JP4347164B2 - Sheet conveying apparatus and image forming apparatus provided with the apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus that includes a plurality of guide ports for guiding a sheet and conveys the sheet, and an image forming apparatus that includes the sheet conveying apparatus in an apparatus main body.

  2. Description of the Related Art Conventionally, a sheet conveying apparatus that conveys a sheet is installed in a sheet handling apparatus such as an image forming apparatus including an electrophotographic system, a sheet processing apparatus, and the like.

  Examples of the image forming apparatus include a copying machine, a printer, a facsimile machine, and a complex machine for forming an image on a sheet. Examples of the sheet processing apparatus include a punching apparatus that punches holes in sheets and sheet bundles, a binding apparatus that binds sheet bundles, and a folding apparatus that folds sheet bundles.

  2. Description of the Related Art A sheet conveying device provided in an image forming apparatus has a structure including a registration roller pair that is a pair of rotating bodies and a sheet feeding port that is a plurality of guide ports (see Patent Documents 1 and 2).

  The plurality of sheet feeding ports guide the sheet to the nip of the registration roller pair. The registration roller pair is disposed between a plurality of paper feed ports and an image forming unit that forms an image on a sheet. The registration roller pair receives the leading edge of the sheet guided from the sheet feeding port in a stopped state, and starts rotating after the sheet is bent between the sheet feeding port and the skew of the sheet is straightened. The sheet is sent to the image forming unit.

Japanese Patent Laid-Open No. 5-124737 (FIG. 1) JP-A-5-221536 (FIG. 1)

  By the way, in the sheet conveying apparatus equipped in the image forming apparatus, the sheet may be bent between the image forming unit and a pair of registration rollers rotated by a sheet feeding motor rotating at a constant rotation speed. When the direction in which the sheet enters the registration roller pair is constant by a conveyance guide or the like, the amount of deflection of the sheet that is bent between the image forming unit and the registration roller pair is the sheet fed from any supply port. Is almost constant. In such a case, there is no problem in the operation of forming an image on the sheet in the image forming unit. The conveyance guide guides the sheet so that the leading edge of the sheet can stably enter the nip of the pair of registration rollers.

  However, in a sheet conveying apparatus that does not include a conveyance guide, the wrapping angle of the sheet around the registration roller of the registration roller pair differs for each sheet feeding port, and the sheet conveyance speed to the image forming unit is somewhat different. It was. For this reason, the amount of bending generated between the image forming unit and the registration roller pair is different.

  As described above, the sheet conveying device has different bend amounts generated between the image forming unit and the registration roller pair, causing skew, increasing back tension, pushing the sheet into the image forming unit, and rubbing the sheet with the guide. In some cases, problems such as an increase in noise generated may occur.

  When such a problem occurs, the change in the sheet conveyance speed to the image forming unit is only a few percent. However, when a large size sheet such as an A3 size sheet or LDGER paper is used, even if there is a difference of only 1%, the amount of deflection is accumulated at the rear end of the sheet and becomes large. For example, when the sheet length is 400 mm, a difference in feed amount of 4 mm occurs at 1%. In particular, in a color image forming apparatus, if there is a variation in the amount of deflection of a sheet, color misregistration occurs and a high-quality image cannot be formed on the sheet. In addition, the color image forming apparatus is more affected by fluctuations in the sheet conveyance speed than the monochrome image forming apparatus.

  The change in the sheet conveyance speed due to the winding angle has occurred due to a plurality of factors. The contact area of the sheet with the registration roller varies depending on the winding angle. If the contact area is small, the registration roller and the sheet are likely to slip. Conversely, if the contact area is large, the registration roller and the sheet are less likely to slip. The sheet conveyance speed also changes depending on the positional relationship between the sheet winding region and the nip portion of the registration roller. Further, the conveying speed also changes depending on the relationship between the rubber hardness of the registration roller, the pressure contact pressure between the registration roller pair, and the winding angle. That is, when the winding angle changes, it is entangled with other constituent factors, and the conveyance speed changes in a complicated manner.

  Therefore, in order to suppress fluctuations in the sheet conveyance speed due to the winding angle, it is necessary to provide a conveyance guide or the like that makes the winding angle constant with respect to the nip of the registration roller pair. However, the provision of the conveyance guide requires a larger space and increases the number of parts, which causes another problem of going against the recent trend toward downsizing and cost reduction of image forming apparatuses. . In particular, in the case of a color image forming apparatus having a vertical in-line configuration, another problem arises that the operability is deteriorated because the height of the main body is increased.

  In the present invention, even if the winding angle of the sheet with respect to one of the rotating bodies of the rotating body pair changes due to different guide openings, the rotational speed of the rotating body pair is adjusted so that the sheet conveyance speed by the rotating body pair is substantially constant. An object of the present invention is to provide a sheet conveying apparatus that can be used.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that includes a sheet conveying apparatus that can make the sheet conveying speed substantially constant and prevents a reduction in image quality formed on the sheet.

In order to achieve the above object, a sheet conveying apparatus of the present invention includes a rotating body pair that rotates and conveys a sheet, guides the sheet with respect to the rotating body pair, and one of the rotating body pair. A plurality of guide ports having different wrapping angles of the guided sheet with respect to the rotating body, driving means for rotationally driving the pair of rotating bodies, and control for adjusting the sheet conveying speed of the rotating body pair by controlling the driving means And when the sheet is supplied from the guide opening having a smaller winding angle than the sheet conveying speed when the sheet is supplied from the guide opening having a large winding angle. as towards the sheet conveying speed is increased, and less than the sheet conveying speed when conveying a sheet of basis weight, better of the sheet conveying speed when transporting the large sheet of basis weight And controls the drive means so Kunar.

  The sheet conveying apparatus of the present invention can convey a sheet at an almost constant conveying speed, regardless of the sheet feeding port, without providing a conveying guide for guiding to the nip of the registration roller. it can.

  Hereinafter, a sheet conveying apparatus according to an embodiment of the present invention and an image forming apparatus including the sheet conveying apparatus in an apparatus main body will be described with reference to the drawings.

  A sheet conveying apparatus for conveying a sheet according to the present invention is equipped in a sheet handling apparatus such as an image forming apparatus including an electrophotographic system and a sheet processing apparatus. Examples of the image forming apparatus include a copying machine, a printer, a facsimile, and a complex machine of these, which form an image on a sheet. Examples of the sheet processing apparatus include a punching apparatus that punches holes in sheets and sheet bundles, a binding apparatus that binds sheet bundles, and a folding apparatus that folds sheet bundles.

  The sheet conveying apparatus of the present embodiment is provided in a color printer as an image forming apparatus, but is not provided only in the color printer. The image forming apparatus of the present embodiment is a color printer, but is not limited to a color printer.

  Note that the material, shape, relative arrangement, and the like of the component parts described in the present embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. In addition, the numerical values are shown for easy understanding of the present invention, and are not values limiting the present invention.

(Color printer)
FIG. 1 is a schematic front sectional view of a color printer as an image forming apparatus according to an embodiment of the present invention.

  In recent years, with the widespread use of electrophotographic color printers, there is an increasing demand for speeding up color output in addition to the demand for color image print quality. In order to meet this demand, several proposals have been made for image forming methods, and among them, there is one called a tandem type. This tandem type color printer uses a Bk (black) toner, a C (cyan) toner, an M (magenta) toner, and a Y (yellow) image on a photosensitive drum as a drum-shaped image carrier. The toner images are sequentially transferred by the respective transfer units to the sheet conveyed by the electrostatic conveyance belt, and finally the toner image is fixed on the sheet.

  The color printer 9 has a transfer unit 5 on the right side of the apparatus main body 10. The sheets S set in the paper feed cassette 17 are taken out from the paper feed cassette 17 one by one by the pickup roller 21 and the cassette paper feed roller pair 18 and are sent to the image forming unit 24 by the resist roller pair 19. The registration roller pair 19 includes a registration roller 19a and a counter roller 19b.

  The electrostatic conveyance belt 11 that conveys the sheet in the image forming unit 24 is stretched flat in the sheet conveyance direction by a plurality of rotating rollers. An adsorption roller 22 is provided on the upper surface side (outer surface side) of the electrostatic conveyance belt 11 at the upstream side in the sheet conveyance direction of the image forming unit 24. By applying a bias to the attraction roller 22, the electrostatic conveyance belt 11 conveys the sheet by electrostatic attraction.

  The four photosensitive drums 1a to 1d arranged in a straight line facing the conveyance surface of the electrostatic conveyance belt 11 form an image forming unit 24 as an image forming unit. Each of the photosensitive drums 1a to 1d is provided with chargers 2a to 2d and developing devices 4a to 4d so as to sequentially surround the vicinity of the peripheral surface. Further, transfer units 12a to 12d are disposed at positions sandwiching the conveyance surface of the electrostatic conveyance belt 11 with respect to the respective photosensitive drums 1a to 1d.

  Bk (black) toner, M (magenta) toner, Y (yellow) toner, and C (cyan) toner are accommodated in the casing of each of the developing devices 4a to 4d from the downstream side (upper side in the drawing). Yes.

  A predetermined gap is provided between the chargers 2a to 2d and the developing devices 4a to 4d. Exposure irradiation with a laser beam is performed from the scanner units 3a to 3d to the peripheral surfaces of the photosensitive drums 1a to 1d through the gap.

  In this color printer 9, the electrostatic conveyance belt 11 circulates clockwise in FIG. 1 and conveys the sheet in the same direction. On the other hand, the chargers 2a to 2d uniformly charge the peripheral surfaces of the corresponding photosensitive drums 1a to 1d with a predetermined charge. The scanner units 3a to 3d expose the peripheral surfaces of the uniformly charged photoreceptor drums 1a to 1d according to image information, and form electrostatic latent images on the peripheral surfaces. Then, the developing devices 4a to 4d transfer the toner to the low potential portion of the electrostatic latent image to form a toner image (development). That is, toner images are formed on the peripheral surfaces of the photosensitive drums 1a to 1d.

  The toner images formed (developed) on the peripheral surfaces of the photosensitive drums 1a to 1d are attracted to the charges generated on the conveyed sheet by the transfer electric field formed by the transfer units 12a to 12d corresponding to the toner images. And transferred to the sheet surface. The sheet onto which the toner image has been transferred is heat-fixed on the toner image by a fixing unit 20 including a pressure roller and a heat generating roller, and is then discharged out of the apparatus main body 10 by a discharge roller pair 23.

  When images are formed on both sides of the sheet, the sheet on which the toner image is formed on one side is protruded out of the apparatus main body 10 by the discharge roller pair 23, and then reversely drawn into the apparatus main body 10 and the reverse conveying path. 16 At this time, the sheet is switched back and turned upside down. Thereafter, the sheet is conveyed through the reverse conveyance path 16 and is sent to the registration roller pair 19 again. Thereafter, a toner image is also formed on the other side of the sheet, and the sheet is discharged out of the apparatus main body 10.

(Sheet Conveying Device of First Embodiment)
In FIG. 2 to FIG. 9, the sheet conveying device 51 rotates the sheet feeding ports 31 to 34 as a plurality of guide ports, the registration roller pair 19 as a rotating body pair, and the registration roller 19a of the registration roller pair 19. A sheet feeding motor 61 as a means and a CPU 62 (see FIG. 9) as a control means for controlling the rotation of the sheet feeding motor 61 are provided.

  As shown in FIG. 2, there are four paper feed ports (31 to 34) to the registration roller 19. As shown in FIGS. 2 and 3, the first paper feed port 31 is an exit of the path X. The path X is a path for guiding the sheet fed from the sheet feeding cassette 17 by the pickup roller 21 and the cassette sheet feeding roller pair 18 to the registration roller pair 19 through the cassette conveying roller pair 41. Further, the winding angle of the sheet guided along the path X with respect to the registration roller 19a is 21 degrees, and only the downstream winding from the nip of the registration roller pair 19 is performed.

  As shown in FIGS. 2 and 4, the second paper feed port 32 is the exit of the path Y. The path Y is a path for guiding the sheet fed by the MP paper feed roller 42c to the registration roller pair 19 through the MP transport roller 42a. The winding angle of the sheet guided along the path Y with respect to the registration roller 19a is 31 degrees. The winding angle upstream of the nip of the registration roller pair 19 is 10 degrees, and the winding angle downstream of the nip is 21 degrees.

  As shown in FIGS. 2 and 5, the third paper feed port 33 is an exit of the path Z. In the path Z, during double-sided printing, the sheet that has once passed through the fixing unit 20 is switched back and passed through the double-sided conveyance roller 43a. This is a route for guiding to the registration roller pair 19. The winding angle of the sheet guided along the path Z with respect to the registration roller 19a is 50 degrees. The wrap angle on the upstream side from the nip of the registration roller pair 19 is 29 degrees, and the wrap angle on the downstream side from the nip is 21 degrees.

  As shown in FIGS. 2 and 6, the fourth paper feed port 34 is an exit of the path W. The path W is a path for guiding a sheet conveyed from a paper supply option cassette (not shown) set below the apparatus main body 10 of the color printer 9. The winding angle of the sheet guided along the path W with respect to the registration roller 19a is 26 degrees. The winding angle on the upstream side from the nip of the registration roller pair 19 is 5 degrees, and the winding angle on the downstream side from the nip is 21 degrees.

  As described above, the winding angles from the paper feed ports 31 to 34 in the paths X, Y, Z, and W are different.

The sheet conveying speed of the registration roller pair 19 in the sheet conveying apparatus 51 of the present embodiment has three speed modes. The three speed modes is determined by the basis weight of the sheet. Basis weight 60 g / ^{m 2} to the speed mode to less than 90 g / ^{m 2} 1, a basis weight of 90 g / ^{m 2} or more to 120 g / ^m to less than ² speed mode 2, a basis weight of 120 g / ^{m 2} or more speed modes 3 ing. Accordingly, the sheet conveyance speed of the registration roller pair 19 is set to 12 kinds of speeds (3 kinds × 4 =) by the three kinds of speed modes 63 (see FIG. 8 ) and the four sheet feeding ports 31 to 34. Yes. The 3 × 4 matrix table shown in FIG. 8 is stored in the speed table of the memory 64 as the storage means of the CPU 62.

  The relationship between the winding angle and the conveyance speed shown in FIG. 8 is obtained by the following experiment. The rotational speed of the paper feed motor 61 is changed so that the speed of each of the paper feed ports 31 to 34 is determined so that the sheet bending shape between the registration roller 19 and the image forming unit 24 is the same. This time, an actuator / loop sensor flag that follows the bending of the sheet is provided between the registration roller pair 19 and the image forming unit 24, and a mechanism is provided to turn on / off the photo interrupter when a predetermined bending occurs. Using this jig / tool, the ON / OFF of the photo interrupter is monitored while the speed of the paper feed motor 61 is swung by 0.07%. As a result, the speed of the paper feed motor 61 is obtained for each of the paper feed ports 31 to 34 so that the amount of deflection is constant, and the fluctuation can be measured.

  The relationship between the speed of the paper feed motor 61 and the winding angle is shown in FIG. The speed of the paper feed motor 61 on the vertical axis in FIG. 7 was obtained as a percentage of the amount of speed deviation based on the speed of the paper feed motor 61 in the path X. The winding angle in the path X is 21 degrees, the winding angle in the path Y is 31 degrees, the winding angle in the path Z is 50 degrees, and the winding angle in the path W is 26 degrees. According to this, although there are slight differences among the three types of sheets having different basis weights, it can be seen that the speed of the sheet feeding motor tends to increase as the winding angle increases.

  Therefore, when the sheet is fed toward the image forming unit 24, the speed is decreased by an increase in the winding angle in order to make the actual conveyance speed constant. The lowering width includes the outer diameter, material and rubber hardness of the registration roller, the outer diameter and material of the opposing roller, the nip direction of the registration roller pair, the contact pressure between the registration roller and the opposing roller, and the positional relationship between the winding area and the registration roller nip. Varies depending on etc.

  In the present embodiment, the registration roller 19a is a urethane elastomer having an outer diameter of 17.45 mm. The hardness of the registration roller 19a is 82 (HS) A. The facing roller 19b is a polyoxymethylene (POM) material having an outer diameter of 20 mm. The counter roller 19b has a metal shaft 19c passing through the center of the roller, and includes a mechanism that strokes in the axial center direction of the registration roller 19. The counter roller 19b is in contact with the registration roller 19a by a spring load of 300 g for each of the left and right sides of the metal shaft end and a total of 600 g. The speed of the sheet feeding motor 61 in the sheet conveying apparatus 51 of the present embodiment is set for each sheet feeding port based on the result of FIG.

(Sheet Conveying Device of Second Embodiment)
As shown in FIG. 9, in the sheet conveying apparatus 51 of the first embodiment, the paper feed port and the speed mode are determined on the printer driver, and based on the information, according to the speed table stored in the memory 64 in the CPU 62. The number of rotations of the paper feed motor 61 is determined. In this case, since the speed is determined for each speed mode, a discrete speed value is obtained. Even if there is a variation in speed, the sheet conveying apparatus according to the first embodiment is sufficient when the amount of fluctuation in speed is small enough not to cause a problem with respect to the occurrence of an image defect due to sheet pressing or back tension. Can respond.

  However, it is preferable to store a continuous speed table in the memory 64 in order to further reduce the color misregistration of the color printer.

  In view of this, the sheet conveying device 52 according to the second embodiment shown in FIG. 10 can continuously control the sheet feeding motor. The sheet conveying device 52 of the present embodiment will be described with respect to parts different from the sheet conveying device 51 of the first embodiment.

  Similarly to the sheet conveying apparatus 51 of the first embodiment, the sheet conveying apparatus 52 of the present embodiment is also provided with information on the sheet feeding port from the printer driver. Then, instead of the speed mode, the basis weight of the sheet is taken into the CPU 65 as the control means by the media sensor 66 for detecting the type of the sheet on the printer driver or the mechanism for detecting the waist of the sheet. A memory 67 serving as a storage unit in the CPU 65 stores in advance a sheet basis weight constant corresponding to the sheet basis weight and a sheet feeding port constant corresponding to each sheet feeding port.

  The CPU 65 reads the sheet basis constant and the sheet feeding port information from the memory 67 on the basis of the sheet feeding port information and the sheet basis weight information, and calculates the number of rotations of the sheet feeding motor 61 by Equation 1 described later. . As a result, the rotation speed of the optimum motor can be continuously determined, and the actual sheet speed by the registration roller pair 19 can be kept substantially constant.

That is, the CPU 65
Number of revolutions = reference speed x sheet basis weight constant x paper feed port constant Equation 1
The optimum rotational speed can be calculated by using an approximate expression that satisfies the following expression and given information or a constant determined based on the detected information. Using the color printer 30 and the sheet conveying device 52 of the present embodiment, the optimum speed of the sheet feeding motor is obtained by obtaining the reference speed, the sheet feeding port constant, and the sheet basis weight constant in advance. Can do. Actually, the multi-order relational expression is obtained depending on the configuration of the color printer and the sheet conveying apparatus.

  Note that the color printer 9 of the present embodiment is capable of conveying a sheet at almost a constant conveyance speed regardless of the sheet feeding port, and the sheet conveying device 51 (or the first one) of the first embodiment. Since the sheet conveying device 52) according to the second embodiment is provided, it is possible to make the deflection of the sheet between the registration roller pair 19 and the image forming unit 24 substantially constant.

  Accordingly, the color printer 9 according to the present embodiment avoids problems such as sheet skew generation, large back tension, sheet pressing into the image forming unit 24, sheet guide rubbing, and noise increase, and color misregistration and the like. Image defects can be prevented.

  Further, since the color printer 9 does not need to be provided with a special mechanism such as a conveyance guide, the space can be reduced correspondingly and the cost can be reduced.

1 is a schematic front sectional view of a color printer as an image forming apparatus according to an embodiment of the present invention. It is a front view of the sheet conveying apparatus of a 1st embodiment. 5 is a diagram illustrating a sheet winding angle of a sheet passing through a path X with respect to a registration roller. FIG. FIG. 6 is a diagram illustrating a sheet winding angle of a sheet passing through a path Y with respect to a registration roller. FIG. 6 is a diagram illustrating a sheet winding angle of a sheet passing through a path Z with respect to a registration roller. 5 is a diagram illustrating a sheet winding angle of a sheet passing through a path W with respect to a registration roller. FIG. It is a figure which shows the relationship between the winding angle of a sheet | seat with respect to a registration roller, and a speed fluctuation. FIG. 6 is a diagram illustrating each speed mode and a set speed of each sheet feeding port in the sheet conveying apparatus of the first embodiment. It is a control part block diagram of the sheet conveying apparatus of 1st Embodiment. It is a control part block diagram of the sheet conveying apparatus of 2nd Embodiment.

Explanation of symbols

S sheet X path Y path Z path W path 9 Color printer (image forming apparatus)
12a to 12d Transfer device (transfer roller)
16 Reverse conveyance path 19 Registration roller pair (rotating body pair)
19a Registration roller 19b Opposing roller 24 Image forming unit (image forming means)
31 to 34 Paper feed port (guide port)
51 Sheet Conveying Device of the First Embodiment 52 Sheet Conveying Device of the Second Embodiment 61 Paper Feed Motor (Drive Unit)
62 CPU (control means)
63 Speed mode 64 Memory (storage means)
65 CPU (control means)
66 Media sensor 67 Memory (storage means)

Claims (4)

A pair of rotating bodies that rotate and convey the sheet,
A plurality of guide openings for guiding the sheet with respect to the pair of rotating bodies and having different winding angles of the guided sheet with respect to one rotating body of the pair of rotating bodies;
Drive means for rotationally driving the pair of rotating bodies;
Control means for adjusting the sheet conveying speed of the pair of rotating bodies by controlling the driving means,
The sheet feeding speed when the sheet is supplied from the guide port having a small wrapping angle is greater than the sheet conveying speed when the sheet is fed from the guide port having a large wrapping angle. The drive unit is controlled so that the sheet conveyance speed when conveying a sheet with a large basis weight is faster than the sheet conveyance speed when conveying a sheet with a small basis weight so as to be faster. A sheet conveying apparatus characterized by: A pair of rotating bodies that rotate and convey the sheet,
A plurality of guide openings for guiding the sheet with respect to the pair of rotating bodies and having different winding angles of the guided sheet with respect to one rotating body of the pair of rotating bodies;
Drive means for rotationally driving the pair of rotating bodies;
Control means for controlling the driving means to adjust the sheet conveying speed of the pair of rotating bodies;
Storage means for storing a guide opening constant determined according to the winding angle for each guide opening and a basis weight constant according to the type of the sheet;
Guide mouth constant and basis weight constant obtained by the control means based on the guide mouth information and the sheet type information to which the sheet is supplied, and the guide mouth constant and basis weight constant stored in the storage means. Accordingly, the sheet conveyance speed when the sheet is supplied from the guide port with a small winding angle is faster than the sheet conveyance speed when the sheet is supplied from the guide port with a large winding angle. And controlling the driving means so that the sheet conveying speed when conveying a sheet with a large basis weight is faster than the sheet conveying speed when conveying a sheet with a small basis weight. A sheet conveying apparatus that is characterized. Image forming means for forming an image on a sheet;
The sheet conveying apparatus according to claim 1 or 2, wherein the sheet is conveyed,
An image forming apparatus. The image forming apparatus according to claim 3 , wherein the pair of rotating bodies of the sheet conveying apparatus is a pair of registration rollers that conveys a sheet to the image forming unit.

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