JP2008020607A - Image heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of turning-on a fixing heater with greater electric power while suppressing the temperature rising of a fixing heater section, by efficiently transmitting heat to a fixing belt during the start-up of a fixing device, and shortening the start-up time of a fixing device and enhancing the on-demand performance. <P>SOLUTION: The fixing device has a fixing heater, a rotating body, such as a fixing belt moving moving together with a paper sheet, a rotating body, such as a pressure roller forming a section pressure-contacting the paper sheet, and conveying a recording material, a fixing motor rotationally driving the pressure roller and the fixing belt, and capable of controlling the rotating speed by switching at a plurality of speeds, and a plurality of temperature detecting means, such as thermistors capable of detecting the temperature of the fixing belt and the fixing heater. During the start-up of the fixing device, the fixing device is driven at a speed for the fixing belt higher that is than the speed at the fixing of the toner image to the paper sheet, until the temperature of the fixing belt section reaches the target temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image heating apparatus for heating an image on a recording material. The present invention also relates to an image forming apparatus in which the image heating apparatus is mounted as a fixing device.

  Examples of the image heating device include a fixing device that heats and fixes an unfixed image on the recording material, and a glossiness increasing device that increases the glossiness of the image by heating the image fixed on the recording material. Can be mentioned.

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers. As an electrophotographic color image forming apparatus, a plurality of photosensitive drums are arranged in a line for each color, and a color image is formed by sequentially superposing toner images of the respective colors formed on the photosensitive drums on a transfer medium. A so-called inline type image forming apparatus has been proposed.

  As a fixing device used in such a color image forming apparatus, a fixing belt having an elastic layer as disclosed in Patent Document 1 is used, which has both shortened warm-up time and stable fixing of a color image. The belt fixing device used is used.

  In such a belt fixing device, the thermal conductivity of the silicone rubber layer used for the elastic layer of the fixing belt is small, and there are many members from the heater to the surface of the fixing belt. Therefore, there is a delay in detection timing due to poor responsiveness until the fixing belt temperature rises after the fixing heater is energized, or due to the position of the thermistor of the fixing belt portion being away from the fixing nip portion. As a result, generally, the tracking of the fixing belt temperature with respect to the temperature of the fixing heater is accompanied by a large delay. For this reason, when the fixing belt is raised to a predetermined temperature, there is a possibility that the temperature of the fixing heater part may overshoot greatly.

As a countermeasure against this, a method of restricting power by prohibiting feedback for a predetermined period as shown in Patent Document 1 is employed. Further, a thermistor capable of detecting the temperature of the fixing heater is provided during startup of the fixing device, and control is performed so that the temperature of the fixing heater portion does not exceed a predetermined temperature.
Japanese Patent Laid-Open No. 2004-70041

  However, in the above conventional example, since the power is limited so that the temperature of the fixing heater does not rise too much, the capacity of the fixing heater cannot be fully used during the start-up of the fixing device. For this reason, the start-up time becomes long, and there is a problem that the on-demand property is lowered. Especially when the width of the fixing nip is narrow or the material used for the elastic layer of the fixing belt has a lower thermal conductivity, the heat of the fixing heater is difficult to transfer to the fixing belt. It is easy to rise and this problem appears more prominently.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to light up a heating body with higher power while suppressing an increase in the temperature of the heating body during startup of an image heating apparatus represented by a fixing device. It is possible to do. Thus, an image heating apparatus that shortens the start-up time and improves on-demand characteristics, and an image forming apparatus equipped with the image heating apparatus are provided.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a heating body that generates heat upon receiving power supply, a power supply unit that supplies power to the heating body, and heating by the heating body. The first rotating body, the second rotating body that forms a pressure contact portion with the first rotating body, the drive source that rotationally drives the second rotating body, and the temperature of the portion different from the heating body First temperature detecting means for detecting the temperature, and control means for controlling the apparatus, the control means from the power supply unit based on the temperature detected by the first temperature detecting means In the image heating apparatus that controls the temperature of the first rotating body by feedback control of the power supplied to the body, and sandwiches and conveys the recording material carrying the image at the press-contact portion, and heats the image, the control means includes: When the device is started up, the first Until the temperature detected by the degree detection means reaches the second temperature T2, which is a temperature set lower than the first temperature T1, which is the target temperature of the temperature control at the time of image heating execution, the rotational speed of the drive source is set. The second speed V2 is set to a speed different from the first speed V1 that is the set rotational speed when the image heating is performed.

  In addition, another representative configuration of the image heating apparatus according to the present invention for achieving the above object includes: a heating body that generates heat upon receiving power supply; a power supply unit that supplies power to the heating body; A first rotating body that is heated by a heating body; a second rotating body that forms a pressure contact portion with the first rotating body; a drive source that rotationally drives the second rotating body; and the heating body. 1st temperature detection means which detects the temperature of a different part, and control means which controls an apparatus, The said control means supplies the said electric power based on the temperature detected by the said 1st temperature detection means In an image heating apparatus that performs temperature control of the first rotating body by feedback control of power supplied from the unit to the heating body, and sandwiches and conveys a recording material carrying an image at the press-contacting portion, and heats the image, A second temperature sensor for detecting the temperature of the heating element; And a temperature detected by the second temperature detection means when the apparatus is started up is higher than a first temperature T1, which is a target temperature for temperature control during image heating. Until the third temperature T3 that is the set temperature is reached, the rotational speed of the drive source is driven at the third speed V3 that is set lower than the first speed V1 that is the set rotational speed at the time of image heating execution. The temperature detected by the first temperature detection means after the temperature detected by the second temperature detection means reaches the third temperature T3 is a second set temperature lower than the first temperature. Until the temperature T2 is reached, control is performed so as to drive at the second speed V2, which is a speed set higher than the first speed V1.

  According to the present invention, during startup of the apparatus, it is possible to turn on the heating body with higher power while suppressing the temperature rise of the heating body, thereby shortening the startup time and improving on-demand performance. An improved image heating apparatus can be provided.

(1) Example of Image Forming Apparatus FIG. 3 is a schematic configuration diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device. The image forming apparatus of this example is an electrophotographic tandem (inline type) full color laser printer.

  Reference numeral 21 denotes a control circuit unit (CPU) as a control unit that performs overall control of the image forming apparatus. A video controller 21A is connected to an external host device 100 such as a computer image reader via an interface 21B. The video controller 21A expands the electrical image information sent from the external host device 100 via the interface 21B into bit data, and sends the bit data to the control circuit unit 21 as a VDO signal.

  Reference numerals 1Y, 1M, 1C, and 1Bk denote first to fourth electrophotographic image forming units (image forming units), which are arranged in a line from the left to the right on the drawing at a constant interval. The four image forming units 1Y, 1M, 1C, and 1Bk each form a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, which are color separation component images of a full color image.

  Photosensitive drums 2a, 2b, 2c, and 2d are installed in the image forming units 1Y, 1M, 1C, and 1Bk, respectively. Further, around the photosensitive drums 2a, 2b, 2c, and 2d, charging rollers 3a, 3b, 3c, and 3d, developing devices 4a, 4b, 4c, and 4d, and primary transfer rollers 5a, 5b, 5c, and 5d, respectively. 5d, drum cleaning devices 6a, 6b, 6c and 6d are installed. Laser exposure devices 7a, 7b, 7c, and 7d are installed above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively. Each of the developing devices 4a, 4b, 4c, and 4d contains color toners of yellow toner, magenta toner, cyan toner, and black toner, respectively.

  An endless belt-like intermediate transfer belt (hereinafter abbreviated as a belt) 40 as a transfer medium (intermediate transfer member) is disposed below each of the image forming units 1Y, 1M, 1C, and 1Bk. The belt 40 is stretched between the drive roller 41, the support roller 42, and the secondary transfer counter roller 43, and is rotated (moved) in the clockwise direction of the arrow by the drive of the drive roller 41. In each of the image forming units 1Y, 1M, 1C, and 1Bk, the primary transfer rollers 5a, 5b, 5c, and 5d are respectively connected to the photosensitive drums 2a and 2b via a belt portion between the driving roller 41 and the support roller 42. -It contacts the lower surface of 2c and 2d. In each of the image forming units 1Y, 1M, 1C, and 1Bk, a contact portion between the photosensitive drums 2a, 2b, 2c, and 2d and the belt 40 is a primary transfer nip portion N.

  A secondary transfer roller 44 is brought into contact with the secondary transfer counter roller 43 via a belt 40. A contact portion between the belt 40 and the secondary transfer roller 44 is a secondary transfer nip portion M. The secondary transfer roller 44 is disposed so as to be in contact with and away from the belt 40.

  A belt cleaning device 45 that removes and collects secondary transfer residual toner remaining on the surface of the belt 40 is installed in a belt suspension portion of the driving roller 41.

  A fixing device (fixing device) 12 is installed downstream of the secondary transfer nip M in the recording material conveyance direction.

  When an image forming operation start signal (print start signal) is input to the control circuit unit 21, the control circuit unit 21 starts device driving.

  The photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1M, 1C, and 1Bk are driven to rotate in the counterclockwise direction indicated by an arrow at a preset process speed. The belt 40 is rotationally driven in the clockwise direction of the arrow at a speed similar to the rotational speed of the photosensitive drums 2a, 2b, 2c, and 2d.

  The photosensitive drums 2a, 2b, 2c, and 2d are uniformly charged by the charging rollers 3a, 3b, 3c, and 3d, respectively. In this embodiment, it is negatively charged. The uniformly charged surface of the photosensitive drum is subjected to scanning exposure by the laser exposure devices 7a, 7b, 7c, and 7d. Thereby, an electrostatic latent image corresponding to the laser scanning exposure pattern is formed on the surface of each photosensitive drum.

  Each of the laser exposure apparatuses 7a, 7b, 7c, and 7d converts the color-separated image signal input from the control circuit unit 21 into an optical signal by a laser output unit (not shown). Laser light, which is the converted optical signal, is scanned and exposed on each of the charged photosensitive drums 2a, 2b, 2c, and 2d to form an electrostatic latent image.

  In the first image forming unit 1Y, the developing device 4a in which a developing bias having the same polarity as the charged polarity (negative polarity) of the photosensitive drum 2a is applied on the photosensitive drum 2a on which the electrostatic latent image is formed. Yellow toner is applied. As a result, the toner is electrostatically adsorbed according to the charged potential on the surface of the photosensitive drum, and the electrostatic latent image is developed as a yellow toner image. This yellow toner image is primarily transferred onto the rotating belt 40 by a primary transfer roller 5a to which a primary transfer bias (opposite polarity (positive polarity) to toner) is applied in a primary transfer portion N. Is done. The belt 40 to which the yellow toner image has been transferred is moved to the second image forming unit 1M side.

  In the second image forming unit 1M, a magenta toner image is formed on the photosensitive drum 2b by the same image forming process as described above. The magenta toner image is superimposed and transferred onto the yellow toner image on the belt 40 at the primary transfer portion N.

  Similarly, in the third image forming unit 1M, a cyan toner image is formed on the photosensitive drum 2c, and in the fourth image forming unit 1Bk, a black toner image is formed on the photosensitive drum 2d. . Then, the cyan toner image and the black toner image are sequentially superimposed and transferred on the yellow toner image and the magenta toner image that have already been superimposed and transferred onto the belt 40 at each primary transfer portion N. As a result, an unfixed full-color toner image composed of four toner images of a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image is synthesized and formed on the belt 40.

  The primary transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d during the primary transfer of the image forming units 1Y, 1M, 1C, and 1Bk is the drum cleaning devices 6a, 6b, 6c, and 6d. Removed and recovered.

  The recording material (transfer material) P is transferred to the secondary transfer nip by the registration roller 46 in accordance with the timing when the leading end of the full-color toner image on the belt 40 is moved to the secondary transfer nip M by the subsequent rotation of the intermediate transfer belt 40. It is conveyed to part M. A full color toner image on the belt 40 is secondarily transferred onto the recording material P at once by a secondary transfer roller 44 to which a secondary transfer bias (opposite polarity (positive polarity) to toner) is applied. The

  The recording material P that has exited the secondary transfer nip M is separated from the surface of the belt 40 and conveyed to the fixing device 12. The secondary transfer residual toner remaining on the belt 40 after separation of the recording material is removed and collected by the belt cleaning device 45.

  The recording material introduced into the fixing device 12 receives heat and pressure, and an unfixed full-color toner image is melted and fixed on the surface of the recording material. Then, the recording material is discharged from the fixing device 12 to the outside as an output image formed product. This completes a series of image forming operations.

  An environmental sensor 50 and a media sensor 51 are installed in the image forming apparatus. The environmental sensor 50 is used for adjusting the density of the toner image formed on the recording material P and for achieving optimum transfer and fixing conditions. The atmosphere environment (temperature, humidity) information in the apparatus detected by the environment sensor 50 is input to the control circuit unit 21. The control circuit unit 21 executes an adjustment program for appropriately changing charging, developing, primary transfer, secondary transfer bias, fixing conditions, and the like according to the input information. The media sensor 51 is also used to achieve optimum transfer and fixing conditions for the recording material P. Discrimination information such as the size and material of the recording material P detected by the media sensor 51 is input to the control circuit unit 21. The control circuit unit 21 executes an adjustment program that appropriately changes the transfer bias, the fixing condition, and the like according to the input information.

(2) Fixing device 12
FIG. 4 is a schematic configuration model diagram of the fixing device 12. The fixing device 12 of this example is an image heating device of a fixing belt heating method and a pressure rotating body driving method (tensionless type).

1) Overall Configuration of Fixing Device 12 Reference numeral 20 denotes a fixing belt as a first rotating body (first fixing member), which has a cylindrical shape (endless belt shape, sleeve shape) in which an elastic layer is provided on the belt-like member. This is a flexible member. The fixing belt 20 has a flexible SUS sleeve having a thickness of about 30 μm as a belt base, a silicone rubber layer having a thickness of about 300 μm is formed on the outer peripheral surface thereof, and a PFA having a thickness of about 30 μm is further formed on the outer peripheral surface thereof. A resin layer is formed.

  Reference numeral 17 denotes a heater holder having a heat resistance and rigidity having a substantially semicircular arc shape in cross section as a heating body holding member, and 16 is a fixing heater as a heating body (heat source). It is arranged along. The fixing belt 20 is loosely fitted on the heater holder 17. The heater holder 17 is made of a liquid crystal polymer resin having high heat resistance, plays a role of holding the fixing heater 16 and guiding the fixing belt 20. In the present embodiment, the fixing heater 16 is a ceramic heater which will be described in detail in section 2) below.

  Reference numeral 22 denotes a pressure roller as a second rotating body (second fixing member). The pressure roller 22 is formed by forming a silicone rubber layer 22b having a thickness of about 3 mm on a stainless steel core 22a by injection molding and coating a PFA resin tube 22c having a thickness of about 40 μm thereon.

  The pressure roller 22 is arranged such that both end portions of the cored bar 22a are rotatably supported by bearings between a side plate (not shown) on the back side and a front side of the apparatus frame 24. Above the pressure roller 22, the fixing belt unit including the heater 16, the heater holder 17, the fixing belt 20 and the like is arranged in parallel with the pressure roller 22 with the heater 16 facing downward. And the longitudinal both ends of the heater holder 17 are urged in the axial direction of the pressure roller 22 by a force of one side 98N (10 kgf) and a total pressure 196N (20 kgf) by a not-shown pressure mechanism. As a result, the downward surface of the fixing heater 16 is pressed against the pressure roller 22 via the fixing belt 20 against the elasticity of the elastic layer 22 b, and between the fixing belt 20 and the pressure roller 22. A fixing nip portion (pressure contact portion) 27 having a necessary width in the recording material conveyance direction is formed. The pressurization mechanism has a pressure release mechanism, and is configured such that the pressurization is released at the time of jam processing or the like so that the recording material P can be easily removed.

  Reference numerals 18 and 19 denote two main and sub thermistors as first and second temperature detecting means. The main thermistor (first temperature detecting means) 18 is disposed in a non-contact manner with the fixing heater 16 as a heating body, and in this embodiment, the main thermistor (first temperature detecting means) is elastically brought into contact with the inner surface of the fixing belt 20 above the heater holder 17. The temperature of the inner surface of the belt 20 is detected. The sub thermistor (second temperature detection means) 19 is disposed at a location closer to the fixing heater 16 than the main thermistor 18. In this embodiment, the sub thermistor 19 is in contact with the back surface of the fixing heater 16 and detects the temperature of the back surface of the fixing heater.

  In the main thermistor 18, a thermistor element is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17. The arm 25 is elastically oscillated so that the thermistor element is always in contact with the inner surface of the fixing belt 20 even when the movement of the inner surface of the fixing belt 20 becomes unstable.

  FIG. 5 is a schematic perspective view showing the positional relationship among the fixing heater 16, the main thermistor 18, and the sub-thermistor 19 in the fixing device of this embodiment. The main thermistor 18 is disposed in the vicinity of the longitudinal center of the fixing belt 20, and the sub-thermistor 19 is disposed in the vicinity of the longitudinal end of the fixing heater 16, and is disposed so as to contact the inner surface of the fixing belt 20 and the back surface of the fixing heater 16, respectively. .

  Electrical information regarding the temperature detected by the main thermistor 18 and the sub-thermistor 19 is A / D converted and input to the control circuit unit 21. The control circuit unit 21 determines the content of the temperature control (temperature control) of the fixing heater 16 based on the input information from the main thermistor 18 and the sub-thermistor 19, and sets the heater drive circuit unit 28 as a power supply unit. And the energization (supply power) to the fixing heater 16 is controlled.

  Reference numeral 29 denotes a fixing motor as a drive source for rotationally driving the pressure roller 22. The rotational driving force of the fixing motor 29 is transmitted to the cored bar 22a of the pressure roller 22 through the power transmission means 30 such as a gear train, and the pressure roller 22 is rotationally driven in the counterclockwise direction indicated by the arrow. The fixing motor 29 is subjected to rotation-stop control and rotation speed change control by the control circuit unit 21 via the motor driver 31.

  Reference numerals 23 and 26 denote an entrance guide and a fixing paper discharge roller assembled to the apparatus frame 24. The entrance guide 23 serves to guide the recording material so that the recording material P that has passed through the secondary transfer nip portion M is accurately guided to the fixing nip portion 27. The entrance guide 23 of the present embodiment is formed of polyphenylene sulfide (PPS) resin.

  When the pressure roller 22 is driven to rotate, a rotational force acts on the fixing belt 20 due to a pressure frictional force at the fixing nip portion 27 between the outer surface of the pressure roller 22 and the fixing belt 20. As a result, the fixing belt 20 is rotated in the clockwise direction indicated by the arrow around the outer side of the heater holder 17 while the inner surface of the fixing belt 20 is in close contact with the downward surface of the fixing heater 16 and slides. Grease is applied to the inner surface of the fixing belt 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing belt 20.

  The pressure roller 22 is rotationally driven, and accordingly, the fixing belt 20 is driven and rotated, and the fixing heater 16 is energized. The temperature of the fixing heater 16 is increased to a predetermined temperature to control the temperature. Is done. Then, the recording material P carrying the unfixed toner image t is guided and introduced along the entrance guide 23 into the fixing nip portion 27, and the toner image carrying surface side closely contacts the outer surface of the fixing belt 20. The fixing nip portion 27 is nipped and conveyed together. In this nipping and conveying process, heat from the fixing heater 16 is applied to the recording material P via the fixing belt 20, and an unfixed toner image on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the fixing nip 27 is separated from the fixing belt 20 by the curvature, and is discharged by the fixing discharge roller 26.

2) Fixing heater 16
In this embodiment, the fixing heater 16 forms a resistance heating element by applying a conductive paste on an alumina substrate by screen printing to form a resistance heating element, on which a glass coating with a pressure-resistant glass is applied. The ceramic heater is used.

  FIG. 6 is a structural model diagram of an example of such a ceramic heater, where (a) is a partially cutaway surface model diagram, (b) is a back model diagram, and (c) is an enlarged cross-sectional model diagram.

The fixing heater 16 is
1: A horizontally long alumina substrate having a direction perpendicular to the paper passing direction as a longitudinal direction
2: Thickness of the conductive paste containing silver palladium (Ag / Pd) alloy which is applied to the surface side of the above-mentioned alumina substrate a along the length by screen printing in a linear or belt shape and generates heat when current flows. Resistance heating element layer b having a width of about 10 μm and a width of about 1 to 5 mm
3: As the power supply pattern for the resistance heating element layer b, the first and second electrode parts c · d and the extended electric circuit part e ·, which are similarly patterned by screen printing of silver paste on the surface side of the alumina substrate a f
4: The resistance heating element layer b and the extension electric circuit portions e and f are formed on the resistance heating element layer b and the extension circuit portions e and f so as to withstand the rubbing with the fixing belt 20 and have a thickness of about 10 μm. Thin glass coat g
5: Contact type thermistor 19 provided on the back side of the alumina substrate a
Etc.

  The fixing heater 16 is supported by being fixed to the heater holder 17 with the surface side exposed downward.

  A power feeding connector 32 is attached to the first and second electrode portions c and d of the fixing heater 16. Power is supplied from the heater drive circuit unit 28 to the first and second electrode units cd through the power supply connector 32. As a result, the resistance heating element layer b generates heat and the fixing heater 16 is quickly heated.

3) Control Sequence of Fixing Device 12 Next, a control sequence when starting up the fixing device 12 in this embodiment will be described. FIG. 1 is a flowchart showing the control, and FIG. 2 is a diagram showing the relationship between the temperature of each part when the fixing device is started up, the lighting power of the fixing heater 16, and the speed of the fixing motor 29.

  Here, in the following description, regarding the rotational speed of the fixing motor 29 that is a driving source, the “first speed V1” is a setting at the time of image fixing (fixing the image heating) for fixing the toner image on the recording material P. Rotation speed. The “second speed V1” is a rotational speed set faster than the first speed V1. The “third speed” V3 is a rotational speed set slower than the first speed V1.

  The “first temperature T1” is a target temperature for temperature control at the time of image fixing execution (when image heating is executed). In the present embodiment, the first temperature T1 is set to 190 ° C. The “second temperature T2” is a temperature set lower than the first temperature T1. In the present embodiment, the second temperature T2 is set to 180 ° C., which is slightly lower than the first temperature T1. The “third temperature T3” is a temperature set higher than the first temperature T1. In this embodiment, the third temperature T3 is a temperature close to the upper limit temperature at which the fixing heater 16 can be safely used, and is set to 250 ° C.

  When an image forming operation start signal is input to the control circuit unit 21 of the image forming apparatus in a standby state, the control circuit unit 21 starts the image forming operation (printing operation) of the image forming apparatus. The fixing device 12 is started up.

  First, the motor driver 31 is controlled to start rotational driving of the fixing motor 29 at the second speed V2 (step S1-1). In the present embodiment, the second speed V2 is set to about 1.5 times the first speed V1. Therefore, the pressure roller 22 and the fixing belt 20 are rotated at a speed approximately 1.5 times faster than when image fixing is performed.

  At the same time, energization from the heater drive circuit 28 to the fixing heater 16 is started, and the lighting power of the fixing heater 16 is controlled so that the detected temperature of the sub-thermistor 19 is maintained at the third temperature T3 (250 ° C.) (S1- 2).

  As shown in FIG. 2, when the temperature detected by the sub-thermistor 19 is sufficiently lower than the third temperature T3, the control circuit unit 21 turns on the fixing heater 16 with substantially maximum power. When the detected temperature of the sub-thermistor 19 approaches the third temperature T3, the electric power is lowered and the control is continued so as to keep the detected temperature of the sub-thermistor 19 at the third temperature T3.

  Thereafter, after the detected temperature of the main thermistor 18 reaches the second temperature T2 (180 ° C.) (S1-3), the control circuit unit 21 changes the speed of the fixing motor 29 from the second speed V2 to the first speed V1. Switch (S1-4).

  Then, the control circuit unit 21 controls the lighting power of the fixing heater 16 so that the detected temperature of the main thermistor 18 is maintained at the second set temperature T2, and the fixing device 12 is supplied from the secondary transfer nip M side. Wait until the recording material P reaches (S1-5, S1-6).

  When the recording material P reaches the fixing device 12, the control circuit unit 21 switches to the first temperature T1 and power setting (temperature adjustment setting for toner image fixing) for heating and pressurizing the toner image on the recording material P. The fixing heater 16 is driven (S1-7). Accordingly, the toner image is fixed on the recording material P in the process in which the recording material P is nipped and conveyed through the fixing nip portion 27.

  The detection and passage detection of the recording material P to the fixing device 12 is controlled based on the input of the leading and trailing edge detection signals of the recording material P from the sheet sensor SW arranged upstream of the fixing device 12 in the recording material conveyance direction. This is done by calculation of the circuit unit 21.

  The control circuit unit 21 waits for the image forming apparatus to wait until the next image forming operation start signal is input after the image forming operation is completed after executing the set image formation for one sheet or a plurality of continuous sheets. Hold on. For the fixing device 12, the energization to the fixing heater 16 is turned off, and the rotation drive of the fixing motor 29 is turned off, and the control sequence of the fixing device 12 is ended.

  FIG. 13 is a control flowchart in the conventional control as a comparative example, and FIG. 14 is a diagram showing the relationship between the temperature of each part when the fixing device is started up, the lighting power of the fixing heater 16 and the speed of the fixing motor 29 in the conventional control. It is. In contrast to this, the effect of this embodiment will be described.

  The conventional control flowchart of FIG. 13 is different from the control flowchart of FIG. 1 in this embodiment. The fixing motor 29 is rotated at the first speed V1 from the start of driving (S1-1B), and the speed in the middle is changed. There is no switching.

  14 is compared with the same diagram in the present embodiment in FIG. 2 and the diagram showing the relationship between the temperature of each part at the time of starting the fixing device in the conventional control of FIG. 14, the lighting power of the fixing heater 16, and the speed of the fixing motor. In this comparison, in the portion where the detected temperature of the sub-thermistor 19 is maintained at the second temperature T2, the present embodiment supplies more electric power to the fixing heater 16. This is because when the fixing device 12 is started up, the fixing motor 29 is rotated at a high speed by setting the rotation speed of the fixing motor 29 to a second speed V2 that is faster than the first speed V1. This is because heat can be transmitted to the fixing belt 20.

  For this reason, the temperature detected by the main thermistor 19 rises faster and the start-up of the fixing device 12 can be completed in a short time.

  In particular, a fixing heater having a narrow fixing nip width, a thicker elastic layer, or a smaller thermal conductivity of a material used for the elastic layer is less likely to transmit the heat of the fixing heater to the fixing belt. The temperature tends to rise, and the above effect is exhibited more greatly.

  Thus, the heat of the heating body such as the fixing heater 16 can be more efficiently transmitted to the first rotating body such as the fixing belt 20, shortening the start-up time and improving the on-demand response. An image heating apparatus and an image forming apparatus can be provided.

  Next, as a second embodiment, a control example in which the rotation amount of the fixing belt 20 is suppressed will be described. This is because it is preferable to suppress the rotation amount of the fixing belt 20 as much as possible from the viewpoint of the life of the fixing belt 20.

  Since the configuration of the fixing device and the image forming apparatus is the same as that of the first embodiment, the description thereof is omitted. FIG. 7 is a control flowchart of the present embodiment, and FIG. 8 is a diagram showing the relationship among the temperatures of the respective portions when the fixing device is started up, the lighting power of the fixing heater 16, and the speed of the fixing motor.

  When an image forming operation start signal is input to the image forming apparatus in the standby state, the control circuit unit 21 causes the image forming apparatus to start an image forming operation. The fixing device 12 is started up.

  First, rotation driving of the fixing motor 29 is started at a third speed V3 that is slower than the first speed V1. In this embodiment, the rotation is performed at the third speed V3 that is about one half of the first speed V1 at the time of image fixing (S2-1). Accordingly, the pressure roller 22 and the fixing belt 20 are rotated at a slow speed that is about a half of that during image fixing.

  At the same time, energization of the fixing heater 16 is started (S2-2). Thereafter, the fixing heater 16 is continuously turned on until the detected temperature of the sub-thermistor 19 reaches the third temperature T3 (250 ° C.) (S2-3). At this time, the energizing power to the fixing heater 16 is fixed at the maximum power in this embodiment as the system having the fastest rise. Of course, the electric power may be variably controlled according to the detected temperature state of the sub-thermistor 19 as a limit of the maximum electric power or as a countermeasure for overshoot.

  When the detected temperature of the sub-thermistor 19 reaches the third temperature T3 (S2-3), the rotation speed of the fixing motor 29 is switched to a second speed V2 that is faster than the first speed V1 during image fixing. In the present embodiment, the second speed V2 is set to a rotational speed that is approximately 1.5 times the first speed V1 during image fixing as in the first embodiment (S2-4).

  Subsequent control (S2-5 to S2-10) is exactly the same as (S1-2 to S1-7) in the first embodiment, and a description thereof will be omitted.

  By performing the control in this manner, it is possible to suppress the rotation amount of the fixing belt 20 and to start up the fixing device at high speed.

  Thus, it is possible to provide an image heating apparatus and an image forming apparatus that can obtain the same effects as those of the apparatus of Embodiment 1 and that suppress the rotation amount of the fixing belt 20.

  Next, as a third embodiment, a control example in the fixing device 12 that does not have the sub-thermistor 19 disposed on the fixing heater 16 will be described. The use of the sub-thermistor 19 is preferable for optimal control. However, it may be difficult to mount the sub-thermistor 19 due to cost reduction and space problems on the fixing heater 16. This embodiment will explain an example of control in that case.

  9 and 10 show the fixing device 12 in this embodiment. This fixing device is obtained by removing the sub-thermistor 19 from the fixing device 12 shown in FIGS. 4 and 5 of the first embodiment. Since the other fixing device configuration and the image forming device configuration are the same as those in the first embodiment, the description thereof will be omitted.

  FIG. 11 is a control flowchart of the present embodiment, and FIG. 12 is a diagram showing the relationship among the temperature of each part when the fixing device is started up, the lighting power of the fixing heater 16, and the speed of the fixing motor.

  Here, the “fixing heater back temperature” shown in FIG. 12 is not used for control because there is no element to be measured in the configuration of this embodiment. However, it is necessary in the control specification determination process, and is shown to assist the explanation of this embodiment.

  When an image forming operation start signal is input to the image forming apparatus in the standby state, the control circuit unit 21 causes the image forming apparatus to start an image forming operation. The fixing device 12 is started up.

  First, rotation driving of the fixing motor 29 is started at a second speed that is faster than the first speed V1. In this embodiment, the rotation is performed at the second speed V2 that is about 1.5 times the first speed V1 at the time of image fixing (S3-1).

  At the same time, energization of the fixing heater 16 is started (S3-2). Thereafter, the fixing heater 16 is continuously turned on until the detected temperature of the main thermistor 18 reaches a fourth temperature T4 (150 ° C. in this embodiment) set to be slightly lower than the second temperature T2 (180 ° C.). (S3-3). At this time, the energizing power to the fixing heater 16 is fixed at the maximum power in this embodiment as the system having the fastest rise. Of course, the electric power may be variably controlled according to the detected temperature state of the main thermistor 18 as a limit of the maximum electric power or as a countermeasure against overshoot.

  When the detected temperature of the main thermistor 18 reaches the fourth temperature T4 = 150 ° C. (S3-3), the energization to the fixing heater 16 is reduced to 50% of the maximum power (S3-4). Waiting until the main thermistor 18 reaches the second temperature T2 (180 ° C.) while being fixed to this electric power (S3-5).

  When the main thermistor 18 reaches the second temperature T3, the speed of the fixing motor 29 is switched from the second speed V2 to the first speed V1 (S3-6). Further, the energization of the fixing heater 16 is controlled so that the lighting temperature of the fixing heater 16 is maintained at the second temperature T2 of the temperature detected by the main thermistor 18.

  Subsequent control (S3-8 to S3-9) is exactly the same as the control (S1-6 to S1-7) in the first embodiment, and thus the description thereof is omitted.

  Here, the switching temperature in step S3-3 (fourth temperature T4 = 150 ° C.) and the energization power in S3-4 (50% of the maximum power) are the maximum temperatures at which the fixing heater back temperature can be used (in this embodiment, It is a numerical value determined in advance so as not to exceed 250 ° C.).

  By rotating the fixing motor 29 at a high speed during start-up as in this embodiment, the speed of the start-up time is compared with the case where the speed of the conventional fixing motor is set at the same speed V1 as that for fixing the toner image. Shortening can be achieved. That is, the switching temperature of S3-3 can be set to a higher temperature, and the energization power of S3-4 can be increased, so that the startup time can be shortened.

  Further, the optimum values of the switching temperature T4 and the energization power vary depending on the fixing nip width, the thermal conductivity of the material used for the elastic layer of the fixing belt 20, and the like. A numerical value will be obtained in advance.

  Furthermore, even in the same configuration, it is necessary to determine a numerical value in consideration of variations between fixing devices and an ambient environment at the time of start-up.

  Since it is necessary to determine the conditions of the switching temperature and the energized power in accordance with such bad conditions, the startup time is slightly longer than in the first embodiment, but even in the configuration without the sub-thermistor 19, The raising time can be shortened.

  1) In Examples 1 to 3, the heating element 16 is not limited to a ceramic heater. An electromagnetic induction heat generating member, a high frequency absorption heat generating member, or the like may be used.

  2) The first rotating body 20 may be a cylindrical or endless resin film member or a belt member.

  3) The second rotating body 22 is not limited to the pressure roller, and may be a cylindrical or endless film member or belt member. Moreover, it is also possible to adopt a device configuration in which a heating body is also provided inside the second rotating body 22 for heating.

3 is a flowchart of fixing device start-up control in Embodiment 1. FIG. 3 is a diagram illustrating a control state of temperatures and speeds of each unit of the fixing device in the control of Embodiment 1. 1 is a schematic configuration diagram of an image forming apparatus in Embodiment 1. FIG. FIG. 2 is a schematic cross-sectional model view of a main part of the fixing device in Embodiment 1. FIG. 3 is a schematic perspective model view of a main part of the fixing device according to the first exemplary embodiment. 2 is a schematic configuration diagram of a heating body of a fixing device in Embodiment 1. FIG. 6 is a flowchart illustrating a fixing device start-up control according to a second exemplary embodiment. FIG. 10 is a diagram illustrating a control state of temperatures and speeds of various parts of the fixing device in the control of Embodiment 2. FIG. 10 is a schematic cross-sectional model view of a main part of a fixing device in Embodiment 3. FIG. 10 is a schematic perspective model view of a main part of a fixing device in Embodiment 3. 6 is a flowchart illustrating a fixing device start-up control according to a third exemplary embodiment. FIG. 10 is a diagram illustrating control states of temperatures, speeds, and the like of various parts of the fixing device in the control according to the third exemplary embodiment. 7 is a flowchart of conventional fixing device start-up control. FIG. 10 is a diagram illustrating control states of temperatures, speeds, and the like of various parts of the fixing device in conventional control.

Explanation of symbols

1M, 1C, 1Y, 1Bk Image forming units 2a, 2b, 2c, 2d Photosensitive drums 3a, 3b, 3c, 3d Charging rollers 4a, 4b, 4c, 4d Developing devices 5a, 5b, 5c, 5d Transfer rollers 6a, 6b, 6c, 6d Drum cleaning device 12 Fixing device 16 Ceramic heater (heating body)
18 Main thermistor (first temperature detection means)
19 Sub-thermistor (second temperature detection means)
20 Fixing belt (first rotating body)
21 Power supply (power supply unit)
22 Pressure roller (second rotating body)
40 Intermediate transfer belt 44 Secondary transfer roller 45 Belt cleaning device 46 Registration roller 50 Environmental sensor 51 Media sensor P Recording material N (Primary) transfer portion M (Secondary) transfer portion t Toner

Claims (5)

A heating body that generates heat upon receiving power supply, a power supply unit that supplies power to the heating body, a first rotating body that is heated by the heating body, and a press contact portion with the first rotating body are formed. A second rotator, a drive source for rotationally driving the second rotator, first temperature detecting means for detecting the temperature of a portion different from the heating body, and control means for controlling the apparatus. The control means feedback controls the power supplied from the power supply unit to the heating body based on the temperature detected by the first temperature detection means, thereby controlling the temperature of the first rotating body. In the image heating apparatus for performing image heating by sandwiching and conveying the recording material carrying the image at the press contact portion,
When the apparatus is started up, the control means has a temperature detected by the first temperature detection means that is lower than a first temperature T1 that is a target temperature for temperature control when performing image heating. Until the second temperature T2 is reached, the rotational speed of the driving source is controlled to a second speed V2 that is a setting speed different from the first speed V1 that is a setting rotational speed at the time of image heating execution. Image heating device.   The image heating apparatus according to claim 1, wherein the second speed V2 is higher than the first speed V1.   Second temperature detection means for detecting the temperature of the heating body is provided, and the control means is detected by the second temperature detection means while the drive source is driven at the second speed V2. The temperature of the heating body is controlled by feedback control of the power supplied from the power supply unit to the heating body based on the measured temperature, and the speed of the drive source is switched to the first speed V1, and then the first The temperature control of the first rotating body is performed by feedback control of the power supplied from the power supply unit to the heating body based on the temperature detected by the temperature detecting means. 2. The image heating apparatus according to 2. A heating body that generates heat upon receiving power supply, a power supply unit that supplies power to the heating body, a first rotating body that is heated by the heating body, and a press contact portion with the first rotating body are formed. A second rotator, a drive source for rotationally driving the second rotator, first temperature detecting means for detecting the temperature of a portion different from the heating body, and control means for controlling the apparatus. The control means feedback controls the power supplied from the power supply unit to the heating body based on the temperature detected by the first temperature detection means, thereby controlling the temperature of the first rotating body. In the image heating apparatus for performing image heating by sandwiching and conveying the recording material carrying the image at the press contact portion,
A second temperature detection unit configured to detect the temperature of the heating body, and the control unit detects a temperature detected by the second temperature detection unit when starting up the apparatus; Until the third temperature T3, which is a set temperature higher than the first temperature T1, which is the control target temperature, is reached, the rotational speed of the drive source is set to be higher than the first speed V1, which is the set rotational speed when performing image heating. Is driven at a low third speed V3, and the temperature detected by the first temperature detecting means after the temperature detected by the second temperature detecting means reaches the third temperature T3. Control is performed so as to drive at the second speed V2, which is a higher speed than the first speed V1, until the second temperature T2, which is a temperature set lower than the first temperature, is reached. Image heating device.   An image forming apparatus comprising: an image forming unit that forms an unfixed image on a recording material; and a fixing unit that heats a recording material carrying the unfixed image to fix the unfixed image on the recording material. An image forming apparatus according to claim 1, wherein the image forming apparatus is an image heating apparatus according to claim 1.