JP2019128476A - Image forming apparatus and image heating device - Google Patents

Abstract

To provide an image forming apparatus and an image heating device capable of effectively cleaning the dirt which is transferred, as dirt relating to a toner image, to a member constituting an image heating part based on an external heating system.SOLUTION: The image forming apparatus includes an image heating part based on an external heating system which transfers offset toner transferred to a heating film 15 to a pressing roller 19 by way of a fixing roller 18 and then exhausts the toner to a rear surface of a recording material for cleaning. The image forming apparatus is configured such that when a count of a counter portion of a warm air counter 200 of a memory unit 43 has reached a predetermined value, the control unit 41 predicts the surface temperature of the fixing roller 18 immediately before cleaning from the count of the warm air counter 200, extends the sheet-to-sheet time immediately before the cleaning according to the value of the warm air counter 200, and performs cleaning after executing sheet-to-sheet temperature correction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus that forms a toner image fixed on a recording material and an image heating apparatus that heats the toner image on the recording material.

  As an external heating type fixing device, there is a configuration in which a nip portion is formed by a fixing roller and a pressure roller, a heating film is provided in contact with the outer peripheral surface of the fixing roller, and the heater heats the fixing roller from the outside through the heating film. Known (Patent Document 1). In this configuration, the temperature of the surface of the fixing roller can be quickly reached to the target fixing temperature.

  Patent Document 1 discloses a configuration in which a bias application unit is provided to suppress adhesion of stains to be transferred to a heating film as stains associated with a toner image.

JP, 2012-128262, A

  However, even if it is intended to provide a bias application configuration to the heating film as in Patent Document 1, the configuration may not be provided due to the configuration, and in this case, dirt will continue to be accumulated.

  When the surface temperature of the heating film, the fixing roller, and the pressure roller rises as the number of sheets to be fed increases, it becomes difficult to clean the surface dirt attached to the heating film only by applying a bias.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and an image heating apparatus that can effectively clean dirt transferred to a member constituting an image heating unit of an external heating system as dirt related to a toner image.

  In order to achieve the above object, an image forming apparatus according to the present invention is provided with an image forming portion for forming a toner image on a recording material, a first rotating body, and the first rotating body facing the first rotating body. An opposing member forming a nip portion for holding and conveying the recording material carrying the toner image together with the rotating member, and the first rotating member being in contact with the first rotating member on the side different from the opposing member; The second rotating body is transferred to the second rotating body during the time when the recording material passes through the nip portion and the next recording material is carried into the nip portion at the time of image formation, and the second rotating body. The dirt associated with the toner image is transferred to the opposing member via the first rotating body, and the next recording material discharges the dirt to the surface opposite to the surface on which the toner image is carried. A control unit that enables the control to pass through the nip portion. If it is determined that the discharge is necessary based on the number of passing recording materials, the discharge information may be determined based on warm-up information predicted as the degree of warming of the first rotary member or temperature information of the first rotary member. The immediately preceding time is corrected to a second time extended with respect to the first reference time, and the target temperature adjustment temperature is corrected to a second temperature lower than the first reference temperature. And a control unit.

  Another image forming apparatus according to the present invention faces an image forming unit that forms a toner image on a recording material based on input image data, a first rotating body, and the first rotating body. An opposing member forming a nip portion for nipping and conveying the recording material carrying the toner image together with the first rotating body, and contacting the first rotating body on the side different from the opposing member, the target temperature adjustment temperature And the time of image formation when the recording material passes through the nip portion and the next recording material is carried into the nip portion. The dirt related to the toner image transferred to the rotating body is transferred to the opposing member via the first rotating body, and the next recording material is transferred to the side opposite to the side on which the toner image is carried A control unit that enables the discharge of the dirt. If it is determined that the discharge is necessary based on density information of the data, immediately before the discharge based on warmth information predicted as the degree of warming of the first rotating body or temperature information of the first rotating body And a control unit that corrects the time to a second time which is extended with respect to the first time which is a reference, and corrects the target temperature adjustment temperature to a second temperature which is lower than the first temperature which is a reference And.

  Further, the image heating apparatus according to the present invention forms a first rotating body, and a nip portion facing the first rotating body and sandwiching and conveying a recording material carrying a toner image together with the first rotating body. Opposing member, the second rotating member which is in contact with the first rotating member on the side different from the opposing member, and is controlled to the target regulated temperature, and at the time of image formation, the recording material is in the nip Of the toner image transferred to the second rotating body through the first rotating body in the time until the next recording material is carried into the nip portion after passing through the first rotating body. A control unit for transferring to the opposite member and enabling discharge of the dirt to the surface opposite to the surface on which the toner image is carried on the next recording material, the recording material passing through the nip portion When it is determined that the spout is necessary based on the number of passes The first time extended immediately before the discharge based on the warm air information predicted as the degree of warming of the first rotating body or the temperature information of the first rotating body And a control unit that corrects the target temperature control temperature to a second temperature that is lower than a reference first temperature.

  According to the present invention, it is possible to provide an image forming apparatus and an image heating apparatus capable of effectively cleaning dirt transferred to a member constituting an image heating unit of an external heating method as dirt related to a toner image.

10 is a flowchart relating to determining execution timing of inter-sheet discharge cleaning control from the number of image formations. 1 is a schematic cross-sectional view illustrating an example of an image forming apparatus 100. FIG. 2 is a cross-sectional view illustrating an example of a fixing device 14 as an image heating device. FIG. FIG. 6 is a view for explaining the relationship between the control temperature of the heater 16 and the temperature at which the toner is heated (surface temperature of the fixing roller). FIG. 7 is a diagram showing the transition of the detected temperature of the thermistor 20 and the surface temperature of the fixing roller 18 according to the number of times of image formation. FIG. 6 is a diagram illustrating a state where the heating nip portion N2 is divided into three in the recording material conveyance direction with respect to the explanation of the heating nip portion N2. FIG. 7 is a diagram for explaining transition of surface temperatures of the heating film 15 and the fixing roller 18 when temperature control is started from the state where the fixing device 14 is cooled. It is a figure showing change of surface temperature C9 of fixing roller 18 to surface temperature C8 of heating film 15 at the time of performing discharge control. The surface temperature C11 of the fixing roller 18 when the discharge control is performed immediately after the 40 sheet passing with respect to the surface temperature of the heating film 15, and the surface temperature C12 of the fixing roller 18 when the discharge control is performed immediately after the 400 sheet passing. FIG. FIG. 6 is a view showing a surface temperature C13 of the heating film 15 and a surface temperature C14 of the fixing roller 18 when two jobs are output when the number of sheets in one job is four (hereinafter, referred to as four sheets intermittently). FIG. 7 is a view showing a surface temperature C15 of the heating film 15 and a surface temperature C16 of the fixing roller 18 when four jobs are output with two sheets per job (hereinafter, referred to as two sheets intermittent sheet passing). FIG. 7 is a diagram showing the sheet interval time before the discharge control according to the temperature adjustment zone of the warm air counter control in the embodiment of the present invention, and the correction of the temperature adjustment temperature of the sheet. 2 is a block diagram illustrating a configuration relating to control of the image forming apparatus 100. FIG. It is a figure which shows the relationship between density | concentration signal [%] of YMCK total, and dirt density (DELTA) D of the heating film 15 surface regarding the 2nd Embodiment of this invention. FIG. 16 is a view showing the relationship between the number of times of image formation and the stain density ΔD on the surface of the heating film 15 in an image of 40% of the total of YMCK density signal values where stains easily accumulate on the heating film 15; It is a figure which shows the relationship between detection area size (length of the printing area of a conveyance direction) and the stain density (DELTA) D of the surface of a heating film. It is a figure explaining an example of the division | segmentation of a detection area. It is a figure explaining the detection area and detection method of a density signal value. It is a flowchart regarding detection of a concentration signal value. FIG. 10 is a flowchart relating to determining the execution timing of the inter-sheet discharge cleaning control from the dirt flag subjected to image analysis.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the components described in this embodiment are merely examples, and the present invention is not limited to those described in the embodiments.

First Embodiment
<Image forming apparatus 100>
The overall configuration and operation of the image forming apparatus 100 will be described. The image forming apparatus according to the present exemplary embodiment is an image forming apparatus 100 including an external heating type fixing device 14 described later. FIG. 2 shows a four-color full-color electrophotographic image forming apparatus 100 having four image forming units as an example of the image forming apparatus. In the present embodiment, the image forming apparatus 100 is described as an example of a full-color intermediate transfer type apparatus, but is not limited thereto.

  For example, it may be a direct transfer apparatus that directly transfers from the photosensitive drum 1 to the recording material P without using an intermediate transfer belt 13 to be described later, or an apparatus that forms a single color toner image (for example, a monochrome machine). It may be Further, the image forming apparatus 100 may be a copying machine, a printer, a facsimile machine, or a multifunction machine having a plurality of functions of these.

  The recording material P is a medium on which a toner image (image) is formed by the image forming apparatus 100. Specific examples of the recording material P include plain paper, thick paper, sheets for overhead projectors, and the like. For convenience, the handling of the recording material (sheet) P will be described using terms related to the paper such as paper passing, paper feeding, paper discharging, but the recording material is not limited to paper.

  In the image forming apparatus 100 according to this embodiment, four stations (four image forming units) corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black) are arranged in a line. It is arranged. The toner images formed at each station are sequentially transferred from each station to the intermediate transfer belt 13. Each station includes a drum-type electrophotographic photosensitive member 1 (hereinafter referred to as a photosensitive drum 1) as an image carrier.

  On the circumferential surface of the photosensitive drum 1, in order along the rotational direction (arrow R1 direction), the charger 2 as the charging means, the exposure device 3 as the exposure means, the developing device 4 as the developing means, the cleaning as the cleaning means An apparatus 7 and a pre-exposure device 8 as pre-exposure means are arranged. The developing device 4 is provided with a developing roller 5 that supplies a developer to the photosensitive drum 1.

  Inside the intermediate transfer belt 9 rotating in the direction of the arrow R3, a primary transfer roller 10 facing the photosensitive drum 1 of each station via the intermediate transfer belt 9 is provided. Further, the inner roller 11 of the secondary transfer portion and the outer roller 12 of the secondary transfer portion are in contact via the intermediate transfer belt 9. The outer roller 12 of the secondary transfer portion rotates in the direction of arrow R4.

  In FIG. 2, 22 is a discharge roller, 23 is a discharge tray, 25 is an environmental temperature / humidity sensor, 40 is an external device, 41 is a control unit (detailed later), 42 is an input image processing unit, and 50 is a conveyance path.

<Image formation>
Next, an outline of processes from when a job is input to when an image is formed on the recording material P will be described with reference to FIG. The job (image forming job, print job) is an image forming instruction to which printing condition information such as image data, designated type of recording material P, basis weight, paper size, number of sheets, number of copies, layout, post-processing, etc. is added (Image formation command).

  In FIG. 13, image data is input to the input image processing unit 42 from an external device 40 (FIG. 2) such as an external connected personal computer. The control unit 41 connected to the input image processing unit 42 sends an instruction signal to the printer unit 45 based on the input image data to cause the image forming unit to form a toner image.

  The image forming apparatus 100 is configured to be connectable to an external personal computer (not shown) via a LAN cable (communication line) (not shown) or the like, and image data is received from the connected external personal computer. It is possible to input. Further, the image forming apparatus 100 may be provided with a reading device (not shown) for reading the placed original, and the image data read by the reading device may be input to the input image processing unit 42.

  The image data input to the input image processing unit 42 includes, for example, data of three color components of R (red), G (green), and B (blue) (hereinafter referred to as RGB image data). Ru. The input image processing unit 42 converts the input RGB image data into image data composed of data of four color components of Y (yellow), M (magenta), C (cyan) and K (black). In the image data composed of the four color components Y, M, C, and K, the color component of each color is expressed as a density for each pixel.

  In the present embodiment, the density of each color component of Y, M, C, and K per pixel is represented by the density [%] of each color component per pixel when the maximum density in a single color is 100%. That is, in the present embodiment, the input image processing unit 42 sets the maximum density of a single color per pixel to 100%, and data (hereinafter referred to as YMCK image) configured with density signal values [%] of each color component for each pixel Data). For example, in monochrome image data, when a certain pixel is black, the density signal value of the K component is 100%, and when a certain pixel is light gray, the density signal value of the K component is 20%.

  The input image processing unit 42 outputs YMCK image data to the control unit 41. The control unit 41 controls the image forming unit so as to form a toner image corresponding to the YMCK image data input from the input image processing unit 42.

  In the following description, the density signal value [%] indicated by the YMCK image data generated by the input image processing unit 42 will be described in the description of the color density of image data to be imaged by the image forming unit. The sum total of the density signal values of YMCK is the sum of density signal values [%] of each color component per pixel. The method of generating YMCK image data is an example, and the present invention is not limited to this.

  Further, in the present embodiment, in order to control the toner deposition amount on the recording material P, the input image processing unit 42 is configured to add up to a total sum of density signal values of four color components per pixel in YMCK image data. % Is converted to YMCK image data. That is, when the sum of the density signal values in the YMCK image data is 200%, the amount of toner carried on the recording material P is maximized.

  Next, steps for forming an image signal input on the recording material P will be described with reference to FIG. In the image forming apparatus 100, during image formation, the photosensitive drum 1 is rotationally driven in the direction of arrow R1 at a predetermined process speed. First, a bias is applied to the surface of the photosensitive drum 1 from a bias power supply (not shown) by the charger 2 so that the surface of the photosensitive drum 1 is charged substantially uniformly to the negative polarity.

  Next, an electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by an exposure laser irradiated by the exposure device 3. The exposure device 3 forms an image pattern on the surface of the photosensitive drum 1 based on the image signal (density signal value of each color in YMCK image data) sent from the output image processing unit 44.

  Specifically, the laser chip provided inside the exposure device 3 irradiates the surface of the photosensitive drum 1 after charging with a laser beam with the exposure amount instructed from the control unit 41. At the portion irradiated with the laser beam by the exposure device 3, the charge held on the surface of the photosensitive drum 1 is removed by charging, so an electrostatic latent image is formed. In the present embodiment, the image density of the toner image is controlled by changing the output of the exposure amount of the exposure device 3.

  The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by the developing device 4 as a toner image. Specifically, a bias is applied to the developing roller 5 carrying the toner charged to the negative polarity, thereby causing the toner of the developing roller 5 to fly and adhere to the photosensitive drum 1. The toner image developed on the photosensitive drum 1 is primarily transferred from the photosensitive drum 1 to the surface of the intermediate transfer belt 9 by the primary transfer roller 10.

  A full-color toner image is formed on the surface of the intermediate transfer belt 9 by superimposing the toner images of the respective colors from the respective photosensitive drums 1. The toner image formed on the surface of the intermediate transfer belt 9 is transferred to the recording material P at a transfer nip portion formed by the secondary transfer outer roller 12 of the secondary transfer portion with the intermediate transfer belt 9. The recording material P stored in the storage portion is sent out from the cassette toward the transfer nip portion by the paper feed roller 21.

  The recording material P on which an unfixed toner image is formed at the transfer nip portion is conveyed to the fixing device 14 via the conveyance path 50. The fixing device 14 nips and conveys the recording material P at the fixing nip portion (nip portion) N1, and heats and presses the unfixed toner image T on the recording material P (on the sheet). As a result, the fixing device 14 fixes the unfixed toner image T on the recording material P to the recording material P. The recording material P fixed by the fixing device 14 passes through the paper discharge roller 22 and is discharged onto the paper discharge tray 23.

  Thus, the four-color full-color image formation on one surface of one recording material P is completed.

<External Heating Fixing Device 14>
Next, the fixing device 14 as the image heating device of the present embodiment will be described with reference to FIG. The fixing device 14 of this embodiment has a configuration of an external heating system that heats the surface of the fixing roller 18 from the outside of the fixing roller 18. In the configuration of the external heating method, the fixing roller 18 is heated from the surface, so that the surface of the fixing roller 18 can quickly reach the target temperature while suppressing power consumption.

  The fixing roller 18 is a rotating member that comes in contact with the unfixed toner image T carried by the recording material P at the fixing nip N1, and heats the unfixed toner image T at the fixing nip N1. The fixing roller 18 is provided with a metal roller from the inside, a rubber layer as an elastic layer, and a release layer on the surface, and the diameter of the fixing roller 18 is 18 mm, for example.

  The fixing roller 18 is connected to a motor (not shown) as a drive source and is rotated by the motor. A pressure roller 19 (pressure rotator) as an opposing member faces the outer peripheral surface of the fixing roller 18, and in cooperation with the fixing roller 18, a fixing nip portion N <b> 1 is formed therebetween. The pressure roller 19 is a metal roller from the inside, a rubber layer as an elastic layer, and a roller provided with a release layer on the surface, and is driven to rotate by the fixing roller 18. In addition, as a pressurization rotary body, the film which has a backup member inside may be sufficient.

  The backup member is a member that supports the film so that the film and the fixing roller 18 form the fixing nip portion N1. The heat conductivity of the fixing nip portion N1 in the longitudinal direction (the direction of the rotation shaft of the fixing roller 18) can be improved by using the film as the pressing rotating body and the backup member made of metal. Thus, for example, in a fixing device capable of passing A3 size paper, even when a small size recording material P such as B5 size or A5 size is continuously passed, the heat of the fixing roller 18 in the longitudinal direction Distribution can be leveled. That is, in such a case, the temperature rise of the non-sheet passing portion of the fixing roller 18 can be suppressed.

  Further, an endless heating film 15 as a heating rotator is in contact with the outer surface of the fixing roller 18. In the present embodiment, the heating film 15 is a thin film film provided with a release layer made of PFA resin with a thickness of 20 μm as a surface layer on a base layer of a polyimide resin with a thickness of 30 μm. The heating film 15 forms a heating nip portion N <b> 2 with the fixing roller 18, and is rotated by the fixing roller 18. Inside the heating film 15, a heater 16 (hereinafter referred to as a heater) is provided as a heating source. The heater 16 of this embodiment is a ceramic heater.

  The heater 16 is provided so as to contact the inner peripheral surface of the heating film 15 in a region where the heating nip portion N2 is formed. The heater 16 externally heats the surface of the fixing roller 18 through the heating film 15 at the heating nip portion N2. The heater 16 is held by a heater holder 17 in order to prevent misalignment and cracking of the heater 16. The heater heat temperature detection sensor 20 provided on the heater holder side (the side not in contact with the heating film 15) of the heater 16 is a thermistor, and is in contact with the surface of the heater 16 on the heater holder side.

  The input / output voltage of the heater 16 is adjusted and controlled so as to maintain the fixing temperature adjustment temperature which is the target of the heat generation temperature of the heater 16 detected from the thermistor 20.

  The fixing device 14 applies heat energy from the heater 16, which is an external heating unit, to the recording material P carrying the unfixed toner image T via the fixing roller 18, and heats the unfixed toner image T. That is, when the recording material P to which the unfixed toner image T is transferred is conveyed to the fixing nip portion N1, the heat of the surface of the fixing roller 18 is transferred to the unfixed toner image T and the recording material P, and the recording material It is fixed on the surface of P as a fixed toner image T2.

<Temperature control of fixing device 14>
Next, temperature adjustment control of the fixing roller 18 in the fixing device 14 will be described with reference to FIG. The heater 16 is electrically connected to the control unit 41, and the control unit (heater control unit) 41 controls the energization of the heater 16. When the control unit 41 accepts a job input in a standby state waiting for a job input without executing image formation, the controller 16 turns on the heater 16 and turns on the heater 16 so that the surface of the fixing roller 18 reaches a target temperature. Control the input voltage.

  The control unit 41 is electrically connected to the thermistor 20 in contact with the heater 16, and controls the input voltage of the heater 16 based on the detection result of the thermistor 20. Controlling the heater 16 so that the surface of the fixing roller 18 reaches the target temperature is referred to as temperature adjustment control (hereinafter, temperature control). The control unit 41 may perform temperature control by repeating on / off of energization of the heater 16. When all the fixing processes corresponding to the input job are completed, the control unit 41 turns off the heater 16 and shifts to the standby state.

  FIG. 4 shows the relationship between the control temperature of the heater 16 and the temperature at which the toner is heated at the fixing nip N1 according to the control temperature (that is, the surface temperature of the fixing roller 18 at the fixing nip N1). Here, the control temperature of the heater 16 is a temperature detected by the thermistor 20 in contact with the heater 16. In addition, the value shown in FIG. 4 is an example, and is not limited to this. The target temperature of the fixing roller 18 is a temperature at which the amount of heat necessary for fixing does not run out when the toner amount of the unfixed toner image T that can be placed on the recording material P is maximum.

  As described above, in the image forming apparatus 100 according to the present embodiment, the applied amount of toner becomes the maximum value of 200% of the total of the density signal values of YMCK. In the example shown in FIG. 4, when the control temperature of the heater 16 is less than 180 ° C., the surface temperature of the fixing roller 18 at the fixing nip portion N1 is a low temperature of less than 100 ° C. At this time, since a sufficient amount of heat is not given to the toner image T at the fixing nip portion N1, the toner may not be completely melted and may not be fixed to the recording material P. That is, a fixing failure may occur.

  Further, in the example shown in FIG. 4, when the control temperature of the heater 16 is 230 ° C. or more, the surface temperature of the fixing roller 18 at the fixing nip portion N1 is as high as 130 ° C. or more. At this time, since an excessive amount of heat is supplied to the toner image T at the fixing nip portion N1, the toner is melted too much. As a result, the toner that has passed through the fixing nip portion N1 may adhere to the surface side of the fixing roller 18 instead of the recording material P.

  Then, there is a possibility that the toner attached to the surface of the fixing roller 18 may be transferred as a stain to the image surface of the recording material P after the fixing roller 18 makes one revolution (image failure due to hot offset). Therefore, in the fixing device 14 of the present embodiment, a temperature range where the fixability can be ensured without causing the fixing defect and the image defect due to the hot offset (a normal fixing region in FIG. Temperature control is performed at a temperature not lower than 230 ° C.

<Temperature control correction control according to the warm air counter of the fixing device 14>
Next, temperature control correction control according to the warm air counter in the fixing device 14 will be described using Tables 1 to 4 and FIG. Here, the warm-up counter counts up warm-up information that predicts the degree of warming (more specifically, the surface temperature) of the rotating body that stores heat, such as the fixing roller 18 and the pressure roller 19. The temperature adjustment correction control according to the warm air counter (hereinafter, warm air counter control) is a control that corrects the temperature adjusted temperature of the heater 16 as the external heating means according to the prediction result of the warm air information by the warm air counter. is there.

  As the number of image formations progresses, the surface temperature of the fixing roller 18 rises due to the effect of increasing the number of sheet intervals, pre-rotations, and post-rotations. For this reason, when the temperature control temperature of the heater 16 is controlled at a uniform temperature, the heat resistance temperature of the elastic layer (rubber layer) exceeds 150 ° C., and deterioration and wrinkling may occur.

  In the present embodiment, the temperature control of the heater 16 and the sheet interval when the recording material P is fed to the fixing nip portion N1 using the warm air counter control in order to prevent the heat resistance temperature exceeding 150 ° C. in the present embodiment. There is a function to set (correct) the temperature control low. In the warm-up counter control, the controller 41 predicts the warming state of the fixing roller 18 according to the sheet passing condition, and determines the temperature adjustment zone based on the accumulated count value of the warm-up counter 200 in the memory unit. And the temperature control of the heater 16 is corrected according to the temperature control zone.

  In the fixing device 14 of the present embodiment, the temperature control zone and the correction temperature as shown in Table 1 are set. What is shown in Table 1 is a temperature adjustment zone according to the cumulative count value of the warm air counter 200, and a correction value of the temperature between sheet passing and paper.

  When the count value of the warm air counter 200 increases and the value of the temperature control zone increases, the surface temperature of the fixing roller 18 is determined to be high temperature, and the temperature control temperature of the heater 16 is corrected so that deterioration or wrinkles do not occur. As a counting method of the warm-up counter control, the following three items are judged (detected) and counted up according to the sheet passing condition.

1) Temperature detected by the thermistor 20 at the start of image formation 2) Interval time from the end of image formation of the previous job to the start of image formation of the current job 3) Cumulative rotation time between sheets during paper passing (at the time of image formation) Here, the cumulative rotation time between sheets refers to the sheet interval time when the fixing roller 18, the pressure roller 19, and the heating film 15 are idle (the recording material passes through the nip portion and the next recording material is in the nip portion). It is the time which accumulated the time until it is carried to

  1) Regarding the detection temperature of the thermistor 20 at the start of image formation, Table 2 shows a table for determining an initial value for starting counting in the warm-air counter according to the detection temperature of the thermistor 20 at the start of image formation. .

  Since the surface temperature of the fixing roller 18 is higher as the temperature detected by the thermistor 20 installed behind the heater 16 is higher, the count value of the warm air counter 200 is set to start from a large value. For example, when image formation is started, if the temperature detected by the thermistor is 200 ° C., the initial value to start counting will start from 1463 counts.

  2) Regarding the interval time from the end of the image formation of the previous job to the start of the image formation of the current job, Table 3 shows the interval from the end of image formation of the previous job to the start of image formation of the current job This is a warm-up count value to be added at the start of image formation according to time.

  In the present embodiment, if the interval time from the end of the image formation of the previous job to the start of the image formation of the current job (the elapsed time since the end of the last temperature adjustment) is less than 20 seconds, the surface temperature of the fixing roller 18 decreases. It reaches the print temperature control right away. That is, the print ready state can be entered. Therefore, since the sheet interval time is short and the surface temperature of the fixing roller 18 only needs to be slightly raised, the warm air count value added at the start of image formation is +2.

  However, when the elapsed time since the end of the previous temperature adjustment (interval time of image formation) is within the range of 21 seconds to 120 seconds, the heater 16 or the heating is performed even though the surface temperature of the fixing roller 18 has not fallen completely. The temperature of a member that easily dissipates heat, such as the film 15, falls. Therefore, when the temperature of the heating film 15 is increased to the target temperature, the pre-rotation and the post-rotation become long, and the surface temperature of the fixing roller 18 that hardly dissipates heat increases due to the lengthening. Therefore, it is necessary to increase the correction value of the temperature adjustment temperature (minus value shown in Table 1) by advancing the temperature control zone earlier by adding the count value to the warm air counter 200 by +4 and preventing the excessive temperature rise.

  Further, when there is no sheet interval (= interval time 0 seconds), the difference between the surface temperature of the heater 16 or the heating film 15 and the surface temperature of the fixing roller 18 is small, so the warm air count is not added. If the warm-air count value is added, the surface temperature of the fixing roller 18 is lost to the recording material P, so that the amount of heat becomes insufficient and there is a possibility of causing a fixing failure.

  In addition, when the interval time of image formation is 121 seconds or more, the surface temperature of the fixing roller 18 is also dissipated and approaches room temperature, so if the count value to the warm air counter is excessively advanced, the correction temperature becomes large. As a result, a fixing defect may occur. Therefore, the count value is not added even if the count value to the warm air counter advances excessively and the correction value of the temperature adjustment temperature (minus value shown in Table 1) does not increase.

  Note that the value added to the warm-up counter 200 described above is a value that is counted when a sheet is fed on one side of the recording material. When passing on both sides, the temperature of the recording material P is also higher than when passing on one side, so a double count value is added to the warm-air counter 200.

  3) With regard to the cumulative rotation time between sheets during sheet passing (during image formation), Table 4 shows an addition count per sheet according to the cumulative rotation time between sheets during sheet passing (during image formation) It is a value.

  Since there is no recording material P taking heat between the fixing roller 18 and the pressure roller 19 between the sheets, the surface temperature of the fixing roller 18 is increased. Therefore, when the accumulated time between sheets increases, the surface temperature of the fixing roller 18 increases. Therefore, the count value to be added to the warm-air counter 200 is set to be increased each time a sheet is passed according to the cumulative time between sheets. Further, since the recording material P temperature is higher in double-sided printing than in single-sided printing, a double count value is added to the warm-up counter 200.

  As described above, in the present embodiment, excessive heating is performed by adding to the warm air counter 200 according to the determination results of 1) to 3), and reflecting the correction value corresponding to each temperature control zone in the temperature control temperature. Therefore, the malfunction of the fixing device 14 due to abnormal images such as paper wrinkles and deterioration due to deterioration is suppressed.

  FIG. 5 is a diagram showing the transition of the detected temperature of the thermistor 20 and the surface temperature of the fixing roller 18 according to the number of times of image formation. The temperature at which heat is constantly generated at the upper limit heating temperature 230 ° C. of the heater 16 necessary for melting the toner on the recording material P is C1, and the transition of the fixing roller surface temperature at that time is C3. When the regulated temperature of the heater 16 is constant and 1500 sheets are output, the fixing roller continues to raise the temperature between sheets.

  In this embodiment, wrinkles and deterioration start when the surface temperature of the fixing roller 18 is 150 ° C. or higher, and failure occurs when the surface temperature is 170 ° C. or higher. Here, when the temperature control is not corrected by the warm air counter control, the occurrence of wrinkles and deterioration in the vicinity of 500 sheets (temperature control zone 3) exceeds 150 ° C. and the failure occurs in the vicinity of 760 sheets (temperature control zone 4) 170 The temperature rises above ° C.

  Therefore, in this embodiment, as shown in Table 1, six temperature control zones are set according to the count value of the warm air counter 200, and the heat generation temperature of the heater 16 is C2 in FIG. 5 according to the temperature control zone. Decrease the temperature step by step as shown. More specifically, the temperature control temperature is set to be lowered by 2 ° C. by increasing the temperature control zone. By the temperature correction according to the warm air counter control, the surface temperature of the fixing roller 18 can moderate the temperature rise between the sheets, and the surface temperature of the fixing roller 18 is wrinkled as shown by C4 in FIG. It is possible to always maintain a temperature of 150 ° C. or lower where generation and deterioration start.

<Mechanism that the heating film 15 becomes dirty>
When the fixing process on the recording material P is repeated while the fixing roller 18 is storing heat, the external heating type fixing device 14 transfers the offset toner Tx offset to the fixing roller 18 to the heating film 15 in a lower heat state. There is a case. That is, toner contamination may be accumulated on the heating film 15 as contamination associated with the toner image.

  First, toner offset to the fixing roller 18 will be described. As described above, in the fixing device 14, the temperature adjustment control is performed in the temperature range in which the fixing property at the maximum applied toner amount (that is, the sum of YMCK density signal values = 200%) is ensured by the control unit 41. It is carried out. Therefore, when an image with a small amount of applied toner (for example, a halftone image with a low density) is formed in a region of the recording material P, the image becomes over-fixed.

  Although not as bad as the image defect due to the above-described hot offset, toner slightly adheres to the surface of the fixing roller 18 according to the same principle as the hot offset (offset toner Tx in FIG. 3). Next, the offset toner Tx adhering to the fixing roller 18 is transferred to the heating film 15. This mechanism will be described with reference to FIG.

  When the offset toner Tx attached to the fixing roller 18 contacts a roller or a film whose surface temperature is lower than that of the fixing roller 18, the offset toner Tx tends to move to the lower surface temperature side. FIG. 6 is an enlarged view of the heating nip portion N2 between the heating film 15 and the fixing roller 18 in the fixing device 14. In FIG. 6, the pressure roller 19 is omitted. For explanation, the heating nip portion N2 is divided into three positions (upstream nip portion N3, central nip portion N4, and downstream nip portion N5) as shown in FIG.

  In the rotational direction of the heating film 15, a point located on the upstream side of the heating nip N2 is on the downstream side of the upstream nip N3, a point located in the center of the heating nip N2, on the central nip N4, and the central nip N4. The point located is referred to as a downstream nip N5. Table 5 shows the surface temperature of the heating film 15 at each nip when 500 sheets of the recording material P are continuously passed to the fixing device 14 as an example showing the case where the fixing roller 18 is thermally stored with continuous sheet passing. The surface temperature of the fixing roller 18 is shown.

  The heating film 15 has no heat storage layer (rubber layer) like the fixing roller 18 and has a thin film thickness, so the heat dissipation is very high, and almost no heat is stored. On the other hand, the fixing roller 18 has a heat storage layer (rubber layer), and is stored with continuous paper passing. Therefore, the surface temperature of the heating film 15 is 80 ° C. in the upstream side nip portion N3, and the surface temperature of the fixing roller 18 in the upstream side nip portion N3 is 110 ° C. The surface temperature is low.

  In the central nip portion N4, the heater 16 is in contact with the inner surface of the heating film 15, so that it is rapidly heated by the heater 16. Therefore, the surface of the heating film 15 reaches 120 ° C., which is a target temperature adjustment temperature. When the surface temperature of the heating film 15 in the central nip portion N4 is 120.degree. C., the surface temperature of the fixing roller 18 which receives the heat from the heater 16 through the heating film 15 is 116.degree.

  Since the surface of the fixing roller 18 is also heated via the heating film 15, the temperature may rise instantaneously to near 120 ° C., but the heat storage layer of the fixing roller 18 deprives the surface heat of the fixing roller 18. The surface rises only to around 116 ° C. However, since the amount of heat stored in the fixing roller 18 increases as the number of sheets of recording material P increases, the surface temperature of the fixing roller 18 at the central nip portion N4 reaches 120 ° C. as continuous sheet passing continues.

  Moreover, in the downstream side nip part N5, since it leaves | separates from the heat generating body of the heater 16, the surface temperature of the heating film 15 with high heat dissipation will fall instantly to 110 degreeC. On the other hand, since the fixing roller 18 has a heat storage layer, the amount of heat radiation is small, and the surface temperature of the fixing roller 18 also decreases to 114 ° C. even at the downstream nip portion N5. That is, the surface temperature of the heating film 15 is lower than the surface temperature of the fixing roller 18 at the downstream nip portion N5. Therefore, the offset toner Tx attached to the fixing roller 18 moves to the surface of the heating film 15 whose surface temperature is lower at the downstream side nip portion N5.

  In the temperature relationship shown in Table 5, the surface temperature of the fixing roller 18 is lower than the surface temperature of the heating film 15 at the central nip portion N4. Therefore, in the temperature relationship shown in Table 5, the offset toner Tx which has moved to the surface of the heating film 15 at the downstream side nip portion N5 is partially transferred to the fixing roller 18 again at the central nip portion N4.

  However, as described above, the surface temperature of the fixing roller 18 at the central nip portion N4 reaches 120 ° C. as heat is accumulated in the fixing roller 18 as continuous sheet passing is continued. Therefore, when the continuous sheet passing is continued, the phenomenon that the offset toner Tx attached to the surface of the heating film 15 is transferred to the fixing roller 18 again hardly occurs in the central nip portion N4. As the heat accumulation of the fixing roller 18 progresses, the temperature difference between the heating film 15 and the fixing roller 18 at the downstream nip portion N5 also increases, so that the offset toner Tx is more easily transferred to the heating film 15 side.

  As described above, the surface temperature of the fixing roller 18 is increased by increasing the number of sheets of the recording material P that are continuously passed through the fixing device 14. As a result, the offset toner Tx attached to the fixing roller 18 is easily transferred to the heating film 15 side, and the heating film 15 continues to store the offset toner Tx.

Occurrence of toner contamination on deliverables
Next, the mechanism by which the toner stains adhere to the product due to the offset toner Tx accumulated on the surface of the heating film 15 will be described in order from FIG. The toner contamination on the product occurs when the temperature adjustment control of the fixing roller 18 is started from the state where the fixing roller 18 is cooled, when the offset toner Tx is accumulated on the surface of the heating film 15 there is a possibility. That is, when the offset toner Tx is accumulated on the surface of the heating film 15 and a job is input to the image forming apparatus 100 in a state where the fixing device 14 is cooled, the back surface of the first sheet of the job Toner contamination may occur on the side opposite to the side to be

  For example, when the job is not input for a while after all the reserved jobs are completed, the heater 16 is kept off for a while (for example, 20 to 30 minutes), so that the fixing roller 18 is cooled. The state where the fixing roller 18 is cooled is, for example, a state where the temperature of the fixing roller 18 is adjusted to room temperature.

  Referring to FIG. 7, it is assumed that the image forming apparatus 100 is installed under the environment of temperature: 25 ° C. and humidity: 50% as the detection result of the environmental temperature and humidity detection sensor 25 (hereinafter, environmental sensor 25). FIG. 7 shows how the temperature control temperature and the temperature of the heating film 15 and the surface temperature of the fixing roller 18 change when the heater 16 starts temperature control control from the state where the fixing device 14 conforms to this environment. .

  In FIG. 7, C5 indicates that the fixing temperature adjustment control is started and the temperature detected by the thermistor 20 rises toward 230 ° C., which is the target temperature adjustment temperature. When the detection result of the environment sensor 25 and the detection temperature of the thermistor 20 are the same temperature, the target temperature of 230 ° C. is reached in a few seconds by energizing the heater 16 with 100% input power to reach the target temperature. To do. C6 shows the transition of the surface temperature of the heating film 15 rising under the influence of the heat generation of the heater 20 which started the fixing temperature adjustment control, and C7 shows the surface temperature of the fixing roller 18 through the heating film 15 Shows the transition of temperature rise.

  The surface temperature C6 of the heating film 15 and the surface temperature C7 of the fixing roller 18 are surface temperatures at the heating nip portion N2. Before the temperature control is started, the heater 16 is in an off state and is familiar with the environment of temperature: 25 ° C. and humidity: 50%. Therefore, the surface temperatures of the heating film 15 and the fixing roller 18 are both about 25 ° C. It is.

  When the temperature control is started, the heating film 15 has a small heat capacity, so that the heating nip portion N2 receives the heat from the heater 16 and quickly rises in temperature. On the other hand, since heat is transferred to the heat storage layer and the cored bar in the fixing roller 18, the surface temperature of the fixing roller 18 rises more slowly than the heating film 15.

  When the heater 16 begins to heat toward the target temperature control temperature of 230 ° C., when the surface temperature C6 of the heating film 15 reaches 120 ° C., the surface temperature C7 of the fixing roller 18 increases only to 105 ° C. In the image forming apparatus 100 according to the present embodiment, since the fixing device 14 of the external fixing method that rises quickly is used, the heater 16 is turned off in a standby state in which waiting for job input after all reserved jobs are completed. .

  The control unit 41 turns on the heater 16 and starts temperature control in response to the job being input in the standby state. In order to shorten the time from when the job is input in the standby state until the first sheet of the job is output, the control unit 41 sets the first recording material of the job at the timing when the heating film 15 reaches 120 ° C. The recording material P is conveyed so that the leading end of P enters the fixing nip portion N1.

  When the temperature control is started from a state in which the fixing device 14 is adapted to the environment of temperature: 25 ° C. and humidity: 50%, the temperature of the fixing device 14 is started until the leading edge of the recording material P enters the fixing nip portion N1. In the meantime, the surface temperature of the fixing roller 18 is lower than the surface temperature of the heating film 15.

  Therefore, when the offset toner Tx has already been transferred to the heating film 15 before the temperature adjustment control is started in the situation shown in FIG. 7, the offset toner Tx accumulated on the surface of the heating film 15 becomes the fixing temperature. During the start-up, it moves to the surface of the fixing roller 18.

  Table 6 shows each nip of the heating nip portion N2 when the leading edge of the first recording material P reaches the fixing nip portion N1 when the temperature control of the fixing device 14 is performed in the situation shown in FIG. The surface temperatures of the heating film 15 and the fixing roller 18 in the section are shown.

  In Table 6, the heater 16 has not yet reached the position of the upstream nip portion N3 (FIG. 6), so the surface temperature of the heating film 15 is 80.degree. Further, the surface temperature of the fixing roller 18 is 66 ° C. at the position of the upstream nip portion N3. Therefore, the offset toner Tx adhering to the surface of the heating film 15 is transferred to the surface of the fixing roller 18.

  At the position of the central nip portion N4, the surface temperature of the heating film 15 becomes 120 ° C., which is the target temperature adjustment temperature. On the other hand, when the temperature control is started from the cooled state, the surface temperature of the fixing roller 18 rises only to 105 ° C. Here again, since the surface temperature of the fixing roller 18 is lower than the surface temperature of the heating film 15, the offset toner Tx adhering to the surface of the heating film 15 moves to the surface of the fixing roller 18.

  At the position of the downstream side nip portion N5, the heating film 15 is not in contact with the heater 16, so the surface temperature of the heating film 15 decreases to 110 ° C. On the other hand, the surface temperature of the fixing roller 18 drops to about 103.degree. Here again, since the surface temperature of the fixing roller 18 is lower than the surface temperature of the heating film 15, the offset toner Tx adhering to the surface of the heating film 15 moves to the surface of the fixing roller 18.

  Further, the pressure roller 19 does not have the heater 16 inside, and has a surface area that is the same as or lower than that of the fixing roller 18 because the heat radiation area is larger than the fixing nip. In temperature control, the fixing roller 18 and the pressure roller 19 are in contact with each other. Therefore, the offset toner Tx, which has moved from the heating film 15 to the fixing roller 18 from the start of the temperature adjustment control to the time when the recording material P reaches the fixing nip N1, is transferred from the fixing roller 18 to the pressure roller 19. Moving.

  As shown in FIG. 7, when the recording material P starts to be passed through the fixing nip portion N1, the heat of the surface of the fixing roller 18 is taken away by the sheet passing, so the surface temperature of the fixing roller 18 is Temporarily decreases from 105 ° C. However, the amount of heat supplied to the recording material P is not enough. When the continuous paper feeding is continued, the heat received from the heater 16 between the papers during the continuous paper feeding is stored in the heat storage layer (rubber layer). Eventually, the temperature relationship between the heating film 15 and the fixing roller 18 at the heating nip N2 is as shown in Table 5.

  As described above together with the example of Table 5, in the state where the fixing roller 18 is accumulating with continuous paper passing, the relationship between the surface temperature of the heating film 15 and the fixing roller 18 in the downstream nip portion N5 is heating film 15 <fixing. The roller 18. Therefore, the hot offset toner Tx adhering to the fixing roller 18 during the fixing process moves to the heating film 15. Then, it continues to be accumulated in the heating film 15.

  However, as described in conjunction with the example of FIG. 7 and Table 6, when the fixing device 14 starts the fixing process of the recording material P from a state (cold state) adapted to an environment of temperature 25 ° C. and humidity 50%. The relationship between the surface temperature of the heating film 15 and the fixing roller 18 is as follows. That is, in the downstream nip portion N5, the heating film 15> the fixing roller 18 is satisfied. In the fixing nip portion N1, the fixing roller 18> the pressure roller 19 is satisfied.

  Therefore, the offset toner Tx accumulated in the heating film 15 moves to the fixing roller 18 side. Then, the offset toner Tx moved to the fixing roller 18 side is transferred to the pressure roller 19. When the recording material P reaches the fixing nip portion N1 at that timing, the offset toner Tx adheres to the back surface of the recording material P (that is, the surface in contact with the pressure roller 19) without cleaning being intended. It will be.

<Paper spout cleaning control>
Here, the inter-paper discharge cleaning control (hereinafter referred to as discharge control) for reducing the offset toner Tx, which is performed in the fixing device 14 of the present embodiment, will be described.

  The discharge control means that the offset toner (dirt on the toner image) Tx adhering to the heating film 15 is transferred to the fixing roller 18 side by utilizing the property of moving to the low surface temperature (low heat) side, and finally the result. It is control which makes it adhere to the back of a thing (recording material P), and is cleaned.

  That is, the surface temperature relationship at the heating nip portion N2 (particularly, the downstream nip portion N5) shown in FIGS. 3 and 6 is set to the state of the heating film 15> the fixing roller 18, thereby accumulating on the surface of the heating film 15. The offset toner Tx can be moved to the fixing roller 18.

  As described above, since the surface temperature of the fixing roller 18 is always high with respect to the surface temperature with the pressure roller 19, if the offset toner Tx is moved (transferred) to the fixing roller 18 side, the pressure roller The offset toner Tx moves (transfers) to 19. After the offset toner Tx is moved (transferred) to the pressure roller 19 between the sheets by utilizing this characteristic, the next recording material P is passed through the fixing nip portion N1 (FIG. 3) to obtain the recording material. The following cleaning is possible with P as a cleaning member.

  That is, under the intention of cleaning the offset toner Tx that can not be visually recognized by the user, it is possible to periodically carry out the cleaning on the back surface of the next recording material P.

  FIG. 8 shows a transition of the surface temperature C8 of the heating film 15 and the surface temperature C9 of the fixing roller 18 when the discharge control is performed. At the time of normal printing, when a job is input, the image formation is finished through the operation of pre-rotation → passing → paper interval → passing →... Post-rotation processing. In the present embodiment, it is determined whether or not the number of sheets to be passed has reached a predetermined number, and discharge control is performed between sheets at the timing when the predetermined number has been reached. Here, it is determined that the predetermined number of threshold values is set to 40 and the discharge control is performed when the threshold value is reached, but the present invention is not limited to this.

  In the discharge control shown in FIG. 8, which is performed when image formation is performed by continuous sheet passing and the number of sheets to be passed reaches a predetermined number (40 sheets), the heater temperature after the sheet interval is rapidly increased to 250 ° C. In this case, the surface temperature of the heating film 15 at the heating nip portion N2 rapidly rises to 130 ° C. By rapidly increasing the temperature control temperature of the heater 16, the relationship between the surface temperatures of the heating film 15 and the fixing roller 18 is set so that the heating film 15> the fixing roller 18, thereby moving the offset toner Tx to the fixing roller 18 side. be able to.

  Table 7 shows the surface temperatures of the heating film 15 and the fixing roller 18 when the recording material P is passed through the fixing device 14 as an example showing the case where the discharge control is performed immediately after the 40th sheet passing. It is shown.

  As shown in Table 7, in the discharge control, the heater is rapidly heated until the temperature detected by the thermistor 20 reaches 250 ° C. At this time, the surface temperature of the heating film 15 in the heating nip portion N4 is 130 ° C., and the surface temperature of the fixing roller 18 is 115 ° C. Therefore, the relationship of the heating film 15 having a higher temperature is maintained. In the heating nip portion N5, the heating film 15 is instantly dissipated and falls to 120 ° C. The fixing roller 18 also has a lower heat dissipation than the heating film 15 due to the effect of the heat storage layer, so the surface temperature is unlikely to decrease, but falls to 113 ° C.

  As a result, the relationship between the surface temperatures can be such that the heating film 15> the fixing roller 18, and the offset toner Tx moves to the surface of the fixing roller. Further, since the fixing temperature is increased, the surface temperature of the fixing roller 18 can be maintained high even if the heating film 15 dissipates heat, and the offset toner Tx is added if it moves to the fixing roller 18 side. It is possible to move to the pressure roller surface in relation to temperature.

  In this way, at the timing when the offset toner Tx has moved to the pressure roller 16, the recording material P enters the fixing nip portion N1, and the offset toner Tx adheres to the back surface of the recording material P for cleaning and printing. Resume operation.

  Note that the discharge control can be performed before the shift to the post-rotation control, and ends in a state where the surface temperature difference between the heating film 15 and the fixing roller 18 is given and discharged to the fixing roller 18 side. By performing the discharge control each time before the shift to the post-rotation, it becomes possible to discharge the offset toner Tx onto the back surface of the first sheet in the next print job.

  As described above, when it is determined that the heating film 15 is soiled, the temperature adjustment temperature of the heater 16 is rapidly increased, and the surface temperature is set to the relationship of the heating film 15> the fixing roller 18, whereby the offset toner Tx is changed. It is possible to move to the recording material P for cleaning.

  However, since the recording material P is heated suddenly at the interval between the sheets not passing through the fixing nip portion N1, and at the timing of the pre-rotation and the post-rotation, the surface temperature of the fixing roller 18 tends to increase due to the influence. Therefore, the surface temperature of the fixing roller 18 is increased by increasing the number of times the discharge control is performed as the number of sheets to be passed increases. As a result, the relationship between the surface temperatures is such that the heating film 15 <the fixing roller 18, and the offset toner Tx adhered to the heating film 15 cannot be moved to the fixing roller 18 by discharging control.

  FIG. 9 shows the surface temperature C11 of the fixing roller 18 when discharging control is performed immediately after passing 40 sheets, and the surface temperature C12 of the fixing roller 18 when discharging control is performed immediately after passing 400 sheets. It is a figure. When the ejection control is performed on the 400th sheet, the surface temperature of the fixing roller 18 which has been increased between the sheets is increased to 130 ° C. or higher as indicated by C12. Therefore, the relationship of the surface temperature becomes the relationship of the heating film 15 <the fixing roller 18, and the offset toner Tx adhering to the heating film 15 is not discharged by the discharge control but continues to adhere.

  Table 8 shows the surface temperatures of the heating film 15 and the fixing roller 18 in the heating nip portion N2 as an example of the case where the discharge control is performed at the 400th sheet when the number of sheets passing increases.

  When the discharge control performed every 40 sheets is performed at the 400th sheet, as described above, the heater is rapidly heated until the temperature detected by the thermistor 20 reaches 250 ° C. At this time, the surface temperature of the heating film 15 in the fixing nip N3 is 102 ° C. However, the surface temperature of the fixing roller 18 is 139 ° C., which is higher than that of the heating film 15 due to the effect of heat storage between the sheets.

  Further, in the heating nip portion N4, the heating film is instantaneously heated and rises to 142 ° C., but the surface temperature rises to 145 ° C. due to the heat accumulated in the fixing roller 18 as well. In the fixing nip portion N5, the surface temperature of the heating film 15 is lowered to 132 ° C. due to the effect of heat dissipation, but the surface temperature of the fixing roller 18 does not radiate heat, so it is decreased only to 143 ° C. In this case, the relationship of the surface temperature becomes already heating film 15 <fixing roller 18 from the fixing nip portion N4, and the offset toner Tx does not move from the heating film to the fixing roller and continues to accumulate on the surface of the heating film 15.

  Therefore, when the image formation is completed in a state where the offset toner Tx is accumulated on the heating film, and the image is formed from a state where the fixing device 14 is cooled with a printing interval, the offset toner is applied to the back surface of the recording material P in an unintended situation. Tx moves and stains the back side of the product.

  What has been described above has been the state in which the surface temperature of the fixing roller 18 easily rises when the paper is continuously passed. In addition to this, there is a state where the surface temperature of the fixing roller 18 is likely to be increased depending on the user's sheet passing method.

  FIG. 10 shows the surface temperature C13 of the heating film 15 and the surface temperature C14 of the fixing roller 18 when the number of sheets for one job is 4 sheets (hereinafter referred to as 4 sheets intermittent sheet feeding) and 2 jobs are output. FIG. As in the case of continuous sheet passing, since there is no recording material P taking heat between the sheets at the fixing nip N1, the surface temperature of the fixing roller 18 is gradually raised.

  When the next image formation data is transmitted to the input image processing unit 42 and the received control unit 41 starts image formation during control of post-rotation and post-rotation, the heating film 15 has heat dissipation. The rotation time before reaching the target temperature becomes longer. Due to the influence, the surface temperature of the fixing roller 18 having no heat radiation property is heated again before the temperature decreases, and the rising temperature tends to be larger than the lowering temperature. When a total of eight sheets of two jobs are passed intermittently for four sheets, the highest temperature reached by the surface temperature of the fixing roller 18 is 110 ° C.

  Next, FIG. 11 shows the heating film 15 surface temperature C15 and the fixing roller 18 surface temperature C16 when the number of sheets for one job is two (two sheets intermittent sheet passing) and four jobs are output. It is a figure. The total number of output sheets is a diagram when the paper is passed so as to be 8 sheets, which is the same as when 4 sheets are intermittently passed. In the case of two-sheet intermittent sheet passing, there are two times of pre-rotation and post-rotation compared to four-sheet intermittent sheet passing. For this reason, the surface temperature of the fixing roller 18 rises with each pre-rotation, and the highest temperature reached for the fourth job rises to 124 ° C.

  As described above, fixing is performed as the number of times of control for performing temperature control increases without the recording material P such as pre-rotation or post-rotation being present in the fixing nip portion N1 including the sheet interval depending on the sheet passing condition. The surface temperature of the roller 18 will rise.

  So far, the phenomenon that the surface temperature of the fixing roller 18 rises when the sheet passing method is different has been described, but it also varies depending on the basis weight setting by the sheet passing mode of the recording material P or the like. For example, when the recording material P to be passed is thin, since the heat amount of the fixing roller 18 taken away by the recording material P during the passing of the paper is small, the surface temperature of the fixing roller 18 is likely to rise between the sheets. However, since the temperature of the heating member such as the heating film 15 and the heater 16 is not taken away by the recording material P in the pre-rotation, the reaching time to the target controlled temperature is short. For this reason, the surface temperature of the fixing roller 18 is unlikely to increase during the pre-rotation and the post-rotation.

  On the other hand, when the recording material P is thick, the heat amount of the fixing roller 18 taken by the recording material P during sheet passing is large, so the surface temperature hardly rises between the sheets. However, in the pre-rotation, the time to reach the target temperature control temperature is slow. Therefore, the amount of heat given to the fixing roller 18 increases, and the surface temperature of the fixing roller 18 tends to increase.

  As described above, in the conventional inter-sheet discharge control, the offset toner Tx attached to the heating film 15 can not be moved to the surface of the fixing roller 18 depending on the number of sheets of the recording material P and sheet passing conditions. I found out that there was a case.

<Paper Spacing Cleaning Control in this Embodiment>
Hereinafter, the discharge control according to the warm-up counter control according to the present embodiment will be described with reference to FIG. As described above, when the same discharge control as in the prior art is always performed, the surface temperature of the fixing roller 18 continues to rise, and the relationship of heating film 15 <surface temperature of the fixing roller 18 results. Therefore, in the discharge control of the present embodiment, the surface temperature of the fixing roller 18 is predicted, and warm-air counter control in which the fixing temperature control is lowered according to the temperature control zone is used for the discharge control.

  More specifically, when it is determined that the sheet discharge control is performed during the sheet passing, the sheet interval immediately before the discharge control is extended according to the temperature control zone of the warm-up counter control at the discharge control execution timing. And the temperature control between papers is corrected downward. The surface temperature state of the heating film 15> the fixing roller 18 can be maintained by correcting the time between the sheets immediately before the discharge control and the temperature control temperature.

  That is, it is possible to secure the cleaning capability of the discharge control for moving the offset toner Tx accumulated on the surface of the heating film 15 to the pressure roller 16 via the fixing roller 18. By causing the recording material P to pass through the fixing nip portion N1 in this state, the offset toner Tx attached to the surfaces of the fixing roller 18 and the pressure roller 16 adheres to the recording material P and is discharged to the outside of the apparatus.

  In this manner, the offset toner Tx accumulated on the heating film 15 and the offset toner Tx moving to the surface of the fixing roller 18 and the pressure roller 16 can be adhered to the recording material P for cleaning.

  FIG. 12 shows the sheet interval time before the discharge control is extended according to the temperature adjustment zone of the warm air counter control in the present embodiment, and the temperature adjustment temperature of the sheet is corrected. In the present embodiment, it is determined that the surface of the heating film 15 is soiled during printing, and it is determined that discharge control is necessary. Based on the judgment result, when discharging control is performed, the temperature control zone is detected from the count value of the warm-up counter at the execution timing, and the temperature control temperature is corrected to extend the inter-paper time immediately before discharging control according to the temperature control zone. Perform the correction.

  FIG. 12 shows the surface temperature C17 of the heating film 15 and the surface temperature C18 of the fixing roller 18 when the ejection control performed for every 40th sheet is performed on the 400th sheet. Immediately after 400 sheets are passed as in the conventional image formation, the surface temperature of the fixing roller 18 rises to around 115 ° C. For this reason, if the discharge control similar to the conventional one is performed, the surface temperature of the fixing roller 18 exceeds the surface temperature of the heating film 15. Therefore, in the present embodiment, the surface temperature of the fixing roller 18 is predicted using the warm air counter control, the paper interval time immediately before the discharge control is performed according to the temperature adjustment zone of the warm air counter, and the paper temperature control. Perform the correction.

  Table 9 is a table showing values for time extension and temperature adjustment correction for the interval between sheets immediately before the discharge control is performed according to the temperature adjustment zone determined from the count value of the warm air counter.

  If it is determined that the timing to carry out the ejection control, the surface temperature relationship between the heating film 15 and the fixing roller 18 is fixed by extending the sheet interval immediately before the ejection control and correcting the temperature control between the sheets. The roller 18 can be kept.

  FIG. 12 shows the heating when the time between the paper immediately before the discharge control is extended and the temperature adjustment is corrected by using the warm-up counter when it is determined that the discharge control is necessary at the end timing of 400 sheets. It is the surface temperature transition of the film 15 and the fixing roller 18. When 400 sheets are passed on one side, the ultimate temperature at which the surface temperature of the fixing roller 18 is highest rises to 125 ° C. and exceeds the surface temperature of the heating film 15.

  Therefore, in this embodiment, when it is determined that the discharge control is necessary when 400 sheets are continuously passed, the temperature adjustment zone is determined from the count value of the warm-up counter. The count value of the warm air counter is 500 counts at the end timing of 400 sheets. In the case of 500 counts, the temperature control zone is set to 2.

  Thereafter, the sheet interval time and the sheet interval temperature control just before the discharge control is performed are corrected according to the temperature adjustment zone. Here, since the temperature control zone is determined to be 2, the time between sheets immediately before the discharge control is extended by +10 seconds. At the same time, a second temperature lower than the first temperature (for example, 115 ° C. as a conventional fixing temperature adjustment temperature) from the first temperature based on the temperature control temperature is set to be lower than the first temperature (reference first temperature). Correct to a second temperature of 5 ° C.

  In the interval between new sheets shown in FIG. 12, since the temperature adjustment zone is determined to be 2, the time is extended by 10 seconds from the conventional interval between sheets. At that timing, the temperature control of the heater 16 is controlled to lower the temperature by 5 ° C. so as to keep the surface of the heating film 15 at 110 ° C. By lowering the target temperature adjustment temperature between the sheets when the interval between sheets is extended, the temperature detected by the thermistor 20 becomes higher than the target temperature adjustment temperature due to the effect that the surface temperature of the fixing roller 18 stores heat, and the heat generation of the heater 16 is suppressed.

  In addition, since the heating film 15 and the pressure roller 19 that are in contact with the fixing roller 18 deprive the surface temperature stored in the fixing roller 18 by rotating idly by extending between the sheets, the member becomes a member that radiates heat to the outside air. It becomes possible to lower the surface temperature. Further, the fixing roller 18 and the pressure roller 19 are rotated, so that heat dissipation is improved as compared with when the fixing roller 18 and the pressure roller 19 are stopped.

  In the configuration of the fixing device 14 of the present embodiment, the surface temperature of the fixing roller can be lowered from 123 ° C. to 100 ° C. by performing the above-described two sheet interval correction. By performing the discharge control from the state where the surface temperature of the fixing roller 18 is lowered to 100 ° C., it becomes possible to make the surface temperature relationship of the heating film 15> the fixing roller 18. Thereby, the dirt toner Tx adhering to the heating film 15 can be moved to the surface of the fixing roller 18 for the purpose of cleaning.

  In this way, the relationship of the surface temperature when the discharge control is performed can be the relationship of the heating film 15> the fixing roller 18, and the cleaning effect can be maintained. Further, the cleaning effect is more effective than the conventional cleaning using the recording material P, and the cleaning can be performed without wasting the recording material P, the toner, and the like.

<Configuration for control>
FIG. 13 is a block diagram showing a configuration related to control of the image forming apparatus 100 of the present embodiment. The control shown in the flowchart to be described later is performed by the control unit 41 executing a control program stored in the memory unit 43. Specifically, the control unit 41 is a CPU (Central Processing Unit).

  In the present embodiment, one CPU functions as the control unit 41 and the input image processing unit 42. Further, the same CPU detects the temperature and humidity of the room in which the image forming apparatus 100 is installed, the environmental temperature and humidity sensor 25, the heater heat generation temperature detection sensor 20 that detects the heat generation temperature of the heater 16, and the heater 16 of the printer unit 45. It also functions as a heater control unit that controls energization. Furthermore, it also functions as an execution unit that executes discharge control for fixing cleaning. The configuration related to the control is not limited to this, and a plurality of CPUs that realize each function may be provided, and the image forming apparatus 100 may be controlled by each CPU and the CPU as the control unit 41.

<Flow chart regarding discharge control>
FIG. 1 is a flowchart showing control for extending the time between sheets immediately before discharge control according to the temperature control zone of warm-air counter control, and determining correction of the heater temperature-adjusting temperature. First, in response to the control unit receiving an input of a job in the standby state, the control shown in the flowchart of FIG. 1 is started. The standby state is a state of waiting for a job input without executing image formation. For example, after all the reserved jobs are finished, the image forming apparatus 100 is in a waiting state.

  In Step 11, temperature control temperature information of the heater 16 detected by the thermistor 20 is acquired from the temperature sensor. In the present embodiment, the temperature adjustment temperature of the heater 16 is detected by the thermistor 20 in response to the input of the print job, and the temperature is acquired.

  In Step 12, based on the temperature adjustment temperature of the heater 16 whose temperature adjustment temperature is detected by the thermistor 20, an initial value for starting the counting by the warm air counter 300 is determined. In the present embodiment, for example, when the print job is received immediately after image formation and the temperature detected by the thermistor 20 is 175 ° C., the process starts from 500 counts. At this time, it corresponds to the temperature adjustment zone 2, and the temperature correction of the temperature adjustment temperature uses the temperature correction value of the temperature adjustment zone 2.

  In Step 13, an interval time from the previous image formation to the current image formation is read from the control unit 41. In the present embodiment, the interval threshold is set to 20 seconds and 120 seconds. In Step 14, a count value to be added to the warm-up counter 200 is determined when image formation is performed once from the read image formation interval time. In Step 15, the cumulative rotation time between sheets of the print job is read from the control unit 41. At Step 16, the value to be added to the warm air counter 200 when image formation is performed once is determined from the cumulative rotation time between the sheets read at Step 15.

  In Step 17, the warm air counter 200 is added to the warm air counter 200 with an addition value according to the image formation interval time determined in Step 14 and a count addition value according to the sheet interval cumulative rotation time determined in Step 16. In the present embodiment, for example, when a print job is received at an image formation interval time of 120 seconds or more and image formation is started, four counts are added to the warm-air counter 200 each time image formation is performed. . When the cumulative rotation time between sheets is 9 seconds or more and 12 seconds or less, four counts are added to the warm-air counter 200 each time image formation is performed.

  In Step 18, the temperature adjustment zone is determined according to the count value to the warm-up counter added in Step 11 to Step 17. In the present embodiment, the fixing temperature adjustment control of image formation is corrected according to the temperature adjustment zone divided into six stages. Although temperature control is used here, correction to control that does not have temperature control may be correct.

  In Step 19, image formation is started by temperature control based on the temperature control zone determined in Step 18. In Step 20, it is determined whether the cumulative number (number) of image formations is equal to or greater than the contamination threshold value of the heating film 15. In the present embodiment, since it is desired to perform discharge control between sheets every 40 sheets, the threshold is set to 40 times. If the cumulative number of image formation has not reached the threshold value, the process proceeds to Step 27.

  If the threshold value has been reached in Step 20, Step 21 reads the temperature adjustment zone value of the warm-up counter when the number of image formations determined in Step 20 has reached the threshold value of 40 sheets. In Step 22, the inter-paper extension time immediately before the discharge control is read in accordance with the temperature control zone read in Step 21. In Step 23, the inter-paper correction temperature immediately before the discharge control is read in accordance with the temperature adjustment zone read in Step 21, as in Step 22.

  In Step 24, the discharge control straight line is extended and the paper temperature is corrected according to the temperature control zone. In this embodiment, for example, when the temperature adjustment zone determined by the count value of the warm-up counter 200 shifts to the discharge control at the timing of 5, the inter-paper time is extended by 50 seconds between the sheets immediately before the discharge control, and the fixing is performed. The temperature control temperature is corrected by -10 ° C. In Step 25, the discharge control is performed after the sheet interval (when the next recording material is carried into the nip portion). The surface temperature of the fixing roller 18 can be reduced to 100 ° C. or less by shifting to the discharge control after extending the sheet interval time and performing the sheet temperature adjustment.

  As described above, if the surface temperature of the fixing roller 18 can be kept at 100 ° C. or lower, the offset toner Tx accumulated on the surface of the heating film 15 when the discharge control is performed is moved to the surface on the fixing roller 18 side. It becomes possible to make it. Thereafter, the recording material P passes through the fixing nip portion N1 at the timing when the offset toner Tx moved to the surface of the fixing roller 18 moves to the surface of the pressure roller 15, so that the back surface of the recording material P is not visible. It is possible to clean by discharging.

  In Step 26, the count value of the image forming number counter 201 in the memory unit 43 (the number of sheets through which images have been formed) is reset. That is, the count value counts the number of times of image formation after prompting the execution of the discharge control. In Step 27, the control unit 41 determines whether or not all of the image forming process and the fixing process corresponding to the input job have been completed. If the image formation has not been completed (Step 27 is No), the process returns to reading of the accumulated rotation time between sheets in the job in Step 15 and is repeated until all the image formation is completed. When all the image formation is completed (Step 27 is Yes), the flowchart of FIG.

  When all the image formation is completed (Yes in Step 27), the control unit 41 turns off the energization of the heater 16 and shifts to the standby state. Further, when all the image forming processing is completed (Yes in Step 27), the control unit 41 starts counting by the timer.

  As described above, the discharge control described above is effective when there is a possibility that the result will be contaminated by the offset toner Tx accumulated on the surface of the heating film 15. In this way, it is possible to detect the warming condition of the surface of the fixing roller 18 based on the prediction by the warm-up counter control, extend the time between sheets immediately before the discharge control, and correct the target temperature, thereby correcting the target temperature. It becomes possible to keep the surface temperature.

  In the prior art, there is no cleaning ability even if the discharge control is performed depending on the conditions of sheet passing, and it is necessary to carry out the conventional fixing cleaning using the recording material P a plurality of times. For this reason, in this embodiment, wasteful toner consumption due to printing of the recording material P and the cleaning image can be reduced.

Second Embodiment
In the first embodiment, the control unit 41 counts the number of sheets of recording material passing through the fixing nip portion by the number counter 201, and the surface of the heating film 15 when the value of the number counter 201 becomes equal to or more than the threshold. It is determined that the offset toner Tx is accumulated on the On the other hand, in the present embodiment, the control unit 41 determines that the offset toner Tx is accumulated in the heating film 15 based on the density information of the image data formed by the image forming unit.

  Specifically, based on the Y, M, C, and K image data, image formation data input from a PC or a document table is determined by the input signal processing unit 42 whether or not there is image data for storing dirt on the heating film 15. The result of the image analysis is sent to the control unit 41. If it is determined that the image analysis result that has been sent has an image that tends to be dirty, the control unit 41 adds one count to the dirt flag counter 203 in the memory unit 43.

  In the dirt flag counter 203, the number of times determined to be image data that accumulates dirt on the heating film 15 is accumulated, and the flag is turned ON when the predetermined number of sheets is reached. When the value of the dirt flag counter 203 reaches the threshold and the dirt flag is turned on, the control unit 41 determines that the offset toner Tx is accumulated on the surface of the heating film 15.

  In the following, the same components as in the first embodiment will be assigned the same reference numerals and detailed explanations thereof will be omitted, and only differences from the first embodiment will be described.

<Threshold of Execution Control Counter by Image Analysis>
FIG. 14 shows the relationship between the sum (%) of YMCK density signal values of the printed image and the stain density ΔD due to the offset toner Tx adhering to the heating film 15. The stain density ΔD is based on the reflection density Dx on the surface of the heating film 15 to which the offset toner Tx is not attached, and the density difference value of the reflection density Dy on the surface of the heating film 15 soiled by the offset toner Tx is defined as the stain density ΔD (toner Dirt adhesion degree). The reflection density is the density of the color of the surface of the heating film 15 and can be measured by a commercially available measuring device.

  FIG. 14 shows a heating film when 40 sheets of recording material P on which an unfixed toner image corresponding to an image of the sum (%) of density signals of YMCK is formed are continuously passed in the configuration of this embodiment. 15 shows the stain density ΔD of the surface. In the configuration of the present embodiment, when the sum of the YMCK density signal values is 30 to 60%, the dirt density ΔD is a high value of 0.15 or more, and the sum of the YMCK density signal values is about 40%. There is a peak.

  Here, in the case where the contamination density ΔD of the heating film 15 is 0.15 or more, when image formation is started from a state where the fixing device 14 is cooled, the offset toner Tx adhering to the first recording material P is visible to human eyes. It is a recognizable level.

  FIG. 15 is a view showing the relationship between the number of times of image formation and the stain density ΔD on the surface of the heating film 15 in an image of 40% in total of the density signal values of YMCK where stains easily accumulate on the heating film 15. According to the result of forming an image of 40% sum of YMCK density signal values up to 60 times in 10 increments, the stain density ΔD is less than 0.15 up to 22 times.

  That is, the amount of the offset toner Tx accumulated in the heating film 15 is a level at which even if image formation is started from the state where the fixing device 14 is cold, it is not visually recognized as a product. However, when an image having a sum of 40% of YMCK density signal values is formed and fixed 23 times or more, the stain density ΔD becomes 0.15 or more. That is, it can be seen that the offset toner Tx accumulates in the heating film 15 to a level visually recognized by the product.

  Therefore, in the present embodiment, the input image processing unit 42 analyzes an image in the case where an image having a density signal of 40% is most likely to be attached to the heating film 15 with the offset toner Tx. Then, from the result of the image analysis, the number of times the image having the sum of density signals of YMCK of 1 to 60% is formed is stored in the dirt flag counter 203, and the control unit 41 determines the timing at which discharge control is necessary. In the present embodiment, the threshold at which it is determined that the discharge control needs to be performed is set to 20 counts.

  Note that the threshold value of the dirt flag counter 203 in the present embodiment is an example, and the present invention is not limited to this. That is, it may be set as appropriate according to the configuration of the apparatus. Further, the value counted by the stain flag counter 203 may be a value corresponding to the number of recording materials P on which an unfixed toner image is formed in the image forming unit. For example, in this embodiment, the count value of the dirt flag counter 203 is incremented by 1 each time an image is formed on one recording material P regardless of the size of the recording material P.

  However, for example, according to the length of the recording material P in the conveyance direction, the count number of the stain flag counter 203 per image which is easily offset may be weighted. Further, for example, the stain flag counter 203 may be configured to add up the absolute values of the lengths of the recording material P in the conveyance direction.

  The stain flag counter 203 counts each time the control unit 41 updates the value of the stain flag counter 203 each time an image which is easily offset is formed on the recording material P. Further, the dirt flag counter 203 counts the number of recording materials P on which an image is formed by the image forming unit after the display prompting the fixing cleaning last time.

<Density signal value of image data and detection area>
The point α in FIG. 16 is based on image data in which the length of an area on which an image with a total sum of density signals of YMCK of 40% is printed in one recording material P is 20 mm in the conveyance direction of the recording material P. The contamination density ΔD is shown in the case where the image forming process is repeated 40 sheets in succession. The horizontal axis represents the difference in the length of an area on which an image with a total sum of density signals of YMCK of 40% is printed on one sheet of recording material P as image data used for image formation processing of 40 sheets in succession. The values shown in FIG. 16 are an example, and the present invention is not limited to this.

  For example, in the example shown in FIG. 16, when the image forming process is repeatedly performed based on image data in which an image having a total of 40% of YMCK density signal values in the conveyance direction of the recording material P continues for 50 mm or more, the stain density ΔD. Becomes 0.15 or more. When the stain density ΔD of the heating film 15 is 0.15 or more, the level at which the offset toner Tx adhering to the first recording material P can be recognized by human eyes when image formation is started from the state where the fixing device 14 is cooled. It is.

  Therefore, the control unit 41 determines that an image (hereinafter, image D) whose YMCK image data input from the input image processing unit 42 has a total sum of density signal values of YMCK in a predetermined density range in the conveyance direction of the recording material P. If the data is longer than the length, it is determined that the dirt flag is on. The fact that the dirt flag is on indicates that the offset toner Tx may be transferred to the heating film 15 due to the fixing process of the recording material P on which the toner image corresponding to the image data is formed.

  In the present embodiment, the predetermined length is 50 mm as an example. Further, the predetermined concentration range is 1 to 60% as an example. These values are merely examples, and may be set as appropriate according to the configuration of the apparatus.

  FIG. 17 is a diagram illustrating an example of a detection area of an image D and an area division. FIG. 4A shows an area that is desired to be detected in this embodiment. When the sum of the density signal values in the image D is 1 to 60% and continues for 50 mm or more in the transport direction, it is a detection target. Also, as shown in (c), even when the image D is divided in one recording material P, the image D is printed with a predetermined length (50 mm in this example) accumulated in the transport direction. The offset toner Tx tends to accumulate on the surface of the heating film 15.

  For example, as shown in FIG. 17C, even when the image D is 10 mm in the conveyance direction of the recording material P, and there is a margin after the image D after 50 mm, the offset toner on the surface of the heating film 15 Tx accumulates. That is, in the present embodiment, the control unit 41 detects when the image D is printed 50 mm or more continuously in the conveyance direction (main scanning direction) of the recording material P as illustrated in FIG. set to target.

  Further, in FIG. 13C, even in the case where the image D is formed by being divided into a plurality of recording materials P in the conveyance direction of the recording material P in one sheet of the recording material P, the width direction orthogonal to the conveyance direction ( If a total of 50 mm or more is printed on the same line where the positions in the sub scanning direction are the same, it is a detection target. On the other hand, as shown in FIG. 17B, the image D is continuously printed only 40 mm continuously in the conveyance direction of the recording material P, and is positioned on the same line whose position in the width direction is the same. If the image D is less than 50 mm even if it is accumulated in one recording material P, it is removed from the detection target.

  FIG. 18 is a diagram illustrating an image detection method. The control unit (acquisition unit) 41 analyzes the YMCK image data for each predetermined area (measurement patch n in FIG. 18), and an image (a total of YMCK density signal values in each predetermined area is a predetermined density range) That is, it is analyzed whether or not the image D). For example, in FIG. 18, the measurement patch n (size of one pixel) is shifted by one pixel in the main scanning direction with the upper left end as the reference position, and each measurement patch has a sum of YMCK density signal values of 1 to 60. Detect whether it corresponds to%. The position of the measurement patch n in the main scanning direction is X, and the position of the measurement patch n in the sub scanning direction is Y.

  In the present embodiment, detection is performed on a pixel-by-pixel basis, but the size of the measurement patch n may be set as appropriate according to the apparatus. For example, a size obtained by combining a plurality of pixels in FIG. 18 may be used as one immediate patch n.

<Image data analysis flow>
FIG. 19 shows a flow of detecting whether or not the image D has a predetermined length or more in the conveyance direction of the recording material P in the image data input to the image forming apparatus 100 in the present embodiment. When a job is input to the image forming apparatus 100 from a personal computer or the like provided outside the image forming apparatus 100, the input image processing unit 42 reads the input RGB image data (image data using RGB signals) (Step 31). ).

  At Step 32, the input image processing unit 42 converts the RGB image data read at Step 31 into YMCK image data (image data of the YMCK signal). The converted YMCK image data is output to the control unit 41. At Step 33, the control unit 41 determines the position X in the sub-scanning direction of the Y, M, C, and K image data to be read out to be the sub-scanning as the reference position = 1. In Step 34, the control unit 41 determines the position Y in the main scanning direction of the YMCK image data to be read out as main scanning = 1 as the reference position.

  In Step 35, the control unit 41 reads the density signal values of Y, M, C, and K at the position of n [main scanning] [sub scanning] in the YMCK image data, and calculates the density signal value of the sum of YMCK. To do. In this embodiment, at Step 33 and Step 34, the position of main scanning = 1 and the position of sub-scanning = 1 are set as reading start positions. At the reading start position, the control unit 41 reads the density signal value at the upper left end shown in FIG.

  At Step 36, the density signal value of the sum of YMCKs obtained at Step 35 is temporarily stored in the storage area of the memory 43 in association with the position of n [main scanning] and [sub scanning] in the YMCK image data.

  In Step 37, the control unit 41 determines whether reading has reached the image end of the YMCK image data in the main scanning direction. When the reading is not completed, the control unit 41 proceeds to Step 38. When the reading is completed, the control unit 41 proceeds to Step 39.

  In Step 38, the control unit 41 adds 1 to the main scanning. By returning to Step 35 after the addition, it is possible to read the density signal while shifting the position for reading the density signal value in the main scanning direction one pixel at a time until the end of the main scanning direction is reached.

  In Step 39, the control unit 41 determines whether reading has reached the image end portion of the YMCK image data in the sub-scanning direction. When the reading is not completed, the control unit 41 proceeds to Step 40. If the reading has been completed, the control unit 41 proceeds to Step 41.

  In Step 40, the control unit 41 adds 1 to the sub-scan. By returning to Step 34 after the addition, the position at which the density signal value is read is moved by one pixel in the sub-scanning direction, and the density signal value at the position moved by one pixel in the sub-scanning direction starts to be read from the left end in the main scanning direction. It becomes possible.

  In Step 41, the control unit 41 determines that in the subscanning direction, the area of the density signal value of the sum of YMCK is 1 to 60% in the subscanning direction at any position X in the main scanning direction in the YMCK image data for one page. Judgment whether or not.

  The distribution of the density signal value of the sum of YMCK in the YMCK image data for one page is stored in the memory unit 43 in Step 36 in the loop of Step 33 to Step 40. In any position X in the main scanning direction, when there is an area where the density signal value of the sum of YMCK is 1 to 60% is 50 mm or more in the sub scanning direction, the control unit 41 proceeds to Step 42. If there is no region where the total density signal value of 1 to 60% of YMCK is 50 mm or more in any position in the main scanning direction, the control unit 41 proceeds to Step 44.

  In Step 42, the control unit 41 performs image formation processing corresponding to the input image data to determine that the contamination is accumulated in the heating film 15, and turns on the contamination flag. In Step 43, the control unit 41 adds 1 to the value of the dirt flag counter 203 counting the number of times the dirt flag is turned ON in Step 42 on the memory unit 43.

  At Step 44, the control unit 41 determines whether the analysis has been completed up to the last page for the input job. If the last page is divided, the control unit 41 proceeds to Step 45. If the analysis is not performed up to the last page, the control unit 41 returns to Step 33 and analyzes the next page.

  In Step 45, the value counted in Step 43 is stored in the memory unit 43.

<Flowchart of Execution of Discharge Control from Image Analysis>
FIG. 20 is a flowchart showing that the control unit 41 determines the timing of executing the discharge control in the sheet interval. First, in response to the control unit 41 receiving an input of a job in the standby state, the control illustrated in the flowchart of FIG. 20 is started. Since Step 51 to Step 59 and Step 11 to Step 19 in FIG.

  In Step 60, the control unit 41 reads from the memory unit 43 a value (the value of the dirt flag counter 203) corresponding to the number of times of image forming processing (number of sheets passing) (number of integration of dirt flag) corresponding to turning on the dirt flag. . The value of the dirt flag counter 203 is a value stored at Step 45 in the flowchart of FIG. In the configuration of the present embodiment, as an example, the threshold is set to 20 times (20 sheets).

  In Step 61, the control unit 41 determines whether or not the value of the dirt flag counter 203 read in Step 60 is greater than or equal to a threshold value. If the value of the dirt flag counter 203 read in Step 61 is equal to or greater than the threshold value, the control unit 41 proceeds to Step 62. If the value of the dirt flag counter 203 read in Step 61 is less than the threshold value, the control unit 41 proceeds to Step 68. Step 62 to Step 66 are the same as Step 21 to Step 25 in FIG. 1, respectively, so the description will be omitted.

  In Step 67, the value of the dirt flag counter 203 stored in the memory unit 44 is reset. Further, the interval time measured by the timer 202 is reset. That is, the dirt flag counter 203 counts the degree of dirt accumulated after the discharge control is executed.

  At Step 68, the control unit 41 determines whether all the image forming processing and fixing processing corresponding to the input job have been completed. If the image formation has not been completed (No at Step 27), the process returns to reading of the accumulated rotation time between sheets in the job at Step 55, and is repeated until all the image formation is completed. When all the steps are completed (Step 68 Yes), the flowchart of FIG. 16 is ended.

  When all the image forming processes are completed (Step 68 Yes), the controller 41 turns off the heater 16 and shifts to a standby state. Further, when all the image forming processing is completed (Yes in Step 68), the control unit 41 starts counting by the timer 201.

  Even in the configuration of the present embodiment, the same effects as those of the first embodiment can be obtained. Furthermore, in the configuration of the present embodiment, the degree of contamination of the heating film 15 is calculated based on the density of the image data that has undergone the image forming process. As a result, even if the image forming process is repeated a plurality of times, if the image data is data that forms an image in which the offset toner Tx is difficult to adhere to the heating film 15, the control unit 41 does not perform the discharge control. As a result, it is possible to minimize the drop in productivity due to the discharge control, and it is possible to suppress the implementation of useless discharge control.

(Modification)
In the above-described embodiment, the preferred embodiment of the present invention has been described. However, the present invention is not limited to this, and various modifications can be made within the scope of the present invention.

(Modification 1)
In the embodiment described above, the count value of the warm air counter is used as the warm air information predicted as the warming degree of the first rotating body (fixing roller 18) when performing the discharge control. However, the present invention is not limited to this. . The temperature information of the first rotating body (temperature information of the fixing roller) can also be used. That is, temperature detection means for detecting the temperature (surface temperature) of the fixing roller may be provided, and discharge control may be performed based on the detection result.

(Modification 2)
In the embodiment described above, the temperature of the heater 16 is detected by the thermistor 20 as a temperature detection unit, but at least one of the heater 16 and the heating film 15 may be detected.

(Modification 3)
In the embodiment described above, the fixing device for fixing the unfixed toner image to the recording material has been described as an example of the image heating device. However, the present invention is not limited thereto, and the recording material may be improved to improve the gloss of the image. The same applies to an apparatus for heating and pressing a toner image that has been temporarily attached.

1 photosensitive drum 9, intermediate transfer belt 12, secondary transfer outer roller 15, heating film 16, heater 20, thermistor 20, fixing roller 18, fixing roller 19, pressure roller , 41 .. Control part, N1 .. Fixing nip part, N2 .. Heating nip part

Claims (10)

An image forming unit that forms a toner image on a recording material;
A first rotating body;
A facing member that forms a nip portion that faces the first rotating body and sandwiches and conveys the recording material carrying the toner image together with the first rotating body;
A second rotating body that is in contact with the first rotating body at a side different from the opposing member and is controlled to a target regulated temperature;
At the time of image formation, the toner image transferred to the second rotary member in the time until the recording material passes through the nip portion and the next recording material is carried into the nip portion A control unit that transfers the dirt to the facing member via the first rotating body, and allows the dirt to be discharged to the surface opposite to the surface on which the toner image is carried with respect to the next recording material. And
If it is determined that the discharge is necessary based on the number of passing recording materials passing through the nip portion, warm-up information predicted as the degree of warming of the first rotating body or temperature information of the first rotating body And corrects the time immediately before the discharge to a second time which is extended with respect to a first time which is a reference, and which is lower than a first temperature which is a target of the target temperature control temperature. A controller for correcting the temperature to 2;
An image forming apparatus comprising: An image forming unit that forms a toner image on a recording material based on input image data;
A first rotating body;
A facing member that forms a nip portion that faces the first rotating body and sandwiches and conveys the recording material carrying the toner image together with the first rotating body;
A second rotating body that is in contact with the first rotating body at a side different from the opposing member and is controlled to a target regulated temperature;
At the time of image formation, the toner image transferred to the second rotary member in the time until the recording material passes through the nip portion and the next recording material is carried into the nip portion A control unit that transfers the dirt to the facing member via the first rotating body, and allows the dirt to be discharged to the surface opposite to the surface on which the toner image is carried with respect to the next recording material. And
When it is determined that the discharge is necessary based on the density information of the image data, the discharge of the discharge based on the warm-air information predicted as the degree of warming of the first rotating body or the temperature information of the first rotating body The time immediately before is corrected to a second time which is extended with respect to the first time which is a reference, and the target temperature adjustment temperature is corrected to a second temperature which is lower than the first temperature which is a reference A control unit,
An image forming apparatus comprising: An input image processing unit that inputs the image data and determines whether there is an image in which the sum of density signal values of each color component is within a predetermined density range;
A counter that integrates the number of times that it is determined that there is an image within the predetermined density range;
The image forming apparatus according to claim 2, wherein the control unit determines that the discharge is necessary when a value of the counter reaches a threshold value. Temperature detecting means for detecting a temperature of a heater for heating the second rotating body or a temperature of the second rotating body;
A first accumulating unit for accumulating time until the recording material at the time of image formation passes through the nip portion and the next recording material is carried into the nip portion;
A second integrating means for integrating the time from completion of image formation in the previous job to image formation in the current job;
A warm-up counter that counts the warm-up information based on the results of the temperature detection unit, the first integration unit, and the second integration unit;
The image forming apparatus according to any one of claims 1 to 3, further comprising:   In the time from when the recording material passes through the nip portion and the next recording material is carried into the nip portion, the first rotating body has a lower heat than the second rotating body, and the second The image forming apparatus according to claim 1, wherein the facing member has a low heat with respect to the rotating body.   The first rotating body and the second rotating body are idly rotated during the time from when the recording material passes through the nip portion and the next recording material is carried into the nip portion. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the stain on the toner image is offset toner.   The image forming apparatus according to any one of claims 1 to 7, wherein the second rotating body is formed of an endless film.   The image forming apparatus according to any one of claims 1 to 8, wherein the first rotating body is a fixing roller, and the opposing member is a pressure roller. A first rotating body;
A facing member that forms a nip portion that faces the first rotating body and sandwiches and conveys a recording material carrying a toner image together with the first rotating body;
A second rotating body that is in contact with the first rotating body at a side different from the opposing member and is controlled to a target regulated temperature;
At the time of image formation, the toner image transferred to the second rotary member in the time until the recording material passes through the nip portion and the next recording material is carried into the nip portion A control unit that transfers the dirt to the facing member via the first rotating body, and allows the dirt to be discharged to the surface opposite to the surface on which the toner image is carried with respect to the next recording material. And
If it is determined that the discharge is necessary based on the number of passing recording materials passing through the nip portion, warm-up information predicted as the degree of warming of the first rotating body or temperature information of the first rotating body And corrects the time immediately before the discharge to a second time which is extended with respect to a first time which is a reference, and which is lower than a first temperature which is a target of the target temperature control temperature. A control unit for correcting the temperature to 2;
An image heating apparatus comprising: