JP5942865B2 - Image forming system - Google Patents

Description

  The present invention relates to an image forming system including a sheet cooling mechanism that cools a sheet downstream of a fixing unit in a sheet conveyance direction.

  In an image forming system, a sheet on which a toner image is fixed by a fixing unit is cooled by a belt nipping type sheet cooling mechanism. The belt-clamping type paper cooling mechanism conveys the paper with the toner image fixed between the upper belt and the lower belt facing the upper belt. At this time, a cooling member made of a metal material is brought into contact with the back side of the surface of the upper belt or the lower belt that contacts the paper, and the paper is cooled through the upper belt or the lower belt.

  For example, Patent Document 1 discloses a configuration including two cooling members corresponding to an upper belt and a lower belt as a belt-clamping type paper cooling mechanism.

JP 2008-112102 A

  In a conventional belt-clamping type paper cooling mechanism, a driving roller that drives the belt is sandwiched between the belt and the belt for the purpose of preventing slippage caused by insufficient frictional force at the contact portion between the belt and the paper when passing thick paper. The structure which provides the press roller which presses by may be taken.

FIG. 6 is a schematic side view of a conventional sheet cooling mechanism and fixing unit.
A belt-clamping sheet cooling mechanism 210 is disposed downstream of the fixing unit 200 including the upper fixing roller 201 and the lower fixing roller 202 in the sheet conveying direction. The sheet cooling mechanism 210 includes an endless upper belt 211, a driving roller 212 that drives the upper belt 211, driven rollers 213, 214, and 215, and a cooling member 216 that cools the upper belt 211. In addition, the sheet cooling mechanism 210 includes a lower belt 221 disposed so as to face the upper belt 211. Inside the lower belt 221, a pressing roller 226 is provided in parallel with the driving roller 212. In the inner space of the lower belt 221, a driving roller 222 that is driven in accordance with driving of the driving roller 212 and driven rollers 223, 224, and 225 are disposed.

  The sheet cooling mechanism 210 rotates the driving roller 212 to drive the upper belt 211, and conveys the sheet conveyed from the fixing unit 200 while making surface contact with the upper belt 211 and the lower belt 221. The friction coefficient between the belt and the paper when transporting with the paper sandwiched between the belts (belt transport) is the friction coefficient between the belt and the paper when transporting the paper with the paper sandwiched between the rollers (roller transport) Smaller, and therefore less frictional force. Therefore, in order to prevent the occurrence of slip when the thick paper is passed, the nip portion formed by the upper belt 211 and the lower belt 221 in the vicinity of the driving roller 212 and the pressing roller 226 is pressed by pressing the pressing roller 226 toward the driving roller 212. The pressure (hereinafter referred to as “nip pressure”) is always set high. However, the belt-clamping type paper cooling mechanism 210 has a problem that paper wrinkles are likely to occur due to the structure in which the paper is sandwiched between the belts and conveyed, and when the nip pressure is increased, paper wrinkles are more likely to occur.

FIG. 7 is an explanatory diagram showing a range of an appropriate pressing force of the roller when passing thin paper and thick paper.
As shown in the left figure of FIG. 7, in the case of roller conveyance, if the pressing force between the rollers is high, paper wrinkles are likely to occur when passing thin paper, and if the pressing force is low, slipping is likely to occur when passing thick paper. Become. Therefore, in the case of roller conveyance, the pressing force of the roller 252 may simply be set to an intermediate level (shaded area in the left diagram of FIG. 7) where no paper wrinkle and slip occur.

Further, in the case of the belt conveyance, that is, the paper cooling mechanism 210 (FIG. 6), the same as in the case of the roller conveyance, but when passing thin paper, the paper and the belt are brought into surface contact as compared with the case of roller conveyance. The upper limit of the pressing force of the pressing roller 226 that does not generate wrinkles is lowered.
On the other hand, since the friction coefficient between the belt and the paper is smaller than in the case of roller conveyance, the lower limit of the appropriate pressing force of the pressing roller 226 for preventing the occurrence of slipping when passing thick paper is increased.
Therefore, as can be seen from FIG. 7, in the case of belt conveyance, there is no range in which the pressing force of the pressing roller 226 can be set in a range where neither paper slip nor paper wrinkle occurs.

  In view of the above situation, there has been a demand for a method of conveying paper without causing paper slip and paper wrinkles in the paper cooling mechanism after fixing.

  An image forming system according to one aspect of the present invention includes a fixing unit that fixes a toner image transferred to a sheet, and a sheet that has passed through the fixing unit, using a first belt and a second belt that faces the first belt. A paper cooling mechanism that cools while sandwiching and conveying is provided. The sheet cooling mechanism includes a driving roller that drives the first belt, a pressing roller that presses the driving roller via the second belt and the first belt, and a pressure adjustment mechanism that adjusts the pressing force of the pressing roller. Then, the control unit determines the type of the paper, and controls the pressing force of the pressing roller by the pressure adjusting mechanism according to the type of the paper.

  According to the above configuration, since the pressing force of the pressing roller is appropriately set according to the type of the sheet, the driving belt and the first belt near the pressing roller and the first belt near the pressing roller are within a range in which the sheet does not slip and wrinkle. The nip pressure of the second belt is adjusted.

  According to the present invention, the paper can be transported in the paper cooling mechanism after fixing without causing paper slip and paper wrinkles.

1 is a schematic diagram illustrating an overall configuration of an image forming system according to an embodiment of the present invention. 1 is a perspective view showing a sheet cooling mechanism of an image forming system according to an embodiment of the present invention. 1 is a front view showing a sheet cooling mechanism of an image forming system according to an embodiment of the present invention. 1 is a block diagram illustrating a hardware configuration of each unit of an image forming system according to an embodiment of the present invention. It is a table which shows the example of a relationship between the kind of paper which concerns on one embodiment of this invention, and the setting of the pressing force of a press roller. It is a schematic side view of a conventional sheet cooling mechanism and a fixing unit. It is explanatory drawing which shows the range of the suitable pressing force of a roller at the time of letting thin paper and thick paper pass.

  Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the accompanying drawings. In the drawings, common components are denoted by the same reference numerals, and redundant description is omitted.

[Example of overall configuration of image forming system]
FIG. 1 is a schematic diagram showing an overall configuration of an image forming system according to an embodiment of the present invention. In FIG. 1, a part considered necessary for the description of the present invention is extracted from the configuration of the image forming system.

  As shown in FIG. 1, the image forming system 1 includes a paper feeding device 20, an image forming device 10 as a first main body, and a fixing device 30 as a second main body.

  The paper feeding device 20 is provided with a plurality of paper storage portions 20a according to the paper size and type. In the paper feeding device 20, the corresponding paper storage unit 20 a is selected based on an instruction from the image forming device 10, the paper S is taken out by a paper feeding unit (not shown), and is sent to the conveyance path C of the image forming device 10. .

  The image forming apparatus 10 employs an electrophotographic system in which an image is formed using static electricity, and toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (Br) are obtained. This is a tandem-type color image forming apparatus for superimposing. The image forming apparatus 10 includes, for example, an operation display unit 105, an image forming unit 5, an intermediate transfer belt 6, and a secondary transfer unit 7.

  The image forming unit 5 includes four image forming units 5Y, 5M, 5C, and 5K in order to form toner images of colors of yellow, magenta, cyan, and black. Further, the image forming apparatus 10 includes a plurality of rollers (conveying rollers) 11, 12, and 13 for conveying paper. The rollers 11, 12, and 13 are usually constituted by a pair of rollers. Each roller described below has the same configuration. The operation display unit 105 has a function as an operation unit that instructs the start of a job such as image forming processing. The image forming apparatus 10 includes a paper storage unit 14. When the operation display unit 105 selects the paper storage unit 14, the paper stored in the paper storage unit 14 is sent to the conveyance path C.

  In the image forming mode, the image forming apparatus 10 charges the photosensitive member included in the image forming units 5Y, 5M, 5C, and 5K, erases the charge in accordance with the original image, and exposes the electrostatic latent image on the photosensitive member. Form. Then, toner is attached to the electrostatic latent images on the yellow, magenta, cyan, and black photoconductors using a developing unit to form toner images of each color. Next, the toner images formed on the yellow, magenta, cyan, and black photoreceptors are sequentially primary-transferred onto the surface of the rotating intermediate transfer belt 6.

  Next, using the secondary transfer unit, the toner image of each color on the intermediate transfer belt 6 is supplied from the sheet feeding device 20 and conveyed by the rollers 11 and 12 using the secondary transfer unit 7. Secondary transfer to. The image forming apparatus 10 discharges the sheet S on which the color toner image is formed to the fixing device 30 by the roller 13.

  The fixing device 30 is a device that performs a fixing process on the paper S on which a color toner image is formed, which is supplied from the image forming apparatus 10. The fixing device 30 includes, for example, a fixing unit 31, a sheet cooling mechanism 32, a first tip detection sensor 33, a second tip detection sensor 34, and a discharge roller 35.

  The fixing unit 31 provided in the fixing device 30 pressurizes and heats the conveyed paper S, and fixes the transferred toner image on the paper S. The fixing unit 8 includes, for example, a fixing upper roller 201 and a fixing lower roller 202 which are a pair of fixing members. The upper fixing roller 201 and the lower fixing roller 202 are arranged in pressure contact with each other, and a fixing nip portion is formed as a pressing portion between the upper fixing roller 201 and the lower fixing roller 202.

  A heating unit is provided inside the fixing upper roller 201. The roller portion on the outer peripheral portion of the fixing upper roller 201 is warmed by the radiant heat from the heating portion. Then, the heat of the roller portion of the fixing upper roller 201 is transmitted to the sheet, whereby the toner image on the sheet is thermally fixed.

  The sheet S is conveyed so that the surface (surface to be fixed) onto which the toner image is transferred by the secondary transfer unit 7 faces the fixing upper roller 201 and passes through the fixing nip portion. Accordingly, the sheet passing through the fixing nip portion is pressed by the upper fixing roller 201 and the lower fixing roller 202 and heated by the heat of the roller portion of the upper fixing roller 201.

  A paper cooling mechanism 32 is disposed downstream of the fixing unit 31 in the paper conveyance direction. The sheet cooling mechanism 32 cools the sheet S after the fixing process. The sheet cooling mechanism 32 is preferably immediately after the fixing unit 31 in the sheet conveyance direction, but is not limited thereto. The basic structure of the paper cooling mechanism 32 is the same as that of the paper cooling mechanism 210 in FIG. The structure of the sheet cooling mechanism 32 will be described later. The sheet S conveyed from the fixing unit 31 is cooled by the sheet cooling mechanism 32 and then discharged to the sheet discharge tray 50 by the discharge roller 35.

  The first leading edge detection sensor 33 is disposed between the fixing unit 31 and the sheet cooling mechanism 32 so as to face the conveyance path C, and has a function as a first leading edge detection unit that detects the leading edge of the conveyed sheet S. . Similarly, a second tip detection sensor 34 having a function as a second tip detection unit is disposed on the discharge side of the sheet cooling mechanism 32. The first leading edge detection sensor 33 and the second leading edge detection sensor 34 particularly detect the leading edge (rear edge) of the sheet S on the downstream side in the sheet conveyance direction.

  It is desirable that the first leading edge detection sensor 33 is disposed immediately after the fixing unit 31 and the second leading edge detection sensor 34 is disposed immediately after the sheet cooling mechanism 32. The first tip detection sensor 33 and the second tip detection sensor 34 include, for example, a transmissive photosensor in which a light emitting member and a light receiving member are arranged to face each other, or a reflective photosensor that detects reflected light from an emitted light object. Etc. are used.

  In the image forming system 1 shown in FIG. 1, an example is shown in which an image is formed on one side of a sheet, but an image is formed on both sides of a sheet, and both sides of the sheet are cooled sequentially or simultaneously by a sheet cooling mechanism. It is good.

[Paper cooling mechanism]
Hereinafter, the sheet cooling mechanism 32 of the image forming system 1 according to the embodiment of the present disclosure will be described.
FIG. 2 is a perspective view showing the sheet cooling mechanism 32. FIG. 3 is a front view showing the sheet cooling mechanism 32.

  The sheet cooling mechanism 32 includes an endless upper belt 211 (an example of a first belt), a driving roller 212 that rotates the upper belt 211, driven rollers 213, 214, and 215 that rotate as the upper belt 211 rotates, A cooling member 216 is provided in the inner space of the upper belt 211. The upper belt 211 is made of a material having excellent thermal conductivity. The driving roller 212 and the driven rollers 213 to 215 are hollow rollers made of light metal such as aluminum. The peripheral speed of the driving roller 212 is substantially the same as the speed of the sheet S being conveyed. As the cooling member 216, a metal member is used, and a plurality of narrow grooves (fins) are formed. Thereby, the surface area becomes larger than the surface area of a normal box, and the heat dissipation effect is enhanced.

  The sheet cooling mechanism 32 includes a lower belt 221 (an example of a second belt) disposed so as to face the upper belt 211. Inside the lower belt 221, a driving roller 222 that rotates the lower belt 221 and driven rollers 223, 224, and 225 that rotate as the lower belt 221 rotates are provided. The driving roller 222 and the driven rollers 223 to 225 have the same configuration as the driving roller 212 and the driven rollers 213 to 215. The peripheral speed of the driving roller 222 is the same as that of the driving roller 212. A pressing roller 226 is provided inside the lower belt 221 in parallel with the driving roller 212 so as to face the driving roller 212 provided on the most downstream side in the paper conveyance direction inside the upper belt 211. . For example, the pressing roller 226 is made of a cylindrical foam rubber (bubble rubber sponge) having a predetermined thickness. For example, acrylonitrile-butadiene rubber (NBR) is used as the foam rubber. Further, the auxiliary pressing rollers 227, 228, and 229 are in pressure contact with the inner side of the lower belt 221 corresponding to the surface contact area between the upper belt 211 and the lower belt 221.

  In the sheet cooling mechanism 32 configured as described above, the upper belt 211 and the lower belt 221 are configured to be in surface contact. When the driving roller 212 rotates and the upper belt 211 is driven, the driven rollers 213 to 215 are rotated. Further, when the driving roller 222 is driven in accordance with the driving of the upper belt 211, the lower belt 221 is driven, and the driven rollers 223 to 225 are rotated.

  When the sheet S is fed into the sheet cooling mechanism 32, the sheet S is sandwiched between the upper belt 211 and the lower belt 221 that are in contact with the surface, and the upper belt 211 and the lower belt 221 are both on the front surface and the back surface of the sheet S. It is conveyed using the frictional force generated between the two. The heat of the sheet S warmed by the fixing unit 31 by this surface contact is transmitted to the upper belt 211 and is radiated through the cooling member 216. In this embodiment, the pressing force of the pressing roller 226 against the driving roller 212 is changed according to the type of paper. Thereby, the pressure of the nip portion by the upper belt 211 and the lower belt 221 near the driving roller 212 and the pressing roller 226 can be adjusted according to the type of paper.

  The auxiliary pressing rollers 227, 228, and 229 are driven for the purpose of maintaining the nip pressure in the region where the upper belt 211 and the lower belt 221 are in surface contact so that the upper belt 211 and the lower belt 221 do not bend. Laura. If the nip pressure in the surface contact portion between the upper belt 211 and the lower belt 221 is maintained at a certain level or more, the pressure assist rollers 227, 228, 229 may be replaced with other configurations, or these The auxiliary pressing roller may not be provided. The nip pressure of the fixing unit 31 is set to be higher than the nip pressure between the driving roller 212 and the pressing roller 226 of the paper cooling mechanism 32 in order to reliably fix the image on the paper S.

Next, a pressing force adjusting mechanism that adjusts the pressing force of the pressing roller 226 will be described.
As shown in FIG. 3, the pressing force adjusting mechanism 230 mainly includes a movable member 231 that pivotally supports the pressing roller 226, elastic members 233-1 and 233-2, and an eccentric cam 235 that rotates about a rotating shaft 235a. And a rotational drive unit (not shown) for rotating the eccentric cam 235.

  The movable member 231 has a main surface portion 231 a that supports the pressing roller 226 and is disposed perpendicular to the contact surface between the lower belt 221 and the paper in the inner space of the lower belt 221. The pressing roller 226 is pivotally supported in a through hole (not shown) formed in the upper portion of the main surface portion 231a of the movable member 231. At the lower part of the movable member 231, latching portions 232-1 and 232-2 having holes for latching one ends of the elastic members 233-1 and 233-2 are formed. Similarly, the fixing device 30 main body is provided with latching portions 234-1 and 234-2 having holes for latching the other ends of the elastic members 233-1 and 233-2. Then, elastic members 233-1 and 233-2 are respectively stretched between the hook portions 232-1 and 232-2 and the hook portions 234-1 and 234-2 provided in the fixing device 30 main body. The movable member 231 is urged upward. That is, the elastic members 233-1 and 233-2 are urged in a direction that increases the pressing force of the pressing roller 226 by the main surface portion of the movable member 231.

  The movable member 231 has an engagement protrusion 231c that protrudes laterally from the lower portion of the main surface portion 231a. An eccentric cam 235 that is rotated by a rotation drive unit (not shown) is in contact with the contact part 231d corresponding to the upper end side of the engagement protrusion 231c. As the rotation drive unit, a combination of a motor and various mechanisms and other actuators such as an air cylinder can be employed. A guide hole 231b extending in the vertical direction is formed at the center of the main surface portion 231a of the movable member 231, and a guide pin 236 fixed to the main body of the fixing device 30 is inserted into the guide hole 231b.

When the eccentric cam 235 rotates, the distance between the rotating shaft 235a and the contact portion 231d of the engaging projection 231c of the movable member 231 changes, and the pressing force is applied against the urging force of the elastic members 233-1 and 233-2. The roller 226 is pressed downward, that is, on the side opposite to the side where the driving roller 212 is located. At this time, the movable member 231 moves while being guided in the vertical direction by the guide hole 231b and the guide pin 236. When the movable member 231 moves in the vertical direction, the pressing roller 226 supported by the movable member 231 moves in the vertical direction, and the pressing roller 226 moves according to the amount of movement (pushing amount) from the reference position of the movable member 231. The pressing force changes. In accordance with the change in the pressing force of the pressing roller 226, the nip pressure by the upper belt 211 and the lower belt 221 in the vicinity of the driving roller 212 and the pressing roller 226 changes.
In the present embodiment, control is performed to rotate the eccentric cam 235 until the movable member 231 moves to the instructed position and stop at that position so that the desired pressing force of the pressing roller 226 is obtained.

  In this embodiment, the movable member 231 and the eccentric cam 235 are used to adjust the pressing force of the pressing roller 226, but the present invention is not limited to this example. Further, although coiled springs are used as the elastic members 233-1 and 233-2, any elastic member that has an elastic force and contributes to the adjustment of the pressing force of the pressing roller may be used.

[Configuration of control system of image forming system]
Next, a control system of the image forming system 1 will be described with reference to FIG.
FIG. 4 is a block diagram illustrating a control system of the image forming system 1.

  As shown in FIG. 4, the image forming system 1 includes a control unit 100. The control unit 100 includes, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing programs and data executed by the CPU 101, and a RAM (Random Access) used as a work area of the CPU 101. Memory) 103. The ROM 102 stores, for example, a control program for various jobs, a table in which setting values for the pressing force of the pressing roller 226 are registered, and the like. Note that, as the ROM 102, for example, a programmable ROM that is normally electrically erasable is used. The control unit 100 controls each block, that is, controls the entire apparatus.

  The control unit 100 is connected to an HDD (Hard disk drive) 104 and an operation display unit 105 via a system bus 107, respectively. The control unit 100 is connected to the image reading unit 4, the image processing unit 106, the image forming unit 5, the secondary transfer unit 7, and the fixing unit 31 via the system bus 107. Further, the control unit 100 is connected to the belt drive mechanism 211M, the pressing force adjustment mechanism 230, the first tip detection sensor 33, and the second tip detection sensor 34 via the system bus 107, respectively.

  The HDD 104 is a large-capacity storage device that stores image data of an original image obtained by reading by the image reading unit 4 and stores output image data and the like.

  The operation display unit 105 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display) and a touch sensor (an example of an operation unit). The operation display unit 105 displays an instruction menu for the user, information about the acquired image data, and the like. Further, the operation display unit 105 includes a plurality of keys, and receives input of various instructions, data such as characters and numbers by a user's key operation, and outputs an input signal.

  The image reading unit 4 is driven and controlled by the control unit 100 to optically read a document image and convert it into an electrical signal. Image data generated by the image reading unit 4 and image data transmitted from a personal computer (PC) 120 which is an example of an external device connected to the image forming system 1 are sent to the image processing unit 106 for image processing. Is done. The image processing unit 106 performs processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  The image forming unit 5 is driven and controlled by the control unit 100, receives the image data image-processed by the image processing unit 106, and forms a toner image on the surface of the photoreceptor of each color of yellow, magenta, cyan, and black.

  The secondary transfer unit 7 is driven and controlled by the control unit 100, and secondarily transfers the toner image that has been primarily transferred from the surface of the photosensitive member of each color to the surface of the intermediate transfer belt 6 onto the sheet S.

  The fixing unit 31 is driven and controlled by the control unit 100 and performs a fixing process on the paper S on which the toner image supplied from the secondary transfer unit 7 is formed.

  The belt driving mechanism 211M is driven and controlled by the control unit 100, and conveys the sheet S on which the toner image supplied from the secondary transfer unit 7 is fixed, sandwiched between the upper belt 211 and the lower belt 221. Thereby, the heat of the sheet S is radiated through the upper belt 211 and the cooling member 216. The belt drive mechanism 211M includes a rotation drive unit that transmits a drive force to at least the drive roller 212 to rotate it.

  The pressing force adjusting mechanism 230 is driven and controlled by the control unit 100 and varies the amount of movement of the movable member 231 that pivotally supports the pressing roller 226 in accordance with the type of paper, thereby changing the pressing force of the pressing roller 226 against the driving roller 212. adjust. By this operation, the nip pressure between the upper belt 211 and the lower belt 221 near the driving roller 212 and the pressing roller 226 is adjusted according to the type of paper.

  The first leading edge detection sensor 33 and the second leading edge detection sensor are driven and controlled by the control unit 100, detect the leading edge of the sheet S on the downstream side in the sheet conveyance direction, and output the detection result to the control unit 100.

  The communication unit 108 receives job information transmitted from the PC 120 which is an external information processing apparatus via a communication line. The received job information is sent to the control unit 100 via the system bus 107.

  In this example, the example in which the personal computer 120 is applied as the external device has been described. However, the present invention is not limited to this, and various other devices such as a facsimile device can be applied as the external device.

[Adjustment of pressing force of pressing roller]
Next, setting of the pressing force of the pressing roller 226 in the sheet cooling mechanism 32 will be described.
In the following description, execution of a job for forming an image on a sheet is referred to as “print”, and the number of sheets on which an image is formed by printing is referred to as “number of prints”.

(Pressing force setting according to paper type)
First, before execution of printing, the user sets job data in advance in the image forming system 1 or an external apparatus. In the image forming system 1, an input operation for starting job execution is received, or a command for starting job execution is received from an external device, and job execution is started. Thereafter, based on the job data, an image forming process and a fixing process are performed on the sheet, and the sheet on which the fixing process has been performed is conveyed to the sheet cooling mechanism 32. The paper cooling mechanism 32 adjusts the pressing force of the pressing roller 226 against the driving roller 212 based on the type of paper. The pressing force of the pressing roller 226 is set for each paper type. The set value of the pressing force is stored in the ROM 102 or the HDD 104, for example.

  The job data is stored in the RAM 103, and the job data includes paper type information. The type information is information indicating the type of paper (type of paper thickness, paper material, basis weight, etc.).

  As described above, since the friction coefficient of the contact portion between the paper and the belt is low, when transporting thick paper with a pair of belts, if the nip pressure between the belts is weak, the frictional force between the paper and the belt becomes small. Therefore, slipping of the paper is likely to occur. That is, it is necessary to increase the nip pressure between the upper belt 211 and the lower belt 221 in order to prevent slippage during paper conveyance. In order to convey the sheet without causing slip between the upper belt 211 and the lower belt 221 and the sheet, it is necessary to increase the friction force between the sheet and the belt by increasing the nip pressure. For this purpose, a high torque is required when driving the driving roller 212 so that the driving roller 212 rotates even when the nip pressure is increased. In other words, a slippery sheet is a sheet that requires high torque when the drive roller 212 is driven.

  Thick paper has a larger paper mass and volume than thin paper, and the frictional force necessary to transport the thick paper increases. Therefore, it is necessary to increase the nip pressure, and high torque is required when driving the drive roller 212. is there. In addition, examples of paper that requires high torque when the driving roller 212 is driven include paper that is slippery and paper that has a large basis weight. For example, this paper can be said to be a slip-prone paper. That is, whether or not a high torque is required to drive the drive roller 212 is specified according to the type of paper. For this reason, the type information can be used as information for determining whether or not the sheet requires a high torque when the driving roller 212 is driven, and for optimally setting the pressing force of the pressing roller 226.

  In the present embodiment, the control unit 100 acquires job data and determines the type of paper at the time of printing. When the type of paper is thick paper that requires high torque to drive the drive roller 212, the set value of the pressing force of the pressing roller 226 of the paper cooling mechanism 32 is read from the ROM 102. The set value of the pressing force of the pressing roller 226 read out at this time is a level value higher than a reference value for a sheet for which high torque is not required to drive the driving roller 212. Then, the pressing force adjusting mechanism 230 adjusts the pressing force of the pressing roller 226 against the driving roller 212 based on the read set value, and the nip pressure between the upper belt 211 and the lower belt 221 near the driving roller 212 and the pressing roller 226. To increase. Similarly, when the paper material of the paper is slippery or has a large basis weight, the paper requires a high torque when the driving roller 212 is driven. Set a higher level than the standard. In the following description, a thick paper is described as an example of a paper that requires a high torque when the drive roller 212 is driven, but the same concept applies to a paper material and a basis weight.

  If the paper is not thick but thin, the paper material is not slippery, or the basis weight is small, the preset standard pressing force is set. The type information is not limited to the exemplified paper thickness, paper material, or basis weight.

  As described above, by appropriately setting the pressing force of the pressing roller 226 according to the type of the sheet, the upper belt 211 in the vicinity of the driving roller 212 and the pressing roller 226 can be used as long as the sheet does not slip and wrinkle. The nip pressure of the lower belt 221 can be adjusted.

(Pressing force setting during standby)
It is not preferable from the viewpoint of life (durability) that the pressing force of the pressing roller 226 against the driving roller 212 continues for a long time. For this reason, it is better that the pressing force of the pressing roller 226 is small during standby other than when printing is performed. Therefore, when the sheet S is not passed through the sheet cooling mechanism 32, the control unit 100 sets the pressing force of the pressing roller 226 to a low level.

  By setting the pressing force of the pressing roller 226 in this way, it is possible to expect an effect of preventing the pressing roller 226 from being deformed or reducing the frictional force between the cooling member 216 and the upper belt 211.

(Pressing force setting when the fixing part is not nipped)
When the thick paper is passed through the paper cooling mechanism 32 as the paper S, and the thick paper is sandwiched between the upper belt 211 and the lower belt 221 and is also sandwiched by the fixing unit 31, the grip force at the fixing unit 31 (friction between the fixing rollers) Because the thick paper does not slip, the pressing force of the pressing roller 226 may be small. Therefore, the control unit 100 sets the pressing force of the pressing roller 226 to a level higher than the reference immediately before the rear end of the transported cardboard passes through the nip portion of the fixing unit 31. That is, when the thick paper is passed through the paper cooling mechanism 32, it is from the time when the rear end of the thick paper passes through the nip portion of the fixing unit 31 to the time when it passes through the nip portion between the driving roller 212 and the pressing roller 226 (in FIG. 1). In the section L), the pressing force of the pressing roller 226 is set to a level higher than the reference.

  The control unit 100 determines from the detection result of the first leading end detection sensor 33 that the rear end of the thick paper has passed through the nip portion of the fixing unit 31. Similarly, it is determined from the detection result of the second leading edge detection sensor 34 that the trailing edge of the thick paper has passed through the nip portion of the paper cooling mechanism 32.

  By setting the pressing force of the pressing roller 226 in this manner, the pressing force of the pressing roller 226 is set to a level higher than the reference only in a section necessary to prevent the occurrence of paper slip and paper wrinkling. Accordingly, it is possible to expect an effect of preventing the deformation of the pressing roller 226 and reducing the frictional force between the cooling member 216 and the upper belt 211 while suppressing the pressing time to a necessary minimum.

(Pressing force setting according to usage history)
When the usage time of the sheet cooling mechanism 32 becomes longer, wear powder of the upper belt 211 generated by friction between the cooling member 216 and the upper belt 211 adheres to the driving roller 212. When the abrasion powder adhering to the driving roller 212 increases, the frictional force between the driving roller 212 and the upper belt 211 decreases and the slip of the sheet is likely to occur. Become. Therefore, when the control unit 100 passes the thick paper as the paper S to the paper cooling mechanism 32, the control unit 100 sets the pressing force of the pressing roller 226 from the normal setting value at the time of passing the thick paper according to the usage history of the paper cooling mechanism 32. Set to a higher level. For example, information on the total number of printed sheets can be used as the usage history. Information on the total number of prints is recorded in the ROM 102.

  As described above, the pressing force of the pressing roller 226 is set according to the decrease in the frictional force between the driving roller 212 and the upper belt 211 due to the secular change. Thereby, even after the paper cooling mechanism 32 has been used for a long time, it is possible to prevent the paper from slipping while preventing the generation of paper wrinkles.

[Specific example of pressing force setting]
Hereinafter, an example of a set value based on the setting guideline of the pressing force of the pressing roller 226 described above will be described.
FIG. 5 is a table showing an example of the relationship between the type of paper and the setting of the pressing force of the pressing roller 226 according to the embodiment of the present invention. This table is an example when the pressing force of the pressing roller 226 is set for each of thin paper and thick paper.

  In FIG. 5, when the sheet conveyed to the sheet cooling mechanism 32 is thin, the pressing force during standby is set to be weak based on the above setting guideline. The pressing force is set to be weak regardless of whether or not the total number of prints recorded in the ROM 102 exceeds a predetermined number of prints.

  If the control unit 100 determines from the job data that the print uses thin paper, the control unit 100 reads the setting information of the table in FIG. 5 from the ROM 102 and sets the pressing force of the pressing roller 226 based on the read setting information of the table. . The control unit 100 supplies a control signal based on the setting to the pressing force adjusting mechanism 230 and adjusts the nip pressure between the upper belt 211 and the lower belt 221 in the vicinity of the driving roller 212 and the pressing roller 226.

In FIG. 5, when the sheet conveyed to the sheet cooling mechanism 32 is a thick sheet, the pressing force during standby is set to be weak based on the above setting guideline. Further, the pressing force based on the total number of prints recorded in the ROM 102 is set according to whether or not the trailing edge of the sheet has passed through the fixing unit 31. In the table, the left side of “/” represents the setting when the trailing edge of the sheet does not pass through the fixing unit 31, and the right side of “/” represents the setting after the trailing end of the sheet has passed through the fixing unit 31. . That is, when passing thick paper, if the total number of printed sheets is less than the predetermined number of printed sheets and the trailing edge of the paper does not pass through the fixing unit 31, the pressing force is set to be weak, and the trailing edge of the paper is The pressing force after passing through the fixing unit 31 is set to medium.
Further, when passing thick paper, if the total number of printed sheets is equal to or greater than the predetermined number of printed sheets and the trailing edge of the paper does not pass through the fixing unit 31, the pressing force is set to be weak, and the trailing edge of the paper is The pressing force after passing through the fixing unit 31 is set to be strong.

  In the example of FIG. 5, the pressing force of the pressing roller 226 is set not only for the type of paper but also for each item of the total number of printed sheets and the paper transport position during standby. Therefore, by using these setting information, the pressing force of the pressing roller 226 can be finely adjusted according to the state of the image forming system 1 (paper cooling mechanism 32).

  When it is determined from the job data that the print uses thick paper, the control unit 100 reads the total number of prints and the setting information in the table of FIG. Then, based on the read table setting information, the pressing force of the pressing roller 226 is set for each of the total number of printed sheets and the sheet transport position. The control unit 100 supplies a control signal based on the setting to the pressing force adjusting mechanism 230 and adjusts the nip pressure between the upper belt 211 and the lower belt 221 in the vicinity of the driving roller 212 and the pressing roller 226.

  In the example of FIG. 5, the setting is distinguished by the paper thickness as the paper type, but the same applies to the paper material and the basis weight. The threshold value for the predetermined number of printed sheets is one, but two or more threshold values may be set, and the pressing force of the pressing roller 226 may be set in multiple stages according to the total number of printed sheets.

  In this way, the pressing force of the pressing roller 226 can be set more appropriately by considering the type of paper, and also the total number of prints and the paper transport position. Accordingly, the nip pressure between the upper belt 211 and the lower belt 221 in the vicinity of the driving roller 212 and the pressing roller 226 can be adjusted more appropriately, so that paper slip and paper wrinkle can be further prevented.

Note that the present invention is not limited to the above-described embodiments, and includes other modifications and application examples without departing from the gist of the present invention described in the claims.
For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, it is possible to add, replace, or delete other configurations of a part of the configuration of the above embodiment.

  In the above-described embodiment, the configuration using the first tip detection sensor 33 and the second tip detection sensor 34 is exemplified. However, only the first tip detection sensor 33 can be used. For example, the time at which the trailing edge of the sheet has passed through the fixing unit 31 can be determined from the detection result of the first leading edge detection sensor 33. Therefore, the moving distance of the trailing edge of the sheet can be determined based on the elapsed time from this time and the sheet conveyance speed. calculate. Then, the pressing force of the pressing roller 226 may be set according to the sheet conveyance position estimated from the moving distance.

  In the above embodiment, the electrophotographic image forming system 1 that forms an image using static electricity has been described. However, the present invention is not limited to this application example. For example, the present invention can be applied to an image forming system including a fixing unit and a belt-clamping type paper cooling mechanism, such as a laser printer using a laser for exposure.

  In the above-described embodiment, the image forming system 1 is exemplified by a configuration in which the image forming apparatus 1 is provided separately from the image forming apparatus 10 and includes the paper feeding device 20 and the fixing device 30, that is, a so-called production printing machine. Absent. For example, the image forming apparatus 10 may be configured to have the function of the fixing device 30, or the image forming apparatus 10 may be configured to have the functions of the fixing device 30 and the paper feeding device 20.

  The present invention is also applicable to a printer apparatus, a copier, a facsimile apparatus, a printing machine, a multi-function machine, and the like that include a fixing unit and a belt-clamping type paper cooling mechanism.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Further, each of the above-described configurations, functions, and the like may be realized by software for interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be held in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or an optical disk. .

  Further, in this specification, the processing steps describing time-series processing are not limited to processing performed in time series according to the described order, but are not necessarily performed in time series, either in parallel or individually. The processing (for example, parallel processing or object processing) is also included.

  DESCRIPTION OF SYMBOLS 1 ... Image formation system, 5 ... Image formation part, 5Y, 5M, 5C, 5K ... Image formation unit, 6 ... Transfer belt, 7 ... Secondary transfer roller, 10 ... Image formation apparatus, 30 ... Fixing apparatus, 31 ... Fixing 32, a sheet cooling mechanism, 33, a first tip detection sensor, 34, a second tip detection sensor, 100, a control unit, 201, an upper fixing roller, 202, a lower fixing roller, 211, an upper belt (first belt). 211M ... Belt drive mechanism, 212-215 ... Drive roller, 216 ... Cooling member, 221 ... Lower belt (second belt), 222-225 ... Driven roller, 226 ... Pressure roller, 230 ... Pressure roller pressure adjustment mechanism, 231 ... movable member, 231a ... main surface part, 231b ... guide hole, 231c ... engagement projection, 231d ... contact part, 232-1-2 ... hanging part 233-1～2 ... elastic member, 234-1～2 ... hook portion, 235 ... eccentric cam, 235a ... rotation axis, 236 ... guide pin

Claims (8)

A fixing unit for fixing the toner image transferred to the paper;
A paper cooling mechanism that cools the paper that has passed through the fixing unit while being sandwiched between a first belt and a second belt facing the first belt;
A driving roller for driving the first belt of the sheet cooling mechanism;
A pressing roller for pressing the driving roller via the second belt and the first belt;
A pressure adjusting mechanism for adjusting the pressing force of the pressing roller;
An image forming system comprising: a control unit that determines a type of the paper and controls a pressing force of the pressure roller by the pressure adjusting mechanism according to the type of the paper. The image forming system according to claim 1, wherein the sheet cooling mechanism is provided in the inner space of the second belt and on the downstream side of the second belt in the sheet conveyance direction. The control unit sets the pressing force of the pressing roller to a level higher than a reference when the paper requires a higher torque than a reference torque when the drive roller is driven. The image forming system described. The said control part determines the paper in which a torque higher than a reference torque is required at the time of the drive roller drive at least according to any of the paper material, paper thickness, and basis weight of the paper. Image forming system. The image forming system according to claim 1, wherein a nip pressure between the fixing rollers of the fixing unit is higher than a nip pressure between the driving roller and the pressing roller of the sheet cooling mechanism. The control unit sets the pressing force of the pressing roller to a sheet that requires a torque higher than a reference torque when the driving roller is driven when the sheet is not passed through the sheet cooling mechanism. The image forming system according to claim 1, wherein the image forming system is set to a level lower than the pressing force. A first leading edge detection unit that detects a leading edge on the downstream side in the transport direction of the sheet that has passed through the fixing unit;
A second leading edge detection unit that detects a leading edge on the downstream side in the transport direction of the paper that has passed through the paper cooling mechanism,
The control unit, based on the detection results of the first tip detection unit and the second tip detection unit, when the sheet cooling mechanism transports a sheet that requires high torque when the drive roller is driven, The pressing force of the pressing roller is set to a level higher than a reference during a period from when the trailing edge of the sheet passes through the nip portion of the fixing unit until it passes through the nip portion of the driving roller and the pressing roller. The image forming system according to any one of 3 to 6. The controller is configured to use the pressing force of the pressure roller as a reference according to the usage history of the sheet cooling mechanism when the sheet cooling mechanism transports a sheet that requires high torque when the driving roller is driven. The image forming system according to claim 3, wherein the image forming system is set to a high level.