JP7479886B2 - Sheet conveying device and image forming apparatus - Google Patents

Description

The present invention relates to a sheet conveying device that conveys a sheet, and an image forming device that forms a toner image on the sheet.

In recent years, electrophotographic image forming devices, taking advantage of the fact that they do not require plates like offset printing machines, have been deployed in the light printing market, where small runs are printed on a wide variety of media. In this light printing market, there is a demand for devices to achieve both the number of sheets per minute (productivity) and high printing precision in the images printed.

Patent document 1 discloses a skew correction device that includes a conveying roller that conveys a sheet, an abutment section that has a reference surface provided along the sheet conveying direction, and a skew roller that conveys the sheet at an angle to the sheet conveying direction and abuts the side edge of the sheet against the reference surface. This makes it possible to correct the skew of the sheet without stopping the sheet being conveyed, achieving high productivity and printing accuracy for the device.

In such a skew correction device, the conveying roller and the skew roller are composed of a drive roller and a driven roller that is pressed or driven by the drive roller. The driven roller can be switched between a pressed state and a separated state, and when the skew roller conveys the sheet toward the abutment section, the driven roller is separated so that the sheet does not twist.

However, when transporting a sheet that is long in the sheet transport direction, such as long paper, it is difficult to separate all of the nip portions of the transport rollers located upstream in the sheet transport direction when transporting with the skew rollers, taking into consideration the need to make the device more compact or complex. Therefore, when transporting such long paper, the skew rollers are separated and the sheet is transported without correcting the skew of the sheet.

Incidentally, in order to clear paper jams that occur inside the device body, the skew correction device, which is equipped with a transport roller and a skew roller, can be moved (pulled out) from the device body, and after being moved, the driven roller can be retracted from the drive roller so that the sheet can be removed.

Japanese Patent Application Laid-Open No. 11-189355

The degree of inclination of the conveyed sheet is affected by the accuracy of the alignment of the conveying roller with respect to the device body. In particular, when the conveying roller is configured to be movable (pulled out) with respect to the device body in consideration of handling paper jams that occur inside the device body, the conveying roller is positioned with respect to the device body via multiple parts, so the accuracy of the alignment of the conveying roller with respect to the device body is likely to decrease. If the accuracy of the alignment of the conveying roller decreases, it will cause the sheet to twist, which will have a significant impact on the inclination of the sheet. If the sheet is conveyed in this state, there is a risk that the sheet will become skewed.

SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS In view of the above problems, an object of the present invention is to provide an image forming apparatus that reduces skew of sheets without deteriorating ease of handling paper jams.

In order to solve the above problems, a sheet transport device of the present invention is an image forming device including an image forming section which forms an image on a sheet, and a drawer unit which can be drawn out to a drawer position drawn out from an apparatus main body including the image forming section, and to an installation position where the drawer unit is installed inside the apparatus main body, the apparatus main body includes a sheet stacking section which stacks sheets, a feed roller which feeds the sheets stacked on the sheet stacking section, a first transport roller which is provided downstream of the feed roller in the sheet transport direction and transports the sheets, and an operation section which inputs information regarding the length of the sheets stacked on the sheet stacking section in the sheet transport direction, and the drawer unit is movable between a drawer position and an installation position where the drawer unit is installed inside the apparatus main body. a second conveying roller pair provided downstream of the first conveying roller in a conveying direction, the second conveying roller pair being changeable between a first state in which the sheet is sandwiched and conveyed, and a second state in which the roller pair is separated from each other so as not to sandwich the sheet; abutting portions provided downstream of the second conveying roller in the sheet conveying direction, extending along the sheet conveying direction, and having reference surfaces with which side ends of the sheet come into contact; and a skew conveying device for conveying a sheet by applying a force to the sandwiched sheet in a direction inclined with respect to the sheet conveying direction so that the sheet approaches the reference surface in a width direction of the sheet perpendicular to the sheet conveying direction as it moves downstream in the sheet conveying direction. a skew roller pair that is changeable between a third state in which the roller pair sandwiches and conveys a sheet and a fourth state in which the roller pair is separated from each other so as not to sandwich the sheet; and a third conveying roller that is provided downstream of the abutting portion in the sheet conveying direction and conveys the sheet, and the device body is further equipped with a control unit that controls the second conveying roller pair to change between the first state and the second state and the skew roller pair to change between the third state and the fourth state based on information regarding the length of the sheet in the sheet conveying direction input to the operation unit, and the control unit controls the second conveying roller pair to change between the first state and the second state and the skew roller pair to change between the third state and the fourth state when the length of the sheet in the sheet conveying direction is equal to or larger than the length of the sheet in the sheet conveying direction, and conveys the sheet. When a second sheet having a length in the sheet conveying direction shorter than that of the first sheet is conveyed by the second conveying roller pair with the second conveying roller pair in the first state, the sheet is conveyed by the second conveying roller pair without contacting the side end of the sheet with the reference surface , with the first conveying roller pair in the second state and the oblique conveying roller pair in the fourth state, and then, with the second conveying roller pair in the second state and the oblique conveying roller pair in the third state, the sheet is conveyed by the oblique conveying roller pair to the third conveying roller while contacting the side end of the sheet with the reference surface .

According to the present invention, it is possible to provide an image forming apparatus that reduces skewed sheets without deteriorating ease of handling paper jams.

FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a perspective view of a conveying roller unit according to an embodiment when the conveying roller unit is pulled out from an apparatus main body; FIG. 1 is a top view of a sheet conveying device according to an embodiment; FIG. 13 is a diagram showing an operation of correcting skew of a sheet according to an embodiment; FIG. 1 is a configuration diagram of a conveying roller unit according to an embodiment; FIG. 1 is a diagram showing a drive unit for a conveying roller according to an embodiment; FIG. 1 is a diagram showing the configuration of a skew correction unit according to an embodiment of the present invention; FIG. 1 is a perspective view of a sheet stacking portion according to an embodiment; 1 is a cross-sectional view of a sheet feeding portion according to an embodiment; FIG. 1 is a block diagram of a sheet conveying device according to an embodiment; FIG. 13 is a diagram showing a screen of an operation unit for setting sheet information according to an embodiment; FIG. 1 is an explanatory diagram of a conveying roller having poor alignment accuracy according to an embodiment; FIG. 1 is a diagram showing a relationship between a nip between an oblique feed roller and a conveying roller according to an embodiment; Table showing nip pressure of conveying roller according to the embodiment Table showing nip pressure of the oblique feed roller according to the embodiment 1 is a flowchart illustrating a conveyance control of a conveyed sheet according to an embodiment.

[Embodiment 1]
An image forming apparatus including a sheet conveying device according to the present invention will be described below with reference to the drawings, together with the operation during image formation. Note that the dimensions, materials, shapes, relative positions, etc. of the components described below are not intended to limit the scope of the present invention, unless otherwise specified.

<Image forming apparatus>
A sheet conveying device according to an embodiment of the present invention and an image forming apparatus including the same will be described with reference to Fig. 1. In the following description, the front (front surface, near side) of the image forming apparatus refers to the near side on the paper surface of Fig. 1, and the back (rear surface, far side) refers to the opposite side. The left and right sides of the image forming apparatus refer to the left and right sides when the image forming apparatus 100 is viewed from the front. The top and bottom refer to the upper and lower sides in the direction of gravity. The upstream and downstream refer to the upstream and downstream of the sheet conveying path in the sheet conveying direction.

Figure 1 shows a cross-sectional view of an image forming apparatus in this embodiment. Generally, there are four types of image formation methods for color image forming apparatuses: a tandem method in which multiple image forming units are arranged side by side, a rotary method in which multiple image forming units are arranged in a cylindrical shape, a direct transfer method in which a toner image is transferred directly from a photoconductor 508 to a sheet material, and an intermediate transfer method in which an image is transferred to an intermediate transfer body and then transferred to a sheet material. In this embodiment, as shown in Figure 1, an intermediate transfer tandem method in which four color image forming units are arranged side by side on an intermediate transfer belt 506 is adopted. The intermediate transfer method does not require the sheet material to be held on a transfer drum or transfer belt as in the direct transfer method, so it can handle a wide variety of sheets such as thick paper and coated paper. Furthermore, the intermediate transfer method is suitable for achieving high productivity due to its features of parallel processing in multiple image forming units and simultaneous transfer of full-color images.

The means for printing an image on a sheet in an image forming device can be divided into two types: a conveying process for conveying a sheet, and an image forming process for forming an image. Each process will be explained in detail below.

First, the conveying process will be described. On the right side of the image forming apparatus, a sheet feeding section 40 is provided to convey the sheet S to the image forming section. The sheet feeding section 40 is composed of a manual feed tray 41, which is a sheet stacking section for stacking the sheet S, and a manual feed section 42, which conveys the sheet S stacked on the manual feed tray 41 to the image forming section. Here, the feeding means of the manual feed section 42 may be a method that uses frictional separation by a feed roller or the like, or a method that uses separation and adsorption by air. In the image forming apparatus 100 in this embodiment, a sheet feeding method using frictional separation by a feed roller is adopted. That is, the sheet stacked on the manual feed tray 41 is fed by a feed roller 46 provided in the sheet feeding section, and the sheet fed to the feed roller 46 is conveyed by a pull-out roller 49, which is a first conveying roller, and is conveyed to the sheet conveying section 50 and the skew correction section 55.

In the skew correction section 55, the sheet S is corrected for skew and the timing toward the image forming section is corrected, and then the sheet S is sent to the secondary transfer section. The secondary transfer section is a sandwiching section formed by the substantially opposing secondary transfer inner roller 503 and secondary transfer outer roller 56, which transfers the toner image to the sheet S, and transfers the toner image to the sheet S by applying a predetermined pressure force and electrostatic load bias.

The image forming process in which the sheet S is conveyed to the secondary transfer unit at the same timing as described above will be described. The image forming unit 513 is mainly composed of a photoconductor 508, an exposure device 511, a developing device 510, a primary transfer device 507, a photoconductor cleaner 509, and the like. The exposure device 511 emits light based on the signal of the image information sent to the photoconductor 508, which rotates in the direction of the arrow A in the figure, and a latent image is formed via the diffraction means 512. The electrostatic latent image thus formed on the photoconductor 508 is developed by the developing device 510 to form a toner image on the photoconductor 508. After that, a predetermined pressure force and an electrostatic load bias are applied by the primary transfer device 507, and the toner image is transferred onto the intermediate transfer belt 506. After that, the transfer residual toner remaining on the photoconductor 508 is collected by the photoconductor cleaner 509 and prepared for the next image formation again. In the case of FIG. 1, the image forming unit 513 described above is equipped with four sets of yellow (Y), magenta (M), cyan (C), and black (Bk).

Next, the intermediate transfer belt 506 will be described. The intermediate transfer belt 506 is stretched by rollers such as a drive roller 504, a tension roller 505, and a secondary transfer inner roller 503, and is driven to rotate in the direction of arrow B in the figure. Therefore, the image formation process for each color, which is processed in parallel by each of the image forming devices 513 for Y, M, C, and Bk described above, is performed at a timing that overlaps with the upstream toner image that has been primarily transferred onto the intermediate transfer belt 506. As a result, a full-color toner image is finally formed on the intermediate transfer belt 506 and is transported to the secondary transfer section.

Through the above-mentioned conveying process and image forming process of the sheet S, a full-color toner image is secondarily transferred onto the sheet S in the secondary transfer section. After that, the sheet S on which the toner image is printed is conveyed to the fixing section 58 by the pre-fixing conveying section 57. The fixing section 58 applies a predetermined pressure force by rollers or belts that are substantially opposed to each other, and generally applies a heating effect by a heat source such as a heater, thereby melting and fixing the toner on the sheet S. The sheet S with the fixed image thus obtained is discharged directly onto the paper discharge tray 500 by the branch conveying section 59, or if double-sided image formation is required, the sheet S is conveyed to the inverting conveying section 501, which is selected as the route. When double-sided image formation is required, the sheet is inverted by the inverting conveying section 501, passes through the double-sided conveying section 502, passes through the sheet conveying section 50, and is conveyed to the skew correction section 55. The conveying process and image forming process described above are the same as those described above when printing an image on the opposite side of the sheet on which the image is formed, so they will not be described here.

As described above, in the image forming apparatus of this embodiment, the conveying process of the sheet S and the image forming process are linked to form an image on the sheet.

Also, FIG. 2 is a diagram showing a state in which the drawer unit 200 including the skew correction unit is drawn out from the image forming apparatus. An exterior cover is provided on the front side of the apparatus body, but is omitted in FIG. 2. As shown in FIG. 2, the drawer unit 200 is provided to improve the maintenance of the apparatus body in order to clear a paper jam when a sheet jam occurs in a sheet conveying path provided inside the image forming apparatus, or to replace components that are configured. In this embodiment, the drawer unit 200 includes a sheet conveying section 50, a skew correction section 70, a registration roller section 7 that is a third conveying roller, a secondary transfer outer roller 56, and a pre-fixing conveying section 57, which are provided in a conveying housing that supports them. The conveying housing is attached to a guide rail that is provided on the apparatus body side and can slide in the directions of the front and rear sides of the apparatus body. As a result, the drawer unit 200 can be moved between an attachment position where it is attached to the apparatus body and a drawer position where it is drawn out from the apparatus body.

The image forming device is equipped with an operation unit 600 on the top side, which displays the operating status of the image forming device and accepts input operations from the user to the device.

<Sheet conveying device>
1, the sheet conveying device used in the image forming apparatus is provided with a skew correction unit 55 for correcting misalignment of the sheet being conveyed. The correction method used in this skew correction unit 55 is a side registration means that abuts the side edge of the sheet being conveyed against an abutment unit 31 having a reference surface to correct the misalignment of the edge of the sheet.

Figure 3 shows a top view of a sheet conveying device including a sheet conveying section 50, a skew correction section 55, and a registration roller 7. The sheet conveying section 50 is composed of multiple rollers 34 (341-344) that can press the driven roller against or separate it from the drive roller, and can switch between a state in which the sheet is clamped and a state in which the sheet is released from the clamp. A pre-registration sensor P that detects the leading edge of the sheet S is provided in the center near the conveying roller 344, which is the second conveying roller arranged at the most downstream position of the sheet conveying section 50. The pre-registration sensor P is an optical sensor that has a light emitting section and a light receiving section, and when the sheet S passes, the light reflected by the sheet S is detected by the light receiving section to detect the timing of the passage of the sheet S.

Furthermore, downstream of the sheet conveying section 50, a skew correction section 55 that corrects skew of the sheet is arranged. The skew correction section 55 is composed of an abutment section 31 having a reference plate extending in the sheet conveying direction, and three skew rollers 32 that convey the sheet toward the abutment section. Like the conveying rollers 34, the skew rollers 32 can be switched between a clamping state in which the sheet is clamped and a release state in which the clamping of the sheet is released. In addition, the skew rollers 32 are inclined by an angle α with respect to the sheet conveying direction, and are configured to apply a force toward the abutment section 31 to convey the sheet.

Furthermore, downstream of the skew correction section 55, a skew sensor R and a registration roller front sensor Q are arranged to detect the leading edge position of the sheet S after the sheet is abutted. Then, a registration roller 7 is arranged so as to be slidable in the width direction perpendicular to the sheet conveying direction in order to match the image position with the sheet position while nipping and pressuring the leading edge of the sheet.

Next, the behavior of the sheet being conveyed will be described with respect to skew correction in the sheet conveying device of this embodiment. Figure 4 is a diagram of the same sheet conveying device as Figure 3.

In FIG. 4, FIG. 4(a) shows the sheet S being conveyed by conveying rollers 34 with a skew angle β relative to the sheet conveying direction. FIG. 4(b) shows the sheet S being conveyed by skew rollers 32a, 32b, and 32c provided in skew correction section 55. FIG. 4(c) shows the sheet S, whose skew has been corrected by skew correction section 55, being conveyed by registration rollers 7. FIG. 4(d) shows the sheet S being conveyed by registration rollers 7 moving in the axial direction.

As shown in FIG. 4(a), the sheet S is conveyed to the skew correction section 55 by the conveying rollers 34 with a skew angle β. The sheet S conveyed to the skew rollers 32 of the skew correction section 55 is conveyed obliquely toward the abutment section 31 as shown in FIG. 4(b). When the sheet S starts to be conveyed by the skew rollers 32, the nips of the pairs of conveying rollers 34 are separated.

As shown in FIG. 4(b) and FIG. 4(c), the sheet S is conveyed while its side edge follows the abutment reference portion 31, so that the skew of the sheet S is corrected. In this state, the sheet S after the skew correction is sandwiched between the registration rollers 7. When the sheet S is sandwiched between the registration rollers 7, the nip between the pair of skew rollers 32 is separated. Then, as shown in FIG. 4(d), the registration rollers 7 are slid a certain amount in the width direction (W) perpendicular to the sheet conveying direction, so that the position of the image formed on the intermediate transfer belt 40 is aligned. The above-mentioned control of the rotation or stop of each roller and the contact or separation of each roller pair is executed by a controller in the main body (not shown). As described above, the series of operations shown in FIG. 4(a) to FIG. 4(d) realizes a highly productive device while correcting the skew of the sheet S without stopping the sheet S. Note that the pull-out roller 49 in this embodiment does not have a mechanism for releasing the nip of the rollers.

<Detachable structure of nip between oblique feed roller and conveying roller>
Next, the above-described nip attachment/detachment configuration of the conveying rollers 34 (341 to 344) and the skew roller 32 will be described in detail. Fig. 5 shows a cross-sectional view of the conveying rollers in the sheet conveying section 50. Fig. 5(a) shows the conveying rollers 34 when the nip is pressed, and Fig. 5(b) shows the conveying rollers 34 when the nip is released. The position of the conveying rollers 34 in Fig. 5(a) is a first position where the sheet is nipped and conveyed, and the position of the conveying rollers 34 in Fig. 5(b) is a second position where the conveying rollers 34 are separated from the sheet.

In the figure, the driven roller 14 is supported via an arm member 101 that supports the driven shaft 20, and the arm member 101 is arranged on the stay member 18 via a swing shaft 102 so as to be swingable. When releasing the nip, the end of the arm member 101 is pressed by rotating the eccentric roller 103, and the nip is rotated in the release direction around the swing shaft 102. FIG. 5(b) shows a cross-sectional view when the nip is released. The conveying roller unit has a pressing means for pressing the arm member 101, which presses the arm member 101 by rotating the stepping motor 104 and rotating the eccentric roller 103 via a gear train (105, 106). This pressing means releases the nip of the driven roller 14 according to the release timing. The device control unit 914 described later drives the stepping motor 104 based on the detection timing of the pre-registration sensor P, making it possible to vary the timing of nip release.

Figure 6 is a perspective view of the drive section of the transport roller of the sheet transport section 50. The drive roller is driven by a pre-registration motor Mp via a pulley and belt 302 on a shaft that is integral with the rubber roller 13. The pre-registration motor Mp is a stepping motor, and the stop timing and transport speed are variable according to the timing of the pre-registration sensor P. A motor is provided for each transport roller.

7 is a diagram showing the skew correction unit 55. FIG. 7(a) is a top view showing the entire skew correction unit 55. The skew roller 32 is arranged at an angle α with respect to the abutment unit 31, and is driven by the skew drive motor Ms via a universal joint 321, a pulley, and a conveying belt 323. FIG. 7(b) is a perspective view of the pressing mechanism or separation mechanism of the driven roller 331 facing the skew roller 32. FIG. 7(c) is a side view of FIG. 7(b). The clamping pressure (clamping pressure of the sheet S) of the driven roller 331 is set by the rotation angle of the skew pressure motor Mk via the link 332, the pressure spring 335, and the pressure gear 334 that rotatably support the driven roller 331. The pressure gear 334 rotates counterclockwise in the figure, pulling the pressure spring 333, causing the link 332 to rotate around the axis and apply nip pressure (third position). The pressure gear 334 further rotates counterclockwise in the figure and pushes in the link 333, causing the link 332 supporting the driven roller 331 and the driven roller 331 to rotate in the nip release direction (upward), and the nip is released (fourth position). The oblique feed pressure motor Mk is a stepping motor, so by setting the step angle, it is possible to separate the driven roller 331 independently from the oblique feed roller 32.

As described above, the conveying roller and the skew roller each have a mechanism for putting the roller nip into a contact state or a release state. This allows the state to be switched between a contact state and a release state in accordance with the timing of the sheet conveyance when correcting the skew of the conveyed sheet.

<Sheet stacking section>
Next, a detailed description will be given of the configuration of the sheet stacking unit 41. Fig. 8 is an explanatory diagram of the manual feed tray 41, which is a sheet stacking unit. The manual feed tray 41 is attached to the right side of the device body.

The manual feed tray 41 is provided with side regulation plates that regulate the position of the sheet in the width direction perpendicular to the sheet transport direction. Two side regulation plates are provided on the manual feed tray 41: a first side regulation plate 48 located downstream in the sheet transport direction, and a second side regulation plate 43 located upstream in the sheet transport direction. The two side regulation plates 43 and 48 have the function of regulating the sheet from skewing when the sheet is transported, and can slide in the width direction according to the size of the stacked sheets. The second side regulation plate 43 is configured to be fixed in position by a fixing screw 44. As a result, the first side regulation plate 48 and the second side regulation plate 43 regulate the sheet width direction with respect to the length of the stacked sheets S in the sheet transport direction, so that a sufficient skewing regulation function can be obtained.

Figure 9 is a cross-sectional view of the sheet feeding section 40. Sheets loaded on the manual feed tray 41 are transported to the sheet transport section 50 by a feed roller 46 and a pull-out roller 49 provided in the manual feed section 42. The sheet feeding section 40 is also attached to the device body.

<Control Unit>
FIG. 10 is an exemplary block diagram showing a control unit of an image forming apparatus according to an embodiment. In the controller unit 800, which is the control unit, a CPU 901 is connected to a ROM 903 in which a control program is written and a RAM 902 in which data for performing processing is stored, via an address bus and a data bus. A PDL control unit 904 and an internal I/F unit 905 are also connected to the CPU 901. The PDL control unit 904 is a processing circuit for processing, storing, and image processing print data. The internal I/F unit 905 is a communication circuit for communicating with the printer control unit 801. An operation unit 600 is also connected to the CPU 901. The CPU 901 controls a display device (e.g., a liquid crystal display device, etc.) and a key input device (e.g., a touch panel, etc.) included in the operation unit 600. The CPU 901 accepts a display switching instruction from an operator through the key input device. The CPU 901 also accepts display and user operations for the operation unit 600 display device.

Meanwhile, the CPU 911 of the printer control unit 801 performs basic control of the image forming operation. The ROM 913 and the RAM 912 are connected to the CPU 911 via an address bus and a data bus. The ROM 913 stores a control program including the control procedures described below. The RAM 912 stores data required for performing the image forming process. The device control unit 914 is an electric circuit including input/output ports for controlling each component of the printer unit. The internal I/F unit 915 is a communication circuit for transmitting and receiving image signals and timing signals to and from the controller unit 800. The CPU 911 receives image signals from the controller unit 800 according to the contents of the control program, and controls the device control unit 914 to transport sheets and form images.

Figure 11 shows a setting screen displayed on the operation unit 600 to prompt the user to set sheets. The user uses this setting screen to set sheets before starting printing. The order in which the setting screen prompts the user is to set the sheet length in Figure 11 (a), set the sheet basis weight in Figure 11 (b), and then set the sheet type in Figure 11 (c). The setting screen displayed on the operation unit 600 allows the user to set the sheet length (L), sheet basis weight (G), and sheet type (T) by pressing the appropriate button. The sheet settings set by the user are saved in RAM 912 by CPU 911.

<Roller alignment accuracy and sheet skew>
12 shows the conveying roller 34 with poor alignment accuracy in the sheet conveying device of this embodiment. The sheet conveying section 50, the skew correction section 55, and the registration roller 7 can be drawn out from the device body as a drawer unit 200, so the alignment accuracy of these rollers may be poor with respect to the device body. The reason for the poor alignment accuracy is that many parts are interposed between the conveying roller 34 that conveys the sheet and the device body (reference position) because a configuration that can be drawn out as a drawer unit with respect to the device body is adopted. In this embodiment, the conveying roller 34 is supported via at least four parts. These are a bearing that rotatably supports the conveying roller 34, a conveying housing of the sheet conveying section 50 that holds the bearing, a drawer section that supports the conveying housing in the drawer unit, and a guide rail section that allows the drawer section and the device body to be drawn out.

On the other hand, as described above, the pull-out roller 49 is provided in the manual feed section 42, which is directly attached to the device body. Therefore, the alignment accuracy of the pull-out roller 49 with respect to the device body (reference position) is unlikely to decrease.

For this reason, as shown in FIG. 12, the conveying roller 34, the registration roller 7, and the skew roller 32 are in a slanted state at an angle γ with respect to the pull-out roller 49. In this state, when the conveying roller 34 is nipped and pressed to convey the sheet 60, the sheet S is skewed. In particular, when a sheet that is long in the sheet conveying direction is conveyed, when the leading edge of the sheet is conveyed to the skew correction section 55, the trailing edge of the sheet is on the manual feed tray 41, which is the sheet stacking section. In other words, the trailing edge of the sheet remains regulated by the side regulation plate 48, which is adjusted and fixed. Therefore, when a sheet that is long in the sheet conveying direction is conveyed, even if the skew roller 32 performs abutment conveyance against the abutment reference member 31 as in the conventional case, the side regulation plate 43 prevents the abutment conveyance, making the skew worse. To prevent this, in this embodiment, the conveying roller 34 is released from the nip, and conveyance is performed only by the pull-out roller 49, which has good alignment accuracy.

Next, depending on the length (L) and basis weight (G) of the sheet, it is necessary to selectively select whether the nip of each roller is in a pressurized state or in a released state, as will be described in detail below. Figure 13 is a cross-sectional view of the conveyance path of sheet S from the pull-out roller 49 to the registration roller 7 from upstream to downstream in the sheet conveyance direction.

In the sheet conveying device of this embodiment, the length of the conveying path from the pull-out roller 49 to the registration roller 7 is 900 mm. Also, the length from the pull-out roller 49 to the oblique feed roller 32 located at the most upstream position is 770 mm.

Figure 13 (A) shows nip pressure and pressure reduction during the transport of a sheet with a length of 760 mm or less. This is when the length of the sheet S plus a margin of 10 mm is 770 mm or less, which is the length from the most upstream roller of the skew roller 32 to the pull-out roller 49. Therefore, when the sheet is skew-corrected by the skew roller 32, the rear end of the sheet is not nipped by the pull-out roller 49. In this case, during skew correction by abutment using the skew roller 32, all the nips of the transport rollers 34 are released, and the rollers other than the skew correction roller 32 are not nipped, so the sheet is skew-corrected as shown in Figure 2. Therefore, when the leading edge of the sheet is transported to the skew roller, the skew rollers 32 and the transport rollers 34 transport the sheet with all nip pressure applied.

Figure 13 (B) shows the nip pressure and pressure reduction during the conveyance of a sheet with a length of 910 mm or more. The length of the sheet S plus a margin of 10 mm is longer than the length of 770 mm from the most upstream roller of the skew roller 32 to the pull-out roller 49. Therefore, when the leading edge of the sheet is conveyed to the skew roller 32, the trailing edge of the sheet is nipped by the pull-out roller 39. As a result, the sheet is twisted during skew correction, so skew correction using the skew roller 32 is impossible. Therefore, since it is necessary to prevent the sheet from being conveyed skewed due to the influence of the alignment accuracy of the conveying rollers in order not to perform skew correction, the sheet is conveyed without using the conveying roller 34. Since the sheet to be conveyed is 900 mm or more, which is the length from the registration roller 7 to the pull-out roller 49, the sheet can be conveyed without using the conveying roller 34. Therefore, in this case, the skew correction roller 32 and the conveying roller 34 convey the sheet in a nip-released state.

Figure 13 (C) shows the nip pressure and decompression of the conveying rollers while conveying a sheet whose length is greater than 760 mm and less than 910 mm. The length of the sheet 60 plus a margin of 10 mm is longer than the length of 770 mm from the most upstream roller of the skew correction roller 32 to the pull-out roller 49. Therefore, the pull-out roller 39 nips the rear end of the sheet 60 during skew correction using the skew correction roller 32, making skew correction using the skew correction roller 32 impossible. On the other hand, as shown in Figure 13 (B), it is necessary to prevent the sheet from being conveyed skewed due to the influence of alignment accuracy. When the nip parts of the skew roller 32 and the conveying roller 34 are all released, there are no rollers that are nipped during sheet conveyance, so the conveying roller 34 nip-presses the most downstream roller. As a result, all of the skew rollers 32 are released from the nip, and the conveying roller 34 nip-presses only the conveying roller 344, and conveys the sheet in a nip-released state.

Figure 13 (D) shows the nip pressure and depressurization of the conveying rollers while conveying a sheet that is 910 mm or more and has a basis weight of 80 gsm or less. As in (B), if the skew correction roller 32 and conveying roller 34 are all in the nip released state while conveying, a sheet with a low basis weight has weak stiffness, and the leading edge may curl while being conveyed by the pull-out roller 39 alone. To prevent curling, the conveying roller 34 nip-presses the most upstream roller to hold down the sheet 60. Therefore, all of the skew correction rollers 32 are in the nip released state, and the conveying rollers 34 only apply nip pressure to the conveying roller 344, and conveying is performed with all others in the nip released state.

Figure 13 (E) shows the nip pressure and pressure reduction of the transport rollers while transporting a sheet of 910 mm or more and made of single-sided or double-sided coated paper. As in (B), if the skew correction roller 32 and transport roller 34 are all in the nip release state during transport, the sheet 60 may slip while being transported by the pull-out roller 39 alone, since the surface of the sheet is single-sided or double-sided coated paper and has a low friction coefficient. To prevent slippage, the transport roller 34 nip-presses the most upstream roller, improving the transport force. Therefore, the skew correction rollers 32 are all in the nip release state, the transport roller 34 nip-presses the transport rollers 344 and 343, and transport is performed with all others in the nip release state.

The above conditions are summarized. FIG. 14 shows the conditions for applying nip pressure to the conveying roller 34 and the rollers that apply nip pressure. Condition number 1 corresponds to (A) in FIG. 13. The condition is that the sheet length is 760 mm or less, and the conveying rollers 34 that apply nip pressure are conveying rollers 344, 343, 342, and 341. Condition number 2 corresponds to (C) in FIG. 13. The condition is that the sheet length is less than 910 mm, and the conveying roller 34 that applies nip pressure is conveying roller 344. Condition number 3 corresponds to (D) in FIG. 13. The condition is that the sheet length is 910 mm or more and the basis weight is 80 gsm or less, and the conveying roller 34 that applies nip pressure is conveying roller 344. Condition number 4 corresponds to (E) in FIG. 13. The condition is that the sheet length is 910 mm or more, and the paper is one-sided coated paper and double-sided coated paper, and the conveying roller 34 that applies nip pressure is conveying roller 344. Condition number 5 corresponds to (B) in FIG. 13. The condition is that the sheet length is 910 mm or more, and there is no nipping conveyor roller 34.

Furthermore, FIG. 15 shows the conditions for nipping and pressurizing the skew correction roller 32. Condition number 1 corresponds to (A) in FIG. 13. The condition is when the sheet length is 760 mm or less, and the skew correction roller 32 is nipped and pressurized. Condition number 2 corresponds to (B), (C), (D), and (E) in FIG. 13. The condition is when the sheet length is greater than 760 mm, and the skew correction roller 32 is not nipped and pressurized.

As described above, in this embodiment, by switching between the contact state and the conveying roller state based on the length of the sheet, it is possible to convey long sheets of paper without being affected by misalignment of the conveying rollers.

<Control flow for sheet transport>
16 is a flowchart showing the operation of feeding a sheet according to the embodiment. This flowchart is realized by the CPU 911 reading and executing a program stored in the ROM 903 or the like. This flowchart starts when a sheet is fed (feed timing).

At the feeding timing, all rollers used for conveying are rotating. Before feeding the sheet, it is necessary to apply and release nip pressure between the skew correction roller 32 and the conveying roller 34 based on the sheet settings. The executed flowchart first executes step S4000.

In step S4000, the sheet setting information for the sheets to be fed that is stored in RAM 912 is read.

In step S4001, it is determined whether the length of the sheet to be fed is such that the skew correction roller 32 can be nipped and pressed to perform skew correction. To make this determination, the sheet setting information stored in RAM 912 is compared with the conditions shown in FIG. 16. For example, if the sheet length read out in step S4000 is 700 mm, this corresponds to condition number 1 in FIG. 15, and skew correction can be performed using the skew correction roller 32, so the skew correction roller 32 is nipped and pressed. If the sheet length stored in RAM 912 is 900 mm, this corresponds to condition number 2 in FIG. 15, and skew correction cannot be performed using the skew correction roller 32, so the skew correction roller 32 is released from the nip. If it is determined that the skew correction roller 32 should be nipped and pressed, step S4002 is executed, and if it is determined that the skew correction roller 32 should be released from the nip, step S4003 is executed.

In step S4002, information on nip pressure of the skew correction roller 32 is stored in RAM 912.

In step S4003, it is determined whether or not to apply nip pressure to the conveying rollers 34 (341-344) depending on the basis weight (G), type (T), and length (L) of the sheet being fed. To make this determination, the sheet settings stored in RAM 912 are compared with the conditions in FIG. 14. For example, if the sheet length of the sheet settings read out in step S4000 is 850 mm, condition number 2 is met. Therefore, the conveying rollers 344 are nip-pressed. If there is a conveying roller 34 that can apply nip pressure, step S4004 is executed, and if not, step S4005 is executed.

In step S4004, the conveying roller 34 that applies nip pressure determined in step S4003 is stored in RAM 912.

In step S4005, the conveying roller 34 and the skew correction roller 32 are nipped or released. To nip or release the nip, information on the nip pressure between the conveying roller 34 and the skew correction roller 32 is read from RAM 912, and the conveying roller 34 and the skew correction roller 32 are nipped or released.

In step S4006, feeding is performed.

By implementing the control described in this embodiment, it is possible to solve the problem of the sheet being skewed and the image being formed in a misaligned state relative to the sheet.

41 Sheet stacking section (manual feed tray)
46 Feeding roller 49 First conveying roller (pulling roller)
34 Second conveying roller (conveying roller)
7 Third conveying roller (registration roller)
31: abutting portion 32: oblique feed roller 600: operation portion 800: control portion

Claims (7)

an image forming unit that forms an image on a sheet;
An image forming apparatus including a drawer unit that is movable between a drawer position where the drawer unit is drawn out from a device body including the image forming unit and an attachment position where the drawer unit is attached inside the device body,
The device body includes:
a sheet stacking section for stacking sheets;
a feeding roller for feeding the sheets stacked in the sheet stacking section;
a first conveying roller provided downstream of the feed roller in a sheet conveying direction and configured to convey a sheet;
an operation unit for inputting information regarding the length of the sheets stacked on the sheet stacking unit in the sheet conveying direction,
The drawer unit comprises:
a second conveying roller pair provided downstream of the first conveying roller in the sheet conveying direction, the second conveying roller pair being changeable between a first state in which the second conveying roller pair sandwiches and conveys a sheet and a second state in which the second conveying roller pair is separated from each other so as not to sandwich the sheet;
abutting portion provided downstream of the second conveying roller in the sheet conveying direction, extending along the sheet conveying direction, and having a reference surface against which a side edge of the sheet comes into contact;
a pair of skew rollers that convey a sheet by applying a force to the sandwiched sheet in a direction inclined with respect to the sheet conveying direction so that the sheet approaches the reference surface in a width direction of the sheet perpendicular to the sheet conveying direction as the sheet moves downstream in the sheet conveying direction, the pair of skew rollers being changeable between a third state in which the sheet is sandwiched and conveyed, and a fourth state in which the roller pair is separated from each other so as not to sandwich the sheet;
a third conveying roller that is provided downstream of the abutting portion in the sheet conveying direction and conveys the sheet,
the apparatus body changes the second conveying roller pair between the first state and the second state based on information regarding the length of the sheet in the sheet conveying direction input to the operation unit;
and a control unit that controls the pair of oblique feed rollers to change between the third state and the fourth state,
The control unit is
When a sheet having a length in the sheet conveying direction is conveyed, the sheet is conveyed to the third conveying roller by the first conveying roller without contacting the side edge of the sheet with the reference surface , with the second conveying roller pair in the second state and the oblique conveying roller pair in the fourth state;
When a second sheet having a length in the sheet transport direction shorter than that of the first sheet is transported, the sheet is transported by the second transport roller pair with the second transport roller pair in the first state, and then, with the second transport roller pair in the second state and the oblique transport roller pair in the third state, the sheet is transported to the third transport roller by the oblique transport roller pair while the side edge of the sheet is abutted against the reference surface .
1. An image forming apparatus comprising: The image forming apparatus according to claim 1, characterized in that the second conveying roller pair and the oblique conveying roller pair are arranged at multiple positions along the sheet conveying direction. The image forming apparatus according to claim 1 or 2, characterized in that the length of the first sheet in the sheet transport direction is longer than 760 mm. The image forming apparatus according to claim 2, characterized in that when a third sheet, which is shorter than the length of the first sheet in the sheet transport direction and longer than the length of the second sheet in the sheet transport direction, is transported, at least one of the second transport roller pairs arranged in a plurality of positions transports the sheet in the first state. The image forming apparatus according to claim 2, characterized in that when a fourth sheet is conveyed, the fourth sheet being longer than the first sheet in the sheet conveying direction and having a basis weight less than 80 gsm of the first sheet, at least one of the second conveying roller pairs arranged in a plurality of positions conveys the sheet in the first state. The image forming apparatus according to claim 2, characterized in that when a fifth sheet is transported, the fifth sheet being longer than the first sheet in the sheet transport direction and the type of the first sheet being coated paper, at least one of the second transport rollers arranged in a plurality of positions transports the sheet in the first state. The image forming apparatus according to any one of claims 4 to 6, characterized in that at least one of the second conveying roller pairs is a roller arranged at the most downstream position in the sheet conveying direction.

Images