JP7547833B2 - Curling device, image forming apparatus and curling method - Google Patents

Description

The present invention relates to a curling device, an image forming device, and a curling method.

In electrophotographic image forming devices, when an image formed on the front side of thin paper, particularly pressure-sensitive paper (registered trademark), is fixed, the paper may curl significantly. In this case, if an image is to be formed on the back side of the paper, the paper may wrap around the secondary transfer roller as the back side passes through the transfer section (transfer nip), or the paper may be unable to enter the fixing nip, increasing the likelihood of a paper jam.

Therefore, the fixing temperature and pressure of the fixing unit are reduced to reduce the amount of curl in the paper after the fixing process, thereby reducing the occurrence of paper jams. There is also an image forming device that arranges a decurler to straighten the curl downstream of the fixing unit in the paper transport direction to straighten the curl in the paper after the fixing process, thereby reducing the amount of curl and reducing the occurrence of paper jams (see Patent Document 1).

JP 2019-179225 A

However, some types of paper have very low stiffness (very low rigidity). For example, pressure-sensitive paper with a Y-grain grain is very weak in itself. With this type of paper, for example, when the surface passes through the transfer nip, the paper may wrap around the secondary transfer roller, causing a paper jam.

The object of the present invention is to provide a curling device, an image forming device, and a curling method that can prevent paper jams.

The curling device according to the present invention comprises:
a curl imparting section that imparts curl to the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curl imparting section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip that transfers an image onto the paper;
a stiffness detection unit that detects stiffness of the paper;
Equipped with
The curl imparting section changes the amount of curl imparted to the paper sheet in accordance with the detected stiffness .
The curling device according to the present invention further comprises:
a curling section that curls the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curling section being located upstream of the transfer nip in the paper conveying direction, unlike a paper guide member that guides the paper to a transfer nip where an image is transferred to the paper;
the curl imparting section has a roller that presses against the paper to curve the paper and thereby imparts a curl to the paper,
The roller has a heating section for heating the paper,
The curl imparting section changes the amount of curl imparted to the paper by changing the amount of heat applied by the heating section.
The curling device according to the present invention further comprises:
a curl imparting section that imparts curl to the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curl imparting section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip where an image is transferred to the paper;
a curl amount detection unit that detects the amount of curl generated in the paper after the curl is applied by the curl application unit;
Equipped with
The curl imparting section changes the amount of curl imparted to the paper in accordance with the detected amount of curl.

The image forming apparatus according to the present invention comprises:
The curling device is provided.
Further, the image forming apparatus according to the present invention comprises:
a curling device including a curling section that curls the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curling section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip where an image is transferred onto the paper;
a transport adjustment unit that adjusts a transport timing of the paper transported to the transfer nip;
a transfer section that transfers the image to the paper at the transfer nip;
a control unit that controls the transfer unit to change a transfer timing for transferring the image onto the paper in accordance with an amount of curl applied to the paper;
Equipped with
The curling device is disposed between the transport adjustment unit and the transfer nip in the transport direction.
Further, the image forming apparatus according to the present invention comprises:
a curling device including a curling section that curls the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curling section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip where an image is transferred onto the paper;
a transport adjustment unit that adjusts a transport timing of the paper transported to the transfer nip;
a leading edge detection unit that detects a leading edge of the paper sheet downstream of the curling device in the conveying direction;
a paper transport unit that transports the paper;
a control unit that controls the paper transport unit to change a transport speed of the paper based on a timing when the leading edge of the paper is detected;
Equipped with
The curling device is disposed between the transport adjustment unit and the transfer nip in the transport direction.

The curling method according to the present invention comprises the steps of:
When curling the paper using a curling unit different from a paper guide member that guides the paper to the transfer nip, the curling unit is arranged to curl the paper in a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, on the upstream side of the transfer nip in the paper transport direction, the transfer nip being arranged to transfer an image onto the paper .
The amount of curl applied to the paper is changed according to the stiffness detected by the stiffness detection unit .

This invention makes it possible to prevent paper jams.

1 is a diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram showing a main part of a control system of the image forming apparatus shown in FIG. 1 . 2 is a schematic diagram illustrating a curling section of the curling device according to the embodiment of the present invention; FIG. 3 is a schematic diagram illustrating a stiffness detection unit of the curling device according to the embodiment of the present invention. FIG. 11A and 11B are diagrams illustrating timing for switching the paper transport speed. FIG. 4 is a flowchart for explaining a curling method according to an embodiment of the present invention, in which feedback control is performed for each sheet of paper. FIG. 7 is a flowchart for explaining a modification of the curling method shown in FIG. 6, in which control is performed for each tray. FIG. 13 is a schematic diagram illustrating a modified example of an image forming apparatus according to an embodiment of the present invention.

The following describes in detail the embodiments of the present invention with reference to the drawings.

[Image forming apparatus]
Fig. 1 is a schematic diagram showing an example of an image forming apparatus 1A according to the present embodiment, and Fig. 2 is a block diagram showing a main part of a control system of the image forming apparatus 1A shown in Fig. 1.

As shown in FIG. 1, the image forming apparatus 1A includes an image forming apparatus main body 10A. The image forming apparatus main body 10A is an intermediate transfer type color image forming apparatus that utilizes electrophotographic process technology. The image forming apparatus main body 10A employs a vertical tandem type in which photosensitive drums corresponding to the four colors CMYK are arranged in series in the running direction (vertical direction) of the intermediate transfer belt, and each color toner image is transferred sequentially to the intermediate transfer belt in a single procedure. That is, the image forming apparatus main body 10A primarily transfers each color toner image of CMYK formed on the photosensitive drum to the intermediate transfer belt, superimposes the four color toner images on the intermediate transfer belt, and then secondary transfers the images to paper S to form an image. C is cyan, M is magenta, Y is yellow, and K is black.

As shown in Figures 1 and 2, the image forming device main body 10A includes an image reading unit 11, an operation display unit 12, an image processing unit 13, an image forming unit 14, a fixing unit 15, a paper feed unit 16, a paper transport unit 17, and a control unit 200.

The image reading unit 11 includes an automatic document feeder (ADF) and an original image scanning device (scanner). In the image reading unit 11, an original document transported from the automatic document feeder onto the contact glass or an original document placed on the contact glass is read by the original image scanning device, and input image data is generated.

The operation display unit 12 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 121 and an operation unit 122 (see FIG. 2). The display unit 121 displays various operation screens, image status display, operation status of each function, etc. according to a display control signal input from the control unit 200. The operation unit 122 has various operation keys such as a numeric keypad and a start key, accepts various input operations by the user, and outputs operation signals to the control unit 200.

The image processing unit 13 performs digital image processing such as compression and various correction processes such as tone correction, color correction, and shading correction according to initial settings or user settings on the input image data. The image forming unit 14 is controlled based on the image data that has been subjected to these processes.

The image forming unit 14 forms an image using the color toners of the Y, M, C, and K components based on the image data. The image forming unit 14 includes a photoconductor drum, a charging device, an exposure device, a developing device, and an intermediate transfer device. In the image forming unit 14, the surface of the photoconductor drum is uniformly charged by the charging device. The charged photoconductor drum is irradiated with laser light based on the image data by the exposure device, forming an electrostatic latent image on the surface of the photoconductor drum. The electrostatic latent image is then visualized by supplying toner to the photoconductor drum with the electrostatic latent image by the developing device, forming a toner image. The toner image is transferred to the intermediate transfer belt 141 of the intermediate transfer device, and then transferred to the paper S at the secondary transfer nip 143 (transfer section) formed by the intermediate transfer belt 141 and the secondary transfer roller 142.

The fixing unit 15 includes an upper fixing unit having a fixing belt 151 and the like arranged on the fixing surface (surface on which the toner image is formed) of the paper S, and a lower fixing unit having a pressure roller 152 and the like arranged on the back surface (surface opposite the fixing surface) of the paper S. The fixing belt 151 is stretched in a loop around a plurality of rollers such as a heating roller, and heats the paper S that is conveyed. The pressure roller 152 is pressed against the fixing belt 151, and forms a fixing nip between the fixing belt 151 and the pressure roller 152 that holds and conveys the paper S. Thus, the fixing unit 15 fixes the toner image to the paper by heating and pressurizing the paper S that has been conveyed after the toner image has been secondarily transferred at the fixing nip.

The paper feed unit 16 has multiple paper feed trays (three trays in FIG. 1). The paper feed trays store paper S, identified based on basis weight, size, etc., in predetermined types.

The paper transport unit 17 transports the paper S fed from the paper feed unit 16 along the transport path P1 to the image forming unit 14 and the fixing unit 15. The paper transport unit 17 is provided with a registration roller 171 (transport adjustment unit), which controls the transport timing of the paper S to the secondary transfer nip 143.

When the paper S transported to the paper transport section 17 passes through the secondary transfer nip 143 of the image forming section 14, the toner images on the intermediate transfer belt 141 are secondary transferred all at once onto the surface of the paper S, and then the toner images are fixed in the fixing section 15. The paper S on which the image has been formed is discharged outside the machine by the paper discharge rollers.

When forming images on both sides of the paper S, the paper S with an image formed on the front side is transported to the inversion path P2 and inverted. The inversion path P2 branches off from the transport path P1 downstream of the secondary transfer nip 143 in the paper transport direction and joins at a junction J upstream of the registration roller 171 in the paper transport direction. After being inverted, the paper S is transported from the junction J to the transport path P1 and transported to the image forming unit 14 and the fixing unit 15.

As shown in FIG. 2, the control unit 200 includes a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, and a RAM (Random Access Memory) 203. The CPU 201 reads a program corresponding to the processing contents from the ROM 202, loads it into the RAM 203, and centrally controls the operation of each block of the image forming apparatus main body 10A in cooperation with the loaded program. At this time, various data such as a LUT (Look Up Table) stored in the memory unit 212 is referenced. The memory unit 212 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.

The control unit 200 transmits and receives various data to and from an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 211. The control unit 200 receives, for example, image data transmitted from an external device, and forms an image on paper based on this image data (input image data). The communication unit 211 is, for example, configured with a communication control card such as a LAN card.

The image reading unit 11, operation display unit 12, image processing unit 13, image forming unit 14, fixing unit 15, paper feed unit 16, and paper transport unit 17 are connected to the control unit 200. The curling device 18A, which will be described later, is also connected to the control unit 200. These perform predetermined processing based on instructions from the control unit 200.

However, some types of paper S have very weak stiffness (very low rigidity). For example, among pressure-sensitive papers, pressure-sensitive paper with a Y-grain direction is very weak in stiffness. With such paper S, for example, when the surface passes through the secondary transfer nip 143, the paper S may wrap around the secondary transfer roller 142, causing a paper jam.

Therefore, in this embodiment, the image forming apparatus main body 10A is equipped with a curling device 18A. Unlike a paper guide member (paper transport guide) that guides the paper S to the secondary transfer nip 143 where an image is transferred to the paper S, the curling device 18A is equipped with a curling section 181 that curls the paper S upstream of the secondary transfer nip 143 in the transport direction of the paper S.

[Curling device]
The curling device 18A including the curling section 181 will be described with reference to FIGS.

First, the configuration of the curl imparting unit 181 will be described with reference to FIG. 3 in addition to FIG. 1. FIG. 3 is a schematic diagram of the curl imparting unit 181 of the curl imparting device 18A.

The curl imparting unit 181 has a moving roller 181a, an entrance side roller 181b, an exit side roller 131c, etc. The moving roller 181a, the entrance side roller 181b, and the exit side roller 131c are configured to be rotatable so as to transport the paper S in the transport direction C. The moving roller 181a is also configured to be movable in the movement directions B1 and B2, that is, to be movable relative to the surface of the paper S.

Therefore, the paper S transported to the entrance roller 181b of the curl imparting unit 181 passes between the moving roller 181a and the entrance roller 181b, and then passes between the moving roller 181a and the exit roller 131c and is transported in the transport direction C. Note that when transporting the paper S, a guide member such as a guide plate may be provided in the curl imparting unit 181 to guide the paper S between the moving roller 181a and the entrance roller 181b or between the moving roller 181a and the exit roller 131c.

When transporting the paper S, the moving roller 181a is moved in the moving direction B1 or the moving direction B2 to adjust the pressure of the moving roller 181a against the paper S (the amount of penetration into the paper S). The moving roller 181a presses against the paper S, curving the paper S to impart a curl to the paper S, and by changing the amount of pressure, the amount of curl imparted to the paper S can be changed.

For example, based on instructions from the control unit 200, the curl imparting unit 181 moves the moving roller 181a in the movement direction B1. This increases the amount of pressure that the moving roller 181a applies to the paper S, making it possible to increase the amount of curl applied to the paper S. On the other hand, based on instructions from the control unit 200, the curl imparting unit 181 moves the moving roller 181a in the movement direction B2. This decreases the amount of pressure that the moving roller 181a applies to the paper S, making it possible to decrease the amount of curl applied to the paper S. In other words, by increasing the amount of pressure that the moving roller 181a applies to the paper S, it is possible to increase the amount of curl applied to the paper S accordingly.

The curl imparting unit 181 is not limited to the above-mentioned configuration, and may have other configurations as long as it can impart a curl to the paper S. For example, the entrance roller 181b and the exit roller 131c may be changed to a single roller that is softer and larger than the moving roller 181a, and the moving roller 181a may be pressed against the roller to form a nip to impart a curl to the paper S. Also, a belt may be stretched in a loop shape between the entrance roller 181b and the exit roller 131c, and the moving roller 181a may be pressed against the belt to form a nip to impart a curl to the paper S.

In addition, a heating section for heating the paper S may be provided in the curl imparting section 181. For example, as shown in FIG. 3, the moving roller 181a has a heater 181d (heating section) therein. A halogen heater or the like can be used as the heater 181d. The heater 181d heats the moving roller 181a, and the heated moving roller 181a heats the paper S.

By pressing and heating the paper S, it is possible to impart a curl to the paper S, and if the amount of pressing is the same, the amount of curl imparted to the paper S can be changed according to the amount of heat (heating temperature). Specifically, by increasing the amount of heat (increasing the heating temperature), the amount of curl imparted to the paper S can be increased accordingly. For this reason, a temperature detection sensor 181e is provided to detect the temperature of the surface of the heated moving roller 181a.

In other words, when transporting the paper S, the surface temperature of the moving roller 181a is adjusted to a predetermined temperature using the temperature detection sensor 181e and the heater 181d, thereby making it possible to adjust the amount of curl imparted to the paper S.

For example, based on instructions from the control unit 200, the curl imparting unit 181 uses the temperature detection sensor 181e and the heater 181d to adjust the surface temperature of the moving roller 181a to a relatively high temperature (higher than room temperature). This increases the heating temperature at which the paper S is heated, and the amount of curl imparted to the paper S can be increased. Also, based on instructions from the control unit 200, the curl imparting unit 181 uses the temperature detection sensor 181e and the heater 181d to adjust the surface temperature of the moving roller 181a to a relatively low temperature (for example, about room temperature). This decreases the heating temperature at which the paper S is heated, and the amount of curl imparted to the paper S can be reduced. In other words, by increasing the heating temperature at which the paper S is heated, the amount of curl imparted to the paper S can be increased accordingly.

It is also desirable to change the amount of curl applied to the paper S depending on the type of paper S, for example, the stiffness of the paper S. Therefore, the curl applying device 18A may be equipped with a stiffness detection unit 182.

Figure 4 is a schematic diagram of the stiffness detection unit 182 of the curling device 18A. The stiffness detection unit 182 detects the stiffness (flexibility) of the paper S, where stiffness is the resistance to bending of the paper S. The stiffness detection unit 182 includes transport rollers 182a and 182b, a first leading edge detection sensor 182c, and a second leading edge detection sensor 182d.

In the stiffness detection unit 182, the transport rollers 182a and 182b transport the paper S in the transport direction C. The first leading edge detection sensor 182c detects the leading edge of the paper S passing through the transport nip of the transport rollers 182a and 182b. The second leading edge detection sensor 182d detects the leading edge of the paper S after it has passed through the transport nip of the transport rollers 182a and 182b. A light-receiving laser sensor or the like can be used as the first leading edge detection sensor 182c and the second leading edge detection sensor 182d.

When the paper S is transported in the transport direction C by the transport rollers 182a and 182b, the stiffness detection unit 182 determines the time from when the leading edge of the paper S is detected by the first leading edge detection sensor 182c to when the leading edge of the paper S is detected by the second leading edge detection sensor 182d.

For example, as shown in FIG. 4, the amount of bending at the leading edge of the paper S1, which has a relatively high degree of stiffness, is relatively small. Therefore, the time from when the leading edge of the paper S1 is detected by the first leading edge detection sensor 182c until the leading edge of the paper S1 is detected by the second leading edge detection sensor 182d is relatively long. Also, as shown in FIG. 4, the amount of bending at the leading edge of the paper S2, which has a lower stiffness than the paper S1, is greater than that of the paper S1. Therefore, the time from when the leading edge of the paper S2 is detected by the first leading edge detection sensor 182c until the leading edge of the paper S2 is detected by the second leading edge detection sensor 182d is shorter than that of the paper S1. Also, as shown in FIG. 4, the amount of bending at the leading edge of the paper S3, which has a lower stiffness than the paper S2, is greater than that of the paper S2. Therefore, the time from when the leading edge of the paper S3 is detected by the first leading edge detection sensor 182c until the leading edge of the paper S3 is detected by the second leading edge detection sensor 182d is shorter than that of the paper S2.

In this way, the stiffness detection unit 182 determines the time from when the leading edge of the paper S is detected by the first leading edge detection sensor 182c until when the leading edge of the paper S is detected by the second leading edge detection sensor 182d. This time correlates with the stiffness of the paper S, and the stiffness of the paper S can be detected based on this time.

Then, based on instructions from the control unit 200, the curl imparting unit 181 changes the amount of curl imparted to the sheet S according to the detected stiffness. Specifically, as the stiffness of the sheet S decreases, the sheet S becomes more likely to wrap around the secondary transfer roller 142, so the curl imparted to the sheet S by the curl imparting unit 181 is increased. At this time, the sheet S is curled so that it has a shape opposite to the shape in which the sheet S is wrapped around the secondary transfer roller 142. For example, if the sheet wraps around the secondary transfer roller 142 so that the edge of the sheet curls downward, the sheet S is curled so that the edge of the sheet curls upward.

The curling device 18A may also include a curl amount detection unit 183 as shown in FIG. 1. The curl amount detection unit 183 detects the amount of curl in the paper S after the curl is applied by the curling unit 181. The curl amount detection unit 183 may have a configuration similar to that of the stiffness detection unit 182 shown in FIG. 4, for example. However, when the curl amount detection unit 183 has a configuration similar to that of the stiffness detection unit 182, it is necessary to detect the leading edge of the paper S whose end is curled upward, and therefore the second leading edge detection sensor 182d is disposed on the upper transport roller 182a.

The curl amount detection unit 183 may use other methods. For example, it may use an imaging unit such as a CCD camera and an irradiation unit such as a laser light source to measure the shape of the paper S using a light cutting method and detect the amount of curl.

Then, based on instructions from the control unit 200, the curl imparting unit 181 changes the amount of curl imparted to the paper S according to the detected amount of curl.

The curling device 18A, which includes the above-mentioned curling section 181, stiffness detection section 182, and curl amount detection section 183, is disposed between the junction J and the secondary transfer nip 143, as shown in FIG. 1. More specifically, the curling device 18A is disposed between the registration roller 171 and the secondary transfer nip 143. In this manner, the curling device 18A is disposed upstream of the secondary transfer nip 143 in the paper transport direction, and imparts the desired amount of curl to the paper S before the paper S is transported to the secondary transfer nip 143.

The image forming apparatus main body 10A may further include a paper leading edge detection unit 191 for adjusting the transfer timing. The paper leading edge detection unit 191 detects the leading edge of the paper S after curling has been imparted by the curl imparting unit 181. The paper leading edge detection unit 191 may be the same as the first leading edge detection sensor 182c described above, and a light receiving type laser sensor or the like may be used.

As described above, the registration roller 171 controls the transport timing of the paper S to the secondary transfer nip 143. The curl imparting unit 181 is disposed downstream of the registration roller 171 in the paper transport direction. When the curl imparting unit 181 imparts a curl to the paper S, the path through which the paper S passes is curved, and the distance from the registration roller 171 to the secondary transfer nip 143 changes. Therefore, after the paper S has passed through the registration roller 171, the timing needs to be corrected by the amount of the distance changed by the curl imparting unit 181.

Therefore, a paper leading edge detection unit 191 that detects the leading edge of the paper S after curling by the curling unit 181 is provided downstream of the curling device 18A in the paper transport direction. Then, based on the timing of detection of the leading edge of the paper S by the paper leading edge detection unit 191, the paper transport unit 17 changes the transport speed when transporting the paper S to the secondary transfer nip 143 to adjust the transfer timing onto the paper S.

Here, FIG. 5 is a diagram explaining the timing of switching the transport speed of paper S. As shown in FIG. 5, paper S is transported at transport speed V1, and at time t1, the leading edge of paper S is detected by paper leading edge detection unit 191. At time t2, which is the speed switching timing Δt after time t1, the transport speed of paper S is changed from transport speed V1 to transport speed V2 (V2<V1) and paper S is transported, and at time t3, transfer of the image onto paper S begins.

When the time t3, which is the timing of transfer to the paper S, is not changed, the speed switching timing Δt is changed according to the amount of curl imparted to the paper S, thereby correcting the timing of transporting the paper S to the secondary transfer nip 143. Specifically, when the amount of curl imparted to the paper S is increased, the distance from the registration roller 171 to the secondary transfer nip 143 increases. The speed switching timing Δt is lengthened by the amount of distance increase, and the time for transporting the paper S at the transport speed V1, which is faster than the transport speed V2, is lengthened, thereby correcting the timing of transporting the paper S to the secondary transfer nip 143.

In FIG. 5, the transport speed when transporting the paper S to the secondary transfer nip 143 is changed based on the timing of detection of the leading edge of the paper S, but it is also possible to change the transfer timing (image formation timing) without changing the transport speed. For example, the image formation timing at which the image forming unit 14 forms the image to be transferred to the paper S at the transfer nip 143 may be changed according to the amount of curl imparted to the paper S, thereby changing the transfer timing at which the image is transferred to the paper S at the transfer nip 143.

Next, the curling method according to this embodiment will be described. Figure 6 is a diagram explaining the curling method according to this embodiment, and is a flow chart for the case where feedback control is performed for each sheet of paper.

(Step S11)
The control unit 200 judges whether an image is to be formed on thin paper. For example, based on the settings of the paper S input by the user from the operation unit 122, the control unit 200 judges whether an image is to be formed on thin paper based on whether the basis weight of the paper S is smaller than a predetermined value (e.g., a basis weight of 40 to 50 g/ ^m2 ). If an image is to be formed on thin paper (YES), the process proceeds to step S12, and if an image is not to be formed on thin paper (NO), the process proceeds to step S20.

(Step S12)
The control unit 200 controls the image processing unit 13, the image forming unit 14, the fixing unit 15, the paper feeding unit 16, the paper transport unit 17 and the curling device 18A based on the image formation conditions set by the user, and starts image formation on the paper S.

(Step S13)
The control unit 200 controls the paper feed unit 16, the paper transport unit 17, and the curling device 18A, and detects the leading edge of the first sheet S in the tray using the stiffness detection unit 182 of the curling device 18A. Specifically, as described in Fig. 4, the first leading edge detection sensor 182c of the stiffness detection unit 182 is used to detect the leading edge of the sheet S passing through the transport nip between the transport rollers 182a and 182b.

(Step S14)
The control unit 200 uses the stiffness detection unit 182 of the curling device 18A to calculate the stiffness of the first sheet S in the tray. Specifically, as described in Fig. 4, the second leading edge detection sensor 182d of the stiffness detection unit 182 is used to detect the leading edge of the sheet S after it has passed through the transport nip between the transport rollers 182a and 182b. Then, the control unit 200 obtains the time from when the leading edge of the sheet S is detected by the first leading edge detection sensor 182c to when the leading edge of the sheet S is detected by the second leading edge detection sensor 182d, and calculates the stiffness of the sheet S based on this time.

(Step S15)
The control unit 200 determines the amount of curl to be applied to the sheet S based on the calculated stiffness of the sheet S. Specifically, as the stiffness of the sheet S decreases, the sheet S becomes more likely to wrap around the secondary transfer roller 142, so the amount of curl applied to the sheet S by the curl applying unit 181 is increased. At this time, the sheet S is curled so that the sheet S has a shape opposite to the shape in which the sheet S wraps around the secondary transfer roller 142.

(Step S16)
Based on the determined amount of curl, the control unit 200 uses the curl imparting unit 181 to impart an amount of curl to the sheet S. Specifically, as described in Fig. 3, the amount of curl imparted to the sheet S is adjusted by adjusting the pressure of the moving roller 181a against the sheet S or by adjusting the surface temperature of the moving roller 181a, thereby imparting an amount of curl to the sheet S.

(Step S17)
The control unit 200 detects the amount of curl of the sheet S after the curl has been imparted by the curl imparting unit 181, using the curl amount detection unit 183 of the curl imparting device 18A.

(Step S18)
Based on the detected amount of curl, the control unit 200 corrects the amount of curl applied to the sheet S. That is, the control unit 200 measures the amount of curl of the sheet S after curl application, relative to the amount of curl applied to the sheet S by the curl application unit 181, and corrects the amount of curl based on the difference between the applied amount and the curl amount, for example, so that the amount of curl becomes the desired amount.

(Step S19)
The control unit 200 judges whether there is a next sheet S. For example, the control unit 200 checks whether the number of sheets S on which images have been formed has reached the number of sheets S on which images are to be formed that was set at the start of image formation, and judges whether there is a next sheet S. If there is a next sheet S (YES), the process returns to step S16, and if there is no next sheet S (NO), the image processing ends.

(Step S20)
If the image is not formed on thin paper, there is no need to curl the paper S, and therefore the control unit 200 does not need to use the curling device 18A. Therefore, the control unit 200 controls the image processing unit 13, the image forming unit 14, the fixing unit 15, the paper feed unit 16, and the paper transport unit 17 based on the image formation conditions set by the user to start image formation on the paper S. Then, the control unit 200 ends the image formation process when the number of sheets of paper S on which images have been formed reaches the number of sheets of paper S on which images will be formed that was set at the start of image formation.

In this way, in steps S11 to S20 above, feedback control is performed for each sheet per tray (type of paper S), so the desired amount of curl can be imparted to the paper S on the upstream side of the secondary transfer nip 143. As a result, it is possible to prevent the paper S from wrapping around itself as it passes through the secondary transfer nip 143.

As described above, the image forming apparatus 1A of this embodiment includes a curling device 18A in the image forming apparatus main body 10A. Unlike a paper guide member that guides the paper S to the secondary transfer nip 143 where an image is transferred to the paper S, the curling device 18A includes a curling section 181 that curls the paper S upstream of the secondary transfer nip 143 in the transport direction of the paper S.

According to this embodiment, which is configured in this manner, the desired curl amount is imparted to each type of paper S and to each individual sheet on the upstream transport side of the secondary transfer nip 143, so that it is possible to prevent the paper S from wrapping around itself as it passes through the secondary transfer nip 143. As a result, it is possible to prevent the occurrence of paper jams.

<Modification 1>
7 is a flowchart for explaining the curling method of this modification, which is a case where control is performed for each tray. In this modification, the image forming apparatus 1A may have the same configuration as that described in the above embodiment. Therefore, the curling method of this modification will be described below using the reference numerals used in the above embodiment.

(Step S21)
The control unit 200 judges whether or not an image is to be formed on thin paper. If it is (YES), the process proceeds to step S22. If it is not (NO), the process proceeds to step S27. This step S21 is the same as the above-mentioned step S11.

(Step S22)
Based on the image formation conditions set by the user, the control unit 200 controls the image processing unit 13, the image forming unit 14, the fixing unit 15, the paper feed unit 16, the paper transport unit 17, and the curling device 18A to start image formation on the paper S. This step S22 is also the same as the above-mentioned step S12.

(Step S23)
The control unit 200 controls the paper feed unit 16, the paper transport unit 17, and the curler 18A, and detects the leading edge of the first sheet S in the tray using the stiffness detector 182 of the curler 18A. This step S23 is the same as the above-mentioned step S13.

(Step S24)
The control section 200 uses the stiffness detection section 182 of the curling device 18A to calculate the stiffness of the first sheet S in the tray. This step S24 is also the same as the above-mentioned step S14.

(Step S25)
The control unit 200 determines the amount of curl to be imparted to the sheet S based on the calculated stiffness of the sheet S. This step S25 is the same as the above-mentioned step S15.

(Step S26)
Based on the determined amount of curl, the control unit 200 uses the curl imparting unit 181 to impart an amount of curl to the sheet S. Specifically, as described in Fig. 3, the amount of curl imparted to the sheet S is adjusted by adjusting the pressure of the moving roller 181a against the sheet S or by adjusting the surface temperature of the moving roller 181a, thereby imparting an amount of curl to the sheet S.

When the same type of paper S is set in a tray, there is not much variation (individual difference) in the stiffness of the paper S in that tray. Therefore, in this modified example, the amount of curl is determined based on the stiffness of the first sheet of paper S in the tray, and the same amount of curl is applied to the number of sheets S set at the start of image formation. In other words, unlike the method shown in FIG. 6, feedback control is not performed for each sheet of paper S. Then, the control unit 200 ends the image formation process when the number of sheets of paper S on which images have been formed reaches the number of sheets of paper S on which images will be formed that was set at the start of image formation.

(Step S27)
If the image is not formed on thin paper, there is no need to curl the paper S, and therefore the control unit 200 does not need to use the curling device 18A. Therefore, the control unit 200 controls the image processing unit 13, the image forming unit 14, the fixing unit 15, the paper feed unit 16, and the paper transport unit 17 based on the image formation conditions set by the user to start image formation on the paper S. Then, when the number of sheets of paper S on which images have been formed reaches the number of sheets of paper S on which images will be formed that was set at the start of image formation, the control unit 200 ends the image formation process. This step S27 is similar to the above-mentioned step S20.

In this way, in steps S21 to S27, control is performed for each tray (type of paper S), so the desired amount of curl can be imparted to the paper S on the upstream side of the secondary transfer nip 143. As a result, it is possible to prevent the paper S from wrapping around itself as it passes through the secondary transfer nip 143, and thus to prevent paper jams.

It should be noted that either the curling method described in FIG. 6 or the curling method described in FIG. 7 may be selectively implemented. In this case, the control unit 200 determines whether or not to perform feedback control for each sheet of paper S. For example, the determination is made based on feedback control settings input by the user from the operation unit 122. If feedback control for each sheet of paper S is to be performed, the curling method described in FIG. 6 is implemented, and if feedback control for each sheet of paper S is not to be performed, the curling method described in FIG. 7 is implemented.

<Modification 2>
Fig. 8 is a schematic diagram of an image forming apparatus 1B according to this modification. In the above embodiment, the image forming apparatus 1A includes a curling device 18A inside the image forming apparatus main body 10A. In this modification, the image forming apparatus 1B includes a paper feeder 20 that feeds paper S to the image forming apparatus main body 10B from outside the image forming apparatus main body 10B, as shown in Fig. 8. In this configuration, when paper S that needs to be curled is fed from the external paper feeder 20, the curling device 18B may be provided outside the image forming apparatus main body 10B.

In this modified example, the image forming device 1B includes an image forming device main body 10B and a paper feed device 20. The image forming device main body 10B has a configuration that is substantially equivalent to the image forming device main body 10A of the above embodiment. Therefore, in the image forming device main body 10B, the configuration that is equivalent to the image forming device main body 10A of the above embodiment is given the same reference numerals, and duplicated explanations are omitted.

As described above, the image forming device main body 10B basically has a configuration substantially equivalent to that of the image forming device main body 10A in the above embodiment. However, while the image forming device main body 10A in the above embodiment has a curling device 18A inside, the image forming device main body 10B does not have a curling device 18A inside. In this modified example, the curling device 18B is disposed outside the image forming device main body 10B. This curling device 18B will be described later.

The paper feeder 20 is an external device capable of storing a large volume of paper S. The paper feeder 20 is connected to the side of the image forming device main body 10B (the right side in FIG. 8 ), and feeds paper one sheet at a time from the paper feeder 20 to the image forming device main body 10B.

The paper feed device 20 includes a paper feed unit 21, a transport path section 22, and the like. In FIG. 8, the paper feed device 20 includes a three-stage paper feed unit 21 as an example. The paper feed unit 21 includes a paper storage section 21a, a suction transport section 21b, and the like.

The paper storage section 21a is configured to be able to store a large volume of paper S. Furthermore, the paper storage section 21a is configured so that the topmost sheet of paper S stored therein is always in a fixed position.

The suction transport section 21b is disposed above the paper storage section 21a. The suction transport section 21b includes a transport belt, multiple transport rollers, a suction fan, etc.

The conveyor belt is an endless belt with many holes over its entire surface. The conveyor belt is stretched in a loop around multiple conveyor rollers. The conveyor rollers are driven by a drive motor (not shown) to rotate the conveyor rollers and cause the conveyor belt to run.

The suction fan is positioned inside the conveyor belt. When the suction fan is activated, it sucks in air below the conveyor belt through holes in the conveyor belt. This causes the topmost sheet S to be sucked through the holes and adhered to the conveyor belt.

With this configuration, the suction conveying section 21b adsorbs the topmost sheet S onto the conveying belt, conveys the adsorbed sheet S, and feeds the sheet S to the conveying path section 22.

The transport path section 22 connects each paper feed unit 21 to the image forming device main body 10B and has multiple transport roller pairs. The transport roller pairs hold the paper S transported from the suction transport section 21b, transport it along the transport path section 22, and feed it to the image forming device main body 10B.

The paper feed device 20 having the above configuration cooperates with the control unit 200 of the image forming apparatus main body 10B to control the operation of the paper feed unit 21, the transport path unit 22, etc. In addition, the paper feed device 20 controls the operation of the curling device 18B described below.

In this modified example, the curling device 18B is disposed on the transport path 22 that transports the paper S from the paper feed device 20 to the image forming device main body 10B. On the transport path 22, the curling device 18B is disposed on the exit side of the paper feed device 20.

The curling device 18B has the same configuration as the curling device 18A in the above embodiment, and includes a curling unit 181, a stiffness detection unit 182, and a curl amount detection unit 183. The functions and operations of the curling unit 181, the stiffness detection unit 182, and the curl amount detection unit 183 in the curling device 18B are as described in the above embodiment, so duplicated explanations will be omitted here.

As described above, the image forming apparatus 1B of this embodiment includes a curling device 18B in the paper feeder 20. Unlike a paper guide member that guides the paper S to the secondary transfer nip 143 where an image is transferred to the paper S, the curling device 18B includes a curling section 181 that curls the paper S upstream of the secondary transfer nip 143 in the transport direction of the paper S.

According to this modified example configured in this way, the desired amount of curl is imparted to the paper S on the upstream side of the secondary transfer nip 143, so that the paper S can be prevented from wrapping around itself as it passes through the secondary transfer nip 143. As a result, the occurrence of paper jams can be prevented.

Here, the paper feeder 20 is provided with the curling device 18B, but the curling device 18B itself may be configured as an independent device, and the curling device 18B may be disposed between the image forming apparatus main body 10B and the paper feeder 20.

The above embodiments are merely examples of how the present invention can be implemented, and the technical scope of the present invention should not be interpreted in a limiting manner based on these embodiments. In other words, the present invention can be implemented in various forms without departing from its gist or main characteristics.

Reference Signs List 1A, 1B Image forming apparatus 10A, 10B Image forming apparatus main body 14 Image forming section 141 Intermediate transfer belt 142 Secondary transfer roller 15 Fixing section 151 Fixing belt 152 Pressure roller 17 Paper transport section 171 Registration roller 18A, 18B Curl imparting device 181 Curl imparting section 182 Stiffness detection section 183 Curl amount detection section 191 Paper leading edge detection section 20 Paper feed device J Junction P1 Transport path P2 Reversal path

Claims (19)

a curl imparting section that imparts curl to the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curl imparting section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip that transfers an image onto the paper;
a stiffness detection unit that detects stiffness of the paper;
Equipped with
the curl imparting unit changes the amount of curl imparted to the paper in accordance with the detected stiffness .
Curl imparting device. the curl imparting section has a roller that presses the paper to curve the paper and thereby imparts a curl to the paper;
The curling device according to claim 1 . The curl imparting unit changes the amount of curl imparted to the paper by changing the amount of pressure applied by the roller.
The curling device according to claim 2 . The roller has a heating section for heating the paper.
The curling device according to claim 2 or 3 . the curl imparting unit changes the amount of curl imparted to the paper by changing the amount of heat applied by the heating unit.
The curling device according to claim 4 . a curling section that curls the paper on the upstream side of the transfer nip in the paper transport direction so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curling section being different from a paper guide member that guides the paper to a transfer nip where an image is transferred to the paper;
the curl imparting section has a roller that presses against the paper to curve the paper and thereby imparts a curl to the paper,
The roller has a heating section for heating the paper,
the curl imparting unit changes the amount of curl imparted to the paper by changing the amount of heat applied by the heating unit.
Curl imparting device. a curl amount detection unit that detects the amount of curl generated in the paper after the curl is applied by the curl application unit,
the curl imparting unit changes the amount of curl imparted to the paper in accordance with the detected amount of curl.
The curling device according to any one of claims 1 to 6. a curl imparting section that imparts curl to the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curl imparting section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip that transfers an image onto the paper;
a curl amount detection unit that detects the amount of curl generated in the paper after the curl is applied by the curl application unit;
Equipped with
the curl imparting unit changes the amount of curl imparted to the paper in accordance with the detected amount of curl.
Curl imparting device. The curl imparting unit curls the paper when the basis weight of the paper is smaller than a predetermined value.
The curling device according to any one of claims 1 to 8 . the curl imparting unit changes the amount of curl imparted to the paper depending on the type of the paper.
The curling device according to any one of claims 1 to 9 . A curling device according to any one of claims 1 to 10 ,
Image forming device. a reversing path that branches off from a downstream side of the transfer nip in the transport direction, turns over the paper, and joins a transport path upstream of the transfer nip in the transport direction,
the curling device is disposed between a junction at which the reversing path joins the conveying path and the transfer nip in the conveying direction;
The image forming apparatus according to claim 11 . a transport adjustment unit that adjusts a transport timing of the paper transported to the transfer nip,
the curl applying device is disposed between the transport adjustment unit and the transfer nip in the transport direction.
The image forming apparatus according to claim 11 . a transfer section that transfers the image to the paper at the transfer nip;
a control unit that controls the transfer unit to change a transfer timing for transferring the image onto the paper in accordance with an amount of curl applied to the paper;
Equipped with
The image forming apparatus according to claim 13 . a curling device including a curling section that curls the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curling section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip where an image is transferred onto the paper;
a transport adjustment unit that adjusts a transport timing of the paper transported to the transfer nip;
a transfer section that transfers the image to the paper at the transfer nip;
a control unit that controls the transfer unit to change a transfer timing for transferring the image onto the paper in accordance with an amount of curl applied to the paper;
Equipped with
the curl applying device is disposed between the transport adjustment unit and the transfer nip in the transport direction.
Image forming device. a leading edge detection unit that detects a leading edge of the paper sheet downstream of the curling device in the conveying direction;
a paper transport unit that transports the paper;
a control unit that controls the paper transport unit to change a transport speed of the paper based on a timing when the leading edge of the paper is detected;
Equipped with
The image forming apparatus according to claim 13 . a curling device including a curling section that curls the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip, the curling section being located upstream of the transfer nip in the paper conveying direction, different from a paper guide member that guides the paper to a transfer nip where an image is transferred onto the paper;
a transport adjustment unit that adjusts a transport timing of the paper transported to the transfer nip;
a leading edge detection unit that detects a leading edge of the paper sheet downstream of the curling device in the conveying direction;
a paper transport unit that transports the paper;
a control unit that controls the paper transport unit to change a transport speed of the paper based on a timing when the leading edge of the paper is detected;
Equipped with
the curl applying device is disposed between the transport adjustment unit and the transfer nip in the transport direction.
Image forming device. a paper feeder that feeds the paper from an external device to the image forming apparatus;
the curling device is disposed on a path along which the paper is transported from the paper feeding device to the image forming device;
The image forming apparatus according to claim 11 . a curling unit that is different from a paper guide member that guides the paper to the transfer nip is used on the upstream side of the transfer nip in the paper transport direction of the transfer nip, to curl the paper so that the paper has a shape opposite to the shape of the paper wound around a transfer roller that forms the transfer nip;
changing the amount of curl to be applied to the paper sheet according to the stiffness detected by the stiffness detection unit ;
Curl imparting method.

Images