JP6003391B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic fixing device and an image forming apparatus.

  As an electrophotographic image forming apparatus that forms an image on a recording medium using toner, a toner image formed on an image carrier is transferred onto the recording medium, and then the recording medium is sandwiched using a fixing device. There is known a system in which an image is fixed on a recording medium by heating and pressing.

  Known fixing devices include a heating rotator that heats a fixing surface of a recording medium onto which a toner image has been transferred, and a pressure member that supports and pressurizes the back surface. In the fixing apparatus, the recording medium is sandwiched between a heating rotator and a pressure member, the fixing surface of the recording medium is heated by the heating rotator, and the contact portion is pressurized by the opposing pressure member, thereby melting the unfixed toner. The image is permeated into the recording medium and fixed on the recording medium.

  As a heating rotator, there are known a fixing device and an image forming apparatus provided with a heating roll provided with a heat source such as a plurality of halogen lamps and heaters having different heating ranges according to the width of the recording medium (for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-244465

  An object of the present invention is to provide a fixing device and an image forming apparatus in which a temperature difference between a central portion and an end portion of a heating rotator is reduced and fixing property is improved.

  In order to solve the above-described problem, the invention according to claim 1 is a heating rotating body that is in contact with a recording medium that moves while holding an unfixed toner image on the surface; and the recording medium is connected to the heating rotating body. A pressure member sandwiched therebetween, a first heating means for heating the central portion in the axial direction of the heating rotator, and a second heating means for heating the central portion and end portions in the axial direction of the heating rotator. A first detector that is disposed at the central portion of the heating rotator and detects the temperature of the central portion; and a second detector that is disposed at the end of the heating rotator and detects the temperature of the end. And a third detection unit that is disposed in a region opposite to the end of the heating rotator that does not contact the recording medium and detects the temperature of the region. Temperature difference detected by the second detection unit and the second detection unit is the third difference Becomes a predetermined threshold value corresponding to the temperature detected by the detecting unit, a fixing device, characterized in that switching to one of said first heating means or said second heating means.

The invention according to claim 2 is the fixing device according to claim 1, wherein in response to at least one of the differences of the paper width or paper quality of the recording medium, wherein the threshold is changed.

According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the first detection unit and the second detection unit are non-contact type detection units, and the third detection unit The detection unit is a contact type detection unit.

According to a fourth aspect of the present invention, there is provided an image forming unit that forms an image by transferring toner to an image carrier having a latent image formed on the surface by a difference in electrostatic potential, and the image formed by the toner is directly or intermediately transferred. A transfer device that transfers the recording medium onto a recording medium via a body, and a fixing device according to any one of claims 1 to 3 that heats and fixes a toner image transferred onto the recording medium. A plurality of predetermined threshold values corresponding to temperatures detected by the third detection unit are stored, and a difference between temperatures detected by the first detection unit and the second detection unit is And a control unit that performs control to switch to either the first heating unit or the second heating unit when the threshold value is predetermined by the temperature detected by the third detection unit. An image forming apparatus characterized by the above.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the control unit changes the threshold value according to at least one of a paper width or a paper quality of the recording medium. And

  In the fixing device according to claim 1, the center of the heating rotator in the width direction of the recording medium is compared with a case where switching is performed based on a difference in temperature detected by the first detection unit and the second detection unit. The temperature difference between the portion and the end portion is reduced, and a fixing device with improved fixing properties can be obtained.

In the fixing device according to claim 2, the temperature difference between the central portion and the end portion in the width direction of the recording medium of the heating rotator is reduced compared to the fixing device not provided with this configuration, and the fixing property is improved. An improved fixing device is obtained.

In the fixing device according to the third aspect , an excessive increase in the temperature of the heating rotator is suppressed.

In the image forming apparatus according to claim 4 Contact and claim 5, the image forming apparatus can be obtained with the aforementioned effects.

1 is a schematic configuration diagram illustrating a full-color printer that is an embodiment of the invention according to the present application. FIG. 2 is a schematic cross-sectional view of a fixing device used in a full color printer. FIG. 3 is a schematic perspective view of a main part of the fixing device. FIG. 2 is a schematic plan view of a fixing device. It is a figure which shows an example of the temperature distribution in a heating roller.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a tandem full-color printer as an image forming apparatus to which a fixing device 100 according to an embodiment of the present invention is applied. Note that this tandem full-color printer includes an image reading device, and functions as a full-color copying machine. Of course, the full-color printer does not have to include an image reading device.

In FIG. 1, the full-color printer includes a full-color printer main body 1, and a scanner 2 as an image reading device (IIT: Image Input Terminal) that reads an image of a document is disposed on the upper portion of the full-color printer main body 1. In the figure, the document is not shown.
The scanner 2 illuminates a document conveyed on a platen glass 5 by an automatic document feeder (ADF) 3 with a light source 6, and reflects a reflected light image from the document into a full-rate mirror 7 and a half-rate mirror 8, The image reading element 11 made of a CCD or the like is scanned and exposed through a reduction optical system consisting of the image forming lens 10 and the image forming lens 10, and an image of the original is scanned at a predetermined dot density (for example, 1200 dpi or 2400 dpi) by the image reading element 11. read.

  The document image read by the scanner 2 is sent to an image processing apparatus (Image Processing System) (not shown) as image data of three colors of red (R), green (G), and blue (B) (each 8 bits), for example. In the image processing apparatus, predetermined image processing such as shading correction, position shift correction, lightness / color space conversion, gamma correction, frame erasure, color / movement editing, and the like is performed on image data of a document.

  The image data subjected to the predetermined image processing by the image processing apparatus as described above is image data of four colors of cyan (C), magenta (M), yellow (Y), and black (K) (each 8 bits). As described below, ROS (RasterOutputScanner) corresponding to the image forming units 13C, 13M, 13Y, and 13K for each color of cyan (C), magenta (M), yellow (Y), and black (K) is used. The images are sent to certain 14C, 14M, 14Y, and 14K, and 14C, 14M, 14Y, and 14K perform image exposure with the laser beam LB in accordance with the image data of each color.

Inside the full-color printer main body 1, four image forming units 13C, 13M, 13Y, and 13K of cyan (C), magenta (M), yellow (Y), and black (K) are spaced at regular intervals in the horizontal direction. Are arranged in series.
The four image forming units 13C, 13M, 13Y, and 13K are basically configured in the same manner. Broadly speaking, the photosensitive drum 15 that rotates at a predetermined speed and the surface of the photosensitive drum 15 are uniform. A primary charging scorotron 16 (which may be a charging roll), an ROS 14 that exposes an image corresponding to each color on the surface of the photosensitive drum 15 to form an electrostatic latent image, and a photosensitive The image forming apparatus includes a developing device 17 that develops the electrostatic latent image formed on the body drum 15 with a corresponding color toner, and a cleaning device 18.

In FIG. 1, when the reference numerals of the same components are attached, there are places where the reference numerals are omitted.
In this embodiment, the diameter of the photosensitive drum 15 used in the black (K) color image forming unit 13K is larger than that of the photosensitive drums 15 of the other color image forming units 13C, 13M, and 13Y. Is set.

  The ROS 14 of each color modulates the semiconductor laser 19 according to the image data, and emits a laser beam LB from the semiconductor laser 19 according to the image data. The laser beam LB emitted from the semiconductor laser 19 is deflected and scanned by the rotary polygon mirror 22 via the reflecting mirrors 20 and 21, and the focal length is adjusted according to the scanning angle by an unshown f-θ lens. Then, scanning exposure is performed on a photosensitive drum 15 as an image carrier through a plurality of reflecting mirrors 23 and 24.

  From the image processing device, cyan (C), magenta (M), yellow (Y), and black (K) image forming units 13C, 13M, 13Y, and 13K ROSs 14C, 14M, 14Y, and 14K The image data of each color is sequentially output, and the laser beam LB emitted according to the image data from these ROSs 14C, 14M, 14Y, and 14K is scanned and exposed on the surface of the photoconductor drum 15 of each color and electrostatically discharged. A latent image is formed. The electrostatic latent images formed on the photosensitive drums 15 of the respective colors are converted into toner images of the respective colors of cyan (C), magenta (M), yellow (Y), and black (K) by the developing devices 17 of the respective colors. Developed.

The cyan (C), magenta (M), yellow (Y), and black (K) toner images sequentially formed on the photosensitive drums 15 of the image forming units 13C, 13M, 13Y, and 13K are illustrated in FIG. As shown in FIG. 1, the images are superposed on each other by primary transfer rolls 26C, 26M, 26Y, and 26K on an intermediate transfer belt 25 as an intermediate transfer member disposed below each of the image forming units 13C, 13M, 13Y, and 13K. It is transcribed in a state.
The intermediate transfer belt 25 is wound around the drive roll 26, the tension roll 28, the steering roll 29, the idle roll 30, the backup roll 31, and the idle roll 32 with a constant tension, and is not illustrated. The drive roll 26 is rotationally driven by a dedicated drive motor excellent in constant speed, and is circulated and driven at a predetermined speed equal to that of the photosensitive drum 15. As the intermediate transfer belt 25, for example, a flexible synthetic resin film such as polyimide is formed in an endless belt shape.

  The cyan (C), magenta (M), yellow (Y), and black (K) toner images transferred in multiple onto the intermediate transfer belt 25 are pressed against the backup roll 31 via the intermediate transfer belt 25. The recording paper P, which is secondarily transferred onto the recording paper P as a recording medium by the secondary transfer roll 33 with a pressing force and an electrostatic force, and moves while holding an unfixed toner image of each color on the surface, It is conveyed to the fixing device 100 by the conveyance belt 35. Then, the recording paper P on which the toner images of the respective colors are transferred is subjected to fixing processing by heat and pressure by the fixing device 100. In the case of single-sided printing, the recording paper P is directly on the discharge tray 37 provided outside the full-color printer main body 1. To be discharged.

  As shown in FIG. 1, the recording paper P has a predetermined size or material from any of a plurality of paper trays 38, 39, 40, 41, and includes a paper feed roller 42 and a pair of paper transport rollers 43. , 44 and 45, the paper is once transported to the registration roll 47 through the paper transport path 46 and stopped. The recording paper P supplied from any one of the paper trays 38, 39, 40, and 41 is sent to the secondary transfer position of the intermediate transfer belt 25 by a registration roll 47 that is rotationally driven at a predetermined timing.

  Further, when images are formed on both sides of the recording paper P by a full-color printer, the recording paper P on which the image is fixed on one side by the fixing device 100 is not discharged out of the apparatus as it is, but by a switching gate (not shown). The conveyance path of the recording paper P is switched downward and once conveyed to the reversal paper conveyance path 48. Then, the recording paper P conveyed to the reversing paper conveyance path 48 is turned upside down via the double-sided paper conveyance path 49 and the normal paper conveyance path 46 with the conveyance direction reversed. In this state, the sheet is conveyed again to the secondary transfer position of the intermediate transfer belt 25, and after an image is formed on the back surface, the fixing device 100 is subjected to a fixing process with heat and pressure, and is provided outside the full-color printer main body 1. It is discharged onto the discharged discharge tray 37.

  Further, the full-color printer main body 1 includes an arithmetic device such as a CPU (Central Processing Unit) and a memory, and includes a control unit 70 that controls the operation of each component of the image forming apparatus 10.

FIG. 2 is a cross-sectional view showing fixing device 100 according to the embodiment of the present invention.
In FIG. 2, the fixing device 100 according to the embodiment includes three first heaters 130 as first heating means, a second heater 131 as second heating means, and a third heater. A heating roll 110 as a heating rotator having a heater 132 and an endless belt 120 as a pressure member that forms a fixing nip portion N by sandwiching the recording paper P between the heating roll 110 and press-contacting the recording paper P are provided. Yes.
The heating roll 110 is driven to rotate at a predetermined rotational speed by a drive motor 57 via a gear (not shown).

  The endless belt 120 is pressed against the surface of the heating roll 110 with a predetermined pressure contact force by a pressing member 121 disposed therein. Specifically, the pressing member 121 is urged so as to be in pressure contact with the surface of the heating roll 110 by the elastic repulsive force of the coil spring 122. Further, the surface of the pressing member 121 is covered with a sheet-like low friction member in order to reduce sliding resistance with the endless belt 120, and the inner surface of the endless belt 120 is a liquid lubricant supply member. The felt member 123 is disposed. The felt member 123 is made of, for example, Nomex (trade name), and the felt member 123 is impregnated with about 2.0 g of oil as a liquid lubricant made of amino Si oil having a viscosity of 300 cs.

The pressing member 121 is mainly composed of an elastic member and a support member made of a metal such as stainless steel that supports the elastic member.
The endless belt 120 is formed in an endless belt shape having an outer diameter of 30 mm and a wall thickness of 75 μm by a synthetic resin such as polyimide, and a release layer made of PFA or the like is provided on the surface as needed. .

  The fixing device 100 includes the heating roll 110 on the heating side and the endless belt 120 on the pressure side, but is not limited to this. The side may be constituted by a belt and the pressure side may be constituted by a roll. Further, both the heating side and the pressure side may be constituted by a belt.

  In FIG. 2, the fixing device 100 includes an inlet chute 58 for guiding recording paper to the fixing nip portion N of the fixing device 100, an outlet chute 59 disposed at the outlet portion of the fixing nip portion N of the fixing device 100, and fixing. An outlet roll 60 disposed at the outlet of the apparatus 100 is provided.

The configuration of the fixing device 100 will be described in detail with reference to FIGS. 3 and 4. FIG. 3 is a schematic perspective view of the main part of the fixing device 100, and FIG. 4 is a schematic plan view of the heating roll 110. The arrows in FIG. 3 indicate the conveyance direction of the recording paper P.
In FIG. 3, the heating roll 110 that comes into contact with the recording paper P is supported so as to be able to rotate about the rotation axis R. For example, a cylindrical metal core 111 having a conductivity wider than the maximum width of the recording paper P to be fixed is provided, and a surface release layer 112 laminated on the metal core. A rotational driving force around the rotation axis R is transmitted to the core metal 111.

  The cylindrical cored bar 111 of the heating roll 110 can be made of metal such as aluminum, iron, and stainless steel having excellent thermal conductivity and rigidity. The surface release layer 112 is formed of a fluororesin tube.

  3 and 4, the heating roll 110 heats the first heater 130 that heats the central portion in the axial direction (rotational axis R direction) of the heating roll 110, and the central portion and the end portion in the axial direction of the heating roll 110. A second heater 131 and a third heater 132 are incorporated.

  In FIG. 4, the first heater 130 has a heating range of 220 mm around the center of the heating roll 110 in the axial direction, for example, the center line C, and the second heater 131 includes the heating roll 110. It has a heating range of 330 mm with the center and the end, for example, the center line C of the heating roll 110 as the center. The third heater 132 has a heating range of 350 mm around the center and end of the heating roll 110, for example, the center line C of the heating roll 110. Also, these heating ranges can be determined by the width of the recording paper P to be used.

Moreover, the heating roll 110 is arrange | positioned in the center part of the heating roll 110, and is arrange | positioned in the edge part of the 1st thermometer 140 as a 1st detection part which detects the temperature of a center part, and the heating roll 110, and ends. And a second thermometer 141 as a second detection unit for detecting the temperature of the unit.
The first thermometer 140 and the second thermometer 141 are non-contact thermometers such as an infrared radiation thermometer so as not to contact the recording paper P when the recording paper P is wound around the heating roll 110. Is preferred.

  Further, the heating roll 110 is arranged on the opposite side of the end of the heating roll 110 where the second thermometer 141 is arranged, in an area that does not come into contact with the recording paper P, and a third temperature for detecting the temperature in this area. A third thermometer 143 is provided as a detection unit. The third thermometer 143 is preferably a contact-type thermometer, such as a thermistor or a thermocouple.

In FIG. 4, for example, the first thermometer 140 is arranged at the center portion 15.5 mm away from the axial center line C of the heating roll 110, and the side opposite to the side on which the first thermometer 140 is arranged. Thus, the second thermometer 141 is disposed at an end portion 138.5 mm away from the center line C. Here, the center part and the end part are relative, and a position near the center line is called a center part, and a position far from the center line is called an end part.
The third thermometer 143 is arranged in a region away from the center line C by 166.5 mm on the side opposite to the side on which the second thermometer 141 is arranged from the axial center of the heating roll 110.

The surface temperature of the heating roll 110 is controlled based on the temperatures detected by the first thermometer 140, the second thermometer 141, and the third thermometer 143. This is performed by switching to one of the heaters 131. These controls are performed by, for example, the control unit 70 shown in FIG.
In the following description, the first heater 130 is used as a sub-heater and the second heater 131 is used as a main heater. However, the third heater 132 may be used as a main heater instead of the second heater 131. Good.

Hereinafter, the control of the surface temperature of the heating roll 110 will be described in detail.
FIG. 5 is a diagram illustrating an example of the surface temperature distribution on the heating roll 110 when the position of the second heater 131 is shifted in the axial direction of the heating roll 110.
The horizontal axis indicates the position of the center line C in the axial direction of the heating roll 110 shown in FIG. 4 as 0, the position on the side where the third thermometer 142 is disposed is a positive value, and the second thermometer 141 The position on the side where is placed is indicated by a negative value. The vertical axis represents the surface temperature.

The position of the first heater 130 shifts due to variations in manufacturing, maintenance such as replacement of the heating roll 110, and the surface temperature distribution on the heating roll 110 changes.
The solid line in FIG. 5 indicates that the position of the first heater 130 is shifted by 5.1 mm on the side where the third thermometer 142 is disposed, and the broken line is 2.1 mm on the side where the third thermometer 142 is disposed. In the case of misalignment, the one-dot chain line is shifted 2.1 mm to the side where the second thermometer 141 is disposed, and the two-dot chain line is deviated 2.1 mm to the side where the second thermometer 141 is disposed. Represents.
In FIG. 5, it can be seen that the temperature in the direction in which the first heater 130 is shifted is high and the temperature in the opposite direction is low.

In the embodiment, the difference between the temperature T 1 detected by the first thermometer 140 and the temperature T 2 detected by the second thermometer 141 is predetermined by the temperature T 3 detected by the third thermometer 142. The threshold value T is switched to one of the first heater 130 and the second heater 131.
The threshold value T changes in accordance with the displacement of at least one of the first heater 130 and the second heater with respect to the axial direction of the heating roll 110.
Further, since the surface temperature distribution varies depending on the paper quality and paper width of the recording paper P passing through, the threshold value T varies depending on the paper quality and paper width of the recording paper P.

Example 1
For example, Table 1 shows threshold values T for recording paper P with a paper width of 240 mm or more and 289.9 mm or less with the arrangement of each component shown in FIG.

  In Table 1, the threshold value T is determined for each temperature region of the temperature T3 detected by the third thermometer 142. For example, the threshold values T are determined to be -15, -23, and -30, respectively, according to three temperature ranges where T3 is higher than 220 ° C, T3 is higher than 214 ° C and lower than 220 ° C, and T3 is lower than 214 ° C. Yes.

When T3 is higher than 220 ° C, the temperature difference (T1-T2) between the temperature T1 detected by the first thermometer 140 and the temperature T2 detected by the second thermometer 141 becomes smaller than -15 ° C. If the absolute value of the temperature difference becomes large, the heater to be operated is switched from the second heater 131 to the first heater 130.
Here, in Table 1, the first heater 130 is denoted as sub, and the second heater 131 is denoted as main.

  When T3 is higher than 214 ° C and lower than or equal to 220 ° C, when (T1-T2) becomes lower than -23 ° C, the heater to be operated is switched from the second heater 131 to the first heater 130.

  When T3 is 214 ° C. or lower, when (T1-T2) becomes smaller than −30 ° C., the heater to be operated is switched from the second heater 131 to the first heater 130.

For example, as a control method, first, the temperatures T1, T2, and T3 detected by the first thermometer 140, the second thermometer 141, and the third thermometer 142 are sent to the control unit 70 of the image forming apparatus 10. Is entered.
The control unit 70 calculates the temperature difference between the temperature T1 detected by the first thermometer 140 and the temperature T2 detected by the second thermometer 141, and the temperature T3 detected by the third thermometer 142. The threshold value T is selected based on The temperature difference (T1-T2) is compared with the threshold value T, and the heating means to be used is switched to either the first heater 130 or the second heater 131.
When the temperature difference (T1-T2) is equal to or greater than the threshold value T, the first heater 130 is switched. When the temperature difference (T1-T2) is less than the threshold value T, the second heater 131 is switched.

When the temperature T3 detected by the third thermometer 142 is high, the temperature range (T1-T2) is changed from a small temperature to the first heater 130 that heats the central portion, so that the heating range becomes the central portion. It changes and the surface temperature distribution approaches uniform.
On the other hand, when the temperature T3 detected by the third thermometer 142 is low, the temperature difference (T1−T2) is heated by the second heater 131 that heats the center and the end when the temperature difference (T1−T2) is small. When (T1-T2) is large, the heating range is changed to the center by switching to the first heater 130, and the surface temperature distribution approaches uniformly.

  The recording paper P may be selected from an operation panel (not shown) provided in the image forming apparatus 10, or a sensor for detecting the width and paper quality of the recording medium instead of information input from the operation panel by the operator. You may perform using a detected value.

Further, the threshold value T can be changed according to the paper weighing (gsm) and the paper width (mm).
Table 2 shows an example of the threshold value T corresponding to the paper weighing G (gsm) and the paper width W (mm) as the paper quality.

(Example 2)
Table 3 shows the threshold value T in Example 2. Example 2 is an example in which the paper weighing G in Table 2 is 177 gsm or less and the paper width W is 290 mm or more.

  When T3 is larger than 220 ° C., if the difference (T1−T2) between the temperature T1 detected by the first thermometer 140 and the temperature T2 detected by the second thermometer 141 becomes smaller than −5 ° C. That is, when the temperature difference becomes large, the heater to be operated is switched from the second heater 131 to the first heater 130.

  When T3 is higher than 214 ° C and lower than or equal to 220 ° C, when (T1-T2) becomes lower than -10 ° C, the heater to be operated is switched from the second heater 131 to the first heater 130.

  When T3 is 214 ° C. or lower, when (T1-T2) becomes smaller than −15 ° C., the heater to be operated is switched from the second heater 131 to the first heater 130.

(Example 3)
Table 4 shows the threshold value T in Example 3. Example 3 is an example in which the paper weighing G in Table 2 is larger than 177 gsm and the paper width W is 290 mm or more.

  When T3 is larger than 220 ° C., if the difference (T1−T2) between the temperature T1 detected by the first thermometer 140 and the temperature T2 detected by the second thermometer 141 becomes smaller than −2 ° C. That is, when the temperature difference becomes large, the heater to be operated is switched from the second heater 131 to the first heater 130.

  When T3 is higher than 214 ° C and lower than or equal to 220 ° C, when (T1-T2) becomes lower than -5 ° C, the heater to be operated is switched from the second heater 131 to the first heater 130.

  When T3 is 214 ° C. or lower, when (T1-T2) becomes smaller than −10 ° C., the heater to be operated is switched from the second heater 131 to the first heater 130.

  A material generally used as the recording paper P of an object for forming an image is a sheet-like material such as a recording paper, a cardboard, a transparent sheet, or a plastic sheet such as an OHP sheet. In addition to these, a bag-like object represented by an envelope can also be used.

The embodiment described above has the following effects.
(1) Switching between the first heater 130 that heats the central portion of the heating roll 110 and the second heater 131 that heats the central portion and the end portion is switched between the first thermometer 140 disposed at the central portion and the end. In addition to the temperature difference detected by the second thermometer 141 disposed in the section, the temperature is detected in advance corresponding to the temperature detected by the third thermometer 142 disposed in the area opposite to the end. This is also performed based on a predetermined threshold T. Therefore, compared with the case where switching is performed based on the difference in temperature detected by the first thermometer 140 and the second thermometer 141, it is based on the temperature detected in a wide range in the axial direction of the heating roll 110. Therefore, the heating means can be switched based on the temperature distribution closer to the actual temperature distribution. As a result, the temperature difference between the central portion and the end portion of the heating roll 110 in the width direction of the recording paper P can be reduced, and the fixing device 100 with improved fixing performance can be obtained.

(2) At least one heating roll 110 of the first heater 130 or the second heater 131 is displaced in the axial direction due to variations in manufacturing, replacement of the heating roll 110, and the like. Even if a temperature difference occurs between the central portion and the end portion in the width direction of the 110 recording paper P, the threshold value T also changes according to the deviation. Therefore, the heating unit can be switched more appropriately, the temperature difference between the central portion and the end portion of the heating roll 110 in the width direction of the recording paper P can be reduced, and the fixing device 100 with improved fixing performance can be obtained. it can.

(3) When at least one of the paper width or quality of the recording paper P changes, the temperature difference in the axial direction of the heating roll 110 changes due to the change in the contact range of the recording paper P with the heating roll 110 and the heat capacity of the recording paper P. Even when this occurs, the threshold value T changes in accordance with at least one of the paper width and the paper quality of the recording paper P. Accordingly, the heating means can be switched according to at least one of the paper width and the paper quality of the recording paper P, and the temperature difference between the center portion and the end portion of the heating roll 110 in the width direction of the recording paper P is reduced. Thus, the fixing device 100 with improved fixing properties can be obtained.

(4) The third thermometer 143 is a contact-type thermometer and is in the region of the heating roll 110 that does not contact the recording paper P. Therefore, even if the recording paper P is wound around the heating roll 110, Temperature can be detected. Therefore, the temperature detected by the third thermometer 143 can be used to set the threshold T for switching to one of the first heater 130 and the second heater 131, and the third thermometer By monitoring the temperature detected at 143, an excessive increase in temperature of the heating roll 110 can be suppressed.

(5) A full-color printer having the above-described effects can be obtained.

The embodiment described above can also be applied to a monochrome image forming apparatus. Even when a color image is formed, a toner image is superimposed on one photosensitive drum, or a toner image sequentially formed on one photosensitive drum is superimposed on an intermediate transfer member. The present invention can be applied to various types of image forming apparatuses.
Further, the fixing device 100 uses the first heater 130, the second heater 131, and the third heater 132 as heating means. However, in addition to the heater, for example, another heating source such as a halogen lamp is used. Can do.
Thus, the present invention is not limited to the above-described embodiments, and can be implemented as other forms within the scope of the present invention.

1 Full Color Printer Body 13 Image Forming Unit 14 ROS
15 Photosensitive drum 16 Scorotron 17 Developing device 18 Cleaning device 38, 39, 40, 41 Paper tray 70 Control unit 100 Fixing device 110 Heating roll 111 Cylindrical core metal 112 Surface release layer 120 Endless belt 130 First heater 131 First Second heater 132 Second heater 140 First thermometer 141 Second thermometer 143 Third thermometer N Fixing nip P Recording paper

Claims (5)

A heating rotator in contact with a recording medium that moves while holding an unfixed toner image on the surface;
A pressure member that sandwiches the recording medium with the heating rotator, and
First heating means for heating a central portion in the axial direction of the heating rotator;
A second heating means for heating a central portion and an end portion in the axial direction of the heating rotating body;
A first detector that is disposed in the central portion of the heating rotator and detects the temperature of the central portion;
A second detector that is disposed at the end of the heating rotator and detects the temperature of the end;
A third detection unit that is disposed in a region opposite to the end of the heating rotator that does not contact the recording medium, and that detects the temperature of the region;
When the difference in temperature detected by the first detection unit and the second detection unit becomes a predetermined threshold corresponding to the temperature detected by the third detection unit,
The fixing device is switched to either the first heating unit or the second heating unit. In response to at least one of the differences of the paper width or paper quality of the recording medium, the fixing device according to claim 1, wherein the threshold is changed. Said first detector and said second detector is a detector of non-contact type, the third detecting unit, according to claim 1 or claim characterized in that it is a detector of the contact type 3. The fixing device according to 2 . An image forming unit that forms an image by transferring toner to an image carrier on which a latent image due to a difference in electrostatic potential is formed on the surface;
A transfer device for transferring an image of the toner directly or via an intermediate transfer member onto a recording medium;
The fixing device according to any one of claims 1 to 3, wherein the toner image transferred onto the recording medium is heated and fixed.
A plurality of predetermined threshold values corresponding to temperatures detected by the third detection unit are stored, and a difference between temperatures detected by the first detection unit and the second detection unit is A control unit that performs control to switch to either the first heating unit or the second heating unit when the predetermined threshold is reached according to the temperature detected by the third detection unit. An image forming apparatus. The image forming apparatus according to claim 4, wherein the control unit changes the threshold according to at least one of a paper width and a paper quality of the recording medium.

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