JP2018058682A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing a step-out of a driving motor for driving a conveying roller arranged on the upstream side in the conveying direction with respect to a loop roller pair and stabilizing sheet conveyance.SOLUTION: The image forming apparatus has: a correction unit (registration roller pair 35) correcting the inclination of a sheet by abutting the tip of the sheet; a loop roller pair 34 arranged on the upstream side in the conveying direction with respect to the correction unit and forming a loop on the sheet abutted against the correction unit; transport roller pairs 31, 32, 33 arranged on the upstream side of the loop roller pair 34 in the conveying direction and feeding the sheet to the loop roller pair 34; and a control unit controlling the nip pressure of the loop roller pair 34.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an electrostatic latent image formed on a photoreceptor is developed with toner to form a toner image, the formed toner image is transferred to a sheet of paper, and the transferred toner image is heated and fixed on the sheet of paper. There is known an electrophotographic image forming apparatus for forming an image.

  In the above image forming apparatus, a registration roller pair is disposed immediately before the transfer roller pair for transferring the toner image to the paper, and the leading edge of the paper is brought into contact with the nip line of the registration roller pair so A process for correcting the inclination of the sheet is performed. After the front end of the sheet is abutted against the nip line of the registration roller pair, a loop (registration loop) is formed on the sheet by feeding the sheet for a predetermined time by a loop roller pair or the like disposed immediately before the registration roller pair.

When the resist loop is formed, a reaction force of the resist loop is generated. In order to form a resist loop against this reaction force, it is necessary to increase the conveyance torque of the pair of loop rollers, but if the conveyance torque is increased, roller marks may remain on the surface of the paper or abnormal images due to frictional charging. There is a risk of causing.
Therefore, in order to solve the above-described problem, a technique is disclosed that includes a torque limiter that controls a pair of loop rollers so that a certain amount or more of conveyance torque is not applied (see, for example, Patent Document 1).

JP 2004-26353 A

  By the way, when the reaction force of the registration loop is applied in the direction opposite to the conveyance direction and the loop roller slips, a load is applied to the conveyance roller (upstream roller) arranged on the upstream side in the conveyance direction with respect to the pair of loop rollers. There is a problem that the drive motor of the upstream roller will step out when restarting after processing. Since the technique described in Patent Document 1 is not configured to prevent the slip of the loop roller, it is difficult to prevent the drive motor of the upstream roller from being stepped out.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of stabilizing paper conveyance by preventing step-out of a drive motor that drives a conveyance roller arranged upstream of a pair of loop rollers. And

The invention described in claim 1 has been made to achieve the above object,
In the image forming apparatus,
A correction unit that abuts the leading edge of the paper to correct the inclination of the paper;
A pair of loop rollers that is arranged on the upstream side of the correction unit in the transport direction and forms a loop on the paper that is abutted against the correction unit;
A transport roller pair that is disposed upstream of the loop roller pair in the transport direction, and that feeds paper to the loop roller pair;
A control unit for controlling the nip pressure of the loop roller pair;
It is characterized by providing.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The correction unit is a pair of registration rollers.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect,
The control unit controls the nip pressure of the loop roller pair to be higher than the nip pressure of the registration roller pair when it is determined that the sheet hits the registration roller pair.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect,
The control unit determines the nip pressure of the loop roller pair from the nip pressure of the registration roller pair until it is determined that the paper hits the registration roller pair after determining that the paper has been nipped by the loop roller pair. Is also controlled to be low.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects,
The control unit controls the nip pressure of the loop roller pair so that the paper does not return to the upstream side in the transport direction with respect to the loop roller pair due to a reaction force of a loop formed by the loop roller pair. To do.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects,
The control unit controls the nip pressure of the loop roller pair based on print information of the paper nipped by the loop roller pair.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects,
The controller is configured to lower the nip pressure of the loop roller pair when it is determined that the sheet has passed through the transport roller pair.

The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7,
The control unit controls the nip pressure of the loop roller pair based on print information of a next sheet.

The invention according to claim 9 is the image forming apparatus according to any one of claims 1 to 8,
A paper detection unit for detecting the paper;
The control unit calculates position information of the paper based on a detection result by the paper detection unit.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects,
The control unit calculates position information of the paper based on a conveyance speed of the paper.

  According to the present invention, it is possible to prevent the step-out of the drive motor that drives the transport roller disposed upstream of the pair of loop rollers in the transport direction, thereby stabilizing the paper transport.

1 is a front view illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a functional block diagram illustrating a control structure of the image forming apparatus according to the present embodiment. FIG. 6 is a diagram illustrating a sheet conveyance path from a reversal path to a secondary transfer roller pair. It is a figure which shows an example of a mode that the loop was formed in the paper. It is a figure which shows the structure of a loop roller pair and a drive part. 5 is a flowchart showing an operation of the image forming apparatus according to the present embodiment. 5 is a flowchart showing an operation of the image forming apparatus according to the present embodiment. It is a figure which shows an example of the table which shows the relationship between print information and loop reaction force. It is a figure which shows an example of the table which shows the relationship between print information and the nip pressure of a loop roller pair. It is a figure which shows an example of a mode that a paper is stopped by a registration shutter.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the image forming apparatus G according to the present embodiment includes an image forming unit 20, and the image forming unit 20 forms an image on a sheet using a color material such as toner.
1 and 2, the image forming apparatus G includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, a communication unit 15, an image generation unit 16, an image reading unit 17, an image memory 18, The image processing unit 19, the image forming unit 20, and the driving unit 30 are provided.

The control unit 11 includes a CPU, a RAM, and the like, and controls each unit by reading and executing various programs from the storage unit 12.
For example, the control unit 11 causes the image processing unit 19 to perform image processing on the original image generated by the image generation unit 16 or the image reading unit 17 and held in the image memory 18, and based on the original image after image processing. Then, the image forming unit 20 forms an image on the sheet.

  The storage unit 12 stores a program that can be read by the control unit 11, a file that is used when the program is executed, and the like. As the storage unit 12, a large-capacity memory such as a hard disk can be used.

As shown in FIG. 1, the operation unit 13 and the display unit 14 are provided on the upper portion of the image forming apparatus G as a user interface.
The operation unit 13 generates an operation signal corresponding to a user operation and outputs the operation signal to the control unit 11. As the operation unit 13, a keypad, a touch panel configured integrally with the display unit 14, or the like can be used.
The display unit 14 displays an operation screen and the like according to instructions from the control unit 11. As the display unit 14, an LCD (Liquid Crystal Display), an OELD (Organic Electro Luminescence Display), or the like can be used.

The communication unit 15 communicates with external devices on the network, for example, user terminals, servers, other image forming systems, and the like.
The communication unit 15 receives vector data in which an instruction content for forming an image is described in a page description language (PDL) via a network from a user terminal.

  The image generation unit 16 rasterizes the vector data received by the communication unit 15 to generate a bitmap-format original image. In the original image, each pixel has pixel values of four colors of C (cyan), M (magenta), Y (yellow), and K (black). The pixel value is a data value representing the density of an image. For example, an 8-bit data value represents a density of 0 to 255 gradations.

  As shown in FIG. 1, the image reading unit 17 includes an automatic document feeder, a scanner, and the like, and reads a document surface set on a document table to generate a bitmap-format original image. In the original image generated by the image reading unit 17, each pixel has pixel values of three colors of R (red), G (green), and B (blue). This original image is color-converted into an original image having pixel values of four colors C, M, Y, and K by a color conversion unit (not shown).

  The image memory 18 is a buffer memory that temporarily holds an original image generated by the image generation unit 16 or the image reading unit 17. As the image memory 18, a DRAM (Dynamic RAM) or the like can be used.

The image processing unit 19 reads an original image from the image memory 18 and performs image processing such as density correction processing and halftone processing.
The density correction process is a process of converting the pixel value of each pixel of the original image into a pixel value corrected so that the density of the image formed on the paper matches the target density.
The halftone process is a process for reproducing halftones in a pseudo manner, and is, for example, an error diffusion process, a screen process using a systematic dither method, or the like.

The image forming unit 20 forms an image having four colors C, M, Y, and K on a sheet according to the pixel values of the four colors of each pixel of the original image subjected to the image processing by the image processing unit 19.
As shown in FIG. 1, the image forming unit 20 includes four writing units 21, an intermediate transfer belt 22, a secondary transfer roller pair 23, a fixing device 24, a paper feed tray 25, and a manual paper feed tray (hereinafter, manual feed tray). Tray) T1, paper discharge tray T2, and the like.

  The four writing units 21 are arranged in series (tandem) along the belt surface of the intermediate transfer belt 22 and form images of C, M, Y, and K colors. Each writing unit 21 has the same configuration except for the color of the image to be formed. As shown in FIG. 1, the optical scanning device 2a, the photosensitive member 2b, the developing unit 2c, the charging unit 2d, the cleaning unit 2e and the primary unit. A transfer roller 2f is provided.

At the time of image formation, each writing unit 21 charges the photosensitive member 2b by the charging unit 2d, and then scans the photosensitive member 2b with a light beam emitted from the optical scanning device 2a based on the original image, thereby forming an electrostatic latent image. Form. When a color material such as toner is supplied and developed by the developing unit 2c, an image is formed on the photoreceptor 2b.
The images formed on the photoreceptors 2b of the four writing units 21 are sequentially transferred onto the intermediate transfer belt 22 and transferred (primary transfer) by the respective primary transfer rollers 2f. As a result, an image composed of each color is formed on the intermediate transfer belt 22. The intermediate transfer belt 22 is an image carrier that is wound around a plurality of rollers and rotates. After the primary transfer, the color material remaining on the photoreceptor 2b is removed by the cleaning unit 2e.

  In the image forming unit 20, paper is fed from the manual feed tray T <b> 1 or the paper feed tray 25 in accordance with the timing at which the image on the rotating intermediate transfer belt 22 reaches the position of the secondary transfer roller pair 23. The pair of secondary transfer rollers 23 constitutes one of a plurality of rollers in which one pair of rollers is pressed against the intermediate transfer belt 22 and the other is wound around the intermediate transfer belt 22. When the image is transferred (secondary transfer) from the intermediate transfer belt 22 onto the sheet by the pressure contact of the secondary transfer roller pair 23, the sheet is conveyed to the fixing device 24, subjected to fixing processing, and discharged to the discharge tray T2. . The fixing process is a process for fixing the image on the sheet by heating and pressing the sheet with the fixing roller pair 241. When images are formed on both sides of the paper, the paper is conveyed to the reversing path 26 to invert the paper surface, and then fed again to the position of the secondary transfer roller pair 23.

  The drive unit 30 controls the nip pressure of the loop roller pair 34 by moving the loop upper roller 341 (see FIG. 3 and the like) of the loop roller pair 34 up and down under the control of the control unit 11.

Next, with reference to FIG. 3, a paper conveyance path from the reverse path 26 to the secondary transfer roller pair 23 will be described.
A plurality of transport roller pairs 31, 32, 33, a loop roller pair 34, and a registration roller pair 35 are arranged in this order from the upstream side in the transport direction on the paper transport path from the reverse path 26 to the secondary transfer roller pair 23. Has been. In the present embodiment, the loop nip portion is formed by press-contacting the loop roller pair 34. Further, a resist nip portion is formed by press-contacting the resist roller pair 35.

The registration roller pair 35 is disposed upstream of the secondary transfer roller pair 23 in the transport direction, and performs a process of correcting the inclination of the sheet at the time of transfer by causing the leading end of the sheet to abut against the registration nip portion. .
The loop roller pair 34 is arranged on the upstream side of the registration roller pair 35 in the transport direction. After the front end of the paper P abuts the registration nip portion of the registration roller pair 35, the paper P is fed into the paper P by feeding the paper P for a predetermined time. A loop (resist loop) L is formed (see FIG. 4).
The plurality of transport roller pairs 31, 32, 33 are arranged on the upstream side of the loop roller pair 34 in the transport direction, and form a transport nip portion by pressing each of the transport roller pairs 31, 32, 33 to form a loop. Sends paper to the roller pair.

The loop roller pair 34 includes a loop upper roller 341 and a loop lower roller 342. The loop lower roller 342 is a driving roller, and the loop upper roller 341 is a driven roller.
A drive unit 30 that controls the nip pressure of the loop roller pair 34 under the control of the control unit 11 is provided above the loop upper roller 341. As shown in FIG. 5, the drive unit 30 includes a cam member 301, a sheet metal member 302 that contacts the lower surface of the cam member 301, a pressing spring 303 attached to the lower surface of the sheet metal member and the shaft of the loop upper roller 341, It is configured with.

  When the cam member 301 rotates, the sheet metal member 302 moves up and down depending on the position of the cam member 301, and the force by which the sheet metal member 302 presses the pressing spring 303 downward increases or decreases. Thereby, the downward urging force with respect to the loop upper roller 341 by the pressing spring 303 is also increased or decreased. In the example shown in FIG. 5, since the cam member 301 is at the position where it is longest downward, the sheet metal member 302 moves to the lowest position, and the force that presses the pressing spring 303 downward becomes maximum. Accordingly, the downward biasing force of the pressing spring 303 against the loop upper roller 341 is maximized, so that the nip pressure of the loop roller pair 34 is maximized.

  Next, the operation of the image forming apparatus G according to the present embodiment will be described with reference to the flowcharts of FIGS. This operation is started when the control unit 11 receives a print job.

First, the control unit 11 acquires print information based on the received print job (step S101). Here, the print information is information relating to image formation based on a print job. In step S101, for example, information such as paper type, basis weight, paper size, environment (temperature and humidity), print volume (number of prints), and the like are acquired.
Next, the control unit 11 starts conveying the paper (step S102).

Next, the control unit 11 determines whether or not the sheet is nipped by the loop roller pair 34 (step S103). In the present embodiment, the control unit 11 calculates paper position information based on the paper conveyance speed. In step S103, the control unit 11 determines whether or not the paper has reached the loop roller pair 34 based on the calculated position information, and determines that the paper has reached the loop roller pair 34. 34, it is determined that the sheet has been nipped.
When it is determined that the sheet is nipped by the loop roller pair 34 (step S103: YES), the control unit 11 proceeds to the next step S104.
On the other hand, when it is determined that the paper is not nipped by the loop roller pair 34 (step S103: NO), the control unit 11 repeats the process of step S103 until it is determined that the paper is nipped by the loop roller pair 34.

  Next, the controller 11 increases the nip pressure of the loop roller pair 34 to the first pressure (step S104). Here, the first pressure is a predetermined pressure lower than the nip pressure of the registration roller pair 35. Therefore, even after the processing in step S104, the nip pressure of the loop roller pair 34 is lower than the nip pressure of the registration roller pair 35. By making the nip pressure of the loop roller pair 34 lower than the nip pressure of the registration roller pair 35, it is possible to prevent the paper from penetrating the registration nip portion.

Next, the control unit 11 determines whether or not the sheet hits the registration nip formed by press-contacting the registration roller pair 35 (step S105). In step S105, the control unit 11 determines whether or not the paper has reached the registration roller pair 35 based on the calculated position information, and determines that the paper has reached the registration roller pair 35. It is determined that the paper hits.
If the control unit 11 determines that the sheet hits the registration nip (step S105: YES), the control unit 11 proceeds to the next step S104.
On the other hand, when the control unit 11 determines that the sheet does not hit the registration nip part (step S105: NO), the control unit 11 repeats the process of step S105 until it is determined that the sheet hits the registration nip part.

  Next, the control unit 11 increases the nip pressure of the loop roller pair 34 to the second pressure (step S106). Here, the second pressure is a predetermined pressure higher than the nip pressure of the registration roller pair 35. Therefore, after the process of step S106, the nip pressure of the loop roller pair 34 is higher than the nip pressure of the registration roller pair 35.

  Note that the second pressure is a pressure that does not cause the sheet to return to the upstream side in the transport direction from the loop roller pair 34 due to the reaction force of the loop formed by the loop roller pair 34 (however, if the pressure is about 1 to 2 mm, the second pressure returns It is also preferable.

The second pressure is preferably determined based on the print information (for example, information such as paper type, basis weight, paper size, environment, print volume, etc.) acquired in step S101.
FIG. 8 shows an example of a table T1 indicating the relationship between print information and loop reaction force. The table T1 has fields of a paper type T11, a paper basis weight T12, a paper size T13, an environment T14 in the apparatus, and a print volume T15 indicating the number of sheets. For example, from the record of “Loop reaction force large”, the paper type T11 is “coated paper”, the basis weight T12 is “heavy”, the size T13 is “large”, and the environment T14 is “LL (low temperature and low humidity; high rigidity)”. It is shown that the loop reaction force increases when the print volume T15 is “large (large roller wear)”. Also, from the record of “low loop reaction force”, the paper type T11 is “plain paper”, the basis weight T12 is “light”, the size T13 is “small”, and the environment T14 is “HH (high temperature and high humidity; low stiffness)”. It is shown that the loop reaction force becomes small when the print volume T15 is “small (small roller wear)”.
In the present invention, it is preferable to increase the nip pressure as the loop reaction force increases and to decrease the nip pressure as the loop reaction force decreases.

Next, the control unit 11 resumes paper conveyance (step S107).
Next, the control unit 11 determines whether or not the sheet has passed through the loop roller pair 34 (step S108). In step S <b> 108, the control unit 11 determines whether the trailing edge of the sheet has passed through the loop roller pair 34 based on the calculated position information.
When it is determined that the sheet has passed through the loop roller pair 34 (step S108: YES), the control unit 11 proceeds to the next step S109.
On the other hand, when it is determined that the sheet has not passed through the loop roller pair 34 (step S108: NO), the control unit 11 repeats the process of step S108 until it is determined that the sheet has passed through the loop roller pair 34.

Next, the control unit 11 lowers the nip pressure of the loop roller pair 34 based on the print information of the next sheet (step S109).
FIG. 9 shows an example of a table T2 showing the relationship between the print information and the nip pressure of the loop roller pair 34. The table T2 has fields of a paper thickness T21, an environment T22 in the apparatus, and a print volume T23 indicating the number of sheets. For example, from the record of “large nip pressure” of the pair of loop rollers 34, the paper thickness T21 is “small”, the environment T22 is “LL (not slipping easily)”, and the print volume T23 is “small (small roller wear)”. In some cases, it is shown that the nip pressure of the loop roller pair 34 is relatively increased in order to secure the conveying force by the loop roller pair 34. Further, from the record of “low nip pressure” of the loop roller pair 34, the paper thickness T21 is “large”, the environment T22 is “HH (easy to slip)”, and the print volume T23 is “large (large roller wear)”. In some cases, it is shown that the nip pressure of the loop roller pair 34 is relatively reduced in order to suppress the leading edge damage of the next sheet.
That is, in the present invention, when the paper thickness of the next paper is thin (when the leading edge of the paper does not collide with the loop roller pair 34) or when it is difficult to slip (when the paper is difficult to transport), the loop roller pair 34 is used. In order to secure the conveying force due to, the nip pressure of the loop roller pair 34 is lowered to a relatively large value. On the other hand, if the next sheet is thick (when the leading edge of the sheet tends to collide with the loop roller pair 34) or if it easily slips (when the sheet is easily transported), the leading edge of the next sheet is suppressed. Therefore, the nip pressure of the loop roller pair 34 is lowered to a relatively small value.

Next, the controller 11 transfers the image from the intermediate transfer belt 22 onto the paper (secondary transfer) by the pressure contact of the secondary transfer roller pair 23 (step S110).
Next, the control unit 11 heats and pressurizes the sheet by the fixing roller pair 241 to fix the image on the sheet (step S111).

Next, based on the received print job, the control unit 11 determines whether or not to form an image on the back surface of the paper subjected to the fixing process in step S111 (step S112).
When it is determined that an image is to be formed on the back surface of the paper subjected to the fixing process (step S112: YES), the control unit 11 conveys the paper to the reversing path 26 and reverses the paper surface (step S113), and proceeds to step S101. The print information is acquired again.
On the other hand, when it is determined that the image is not formed on the back surface of the paper subjected to the fixing process (step S112: NO), the control unit 11 performs a paper discharge process for the paper (step S114).

Next, the control unit 11 determines whether an image has been formed on all sheets based on the received print job (step S115).
When it is determined that the image has been formed on all sheets (step S115: YES), the control unit 11 ends the process.
On the other hand, when it is determined that the image is not formed on all the sheets (step S115: NO), the control unit 11 proceeds to step S101 and acquires print information again.

As described above, the image forming apparatus G according to the present embodiment is disposed on the upstream side in the transport direction with respect to the correction unit (registration roller pair 35) that corrects the inclination of the paper by abutting the leading edge of the paper. , A loop roller pair 34 that forms a loop on the paper abutted against the correction unit, and a transport roller pair 31, 32 that is disposed upstream of the loop roller pair 34 in the transport direction and sends the paper to the loop roller pair 34. 33 and a control unit 11 that controls the nip pressure of the loop roller pair 34.
Therefore, according to the image forming apparatus G according to the present embodiment, since the loop reaction force at the time of forming the registration loop can be stopped by controlling the nip pressure of the loop roller pair 34, the conveyance direction is more than that of the loop roller pair 34. It is possible to prevent the step-out of the drive motor that drives the transport rollers 31, 32, and 33 disposed on the upstream side, and to stabilize the paper transport.

Further, according to the image forming apparatus G according to the present embodiment, the correction unit is the registration roller pair 35.
Therefore, according to the image forming apparatus G according to the present embodiment, the loop reaction force at the time of forming the registration loop can be stopped in the existing configuration using the registration roller pair 35, so that the conveyance roller can be provided without providing a new mechanism. It is possible to prevent the step-out of the drive motor that drives 31, 32, and 33, and to stabilize the sheet conveyance.

Further, according to the image forming apparatus G according to the present embodiment, the control unit 11 determines that the nip pressure of the loop roller pair 34 is greater than the nip pressure of the registration roller pair 35 when it is determined that the sheet hits the registration roller pair 35. Is also controlled to be higher.
Therefore, according to the image forming apparatus G according to the present embodiment, since the loop reaction force at the time of forming the resist loop can be more reliably stopped, even when the loop reaction force at the time of forming the resist loop is large, It is possible to surely prevent the loop reaction force from escaping upstream of the pair of loop rollers 34 in the transport direction.

Further, according to the image forming apparatus G according to the present embodiment, after the control unit 11 determines that the paper has been nipped by the loop roller pair 34, the control unit 11 performs the loop until it is determined that the paper hits the registration roller pair 35. The nip pressure of the roller pair 34 is controlled to be lower than the nip pressure of the registration roller pair 35.
Therefore, according to the image forming apparatus G according to the present embodiment, it is possible to stop the force downstream of the registration roller pair 35 in the transport direction when the registration loop is formed, thereby preventing the paper from penetrating the registration nip portion. be able to.

Further, according to the image forming apparatus G according to the present embodiment, the control unit 11 prevents the sheet from returning to the upstream side in the transport direction from the loop roller pair 34 due to the reaction force of the loop formed by the loop roller pair 34. The nip pressure of the loop roller pair 34 is controlled.
Therefore, according to the image forming apparatus G according to the present embodiment, it is possible to prevent the image forming position from being shifted due to the sheet returning to the upstream side in the transport direction, and thus the accuracy of the image forming position can be improved. .

Further, according to the image forming apparatus G according to the present embodiment, the control unit 11 controls the nip pressure of the loop roller pair 34 based on the print information of the paper nipped by the loop roller pair 34.
Therefore, according to the image forming apparatus G according to the present embodiment, the nip pressure of the loop roller pair 34 can be controlled in accordance with the loop reaction force at the time of forming the registration loop. Can be prevented.

Further, according to the image forming apparatus G according to the present embodiment, the control unit 11 decreases the nip pressure of the loop roller pair 34 when it is determined that the paper has passed through the transport roller pairs 31, 32, and 33.
Therefore, according to the image forming apparatus G according to the present embodiment, the next sheet can easily pass through the loop nip portion of the loop roller pair 34, so that the leading edge of the next sheet can be prevented from being damaged. .

Further, according to the image forming apparatus G according to the present embodiment, the control unit 11 controls the nip pressure of the loop roller pair 34 based on the print information of the next sheet.
Therefore, according to the image forming apparatus G according to the present embodiment, the next sheet can easily pass through the loop nip portion of the loop roller pair 34, so that the leading edge of the next sheet can be prevented from being damaged. .

Further, according to the image forming apparatus G according to the present embodiment, the control unit 11 calculates the position information of the sheet based on the sheet conveyance speed.
Therefore, according to the image forming apparatus G according to the present embodiment, the sheet position information can be fed back to the nip pressure control of the loop roller pair 34 with the existing configuration, so that the loop roller pair can be provided without providing a new mechanism. 34 nip pressure controls can be implemented.

  As mentioned above, although concretely demonstrated based on embodiment which concerns on this invention, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.

  For example, in the above embodiment, the registration roller pair 35 is described as an example of the correction unit of the present invention, but the present invention is not limited to this. For example, as illustrated in FIG. 10, the registration roller pair 35 is a conveyance roller pair 36 that does not have a paper stop function, and the correction unit of the present invention is between the loop roller pair 34 and the conveyance roller pair 36. A registration shutter 37 that stops the sheet P and corrects the inclination of the sheet P may be newly provided. In the case of the above configuration, when the sheet is stopped, the registration shutter 37 is positioned above (see FIG. 10), and when the sheet is conveyed, the registration shutter 37 is positioned below. .

  In the above embodiment, the nip pressure of the loop roller pair 34 is lowered when it is determined in step S108 that the sheet has passed the loop roller pair 34 (see step S109). However, the present invention is not limited to this. It is not something. For example, the nip pressure of the loop roller pair 34 may be decreased when it is determined that the sheet has passed the transport roller pair 33 on the most downstream side in the transport direction.

In the above-described embodiment, the paper position information is calculated based on the paper conveyance speed. However, the present invention is not limited to this. For example, a sensor as a paper detection unit that detects paper may be provided, and the position information of the paper may be calculated based on the detection result of the sensor. In the case of the above configuration, the sensor may be provided immediately before the registration roller pair 35. This makes it possible to detect the timing for controlling the nip pressure of the loop roller pair 34. Further, when detecting the timing at which it is determined that the paper has passed through the loop roller pair 34 (see step S108) and the timing at which it is determined that the paper has passed through the transport roller pair 33, the loop roller pair 34 and the transport roller pair 33 are detected. It is recommended that a sensor be provided immediately after.
Further, a calculation method based on the sheet conveyance speed and a calculation method based on the detection result by the sensor may be used in combination.

  As described above, the sheet detection unit for detecting the sheet is provided, and the position information of the sheet is calculated based on the detection result by the sheet detection unit, so that the actual sheet position is detected and the nip of the loop roller pair 34 is detected. Since feedback can be provided to the pressure control, the nip pressure control of the loop roller pair 34 can be performed at an appropriate timing.

  Moreover, in the said embodiment, although the conveyance roller pair 31,32,33 in the inversion path | route 26 is illustrated and demonstrated as a conveyance roller pair of this invention, it is not limited to this. For example, the transport roller pair 40 (see FIGS. 1 and 3 etc.) in the transport path for transporting paper fed from the manual feed tray T1 or the paper feed tray 25 is used as the transport roller pair of the present invention. Also good.

  In addition, the detailed configuration of each apparatus constituting the image forming apparatus and the detailed operation of each apparatus can be changed as appropriate without departing from the spirit of the present invention.

G image forming apparatus 11 control unit 20 image forming unit 21 writing unit 22 intermediate transfer belt 23 secondary transfer roller pair 24 fixing device 25 paper feed tray 26 reverse path 30 driving unit 301 cam member 302 sheet metal member 303 pressing springs 31 to 33, 40 Transport roller pair 34 Loop roller pair 341 Loop upper roller 342 Loop lower roller 35 Registration roller pair (correction unit)
36 Transport roller pair 37 Registration shutter T1 Bypass tray T2 Discharge tray

Claims (10)

A correction unit that abuts the leading edge of the paper to correct the inclination of the paper;
A pair of loop rollers that is arranged on the upstream side of the correction unit in the transport direction and forms a loop on the paper that is abutted against the correction unit;
A transport roller pair that is disposed upstream of the loop roller pair in the transport direction, and that feeds paper to the loop roller pair;
A control unit for controlling the nip pressure of the loop roller pair;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the correction unit is a pair of registration rollers.   The control unit controls the nip pressure of the loop roller pair to be higher than the nip pressure of the registration roller pair when it is determined that a sheet hits the registration roller pair. The image forming apparatus described in 1.   The control unit determines the nip pressure of the loop roller pair from the nip pressure of the registration roller pair until it is determined that the paper hits the registration roller pair after determining that the paper has been nipped by the loop roller pair. The image forming apparatus according to claim 2, wherein the image forming apparatus is controlled to be lower.   The control unit controls the nip pressure of the loop roller pair so that the paper does not return to the upstream side in the transport direction with respect to the loop roller pair due to a reaction force of a loop formed by the loop roller pair. The image forming apparatus according to any one of claims 1 to 4.   6. The image according to claim 1, wherein the control unit controls a nip pressure of the loop roller pair based on print information of a sheet nipped by the loop roller pair. Forming equipment.   The image forming apparatus according to claim 1, wherein the control unit lowers a nip pressure of the loop roller pair when it is determined that a sheet has passed through the transport roller pair. apparatus.   The image forming apparatus according to claim 1, wherein the control unit controls a nip pressure of the loop roller pair based on print information of a next sheet. A paper detection unit for detecting the paper;
The image forming apparatus according to claim 1, wherein the control unit calculates position information of the paper based on a detection result by the paper detection unit.   The image forming apparatus according to claim 1, wherein the control unit calculates position information of the sheet based on a conveyance speed of the sheet.

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