JP5168068B2 - Reversed duplex unit and image forming apparatus - Google Patents

Description

  The present invention relates to a reversing duplex unit in an image forming apparatus such as a copying machine, a printer, or a facsimile.

Japanese Patent Laying-Open No. 2003-212412 JP 2003-2503 A

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a complex machine thereof, a recording medium (hereinafter referred to as a sheet) on which an image is formed in an image forming unit for double-sided recording or for arranging printed materials in page order. A device having a duplex reversing unit (also referred to as a reversing duplex unit or a duplex unit or a reversing unit) for reversing the front and back and discharging or refeeding the image forming unit is known.

  As the double-side reversing unit, there is a unit provided with a reversing roller that can change the rotation direction in order to reverse the paper conveyance direction and convey it in the reverse direction. With the recent increase in production of image forming apparatuses, the paper conveyance speed has been increased and the paper interval has been shortened. In particular, in order to reverse long paper such as A3, the paper to be fed into the reverse roller and the reverse roller When the paper unloaded from the sheet is being conveyed by the carry-in roller and the carry-out roller, respectively, the nip of the reversing roller is released at one end so that the reversing roller unit can pass through.

  As a condition for releasing the nip of the reversing roller, a plurality of paper detecting means (for example, optical sensors) capable of detecting the presence or absence of paper are arranged near the reversing roller, the carry-in roller, and the carry-out roller, and the paper position is detected by them. In many cases, the timing is measured and whether or not the nip is released is set in advance according to the paper size and the conveyance path of the duplex reversing unit. However, of course, it is desirable not to release the nip of the reverse roller as much as possible in terms of paper conveyance. For example, with thick paper, the nip release causes insufficient paper conveyance force, which causes problems such as jams and skews. There are concerns.

  Regarding the nip release of the reversing roller, for example, Patent Document 1 discloses that control is performed using a plurality of paper detection sensors, but the control is complicated due to a plurality of information (information from a plurality of paper sensors). There is a problem of becoming.

Further, in Patent Document 2, since the control is changed depending on the sheet size, there is a problem in that the nip may be released even when it is not necessary as the state of the reversal unit.
In addition, the duplex reversing unit often has a small-curvature conveyance path for refeeding the reversed paper to the image forming unit. For example, if thin paper is transported with the same transport force as thick paper, there is a risk of damage to the paper due to the excessive nip pressure of the transport roller. Conversely, transporting thick paper with the same transport force as thin paper It becomes insufficient. That is, although it is necessary to carry with the conveyance force suitable for every paper type, there exists a problem that it is not solved in the conventional apparatus.

  The present invention solves the above-described problems in the conventional image forming apparatus, simplifies the reversing operation and reduces the control load, improves the paper transport performance in the reversing unit, and enables proper paper transport regardless of the paper type. It is an object of the present invention to provide a reversing duplex unit and an image forming apparatus that can be performed.

  According to the present invention, the above-described problems are a carry-in path through which paper is carried in, a reverse conveyance path that reverses the paper carried from the carry-in path, and a paper discharge conveyance path that discharges the paper carried out from the reverse conveyance path. And a refeeding conveyance path for refeeding the paper carried out from the reversal conveyance path to the image forming unit of the image forming apparatus, and a reversing duplex unit for discharging or refeeding the reversed paper, A reversing roller disposed in the reversing conveyance path and capable of rotating in the forward and reverse directions is provided so as to be able to release a roller nip, and a first sheet detecting unit capable of detecting the presence or absence of a sheet is disposed in the carry-in path, and A second sheet detecting unit capable of detecting the presence or absence of the sheet and the number of sheets is disposed in the vicinity of the upstream side of the reversing roller in the paper carry-in direction of the sheet, and based on the detection information of the first sheet detecting unit, Control rotation Together, it is solved by controlling the release or non-release the nip of the reverse roller based on the detection information of the second paper detecting means.

Further, it is preferable that the nip of the reversing roller is released when the second sheet detecting unit detects two sheets.
The reversing roller is preferably provided so that the nip pressure can be adjusted.

Further, it is preferable that the first paper detection means is provided so as to be able to detect the paper type, and the nip pressure of the reverse roller is adjusted according to the paper type detected by the detection means.
Further, it is preferable to increase the nip pressure of the reversing roller when the paper type is the thickness of the paper and the detected paper is thick paper, and to decrease the nip pressure of the reversing roller when the detected paper is thin paper.

  Further, the nip pressure of the reversing roller when the paper after reversing in the reversing conveyance path is sent to the refeed conveyance path is larger than the nip pressure when the reversing paper is sent to the paper discharge conveyance path. It is preferable to adjust to.

Moreover, it is preferable that the user can set the nip pressure of the reverse roller.
In addition, a third paper detection unit capable of detecting the presence or absence of paper is disposed in the paper discharge conveyance path, and based on the detection information of the second paper detection unit and the detection information of the third paper detection unit Preferably, the nip of the reversing roller is controlled to be released or not released.

Further, it is preferable that the nip of the reversing roller is released when the second sheet detecting unit detects two sheets and the third sheet detecting unit detects the presence of the sheet.
An inversion roller disposed in the carry-in path for carrying the paper; and an exit roller for sending the paper reversed by the reversing roller to the paper discharge conveyance path or the refeed conveyance path; It is preferable that the number of rotations of each of the entrance roller and the exit roller can be controlled.

  Further, when the second sheet detecting unit detects two sheets and the third sheet detecting unit detects no sheet, the preceding sheet unloading speed is increased or the succeeding sheet unloading speed is decreased. Thus, it is preferable to control the rotation speed of each roller.

  In the case where the second sheet detecting unit detects two sheets and releases the nip of the reversing roller, it is preferable to control the rotation direction of the reversing roller based on the sheet length of the preceding sheet.

  In addition, an entrance roller for carrying paper into the carry-in path is provided, and a paper length is calculated based on detection information when the first paper detection means detects the paper and the number of rotations of the entrance roller per unit time. It is preferable.

In addition, it is preferable that the rotation direction of the reverse roller is switched from the carry-out side to the carry-in side when the rear end of the preceding paper passes through the nip of the reverse roller after the reverse of the preceding paper.
An inlet roller disposed in the carry-in path for carrying the paper; and an outlet roller for feeding the paper reversed by the reverse roller to the paper discharge transport path or the re-feed transport path. The carry-out speed that is the carry speed at the time of carrying out the paper by the exit roller is provided so as to be changeable, and the carry-out speed is set higher than the carry-in speed that is the carry speed by the entrance roller, It is preferable to change the carry-out speed depending on whether the paper discharge conveyance path or the refeed paper conveyance path.

  Further, the carry-out speed when the reversed paper conveyance path is the paper discharge conveyance path is set to be higher than the carry-out speed when the reversed paper conveyance path is the re-feed conveyance path. And preferred.

Further, it is preferable that the first paper detection means is provided so as to be able to detect the paper thickness, and the carry-out speed is changed according to the paper thickness detected by the first paper detection means.
Further, according to the present invention, the above problem is solved by an image forming apparatus comprising the reversing duplex unit according to any one of claims 1 to 18.

  According to the reversing duplex unit and the image forming apparatus of the present invention, the rotation of the reversing roller is controlled based on the detection information of the first paper detecting means, and the reversing roller of the reversing roller is controlled based on the detection information of the second paper detecting means. Since the nip is controlled to be released or not released, it is possible to simplify the paper reversing operation and reduce the control load, improve the paper conveying performance at the reversing unit, and perform appropriate paper conveying regardless of the paper type.

  According to the configuration of the second aspect, since the nip of the reversing roller is released when the second paper detecting unit detects two sheets, only one sheet is obtained by releasing the nip of the reversing roller only when necessary. In this case, it is possible to avoid nip release and prevent paper conveyance failure and paper jam.

  According to the configuration of the third aspect, the reversing roller is provided so that the nip pressure can be adjusted, so that the conveying force of the reversing roller can be adjusted, and the sheet can be conveyed with an appropriate conveying force without applying an excessive load to the sheet. It becomes possible to carry.

  According to the configuration of the fourth aspect, the first paper detection means is provided so as to detect the paper type, and the nip pressure of the reverse roller is adjusted according to the paper type detected by the detection means. The conveying force of the reversing roller can be adjusted according to the type of paper to be printed.

  According to the configuration of claim 5, when the paper type detected by the first paper detection means is the paper thickness, when the detected paper is a thick paper, the nip pressure of the reverse roller is increased, and when the detected paper is a thin paper Since the nip pressure of the reversing roller is reduced, it is possible to prevent the conveyance failure of the thick paper and to suppress the adverse effect on the paper and the image.

  According to the configuration of the sixth aspect, the nip pressure of the reversing roller when the paper after reversing in the reversing conveyance path is sent to the refeed conveyance path is larger than the nip pressure when the reversing paper is sent to the paper discharge conveyance path. Therefore, even when a path with a small curvature is provided, the paper can be reliably fed again.

  With the configuration of the seventh aspect, since the user can set the nip pressure of the reverse roller, the conveyance force of the reverse roller can be selected as desired by the user. In addition, the impossibility of control can be reduced.

  According to the configuration of the eighth aspect, the third sheet detecting unit capable of detecting the presence or absence of the sheet is arranged in the sheet discharge conveyance path, and the detection information of the second sheet detecting unit and the detection information of the third sheet detecting unit are used. Based on this, since the nip of the reverse roller is controlled to be released or not released, it is possible to further ensure the passing of the paper at the reverse roller portion and further improve the paper transportability in the reverse duplex unit.

  According to the configuration of the ninth aspect, when the second sheet detecting unit detects two sheets and the third sheet detecting unit detects the presence of the sheet, the nip of the reversing roller is released. Even if there is a sheet passing, it is possible to reliably carry out the preceding sheet.

  According to the structure of claim 10, the reversing roller includes an entrance roller that is disposed in the carry-in path and carries the paper, and an exit roller that feeds the paper that has been reversed by the reversing roller to the discharge conveyance path or the refeed conveyance path. Since the number of rotations of each of the entrance roller and the exit roller can be controlled, the nip can be reliably released in a state where the preceding sheet is conveyed by the exit roller when the sheet is rubbed in the reverse roller section.

  According to the configuration of the eleventh aspect, when the second sheet detecting unit detects two sheets and the third sheet detecting unit detects no sheet, the preceding sheet unloading speed is increased or the succeeding sheet unloading speed is detected. Since the number of rotations of each roller is controlled so as to slow down the sheet, it is possible to ensure the sheet rubbing operation at the reverse roller portion.

  According to the structure of the twelfth aspect, when the second sheet detecting unit detects two sheets and releases the nip of the reversing roller, the rotation direction of the reversing roller is controlled based on the sheet length of the preceding sheet. It is possible to perform the passing only when the operation is necessary, and reliably prevent the paper from being stained or scratched or causing image degradation.

  According to the configuration of the thirteenth aspect, the entrance roller for carrying the paper into the carry-in path is provided, and the paper length is determined based on the detection information when the paper is detected by the first paper detection means and the number of rotations of the entrance roller per unit time. Therefore, the rotation direction of the reversing roller 121 can be switched without knowing in advance the size of the paper carried into the reversing duplex unit.

  According to the configuration of claim 14, after the preceding sheet is reversed, the rotation direction of the reversing roller is switched from the carry-out side to the carry-in side when the trailing edge of the preceding sheet passes through the nip of the reversing roller. The reversing roller is not rubbed, and it is possible to prevent the paper from being stained, scratched, or deteriorated.

According to the configuration of the fifteenth aspect, it is possible to reduce the risk of passing at the time of paper reversal as much as possible and to perform good reversal operation.
According to the configuration of the sixteenth aspect, even when the paper is discharged to the paper refeeding conveyance path having a large curvature (the radius of curvature is small) in order to refeed the paper, the paper is not damaged. , Paper slip can be prevented.

According to the configuration of the seventeenth aspect, since the carry-out speed is changed according to the sheet thickness, an appropriate conveying force corresponding to the sheet thickness can be obtained.
According to the configuration of the eighteenth aspect, an appropriate conveying force can be obtained even for thick paper that requires a high conveying force, and the sheet can be reliably conveyed while preventing slippage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is configured as a copying apparatus, and an image forming unit 1 is disposed almost at the center of the apparatus main body, and a paper feeding unit 2 is disposed below the image forming unit 1. The paper feed unit 2 includes a plurality of paper feed stages, and each paper feed stage includes a paper feed tray 21. A reading unit 3 for reading a document is disposed above the image forming unit 1. A paper discharge storage unit 4 is formed on the left side of the image forming unit 1, and a sheet on which an image is formed is discharged and stored.

  An image forming unit 10 is disposed in the image forming unit 1, and around a photosensitive drum 11 that is an image carrier, a charger 12 that performs a charging process on the surface of the photosensitive member, and an electrostatic latent image formed on the surface of the photosensitive member. A developing device 13 that visualizes an image, a cleaning device 14 that removes and collects toner remaining on the photoreceptor, and the like are disposed. Above the image forming unit 10, an exposure device 5 for irradiating image information onto the surface of the photosensitive member with laser light is disposed. A transfer device 15 for transferring a toner image formed on the photoconductor onto a sheet is disposed under the photoconductor drum 11. At the side of the transfer device 15, there is disposed a fixing device 6 for fixing the toner image by applying heat and pressure to the toner transferred onto the paper through a pair of rollers. The paper that has passed through the fixing device 6 is discharged to the paper discharge storage unit 4 by the paper discharge roller 17 of the paper discharge unit 16.

  At the time of duplex printing, the sheet after fixing is branched at the branch portion of the paper discharge unit 16 and conveyed to the reverse duplex unit 100 via the relay roller 18 where the sheet is reversed and the intermediate roller 20 is turned on. Then, the registration roller 8 corrects the skew of the sheet, and the rear surface image forming operation is performed.

  In the paper feed unit 2, unused paper is stored in the paper feed tray 21, and the bottom plate 24 that is rotatably supported raises the uppermost paper to a position where the pickup roller 25 can abut. The uppermost sheet is fed out from the sheet feed tray 21 by the rotation of the sheet feed roller 26 and is transported from the transport roller 27 to the registration roller 8 via the intermediate roller 20. The registration roller 8 temporarily stops the conveyance of the sheet, corrects the skew of the sheet, and starts rotating at a timing so that the positional relationship between the toner image on the surface of the photosensitive drum 11 and the leading end of the sheet is a predetermined position. The

  In the reading unit 3, in order to read and scan a document placed on the contact glass 31, the reading traveling bodies 32 and 33 including a document illumination light source and a mirror reciprocate. Image information scanned by the reading traveling bodies 32 and 33 is read as an image signal into a CCD 35 installed behind the lens 34. The read image signal is digitized and image processed by an image processing unit (not shown). In the image forming unit 1, an electrostatic latent image is formed on the surface of the photosensitive drum 11 by light emission of a laser diode (not shown) in the exposure device 5 based on the image signal processed by the image processing unit. The optical signal from the LD reaches the photosensitive member via a known polygon mirror or lens. An automatic document feeder 7 for automatically feeding a document is attached above the reading unit 3.

  The image forming apparatus of the present example exchanges image information of an original with a remote place by a control unit (not shown) in addition to a function as a so-called digital copier, which reads and digitizes an original and copies it onto a sheet as described above. This is a multifunction image forming apparatus having a facsimile function and a so-called printer function for printing image information handled by a computer on a sheet. The setting as the copying machine is performed by an operation unit (not shown) that can be arbitrarily set by the operator. In addition, all sheets are discharged to the discharge storage unit 4 regardless of which function is used to form an image.

  By the way, the sheet on which the toner image is transferred from the photosensitive drum 11 is discharged to the paper discharge storage unit 4 after the toner image is fixed by the fixing device 6, but is discharged to the paper discharge storage unit 4 as it is from the fixing device 6. Since the image surface is on the upper side, when an image is formed (single-sided printing) on a printed matter of a plurality of pages, it is stacked face-up in the paper discharge storage unit 4. Therefore, in the image forming apparatus of this example, the front and back sides of the paper can be reversed using the reversing duplex unit 100 during single-sided printing. That is, the paper after fixing is sent to the reverse duplex unit 100 via the relay roller 18 to reverse the paper, and is discharged from the paper discharge roller 17 to the paper discharge storage unit 4 via the reverse paper discharge roller 19. In this case, the paper stacked in the paper discharge storage unit 4 is in a state where the image surface is the bottom surface, and even if the processing order of originals handled by copying, printers, and facsimiles is started from one page and printed, When taken out from the storage unit 4, the first page is at the top, and is freed from work such as aligning the pages anew.

  Next, the reverse double-sided unit, which is a feature of the present invention, will be described with reference to four examples.

[First embodiment]
As shown in FIG. 2, the reversing duplex unit 100 includes an inlet transport path 110, a reverse transport path 120, a discharge transport path 130, and a refeed transport path as a paper transport path (transport path) guided by a guide plate or the like. 140, and the boundary between the entrance conveyance path 110 and the reverse conveyance path 120 is a reverse branching section 150. An entrance roller 111 is disposed in the entrance transport path 110, a reverse roller 121 is disposed in the reversal transport path 120, and re-feed transport rollers 141 to 144 are disposed in the re-feed transport path 140. A reversing exit roller 131 is disposed at a portion from the reversing branching unit 150 toward the discharge conveyance path 130 and the refeed conveyance path 140. Each of these rollers is configured as a roller pair and is rotationally driven through a drive source and a drive path (not shown). The entrance roller 111 and the re-feed conveyance rollers 141 to 144 are driven to rotate counterclockwise in the drawing. Further, the reverse exit roller 131 is driven to rotate clockwise in the drawing. The reversing roller 121 can rotate both counterclockwise in the figure and clockwise in the figure, that is, both forward and reverse.

  Further, a first paper detection unit 112 is disposed on the upstream side of the entrance roller 111 in the entrance transport path 110. In addition, a second paper detection unit 122 is disposed in the reversal branching unit 150 that is an entrance portion of the reversal conveyance path 120. The paper detection means 112 and 122 are paper detection means capable of detecting the presence / absence of paper and the number of paper, and are configured as, for example, an optical sensor including a light emitting part and a light receiving part.

  Further, a reversal switching claw 160 is disposed in the reversing branch unit 150, and a branch switching claw 170 is disposed in a branching portion between the discharge conveyance path 130 and the refeed conveyance path 140. The reversing switching claw 160 and the branch switching claw 170 are pivotally supported so as to be swingable, and are respectively driven by a driving source (not shown) such as a solenoid, so that switching between a position indicated by a solid line and a position indicated by a broken line is possible. ing.

  Now, the paper after fixing is branched at the branch portion of the paper discharge unit 16 and is fed into the reversing duplex unit 100 via the relay roller 18 as indicated by an arrow A in FIG. The sheet is first transported along the entrance transport path 110 by the entrance roller 111. At this time, the reverse switching claw 160 is held at a position indicated by a solid line in FIG. 3, and the reversing roller 121 is driven to rotate counterclockwise in the drawing, whereby the paper is fed to the reverse conveying path 120 (switchback conveying path). ). When the rear end of the sheet is detected by the second sheet detecting means 122, the reverse roller 121 is rotated reversely (driven clockwise in the figure), and the reverse switching claw 160 is switched to the position indicated by the broken line. As a result, the sheet is conveyed from the reverse conveyance path 120 to the reverse exit roller 131 via the reverse branching unit 150.

  The reversing outlet roller 131 is driven to rotate clockwise in the figure, and the sheet is reversed by setting the branch switching claw 170 to the position shown in FIG. It is unloaded from the duplex unit 100 (arrow B). In this case, as described in FIG. 1, the sheet is discharged from the discharge roller 17 to the discharge storage unit 4 via the reverse discharge roller 19.

  When duplex printing is performed, the branch switching claw 170 is switched to the position shown in FIG. 4 in order to transport the sheet from the reverse branching unit 150 to the refeed conveyance path 140. As a result, the reversed paper is sent to the refeed conveyance path 140, conveyed by the refeed conveyance rollers 141 to 144 that are driven to rotate counterclockwise in the drawing, and discharged from the reverse duplex unit 100 to the side. (Arrow C). Thereafter, as described with reference to FIG. 1, the sheet is fed again to the registration roller 8 via the intermediate roller 20.

  As shown in FIG. 5, the reverse roller 121 includes a reverse drive roller 121a and a reverse driven roller 121b. The reverse driven roller 121b can be separated from the reverse drive roller 121a as indicated by a broken line in the figure. The reversing driven roller 121b is separated from the reversing driving roller 121a by driving means such as a solenoid (not shown) so that the nip of the reversing roller 121 can be released. Therefore, a so-called passing occurs in which the carry-in paper (paper carried into the reverse double-side unit 100) and the carry-out paper (paper carried out (discharged or re-feed)) from the reverse double-side unit 100 are overlapped by the reverse roller 121. Even in this case, the paper can be reversed.

  A reversing operation in the reversing duplex unit 100 will be specifically described with reference to FIGS. 6 shows the operation when the reversing roller 121 does not release the nip, that is, when there is no difference in rubbing, and FIG. 7 shows the operation when the reversing roller 121 releases the nip, that is, when there is a difference in rubbing. FIGS. 6 and 7 show specific states at predetermined time points of paper conveyance in the reversing duplex unit 100, and FIG. 6B shows the rotation direction of the reversing roller 121 at each time point and first paper detection. The sheet detection state of the means 112 and the second sheet detection means 122, the nip release state of the reversing roller 121, etc. are shown as a chart in FIG.

First, a description will be given of the case of no friction in FIG.
The first sheet that passed through the first sheet detection unit 112 and the second sheet detection unit 122 and was carried into the reverse conveyance path 120 was conveyed by a certain distance after the trailing end of the sheet was removed from the first sheet detection unit 112. Later, the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side, and at the same time, the reverse switching claw 160 is switched to guide in the carry-out direction. Note that the first paper detection unit 112 detects the presence or absence of the first paper and also detects paper information.

  After that, the trailing edge of the first sheet that has been unloaded is removed from the second sheet detecting unit 122, and when the second sheet detecting unit 122 detects that there is no sheet, the rotation direction of the reverse roller 121 is switched from the unloading side to the loading side. The eye sheet is carried into the reverse conveyance path 120. This operation is repeated.

In this case, although the sheet information of the sheet is detected by the detecting unit 112, the sheet is not rubbed by the detecting unit 122, so that the nip release of the reversing roller 121 is not performed.
The details of the operation at each time point will be described with reference to the drawings. When the first sheet P1 is guided to the reversing duplex unit 100, the sheet information is detected when the leading edge of the sheet reaches the first sheet detecting means 112. Start (1). Then, the leading edge of the paper reaches the second paper detection means 122 (2). Further, when the trailing edge of the first sheet passes through the first sheet detecting means 112, the detection of the sheet information is finished (3). When the sheet is conveyed by a predetermined distance after the trailing edge of the sheet passes through the first sheet detecting means 112, the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side. At the same time, the reverse switching claw 160 is switched (the position indicated by the broken line in FIG. 2), and after the paper is conveyed by a certain distance, it is returned to the original position (the position indicated by the solid line in FIG. 2) (4). Then, the second sheet P2 is guided to the reversing duplex unit 100, and the leading end of the sheet reaches the first sheet detecting means 112 (5). On the other hand, the rotation direction of the reverse roller 121 is switched from the carry-out side to the carry-in side when the rear end of the first sheet P1 passes through the second sheet detection unit 122 and the second sheet detection unit 122 detects the absence of sheet (6). )

Next, a description will be given when there is a difference in rubbing in FIG.
The first sheet that has passed through the first sheet detection unit 112 and the second sheet detection unit 122 and is carried into the reverse conveyance path 120 is conveyed by a certain distance after the trailing end of the sheet is removed from the first sheet detection unit 112. Later, the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side, and at the same time, the reverse switching claw 160 is switched to guide the first sheet in the carry-out direction. The first paper detection unit 112 detects the presence of paper and also detects paper information.

  Thereafter, the first sheet is carried out, but the leading edge of the second sheet reaches the second sheet detecting means 122 with the trailing edge of the first sheet remaining in the second sheet detecting means 122 as shown in (6). In this case, a difference in rubbing occurs in the reversing roller 121, so that the nip of the reversing roller 121 is released. At the same time, the rotation direction of the reversing roller 121 is switched from the carry-out side to the carry-in side. However, since the nip is released, the discharge of the first sheet is not affected.

  Then, when the trailing edge of the first sheet passes through the second sheet detecting means 122, the nip of the reversing roller 121 is returned (release → contact), and the second sheet is conveyed by the reversing roller 121. This operation is repeated.

  Specifically, as shown in FIG. 7, when the first sheet P1 is guided to the reversing duplex unit 100, detection of sheet information is started when the leading end of the sheet reaches the first sheet detecting means 112. (1) Then, the leading edge of the paper reaches the second paper detection means 122 (2). Further, when the trailing edge of the first sheet passes through the first sheet detecting means 112, the detection of the sheet information is finished (3). When the sheet is conveyed by a predetermined distance after the trailing edge of the sheet passes through the first sheet detecting means 112, the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side. At the same time, the reverse switching claw 160 is switched (the position indicated by the broken line in FIG. 2), and after the paper is conveyed by a certain distance, it is returned to the original position (the position indicated by the solid line in FIG. 2) (4). Then, the second sheet P2 is guided to the reversing duplex unit 100, and the leading end of the sheet reaches the first sheet detecting means 112 (5). When the leading edge of the second sheet reaches the second sheet detecting unit 122 and the second sheet detecting unit 122 detects two sheets, the nip of the reversing roller 121 is released (6). Then, the rear end of the first sheet passes through the second sheet detection unit 122, and the nip of the reverse roller 121 is returned when the second sheet detection unit 122 detects one sheet (7).

  As described above, it is possible to perform a reversing operation including the presence / absence of paper passing in the reversing unit based on the paper presence / absence information and the number of papers information detected by the first paper detection unit 112 and the second paper detection unit 122. In such a case, the nip of the reversing roller 121 is released so as to perform the passing only. Therefore, the reversing operation is simplified, the control load is reduced, and the passing is not performed more than necessary. Although the above has specifically described the case of reverse paper discharge printing, the same applies to double-sided printing as shown in FIG. Further, the first paper detection means 112 and the second paper detection means 122 capable of detecting the presence / absence of paper, the number of paper sheets, and paper information are separated into a light emitting side and a light receiving side as shown in the figure, and the paper is determined depending on the amount of light received on the light receiving side It may be a type that obtains presence / absence, number of sheets, and sheet information (for example, information on thin paper, plain paper, thick paper, etc.), may use ultrasonic waves, or may be different. Further, a third paper detection means 132 (to be described later) can detect the presence or absence of paper, and may be an optical type or a different type.

  Here, to summarize the features of the first embodiment, the second sheet detecting means 122 capable of detecting the number of sheets immediately before the reversing roller 121 (immediately upstream when the sheet is carried in) is provided. As the control of the reversing roller 121, when the second sheet detecting means 122 detects one sheet, the nip of the reversing roller 121 is maintained in contact. When the second sheet detection unit 122 detects two sheets, the nip of the reversing roller 121 is released. When the second sheet detecting unit 122 detects one sheet after detecting two sheets, the nip of the reversing roller 121 is brought into contact. With this feature, the nip of the reversing roller 121 can be released only when there are two sheets in the reversing duplex unit. That is, it is possible to prevent the nip of the reversing roller 121 from being released when there is only one sheet in the reversing duplex unit, and it is possible to prevent sheet conveyance failure and sheet jamming.

[Second Embodiment]
Next, a second embodiment of the reversing duplex unit will be described. Since the basic configuration and operation of the second embodiment are the same as those of the first embodiment, overlapping description will be omitted and different portions will be mainly described.

  In the reversing duplex unit of the second embodiment, the reversing roller 121 is provided so that the nip can be released, as in the first embodiment, but in addition, the nip pressure can be adjusted. . That is, as shown in FIG. 8, the reverse driven roller 121b constituting the reverse roller 121 is pressed against the reverse drive roller 121a via the compression springs 311 and 311 by the pressure arm 312. By lifting the shaft of the reverse driven roller 121b by the nip release arm 301, the nip of the reverse roller 121 can be released against the urging force of the compression springs 311 and 311. The lower end portion of the nip releasing arm 301 lifts the shaft of the reverse driven roller 121b via a bearing, and is lifted and lowered by a link mechanism or a cam mechanism (not shown) using a solenoid or a stepping motor or other alternative means. The nip pressure can be adjusted by adjusting the operation amount.

  In the second embodiment, as described above, the reversing roller 121 includes a mechanism for adjusting the nip pressure (hereinafter referred to as a pressure adjusting mechanism), so that the inside of the reversing duplex unit 100 detected by the first sheet detecting means 112 is used. It becomes possible to adjust the conveying force of the reversing roller 121 according to the type of paper carried into the paper.

  Here, the reversing roller 121 carries in the paper only by its conveying force, and temporarily stops and carries out the reversing. For example, in the thick paper conveyance, slippage and skew at the reversing roller 121 nip are prevented. Therefore, a higher conveying force than that of plain paper is required. Therefore, when the paper detected by the first paper detection means 112 is a thick paper, the pressure adjusting mechanism is controlled so as to have the conveying force shown in the following Table 1. On the other hand, in the case of thin paper, the pressure adjusting mechanism is controlled so that the conveyance force is lower than that of plain paper in order to prevent side effects on the paper and images caused by pressing the thin paper strongly with excessive pressure.

  In this way, by controlling the pressure adjusting mechanism according to the type of paper such as thick paper and thin paper detected by the detecting means 112, the reversing operation can be performed with an appropriate transport force without applying an unnecessary load on the paper. Is possible.

  The reversing duplex unit 100 includes two transport paths after reversal, such as a discharge transport path 130 (FIG. 2) and a refeed transport path 140 (FIG. 2). Has a path with a large curvature (with a small radius of curvature) in order to refeed the sheet to the image forming unit 1. In order to convey the large curvature path with thick paper, the reversing roller 121 needs to have a high conveying force depending on the conveying force of the reversing exit roller 131. Since the discharge conveyance path 130 has a smaller curvature than that of the refeed conveyance path 140, the conveyance force may be equal to or less than that on both sides (refeeding). In this way, when the carry-out path after reversal is different, the conveyance force of the reversing roller 121 is adjusted as shown in Table 2 depending on the paper type, so that the paper after reversal can be performed with an appropriate conveyance force without applying an unnecessary load on the paper. It becomes possible to carry.

  Note that the sheet conveying force of the reversing roller 121 shown in Tables 1 and 2 may be a measured value obtained by an evaluation test performed in advance or a calculated value obtained from a simulation or the like. The magnitude relationship of the conveyance force in Table 1 is Fa> Fb> Fc> Fd. Further, the magnitude relationship of the conveying force in Table 2 is Fra> Frb> Frc> Frd, Fda> Fdb> Fdc> Fdd, and Fda> Fra, Fdb> Frb, Fdc> Frc, Fdd> Frd. The sheet conveying force of the reversing roller 121 is adjusted by adjusting the nip pressure. When the nip pressure is increased (increased), the sheet conveying force increases, and when the nip pressure is decreased (decreased), the sheet conveying force decreases.

  The sheet conveying force of the reversing roller 121 is described in FIG. 8 according to Table 1 or Table 2 according to Table 1 or Table 2 according to the sheet type determined by the copier control unit based on the detection output of the first sheet detecting unit 112. Adjustment is performed by operating the pressure adjusting mechanism. As shown in FIG. 9, whether or not the conveyance force is adjusted according to the user's needs is set by the input unit 200 provided in the copying machine operation unit (not shown). It is configured to be able to. That is, when the default designation button 201 is pressed, the sheet conveying force set in advance based on the sheet type information detected by the first sheet detecting unit 112 is adjusted. Further, it is also possible to select non-adjustment of the conveyance force by pressing the OFF designation button 202. Alternatively, by pressing any of the paper type designation buttons 203, the user can set the conveying force of the reversing roller 121 to the thick paper setting, the plain paper setting, the thin paper setting, etc. regardless of the paper type information detected by the first paper detection unit 112. Can also be set directly.

  The basic reversing operation other than the adjustment of the sheet conveying force of the reversing roller 121 is the same as that of the first embodiment, and the operations when there is no rubbing difference and when there is a rubbing difference in reverse discharge printing are shown in FIGS. This is the same as described above, and the reverse operation during duplex printing is also the same.

[Third embodiment]
Next, a third embodiment of the reversing duplex unit will be described. Since the basic configuration and operation of the third embodiment are the same as those of the first embodiment, the description will be repeated with a focus on different parts without redundant description.

  In the third embodiment, as shown in FIG. 10, a third paper detection unit 132 is provided in the discharge conveyance path 130 immediately after the reverse exit roller 131. Also in the third embodiment, the basic reversing operation in the reversing duplex unit 100 is the same as that of the first embodiment, and the operations when there is no rubbing and when there is a rubbing in reverse discharge printing have been described with reference to FIGS. This is the same as the case, and the reverse operation during double-sided printing is also the same.

  In the third embodiment, the third paper detection means 132 is added as described above, and the detection output is used for the control of the reversing roller 121, so that the paper passing at the reversing roller 121 is more reliably performed. This further improves the paper transportability in the reversing duplex unit. The points peculiar to the third embodiment will be described below.

  In the operation when there is a difference in paper rubbing in the reversing duplex unit 100 (reversed paper discharge printing and duplex printing), for example, when reversing when the sheet interval (between sheets) is short, the front end of the first sheet after reversing is the reversing exit roller Before reaching 131, the leading edge of the second sheet reaches the second sheet detection unit 122, and the second sheet detection unit 122 may detect two sheets. If the nip of the reverse roller 121 is released in this state, the first sheet cannot be carried out. That is, in order to reliably carry out the first sheet, it is indispensable that the first sheet is reliably conveyed by the reverse exit roller 131. Therefore, when the sheet is detected by the third sheet detecting means 132 provided in the discharge conveyance path 130, Control is performed to release the nip of the reverse roller 121. In other words, the nip release condition of the reversing roller 121 when there is a sheet rubbing is based on the number of sheets detected by the second sheet detecting unit 122 and the information on the presence / absence of the sheet detected by the third sheet detecting unit 132. A reliable inversion operation is possible.

  In addition, since it is essential to release the nip of the reversing roller 121 when there is paper rubbing before the leading edge of the second sheet reaches the reversing roller 121, the second paper detecting unit 122 uses two sheets of paper, In addition, when the third sheet detecting unit 132 detects the absence of the sheet, the first sheet unloading speed (the number of rotations of the reverse roller 121) is increased, or the second sheet unloading speed (the number of rotations of the reverse roller 121) is increased. By lowering the nip, it is possible to reliably release the nip while the first sheet is being conveyed by the reversing exit roller 131 when the reversing roller 121 is rubbing.

The relationship between the carry-in speed Vin and the carry-out speed Vout will be described with reference to FIG.
FIG. 11 shows the moment when the leading edge of the second sheet P2 reaches the second sheet detecting means 122 and two sheets are detected. At this time, the first sheet P1 is being carried out by the reversing roller 121, the distance between the tip of P1 and the second sheet detecting means 122 is A, and the distance between the second sheet detecting means 122 and the reversing roller 121. Is X, and the distance between the second paper detection means 122 and the third paper detection means 132 is Y, the leading edge of the carry-out sheet (P1) is detected before the leading edge of the carry-in sheet (paper P2) reaches the reverse roller 121. Since it is necessary to reach 132, the relational expression is the following expression (1).
(YA) / Vout <X / Vin (1)
That is, the relationship between Vin and Vout is expressed by the following equation (2).
Vout / Vin> (Ya) / X (2)

  By changing Vout or Vin so that the formula (2) is satisfied, that is, by controlling the rotation speed of each of the conveying rollers 111, 121, 131, the difference in rubbing at the reversing roller 121 portion is ensured.

  The nip release conditions, the carry-in speed Vin, and the carry-out speed Vout are controlled and changed by a control unit (not shown) of the copying machine. In addition, about Vin and Vout, the method of fixing one and changing the other may be sufficient, and the method of changing both may be sufficient. Alternatively, the speed experimentally confirmed in advance may be stored as a table in the storage means, and the conveying roller linear velocity satisfying the above equation may be selected from the table, or the conveying roller linear velocity satisfying the above equation may be simply selected. It may be adjusted in a timely manner.

An operation when there is a sheet passing when controlling the linear speed (number of rotations of the conveyance roller) of the conveyance roller will be described.
The first sheet that has passed through the first sheet detection unit 112 and the second sheet detection unit 122 and is carried into the reverse conveyance path 120 is conveyed by a certain distance after the trailing end of the sheet is removed from the first sheet detection unit 112. Later, the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side, and at the same time, the reverse switching claw 160 is switched to guide the first sheet in the carry-out direction. The first paper detection unit 112 detects the presence of paper and also detects paper information.

  Thereafter, the first sheet P1 is unloaded, and the leading edge of the second sheet is the second sheet with the trailing edge of the first sheet remaining in the second sheet detecting means 122 as shown in (6) of the detailed operation diagram. When the detection means 122 is reached, the second paper detection means 122 detects two sheets, and determines that a paper passing occurs. However, since the first sheet has not yet reached the third sheet detecting means 132, the speed of the reversing roller 121 is increased. When the first sheet reaches the third sheet detecting means 132 and is conveyed (unloaded) by the reversing exit roller 131, the nip of the reversing roller 121 is released, and at the same time the rotation direction of the reversing roller 121 is loaded from the unloading side. Switch to the side. Of course, since the nip of the reverse roller 121 is released at this time, the discharge of the first sheet is not affected.

  Then, when the trailing edge of the first sheet passes through the second sheet detection unit 122 and the detection unit 122 detects one sheet, the nip of the reversing roller 121 is returned, and the reversing roller 121 conveys the second sheet. Do. Thereafter, this operation is repeated.

  Details of the operation will be described with reference to FIG. 12. Since the operations (1) to (5) are the same as those in FIG. After the second sheet P2 passes through the first sheet detection unit 112, the leading end of the sheet reaches the second sheet detection unit 122, and the second sheet detection unit 122 detects two sheets. At this time, the leading edge of the first sheet P1 has not reached the third sheet detecting means 132, and the speed of the reverse roller 121 is increased (6). When the leading edge of the first sheet P1 reaches the third sheet detecting means 132, the nip of the reverse roller 121 is released, and the rotation direction is switched from the carry-out side to the carry-in side. The roller speed is also returned to the normal speed (7). When the rear end of the first sheet P1 comes off from the second sheet detecting means 122 and the second sheet detecting means 122 detects one sheet, the nip of the reverse roller 121 is returned (8). Thereafter, when there is a succeeding sheet, the operations (3) to (8) are repeated. Here, the case of reverse paper discharge has been described, but the reverse operation at the time of duplex printing is also the same.

  In this way, in the third embodiment, based on the paper presence / absence and number information detected by the first paper detection means 112 and the second paper detection means 122 and the paper presence / absence information detected by the third paper detection means 132. Therefore, since the nip release of the reverse roller 121 and the speed control of each transport roller are performed, it is possible to perform the reverse operation including the presence / absence of sheet passing in the reverse roller 121 more reliably and when necessary. Since the nip of the reversing roller 121 is released to perform only sheet passing, sheet passing is not performed more than necessary, and the sheet conveying performance in the reversing duplex unit is improved.

[Fourth embodiment]
Next, a fourth embodiment of the reversing duplex unit will be described. Since the basic configuration and operation of the fourth embodiment are the same as those of the first embodiment, overlapping description will be omitted and different portions will be mainly described. In the fourth embodiment, the control of the reversing roller 121 when there is a sheet slip is different from the above embodiments. In the fourth embodiment, the third sheet detecting means is not provided, and the configuration is the same as that shown in FIGS. Further, the reversing operation when there is no difference in paper rubbing between the reversed paper discharge printing and the double-sided printing is the same as that described with reference to FIG.

  On the other hand, if there is a paper rubbing difference between the reverse discharge printing and the double-sided printing, it is determined that there is a paper slip at the reverse roller 121, and the rotation direction of the reverse roller 121 is carried in from the carry-out side simultaneously with the nip release of the reverse roller 121 When switched to the side, the conveyance direction of the first sheet and the roller rotation direction are reversed. Although the nip of the reversing roller 121 is released, there is no effect on the carry-out of the first sheet. However, the reversing roller 121 contacts the sheet and rubs the sheet. Paper dust or the like may adhere to the paper, or the reverse roller 121 may damage the paper. Also, if they are paper image surfaces, the print quality will be affected.

  Therefore, in the fourth embodiment, when there is a paper rubbing difference in reverse paper discharge printing and double-sided printing, the timing for switching the rotation direction of the reverse roller 121 (switching from the carry-out side to the carry-in side after paper reverse) is set to the first sheet. Control is performed so that the trailing edge of the sheet is carried out at the same time as when the reverse roller 121 is removed. That is, after the first sheet is reversed, the reversing roller 121 is rotated in the carry-out direction by the length of the sheet, and then the rotation direction of the reversing roller 121 is switched to the carry-in direction. As described above, after the paper is reversed, the reverse roller 121 is rotated in the carry-out direction by the length of the paper and then the rotation direction of the reverse roller 121 is changed in the carry-in direction. It is possible to prevent the occurrence of adhesion, scratching, image degradation, and the like.

  The sheet length is calculated from the time when the first sheet detecting unit 112 detects the sheet (the time from the presence of the sheet to the absence of the sheet) and the sheet conveyance speed based on the rotation speed of the entrance roller 111 (the rotation speed per unit time). calculate. Therefore, even if the paper size carried into the reversing duplex unit is not recognized in advance, there is no trouble in switching the rotation direction of the reversing roller 121.

This will be described in more detail with reference to FIG.
FIG. 13 shows a state in which the first sheet P1 is conveyed by a predetermined distance after passing through the first sheet detecting means 112, and the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side. This corresponds to (4) of (b) (in FIG. 13, the reverse switching claw 160 is shown in the state when the paper is carried in). The rear end of the paper (the rear end of the paper at the time of carry-in) is located at the reverse branching section 150 (see FIG. 2), and the rear end position of the paper is the paper conveyance direction switching position. Assuming that the distance from the switching position to the reverse roller 121 is X and the paper length is Y, in the fourth embodiment, after the paper P1 is conveyed in the carry-out direction by (Y-X), the rotation direction of the reverse roller 121 is changed. Switch to the loading side. The paper length is calculated as Y = Vin × T from the time T from the presence of paper in the first paper detection unit 112 and the conveyance speed Vin of the entrance roller 111 as described above. Note that the nip release and rotation direction switching of the reversing roller 121 are controlled by the copier control unit.

  The details of the operation when there is a sheet passing in the fourth embodiment will be described with reference to FIG. Since the operations (1) to (5) are the same as those in FIG. When the second sheet P2 passes through the first sheet detection means 112, the leading edge of the sheet reaches the second sheet detection means 122, and the detection means 122 detects two sheets (P1, P2), the reverse roller The nip 121 is released (6). When the trailing edge of the first sheet P1 passes through the nip of the reverse roller 121, the rotation direction of the reverse roller 121 is switched from the carry-out side to the carry-in side (7). Further, the rear end of the first sheet P1 passes through the second sheet detection unit 122, and when the second sheet detection unit 122 detects one sheet, the nip of the reversing roller 121 is returned to the second sheet by the reversing roller 121. The sheet P2 is conveyed (8). Thereafter, the operations (3) to (8) are repeated.

  Thus, based on the sheet presence / absence and number information obtained by the first sheet detection unit 112 and the second sheet detection unit 122 and the sheet information calculated as described above, a sheet reversal operation is performed only when necessary. In addition, it is possible to reliably prevent the occurrence of paper stains, scratches, image degradation, and the like. Although the above description of the operation has been made in the case of reverse paper discharge, the reverse operation in the case of duplex printing is also the same.

[Fifth embodiment]
Next, a fifth embodiment of the reversing duplex unit will be described. In the fifth embodiment, the carry-out speed (Vout) at the time of paper reversal is set to be higher than the carry-in speed (Vin), and the carry-out speed is changed depending on the paper carry-out path after reversal. Since the basic configuration is the same as that of the third embodiment, the description will be made in comparison with the third embodiment.

  In the third embodiment, the operation when there is no difference in sheet rubbing in reverse discharge printing is the same as that in the first embodiment, and is the same as the case described with reference to FIG. However, FIG. 6 does not show the third paper detection means 132 provided in the third embodiment (and the fifth embodiment), so that the structure including the third paper detection means 132 is shown in FIG. Show. FIG. 15 (a) shows how the third sheet detecting means 132 detects the sheet after the sheet is reversed.

  Further, in the third embodiment, the operation when there is a paper rubbing difference in the reverse discharge printing is as described with reference to FIG. 12, and after the first sheet P1 is reversed, it is carried out by the reverse exit roller 131. 12 (6), when the leading edge of the second sheet reaches the second sheet detecting means 122 with the trailing edge of the first sheet remaining on the second sheet detecting means 122, the second sheet detecting means 122 Two sheets of paper are detected and it is determined that a paper misplacement occurs. However, since the first sheet has not yet reached the third sheet detecting means 132, the first sheet reaches the reversing exit roller 131 before the second sheet reaches the nip of the reversing roller 121. Then, the rotation speed of the reversing roller 121 is increased to increase the first sheet carry-out speed Vout (or even if the rotation speed of the entrance roller 111 is lowered to lower the second sheet carry-in speed Vin). good).

  However, it goes without saying that it is possible to reduce the risk of sheet passing by setting the upper limit speed from the start of unloading rather than increasing (acceleration) the unloading speed Vout during sheet unloading. The carry-in speed Vin may not be variable because the image forming apparatus is often provided with a fixing device before the reversing unit (upstream in the paper carrying direction).

  Therefore, in the fifth embodiment, the carry-out speed Vout at the time of paper reversal is set to be higher than the carry-in speed Vin, and the carry-out speed Vout can be changed, and the carry-out speed Vout is set according to the paper carry-out path after reversal. change. More specifically, a relationship table between the carry-out path and the carry-out speed Vout is stored in the storage unit of the control unit, and the carry-out speed Vout is determined (selected) according to the reversed paper carry-out path. Table 3 below shows an example of a relationship table between the carry-out route and the carry-out speed Vout. In this embodiment, the carry-out speed Vout is also changed depending on the paper type (here, the paper thickness).

  In the present embodiment, as shown in FIG. 2, there are provided two conveyance paths having different curvatures after inversion such as a discharge conveyance path 130 and a refeed conveyance path 140, and in particular, a refeed conveyance path. 140 has a large curvature in order to refeed the paper. If the curvature of the conveyance path is large, there is a concern that when the conveyance speed is high, the leading edge of the sheet is damaged, or the force of conveying the sheet by the reverse exit roller 131 is insufficient and the sheet slips. Therefore, the carry-out speed when the paper is carried out to the refeed conveyance path 140 is set lower than the carry-out speed when the paper is carried out to the discharge conveyance path 130.

It is also preferable to change (select) the carry-out speed Vout depending on the difference in sheet thickness detected by the first sheet detection unit 112. For example, it is needless to say that thick paper (basis weight 200 g / m ² ) requires a conveying force of the reverse exit roller 131 rather than plain paper (basis weight 80 g / m ² ). is there. Therefore, the carry-out speed when carrying out thick paper is set lower than the carry-out speed when carrying out plain paper.

  In Table 3, when the paper types are the same, the carry-out speed Vout1 when the paper is carried out to the discharge conveyance path 130 is set larger than the carry-out speed Vout2 when the paper is carried out to the refeed conveyance path 140. Yes. That is, Vout1> Vout2, Vout1_a> Vout2_a, and Vout1_b> Vout2_b. Further, when compared with the types of paper (the conveyance path is the same), Vout1 <Vout1_a <Vout1_b and Vout2 <Vout2_a <Vout2_b.

  In this way, by discharging the inverted paper at a speed selected according to the discharge path and the paper type (thickness), the risk of passing at the time of paper reversal is reduced as much as possible, and a favorable reversing operation becomes possible. . In addition, what is necessary is just to set the specific numerical value of carrying-out speed suitably by an apparatus structure (the curvature of a conveyance path | route, the material of a conveyance roller, etc.) etc. Further, the carry-out speed Vout may be a value obtained from an experimental result of an actual image forming apparatus or a value calculated by simulation.

  Details of the operation in the fifth embodiment will be described with reference to FIG. 16. The operations (1) to (3) are the same as those in FIG. When the sheet is conveyed by a predetermined distance after the trailing edge of the sheet passes through the first sheet detecting means 112, the rotation direction of the reverse roller 121 is switched from the carry-in side to the carry-out side. The carry-out speed at this time (speeds of the reverse roller 121 and the reverse outlet roller 131) is selected from the table in Table 3 according to the discharge path and the paper type. At the same time, the reverse switching claw 160 is switched (the position indicated by the broken line in FIG. 2), and after the paper is conveyed by a certain distance, it is returned to the original position (the position indicated by the solid line in FIG. 2) (4). Then, the second sheet P2 is guided to the reversing duplex unit 100, and the leading end of the sheet reaches the first sheet detecting means 112 (5). When the leading edge of the second sheet reaches the second sheet detecting means 122 and the second sheet detecting means 122 detects two sheets, the leading edge of the first sheet P1 reaches the third sheet detecting means 132. Therefore, the nip of the reverse roller 121 is released. At the same time, the rotation direction of the reverse roller 121 is switched from the carry-out side to the carry-in side (6). Then, the rear end of the first sheet passes through the second sheet detection unit 122, and the nip of the reverse roller 121 is returned when the second sheet detection unit 122 detects one sheet (7). Thereafter, if there is a subsequent sheet, the above operation is repeated.

  Note that it is determined that a pass occurs also in the case of FIG. 11 in which the second sheet detection unit 122 detects two sheets before the leading edge of the first sheet P1 reaches the third sheet detection unit 132. In this case, according to the third embodiment, the carry-out speed Vout is changed until the third sheet detection unit 132 detects the leading edge of the first sheet.

  As described above, the fifth embodiment has been described when there is a sheet passing. However, if the carry-out speed Vout is set higher than the carry-in speed Vin, the “no passing” as shown in FIG. Needless to say, risk can be reduced.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, the shape and path length of each conveyance path provided in the reversing duplex unit can be set as appropriate. In addition, paper detection means having an appropriate configuration can be adopted. Any mechanism for releasing the nip of the reversing roller can be used.

  The basic configuration of the image forming apparatus is also arbitrary, and the present invention can be applied not only to a monochrome apparatus but also to a multi-color machine or a full-color image forming apparatus. Of course, the image forming apparatus is not limited to a copying machine, but may be a printer, a facsimile machine, or a multifunction machine having a plurality of functions.

It is sectional drawing which shows schematic structure in an example of an image forming apparatus provided with the inversion double-sided unit which concerns on this invention. It is sectional drawing which shows the structure of an inversion double-sided unit. It is a figure for demonstrating operation | movement of the inversion duplex unit. It is a figure explaining the operation | movement at the time of re-feeding in the inversion duplex unit. It is a figure which shows a mode that the nip of a reverse roller is cancelled | released. It is a figure explaining the operation | movement of the reversing duplex unit in case there is no nip cancellation | release of a reversing roller. It is a figure explaining operation | movement of the reversing duplex unit in case the nip cancellation | release of a reversing roller exists. It is a perspective view which shows the nip pressure adjustment mechanism of the reverse roller in 2nd Example of a reverse double-sided unit. It is a top view which shows an example of the input means for a user to set the nip pressure of a reverse roller. It is sectional drawing which shows 3rd Example of an inversion double-sided unit. It is a figure for demonstrating the relationship between the paper carrying-in speed and carrying-out speed in the inversion duplex unit. It is a figure explaining operation | movement in the case of nip cancellation | release with the reversing roller in 3rd Example. It is a figure for demonstrating the switching timing of the rotation direction of the inversion roller in 4th Example of an inversion double side unit. It is a figure explaining operation | movement in case the nip cancellation | release of a reverse roller in 4th Example exists. It is the figure which added the 3rd paper detection means to FIG. It is a figure explaining the operation | movement in the case of nip cancellation | release with the reverse roller in 5th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Paper feed part 4 Paper discharge storage part 6 Fixing device 10 Image forming unit 100 Reversed duplex unit 110 Inlet conveyance path 111 Inlet roller 112 First paper detection means 120 Reverse conveyance path 121 Reverse roller 122 Second paper Detection means 130 Discharge conveyance path 131 Reverse exit roller 132 Third paper detection means 140 Refeed conveyance path 141-144 Refeed conveyance roller 150 Reverse branching section 160 Reverse switching claw 170 Branch switching claw

Claims (19)

A carry-in path through which paper is carried in, a reverse conveyance path for reversing the paper carried in from the carry-in path, a paper discharge conveyance path for discharging the paper carried out from the reverse conveyance path, and the reverse conveyance path A reversing duplex unit that refeeds paper to the image forming unit of the image forming apparatus, and discharges or refeeds the reversed paper.
A reversing roller disposed in the reversing conveyance path and capable of rotating forward and reverse is provided so as to be able to release the roller nip,
The first paper detection means capable of detecting the presence or absence of paper in the carry-in path is arranged, and the presence or absence of paper and the number of sheets can be detected in the vicinity of the upstream side of the reverse roller in the paper carry-in direction to the reverse conveyance path. A second paper detection means is arranged,
The rotation of the reversing roller is controlled based on the detection information of the first paper detection means, and the nip of the reversing roller is controlled to be released or not released based on the detection information of the second paper detection means. Reversing duplex unit characterized by.   2. The reversing duplex unit according to claim 1, wherein the nip of the reversing roller is released when the second sheet detecting unit detects two sheets.   The reversing duplex unit according to claim 1, wherein the reversing roller is provided so that a nip pressure can be adjusted.   4. The reversing according to claim 3, wherein the first paper detecting means is provided so as to be able to detect the paper type, and the nip pressure of the reversing roller is adjusted according to the paper type detected by the detecting means. Double-sided unit.   When the paper type is paper thickness and the detected paper is thick paper, the nip pressure of the reverse roller is increased, and when the detected paper is thin paper, the nip pressure of the reverse roller is reduced. The reversing duplex unit according to claim 4.   Adjust so that the nip pressure of the reversing roller when the paper after reversing in the reversing conveyance path is sent to the refeed conveyance path is larger than the nip pressure when the reversing paper is sent to the discharge conveyance path The reversing duplex unit according to claim 4 or 5, characterized in that:   The reversing duplex unit according to any one of claims 4 to 6, wherein a nip pressure of the reversing roller can be set by a user.   Third paper detection means capable of detecting the presence or absence of paper is arranged in the paper discharge conveyance path, and the inversion is performed based on detection information of the second paper detection means and detection information of the third paper detection means. 2. The reversing duplex unit according to claim 1, wherein the nip of the roller is controlled to be released or not released.   9. The nip of the reversing roller is released when the second sheet detecting unit detects two sheets and the third sheet detecting unit detects the presence of a sheet. Reversing duplex unit as described.   An inlet roller disposed in the carry-in path for carrying paper, and an outlet roller for sending the paper reversed by the reverse roller to the paper discharge conveyance path or the refeed conveyance path; The reversing duplex unit according to claim 8 or 9, wherein the number of rotations of each of the roller and the exit roller can be controlled.   When the second paper detection means detects two sheets and the third paper detection means detects the absence of paper, the preceding paper carry-out speed is increased or the subsequent paper carry-in speed is decreased. The reversing duplex unit according to claim 10, wherein the number of rotations of each roller is controlled.   The rotation direction of the reversing roller is controlled based on the sheet length of the preceding sheet when the second sheet detecting unit detects two sheets and releases the nip of the reversing roller. 2. The reversing duplex unit according to 1.   An entrance roller for carrying the paper into the carry-in path is provided, and the paper length is calculated based on detection information when the first paper detection means detects the paper and the number of rotations of the entrance roller per unit time. The reversing duplex unit according to claim 12, characterized in that:   13. The rotation direction of the reverse roller is switched from the carry-out side to the carry-in side when the trailing edge of the preceding paper passes through the nip of the reverse roller after the preceding paper is reversed. Inverted duplex unit. An entrance roller disposed in the carry-in path for carrying paper, and an exit roller for feeding the paper reversed by the reversing roller to the paper discharge conveyance path or the refeed conveyance path,
The carry-out speed that is the carry speed at the time of carry-out of the paper by the reverse roller and the exit roller is provided to be changeable, and the carry-out speed is set higher than the carry-in speed that is the carry speed by the inlet roller,
2. The reversing duplex unit according to claim 1, wherein the carry-out speed is changed depending on whether a paper conveyance path after reversal is the paper discharge conveyance path or the re-feed conveyance path.   The carry-out speed when the paper conveyance path after reversal is the paper discharge conveyance path is set to be larger than the carry-out speed when the paper conveyance path after reversal is the re-feed conveyance path. 16. The reversing duplex unit according to claim 15, characterized in that   The first sheet detection means is provided so as to be able to detect a sheet thickness, and the carry-out speed is changed according to the sheet thickness detected by the first sheet detection means. 16. The reversing duplex unit according to 16.   18. The reversing duplex unit according to claim 17, wherein when the paper thickness detected by the first paper detection means is thin, the carry-out speed is increased, and when the paper thickness is thick, the carry-out speed is changed small.   An image forming apparatus comprising the reversing duplex unit according to claim 1.

Images