JP6891523B2 - Image forming device and transfer control method - Google Patents

Description

The present invention relates to an image forming apparatus and a transport control method.

In general, an image forming apparatus (printer, copier, facsimile, etc.) using electrophotographic process technology irradiates (exposes) a charged photoconductor drum (image carrier) with a laser beam based on image data. Form an electrostatic latent image. Then, by supplying toner from the developing device to the photoconductor drum on which the electrostatic latent image is formed, the electrostatic latent image is visualized and the toner image is formed. Further, after the toner image is directly or indirectly transferred to the paper, the toner image is formed on the paper by heating and pressurizing with the fixing nip to fix the toner image.

A resist roller pair, for example, is provided as a transport roller pair on the upstream side of the transfer nip for transferring an image to paper (see, for example, Patent Document 1). When the paper is sandwiched between the resist roller pairs, the resist roller pairs move in the width direction to move the paper before the tip of the paper rushes into the transfer nip, thereby correcting the position of the paper in the width direction.

Further, in general, the paper transfer speed in the resist roller pair is set to be faster than the paper transfer speed in the transfer nip. By doing so, as shown in FIG. 1A, slack is generated in the paper S between the transfer nip (the portion sandwiched between the rollers 423B and 424) and the resist roller pair 53a.

There is a difference in transfer speed due to a difference in roller diameter and a difference in transfer speed due to a difference in alignment between the transfer nip and the resist transfer between the resist roller pair 53a and between the fixing nip and the transfer nip. .. Due to this difference in transport speed, the paper S is pulled between the resist transfers and the fixing transfers, and eventually image defects occur. Therefore, the occurrence of the image defect is suppressed by causing the paper S to loosen during the resist transfer or the like, or by controlling the transport speed in the fixing portion to cause the paper S to loosen during the fixing transfer.

JP-A-2007-163854

By the way, when an image is formed on a long paper having a length larger than the A3 size, the longer the length of the long paper, the larger the amount of paper S conveyed. Therefore, in order to suppress image defects due to differences in roller diameters and transfer speeds due to alignment differences, it is necessary to make a difference between the transfer speed at the transfer nip and the transfer speed at the resist roller pair 53a. The slack of the length paper S1 becomes larger than that of the non-long paper (see FIG. 1A).

Therefore, when the rear end of the long paper S1 passes through the resist roller pair 53a or the resist roller pair 53a is separated during the transportation of the long paper S1, as shown in FIG. 1C, the long paper S1 The amount of return of the paper becomes large, and there is a possibility that image defects such as shock noise may occur at the transfer nip.

An object of the present invention is to provide an image forming apparatus and a transfer control method capable of suppressing the occurrence of image defects in a transfer nip due to loosening of paper between a transfer nip and a transfer roller pair.

The image forming apparatus according to the present invention is
A transfer unit that forms a transfer nip that transfers an image to paper,
A pair of transfer rollers arranged upstream of the transfer nip in the transfer direction of the paper, and a transfer roller pair.
The paper conveyed to the transfer nip formed by the transfer roller pair is conveyed at a predetermined nip pressure, and the transfer speed of the paper at the transfer nip is made faster than the transfer speed of the paper at the transfer nip. A control unit that causes the paper to slacken between the transfer nip and the transport nip by controlling the paper.
With
The control unit has a transfer speed changing process that reduces the difference between the transfer speed of the paper in the transfer nip and the transfer speed of the paper in the transfer nip in response to an increase in the transfer amount of the paper in the transfer nip. At least one of the nip pressure changing process for reducing the nip pressure in the transport nip is executed.

The transport control method according to the present invention is
A transfer unit that forms a transfer nip that transfers an image to paper,
A transport control method for an image forming apparatus including a transport roller pair that is arranged upstream of the transfer nip in the paper transport direction and that moves in the width direction of the paper to correct the position of the paper during transport. And
The paper conveyed to the transfer nip formed by the transfer roller pair is conveyed at a predetermined nip pressure, and the transfer speed of the paper at the transfer nip is made faster than the transfer speed of the paper at the transfer nip. By controlling, the paper is slackened between the transfer nip and the transfer nip.
A transfer speed changing process for reducing the difference between the transfer speed of the paper in the transfer nip and the transfer speed of the paper in the transfer nip according to an increase in the transfer amount of the paper in the transfer nip, and a nip in the transfer nip. At least one of the nip pressure change process for reducing the pressure is performed.

According to the present invention, it is possible to suppress the occurrence of image defects in the transfer nip due to the looseness of the paper between the transfer nip and the transfer roller pair.

It is a figure which shows the transfer of the paper between a transfer nip and a pair of resist rollers. It is a figure which shows schematic the whole structure of the image forming apparatus in this embodiment. The main part of the control system of the image forming apparatus in this embodiment is shown. It is a figure which shows the transfer of the paper between a secondary transfer nip and a pair of resist rollers. It is a figure which shows the paper transfer between a secondary transfer nip and a resist roller pair after changing a transfer speed. It is a figure which shows the transfer of the paper between a secondary transfer nip and a resist roller pair after changing a nip pressure. It is a flowchart which shows an example of the operation example of the transfer control in an image forming apparatus.

Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 2 is a diagram schematically showing the overall configuration of the image forming apparatus 1 according to the present embodiment. FIG. 3 shows a main part of the control system of the image forming apparatus 1 in the present embodiment.

The image forming apparatus 1 of the present embodiment uses long paper or non-long paper as the paper S, and forms an image on the paper S.

In the present embodiment, the long paper is a sheet of paper having a length in the transport direction longer than the commonly used A4 size, A3 size, etc. paper, and cannot be accommodated in the in-machine paper feed tray units 51a to 51c. Has a length. Hereinafter, the term "paper" may include both long paper and non-long paper.

The image forming apparatus 1 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 primary transfers the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photoconductor drum 413 to the intermediate transfer belt 421. After superimposing the toner images of four colors on the intermediate transfer belt 421, the toner image is formed by secondary transfer to paper.

Further, in the image forming apparatus 1, the photoconductor drums 413 corresponding to the four colors of YMCK are arranged in series in the traveling direction of the intermediate transfer belt 421, and the toner images of each color are sequentially transferred to the intermediate transfer belt 421 in one procedure. The tandem method is adopted.

As shown in FIG. 3, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, a control unit 100, and the like.

The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program according to the processing content from the ROM 102, develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the expanded program. At this time, various data stored in the storage unit 72 are referred to.

The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or WAN (Wide Area Network) via the communication unit 71. Do. The control unit 100 receives, for example, image data transmitted from an external device, and forms a toner image on paper based on the image data (input image data).

The image reading unit 10 includes an automatic document feeding device 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

The automatic document feeding device 11 conveys the document D placed on the document tray by the conveying mechanism and sends it out to the document image scanning device 12. The automatic document feeding device 11 can continuously read a large number of images (including both sides) of the documents D placed on the document tray at once.

The document image scanning device 12 optically scans the document conveyed on the contact glass from the automatic document feeding device 11 or the document placed on the contact glass, and the reflected light from the document is a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and the original image is read. The image scanning unit 10 generates input image data based on the scanning result by the document image scanning device 12. The image processing unit 30 performs predetermined image processing on the input image data.

The operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like according to a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

The image processing unit 30 includes a circuit or the like that performs digital image processing according to initial settings or user settings on the input image data. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table LUT) in the storage unit 72 under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, compression processing, and the like, in addition to gradation correction, on the input image data. The image forming unit 40 is controlled based on the image data subjected to these processes.

The image forming unit 40 is an image forming unit 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image with each colored toner of Y component, M component, C component, and K component based on the input image data. Etc. are provided.

The image forming units 41Y, 41M, 41C, 41K for the Y component, the M component, the C component, and the K component have the same configuration. For convenience of illustration and description, common components are indicated by the same reference numerals, and when they are distinguished from each other, they are indicated by adding Y, M, C, or K to the reference numerals. In FIG. 2, the reference numerals are given only to the components of the image forming unit 41Y for the Y component, and the reference numerals are omitted for the other components of the image forming units 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 411, a developing device 412, a photoconductor drum 413, a charging device 414, a drum cleaning device 415, and the like.

The photoconductor drum 413 has, for example, an undercoat layer (UCL: Under Coat Layer), a charge generation layer (CGL: Charge Generation Layer), and a charge transport layer (CGL) on the peripheral surface of a conductive cylindrical body (aluminum tube) made of aluminum. It is a negatively charged organic photo-conductor (OPC) in which CTL: Charge Transport Layer) is sequentially laminated.

The control unit 100 rotates the photoconductor drum 413 at a constant peripheral speed (linear speed) by controlling the drive current supplied to the drive motor (not shown) that rotates the photoconductor drum 413.

The charging device 414 uniformly charges the surface of the photoconductor drum 413 having photoconductivity to a negative electrode property. The exposure apparatus 411 is composed of, for example, a semiconductor laser, and irradiates the photoconductor drum 413 with a laser beam corresponding to an image of each color component. As a result, an electrostatic latent image of each color component is formed on the surface of the photoconductor drum 413 due to the potential difference from the surroundings.

The developing device 412 is, for example, a developing device of a two-component developing method, and forms a toner image by visualizing an electrostatic latent image by adhering toner of each color component to the surface of the photoconductor drum 413.

The drum cleaning device 415 has a cleaning member or the like that is slidably contacted with the surface of the photoconductor drum 413. The drum cleaning device 415 removes the transfer residual toner remaining on the surface of the photoconductor drum 413 after the primary transfer with a cleaning blade.

The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

The intermediate transfer belt 421 is composed of an endless belt, and is stretched in a loop on a plurality of support rollers 423. At least one of the plurality of support rollers 423 is composed of a driving roller, and the other is composed of a driven roller. For example, it is preferable that the roller 423A arranged on the downstream side in the belt traveling direction with respect to the primary transfer roller 422 for the K component is the drive roller. This makes it easier to keep the running speed of the belt in the primary transfer unit constant. As the drive roller 423A rotates, the intermediate transfer belt 421 travels at a constant speed in the direction of arrow A.

The primary transfer roller 422 is arranged on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photoconductor drum 413 of each color component. By pressing the primary transfer roller 422 against the photoconductor drum 413 with the intermediate transfer belt 421 sandwiched between them, a primary transfer nip for transferring the toner image from the photoconductor drum 413 to the intermediate transfer belt 421 is formed.

The secondary transfer roller 424 is arranged on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the backup roller 423B arranged on the downstream side of the drive roller 423A in the belt traveling direction. By pressing the secondary transfer roller 424 against the backup roller 423B with the intermediate transfer belt 421 sandwiched between them, a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S is formed.

The intermediate transfer belt 421, the backup roller 423B, and the secondary transfer roller 424 correspond to the "transfer portion" of the present invention. The secondary transfer nip corresponds to the "transfer nip" of the present invention.

When the intermediate transfer belt 421 passes through the primary transfer nip, the toner image on the photoconductor drum 413 is sequentially superimposed on the intermediate transfer belt 421 and the primary transfer is performed. Specifically, by applying a primary transfer bias to the primary transfer roller 422 and applying a charge having the opposite polarity to the toner on the side in contact with the primary transfer roller 422 of the intermediate transfer belt 421, the toner image is obtained by the intermediate transfer belt 421. Is electrostatically transferred to.

After that, when the paper passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the paper. Specifically, by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having the opposite polarity to the toner on the side of the paper in contact with the secondary transfer roller 424, the toner image is electrostatically charged on the paper. Is transcribed. The paper on which the toner image is transferred is conveyed toward the fixing portion 60.

The belt cleaning device 426 has a belt cleaning blade or the like that is in sliding contact with the surface of the intermediate transfer belt 421, and removes the transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

The fixing portion 60 includes an upper fixing portion 60A having a fixing surface side member arranged on the fixing surface side of the paper, and a lower fixing portion 60B having a back surface side supporting member arranged on the opposite surface side of the fixing surface of the paper. And a heating source 60C and the like. By pressing the back surface side support member against the fixing surface side member, a fixing nip that narrowly holds and conveys the paper is formed.

The fixing unit 60 fixes the toner image on the paper by secondarily transferring the toner image and heating and pressurizing the conveyed paper with the fixing nip. The fixing unit 60 is arranged as a unit in the fixing device F.

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on the basis weight (rigidity), size, etc. is set for each type. Be housed. The transport path portion 53 includes a plurality of transport rollers such as a resist roller pair 53a, a double-sided transport path for forming an image on both sides of the paper, and the like. The resist roller pair 53a corresponds to the "conveying roller pair" of the present invention.

The resist roller pair 53a corrects the position of the paper S in the width direction under the control of the control unit 100. Specifically, when the paper S is sandwiched between the resist roller pair 53a, the resist roller pair 53a moves in the width direction to move the paper S before the tip of the paper rushes into the secondary transfer nip. The position of the paper S in the width direction is corrected.

After correcting the position of the paper S in the width direction, the resist roller pair 53a is separated before the paper S finishes passing through the resist nip formed by the resist roller pair 53a, that is, in the middle of transporting the paper S. It is returned to the position before it was moved. Then, the resist roller pair 53a is crimped again after the rear end of the paper S has passed through the resist nip. The resist nip corresponds to the "conveying nip" of the present invention. The resist roller pair 53a may be left pressed while the paper S is being conveyed.

Further, the transfer speed of the resist roller pair 53a, that is, the paper S at the resist nip is controlled by the control unit 100, and the transfer of the paper S at the backup roller 423B and the secondary transfer roller 424, that is, the secondary transfer nip. Set faster than speed. Specifically, the transport speed of the paper S at the resist nip is a transport speed increased by 0.5% with respect to the transport speed of the paper S at the secondary transfer nip.

Further, the resist roller pair 53a is controlled so as to convey the paper S at a predetermined nip pressure at the resist nip. The predetermined nip pressure is such that the transfer amount of the paper S in the resist nip is larger than the transfer amount of the paper S in the secondary transfer nip at each transfer speed set in the resist nip and the secondary transfer nip. It's pressure.

By doing so, the amount of paper S conveyed in the resist nip becomes larger than the amount of paper S conveyed in the secondary transfer nip, and the amount between the secondary transfer nip and the resist nip (hereinafter, "resist transfer"). The paper S is loosened in the space (referred to as).

Between resist transfer and between fixing nip and secondary transfer nip (hereinafter referred to as "fixing transfer"), there is a difference in transfer speed due to a difference in roller diameter and a difference in transfer speed due to a difference in alignment. .. Due to this difference in transport speed, the paper S is pulled between the resist transfers and the fixing transfers, and eventually image defects occur. Therefore, the occurrence of the above-mentioned image defects is suppressed by causing the paper S to loosen between the resist transfers and by controlling the transport speed in the fixing unit 60 to cause the paper S to loosen between the fixing transfers.

Further, when controlling the transport speed in the fixing unit 60 so that the paper S has slack during the fixing transfer, it is preferable to provide a detecting unit for detecting the slack of the paper S between the fixing and transferring.

The paper S housed in the paper feed tray units 51a to 51c is sent out one by one from the uppermost portion, and is conveyed to the image forming unit 40 by the transfer path unit 53. At this time, the resist roller pair 53a corrects the inclination of the fed paper S and adjusts the transfer timing.

Then, in the image forming unit 40, the toner image of the intermediate transfer belt 421 is collectively secondarily transferred to one surface of the paper S, and the fixing step is performed in the fixing unit 60. The image-formed paper S is discharged to the outside of the machine by the paper ejection unit 52 provided with the paper ejection roller 52a.

By the way, when an image is formed on a long paper having a length larger than the A3 size, the longer the length of the long paper, the larger the amount of paper S conveyed. Since the amount of paper S conveyed at the resist nip is larger than the amount of paper S conveyed at the secondary transfer nip between resist transfers, the amount of slack of the paper S increases as the amount of paper S conveyed increases.

For example, when the transport speed of the paper S at the resist nip is increased by 0.5% with respect to the transport speed of the paper S at the secondary transfer nip, the maximum length of the paper S having a length in the transport direction of 488 mm is increased. The amount of slack is 2.4 mm. The amount of slack is the length of the paper S between resist transfers. On the other hand, when the paper S having a length of 1200 mm in the transport direction is transported, the maximum amount of slack is 6 mm between the resist transfers.

In this way, in order to suppress image defects due to differences in roller diameter and transfer speed due to alignment differences, if there is a difference between the transfer speed at the secondary transfer nip and the transfer speed at the resist nip, an image is formed on long paper. The amount of slack in the paper S becomes larger than that in the case of non-long paper.

For example, in the case of a long paper having a length of 1200 mm in the transport direction, the difference in the amount of slack is 3 mm or more as compared with the non-long paper having a length of 488 mm in the transport direction, which is more than double the amount of slack of the non-long paper. Will be.

Therefore, when the rear end of the paper S passes through the resist nip or the resist roller pair 53a is separated during the transportation of the paper S, the return amount of the paper S becomes large as shown in FIG. Image defects such as shock noise may occur at the next transfer nip.

Therefore, in the present embodiment, the control unit 100 causes at least one of the following transfer speed change process and nip pressure change process to be executed according to the increase in the transfer amount of the paper S in the resist nip.

The transport speed changing process is a process of reducing the difference between the transport speed of the paper S in the resist nip and the transport speed of the paper S in the secondary transfer nip. Specifically, as shown in FIG. 4, the control unit 100 sets the transport speed at the resist nip to the transport speed in the initial state until the transport amount of the paper S reaches a predetermined transport amount, and transports the paper S. Control the speed.

Then, as shown in FIG. 5, when the transport amount of the paper S reaches a predetermined transport amount, the control unit 100 reduces the transport speed at the resist nip to be slower than the transport speed before the change, thereby increasing the transport speed. Make the difference smaller. The transfer speed of the changed paper S is set to, for example, the same transfer speed as the transfer speed in the secondary transfer nip.

The predetermined transport amount is, for example, a transport amount corresponding to the slack amount of the paper S to the extent that image defects due to the slack of the paper S do not occur, and is appropriately changed depending on the space between the resist transfers of the image forming apparatus 1. You may. For example, when the slack amount of the paper S to the extent that image defects do not occur on the paper S having a length of 488 mm in the transport direction is 2.4 mm, the predetermined transport amount is the transport amount corresponding to the 2.4 mm. .. The predetermined transport amount can be appropriately set according to the type of paper S and the like.

By controlling in this way, the remaining portion of the long paper can be conveyed while maintaining the slack of the paper S to the extent that image defects do not occur between the resist transfers. Therefore, it is possible to prevent the amount of slack of the paper S from becoming too large during the transfer of long paper, and it is possible to suppress the occurrence of image defects in the secondary transfer nip due to the slack of the paper S during resist transfer. be able to.

Further, the nip pressure changing process is a process of gradually reducing the nip pressure in the resist nip from a predetermined nip pressure. Specifically, as shown in FIG. 4, the nip pressure at the resist nip remains at the predetermined nip pressure under the control of the control unit 100 until the transport amount of the paper S at the resist nip reaches the predetermined transfer amount. Paper S is conveyed. Then, when the amount of paper S conveyed in the resist nip reaches a predetermined amount, as shown in FIG. 6, the paper S is conveyed in a state where the nip pressure in the resist nip is reduced under the control of the control unit 100. To.

Further, as a control for reducing the nip pressure, there is a control for changing the pressure bonding amount of the resist roller pair 53a by controlling a cam or the like (not shown) for crimping the resist roller pair 53a. That is, the control unit 100 reduces the nip pressure in the resist roller pair 53a by moving the rollers in the resist roller pair 53a to the side away from each other (see the broken line arrow in FIG. 6).

As a result, the amount of paper S conveyed by the resist roller pair 53a is gradually reduced, so that the slack of the paper S does not become too large during the resist transfer, and the state at the start of control is maintained. Therefore, it is possible to suppress the occurrence of image defects in the secondary transfer nip due to the looseness of the paper S between resist transfers.

By the way, when the stiffness of the paper S is weak, the paper S tends to loosen. Therefore, if the nip pressure is loosened at the resist nip, the conveying force of the paper S at the resist nip is not secured, and it becomes difficult to control the looseness of the paper S. there is a possibility. Therefore, when the stiffness of the paper S is weak, it is desirable to transport the paper S by the transfer speed changing process.

On the other hand, when the stiffness of the paper S is strong, the restoring force of the paper S to return to its original state becomes strong when the rear end of the paper S passes through the resist nip or when the resist rollers 53a are separated from each other.

Considering the viewpoint of utilizing the restoring force of the paper S, rather than forcibly controlling the slack of the paper S while maintaining the nip pressure by the transfer speed changing process, the nip pressure at the resist nip is weakened to increase the transfer force. Loosening makes it easier to maintain an appropriate amount of slack in the paper S. Therefore, when the paper S is strong, it is desirable to convey the paper S by the nip pressure changing process.

Therefore, the control unit 100 causes either the transfer speed change process or the nip pressure change process to be executed according to the rigidity of the paper S. Specifically, the control unit 100 executes a transfer speed change process when the paper S is a thin paper having a weak stiffness (for example, a basis weight of 80 gsm or less). Further, the control unit 100 executes a nip pressure changing process when the paper S is a thick paper having a strong stiffness (for example, a basis weight of 211 gsm or more). As a result, appropriate transport control can be performed according to the rigidity of the paper S.

Further, since the stiffness of the paper S fluctuates according to the environment around the image forming apparatus 1, the control unit 100 performs the transfer speed changing process and the nip pressure changing process according to the environment around the image forming apparatus 1. Have one of them executed.

Specifically, the control unit 100 executes a transfer speed changing process when the stiffness of the paper S becomes weak as in a high temperature and high humidity environment. Further, the control unit 100 executes a nip pressure changing process when the paper S becomes stiff as in a low temperature and low humidity environment. As a result, it is possible to perform appropriate transport control according to the surrounding environment of the image forming apparatus 1.

By the way, in double-sided printing, after the image is formed on the first surface (for example, the front surface) of the paper S, the image is formed on the second surface (for example, the back surface) opposite to the first surface. To. When the image is formed on the first surface, the image is not formed on both sides, but when the image is formed on the second surface, the image is formed on the first surface.

Therefore, the slip amount in the resist nip differs between the case where the image is formed on the first surface and the case where the image is formed on the second surface. Specifically, when an image is formed on the paper S, it is more likely to slip at the resist nip than when an image is not formed. Therefore, when forming an image on the second surface during double-sided printing, It is necessary to secure a certain amount of nip pressure.

Therefore, in double-sided printing, the control unit 100 performs a transfer speed change process and a pressing force change process depending on whether an image is formed on the first surface of the paper S or an image is formed on the second surface of the paper S. Have one of them executed.

When an image is formed on the first surface of the paper S and then an image is formed on the second surface, the image is formed on the first surface, so that the resist nip tends to slip. Therefore, the control unit 100 executes the pressing force changing process.

Further, when forming an image on the first surface of the paper S, the control unit 100 may select an appropriate one according to the rigidity of the paper S and the surrounding environment of the image forming apparatus 1. When the coverage of the image formed on the first surface is small, it becomes difficult for the resist nip to slip. In this case, an appropriate one is used depending on the rigidity of the paper S and the surrounding environment of the image forming apparatus 1. It is good to select.

By doing so, in the case of double-sided printing, it is possible to perform appropriate transport control according to the image formation state on the paper S.

Further, by storing the tables shown in Tables 1 to 3 below in the storage unit 72 (see FIG. 3), the control unit 100 can perform the transfer speed change process and the nip pressure change process while referring to the table. To execute one of the above.

Table 1 is a table showing the susceptibility of image defects to each process for each basis weight of the paper S under normal temperature and humidity conditions. Table 2 is a table showing the susceptibility of image defects to each process for each basis weight of the paper S under high temperature and high humidity conditions. Table 3 is a table showing the susceptibility of image defects to each process for each basis weight of the paper S under low temperature and low humidity conditions. In addition, "◯" in Tables 1 to 3 indicates that image defect does not occur, and "x" indicates that image defect is likely to occur.

By referring to the table as described above, for example, a process corresponding to a condition in which image defects are likely to occur, such as a nip pressure change process when the basis weight of the paper S is 50 to 80 gsm as shown in Table 1, is not selected. Can be done. Therefore, the transport control can be performed after accurately selecting the conditions under which image defects do not occur.

Here, for example, when the basis weight in Table 1 is in the range of 81 to 210 gsm, it is a condition that no image defect occurs in any of the transport speed changing process and the nip pressure changing process. In such a case, the control unit 100 may select whether to execute either the transfer speed change process or the nip pressure change process, or to execute the transfer speed change process and the nip pressure change process at the same time. good.

By doing so, it is possible to widen the range of selections in the transfer control, so that it is possible to facilitate appropriate transfer control according to the conditions.

Further, the control unit 100 may alternately execute the transfer speed change process and the nip pressure change process. By doing so, for example, even when the type of paper S changes in the same print job, it is possible to perform appropriate transport control corresponding to the rigidity of the paper S during transport, and it is possible to perform appropriate transport control for one sheet. During the image formation of the paper S, the transport speed changing process and the nip pressure changing process can be flexibly used according to the situation of the paper S.

Further, the user may be able to select either one or both of the transfer speed change process and the nip pressure change process based on the tables in Tables 1 to 3 above depending on the usage conditions. In this case, it is necessary for the operation unit 22 (see FIGS. 2 and 3) to allow the user to select either or both of the transport speed change process and the nip pressure change process.

Then, the control unit 100 can execute at least one of the transfer speed change process and the nip pressure change process according to the operation information in the operation unit 22, that is, the user's instruction. Thereby, the user can select an appropriate transfer control according to the type of the paper S and the environment of the image forming apparatus 1 while referring to the above table.

Further, the user may arbitrarily select at least one of the transfer speed change process and the nip pressure change process after confirming the state of the paper S after the image formation.

An example of the operation of the transport control in the image forming apparatus 1 configured as described above will be described. FIG. 7 is a flowchart showing an example of an operation example of transport control in the image forming apparatus 1. The process shown in FIG. 7 is appropriately executed when the print job is performed. The process in the figure is an example of control when the paper S is a long paper under normal temperature and humidity conditions.

As shown in FIG. 7, the control unit 100 determines whether or not the amount of paper S conveyed is equal to or greater than the predetermined amount (step S101). As a result of the determination, when the conveyed amount of the paper S is not equal to or more than the predetermined conveyed amount (steps S101, NO), the process of step S101 is repeated.

On the other hand, when the conveyed amount of the paper S becomes equal to or more than a predetermined conveyed amount (YES in step S101), the control unit 100 determines whether or not the basis weight of the paper S is, for example, 80 gsm or less (step S102). .. As a result of the determination, when the basis weight of the paper S is 80 gsm or less (step S102, YES), the control unit 100 executes the transport speed change process (step S103).

On the other hand, when the basis weight of the paper S is not 80 gsm or less (step S102, NO), the control unit 100 determines whether or not the basis weight of the paper S is 211 gsm or more (step S104). As a result of the determination, when the basis weight of the paper S is 211 gsm or more (step S104, YES), the control unit 100 executes the nip pressure changing process (step S105).

On the other hand, when the basis weight of the paper S is not 211 gsm or more (step S104, NO), the control unit 100 transitions to, for example, the process of step S103. That is, the control unit 100 executes the transport speed change process. If NO is determined in step S104, the process of step S105, that is, the nip pressure change process may be executed, or both the transfer speed change process and the nip pressure change process may be executed at the same time.

After step S103 and step S105, the control unit 100 determines whether or not the print job has been completed (step S106). As a result of the determination, if the print job is not completed (step S106, NO), the process returns to step S101. On the other hand, when the print job ends (step S106, YES), this control ends.

According to the present embodiment configured as described above, it is possible to prevent the amount of slack of the paper S from becoming too large during the transportation of the long paper, which is caused by the slack of the paper S during the resist transfer. It is possible to suppress the occurrence of image defects in the secondary transfer nip.

Further, even in the case of non-long paper, if there is a possibility that shock noise may occur in the latter half of the transfer of the paper S, the secondary transfer nip is performed by performing the transfer speed change process or the nip pressure change process during the transfer. It is possible to suppress the occurrence of image defects in.

Further, since either the transfer speed change process or the nip pressure change process is executed according to the rigidity of the paper S and the environment around the image forming apparatus 1, it is possible to perform appropriate transfer control according to the situation.

In addition, the above-described embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

1 Image forming device 53a Resist roller vs. 100 Control unit 421 Intermediate transfer belt 423B Backup roller 424 Secondary transfer roller

Claims (8)

A transfer unit that forms a transfer nip that transfers an image to paper,
A pair of transfer rollers arranged upstream of the transfer nip in the transfer direction of the paper, and a transfer roller pair.
The paper conveyed to the transfer nip formed by the transfer roller pair is conveyed at a predetermined nip pressure, and the transfer speed of the paper at the transfer nip is made faster than the transfer speed of the paper at the transfer nip. A control unit that causes the paper to slacken between the transfer nip and the transport nip by controlling the paper.
With
The control unit has a transfer speed changing process that reduces the difference between the transfer speed of the paper in the transfer nip and the transfer speed of the paper in the transfer nip in response to an increase in the transfer amount of the paper in the transfer nip. At least one of the nip pressure changing process for reducing the nip pressure in the transport nip is executed, and in the case of double-sided printing, an image is formed on the first surface of the paper or a second surface opposite to the first surface. Either the transfer speed change process or the nip pressure change process is executed depending on whether an image is formed on the surface.
Image forming device. A transfer unit that forms a transfer nip that transfers an image to paper,
A pair of transfer rollers arranged upstream of the transfer nip in the transfer direction of the paper, and a transfer roller pair.
The paper conveyed to the transfer nip formed by the transfer roller pair is conveyed at a predetermined nip pressure, and the transfer speed of the paper at the transfer nip is made faster than the transfer speed of the paper at the transfer nip. A control unit that causes the paper to slacken between the transfer nip and the transport nip by controlling the paper.
With
The control unit has a transfer speed changing process that reduces the difference between the transfer speed of the paper in the transfer nip and the transfer speed of the paper in the transfer nip in response to an increase in the transfer amount of the paper in the transfer nip. At least one of the nip pressure changing process for reducing the nip pressure in the transport nip is executed, and the transport speed changing process and the nip pressure changing process are alternately executed.
Image forming device. When the transport amount of the paper reaches a transport amount corresponding to the slack amount of the paper to the extent that image defects due to the slack of the paper do not occur, the control unit performs the transport speed change process and the nip pressure. Have at least one of the change processes performed,
The image forming apparatus according to claim 1 or 2. The control unit executes either the transport speed change process or the nip pressure change process according to the rigidity of the paper.
The image forming apparatus according to any one of claims 1 to 3. The control unit executes either one of the transfer speed change process and the nip pressure change process according to the environment around the image forming apparatus.
The image forming apparatus according to any one of claims 1 to 4. The control unit executes at least one of the transfer speed change process and the nip pressure change process according to a user's instruction.
The image forming apparatus according to any one of claims 1 to 5. A transfer unit that forms a transfer nip that transfers an image to paper,
A transport control method for an image forming apparatus including a transport roller pair that is arranged upstream of the transfer nip in the paper transport direction and that moves in the width direction of the paper to correct the position of the paper during transport. And
The paper conveyed to the transfer nip formed by the transfer roller pair is conveyed at a predetermined nip pressure, and the transfer speed of the paper at the transfer nip is made faster than the transfer speed of the paper at the transfer nip. By controlling, the paper is slackened between the transfer nip and the transfer nip.
A transfer speed changing process for reducing the difference between the transfer speed of the paper in the transfer nip and the transfer speed of the paper in the transfer nip according to an increase in the transfer amount of the paper in the transfer nip, and a nip in the transfer nip. At least one of the nip pressure changing process for reducing the pressure is executed, and in the case of double-sided printing, an image is formed on the first surface of the paper or an image is formed on the second surface opposite to the first surface. A transport control method for executing either the transport speed change process or the nip pressure change process according to the case. A transfer unit that forms a transfer nip that transfers an image to paper,
A transport control method for an image forming apparatus including a transport roller pair that is arranged upstream of the transfer nip in the paper transport direction and that moves in the width direction of the paper to correct the position of the paper during transport. And
The paper conveyed to the transfer nip formed by the transfer roller pair is conveyed at a predetermined nip pressure, and the transfer speed of the paper at the transfer nip is made faster than the transfer speed of the paper at the transfer nip. By controlling, the paper is slackened between the transfer nip and the transfer nip.
A transfer speed changing process for reducing the difference between the transfer speed of the paper in the transfer nip and the transfer speed of the paper in the transfer nip according to an increase in the transfer amount of the paper in the transfer nip, and a nip in the transfer nip. A transport control method in which at least one of a nip pressure changing process for reducing the pressure is executed, and the transport speed changing process and the nip pressure changing process are alternately executed.

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