JP2023109588A - Image forming apparatus - Google Patents

Abstract

To reduce the amount of skew of a sheet during image formation on the back of the sheet in an image forming apparatus having at least two housings.SOLUTION: An image forming apparatus comprises a first unit that corrects skew of a sheet, and a second unit 20 that is provided on a double-sided conveyance path and corrects skew of the sheet. A second housing 220 has a front column 222 and a rear column 223 facing a first housing 210, and positioning parts 224, 225 provided on the front column 222 and the rear column 223 and determining the position of the first housing 210. The second unit 20 is attached to the front column 222 and the rear column 223 with at least part thereof projecting toward the first housing 210 beyond the front column 222 and the rear column 223 in a conveyance direction of the sheet conveyed on the double-sided conveyance path.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine using an electrophotographic system or an electrostatic recording system, or a multifunction machine having a plurality of these functions.

2. Description of the Related Art In recent years, in the field of commercial printing, where products output by image forming apparatuses are sold as products, image forming apparatuses with high quality and high productivity are required. In order to achieve high productivity, it is necessary to stably supply an appropriate amount of heat to the sheet, which requires a heat-fixing section with a large heat capacity, which increases the size of the fixing section. In addition, in order to handle a variety of deliverables, an image forming system equipped with a long two-sided transport path for the purpose of automatic two-sided printing (hereafter referred to as two-sided printing) of so-called long paper exceeding the standard size (up to 19 inches). devices are increasing. If the size of the image forming apparatus is increased in this way, the housing may become too large to be transported to the user's installation site. Therefore, the housing is divided into multiple parts. For example, it may be divided into a first housing in which an image forming section such as a developing section and a transfer section, a sheet cassette, and the like are mounted, and a second housing in which a fixing section, a sheet ejection section, a reversing section, and the like are mounted. .

On the other hand, one aspect of achieving a high-quality product is the relative positional accuracy (hereinafter referred to as front/back register accuracy) between the image on the front side of the sheet and the image on the back side when the sheet is double-sided printed. . In order to stabilize front-to-back registration accuracy, image forming apparatuses equipped with a skew correction unit (registration unit) that corrects the orientation of the sheet while conveying it with high precision just before transferring the image onto the sheet have become widespread. there is According to such an image forming apparatus, it is possible to achieve both high productivity and high print position accuracy of a product.

Here, when the housing is divided into a plurality of parts as described above, the conveying path from image formation on the front side to image formation on the back side becomes long, and when the sheet on which the image is to be formed on the back side reaches the skew correction unit, There is a risk that the skew will become excessive. Therefore, an image forming apparatus has been developed in which, when the skew correction unit described above is used as the first skew correction unit, a second skew correction unit is provided in the conveying path from image formation on the front surface to image formation on the back surface. (see Patent Document 1). In this image forming apparatus, the second skew correction unit provided in the second housing performs skew correction in the sheet conveying direction of the first housing, and the first skew correction unit provided in the first housing By performing the skew correction step by step, the input skew amount of the sheet is relaxed.

The second skew correction unit is provided in the second housing from the end portion on the side of the first housing to the central portion in the left-right direction. Specifically, for example, among the frames that constitute the second housing, it is attached to a frame that faces the first housing and whose longitudinal direction is the left-right direction.

JP 2021-187631 A

However, in the image forming apparatus described in Patent Document 1, the second skew correction unit includes a plurality of frames, positioning units for the first housing and the second housing, and the like, with respect to the sheet conveying direction of the first housing. , are arranged through many members. Therefore, there is a possibility that many component tolerances are accumulated from the second skew correction unit to the sheet conveying direction of the first housing. There is a possibility that skew correction cannot be performed with sufficient accuracy in the sheet conveying direction of one housing. As a result, even in the first skew correction unit, which conveys a sheet that has not been sufficiently skew-corrected, skew correction cannot be performed with sufficient accuracy, and there is a risk that the front-to-back register accuracy will be greater than the standard range in the field of commercial printing. There was a problem that there is

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having at least two housings, which can reduce the sheet skew amount when forming an image on the back surface of the sheet.

The image forming apparatus of the present invention includes an image forming section that forms an image on a sheet, a first conveying path along which the sheet conveyed to the image forming section is guided, and a sheet on which an image is formed by the image forming section. a reversing section for reversing the front and back; a second conveying path for guiding the sheet reversed by the reversing section to the first conveying path; a row correction unit, a second skew correction unit provided on the second conveying path for correcting skew of the sheet, and a first housing housing the image forming section and the first skew correction unit. and a second housing connected to the first housing and housing the reversing section and the second skew correcting unit, wherein the second housing faces the first housing. and a positioning portion provided on the frame portion and positioned with respect to the first housing, wherein the second skew correction unit conveys a sheet conveyed on the second conveying path. It is attached to the frame portion in a state in which at least a part thereof protrudes toward the first housing from the frame portion.

According to the present invention, in an image forming apparatus having at least two housings, it is possible to reduce the sheet skew amount during image formation on the back surface of the sheet.

1 is a cross-sectional view showing an image forming apparatus according to a first embodiment; FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the first embodiment; FIG. 3 is a perspective view showing frame structures of a first housing and a second housing according to the first embodiment; FIG. 8A and 8B are plan views showing the first unit according to the first embodiment, in which (a) is a state in which a sheet has been conveyed, (b) is a state in which the leading edge of the sheet hits a nip portion, and (c) is skew feeding; It is in a state of being conveyed after correction. 8 is a graph showing the relationship between the input skew amount and the output skew amount in the first unit according to the first embodiment; (a) is a plan view showing a first unit and a second unit according to a reference example, and (b) is a plan view showing a first unit and a second unit according to a first embodiment. FIG. 4 is a side view showing the frame structure of the second housing according to the first embodiment; 1 is a perspective view showing an image forming apparatus according to a first embodiment; FIG. (a) is the skew amount when the second unit is not provided, (b) is the skew amount when the second unit is provided in the reference example, and (c) is the skew amount when the second unit is provided in this embodiment. is a graph showing the amount of skew of each. It is a top view showing the 1st unit and the 2nd unit concerning a 2nd embodiment.

<First Embodiment>
A first embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 9. FIG. In this embodiment, as an example of the image forming apparatus 1, a tandem-type full-color printer that forms an image on a recording material using an electrophotographic method is described. The image forming apparatus 1 is not limited to a tandem type in which a plurality of image forming units are arranged side by side, and may be a rotary type in which the image forming units are arranged in a cylindrical shape. In addition, a direct transfer method in which a toner image is directly transferred from a photosensitive member to a sheet may be used instead of the intermediate transfer method in which the toner image is primarily transferred to the intermediate transfer member and then secondarily transferred to the sheet S, which is a recording material. Furthermore, it is not limited to being full color, it may be monochrome or monocolor, it may be an inkjet printer or a dye sublimation printer, and various applications such as printers, various printing machines, copiers, FAX, multifunction machines, etc. can be implemented in The recording material is the sheet S, which includes not only plain paper but also special paper such as coated paper, special-shaped recording materials such as envelopes and index paper, and plastic films and cloth for overhead projectors. Further, in this embodiment, a two-component developer in which a magnetic carrier and a non-magnetic toner are mixed is used. However, the developer is not limited to this, and a one-component developer may be used.

[Image forming apparatus]
The structure and operation of the image forming apparatus 1 of the present invention will be described. FIG. 1 is a cross-sectional view showing the structure of an image forming apparatus 1 according to this embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a first housing 210 and a second housing 220 connected to the first housing 210. As shown in FIG. In this embodiment, when the image forming apparatus 1 is installed as shown in FIG. 1, the front side is the front side and the back side is the rear side.

The first housing 210 includes a control board that accommodates each mechanism that constitutes the print engine section, an engine control section that controls each printing process (for example, paper feed processing, etc.) by each mechanism, and a printer controller. A storage unit (not shown) is built in. As a mechanism constituting the print engine unit, an electrostatic latent image is formed on the photosensitive drum 105 by laser beam scanning, the electrostatic latent image is visualized, and the visualized image is multiple-transferred onto the intermediate transfer belt 106. There is a transfer mechanism for further transferring the multi-transferred color image to the sheet S. In addition, as mechanisms constituting the print engine section, a fixing mechanism for fixing the toner image transferred to the sheet S, a sheet feeding mechanism for the sheet S, and a conveying mechanism for the sheet S are provided.

The first housing 210 accommodates the image forming section 2 that forms an image on a sheet. The image forming section 2 has a Y (yellow) station 120, an M (magenta) station 121, a C (cyan) station 122, a K (black) station 123, an intermediate transfer belt 106, a transfer roller 114, and the like. . Since the stations 120, 121, 122, and 123 have the same configuration except for their different colors, the Y station 120 will be described below as a representative.

The optical mechanism has a laser driver for turning on/off the laser beam emitted from the semiconductor laser 108 in accordance with the image data supplied from the image formation control unit 35 (see FIG. 2) in the laser scanner unit 107. ing. A laser beam emitted from a semiconductor laser 108 is swung in a scanning direction by a rotating polygonal mirror. Here, the laser light oscillated in the main scanning direction is guided to the photosensitive drum 105 via the reflecting mirror 109, and exposes the surface of the photosensitive drum 105 in the main scanning direction.

On the other hand, an electrostatic latent image that is charged by the primary charger 111 and formed on the photosensitive drum 105 by scanning exposure with laser light is developed into a toner image by toner supplied by a developer 112, which will be described later. A developed toner image on the photosensitive drum 105 is primarily transferred onto an intermediate transfer belt 106 to which a voltage having a reverse characteristic to that of the toner image is applied. When forming a color image, the stations 120 , 121 , 122 and 123 sequentially form respective colors onto the intermediate transfer belt 106 , thereby forming a full-color visible image on the intermediate transfer belt 106 .

Also, the sheet S fed from the sheet cassette 113 is conveyed through the conveying path 143 and reaches the first unit 10 . The conveying path 143 is an example of a first conveying path along which the sheet S is guided from the sheet cassette 113 through the transfer roller 114 to the fixing cooling section 110 and conveyed to the image forming section 2 . The first unit 10 is an example of a first skew correcting unit arranged in the first housing 210 and provided on the conveying path 143 to correct the skew of the sheet S, and is abbreviated as a first registration unit. is.

The visible image formed on the intermediate transfer belt 106 is brought into pressure contact with the intermediate transfer belt 106 and the transfer roller 114 against the sheet S whose tilt attitude and position have been corrected by the first unit 10 . A toner image is secondarily transferred onto the sheet S by applying a bias voltage having a characteristic opposite to that of the toner to the transfer roller 114 at the same time as the pressure contact. As described above, the image forming unit 2 includes the intermediate transfer belt 106, which is an example of an image bearing member on which a toner image is formed, and an example of a transfer unit that transfers the toner image formed on the intermediate transfer belt 106 to the sheet S. and a transfer roller 114 . Around the intermediate transfer belt 106, an image position detection sensor 115 for determining the print start position when transferring an image onto the sheet S, and a sheet edge timing sensor for measuring the entry timing of the sheet S into the transfer roller 114. A sensor 116 is arranged.

In the second housing 220, the fixation cooling section 110, which is enlarged in order to achieve high productivity, and a reversal conveying path corresponding to long sheets are arranged. The fixing cooling section 110 has a fixing device 150 and a cooling unit 160 for fixing the toner image transferred to the sheet S by heat and pressure. The fixing device 150 has a fixing roller 151 for applying heat to the sheet S, a pressure roller 152 for pressing the sheet S against the fixing roller 151, and a post-fixing sensor 153 for detecting completion of fixing. . The fixing roller 151 and the pressure roller 152 are hollow rollers, each having a heater inside to maintain a constant amount of heat, and are configured to convey the sheet S at the same time as they are driven to rotate. That is, the fixing device 150 is an example of a fixing unit that is housed in the second housing 220 and fixes the toner image transferred onto the sheet S by the transfer roller 114 .

The cooling unit 160 is located downstream of the fixing device 150 in the conveying path of the sheet S, lowers the temperature of the sheet S fixed by the fixing device 150, and supplies heat from the sheet to the image forming portion during double-sided printing. and reduce the amount of curl in the artifact. The cooling unit 160 transfers the heat of the sheet S to the rollers 161 and 162 by nipping the sheet S with a nip formed by the rollers 161 and 162, and the heat transferred to the rollers 161 and 162 by a cooling fan (not shown). is configured to dissipate heat.

In the case of single-sided printing, the sheet S conveyed from the fixing/cooling unit 110 is guided to the discharge path 139 by the switching member 132 and discharged to the downstream discharge tray 700 . On the other hand, in the case of double-sided printing, the sheet S conveyed from the fixing/cooling unit 110 is guided to the conveying path 133 by the switching member 132 , and the leading edge of the sheet S is detected by the reversing sensor 137 . After that, the sheet S performs a switchback operation in the reversing section 138, so that the leading and trailing ends and the front and back sides of the sheet S are switched. That is, the reversing section 138 reverses the sheet S on which the image is formed by the image forming section 2 .

The sheet S is conveyed on the double-sided conveying path 140, passes through the second unit 20, reaches the first housing 210, is conveyed on the double-sided conveying path 141, passes through the junction 142 with the conveying path 143, and is conveyed again. It is transported to the first unit 10 on path 143 . The two-sided conveying paths 140 and 141 are an example of a second conveying path along which the sheet S reversed by the reversing section 138 is guided to the conveying path 143 . The second unit 20 is an example of a second skew correction unit that is arranged in the second housing 220 and provided in the double-sided conveying path 140 to correct the skew of the sheet S. It is an abbreviation. The sheet S conveyed to the first unit 10 through the merging portion 142 is again subjected to correction of the tilted attitude and position in the first unit 10 . The sheet S on which the image on the back side has been transferred passes through the fixing device 150 and the cooling unit 160 in the same manner as the front side, so that the image is fixed and the sheet S is cooled. , is discharged to the discharge tray 700 .

[Control block]
FIG. 2 is a control block diagram showing the control section 30 of the image forming apparatus 1. As shown in FIG. The control section 30 has a CPU 31 , a memory 32 , an operation section 33 , an image formation control section 35 , a sheet conveyance control section 36 and a sensor control section 37 . The CPU 31 implements various processes performed by the image forming apparatus 1 by executing a predetermined control program or the like. The memory 32 is composed of, for example, RAM and ROM, and stores various programs and various data in a predetermined storage area. The operation unit 33 receives input of various information about the sheet S (for example, sheet size, basis weight of the sheet, surface properties of the sheet, etc.), execution or cancellation of the job, and the like. The CPU 31 can be connected to, for example, an external computer 34 connected via a network, and can receive various information about the sheet S, print jobs, and the like from the computer 34 .

The image forming control section 35 is connected to the image forming section 2, transmits an instruction signal to the image forming section 2, and controls the image forming operation. The sheet conveying control unit 36 is connected to the first pre-driving motor 15, the first driving motor 16, the reverse driving motor 136, the second pre-driving motor 25, the second driving motor 26, etc., and transmits instruction signals to these. do. Thereby, the conveying operation of the sheet S is controlled. The sensor control unit 37 is connected to the first sensor 13, the reversing sensor 137, the second sensor 23, etc., issues instructions to start and stop detection, and receives detection results from these sensors.

[First housing and second housing]
FIG. 3 is a schematic diagram showing the frame structure of the first housing 210 and the second housing 220. As shown in FIG. As shown in FIG. 3 , the first housing 210 has a front strut 212 and a rear strut 213 as part of the frame 211 . The front strut 212 and the rear strut 213 are an example of a frame portion facing the second housing 220 . In addition, the first housing 210 includes a front positioning portion 214 provided on the front support 212 and positioned with respect to the second housing 220, and a rear positioning portion provided on the rear support 213 and positioned with respect to the second housing 220. 215 and . The front positioning part 214 and the rear positioning part 215 are integrated with the front strut 212 and the rear strut 213 by screwing or welding, respectively.

The second housing 220 has a front strut 222 and a rear strut 223 as part of the frame 221 . The front strut 222 and the rear strut 223 are struts whose longitudinal direction is the vertical direction, and are an example of a frame portion facing the first housing 210 . The second housing 220 includes a front positioning portion 224 provided on the front support 222 and positioned with respect to the first housing 210, and a rear positioning portion provided on the rear support 223 and positioned with respect to the first housing 210. 225 and . The front positioning part 224 and the rear positioning part 225 are integrated with the front strut 222 and the rear strut 223 by screwing or welding, respectively. The frame 221 of the second housing 220 has, for example, lateral frames 226 and 227 that are fixed to the front strut 222 and the rear strut 223 and extend sideways.

The front positioning portion 214 and the front positioning portion 224 position the first housing 210 and the second housing 220 by, for example, engaging a pin portion and a hole portion provided with each other. Similarly, the rear positioning part 215 and the rear positioning part 225 position the first housing 210 and the second housing 220 by, for example, engaging a pin and a hole provided with each other.

[First unit]
The operation of the first unit 10 will be described with reference to FIGS. 4(a) to 4(c). 4A to 4C are top views of the behavior of the sheet S when it passes through the first unit 10, showing the attitude of the sheet S in three steps in time series. The first unit 10 includes a pre-registration roller pair 11 rotationally driven by a first pre-driving motor 15 (see FIG. 2) and a registration roller pair 12 rotationally driven by a first driving motor 16 (see FIG. 2). and a first sensor 13 .

First, the sheet S fed from the sheet cassette 113 is conveyed to the pre-registration roller pair 11 . Here, it is assumed that the conveyed sheet S rotates clockwise with respect to the conveying direction D1 and is skewed as shown in FIG. 4A. The controller 30 stops the registration roller pair 12 and drives the pre-registration roller pair 11 based on the detection result of the first sensor 13 . As a result, the leading edge of the conveyed sheet S abuts against the nip portion of the stopped registration roller pair 12 . Thereafter, the pre-registration roller pair 11 feeds the sheet S by the set feed amount, thereby forming a loop of a predetermined amount on the sheet S (see FIG. 4B). In this manner, when the skew correction of the sheet S is completed and the rotation of the registration roller pair 12 is started, the leading edge of the sheet S is positioned at the position of the registration roller pair 12 as shown in FIG. 4C. , and conveyed to the transfer roller 114 while maintaining a parallel state.

Here, the registration roller pair 12 needs to maintain parallelism with the transfer roller 114 with high precision. In the image forming apparatus 1, the first unit 10 and the transfer roller 114 are often divided unit by unit in consideration of usability such as workability of removing a sheet when a sheet is jammed. Since it is difficult to guarantee the parallelism with high accuracy when the parts are assembled and not adjusted, the parallelism is maintained with high accuracy by adjusting the inclination of the entire first unit 10 and assembling. Since the adjustment is made inside the first housing 210, a tool capable of measuring the parallelism of the transfer roller 114 and the registration roller pair 12 with high accuracy by optical means or measuring the meandering condition of the output image is required. By doing so, parallelism can be adjusted relatively easily.

However, the skew correction capability of the first unit 10 is also limited. In particular, when the input skew of the sheet S fed from the sheet cassette 113 is large, when the loop formation is completed in FIG. It makes a big difference. That is, as shown in FIG. 4(b), the front side is a region 3a with excessive loops, and the back side is a region 3b where no loops are formed and the pre-registration roller pair 11 is stretched. In proportion to the input skew amount of the sheet S, the difference in the pulling force between the excessively looped region 3a and the stretched region 3b increases. The tension of the sheet S due to the stretched region 3b overcomes the nip holding force of the registration roller pair 12 to cause slipping, and after the rotation of the registration roller pair 12 is started, the posture of the sheet S returns to its original position. There is a possibility that a phenomenon of squeezing may occur. This phenomenon is hereinafter referred to as the oblique return phenomenon.

In view of the skew return phenomenon that occurs in this way, FIG. is a graph showing the relationship between The sheet S here is an example of 300 g/m ² , which has been in great demand in the field of commercial printing in recent years. A sheet material having a thicker thickness and a higher rigidity tends to be more likely to slip in the roller nip conveying portion and less likely to form a loop. In the field of commercial printing, in order to be acceptable in terms of product quality, it is necessary to keep the skew amount variation within approximately ±0.3 mm. It can be said that it needs to be within 2.0 mm. In order to provide the image forming apparatus 1 with a reduced size, it is necessary to shorten the sheet conveying path and package it with a small cross section. As a result, the above-described skew correction capability is also reduced. Thus, the skew correction capability of the first unit 10 is determined based on the overall size specifications of the image forming apparatus 1 .

[Skew Correction for Reverse Side Printing]
FIGS. 6A and 6B schematically show how skew correction is performed when the sheet S is conveyed by the double-sided conveying paths 140 and 141 when an image is formed on the back surface of the sheet S. . L1 to L8 represent dimensions including the tolerance of each part.

In order to keep the skew correction capability within the allowable range, the input skew amount of the sheet S must be reduced. When the fixing and cooling unit 110 and the conveying path, which are compact but enlarged to improve productivity, are mounted, the housing is divided into a first housing 210 and a second housing 220 as shown in FIG. The transport path length that must be passed for automatic double-sided printing becomes longer. As the conveying path length becomes longer and the housing is divided into a plurality of parts, the accumulation of tolerance increases due to the intervening of many parts, and the input skew to the first unit 10 on the back side during automatic double-sided printing increases. There is a possibility that In order to solve such a problem, in the present embodiment, the second unit 20 is provided in the double-sided conveying paths 140 and 141 . The first unit 10 performs skew correction.

[Second unit]
The second unit 20 includes a pre-registration roller pair 21 rotationally driven by a second pre-driving motor 25 (see FIG. 2) and a registration roller pair 22 rotationally driven by a second driving motor 26 (see FIG. 2). and a second sensor 23 . The second unit 20 has a support case 27 (see FIG. 7) as an example of a support that rotatably supports the pre-registration roller pair 21 and the registration roller pair 22 . The registration roller pair 22 is an example of a conveying roller pair rotatably provided in the support case 27 .

The sheet S whose front and back sides have been reversed by the reversing section 138 (see FIG. 1) is conveyed to the pre-registration roller pair 21 via the double-sided conveying path 140 . The controller 30 stops the registration roller pair 22 and drives the pre-registration roller pair 21 based on the detection result of the second sensor 23 . As a result, the leading edge of the conveyed sheet S abuts against the nip portion of the stopped registration roller pair 22 . After that, the sheet S is fed by the pre-registration roller pair 21 by the set feed amount, thereby forming a loop of a predetermined amount on the sheet S. FIG. That is, the leading edge of the sheet S contacts the nip portion of the registration roller pair 22 whose rotation is stopped to form a loop, thereby correcting the skew of the sheet S. FIG. In this manner, when the skew correction of the sheet S is completed and the rotation of the registration roller pair 22 is started, the leading edge of the sheet S is kept parallel to the registration roller pair 22 and is double-sided. A conveying path 141 is conveyed.

Here, the parallelism of the first unit 10 is adjusted with high accuracy with respect to the transfer roller 114 . Therefore, the parallelism of the second unit 20 with respect to the transfer roller 114 is positioned with high accuracy, so that the input skew amount of the sheet S to the first unit 10 during printing on the back side can be greatly reduced. Become. That is, as shown in FIG. 6A, the dimension including the tolerance from the support portion on the rear side of the registration roller pair 12 to the transfer roller 114 is L3, and the dimension from the support portion on the front side of the registration roller pair 12 to the transfer roller 114 is L3. L4 is the dimension including the tolerance up to At this time, the parallelism of the first unit 10 to the transfer roller 114 is represented by (L3-L4), and the cumulative number of tolerances is the minimum necessary.

On the other hand, the transfer roller 114 is positioned, for example, on lateral frames 226 and 227 in the first housing 210 . Therefore, when the second unit 20 is positioned inside the second housing 220 via a plurality of members, the second unit 20 will have an inclination θ corresponding to the accumulated tolerance. That is, as shown in FIG. 6A, the dimension including the tolerance from the transfer roller 114 to the rear strut 223 is L1, and the dimension including the tolerance from the transfer roller 114 to the front strut 222 is L2. In addition, the dimension including the tolerance of the rear strut 223 is L5, the dimension including the tolerance of the front strut 222 is L6, the dimension including the tolerance of the lateral frame 227 is L7, and the dimension including the tolerance of the lateral frame 226 is L8. At this time, the parallelism of the second unit 20 to the transfer roller 114 is represented by {(L1+L5+L7)-(L2+L6+L8)}. For this reason, the tolerance cumulative number included in the inclination of the first unit 10 with respect to the transfer roller 114 in the first housing 210 is greater than the number, and as a result, the input skew amount of the sheet S during back side printing increases. There is a possibility that

Therefore, in this embodiment, the second unit 20 is directly fixed to the front strut 222 and the rear strut 223 of the second housing 220 facing the first housing 210 for positioning. As shown in FIG. 7 , the second unit 20 has a support case 27 , a mounting portion 28 projecting forward from the support case 27 , and a mounting portion 29 projecting rearward from the support case 27 . The attachment portion 28 is directly attached to the front strut 222 by screwing, for example, and the attachment portion 29 is directly attached to the rear strut 223 by screwing, for example. Here, direct attachment includes, for example, the case where the attachment portion 28 and the front strut 222 are in direct contact, as well as the case in which a fastening member such as a washer is sandwiched in substantial direct contact. .

Thus, the support case 27 is attached to the front strut 222 and the rear strut 223 by the mounting portions 28 and 29 . Thus, in this embodiment, the second unit 20 is directly positioned with respect to the positioning surface of the second housing 220 with the first housing 210 . That is, in the second housing 220, the second unit 20 is positioned on the plane P9-P10-P11-P12 (see FIG. 8).

A portion of the support case 27 on the first housing 210 side protrudes further toward the first housing 210 than the frame 221 of the second housing 220 (see FIG. 3). That is, in the conveying direction of the sheet S conveyed on the double-sided conveying path 140, the second unit 20 is arranged such that at least a part of the second unit 20 protrudes toward the first housing 210 from the front support 222 and the rear support 223. and attached to the rear strut 223 . That is, in the second housing 220, the second unit 20 is attached so as to protrude from the plane P9-P10-P11-P12 (see FIG. 8).

As a result, the parallelism of the second unit 20 with respect to the transfer roller 114 is represented by (L1-L2) shown in FIG. 6(b). Thus, according to the present embodiment, it is possible to arrange the second unit 20 with the minimum cumulative number of tolerances in the same manner as the first unit 10 in the first housing 210 .

The cumulative number of tolerances from transfer roller 114 to first housing 210 and second housing 220 will be described below. FIG. 8 is a layout bird's-eye view of the first housing 210, the second housing 220, and the second unit 20 in this embodiment. The first housing 210 has a frame structure composed of frame surfaces P1-P2-P3-P4 and frame surfaces P5-P6-P7-P8. supported and positioned by a surface; Therefore, on the surface P1-P4-P8-P5 arranged on the side facing the second housing 220, when the transfer roller 114 is used as a reference, the tolerance accumulated as the inclination tolerance is only one member. Next, in the second housing 220, the second unit 20 is positioned on the plane P9-P10-P11-P12. The surfaces P9-P10-P11-P12 are integrated by engaging with the surfaces P1-P4-P8-P5 of the first housing 210 when the image forming apparatus 1 is installed at the installation position. In other words, the second unit 20 is equivalent to being directly positioned on the surface P1-P4-P8-P5 of the first housing 210, and the cumulative tolerance for the transfer roller 114 is only one member. ) can be reduced to a minimum in terms of part manufacturing.

FIGS. 9A to 9C show the skew amount of input skew and the skew amount of output with respect to the number of printed pages when double-sided printing is performed. FIG. 9(a) shows a case in which the second unit 20 does not perform skew correction. It's closed. FIG. 9(b) shows the case where the second unit 20 is attached at the position shown in FIG. 6(a). In this case, since the tolerance accumulation is large, even if the skew amount itself is stable, the absolute value exceeds the allowable value of the first unit 10, and as a result, the skew amount of the product also exceeds the reference range. FIG. 9C shows the case of this embodiment. According to this embodiment, by minimizing the tolerance accumulation, it is possible to reduce the input skew amount to within the allowable value of the first unit 10. It becomes possible to stably fit within the reference range.

In addition, as shown in FIG. 1, the second unit 20 is provided in the double-sided conveying path 141 and the conveying path 143 so as to be separated from the first unit 10 by at least the length of the longest sheet that can be reversed by the reversing section 138 . It is As a result, it is possible to avoid the possibility of buckling caused by simultaneously conveying one sheet S in the first unit 10 and the second unit 20 . That is, when arranging the second unit 20 on the two-sided conveying paths 140 and 141, the most downstream portion of the two-sided conveying paths 140 and 141 should be arranged so that the sheet S passing through the two-sided conveying paths 140 and 141 is skewed. Good for suppression. However, in the case of the loop register, it is necessary to stop the sheet S once. There is a possibility that one sheet S may be sandwiched between the two. In this case, the sheet S may be buckled, so the second unit 20 is provided with a distance longer than the length of the longest sheet to be used from the first unit 10 .

As described above, according to the image forming apparatus 1 of the present embodiment, the second unit 20 is configured such that at least a portion of the second unit 20 protrudes toward the first housing 210 from the front support 222 and the rear support 223 . and attached to the rear strut 223 . As a result, the accumulation of tolerances of the second unit 20 with respect to the transfer roller 114 can be minimized, the amount of sheet skew during image formation on the back side of the sheet can be reduced, and the front-back registration accuracy can be kept within the standard range in the field of commercial printing. You can print on both sides of the paper.

According to the image forming apparatus 1 of the present embodiment, in the image forming apparatus 1 divided into a plurality of housings and performing one function, the inclination of the reference portion in the double-sided registration means is Allows for minimal configuration. By reducing input skew to the first unit 10 on the back side during automatic double-sided printing, it is possible to stabilize front-to-back register accuracy.

<Second embodiment>
A second embodiment of the present invention will now be described in detail with reference to FIG. The present embodiment differs from the first embodiment in that the second unit 320 has a shutter 324 against which the sheet S abuts. However, since other configurations are the same as those of the first embodiment, the same reference numerals are used and detailed description thereof is omitted.

In the first embodiment, a registration method is adopted in which the skew of the sheet S is reduced by abutting the sheet S against the registration roller pair 22 stopped in the second unit 20 . However, the present invention is not limited to this, and a similar effect can be obtained by adopting a shutter registration method in which the leading edge of the sheet S abuts against the shutter 324 to reduce the skew of the sheet S, as shown in FIG.

The second unit 320 has a pre-registration roller pair 321 , a registration roller pair 322 , a second sensor 323 and a shutter 324 . In this shutter registration method, a shutter 324 is additionally installed immediately before the registration roller pair 22 of the second unit 20 of the first embodiment. structure. The tilt of the leading edge of the sheet S is abutted against the shutter 324 while the pre-registration roller pair 321 feeds the sheet S, thereby correcting the skew. After the loop is formed in the sheet S by feeding a set amount by the pre-registration roller pair 321, the shutter 324 is separated from the double-sided conveying path 140 by a driving source such as a motor M. Almost at the same time, the leading edge of the sheet S is nipped by the registration roller pair 322 and conveyed downstream.

That is, the shutter 324 can move between a regulating position where the leading edge of the sheet S conveyed toward the second unit 320 abuts to regulate the conveyance of the sheet S, and a permitting position where the conveyance of the sheet S is permitted. It is an example of a regulating member. The motor M is an example of a drive mechanism that moves the shutter 324 between the restricted position and the permitted position. The skew of the sheet S is corrected by forming a loop when the leading edge of the sheet S abuts against the shutter 324 at the regulating position. The shutter is biased by a spring or the like from the downstream side to the upstream side in the sheet conveying direction. may be moved to

As described above, according to the present embodiment, since the shutter 324 is directly positioned on the second unit 320, the tolerance accumulation amount can be configured in the same manner as in the first embodiment. Therefore, it is possible to minimize the accumulation of tolerances from the transfer roller 114 of the first housing 210, so that the amount of skew of the product can be stably kept within the standard range in the field of commercial printing. Become.

In the first and second embodiments described above, the image forming apparatus 1 has two housings, but is not limited to this, and may have three or more housings. For example, the present invention can be applied even when a housing having a sheet processing function is provided downstream of the second housing 220 .

REFERENCE SIGNS LIST 1 image forming apparatus 2 image forming section 10 first unit (first skew correcting unit) 20, 320 second unit (second skew correcting unit) 22 registration roller pair (conveyance Roller pair), 27 Support case (support) 106 Intermediate transfer belt (image carrier) 114 Transfer roller (transfer unit) 138 Reversing unit 140, 141 Double-sided conveying path (second conveying path ), 143 Conveying path (first conveying path), 150 Fixing device (fixing section), 210 First casing, 220 Second casing, 222 Front strut (frame part, strut), 223 Rear Column (frame portion, column) 224 Front positioning portion 225 Rear positioning portion 324 Shutter (regulating member) M Motor (driving mechanism) S Seat

Claims (6)

an image forming unit that forms an image on a sheet;
a first transport path along which a sheet transported to the image forming unit is guided;
a reversing unit for reversing the sheet on which an image is formed by the image forming unit;
a second transport path along which the sheet reversed by the reversing unit is guided to the first transport path;
a first skew correction unit provided in the first conveying path for correcting skew of the sheet;
a second skew correction unit provided on the second conveying path for correcting skew of the sheet;
a first housing that houses the image forming section and the first skew correction unit;
a second housing connected to the first housing and housing the reversing section and the second skew correcting unit;
The second housing has a frame portion facing the first housing, and a positioning portion provided in the frame portion and positioned with respect to the first housing,
The second skew correction unit is attached to the frame portion in a state in which at least a portion of the second skew correction unit protrudes toward the first casing from the frame portion in the conveying direction of the sheet conveyed on the second conveying path. is being
An image forming apparatus characterized by: The frame portion is a support column having a vertical direction as a longitudinal direction,
2. The image forming apparatus according to claim 1, wherein: The second skew correction unit is provided in the second conveying path and the first conveying path so as to be separated from the first skew correcting unit by at least the length of the longest sheet that can be reversed by the reversing section. is being
3. The image forming apparatus according to claim 1, wherein: The image forming unit has an image carrier on which a toner image is formed, and a transfer unit for transferring the toner image formed on the image carrier to a sheet,
a fixing unit that is housed in the second housing and fixes the toner image transferred onto the sheet in the transfer unit;
4. The image forming apparatus according to claim 1, wherein: The second skew correction unit includes:
a support attached to the frame portion;
a conveying roller pair rotatably provided on the support,
The leading edge of the sheet abuts against the nip portion of the conveying roller pair that has stopped rotating to form a loop, thereby correcting the skew of the sheet.
5. The image forming apparatus according to claim 1, wherein: The second skew correction unit includes:
a regulating member movable between a regulating position where the leading edge of the sheet conveyed toward the second skew correction unit abuts and regulating conveyance of the sheet, and a permitting position where conveyance of the sheet is permitted;
a driving mechanism for moving the regulating member between the regulating position and the allowable position;
The leading edge of the sheet abuts against the regulating member at the regulating position to form a loop, thereby correcting the skew of the sheet.
5. The image forming apparatus according to claim 1, wherein:

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