JP2012042826A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device for separating a sheet, which is conveyed while being wound around a fixing member, from the fixing member without using a separating claw.SOLUTION: A fixing device comprises: a S-shaped conveyance path Fr for conveying a sheet which has passed through a fixing nip portion NP; and a ventilation portion for allowing the sheet being conveyed through the S-shaped conveyance path Fr to be conveyed along a second guide portion 56 by making use of the gas flow. Here, the second guide portion 56 forming the S-shaped conveyance path Fr includes: a first curved surface which extends along the outer peripheral shape of a fixing upper roller 51 and forms a conveyance path for a sheet P between the first curved surface and the fixing upper roller 51; and an arc-shaped third curved surface (a second guide surface) which is connected to the first curved surface and reverses the curvature of the conveyance path in the sheet conveyance direction.

Description

  The present invention relates to a fixing device and an image forming apparatus using the same.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses are known as printers, copiers, and the like. In this image forming apparatus, when a toner image is formed on a sheet, the toner image is transferred to the sheet, and then the sheet passes through a pressure contact portion (fixing nip portion) of a pair of fixing members constituting the fixing device. A process of fixing a toner image on a sheet is executed. By the way, in this type of fixing device, there is a problem that the paper that has passed through the fixing nip portion is wound around the fixing member (for example, a fixing roller) and is not separated from the fixing member. Therefore, a fixing device having a fixing claw for mechanically separating the paper wound around the fixing member is known.

  For example, Patent Document 1 discloses a technique that can suppress damage to the fixing roller while separating paper with a fixing claw. Specifically, when the paper discharged from the fixing nip portion is conveyed in close contact with the surface of the fixing roller, the paper passes through a gap between the separation guide and the fixing roller, which are separated from the fixing roller. The leading edge of the paper hits the leading edge of the separation claw. This sheet is separated from the fixing roller along the tapered shape of the tip of the separation claw, and is conveyed downstream along the sheet guide. On the other hand, if the leading edge of the paper ejected from the fixing nip is lifted from the surface of the fixing roller, such as a stiff paper, the paper is fixed by a separation guide positioned in front of the separation claw. It is separated from the roller and conveyed downstream along this separation guide.

JP 2008-46401 A

  However, according to the technique disclosed in Patent Document 1, the paper that has passed through the separation guide is separated from the fixing member by using the separation claw. There is concern about the deterioration of quality and the separation performance due to the degradation of the separation claw.

  The present invention has been made in view of such circumstances, and an object thereof is to efficiently separate a sheet conveyed while being wound around the fixing member from the fixing member without using a separation claw.

  In order to solve such a problem, a first invention includes a fixing unit that allows a sheet to pass through a fixing nip formed by pressing a pair of fixing members and fixes a toner image on a fixing target surface of the sheet; A sheet guide unit configured to guide a sheet, and a sheet guide unit configured to convey a sheet conveyed through the first conveyance path using a gas flow and a first conveyance path that conveys the sheet that has passed through the fixing nip. And a ventilation section that runs along the road. The paper guide portion extends along the outer peripheral shape of the fixing member, and is connected to the first guide surface and a first guide surface that form a paper conveyance path with the fixing member, An arcuate second guide surface that reverses the curved state of the conveyance path in the sheet conveyance direction.

  Here, in the first invention, it is preferable that the ventilation portion includes suction means for attracting the sheet toward the first guide surface side by suction of gas. Alternatively, it is desirable that the ventilation section includes a blowing unit that presses the sheet toward the first guide surface by blowing out gas. Moreover, the ventilation part may be provided with both the above-mentioned suction means and ventilation means.

  In the first invention, the fixing device may further include a second conveyance path for conveying the sheet that has passed through the fixing nip portion. In this case, the second conveyance path constitutes a linear path extending in the tangential direction of the fixing member in the fixing nip portion, and the first conveyance path and the second conveyance path pass through the fixing nip portion. It is preferable that a branched path is formed in which the sheet is transported to one of the transport paths.

  In the first invention, the second conveyance path conveys a sheet having a separation point where the sheet is separated from the fixing member on the fixing nip portion side as compared with the sheet conveyed on the first conveyance path. It is preferred that

  In the first invention, the fixing device is provided in the first or second conveyance path, and detects a sheet to be conveyed, a first detection path based on a detection result of the sheet detection section. It is preferable to further include a control unit that operates the ventilation unit when it is determined that the sheet has entered.

  Further, in the first invention, the fixing device restricts the entry of the sheet into the second conveyance path and the normal position that allows the entry of the sheet into the second conveyance path, and moves only to the first conveyance path. You may further have the gate part which can be switched to the control position which conveys a sheet | seat, and the drive means which drives a gate part. In this case, the control unit switches the gate unit from the normal position to the restricted position by controlling the driving unit based on the printing rate of the fixing target surface, the type of paper, or the curl correction instruction by the user.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image forming unit that transfers a toner image onto a sheet; and a fixing device that fixes the transferred toner image onto the sheet. As this fixing device, the fixing device described in the first invention can be used.

  According to the present invention, it is possible to secure a separation point where the paper is separated from the fixing member in a wide range on the outer periphery of the fixing member by passing the paper through the first conveyance path. That is, by securing the separation points in a wide range, separation of the paper due to the repulsive force and the weight of the paper can be promoted in the transport process. Further, according to the present invention, by providing the ventilation portion, it is possible to promote separation of the paper through the gas flow. As described above, due to the action of a wide range of separation points and the gas flow, it is possible to effectively achieve the separation of the paper without providing a separation claw on the fixing member. Accordingly, it is possible to suppress damage to the fixing member due to the separation claw and deterioration of image quality.

1 is an explanatory diagram schematically showing a configuration of an image forming apparatus 1 according to a first embodiment. Explanatory drawing which shows the structure of the fixing apparatus 50 typically. 1 is a block diagram schematically showing a control system of an image forming apparatus 1 according to a first embodiment. A flowchart showing an operation procedure of the fixing device 50 according to the first embodiment. Explanatory drawing which shows typically the structure of the fixing device 50 concerning 2nd Embodiment. FIG. 2 is a block diagram schematically showing a control system of an image forming apparatus 1 according to a second embodiment. A flowchart showing an operation procedure of the fixing device 50 according to the second embodiment. Explanatory drawing which shows typically the structure of the fixing device 50 concerning 3rd Embodiment.

(First embodiment)
FIG. 1 is an explanatory diagram schematically showing a configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an electrophotographic image forming apparatus such as a copying machine, for example, and forms a full-color image by arranging a plurality of photoconductors facing a single intermediate transfer belt in a vertical direction. A tandem type color image forming apparatus. In this specification, when the direction of each member constituting the paper P and the image forming apparatus 1 is defined, the transport direction of the paper P is used as a reference, and the direction parallel to the transport direction of the paper P is “ The paper conveyance direction FD ”is referred to as the“ paper width direction CD ”.

  The image forming apparatus 1 includes a document reading unit 10, exposure units 20Y, 20M, 20C, and 20K, image forming units 30Y, 30M, 30C, and 30K, an intermediate transfer unit 40, a fixing device 50, a paper discharge reversing unit 70, and a refeed. The paper unit 80 and the paper supply unit 90 are mainly configured, and these are housed in one housing.

  The document reading unit 10 includes an automatic document feeder ADF at the top thereof. The documents D placed on the document placement table 15 of the automatic document feeder ADF are separated one by one, sent out to the document conveyance path, and conveyed by the conveyance drum 16. The first transport guide G 1 and the document discharge roller 17 discharge the document D transported by the transport drum 16 to the document discharge tray 18.

  The document reading unit 10 reads an image of the document D being conveyed by the conveyance drum 16 at the document image reading position RP. Specifically, the image of the document D is irradiated with the lamp L at the document image reading position RP. Reflected light by irradiation is guided by the first mirror unit 11, the second mirror unit 12, and the lens unit 13 and forms an image on the light receiving surface of the image sensor CCD. The imaging device CCD photoelectrically converts incident light and outputs a predetermined image signal. The output image signal is created as input image data by performing A / D conversion.

The image reading control unit 14 performs processing such as shading correction, dither processing, and compression on the input image data, and uses the data obtained by this processing as output image data in the RAM of the image formation control unit 2 (see FIG. 3). Stored in the storage unit. Note that the output image data may be received from a personal computer connected to the image forming apparatus 1 or another image forming apparatus as well as data output from the document reading unit 10.

  The exposure units 20Y to 20K are composed of a laser light source, a polygon mirror, a plurality of lenses and the like (not shown), and generate a laser beam. The exposure units 20Y to 20K correspond to the output information output from the image formation control unit 2 based on the output image data, and the photosensitive members 31Y, 31M, 31C, and 31K that are constituent elements of the image formation units 30Y to 30K. The surface is exposed by scanning with a laser beam. A latent image is formed on the photoconductors 31Y to 31K by scanning exposure of the laser beam.

  The image forming unit 30Y includes a photoconductor 31Y, and a main charging unit 32Y, a developing unit 33Y, a first transfer roller 34Y, and a cleaning unit 35Y disposed around the photoconductor 31Y. The other image forming units 30M, 30C, and 30K have the same configuration as that of the image forming unit 30Y. Around the photoreceptors 31M, 31C, and 31K, main charging units 32M, 32C, and 32K, developing units 33M, 33C, and 33K, First transfer rollers 34M, 34C, 34K and cleaning units 35M, 35C, 35K are arranged, respectively.

  The surfaces of the photoreceptors 31Y to 31K are uniformly charged by the main charging units 32Y to 32K. The developing units 33Y to 33K develop latent images on the photoreceptors 31Y to 31K by developing with toner. As a result, toner images are formed on the photoreceptors 31Y to 31K.

  The first transfer rollers 34 </ b> Y to 34 </ b> K sequentially transfer the toner images formed on the photoreceptors 31 </ b> Y to 31 </ b> K to predetermined positions on the intermediate transfer belt 41 of the intermediate transfer unit 40. The cleaning units 35Y to 35K remove the toner remaining on the surfaces of the photoreceptors 31Y to 31K after the transfer of the toner image.

  The second transfer roller 42 of the intermediate transfer unit 40 transfers the toner image transferred onto the intermediate transfer belt 41 to the paper P. The paper P to be transferred is supplied from one of the trays PG 1, PG 2, and PG 3 constituting the paper feed unit 90, and is sent to the second transfer roller 42 while being timed by the paper feed roller 91. The belt cleaning unit 43 cleans the surface of the intermediate transfer belt 41 that has finished transferring the toner image onto the paper P. The cleaned intermediate transfer belt 41 is used for the next image transfer.

  Here, the above-described elements, that is, the exposure units 20Y to 20K, the image forming units 30Y to 30K, and the intermediate transfer unit 40 constitute an image forming unit. That is, the image forming unit (1) charges the photosensitive drums 31Y to 31K, (2) forms electrostatic latent images on the photosensitive drums 31Y to 31K by the exposure units 20Y to 20K, and (3) is formed. (4) The toner images on the photoconductive drums 31Y to 31K are primarily transferred to the intermediate transfer belt 41. (5) The toner images on the intermediate transfer belt 41 are transferred to the sheet P two times. The toner image is transferred onto the paper P through a series of processes of next transfer.

  The sheet P having the transferred toner image, that is, the unfixed toner image on the surface to be fixed, is sent to the fixing device 50. The fixing device 50 fixes the toner image on the fixing target surface of the paper P by pressurizing and heating the paper P. The details of the fixing device 50 will be described later.

  The paper discharge unit 70 conveys the paper P that has been subjected to the fixing process by the fixing device 50 and discharges it to the paper discharge tray 75. When the paper P is reversed and discharged, the paper discharge guide 72 once guides the paper P downward. The paper discharge reversing roller 73 holds the rear end of the paper P and then reversely conveys the paper P. Then, the paper discharge guide 72 guides the paper P to the paper discharge roller 74 so that the paper P is discharged to the paper discharge tray 75. Is done.

  In addition, in the case of double-sided printing in which image formation is performed on each of the front and back surfaces of the paper P instead of single-sided printing in which image formation is performed only on the front surface of the paper P, the paper discharge guide 72 is used for the toner image on the front surface of the paper P. The sheet P that has been subjected to the fixing process is conveyed to the refeed unit 80 located below. A refeed reverse roller 81, which is one of the components of the refeed unit 80, reverses the paper P by nipping the rear end of the paper P and feeds it to the refeed conveyance path 82. As a result, the paper P is used for image formation on the back surface via the re-feed conveyance path 82.

  FIG. 2 is an explanatory diagram schematically showing the configuration of the fixing device 50. The fixing device 50 is mainly configured by an upper fixing roller 51 and a lower fixing roller 52 which are a pair of fixing members constituting a fixing unit. The upper fixing roller 51 and the lower fixing roller 52 are arranged in pressure contact with each other, and a fixing nip portion NP is formed at the press contact portion between the upper fixing roller 51 and the lower fixing roller 52. Here, when the paper P passes through the fixing nip NP, an upper fixing roller 51 is disposed above the paper surface, and a lower fixing roller 52 is disposed below the paper surface.

  The fixing upper roller 51 is configured by laminating an elastic layer such as silicone rubber or sponge on the surface of cylindrical steel or aluminum. The fixing upper roller 51 includes a heater 53 that is a heat source for heating the fixing upper roller 51, that is, for thermally fixing the toner image on the paper P. As the heater 53, for example, a halogen lamp can be used. The fixing upper roller 51 is heated by the radiant heat from the heater 53.

  The lower fixing roller 52 is configured by laminating an elastic layer such as silicone rubber and a release layer made of fluorine resin or the like on the surface of a cylindrical steel or aluminum pipe.

  The sheet P is conveyed in such a manner that the surface to be fixed faces the upper fixing roller 51 and passes through the fixing nip NP in the process of conveying the sheet P. As a result, the toner image is fixed to the fixing target surface of the paper P through the action of the pressure applied by the upper fixing roller 51 and the lower fixing roller 52 and the heat of the upper fixing roller 51.

  As shown in FIG. 2, in the fixing device 50, first to third guide portions 55, 56, and 57 are provided at the subsequent stage of the fixing nip portion NP in the paper transport direction FD. The first to third guide portions 55 to 57 are arranged in order of the first guide portion 55, the second guide portion 56, and the third guide portion 57 from the lower side on the basis of the sheet surface of the conveyed sheet P. It is arranged over the top.

  The three guide portions 55 to 57 constitute a conveyance path for conveying the paper P that has passed through the fixing nip NP. Specifically, a linear conveyance path (hereinafter referred to as “straight conveyance path”) extending in the tangential direction of the fixing nip NP in the upper fixing roller 51 by the first guide portion 55 and the second guide portion 56. Fs is formed (second transport path). On the other hand, the second guide portion 56 and the third guide portion 57 form a curved S-shaped transport path (hereinafter referred to as “S-shaped transport path”) Fr (first transport path). The straight conveyance path Fs and the S-shaped conveyance path Fr are branched on the discharge side of the fixing nip portion NP, and the branched conveyance paths Fs and Fr are joined at the subsequent stage of the conveyance path.

  The 1st guide part 55 is formed with the plate-shaped member provided with a flat shape. The first guide portion 55 faces the surface on the back side of the fixing target surface of the paper P in the straight transport path Fs (hereinafter referred to as “non-fixing target surface”), and guides the transport of the paper P.

  The second guide part 56 is formed of a cylindrical hollow member extending in the paper width direction CD, and includes a flat part 56a and a curved part 56b integrally formed above the flat part 56a. It is configured. The flat surface portion 56a is formed of a plate-like member having a flat shape. The flat portion 56a faces the fixing target surface of the paper P in the straight transport path Fs and guides the transport of the paper P. On the other hand, the curved portion 56b is formed of a plate-like member having a U-shape that protrudes upward (in a direction away from the plane portion 56a). The curved portion 56b is mainly composed of three surfaces. Specifically, the surface facing the fixing upper roller 51 has a shape along the outer peripheral shape of the fixing upper roller 51 (first curved surface), and the surface facing the first curved surface is: It has a shape depicting a curve with a gradually decreasing inclination (second curved surface). The surface located between the first curved surface and the second curved surface is connected to the first curved surface and the second curved surface, respectively, and is conveyed from the first curved surface to the second curved surface. It has an arc shape that reverses the curved state of the road (third curved surface). Such a curved portion 56b faces the non-fixing target surface of the paper P in the S-shaped transport path Fr and guides the transport of the paper P.

  The third guide portion 57 is formed of a plate-like member having a curved shape corresponding in shape to the curved portion 56 b of the second guide portion 56. The third guide portion 57 faces the fixing target surface of the paper P in the S-shaped transport path Fr and guides the transport of the paper P.

  In addition, as one of the features of the present embodiment, a plurality of fans 58 are provided inside the second guide portion 56 so as to face the first curved surface of the curved portion 56b. For example, the individual fans 58 are arranged at equal intervals over the sheet width direction CD. In addition, as shown in FIG. 2B, a plurality of slits 56c are provided on the first curved surface of the curved portion 56b. For example, the individual slits 56c are arranged at equal intervals in the paper width direction CD.

  The fan 58 is, for example, a multi-blade fan that rotatably includes a number of forward blades. The fan 58 takes in external air from the air intake port formed in the fan main body through rotation of the forward blades, and blows out the air thus taken in through the air discharge port formed in the fan main body. The air intake port included in the fan 58 is formed on the surface of the fan body, for example, while the air discharge port is formed on the back surface of the fan body, for example. The fan 58 is arranged so that the air intake port faces the slit 56c of the curved portion 56b.

  By operating the fan 58, the air around the second guide portion 56 flows toward the slit 56c and flows into the second guide portion 56 through the slit 56c. The sheet P is sucked toward the curved portion 56b by the air flow. That is, when the paper P passes through the S-shaped transport path Fr, the suction of the air promotes the separation of the paper P from the fixing upper roller 51, or the paper P separated from the fixing roller 51 is second guide portion. 56 (curved portion 56 b), and the sheet P is transported along the second guide portion 56. Note that the air discharged from the air discharge port is discharged outside the fixing device 50 (or the image forming apparatus 1), for example, via the inside of the second guide portion 56.

  A straight conveyance path Fs and an S-shaped conveyance path Fr are formed by such first to third guide portions 55 to 57, and the conveyance path through which the sheet P passes is the sheet P to the fixing upper roller 51. It is automatically selected according to the ease of winding. Here, the position on the upper fixing roller 51 where the paper P that has passed through the fixing nip NP is separated from the upper fixing roller 51 is referred to as a “separation point”. The separation point of the paper P basically starts from the fixing nip NP.

  For example, the paper P that is difficult to be wound around the upper fixing roller 51 such as thick paper is separated from the upper fixing roller 51 at a position immediately after passing through the fixing nip NP or at a position close to the fixing nip NP. The paper P discharged from the fixing nip NP is gradually separated from the front end side of the paper at the separation point of the paper P. The sheet P separated from the fixing upper roller 51 extends linearly and enters the straight conveyance path Fs as it is. As a result, the paper P is guided by the flat portion 56a of the first guide portion 55 and the second guide portion 56, and is transported along the straight straight transport path Fs.

  On the other hand, a sheet P that is easily wound around the upper fixing roller 51, such as a thin sheet or a sheet P having a high printing rate on the surface to be fixed, remains wrapped around the upper fixing roller 51 even after passing through the fixing nip NP. Therefore, the sheet P is conveyed while being wound around the rotating upper fixing roller 51 and enters the S-shaped conveyance path Fr. While the sheet P that has entered the S-shaped conveyance path Fr is conveyed on the first curved surface of the curved portion 56 b facing the fixing upper roller 51, the repulsive force and the own weight of the sheet P and the suction of the fan 58 are conveyed. The force acts to reach the separation point. The paper P discharged from the fixing nip NP is gradually separated from the front end side of the paper at the separation point of the paper P. The sheet P separated from the fixing upper roller 51 is conveyed along the curved portion 56b because the suction force of the fan 58 acts. Then, the paper P is conveyed while being guided by the second curved surface and the third guide portion 57 while being reversed via the third curved surface. As described above, when the paper P is transported through the S-shaped transport path Fr, initially, the paper P is transported while being wound around the fixing upper roller 51, and then the curved portion 56 b of the second guide portion 56. As the paper P advances along the path, the paper P follows an S-shaped path.

  FIG. 3 is a block diagram schematically showing a control system of the image forming apparatus 1 according to the present embodiment. The control system of the image forming apparatus 1 is mainly composed of an image forming control unit 2 and a fixing control unit 3. The image formation control unit 2 and the fixing control unit 3 are configured to be able to communicate with each other.

  As the image formation control unit 2, for example, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The image formation control unit 2 performs various calculations according to a control program stored in the ROM, and controls the operation state of the image forming apparatus 1 based on the calculation results.

  This image formation control unit 2 is based on information set through an operation unit (not shown) provided at the top of the main body of the image forming apparatus 1 or information received together with output image data from a personal computer or other image forming apparatus. It is possible to acquire printing conditions such as single-sided / double-sided printing type, paper information (eg, size, paper type such as thin paper / plain paper / thick paper, amount of paper, etc.), image density, magnification, and the like. As the operation unit, for example, a touch panel capable of performing an input operation according to information displayed on the display can be used.

The image forming control unit 2 controls each unit (image forming unit) of the image forming apparatus 1 to execute the following series of processes, thereby transferring the toner image onto the conveyed paper P.
(1) Charge the photoreceptors 31Y to 31K. (2) Form electrostatic latent images on the photoreceptors 31Y to 31K by the exposure units 20Y to 20K. (3) Adhere toner to the formed electrostatic latent images ( 4) Primary transfer of toner images on photoreceptors 31Y-31K to intermediate transfer belt 41 (5) Transport of paper P (6) Secondary transfer of toner image on intermediate transfer belt 41 to paper P

  As the fixing control unit 3, for example, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The fixing control unit 3 performs various calculations according to a control program stored in the ROM, and controls the operation state of the fixing device 50 based on the calculation results.

  Sensor signals from various sensors including the sheet detection sensors 59 and 60 and signals from the image formation control unit 2 are input to the fixing control unit 3. Here, one sheet detection sensor 59 is provided on the upstream side of the fixing nip portion NP in the conveyance path of the sheet P (see FIG. 2), and the arrival of the sheet P to the entrance side of the fixing nip portion NP. Detect (entrance detection). The other paper detection sensor 60 is provided in the downstream (downstream) of the fixing nip portion NP in the transport path of the paper P and on the straight transport path Fs, and detects the paper P transported on the straight transport path Fs ( Straight conveyance path detection). The other sheet detection sensor 60 is provided on the downstream side (downstream) of the fixing nip NP in the conveyance path of the paper P and on the S-shaped conveyance path Fr, and detects the sheet P conveyed on the S-shaped conveyance path Fr. It may be detected. That is, if the other sheet detection sensor 60 is configured to detect that the sheet P has entered the S-shaped conveyance path Fr by detecting the sheet P, either one or both of the conveyance paths Fs. , Fr. Each of the paper detection sensors 59 and 60 includes, for example, a light emitting element and a light receiving element. When the paper P does not pass through the sensor position, the detection signal is turned off, and the paper P passes through the sensor position. The detection signal is turned on.

  The fixing controller 3 controls the fixing of the toner image onto the fixing target surface of the paper P by controlling each part of the fixing device 50. The fixing controller 3 manages the fixing temperature at the fixing nip NP by controlling the heater 53. The fixing controller 3 controls the rotation timing and rotation speed of the upper fixing roller 51 and the lower fixing roller 52, respectively.

  In relation to the present embodiment, as shown in FIG. 3, the fixing control unit 3 starts and stops the fan 58 in accordance with the conveyance timing and conveyance path of the paper P, so that the operation of the fan 58 is performed. Switch to non-operation. In such control of the fan 58, the fixing control unit 3 refers to the detection results of the respective sheet detection sensors 59 and 60.

  FIG. 4 is a flowchart showing an operation procedure of the fixing device 50 according to the first embodiment. The processing shown in this flowchart is executed by the fixing control unit 3 using a print start command output from the image formation control unit 2 as a trigger. Here, when the user performs printing using the image forming apparatus 1, the image forming control unit 2 sends the print conditions through the operation of the operation unit or print conditions / output image data from a personal computer or another image forming apparatus. A print start command is input. In this case, when the image formation control unit 2 receives the print start command, it outputs this to the fixing control unit 3.

  First, in step 10 (S10), the fixing control unit 3 reads the detection signal of the paper detection sensor 59 for detecting the entrance, and determines whether or not the detection signal of the paper detection sensor 59 has been switched from OFF to ON. That is, by the determination in step 10, it is determined whether or not the leading edge of the paper P has reached the entrance side of the fixing nip NP, specifically, the sensor position of the paper detection sensor 59.

  If the determination in step 10 is affirmative, that is, if the leading edge of the sheet P has reached the entrance side of the fixing nip NP, the process proceeds to step 11 (S11). On the other hand, if a negative determination is made in step 10, that is, if the sheet P has not reached the entrance side of the fixing nip NP, the present routine is exited.

  In step 11, the fixing control unit 3 refers to a timer that is counted starting from the timing at which the leading edge of the paper P reaches the sensor position of the paper detection sensor 59, and the count value of the timer uses the first determination time Ta. Judge whether or not it has passed. The first determination time Ta is set based on the conveyance speed of the paper P and the conveyance distance of the paper P from the paper detection sensor 59 for detecting the entrance to the paper detection sensor 60 for detecting the straight conveyance path. . Specifically, the first determination time Ta corresponds to the time required for the conveyed paper P to reach the paper detection sensor 60 for straight conveyance path detection from the paper detection sensor 59 for entrance detection.

  If an affirmative determination is made in step 11, that is, if the count value of the timer has passed the first determination time Ta, the process proceeds to step 12 (S12). On the other hand, if a negative determination is made in step 11, that is, if the count value of the timer has not passed the first determination time Ta, the process returns to step 11 again.

  In step 12, the fixing control unit 3 reads the detection signal of the paper detection sensor 60 for detecting the straight conveyance path, and determines whether or not the detection signal of the paper detection sensor 60 has been switched from OFF to ON. That is, based on the determination in step 12, it is determined whether the sheet P has entered the straight conveyance path Fs or the sheet P has entered the S-shaped conveyance path Fr.

  If the determination in step 12 is affirmative, that is, if the sheet P enters the straight transport path Fs, the routine is exited. On the other hand, if a negative determination is made in step 12, that is, if the sheet P has not entered the straight transport path Fs, the process proceeds to step 13 (S13).

  In step 13, the fixing control unit 3 starts the fan 58.

  In step 14 (S14), it is determined whether or not the count value of the timer has passed the second determination time Tb. The second determination time Tb is set based on the conveyance speed of the sheet P and the conveyance distance of the sheet P from the sheet detection sensor 59 for detecting the entrance to the slit 56c of the second guide unit 56. Specifically, during the second determination time Tb, after the leading edge of the paper P passes through the paper detection sensor 59 for detecting the entrance, the trailing edge of the paper P passes through the slit 56c of the second guide portion 56. It corresponds to the time until.

  If an affirmative determination is made in step 14, that is, if the count value of the timer has passed the second determination time Tb, the process proceeds to step 15 (S15). On the other hand, if a negative determination is made in step 14, that is, if the count value of the timer has not passed the second determination time Tb, the process returns to step 14 again.

  In step 15, the fixing control unit 3 stops the fan 58.

  As described above, in the present embodiment, the fixing device 50 includes the S-shaped transport path Fr configured to include the second guide portion 56 that guides the paper and transports the paper P that has passed through the fixing nip NP, and the gas flow. And a ventilation portion that causes the sheet P conveyed on the S-shaped conveyance path Fr to run along the second guide portion 56. Here, the second guide portion 56 extends along the outer peripheral shape of the upper fixing roller 51 and forms a first curved surface (first first surface) that forms a conveyance path for the sheet P with the upper fixing roller 51. A guide surface) and an arcuate third curved surface (second guide surface) that is connected to the first curved surface and reverses the curved state of the conveyance path in the paper conveyance direction. Thereby, the S-shaped conveyance path Fr forms an S-shaped path.

  According to such a configuration, the S-shaped conveyance path Fr includes the first curved surface, thereby securing a separation point where the paper P is separated from the fixing upper roller 51 in a wide range on the circumference of the fixing upper roller 51. be able to. That is, by securing the separation points in a wide range, separation of the paper P from the fixing upper roller 51 can be naturally promoted through the repulsive force and the weight of the paper P. Further, according to the present embodiment, since the air flow unit is provided with the ventilation portion that causes the paper P to follow the second guide portion 56 using the air flow, the paper P from the fixing upper roller 51 is caused by the air flow. Can be separated. As described above, due to the action of a wide range of separation points and the gas flow, the separation of the paper P can be effectively achieved without providing the separation upper claw on the fixing upper roller 51. Thereby, it is possible to suppress damage to the fixing upper roller 51 due to the separation claw and deterioration of image quality.

  Furthermore, according to the present embodiment, when the paper P passes through the S-shaped transport path Fr, the curved state of the transport path is reversed by the third curved surface, so that the paper P is passed through the shape of the transport path. It is possible to correct the curl that has occurred. The paper P that passes through the S-shaped conveyance path Fr, that is, the paper P that easily winds around the fixing upper roller 51, is likely to curl by passing through the fixing nip NP. In this regard, in the present embodiment, the paper P that is likely to be curled is transported to the S-shaped transport path Fr, so that the curl generated on the paper P can be corrected effectively. In particular, by performing curl correction immediately after passing through the fixing nip NP, the curl correction is performed in a state where the paper P is at a high temperature, so that the curl can be corrected more effectively.

  In the present embodiment, the ventilation portion is a fan 58 (suction unit) that attracts the paper P toward the first curved surface side by suction of gas. By sucking air with the fan 58, the paper P can be conveyed along the first curved surface. In addition, since air is sucked, it is possible to suppress a situation in which heat accompanying the fixing process is dispersed to the image forming unit side, so that the thermal influence on the image forming unit can be reduced.

  In the present embodiment, the fixing device 50 further includes a straight conveyance path Fs that conveys the paper P that has passed through the fixing nip NP. Here, the straight conveyance path Fs forms a linear path extending in the tangential direction of the fixing upper roller 51 in the fixing nip NP. The straight conveyance path Fs and the S-shaped conveyance path Fr form a branched path in which the paper P that has passed through the fixing nip NP is conveyed to one of the conveyance paths. Accordingly, the transport paths Fs and Fr can be selected according to the characteristics of the paper P.

  In the present embodiment, the straight conveyance path Fs has a separation point on the fixing nip portion NP side where the sheet P is separated from the fixing upper roller 51 compared to the sheet P conveyed on the S-shaped conveyance path Fr. The positioned paper P is conveyed. According to this configuration, the paper P that is harder to separate from the fixing upper roller 51 tends to be transported to the S-shaped transport path Fs. As a result, the paper P follows the conveyance path in which a wide separation point is secured, so that even the paper P that is easily wound around the upper fixing roller 51 can be urged to be separated. Further, for example, a sheet P such as a thick sheet that is difficult to wind around the fixing upper roller 51 reaches the separation point early after passing through the fixing nip NP and enters the straight conveyance path Fs. Since cardboard and the like are not easily curled, it is possible to pass through the straight conveyance path Fs.

  Further, in the present embodiment, the fixing device 50 detects the paper detection sensors 59 and 60 as a conveyance path detection unit that detects the conveyance path into which the paper P has entered, and the entry of the paper P into the S-shaped conveyance path Fs. In this case, the image forming apparatus further includes a fixing control unit 3 that operates the fan 58. Thus, the fan 58 can be operated at a necessary timing and period, and unnecessary operations can be reduced.

  The shape and configuration of the fan 58 are not limited to the above, and any shape and configuration may be adopted as long as the fan can satisfy the air suction function.

(Second Embodiment)
FIG. 5 is an explanatory diagram schematically showing the configuration of the fixing device 50 according to the second embodiment. The fixing device 50 according to the present embodiment is different from that of the first embodiment in that the passage of the paper P with respect to the straight conveyance path Fs can be controlled. The description of the configuration common to the first embodiment will be omitted, and the following description will be focused on the differences.

  As shown in FIG. 5, a movable gate portion 61 is provided at the subsequent stage of the fixing nip portion NP in the paper conveyance path. The gate portion 61 is a rectangular plate-like member whose longitudinal direction is the paper width direction CD. As shown by the arrows in the figure, the gate portion 61 is configured to be swingable about one of the long sides, and can be switched between a normal position and a restriction position. In the normal position, the gate portion 61 is in parallel with the first guide portion 55 as indicated by the broken line in the drawing. In this case, the sheet P can be selected from the straight conveyance path Fs or the S-shaped conveyance path Fr according to the separation point with respect to the fixing upper roller 51. On the other hand, at the restricted position, as shown by the solid line in the figure, the gate portion 61 is close to the fixing upper roller 51 and forms a part of the conveyance path together with the curved portion 56b of the second guide portion 56. In this case, the sheet P is restricted from entering the straight conveyance path Fs and allowed to enter only the S-shaped conveyance path Fr.

  FIG. 6 is a block diagram schematically showing a control system of the image forming apparatus 1 according to the present embodiment. In the present embodiment, the fixing control unit 3 controls the gate driving unit 62 that drives the gate unit 61 described above. As the gate driving unit 62, for example, an electric motor that swings the gate unit 61 through rotation of the output shaft can be used. The fixing control unit 3 controls the gate driving unit 62 to control the gate unit 61 to the normal position or the restriction position.

  FIG. 7 is a flowchart illustrating an operation procedure of the fixing device 50 according to the second embodiment. The processing shown in this flowchart is executed by the fixing control unit 3 using a print start command output from the image formation control unit 2 as a trigger. The gate unit 61 described above is initially set to the normal position.

  First, in step 20 (S20), the fixing control unit 3 determines whether or not a gate switching condition is satisfied. As the gate switching condition, (1) the curl correction mode is specified in the operation of the image forming apparatus 1 by the user setting through the operation unit, and (2) the sheet P to be fixed needs to be curled. And the like (for example, the paper type is thin paper or plain paper, and the printing rate of the fixing target surface is equal to or higher than a specified value).

  If an affirmative determination is made in step 20, that is, if the gate switching condition is satisfied, the process proceeds to step 21 (S21). On the other hand, if a negative determination is made in step 20, that is, if the gate switching condition is not satisfied, the process proceeds to step 22 (S22).

  In step 21, the fixing control unit 3 controls the gate driving unit 62 to set the gate unit 61 to the restriction position. On the other hand, in step 22, the fixing control unit 3 controls the gate driving unit 62 to set the gate unit 61 to the normal position.

  In the processing after step 23 (S23), the operation of the fan 58 is controlled according to the detection results of the paper detection sensors 59 and 60, as in the processing after step 10 in the first embodiment. In addition, when the gate part 61 is set to the restriction position by the process of step 21, the process of step 25 may be omitted.

  As described above, in the present embodiment, the fixing device 50 restricts entry of the sheet P into the straight conveyance path Fs and the normal position that allows the sheet P to enter the straight conveyance path Fs, and only the S-shaped conveyance path Fr. Further, a gate portion 61 that can be switched to a restriction position for transporting the paper P to the center, and a gate drive portion (drive means) 62 that drives the gate portion 61 are further provided. Here, the fixing control unit 3 controls the gate unit 61 from the normal position by controlling the gate driving unit 62 based on the image density of the surface to be fixed, the type of the paper P, or the instruction of the curl correction by the user. Switch to position.

  According to such a configuration, even if the paper P is transported to the straight transport path Fs according to the separation point of the paper P, the S-shaped transport path Fr is forcibly transported according to the switching of the gate unit 61. It becomes possible. As a result, curling occurring on the paper P can be intentionally corrected, and high-quality image formation can be performed.

(Third embodiment)
FIG. 8 is an explanatory diagram schematically showing the configuration of the fixing device 50 according to the third embodiment. The difference between the fixing device 50 according to the present embodiment and that of the first embodiment is a method for conveying the paper P along the second guide portion 56. The description of the configuration common to the first embodiment will be omitted, and the following description will be focused on the differences.

  As shown in the figure, in the present embodiment, the fan 58 is not provided inside the second guide portion 56, and instead includes an air nozzle 63 connected to a blower such as a blower fan, an air pump, or a compressor. Blowing means is provided. The air nozzle 63 is provided so as to blow air in the tangential direction from above the fixing upper roller 51, and the air blown from the air nozzle 63 causes the paper to move toward the first guide surface side of the second guide portion 56. P can be pressed.

  As described above, according to the present embodiment, in addition to sucking the paper P, the paper P can be transported along the second guide portion 56 by blowing out air. Thus, since the paper P can be run along the second guide portion 56 with various configurations, various variations as an apparatus can be provided. The fixing unit may be configured by combining the air blowing unit in the third embodiment with the suction unit in the first and second embodiments, and the configuration further improves the sheet separation performance. It becomes possible to make it.

  The image forming apparatus according to the embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention. . Further, the fixing device itself constituting the image forming apparatus also functions as part of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image formation control part 3 Fixing control part 10 Document reading part 20Y-20K Exposure part 30Y-30K Image forming part 40 Intermediate transfer part 50 Fixing apparatus 51 Upper fixing roller 52 Lower fixing roller 53 Heater 55 First guide Part 56 second guide part 56a flat part 56b curved part 56c slit 57 third guide part 58 fan 59 paper detection sensor 60 paper detection sensor 61 gate part 62 gate drive part 63 air nozzle

Claims (8)

A fixing unit that passes the sheet through a fixing nip formed by pressing a pair of fixing members and fixes a toner image on a fixing target surface of the sheet;
A first conveyance path configured to convey a sheet that has passed through the fixing nip, and includes a sheet guide unit that guides the sheet;
Using a gas flow, and having a ventilation section that causes the sheet conveyed through the first conveyance path to follow the sheet guide section,
The paper guide portion is
A first guide surface that extends along the outer peripheral shape of one fixing member disposed on the fixing target surface side of the paper and forms a paper conveyance path with the fixing member;
A fixing device comprising: an arcuate second guide surface that is connected to the first guide surface and reverses a curved state of the conveyance path in the sheet conveyance direction.   The fixing device according to claim 1, wherein the ventilation unit includes a suction unit that draws a sheet toward the first guide surface by suction of a gas.   The fixing device according to claim 1, wherein the ventilation unit includes a blowing unit that presses a sheet toward the first guide surface by blowing out a gas. A second conveyance path for conveying the sheet that has passed through the fixing nip portion;
The second conveying path constitutes a linear path extending in a tangential direction of the fixing nip portion of the fixing member,
The first transport path and the second transport path form a branched path in which the sheet that has passed through the fixing nip is transported to one of the transport paths. The fixing device according to any one of the above.   The second conveyance path is configured to convey a sheet in which a separation point at which the sheet is separated from the fixing member is located on the fixing nip portion side as compared with the sheet conveyed through the first conveyance path. The fixing device according to claim 4, wherein the fixing device is characterized in that: A paper detection unit that is provided in the first or second transport path and detects the transported paper;
A control unit that operates the ventilation unit when it is determined that a sheet has entered the first conveyance path based on the detection result of the sheet detection unit;
The fixing device according to claim 4, further comprising: Switching between a normal position that allows entry of paper into the second conveyance path and a restriction position that restricts entry of paper into the second conveyance path and conveys paper only to the first conveyance path. Possible gate part,
Drive means for driving the gate portion,
The control unit switches the gate unit from a normal position to a restricted position by controlling the driving unit based on a printing rate of the fixing target surface, the type of paper, or a curl correction instruction by a user. The fixing device according to claim 4, wherein the fixing device is a magnetic head. An image forming unit for transferring a toner image to paper;
The fixing device according to claim 1, wherein the transferred toner image is fixed on a sheet.
An image forming apparatus comprising:

Images