JP2004240447A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of more effectively cleaning a pair of rollers for a fixing device, especially, a fixing roller. <P>SOLUTION: The image forming apparatus is provided with a thermal fixation system fixing device 17, a recording material carrying device, an image storage device for storing a prescribed pattern image and an optical writing device for forming the image on an image carrier, and wherein the fixing device 17 is cleaned while making the recording material with the image recorded recorded thereon pass through the fixing device 17 again, and in the case of forming the prescribed pattern image, the apparatus is controlled so that a toner weight per unit area to be transferred to the recording material may be heavier than that required when a normal image is formed by changing at least one of a developing bias, a writing light quantity, the rotating speed of a developing roller, a transfer current and the image carrier current. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a facsimile, a laser printer, and a copying machine, and more particularly, to a fixing method in which a transfer material having unfixed toner is passed through a pair of rollers and heated and pressed to fix the toner. The present invention relates to an image forming apparatus provided with the device.

  A fixing device used for fixing image information placed as a toner image on a transfer material to the transfer material includes a heating roller having a built-in heater and a pressure roller. Configurations in the state are well known.

  In such an apparatus, toner or paper dust adheres to the surface of the heating roller or the pressure roller due to long-term use, so that the image on the transfer material is contaminated by the toner adhered to the roller, or the transfer material There have been problems such as the occurrence of back stains and, in some cases, the transfer material wrapping around the rollers to cause paper jams.

  Therefore, various methods and configurations for removing toner and the like adhering to the surface of the heating roller or the surface of the pressure roller have been proposed.

  For example, in Japanese Patent Application Laid-Open No. 5-158375, in order to clean a pair of fixing rotators having a controlled surface temperature, a cleaning layer exhibiting adhesiveness is formed on a cleaning sheet, and the sheet is formed of a rotator. It describes that the surface temperature of the rotating body is maintained at a cleaning temperature higher than a fixing temperature for the transfer material when passing through the nip portion.

  However, in such a method, a special cleaning sheet must be prepared in order to clean the rotating body for fixing, and the cleaning sheet is supplied by the operator from the manual sheet feeding unit every time the cleaning is performed. There is a need. Therefore, the following inconveniences exist.

  (1) It costs extra to prepare the cleaning sheet, (2) It is troublesome to prepare and store the cleaning sheet in advance for cleaning every predetermined number of sheets, and (3) It is necessary to handle the cleaning sheet by hand. An operator must accompany the apparatus main body in order to supply the paper from the sheet feeding unit, which may cause a large amount of time loss depending on the installation location. That's pretty annoying.

  Also, by utilizing the property that the toner and paper powder attached to the surface of the pressure roller easily adhere to the solid image printed on the transfer material, the transfer material on which the solid image is printed can be used as the printing surface. There has been proposed a method of cleaning the sheet by re-passing the sheet so as to be in contact with the sheet. For example, in Japanese Patent Application Laid-Open No. 3-39871, at a stage where a predetermined number of prints have been made, a cleaning image stored in advance in an image data storage unit is output by an image output unit. And cleaning the pressure roller. This eliminates the need to store a transfer material for cleaning having a solid image.

  Furthermore, it covers a temperature detection element that detects the surface temperature of the roller even when cleaning is performed periodically, and a safety device that shuts off the power supply to the heating source when the surface temperature of the heating roller reaches a temperature higher than the set temperature. Toner accumulates between the polyimide tape and the roller, and the accumulated toner cannot be removed by the cleaning transfer material. The amount of toner accumulated between the roller and the roller increases, and a part of the accumulated toner slips through between the polyimide tape and the heating roller, causing stains on a transfer material to be fixed later, or an excessive amount of pressure on the pressure roller. There is also a problem that the transfer material for cleaning may be wound around the pressure roller when it becomes dirty. In order to solve these problems, Japanese Patent Application Laid-Open No. 4-134377 discloses a method in which the surface temperature of a fixing roller is set higher than the fixing temperature, the toner attached to the roller is heated from the time of fixing, and a part of the toner is sufficiently removed. It has been proposed that a cleaning image stored in a ROM be formed on a transfer material and cleaning is performed using the transfer material.

  As described above, in the method in which the specific pattern is printed out on the transfer material and the pressure roller is cleaned by feeding the specific pattern to the fixing device, the problems (1) to (4) described above occur. When the conveyance path is switched, cleaning can be performed not only on the pressure roller but also on the fixing roller.

  An object of the present invention is to provide an image forming apparatus that can more effectively perform cleaning on a roller pair of a fixing device, particularly a fixing roller, in view of such a conventional technology.

  In order to solve this problem, according to the present invention, a fixing device for fixing a toner image by a thermal action by passing a recording material onto which a toner image formed on an image carrier has been transferred, and supplying the recording material. A conveyance device for feeding the image, a storage device for storing the image of the predetermined pattern, and an optical writing device for forming the image of the predetermined pattern on the image carrier, and a recording material on which the image of the predetermined pattern is recorded is fixed again. When forming an image of a predetermined pattern in an image forming apparatus that cleans a fixing device by passing the paper through the apparatus, at least one of a developing bias, a writing light amount, a rotation speed of a developing roller, a transfer current, and a drum current is changed. In this way, the configuration is such that the weight of the toner per unit area transferred to the recording material is controlled to be larger than that during normal image formation.

  It is preferable that a recording material size detection device is provided to detect the size of the recording material on which the image is to be formed when forming an image of a predetermined pattern, and to control the feeding of the recording material according to the result. It is.

  When a recording material on which an image of a predetermined pattern is recorded is passed through the fixing device, at least one of lowering the sheet passing speed than at the time of normal fixing and setting the fixing device to a temperature higher than the fixing temperature is performed. For example, it is still preferable.

  When a recording material on which an image of a predetermined pattern is recorded is passed through a fixing device, it is convenient if the transport direction is configured to be reversible.

  It is more preferable that the image forming apparatus is provided with a reversing section in the conveying device and is capable of forming an image on both sides of the recording material, and is configured to be able to select whether or not the recording material on which the image of the predetermined pattern is recorded can be reversed.

  When a predetermined pattern image is recorded on one side of the recording material, the recording material is reversed at the reversing unit, and when the same pattern image is recorded on the other surface, cleaning is performed using the previously recorded image, and then the reversal is performed. It is preferred that the fixing device be cleaned again without the need for cleaning.

  According to the apparatus according to the first aspect, when forming an image of a predetermined pattern, at least one of a developing bias, a writing light amount, a rotation speed of a developing roller, a transfer current, and a drum current is changed to transfer to a recording material. Since the toner weight per unit area is controlled to be larger than that in normal image formation, the adhesiveness for cleaning when the fixing device is cleaned is improved, and better cleaning can be performed.

  According to the apparatus according to the second aspect, the size of the recording material is detected, and the feeding control of the recording material is performed according to the result, so that the optimum size is selected and the cleaning is performed.

  According to the apparatus according to the third aspect, when the recording material on which the image of the predetermined pattern is recorded passes through the fixing device, the sheet passing speed is set lower than at the time of normal fixing, or is set to a temperature higher than the fixing temperature. Since the fixing device is used, cleaning can be performed using a toner having higher viscosity.

  According to the apparatus according to the fourth aspect, when the recording material on which the image of the predetermined pattern is recorded passes through the fixing device, the transport direction is configured to be reversible in the forward and reverse directions, so that the fixing device is more reliably cleaned. You.

  According to the apparatus according to the fifth aspect, since it is configured to be able to select whether or not the recording material on which the image of the predetermined pattern is recorded can be inverted, a necessary surface of the fixing device is cleaned.

  According to the apparatus according to claim 6, an image of a predetermined pattern is recorded on one side of the recording material, and the recording material is first recorded when the recording material is reversed by the reversing unit and the image of the same predetermined pattern is recorded on the other surface. Since the fixing device is cleaned again without reversing the image, the both sides of the fixing device are cleaned at one time with one sheet of recording material.

The details of the present invention will be described based on an embodiment shown in the drawings.
The basic configuration of the image forming apparatus and the operation in the normal image forming mode are basically the same as those of the conventional one, and are as follows.

  In the double-sided recording laser printer shown in FIG. 1 in which the apparatus main body 10 is mounted on a sheet unit 11, the apparatus main body 10 is composed of an upper structure 10a and a lower structure 10b, and the upper structure 10a is positioned downward. It is attached to the structure 10b using a shaft 10c so that it can be opened and closed freely. A belt-shaped photoconductor 12 is provided substantially at the center of the apparatus main body 10. A charger 13, a developing device 14, a transfer device 15, and a cleaning device 16 are arranged around the photosensitive member 12 in the order of the driving directions indicated by arrows. In the publication of the photoconductor 12, a fixing device 17 is provided, and an optical writing device 18 is disposed above the charging device 13 and the cleaning device 16. The static eliminator 9 is disposed downstream of the cleaning device 16.

  On the bottom wall 10d of the apparatus main body 10, a paper feed port 19 is provided on the operation side on the right side in the figure, and a paper feed roller 20 is provided in the paper feed port 19. A conveyance path 21 that passes under the photoconductor 12 is provided between the paper supply roller 20 and the fixing device 17, and a conveyance roller pair is provided between the paper supply roller 20 and the photoconductor 12 in the conveyance path 21. 22 and a registration roller 23 are provided.

  At the outlet side of the fixing device 17, a paper discharge guide 25 for guiding the sheet to the upper stack portion 24 on the upper surface of the upper structure 10a is provided, and two paper discharge roller pairs 26 are provided below the paper discharge guide 25. And 27 are provided. A lower stack portion 28 is provided on the sheet discharge side of the discharge roller pair, and the sheet conveying direction is set between the upper stack portion 24 and the lower stack portion 28 between the lower stack portion 28 and the discharge roller pair 27. And a second switching claw 29 for switching to. Further, a switchable first switching claw 30 is provided between the paper discharge roller pair 26 and the paper discharge roller pair 27. A discharge port 31 for refeeding paper is provided on the bottom wall 11d below the first switching claw 30. A guide 32 for guiding the sheet to the discharge port 31 is provided between the first switching claw 30 and the discharge port 31. Is provided integrally with the lower frame 17 a of the fixing device 17. The guide 32 is formed of, for example, a resin material having high heat resistance.

  A manual feed device 33 is provided on the operation side of the lower structure 10b so that sheets can be manually fed one by one without using automatic feeding. The receiving portion 33a for receiving the trailing end of the manually fed paper sheet is attached to the operation side surface of the sheet unit 11 so that the position can be freely changed in three steps, upper, middle and lower, according to the length of the sheet. Can be.

  On the other hand, the sheet unit 11 has a plurality of paper feed cassettes 40 detachably mounted vertically from the operation side. On the lower side of the paper feed cassette 40, a push-up lever 34 whose one end is urged upward by a spring or the like is provided. On the sheet feeding side of the lower cassette 40, a sheet feeding roller 20 similar to that of the apparatus main body 10 is provided.

  The paper feed cassette 40 is box-shaped, and guide plates 41 and 42 are set up front and rear thereof, and a bottom plate 43 that is rotatable upward is attached to the front side from the center, and a separation member 44 attached with a separation pad or the like at the front end. Is provided. At the front side, a sheet conveying path 45 is vertically penetrated, and a pulling handle 46 is provided at the front end of the sheet cassette.

  When recording is performed by automatic sheet feeding, one of the sheet feeding rollers 20 is selectively driven to separate sheets one by one from a top sheet by a separating member 44 and the sheet feeding roller 20 so that the sheet is conveyed. 21 or through the upper sheet conveying path 45 to the conveying path 21. When manual paper feeding is performed instead of automatic paper feeding, sheets are manually fed one by one from the manual feeding device 33 and sent out into the transport path 21.

  The sheet fed from the paper feed cassette 40 or the manual feed device 33 into the conveyance path 21 is conveyed to the registration roller pair 23 via the conveyance roller pair 22, and the sheet of the photoconductor 12 is timed by the registration roller pair 23. It is transported down.

  The photoconductor 12 is driven in a clockwise direction as indicated by an arrow. At this time, the surface is uniformly charged by the charger 13, and the photoreceptor 12 is irradiated with laser light from the optical writer 18 to electrostatically charge the photoconductor 12. Form a latent image. This latent image is visualized by toner when passing through the developing device 14.

  This visible image is transferred by the transfer device 15 onto the upper surface of the sheet conveyed below the photoconductor 12. The transferred sheet is conveyed to the fixing device 17 to fix the transferred image, and the sheet is sent from the fixing device 17 to the sheet discharge roller pair 26 and sent to the sheet discharge roller pair 27 by the first switching claw 30. The two switching claws 29 are used to switch to the upper stack portion 24 or the lower stack portion 28 and discharge to either of them.

  In this laser printer, a sheet cassette 40 can be mounted in the sheet unit 11 instead of the sheet re-feed unit 50, and the sheet re-feed cassette 50 is mounted on the front side similarly to the sheet cassette 40 described above. Has a box-like shape in which a sheet conveying path 51 is vertically penetrated and a handle 52 for pulling out is provided at a front end. In the re-feed unit 50, there is provided a transport path 53 extending from left to right in the figure and continuing to the lower reversing path 53a.

  The transport path 53 is provided with transport roller pairs 54, 55, 56, and a forward / reverse roller pair 57 is provided at a position past the reversing portion at the right end of the transport path 53 in the drawing. Further, at the front side inside the re-feeding unit 50, when the re-feeding unit 50 is attached to the apparatus main body 10, a paper feeding roller 58 that comes into pressure contact with the paper feeding roller 20 of the apparatus main body 10 is provided. A third switching claw 59 for guiding the sheet is switchably attached to the reversing section. By switching the first switching claw 30, the sheet after the image transfer is sent from the pair of discharge rollers 26 to the discharge port 31, and guided to the transport path 53 by the guide 32.

  Then, the sheet after fixing is transported in the transport path 53 of the re-feed unit 50 by the transport roller pairs 54, 55, 56, sent to the forward / reverse roller pair 57 by the third switching claw 59, and forward / reverse roller pair By the forward rotation of 57, the vehicle enters the reversing path 53a. Further, when the sheet is further fed and the rear end passes through the third switching claw 59, the forward / reverse rotation roller 57 rotates in the reverse direction, and the sheet is inverted and fed from the rear end to the nip portion between the sheet feeding roller 20 and the sheet feeding roller 58. Then, the sheet is fed again into the apparatus main body 10. Then, the toner image is transferred to the back surface of the sheet, and is discharged onto the stack unit 24 or 28 via the fixing device 17. That is, images are formed on both sides of the sheet.

  When the third switching claw 59 is at the position indicated by the solid line as shown in FIG. 1, the sheet (image-formed) conveyed by the conveying roller pairs 54, 55, 56 does not enter the reversing path 53a. The paper is re-fed into the apparatus main body 10 by the paper feed roller pair 20, 58, and additional information can be written on the already formed image surface.

  The above-described image forming process, sheet conveyance control, temperature control in the fixing device, and the like are controlled by a CPU (not shown). The control unit including the CPU is also provided with a ROM (not shown) for storing an image signal of a test pattern, which is a cleaning image. For example, the ROM is output from the ROM by pressing a test print switch (not shown). The laser beam is modulated by the image signal to form a fixed pattern image on the sheet.

  In FIG. 2 showing a schematic configuration of the fixing device, the fixing device 17 includes a lower frame 17a and an upper frame 17b indicated by two-dot chain lines, and a heater 172 is fixed inside the hollow fixing roller 170. I have. The surface of the fixing roller 170 is processed to improve the releasability of the toner, and a temperature detecting element and a device for ensuring safety are arranged around the fixing roller 170 although not shown. . Further, both ends of the fixing roller 170 are rotatably supported by bearings (not shown) and a gear 171 is coaxially attached thereto, and is rotated by a driving gear (not shown). On the other hand, the pressure roller 173 is formed of a material such as rubber on the outer periphery of the shaft 173a, and both ends thereof are rotatably supported by bearings 174, and are pressed against the fixing roller 170 by a compression spring 175. When the recording sheet passes through the nip formed at the press-contact portion, the toner on the sheet is fixed by heat and the pressure generated by press-contact of both rollers.

  As the number of sheets passing therethrough increases, dirt such as toner gradually adheres to the surface of the fixing roller 170 and the pressure roller 173, which is transferred to the recording sheet and causes an image defect. It is necessary to remove the dirt from the fixing roller or the pressure roller at the stage where the occurrence of occurs. Therefore, when the number of printed sheets is counted and a predetermined value is reached, a signal is given to the CPU from a counter unit (not shown), or a signal is given to the CPU when the operator presses a test print switch. The sheet to be used as the cleaning sheet is sent out by the sheet feed roller 20 from 40-1 or 40-2. On the other hand, a pattern as shown in FIG. 3, for example, is formed on the photoconductor 12 by the optical writing unit 18 according to the image signal output from the ROM. The pattern is formed on a sheet by development and transfer processing. At this time, at least one control value of a developing bias, a writing light amount, a rotation speed of a developing roller, a transfer current and a drum current is changed by a command of a control system, and a toner amount per unit area (M / M A) is adjusted so as to be larger than that in normal image formation. The adjustment improves the adhesiveness of the cleaning sheet when the toner is dissolved.

  The sheet to which the cleaning pattern has been transferred is fixed by the fixing device 17, and is re-fed to the fixing device via the conveyance path by the switching adjustment of the switching claw such that the pattern comes into contact with the roller to be cleaned. Refeeding can also be performed manually. The pattern on the sheet re-fed to the fixing device 17 is partially melted by the heat in the fixing device, develops viscosity, and cleans the roller. At this time, in order to further improve the adhesiveness of the toner and enhance the cleaning effect, it is preferable to increase the control temperature of the fixing device when passing the cleaning pattern or to reduce the paper passing speed.

  The cleaning sheet used for cleaning the fixing device may be a sheet used for normal printing.However, the size of the cleaning sheet is set in the longitudinal direction of the roller, that is, in order to prevent residual cleaning on the roller, particularly in the edge area, that is, the sheet. It is necessary in principle to have the maximum paper passing width in the width direction. As in the apparatus shown in FIG. 1, an apparatus that includes a plurality of paper feed cassettes and forms an image on sheets of a plurality of sizes is often provided with a mechanism capable of arbitrarily selecting a sheet size. In the case of such an apparatus, it is preferable that the apparatus automatically selects the size of the maximum sheet passing width during the cleaning process and uses the size for cleaning. Since such an apparatus generally includes a means for detecting a sheet size, the size of the cleaning sheet is also detected during the cleaning process to determine whether or not the sheet has the maximum width. It is more appropriate if it is configured as follows. This control flow is illustrated in FIG. That is, when a roller cleaning instruction is issued from the CPU, the size of the set sheet is detected by the size detecting means, and the set sheet is determined by whether or not the information matches that of the sheet having the maximum width. Is determined. If the sheet has the maximum width, a roller cleaning mode is started. If the set sheet is not of the maximum width, the fact that an appropriate size for cleaning is not set is displayed on an operation unit (not shown). Since the width requiring cleaning at that time may be narrow, the roller cleaning mode is started when cleaning with the small size sheet is permitted. If the cleaning should not be performed forcibly, set the correct size paper and start again.

  In order to more reliably clean the rollers, as shown in FIG. 5, while the cleaning sheet is being held by the fixing device, the conveying direction is reversed a plurality of times, and the adhesive toner area is formed a plurality of times. The drive may be controlled so as to be in contact with the roller to be cleaned.

  As shown in FIG. 1, when automatic printing can be performed on both sides of the recording sheet, it is possible to determine which of the fixing roller and the pressure roller is to be cleaned and to make a selection. Can automate the process up to cleaning. For this determination / selection, the apparatus may be automatically selected according to conditions such as the number of sheets passed through the apparatus, or a message may be issued to the operator to select cleaning from dirt or the like of a printed image. Good. The operation of each of the fixing roller and the pressure roller will be described below with reference to the example of FIG.

  When cleaning the fixing roller, the recording sheet on which the pattern shown in FIG. 3 is fixed is sent to the sheet re-feeding unit 50, the third switching claw 59 is switched to the solid line position in FIG. If the cleaning pattern is sent to the paper feeder 20 and passed through the fixing device 17, the cleaning pattern comes into contact with the surface of the fixing roller, so that the toner adhering as dirt on the fixing roller is removed by the cleaning pattern portion.

  When cleaning the pressure roller, the recording sheet on which the pattern shown in FIG. 3 is fixed is sent to the re-feeding unit 50, the third switching claw 59 is switched to the position indicated by the broken line in FIG. When the cleaning pattern is passed through the fixing unit 17 again through the image forming unit by reversing the pair 57, the cleaning pattern abuts on the surface of the pressure roller, so that the toner adhering as dirt on the pressure roller is removed by the cleaning pattern unit. Removed.

  The operation for cleaning the fixing roller and the pressure roller at the same time will be described below with reference to FIG.

  First, the recording sheet on which the cleaning pattern shown in FIG. 3 is formed and fixed on one side is sent to the re-feeding unit 50, and sent to the reversing path 53a by the third switching claw 59. Next, the roller pair 57 is reversed to be sent to the image forming unit, where the cleaning pattern is formed on the back surface of the recording sheet in the forming unit (image forming unit). The recording sheet is conveyed to the fixing device 17 and the rear surface is fixed. At the same time, the pressure roller is cleaned by the cleaning pattern formed on the rear surface. The recording sheet is sent to the re-feeding unit 50 again after passing through the fixing unit 17, and is sent to the image forming unit without being inverted by the third switching claw 59, and the image is formed in the forming unit. Without being transported to the fixing device 17. In the fixing device 17, the cleaning pattern formed on the back surface of the sheet comes into contact with the fixing roller, and the fixing roller is cleaned. In this case, since the cleaning pattern on the front surface is in contact with the pressure roller, the pressure roller is simultaneously cleaned again. Thereafter, the sheet is discharged without being guided again to the sheet re-feeding unit 50, but may be sent to the sheet re-feeding unit again in order to repeat the above steps in order to ensure reliable cleaning.

  In the above embodiment, the fixing device has a configuration including a fixing roller and a pressure roller.However, an endless belt is arranged on the outer periphery of the heat source, and the pressure roller is installed facing the heat source. Naturally, the present invention is also applied to a fixing device configured to pass a sheet between a roller and an endless belt.

1 is an overall schematic diagram of an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram of a fixing device in the image forming apparatus of FIG. 1. FIG. 3 is a schematic diagram illustrating an example of a recording sheet provided with an image of a cleaning pattern. FIG. 9 is a diagram illustrating a cleaning flow when detecting the size of a recording sheet. FIG. 3 is a conceptual diagram illustrating a state in which the fixing device performs normal / reverse rotation.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Apparatus main body 11 Sheet unit 12 Photoreceptor 13 Charger 14 Developing device 15 Transfer device 16 Cleaning device 17 Fixing device 18 Optical writing device 19 Paper feed port 20 Paper feed roller 21 Transport path 22 Transport roller pair 23 Registration roller pair 24 Upper stack Unit 25 Discharge Guide 26, 27 Discharge Roller Pair 28 Lower Stack 29 Second Switching Claw 30 First Switching Claw 31 Discharge Port 32 Guide 33 Manual Feeder 33a Receiving Unit 34 Push-Up Lever 40 Paper Cassette 41, 42 Guide Plate 43 Bottom plate 44 Separation member 45 Sheet transport path 46 Handle 50 Re-feed unit 51 Sheet transport path 52 Handle 53 Transport path 53a Reverse path 54, 55, 56 Transport roller pair 57 Forward / reverse roller pair 58 Feed roller 59 Third switching claw

Claims (6)

  A fixing device for fixing the toner image by a thermal action by passing a recording material onto which a toner image formed on an image carrier is transferred, and a conveying device for feeding the recording material; and storing an image of a predetermined pattern. An image storage device, and an optical writing device for forming the image of the predetermined pattern on the image carrier, and an image for cleaning the fixing device by passing a recording material on which the image of the predetermined pattern is recorded again to the fixing device. In the forming apparatus, when forming the image of the predetermined pattern, at least one of a developing bias, a writing light amount, a rotation speed of a developing roller, a transfer current, and a drum current is changed to change a unit area per unit area transferred to a recording material. An image forming apparatus for controlling the weight of the toner to be larger than that in normal image formation.   A recording material size detection device, wherein when forming the image of the predetermined pattern, the size of the recording material on which the image is to be formed is detected, and the recording material feeding control is performed according to the result. The image forming apparatus according to claim 1.   When the recording material on which the image of the predetermined pattern is recorded is passed through a fixing device, at least one of lowering the sheet passing speed than during normal fixing and setting the fixing device to a temperature higher than the fixing temperature is performed. The image forming apparatus according to claim 1, wherein the image formation is performed.   4. The image forming apparatus according to claim 1, wherein when a recording material on which the image of the predetermined pattern is recorded passes through a fixing device, a conveyance direction is configured to be reversible. .   2. The image forming apparatus according to claim 1, wherein the transport device includes a reversing unit, and the image forming apparatus is capable of forming an image on both surfaces of the recording material. The image forming apparatus according to any one of claims 1 to 4.   When a predetermined pattern image is recorded on one side of the recording material, the recording material is reversed at the reversing unit, and when the same pattern image is recorded on the other surface, cleaning is performed using the previously recorded image, and then the reversal is performed. The image forming apparatus according to claim 5, wherein the fixing device is cleaned again without performing the cleaning.

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