JP5219492B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus used in, for example, a printer, a facsimile machine, a copying machine, or a multifunction machine having these functions, and an image forming apparatus including the sheet conveying apparatus.

  Various methods such as an electrophotographic method, an offset printing method, and an ink jet method are used for an image forming apparatus. Here, a color image forming apparatus using an electrophotographic method is taken as an example to explain the conventional technology. To do.

  Electrophotographic color image forming apparatuses include a tandem method in which a plurality of photosensitive drums are arranged side by side, and a rotary method in which a plurality of photosensitive drums are arranged in a cylindrical shape. As a transfer method, a direct transfer method in which a toner image is directly transferred from a photosensitive drum to a sheet or an intermediate transfer in which a toner image is transferred from a photosensitive drum to an intermediate transfer member and then transferred from the intermediate transfer member to a sheet. It is classified as a method.

  In recent years, in such an electrophotographic image forming apparatus, an apparatus aimed at a light printing market (POD: Print On Demand market) that performs printing of a small number of copies, taking advantage of the fact that a plate is not required compared to an offset printing machine or the like. Has been provided. However, in order to be accepted in such a light printing market, it is necessary to achieve high image quality, and as one of the factors, importance is placed on image position accuracy with respect to the sheet. Note that the image position accuracy includes a misalignment between front and back images when a double-sided image is formed on a sheet.

  The image position with respect to the sheet is affected by factors such as the position in the sheet conveyance direction, the position in the direction orthogonal to the sheet conveyance direction, the image magnification, and the skew of the sheet. The accuracy is determined.

  Under these factors, the sheet conveyance position and the image magnification can be easily corrected by electrical control, but it is difficult to correct sheet skew by electrical control. For example, the sheet conveyance position can be corrected by adjusting the irradiation timing and irradiation position of the laser beam based on the image signal to the photosensitive drum, and the magnification of the image is also irradiated with the laser beam to the photosensitive drum. Correction can be made by adjusting the range.

  On the other hand, as an electrical control for the skew of the sheet, it is possible to correct the image position with respect to the sheet by detecting the skew of the sheet and creating an image tilted accordingly. is there. However, particularly in the case of a color image in which three or four colors are superimposed, if the image is tilted for each sheet, the color changes for each sheet having a different skew amount due to misalignment of dot formation for each color. In addition, the calculation for tilting the image takes time, which causes a significant reduction in productivity. Therefore, the correction of the skew of the sheet is generally performed mechanically.

  As a mechanism for correcting the skew of the sheet, there are methods roughly described below.

  First, as a commonly used method, a pair of registration rollers (hereinafter referred to as registration rollers) is arranged upstream of the transfer unit, and the leading edge of the sheet that is the transferred transfer material is stopped. There is a method of correcting skew by hitting the nip portion of the registration roller. In this system, skew correction is performed by feeding the sheet further in a state where the leading edge of the sheet is in contact with the nip portion of the registration roller, and forming a loop so that the leading edge of the sheet follows the nip portion.

  As another method, there is a method including a means for calculating the amount of skew of the sheet based on detection of the inclination of the leading end of the sheet, and two independently drivable rollers in the direction perpendicular to the conveyance. In this method, the skew is corrected by turning the sheet by changing the conveyance speed of each independent driving roller in accordance with the calculated skew amount of the sheet.

  Furthermore, as another method, the sheet is conveyed obliquely by a skew feeding roller with respect to a reference surface provided along the sheet conveyance direction and conveyed while abutting the side surface of the sheet against the reference surface. There is a method for correcting skew.

  Here, an example of a method of correcting skew feeding by abutting the side edge of the sheet against the reference surface will be described with reference to the drawings.

  FIG. 16 is a view of the skew correction unit for correcting the skew of the sheet as viewed from the sheet conveyance direction. The sheet is conveyed from the front to the back of the drawing. The skew feeding correction unit sandwiches the sheet S between the skew feeding correction roller 32 and the pressure roller 34 and conveys the sheet S obliquely, and the side edge of the sheet S hits a reference surface 311 provided in the reference guide unit 31. In this configuration, the skew is corrected by applying. As shown in FIG. 16A, the side ends of the sheet S that is obliquely fed by the skew feeding correction roller 32 and the pressure roller 34 are the upper guide 312 and the lower guide 313 that are arranged above and below the reference guide portion 31. To the reference plane 311. Further, the seat is prevented from buckling by regulating the seat between the upper guide 312 and the lower guide 313.

  Here, the method of correcting the skew by abutting the side edge of the sheet using the reference surface has the following advantages. When images are formed on both sides of a sheet, the leading edge and the trailing edge of the sheet are switched between the first and second surfaces by switching back the sheet, but the side edges are not interchanged. Since skew correction can be corrected at the same position in the direction orthogonal to the sheet conveyance direction on both the first and second sides of the sheet, the accuracy of the position of the image with respect to the side edge of the sheet is increased, and the deviation of the front and back images is reduced. It becomes possible.

  In the other skew correction methods, skew correction is performed at the leading edge of the sheet, and correction in the direction orthogonal to the sheet conveyance direction cannot be performed on the first and second surfaces, so that the skew correction capability is high. There is also a risk that the front and back of the sheet will be displaced from the side edges.

On the other hand, in the quick printing market, a wide a variety of materials that correspond are required, for ^{example, 40g / m 2 ~350g / m} 2 basis weight of not less than plain paper or less, a special such as coated paper or film sheet It has been required to form an image on a variety of materials such as those using various materials.

  Here, as described above, the skew correction is performed by abutting the side edge of the sheet against the reference surface by conveying the sheet obliquely toward the reference surface and abutting the side edge of the sheet and conveying the sheet. In this configuration, the skew of the sheet is corrected. However, in recent years, the need to transport sheets with the various thicknesses and materials described above has increased, so if the sheet to be transported is made of a material with low rigidity, such as a thin sheet, it will abut against the reference surface. There was a risk that the sheet would buckle when it was pressed.

  That is, as shown in FIG. 16B, when the sheet S having low rigidity is abutted against the reference surface 311, the sheet as illustrated between the upper guide 312 and the lower guide 313 arranged vertically is formed. Buckling may occur. In this case, the accuracy of the skew correction is deteriorated, and the accuracy of the image position with respect to the sheet is lowered. Further, jamming (sheet clogging) may occur due to the buckling of the sheet, or damage such as breakage or breakage may occur on the side edge of the sheet. The interval between the upper guide 312 and the lower guide 313 is set larger than the maximum thickness sheet so that the maximum thickness sheet that can be conveyed by the apparatus can be conveyed. For this reason, a thin sheet cannot be sufficiently regulated between the upper guide 312 and the lower guide 313, and buckling occurs.

In view of this, a device has been proposed that adjusts the interval between the guides arranged vertically according to the thickness of the sheet so that the sheet can be conveyed while abutting the side edge of the sheet against the reference surface without causing buckling. (See Patent Document 1). With this configuration, in the case of a sheet with low rigidity such as a thin sheet, the interval between the upper and lower guides is narrowed to restrict the side edge of the sheet that is abutted against the reference surface 311 to suppress the occurrence of buckling. ing.
JP 2002-356250 A

  However, in the above-described conventional example, the thickness of the sheet is detected to adjust the distance between the upper and lower guides, which causes a problem of detection accuracy of the detection means. That is, as a detecting means for detecting the thickness of the sheet, the thickness of the sheet is directly detected using a contact sensor or a reflective optical sensor, or based on the displacement amount of the roller when the conveying roller sandwiches the sheet. The method of calculating is common. However, when detecting while conveying a sheet, in addition to the error of the sensor itself, a detection error of about 10% may occur due to flapping during conveyance of the sheet or eccentricity of the conveyance roller. In addition, the sheet thickness is detected based on the amount of displacement of the roller when the conveyance roller pinches the sheet. In the case of a thin sheet, the displacement of the roller is small, so the sheet thickness is accurately detected. Difficult to do.

  Even if the sheet thickness is not automatically detected, it may be possible to adjust the vertical guide interval based on the sheet thickness information directly input by the user. There may be a setting error.

  Furthermore, the parameter for preventing the buckling of the sheet when it abuts against the reference plane is actually based on the stiffness of the sheet, not the thickness of the sheet. FIG. 15 is a graph in which the thicknesses and stiffnesses of various types of sheets are plotted. It can be seen from the fact that the stiffness varies greatly depending on the types of sheets having the same thickness. Further, as can be seen from this graph, paper with a thin sheet tends to have extremely low stiffness due to a slight difference in thickness. From these, it can be seen that it is difficult to prevent buckling simply by adjusting the upper and lower guide intervals based on the thickness of the sheet. That is, even if it is a thick sheet, if the stiffness is low, it is necessary to narrow the guide interval in order to prevent buckling, but in conventional devices, the guide interval is adjusted by the thickness of the sheet. Such buckling of the thick and low-stiffness sheet cannot be prevented.

  In addition, providing a mechanism for adjusting the distance between the upper and lower guides as in the conventional apparatus requires a driving unit such as a motor and a control unit for controlling the driving unit, which increases the apparatus cost. Become.

The present invention has been made in view of the above problems, and without using a complicated structure, skew correction can be reliably performed without causing buckling even when a sheet having low rigidity is abutted against a reference surface. An object of the present invention is to provide a sheet conveying apparatus that can perform this.

The present invention is arranged along a sheet conveying direction, and a reference surface for positioning the side edge of the sheet, and a skew feeding mechanism for conveying the sheet so that the side edge of the sheet is abutted obliquely toward the reference surface And a first guide having a sheet conveying surface disposed between the skew feeding mechanism and the reference surface and facing one surface side of the sheet conveyed by the oblique feeding mechanism, and on the second surface side of the sheet A second guide having an opposing sheet conveying surface; a guide portion for guiding a side edge of the sheet conveyed by the oblique feeding mechanism that is abutted against the reference surface; and a sheet conveying surface of the first guide. A concave portion or a convex portion provided along the sheet conveying direction, and a convex portion provided on the sheet conveying surface of the second guide along the sheet conveying direction and opposed to the concave portion of the first guide. Or the first guy Of and a recess which faces the convex portion, and a deflection forming means to deflect the wave-shape side edge of the abutted sheets to said reference plane between said concave portion and the convex portion facing thereto, The convex portion of the bending forming means is formed of a protruding portion that is provided so as to protrude from the sheet conveying surface of the first guide or the second guide and is urged to protrude. And

  According to the present invention, when the sheet is abutted against the reference surface by forming a deflection along the reference surface at the side edge of the sheet that is abutted against the reference surface by the deflection forming means, and increasing the rigidity of the portion where the sheet abuts. The buckling of the sheet can be prevented.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the entire electrophotographic image forming apparatus 1 to which the present invention is applied will be schematically described with reference to FIG.

  The sheet S as a transfer material is stacked and stored on a lift-up device 11 included in the sheet feeding device 10, and the sheet feeding unit 12 feeds the sheet in accordance with the image forming timing of the image forming mechanism 90. Transmission starts. Here, as the sheet feeding means 12, there are a system using friction separation by a feeding roller or the like, a system using separation adsorption by air, and the like. In this embodiment, a sheet feeding system by air is taken as an example. Cite.

  The sheet S sent out by the sheet feeding unit 12 passes through the transport path of the transport unit 20 and is transported to the registration unit 30. The sheet S is subjected to skew correction by a skew correction device, which will be described later, provided in the registration unit 30, and then subjected to timing correction for alignment with an image at the secondary transfer unit to perform secondary correction. Sent to the transfer section. The secondary transfer portion is a transfer nip portion formed by the opposing secondary transfer inner roller 43 and secondary transfer outer roller 44, and provides intermediate transfer onto the sheet S by applying a predetermined pressure and electrostatic load bias. The toner image (unfixed image) on the belt 40 is transferred.

  Next, an image forming process in which the toner image to be transferred to the sheet is formed and sent to the secondary transfer unit will be described.

  In FIG. 7, an image forming mechanism 90 mainly includes a photosensitive drum 91, an exposure device 93, a developing device 92, a primary transfer device 45, a photoconductor cleaner 95, and the like. The exposure device 93 emits light to the photosensitive drum 91 whose surface is uniformly charged in advance by the charging means and rotates in the counterclockwise direction in the drawing based on the signal of the transmitted image information, and passes through the reflecting means 94. As a result, a latent image is formed. The electrostatic latent image formed on the photosensitive drum 91 in this way is subjected to toner development by the developing device 92, and a toner image is formed on the photosensitive member. Thereafter, a predetermined pressing force and an electrostatic load bias are applied by the primary transfer device 45, and the toner image is transferred onto the intermediate transfer belt 40. The photoreceptor cleaner 95 collects the transfer residual toner that has been primarily transferred and remains on the photosensitive drum 91.

  In the case of the image forming mechanism 90 described above, four image forming units of yellow (Y), magenta (M), cyan (C), and black (Bk) are provided. Note that the colors are not limited to four colors, and the color arrangement order is not limited to this.

  Next, the intermediate transfer belt 40 will be described. The intermediate transfer belt 40 is stretched by rollers such as a drive roller 42, a tension roller 41, and a secondary transfer inner roller 43, and is driven to rotate in the direction of arrow B in the figure. The respective color images processed in parallel by the above-described Y, M, C, and Bk image forming units are sequentially superimposed on the upstream toner image primarily transferred onto the intermediate transfer belt 40. As a result, a full-color toner image is finally formed on the intermediate transfer belt 40 and conveyed to the secondary transfer unit.

  As described above, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer portion by the sheet conveying process and the image forming process described above. The transfer residual toner that has been secondarily transferred and remains on the surface of the intermediate transfer belt 40 is collected by the belt cleaner 46.

  The sheet S on which the image has been transferred is conveyed to a fixing device 50 by a pre-fixing conveyance unit 51, and in the fixing device 50, a predetermined pressurizing force by an opposing roller or belt, and generally a heat source such as a halogen heater. The toner is melted and fixed on the sheet S by being heated. The sheet S having a fixed image obtained in this way is discharged as it is onto the paper discharge tray 61 by the branch conveyance device 60, or is conveyed to the reverse conveyance device 70 when double-sided image formation is performed.

  The sheet S sent to the reverse conveying device 70 is switched back and forwards by a switchback operation, and is conveyed to the duplex conveying device 80. Thereafter, the sheet is fed to the conveyance unit 20 in synchronization with the sheet S conveyed from the sheet feeding apparatus 10 and is sent to the secondary transfer unit. Since the image forming process on the second side is the same as that on the first side, description thereof is omitted.

  In the present embodiment, an image forming unit that forms an image on a sheet is a secondary transfer unit configured by an image forming mechanism 90, an intermediate transfer belt 40, a secondary transfer inner roller 43, and a secondary transfer outer roller 44. And a fixing device 50.

  Here, the configuration of the skew feeding correction device provided in the registration unit 30 for correcting the skew feeding of the sheet will be described in detail. First, an overall schematic configuration of the skew feeding correction apparatus will be described with reference to FIG.

  The skew correction device includes a movable guide 55, a fixed guide 33, and the like. The movable guide 55 is movable in a direction (sheet width direction) orthogonal to the sheet conveying direction according to the size of the sheet S. The movable guide 55 includes a reference guide portion 31, a plurality of skew correction rollers 32a, 32b, and 32c, and pressure rollers 34a, 34b, and 34c that are in pressure contact with the skew correction rollers 32a, 32b, and 32c. And can be moved together. The fixed guide 33 is fixed to the apparatus frame and functions as a conveyance guide for the sheet S.

  Next, the skew correction apparatus will be described with reference to FIGS. FIG. 1 is a side view of the skew correction device as viewed from a direction orthogonal to the sheet conveying direction, and FIG. 4 is a perspective view of the skew correction device as viewed from obliquely above. 3 and 4 are partially enlarged views of FIG. FIG. 5 is a top view, and shows a cross section in which an upper guide 312 of a reference guide portion 31 described later is omitted.

  As shown in FIGS. 1 and 2, the skew feeding correction device is provided with a reference guide portion 31, and this reference guide portion 31 has a U-shaped cross-sectional shape when viewed from the upstream side in the sheet conveyance direction. I am doing. The reference guide portion 31 abuts the side edge of the sheet to correct the skew of the sheet and positions the side edge of the sheet, and the upper guide 312 and the first guide as the first guide. And a lower guide 313 as a second guide. The upper guide 312 is formed with a sheet conveying surface 312a facing the one surface side (upper surface side) of the conveyed sheet, and the lower guide 313 is a sheet facing the second surface side (lower surface side) of the sheet. A conveyance surface 313a is formed. The upper guide 312 and the lower guide 313 have a guide function for guiding the side edge of the sheet to the reference surface 311 and a function of suppressing the buckling by regulating the sheet when the sheet hits the reference surface 311. Have.

  As shown in FIG. 5, a plurality of skew feeding correction rollers 32a, 32b, and 32c, which are skew feeding mechanisms, are arranged with an angle α with respect to the sheet conveyance direction. Then, the sheet is conveyed obliquely with respect to the reference surface 311 of the reference guide portion 31 (slope feeding), the sheet side edge is abutted against the reference surface 311, and the sheet side edge is along the reference surface 311. It is comprised so that it may convey in the state which carried out.

  As shown in FIG. 5, the skew feeding correction rollers 32a, 32b, and 32c arranged along the sheet conveying direction are driven by a driving motor 322 via timing belts 323, 324, and 325 and couplings 321a, 321b, and 321c. Has been communicated. For this reason, variations in driving speed for each of the skew feeding correction rollers 32a, 32b, and 32c are reduced.

Next, the bending forming means for bending the sheet side end that abuts against the reference surface 311, which is a unique configuration of the present invention, will be described with reference to FIGS. 1 to 6.
As shown in FIG. 1, concave portions 314 are formed at a plurality of locations (two locations in the present embodiment) along the sheet conveyance direction of the lower guide portion 313. Since the concave portion 314 is smoothly connected to the sheet conveying surface 313a of the lower guide 313 by an inclined surface, the leading edge of the sheet conveyed by the concave portion 314 is configured not to be caught.

  In the upper guide 312, spherical members 35 (35 a, 35 b) as protruding portions are arranged so as to protrude from the sheet conveying surface 312 a at positions facing the concave portions 314 provided in the lower guide. The spherical member 35 (35a, 35b) is fitted in a hole provided on the upper guide 312 side with a gap, and the spherical member 35 is pulled out downward by a flange portion formed at the lower end of the hole. It is prevented. The lower end of the spherical member 35 (35a, 35b) is provided so as to protrude from the sheet conveying surface 312a, and can be slidably contacted with the conveyed sheet. With this configuration, the spherical member 35 (35a, 35b) can be rotated in either direction, even if the sheet conveyance direction changes during the sheet abutting operation or when the sheet is conveyed by the registration roller 37. By following the above, the conveyance resistance applied to the sheet can be reduced.

  The spherical member 35 (35a, 35b) is formed of a low friction resin such as POM (polyacetal resin), and can press the sheet S conveyed by its own weight. In the present embodiment, the weight of the spherical member 35 is 1 g. The spherical member 35 (35a, 35b) is urged to protrude from the sheet conveying surface 312a by its own weight, but may be urged to protrude by an elastic member such as a weak spring.

  With this configuration, in the case of the sheet Sn with low rigidity, as shown in FIG. 4A, the side edge of the sheet is bent between the spherical member 35 (35a, 35b) and the recess 314, and the sheet Sn Is abutted against the reference surface 311 in a state of being formed in a wave shape along the sheet conveying direction. That is, it is possible to form a deflection at the end portion of the sheet by the convex shape formed by the spherical member 35 (35a, 35b) and the concave portion 314 opposed to the convex shape. As shown in FIG. 4B, the sheet Sk having high rigidity is moved upward by the spherical member 35 (35a, 35b) being pushed by the sheet Sk, and the reference surface 311 is in a state where the sheet Sk is straight. It is hit by. Note that the amount of movement of the spherical member 35 (35a, 35b) changes substantially in proportion to the stiffness of the sheet, so the amount of deflection changes according to the stiffness of the sheet. That is, the amount of bending becomes smaller as the stiffness of the sheet becomes higher.

In the present embodiment, in FIG. 3, the gap G1 (base interval) between the sheet conveying surface 312a of the upper guide 312 and the sheet conveying surface 313a of the lower guide 313 is set to 1 mm. This is to prevent variations in sheet thickness and jamming due to curling when the thickness of 350 g / m ² as the thickest sheet that can be used by the image forming apparatus in the present embodiment is 0.4 mm. It is set with consideration. The height difference G2 between the sheet conveyance surface 313a of the lower guide 313 and the bottom surface of the recess 314 is set to 1 mm.

In general, it is known that the buckling of the sheet occurs in proportion to the cross-sectional secondary moment I. For example, when the height difference of bending when a 40 g / m ² sheet having a thickness of 0.05 mm is bent into a corrugated shape is 2 mm, the cross-sectional secondary moment I is about 6300 times that of the flat plate state. This shows that the moment of inertia of the cross section of the thickest sheet (thickness 0.4 mm) is far exceeded.

  Here, an example of the relationship between the height difference of the sheet deflection and the secondary moment I of the cross section is shown in FIG. 9, the horizontal axis indicates the secondary moment I of the cross section, and the solid line indicates the sheet thickness t of plain paper. The change of the sectional secondary moment I is shown. A broken line indicates a change in the secondary moment I of the cross section when the height difference a of the wave shape of the sheet when the thickness of the plain paper is t = 0.05 mm is changed.

  As can be seen from this, by forming a deflection even in a sheet having low rigidity, it is possible to increase the sectional secondary moment I to such an extent that the sheet does not buckle, and it is possible to reliably abut against the abutting surface, The occurrence of jam and skew can be suppressed.

  From this, even in the sheet Sn having low rigidity, as shown in FIG. 4A, the side end of the sheet Sn is bent into a corrugated shape along the sheet conveying direction of the reference surface 311, so that the sheet Sn is conveyed in the sheet conveying direction. The rigidity (buckling force) in the direction orthogonal to the direction can be increased. As a result, it is possible to prevent the low-stiffness sheet from buckling when it hits the reference surface 311. Further, the amount of bending of the sheet (the difference in level of wave-shaped bending) differs depending on the rigidity of the sheet, and the greater the rigidity of the sheet, the smaller the amount of bending and the lower the conveyance resistance. As a result, the sheet with low rigidity increases the deflection and increases the abutting rigidity to prevent buckling, and the sheet with high rigidity reduces the bending and decreases the conveyance resistance, enabling smooth conveyance, and the high-precision skew. Line correction can be performed.

  In addition, the spherical members 35a and 35b are formed at positions substantially corresponding to the center between the skew feeding correction rollers 32a, 32b, and 32c in the sheet conveyance direction in order to stably form the corrugated shape of the sheet having low rigidity. It is arranged. That is, since the side edges of the sheet are bent in a substantially symmetrical shape between the skew correction rollers, stable conveyance can be performed in a state where the bending is formed.

  In addition, if the conveyance speed of the plurality of skew feeding correction rollers 32a, 32b, and 32c is faster on the downstream side, the sheet is pulled, and the corrugated shape of the formed sheet is eliminated. The function of increasing the rigidity of the side end of the can not be exhibited. Therefore, in this embodiment, as shown in FIG. 6, the skew feeding angle α in the skew feeding direction with respect to the sheet conveying direction of the skew feeding correction rollers 32a, 32b, and 32c is increased toward the downstream side (αc> αb> αa). As a result, the speed component in the sheet conveying direction becomes smaller as it goes downstream, and the speed in the sheet conveying direction becomes slower. Each skew feeding angle is set so that the skew correction roller on the downstream side does not become fast even if the size varies to the maximum in consideration of the outer diameter tolerance of the skew correction rollers 32a, 32b, 32c.

  In the present embodiment, the velocity component in the sheet conveyance direction by the skew feeding correction roller on the downstream side is reduced by the sheet conveyance angle (skew feeding angle) of each of the skew correction rollers 32a, 32b, and 32c. However, the present invention is not limited to this. For example, the outer diameters of the skew correction rollers 32a, 32b, and 32c may be changed as going downstream in the sheet conveyance direction. Alternatively, the skew feeding correction rollers 32a, 32b, and 32c may be provided with drive motors independently to change the driving speed of each roller to slow down the sheet feeding direction in the sheet feeding direction by the downstream skew correction rollers. .

  In addition, for the buckling of a low-rigidity sheet, it is preferable that the positions of the spherical members 35a and 35b be as close as possible to the abutting surface. Therefore, in this embodiment, the upper guide 312 is not necessarily disposed. It is not necessary to provide the reference guide portion 31. That is, any position between the skew correction rollers 32a, 32b, and 32c and the reference surface 311 may be used, so that it may be determined as appropriate according to the corresponding material and apparatus configuration. Further, the number of skew feeding correction rollers, concave portions, and spherical members may be increased or decreased according to the corresponding material and device configuration.

  Here, the sheet alignment operation in the registration unit 30 will be schematically described with reference to FIGS.

  First, as shown in FIG. 8A, it is assumed that the sheet S is sent to the skew correction device in an inclined state with an angle β, for example. The sheet S sent to the skew feeding correction rollers 32a, 32b, and 32c by the sheet feeding roller pair 21 is sequentially conveyed by the skew feeding correction rollers 32a, 32b, and 32c, and as shown in FIG. It is sent obliquely toward the part 31. When the sheet S starts to be conveyed by the skew feeding correction roller 32a, the nip of the sheet conveying roller pair 21 is already released by an actuator (not shown). Next, as illustrated in FIG. 8C, the skew of the sheet is corrected by being conveyed while the side edge of the sheet S abuts on the reference surface 311 of the reference guide portion 31 and follows the reference surface 311. At the same time, the side edge of the sheet is positioned. In this state, the sheet is conveyed toward the registration roller 37.

  When the sheet reaches the registration roller 37 and is nipped, the nips of the pressure rollers 34a, 34b, and 34c facing the skew correction rollers 32a, 32b, and 32c are released by an actuator (not shown). Thereafter, as shown in FIG. 8D, the registration roller 37 is slid in a direction orthogonal to the sheet conveying direction while the sheet is held, and the sheet and the image on the intermediate transfer belt 40 are aligned. . In this case, since the side edge of the sheet is positioned in the reference guide portion 31, the registration roller 37 is slid to fit the image based on this position. Thereafter, the sheet is sent to the secondary transfer portion by the registration roller 37.

  Next, another embodiment will be described. FIG. 10 is a view of the device looking down from above in order to represent a second embodiment of the present invention. In the configuration of this embodiment, the spherical members 35a and 35b as the projecting portions are replaced with columnar cylindrical rollers 38a and 38b, and the other configurations are the same as those of the first embodiment, and thus description thereof is omitted. .

  The cylindrical rollers 38a and 38b are disposed in holes provided in the upper guide 312, and are provided so as to protrude from the sheet conveying surface 312a. The shafts of the cylindrical rollers 38a and 38b enter grooves formed on the sides of the holes, whereby the cylindrical rollers 38a and 38b are held so as to be rotatable and vertically movable along the sheet conveying direction.

  As with the spherical members 35a and 35b, the cylindrical rollers 38a and 38b, with respect to a sheet having low rigidity, bend the side edge of the sheet between the opposing recesses 314 to increase the rigidity, thereby ensuring reliable skew correction. Can be done. Further, when a highly rigid sheet is conveyed, the sheet moves upward while losing the rigidity of the sheet. As described above, the skew feeding correction operation according to the configuration of the second embodiment is the same as that of the first embodiment.

  In this configuration, since the shaft portion is supported by the groove compared to the configuration in which the spherical members 35a and 35b are supported so as to rotate smoothly, the support structure is simple, and the ball member 35a and 35b is formed with high accuracy like a sphere. Since it is not necessary, it can be manufactured at low cost.

  Next, FIG. 11 shows a third embodiment of the present invention. Compared to the first embodiment, the lower guide 313 instead of forming the recess 314 on the sheet conveying surface 313a of the lower guide 313. The lower guide roller 39 protrudes from the sheet conveying surface 313a. The lower guide roller 39 is rotatably provided. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  In the present embodiment, a pair of lower guide rollers 39 are disposed on both the upstream side and the downstream side of the spherical members 35a and 35b with respect to the sheet conveying direction to form a concave shape. The spherical members 35a and 35b have a staggered arrangement in a side view. That is, the end of the sheet can be bent by the convex shape formed by the spherical members 35a and 35b and the concave shape formed by the pair of lower guide rollers 39 opposed thereto.

  As a result, when skew correction of a sheet having low rigidity is performed, the side edge of the sheet is bent into a corrugated shape by the lower guide roller 39 and the spherical members 35a and 35b and abuts against the reference surface 311. The skew of the sheet is reliably corrected without buckling.

  In this configuration, since the lower guide roller 39 and the spherical members 35a and 35b rotate smoothly when the sheet is conveyed, the frictional resistance applied to the sheet can be reduced more reliably than in the first embodiment. In addition, skew can be corrected with high accuracy.

  FIG. 12 shows a fourth embodiment of the present invention, in which a corrugated shape is formed at the side edge of the sheet by controlling the sheet conveyance speed of the skew feeding correction roller without providing an uneven shape in the reference guide portion 31. Is. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  The skew correction rollers 32a, 32b, and 32c are coupled to drive motors M1, M2, and M3, which are drive sources for driving the skew correction rollers 32a, 32b, and 32c, respectively, so that rotation is controlled independently. In addition, sheet detection sensors 330a, 330b, and 330c for detecting the conveyed sheet are disposed in the vicinity of the nip of the skew correction rollers 32a, 32b, and 32c.

  As shown in the control block diagram of FIG. 13, the controller C is connected to drive motors M1, M2, and M3, which are drive sources for driving the skew feeding correction rollers 32a, 32b, and 32c. Control signals are output to the drive motors M1, M2, and M3. Further, sheet detection sensors 330a, 330b, and 330c that are provided so as to be able to detect the sheets conveyed to the skew correction rollers 32a, 32b, and 32c are connected to the controller C. Then, detection signals from the sheet detection sensors 330a, 330b, and 330c are input to the controller C.

  With this configuration, it is detected that the sheet reaches the nip of the skew feeding correction rollers 32a, 32b, and 32c based on detection by the sheet detection sensors 330a, 330b, and 330c. Based on the detection by these sensors, the rotation of the drive motors M1, M2, and M3 is sequentially started, and the skew correction rollers 32a, 32b, and 32c are sequentially rotated.

  FIG. 17 shows this control flowchart. Explaining this, when skew correction control is started in Step 1 (Step 1), it waits for the sheet detection sensor 330a to detect a sheet in Step 2 (Step 2). Here, when the sheet detection sensor 330a detects the sheet, the rotation of the drive motor M1 is started in Step 3 (Step 3), and the skew feeding correction roller 32a is driven to continuously convey the sheet. Subsequently, in step 4 (Step 4), it waits for the sheet detection sensor 330b to detect the sheet conveyed by the skew feeding correction roller 32a. Here, when the sheet detection sensor 330b detects the sheet, in step 5 (Step 5), the rotation of the drive motor M2 is started, and the skew feeding correction roller 32b is driven to continuously convey the sheet. At this time, there is a time difference between the sheet detection sensor 330b detecting the sheet and the rotation of the drive motor M2 until the sheet is conveyed, and the sheet is temporarily conveyed at a low speed or temporarily. Be stopped.

  Subsequently, in step 6 (Step 6), it waits for the sheet detection sensor 330c to detect the sheet conveyed by the skew feeding correction roller 32b. Here, if the sheet detection sensor 330bc is detected, the rotation of the drive motor M3 is started in Step 7 (Step 7), and the skew feeding correction roller 32c is driven to continuously convey the sheet. Also at this time, there is a time difference between the detection of the sheet by the sheet detection sensor 330c and the rotation of the drive motor M3 until the sheet is conveyed, and the sheet is temporarily conveyed at a low speed or temporarily. To be stopped. Then, the skew feeding correction roller sequentially rotates and the sheet is sent obliquely, and the side edge of the sheet is abutted against the reference surface 311 so that the skew feeding correction of the sheet is performed.

  As described above, since each of the skew feeding correction rollers 32a, 32b, and 32c has a rise time loss at the start of rotation, there is a time difference between the timing at which the sheet detection sensor detects the sheet and the timing at which the drive motor starts to rotate. Occurs. For this reason, the conveyed sheet is conveyed at a low speed when nipped by the skew feeding correction roller to be delivered, or stopped before being nipped. Therefore, in the case of a sheet having low rigidity, the skew correction rollers 32a, 32b, and 32c are bent by the low-speed conveyance or temporary stop of the sheet, and the side edges of the sheet are formed in a corrugated shape. Is done. In this state, since the side edge of the sheet is abutted against the reference surface 311, it is possible to reliably perform skew correction without causing buckling even for a sheet having low rigidity.

  On the other hand, in the case of a highly rigid sheet such as a thick sheet, the sheet is conveyed without slippage due to slippage at the nip portion of the roller.

  Each sheet detection sensor 330a, 330b, 330c is arranged on the upstream side of each skew feeding correction roller 32a, 32b, 32c, and a predetermined time is measured by a timer after each sensor detects the sheet. The start of rotation of each skew feeding correction roller may be controlled. In this case, the sheet is deflected by rotating the skew feeding correction roller after a time longer than the time from when the sheet is detected by the sensor until it reaches the skew feeding correction roller. By repeating this in sequence, corrugated bends are formed at the side edges of the sheet. Further, the peripheral speed of each skew correction roller 32a, 32b, 32c is controlled, and the peripheral speed is gradually decreased as the downstream skew correction roller is formed, thereby forming a wave shape at the side edge of the sheet. You may do it.

  In this way, by controlling the rotation of the skew feeding correction roller, a corrugated shape can be formed on the side edge of the sheet, and reliable skew feeding correction can be performed. As described above, since the corrugated shape can be formed only by controlling the rotational speed of the skew feeding correction roller, it is possible to further prevent the occurrence of jam or the like with respect to the roller using the roller.

  The example in which the present invention is applied to an image forming apparatus using an electrophotographic method has been described above, but the present invention may be applied to other image forming apparatuses such as a BJ method and a thermal transfer method.

The side view which shows an example of the skew feeding correction apparatus which is the characteristic structure of this invention 1 is a perspective view of the skew correction device shown in FIG. Cross-sectional enlarged view of the reference guide shown in FIG. The enlarged view which shows the operation state of the reference | standard guide part of FIG. 1 is a top view of the skew correction device shown in FIG. 1 is a top view of the skew correction device shown in FIG. Sectional drawing explaining the whole structure of the image forming apparatus to which this invention is applied Top view of the resist unit shown in FIG. The figure showing the relationship between the cross-sectional secondary moment I of the Example of this invention, the thickness of a sheet | seat, and a guide height difference. The perspective view of the skew feeding correction apparatus of 2nd Embodiment of this invention Side view of the third embodiment of the present invention Side view of the fourth embodiment of the present invention Block diagram of control used in the fourth embodiment of the present invention The flowchart which shows control of the block diagram of FIG. Diagram showing the relationship between sheet thickness and stiffness Figure viewed from the sheet conveyance direction of a conventional skew correction device

Explanation of symbols

30 Registration unit 31 Reference guide portion 32a, 32b, 32c Skew correction roller (slope feeding mechanism)
34a, 34b, 34c Pressure roller (slope feeding mechanism)
35a, 35b Spherical member (protrusion)
38a, 38b Cylindrical roller (protrusion)
39 Lower guide roller 311 Reference surface 312 Upper guide 313 Lower guide 322, M1, M2, M3 Drive motor 330a, 330b, 330c Sheet detection sensor

Claims (5)

A reference surface that is arranged along the sheet conveyance direction and positions the side edges of the sheet;
A skew feeding mechanism that conveys the sheet so as to obliquely abut the side edge of the sheet toward the reference surface;
A first guide that is disposed between the skew feeding mechanism and the reference surface and has a sheet conveying surface facing the one surface side of the sheet conveyed by the oblique feeding mechanism, and opposite the two surface sides of the sheet. A second guide having a sheet conveying surface, and a guide portion that guides a side edge of the sheet conveyed by the oblique feeding mechanism that is abutted against the reference surface;
A concave portion or a convex portion provided along the sheet conveyance direction on the sheet conveyance surface of the first guide, and a sheet conveyance surface of the second guide provided along the sheet conveyance direction, the first guide side of the guide of the convex portion or the first opposing the recess of the guide and the recess opposite the protruding portion of provided with, the abutted sheet to said reference plane between said concave portion and the convex portion facing thereto Bending forming means for bending the end into a wave shape;
Equipped with a,
The convex portion of the bending forming means is formed of a protruding portion that is provided so as to protrude from the sheet conveying surface of the first guide or the second guide and is urged to protrude. A sheet conveying apparatus. The protrusions sheet conveying apparatus according to claim 1, characterized in that a spherical member rotatably held by the first guide or the second guide. The protrusions sheet conveying apparatus according to claim 1, characterized in that the said first guides or cylindrical rollers which are rotatably held by the second guide.   A pair of rotatably supported guide rollers that protrude from the sheet conveying surface on the upstream side and the downstream side of the protruding portion in the sheet conveying direction on the sheet conveying surface that faces the sheet conveying surface on which the protruding portion is disposed. The sheet conveying apparatus according to any one of claims 1 to 3, further comprising: The sheet conveying apparatus according to any one of claims 1 to 4 ,
And an image forming unit that forms an image on the sheet conveyed by the sheet conveying device.

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