit that transfers the toner image on the image carrier to the paper,
A paper feed roller provided upstream of the transfer unit in the paper transport direction and transports the paper in the direction of the transfer unit;
A registration roller that is provided between the transfer unit and the paper feed roller and adjusts the conveyance timing of the paper so that the toner image is transferred to the paper by the transfer unit; and a front end of the paper is the registration roller The paper feed roller is switched from the driven state to the non-driven state at a timing before it reaches the transfer section after passing through the paper feed, and the paper feed is again performed for a predetermined time before and after the trailing edge of the paper passes through the paper feed roller. A paper transport device comprising paper feed roller control means for driving a paper roller. A paper merging point is provided between the paper feed roller and the registration roller,
2. The sheet conveying apparatus according to claim 1, wherein the predetermined time is set to a time shorter than a sheet conveying time from when the leading end of the sheet passes through the sheet feeding roller to the sheet merging point.   The sheet conveying apparatus according to claim 1, wherein the sheet feeding roller and the registration roller are driven by the same driving source. A driving force transmitting member that transmits a driving force from the driving source; and a clutch that is provided between the driving force transmitting member and the paper feeding roller and switches between a driving state and a non-driving state of the paper feeding roller. The paper conveyance device according to claim 1, further comprising a mechanism. It is provided in a paper transport path through which the paper is transported. A guide member for guiding the paper;
5. The paper transport apparatus according to claim 1, wherein a guide surface of the guide member at a position near the downstream side of the paper feed roller in the paper transport direction is a smooth surface.   An image forming apparatus comprising the sheet conveying device according to claim 1.

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