JP2007316463A - Belt fixing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt fixing unit which can provide satisfactory fixing performance up to the end of a nip section of the fixing belt in spite of starting paper feeding from a long standby state and can provide stable traveling property of the fixing belt. <P>SOLUTION: At the start of the continuous paper feeding after the long-time standby state, the ON/Off control of a heater lamp 5a having the light distribution uniform both in the central part and both end parts within a heating roller 5 based on the detection temperature of a contactless type thermistor 7 disposed in the central part of the fixing belt 2 is performed while a main motor 21 is actuated, and based on the detection temperature of a contact type thermistor 8 disposed outside the largest paper feed area of the fixing belt 2, a heater lamp 5a inside the heating roller 5 and a second heater lamp 6b higher in the light distribution in both end parts within an inside heating roller 6 than the central part are subjected to the ON/OFF control by alternate switching of the heater lamps. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing belt type fixing device used in an image forming apparatus such as a copying machine or a laser printer.

  Generally, a fixing method of a fixing device provided in an image forming apparatus such as a copying machine or a printer is a method in which an unfixed toner image is fixed on a sheet by heating and pressing. In recent years, in addition to such a heat pressure roller type fixing device, a fixing belt type fixing device using a thin-walled (low heat capacity type) fixing belt is known. The fixing belt fixing device includes a fixing roller and a heating roller, an endless fixing belt stretched between the two rollers, and a pressure roller provided to face the fixing roller through the fixing belt. is doing.

  The unfixed toner image on the paper conveyed to the belt fixing device is pressed and fixed by a nip portion formed between the fixing roller and the pressure roller via the heating and fixing belt. Here, as the fixing roller and the pressure roller, a rubber roller is used in which a thick rubber layer (elastic layer) having a large heat capacity is arranged on the outer periphery of a central cylindrical metal core.

  When an image forming apparatus equipped with such a belt fixing device is in a standby state, the fixing roller and the pressure roller cause heat to escape from the bearing portion supporting them to the side plate supporting them. The temperature at both ends of each roller in the roller axial direction generally decreases.

  Therefore, when continuous sheet feeding is started in the belt fixing device in such a state, the temperature at both ends in the roller axial direction of the nip portion of the fixing belt becomes lower than the temperature necessary for obtaining good fixability. As a result, gloss unevenness and poor fixing may occur at the edge of the paper.

Therefore, as a countermeasure, Patent Document 1 discloses a heater lamp in which the heating amount (light distribution distribution) at both ends provided in the fixing roller and the pressure roller is larger than that in the central portion, and the heating roller. Two heater lamps having a heating amount (light distribution distribution) at both ends provided in the interior that is smaller than that in the central portion, and when the image forming apparatus is in a standby state, a heater lamp inside the fixing roller; By turning on at least one of the heater lamps inside the pressure roller and increasing the heating amount at both ends of the nip portion of the fixing belt from the central portion, both ends of the nip portion of the fixing belt after the start of paper feeding The temperature is not lowered to a temperature at which the fixability deteriorates. When small-size paper is fed into the nip portion, the heater lamps inside the fixing roller and the pressure roller are turned off, and the two heater lamps inside the heating roller are turned on, so that the fixing belt during continuous paper feeding is turned on. The temperature rise at both ends is suppressed.
Japanese Patent Laying-Open No. 2005-17757 (paragraphs 0022, 0026, FIG. 1 and FIG. 3)

  However, according to the belt fixing device proposed in Patent Document 1, since the fixing roller and the pressure roller have thick elastic layers, the elastic layer at the core metal interface inside the fixing roller becomes high in the standby state. There is a problem that the elastic body causes curing deterioration and liquefaction, and the life is shortened. Further, during continuous passage of small-size paper, there is a problem that temperature unevenness occurs on the surface of the fixing belt having a low heat capacity at the portion wound around the heating roller, and the running performance of the fixing belt becomes unstable.

  The present invention has been made in view of the above-described problems. Even when paper feeding is started from a long standby state, good fixing performance can be obtained up to the end of the nip portion of the fixing belt. An object of the present invention is to provide a belt fixing device capable of obtaining stable running performance.

  In order to achieve the above object, the present invention spans between a pair of fixing rollers and a pressure roller arranged opposite to each other, a heating roller containing a heat source, and the fixing roller and the heating roller. A fixing belt formed of an endless belt; and an internal heating roller including first and second heat sources that are driven to rotate together with the fixing roller and heat the surface of the fixing roller in a hollow portion formed inside the fixing belt. A driving means for rotationally driving the fixing roller; and the driving means for rotationally driving the fixing roller and heating the fixing belt by the heating roller, whereby a nip portion between the fixing belt and the pressure roller. In a belt fixing device that heats and fixes a paper carrying a fixed toner image on it, the heat source inside the heating roller is at both ends and the center. The first heat source inside the internal heating roller has a light distribution distribution whose both ends are lower than the central portion, and the second heat source inside the internal heating roller has both ends at the both ends. It has a light distribution that is higher than the central portion.

  In a conventional belt fixing device, the heat source controls the fixing belt temperature using only the heat source inside the heating roller. The heat source inside the heating roller has a uniform light distribution at both ends and the center. However, if the standby state continues for a long time, heat loss at both ends of the fixing roller is large, and the fixing belt winds at the fixing roller winding portion. The heat at both end portions of the fixing belt is deprived, and temperature unevenness occurs in which the temperature at both end portions of the nip portion of the fixing belt is lower than that at the central portion. On the other hand, when small-size paper is continuously fed, the temperature rises significantly at both ends of the fixing belt, and contrary to the above, temperature unevenness occurs in which the temperature at both ends of the nip portion of the fixing belt is higher than that at the center. .

  According to the belt fixing device of the present invention, the first heat source inside the internal heating roller has a light distribution that contradicts the temperature unevenness that occurs in the nip portion of the fixing belt when continuously passing small size paper, and the internal heating roller The internal second heat source has a light distribution that contradicts the temperature unevenness generated in the nip portion of the fixing belt during standby. Therefore, at the start of continuous paper feeding, the heat source inside the heating roller is switched from the heat source inside the heating roller to the second heat source inside the internal heating roller as necessary. By switching from this heat source to the first heat source inside the internal heating roller, it becomes possible to eliminate temperature unevenness, and belt running performance and fixing performance are stabilized.

  Specifically, according to the present invention, the internal temperature of the heating roller is determined based on the temperature detected by the belt temperature detecting means provided at the center of the fixing belt while operating the driving means at the start of continuous paper feeding after a long standby state. And the second heat source inside the heating roller and the second heat source inside the inner heating roller based on the detected temperature of the belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt. It is characterized by ON / OFF control by alternate switching.

  For example, at the start of continuous paper feeding after a long standby state, in order to eliminate the temperature unevenness in which the temperature at both ends of the nip portion of the fixing belt decreases, the light distribution is even at both the center and both ends inside the heating roller. By turning off the heat source having the distribution and turning on the second heat source in which the light distribution distribution at both ends inside the internal heating roller is higher than the center portion, the temperature at both ends of the fixing roller is raised, and the nip portion of the fixing belt Increase the temperature at both ends. Thereafter, when the belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt detects a predetermined temperature or more, the second heat source inside the internal heating roller is turned off, the heat source inside the heating roller is turned on, and the fixing belt When the belt temperature detecting means provided outside the maximum sheet passing area detects a temperature below a predetermined temperature, the second heat source inside the internal heating roller is turned on and the heat source inside the heating roller is turned off. By alternately performing the above operations, the temperature unevenness at the nip portion of the fixing belt is eliminated, and the fixing property at both ends of the sheet is improved and the belt running property is stabilized.

  More specifically, the present invention provides a heat source inside the heating roller based on the temperature detected by the belt temperature detecting means provided at the center of the fixing belt while operating the driving means during continuous passage of small size paper. ON / OFF control of the heat roller, and switching between the heat source between the heat source inside the heating roller and the first heat source inside the internal heating roller based on the detected temperature of the belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt It is characterized by ON / OFF control by.

  For example, in order to eliminate temperature unevenness in which the temperature at both ends of the nip portion of the fixing belt becomes high during continuous passage of small size paper, a belt temperature detecting means provided with a heat source inside the heating roller in the center portion of the fixing belt In addition to the ON / OFF control based on the above, when the belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt detects a predetermined temperature or more, the light distribution distribution at both ends inside the internal heating roller is in the center. A belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt is turned on by turning on a first heat source lower than the heat source, turning off a heat source having a uniform light distribution at both the center and both ends inside the heating roller. When the temperature is detected, the first heat source inside the internal heating roller is turned off, and the heat source inside the heating roller is turned on. By alternately performing the above operations, the temperature unevenness at the nip portion of the fixing belt is eliminated, and the fixing property at both ends of the sheet is improved and the belt running property is stabilized. By alternately performing the above operations, the temperature unevenness at the nip portion of the fixing belt is eliminated, and the fixing property at both ends of the sheet is improved and the belt running property is stabilized.

  Also, in the conventional belt fixing device, after continuously passing small size paper using the heat source inside the heating roller, both ends of the fixing belt are overheated, and the temperature at both ends of the nip portion of the fixing belt is increased. Temperature unevenness occurs. Alternatively, after a long standby state as described above, when temperature unevenness occurs at which both ends of the fixing belt are lowered, when only a few sheets of the maximum size are passed, even after the end of the passing, Temperature unevenness before the paper is maintained, and temperature unevenness occurs in which the temperature at both ends of the nip portion of the fixing belt is lowered.

  Therefore, in the present invention, in order to eliminate the temperature unevenness of the fixing belt after the completion of the sheet passing, the belt temperature detecting means provided in the central portion of the fixing belt is operated while the driving means is operated after the sheet passing. On / off control of the heat source inside the heating roller is performed based on the detected temperature, and the first or second heat source inside the internal heating roller is turned on based on the detected temperature of the belt temperature detecting means provided in the center portion of the fixing belt. / OFF control is performed.

  For example, when the temperature at both ends of the nip portion of the fixing belt rises, the ON / OFF control of the heat source inside the heating roller is performed on the basis of the belt temperature detection means provided at the center portion of the fixing belt after the end of paper feeding. In addition, when the belt temperature detecting means provided in the center portion of the fixing belt detects a predetermined temperature or more, the first heat source inside the internal heating roller is turned on, and the fixing belt is driven to rotate, thereby causing temperature unevenness. Can be resolved. Similarly, when the temperature at both ends of the nip portion of the fixing belt is lowered, after the end of paper feeding, the heat source inside the heating roller is controlled to be turned on / off based on the belt temperature detecting means provided at the center portion of the fixing belt. In addition, temperature unevenness can be eliminated by turning on the second heat source inside the internal heating roller and rotationally driving the fixing belt.

  In this case, the temperature unevenness of the fixing belt can be efficiently eliminated by determining the driving time by the belt temperature detecting means provided outside the maximum sheet passing area of the fixing bell.

  According to the present invention, even when paper is started from a long standby state, good fixing performance can be obtained up to the end of the nip portion of the fixing belt, and stable running performance of the fixing belt can be obtained.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram showing a schematic configuration of a belt fixing device 1 according to an embodiment of the present invention. The belt fixing device 1 is installed in a color copying machine (not shown). A color copying machine (not shown) reads an original image by a reading unit, forms a toner image corresponding to the original image on an image forming unit, transfers the image to a sheet, and fixes the toner image transferred to the sheet. The belt fixing device 1 is used when fixing a toner image.

  The belt fixing device 1 according to this embodiment includes a fixing belt 2, a fixing roller 3, a pressure roller 4, a heating roller 5, and an internal heating roller 6 (auxiliary heating roller). A heater lamp 5a (heat source) is disposed in the hollow of the heating roller 5, and first and second heater lamps 6a and 6b (first and second heat sources) are disposed in the hollow of the internal heating roller 6. ing.

  The fixing belt 2 is wound around the fixing roller 3 and the heating roller 5 and is driven in the direction of arrow A by the fixing roller 3. The fixing belt 2 is an endless belt made of a nickel thin plate having a thickness of 40 μm, and has an outer peripheral surface coated with an offset preventive agent such as a silicon rubber film.

  The fixing roller 3 and the pressure roller 4 are rubber rollers arranged so as to face each other. The pressure roller 4 is pressed toward the center of the fixing roller 3 via the fixing belt 2, so that the nip portion N is formed. Form. The heating roller 5 applies tension to the fixing belt 2 and is made of a cylindrical aluminum tube having a constant thickness in the axial direction. Then, heat from the heater lamp 5 a disposed in the hollow of the heating roller 5 is transmitted to the fixing belt 2 through the heating roller 5, and the fixing belt 2 is heated.

  Further, the belt fixing device 1 according to the present embodiment has an internal heating roller 6 pressed against the fixing roller 3 in a hollow portion formed inside the endless fixing belt 2, and the internal heating roller 6 is a fixing roller. 3 is engaged with the fixing roller 3 by a gear structure (not shown) at a position corresponding to the non-sheet-passing region 3, and rotates following the rotation of the fixing roller 3. Then, the heat transmitted from the first or second heater lamp 6 a or 6 b disposed in the hollow of the internal heating roller 6 to the surface of the fixing roller 3 via the internal heating roller 6 is transmitted to the fixing belt 2. Will be.

  That is, the internal heating roller 6 and the first and second heater lamps 6 a and 6 b constitute a heating unit that heats the surface of the fixing roller 3.

  In the belt fixing device 1 having the above-described configuration, the paper P (sheet-like medium) after the toner image is formed is conveyed in the direction of the arrow B, and the toner image T is fixed by being heated and pressed in the nip portion N. .

  FIG. 2 is a schematic plan view showing the vicinity of the nip portion of the fixing belt for explaining the arrangement of the belt temperature detecting means and the thermometer.

  As shown in FIGS. 1 and 2, the belt fixing device 1 has a non-contact type thermistor 7 (belt temperature detecting means) at one end (on the upstream side of the nip portion N of the fixing belt 2 in the center in the axial direction. A contact thermistor 8 (belt temperature detecting means) is provided outside the maximum sheet passing area. Then, as shown in FIG. 2, a thermometer 9 is provided at the center of the sheet passing area in the fixing belt width direction, and distances of 120 mm from the center to the left and right so that these thermistors 7 and 8 are at the same position in the fixing belt rotation direction. The thermometers 10 and 11 are disposed at positions of 140 mm and the thermometers 12 and 13 are disposed at distances of 140 mm from the center to the left and right, respectively, and the temperature of the surface of the fixing belt 2 can be measured at a fixed point at each position.

  In FIG. 2, a sheet passing area (B4 vertical width) of B4 size paper conveyed in the vertical direction (the direction in which the long side of the paper is parallel to the conveyance direction) and the horizontal direction (the short side of the paper in the conveyance direction). A paper passing area (A4 horizontal width) of A4 size paper conveyed in a parallel orientation is also shown. The B4 vertical width is a distance range of 128.5 mm from the center of the paper passing area in the fixing belt width direction to the left and right, respectively, and the A4 horizontal width is 148.5 mm from the center of the paper passing area in the fixing belt width direction to the left and right, respectively. The distance range. Therefore, the thermometers 10 and 11 are located inside the B4 vertical width, and the thermometers 12 and 13 are located outside the B4 vertical width and inside the A4 horizontal width. The A4 horizontal width defines the maximum value (maximum paper passing area) of the paper passing area of various sizes of paper.

  FIG. 3 is a diagram showing the light distribution in the axial direction of the heater lamp (a) inside the heating roller and the heater lamp (b) inside the internal heating roller.

  As shown in FIG. 3 (a), the heater lamp 5a inside the heating roller 5 has the same both ends (A4 vertical width outside and A4 horizontal width inside) and central portion (A4 vertical width inside) (100). %), The distribution outside the maximum sheet passing area (outside the A4 horizontal width) is set to a light distribution that monotonously decreases from 100% to 0%. Note that the light distribution may be such that both ends are higher than the center.

  On the other hand, as shown in FIG. 3 (b), the first heater lamp 6a inside the internal heating roller 6 has a constant value of 100% in the central portion (inside the A4 vertical width), and the maximum passage outside the central portion. The inside of the paper area (outside of A4 vertical width and inside of A4 horizontal width) decreases monotonously from 100% to a constant value of 30%, and the outside of the maximum paper passing area (outside of A4 horizontal width) starts from 30%. The light distribution is set to monotonously descend to 0%. As a result, the surface temperature distribution of the internal heating roller 6 is equal to or greater than the width of the fixing belt, and the temperatures at both ends are lower than those at the center.

  Further, as shown in FIG. 3C, the second heater lamp 6b inside the internal heating roller 6 has a constant value of 90% in the central portion (inside the A4 vertical width), and the maximum passage outside the central portion. The inside of the paper area (outside of A4 vertical width and inside of A4 horizontal width) increases monotonously from 90% to a constant value of 100%, and the outside of the maximum paper passing area (outside of A4 horizontal width) starts from 100% The light distribution is set to monotonously descend to 0%. As a result, the surface temperature distribution of the internal heating roller 6 is equal to or greater than the width of the fixing belt, and the temperatures at both ends are higher than those at the center.

  FIG. 4 is a cross-sectional view through the fixing roller 3 of the belt fixing device and the roller shaft of the heating roller 5 showing a control system of the heater lamp 5 a inside the heating roller 5 and the heater lamp 6 a inside the internal heating roller 6.

  As shown in FIG. 4, the heater lamp 5a inside the heating roller 5 and the first and second heater lamps 6a and 6b inside the internal heating roller 6 are turned on and off by the heater lamp 5a, the first and second heater lamps 5a, 6b. The heaters 6a and 6b are controlled by switching the driving of the drivers 13, 14 and 15 energized to the heater lamps 6a and 6b, respectively. The fixing roller 3 is rotationally driven by the main motor 21. The control unit 16 includes a non-contact type thermistor 7, a contact type thermistor 8, a color copier power switch 17, a print switch 18 for starting an image forming operation during standby of the color copier, and a belt in the paper conveyance path of the color copier. Based on detection signals from a registration switch 19 provided upstream of the fixing device 1 and a discharge switch 20 provided downstream of the belt fixing device 1 in the paper conveyance path of the color copying machine, drivers 13 and 14 and 15 drive is controlled.

  Next, an example of the operation of the belt fixing device of the present invention will be described in comparison with a belt fixing device of the conventional configuration. FIG. 5 shows a heater inside the heating roller 5 having a light distribution as shown in FIG. 3A when a B4 size paper on which a toner image is formed is passed vertically through the belt fixing device of the present invention. The first heater lamp 6a inside the lamp 5a and the internal heating roller 6 having a light distribution as shown in FIG. 3B and the inside of the internal heating roller 6 having the light distribution as shown in FIG. FIG. 6 is an example of an ON / OFF timing chart with respect to the second heater lamp 6b. FIG. 6 shows a conventional example having only the heater lamp 5a inside the heating roller 5 having a light distribution as shown in FIG. The belt fixing device (a) having the configuration, the heater lamp 5a inside the heating roller 5 having a light distribution as shown in FIG. 3 (a), and the internal heating roller having a light distribution as shown in FIG. 3 (b). 1st heater in 6 In the belt fixing device (b) according to the present invention having the belt 6a and the second heater lamp 6b in the internal heating roller 6 having the light distribution as shown in FIG. FIG. 7 is a diagram showing an example of a result of a fixed point measurement of the temperature of the fixing belt surface at the start of continuous feeding of B4 size paper on which a toner image is formed in the vertical direction. FIG. A conventional belt fixing device (a) having only a heater lamp 5a inside the heating roller 5 having a light distribution as shown in FIG. 3 and a heater inside the heating roller 5 having a light distribution as shown in FIG. The first heater lamp 6a inside the lamp 5a and the internal heating roller 6 having a light distribution as shown in FIG. 3B and the inside of the internal heating roller 6 having the light distribution as shown in FIG. Second heater lamp 6b In the belt fixing device (b) according to the present invention, an example of the result of fixed point measurement of the temperature of the fixing belt surface before and continuously passing B4 size paper on which a toner image is formed in the vertical direction is shown. FIG.

  The power switch 17 is always in an ON state, and the color copying machine is in a standby state before the print switch 18 is turned ON. At this time, the heater lamp 5a inside the heating roller 5 is ON / OFF controlled by the driver 15 based on the temperature detected by the non-contact type thermistor 7 at the center, and the surface temperature of the fixing belt 2 is controlled to 140 ° C.

  In this state, for example, when a portrait B4 size paper is selected and the print switch 18 is turned on, the main motor 21 is turned on and the fixing roller 3 is driven to rotate in preparation for fixing the toner image. As a result, the fixing belt 2 is rotated, and the heater lamp 5a inside the heating roller 5 is ON / OFF controlled by the driver 15 based on the temperature detected by the non-contact thermistor 7 at the center, and the nip N of the fixing belt 2 is controlled. The surface temperature is controlled at 165 ° C.

  A plurality of B4 size sheets are continuously conveyed, and after the toner images are transferred to the sheets in the image forming unit, the toner images on the sheets are fixed one after another in the belt fixing device 1.

  However, in the belt fixing device 1 of the conventional configuration, the heater lamp 5a inside the heating roller 5 is ON / OFF controlled based on the detected temperature (control temperature 165 °) of the non-contact type thermistor 7 in the center. When the standby state is long, as shown in FIG. 6A, when the sheet is started, a temperature drop occurs at both ends of the fixing roller 3, and the maximum sheet passing area has a uniform light distribution (see FIG. 6). 3 (a)) Even if the fixing belt 2 is heated at a uniform temperature by the heater lamp 5a inside the heating roller 5, the nip N of the fixing belt 2 is affected by the temperature unevenness of the fixing roller elastic body having a large heat capacity. The temperature at both ends of the plate decreases. In this state, if B4 size paper is continuously passed in the vertical direction, uneven glossiness and poor fixing properties occur at both ends of the paper.

  Therefore, in the belt fixing device 1 according to the present invention, when the print switch 18 is turned ON, as shown in FIG. 5, the heater lamp 5a inside the heating roller 5 is detected by the non-contact type thermistor 7 at the center (control). In addition to ON / OFF control based on the temperature 165 °), the heater lamp 5a inside the heating roller 5 is turned off, and the inside of the internal heating roller 6 having a light distribution as shown in FIG. The second heater lamp 6b is turned on, and then the switching control between the heater lamp 5a in the heating roller 5 and the second heater lamp 6b in the internal heating roller 6 (control to turn on one and turn off the other) is maximized. This is performed based on the detected temperature (control temperatures 170 ° C. and 169 ° C.) of the contact type thermistor 8 outside the paper passing area. That is, when the contact thermistor 8 outside the maximum sheet passing area detects 170 ° C., the second heater lamp 6b inside the internal heating roller 6 is turned off, the heater lamp 5a inside the heating roller 5 is turned on, and then When the contact type thermistor 8 outside the maximum sheet passing area detects 169 ° C., the second heater lamp 6b inside the internal heating roller 6 is turned on and the operation of turning off the heater lamp 5a inside the heating roller 5 is repeated alternately. Like that.

  As a result, a temperature distribution is formed on the surface of the fixing roller 3 such that the temperature at both ends is higher than that at the center, and the decrease in the temperatures at both ends of the nip portion N of the fixing belt 2 is eliminated as shown in FIG. Further, uneven glossiness and poor fixing properties at both ends of the paper can be prevented.

  Note that the control temperature at which the heater lamp switching control is performed may be changed according to the size of the sheet on which continuous paper is passed.

  However, if the B4 size paper is further continuously passed in this state, the belt fixing device 1 having the conventional configuration allows the heater lamp 5a inside the heating roller 5 to be connected to the central non-contact type thermistor 7 even during continuous paper passing. Since ON / OFF control is performed based on the detected temperature (control temperature 165 °), as shown in FIG. 7A, the temperature of the end portion of the fixing belt 2 is higher than that of the central portion. As a result, temperature unevenness close to 40 ° C. occurs in the fixing belt 2.

  Such temperature unevenness of the fixing belt 2 is transmitted to the elastic body of the fixing roller 3 having a larger heat capacity than that of the fixing belt 2 via the winding portion around the fixing roller 3, and the elastic body at the center of the fixing roller 3 There is a problem of causing softening and making the running performance of the fixing belt 2 unstable. In addition, if an A4 size paper larger than the B4 size is immediately passed in this state, fixing failure and gloss unevenness may occur at both ends of the paper.

  Therefore, in the belt fixing device 1 according to the present invention, as shown in FIG. 5, the heater lamp 5a inside the heating roller 5 is turned on / off based on the detected temperature (control temperature 165 °) of the non-contact thermistor 7 at the center. In addition to the OFF control, switching control of the heater lamp 5a inside the heating roller 5 and the first heater lamp 6a inside the internal heating roller 6 (control to turn on one and turn off the other) is outside the maximum sheet passing area. This is performed based on the temperature detected by the contact type thermistor 8 (control temperatures 180 ° C. and 179 ° C.). That is, when the contact thermistor 8 outside the maximum sheet passing area detects 180 ° C., the first heater lamp 6a inside the internal heating roller 6 is turned on, the heater lamp 5a inside the heating roller 5 is turned off, and then When the contact type thermistor 8 outside the maximum sheet passing area detects 179 ° C., the operation of turning off the first heater lamp 6a inside the internal heating roller 6 and turning on the heater lamp 5a inside the heating roller 5 are repeated alternately. Like that.

  Thus, after the belt temperature outside the maximum sheet passing area reaches 180 ° C. during continuous passing of B4 size paper, the heater lamp 5a inside the heating roller 5 and the first heater lamp 6a inside the internal heating roller 6 are used. Are alternately controlled ON / OFF, and the temperature unevenness which has been close to 40 ° C. in the belt fixing device of the conventional configuration is reduced to within 20 ° C.

Note that the control temperature at which the heater lamp switching control is performed may be changed depending on the size of the sheet on which continuous paper is passed. For example, as shown in Table 1, when the paper size is larger than A4 vertical width and smaller than A4 horizontal width and smaller than A4 vertical width, the switching reference temperature X ° C. is set separately, and the contact thermistor 8 outside the maximum sheet passing area is set. Detects X.degree. C., the first heater lamp 6a inside the internal heating roller 6 is turned on and the heater lamp 5a inside the heating roller 5 is turned off. Thereafter, the contact type thermistor 8 outside the maximum sheet passing area is ( X-1) When the temperature is detected, the first heater lamp 6a inside the internal heating roller 6 is turned off and the operation of turning on the heater lamp 5a inside the heating roller 5 is alternately repeated.

  When the discharge switch 20 is turned off and the continuous sheet passing is finished, the first heater lamp 6a inside the internal heating roller 6 is turned off, and after a predetermined time has passed, the main motor 21 is also turned off and the fixing belt 2 rotates. Stops and returns to the standby state.

  Further, like the conventional belt fixing device, after continuously passing small size paper using only the heater lamp 5a inside the heating roller 5, both ends of the fixing belt 2 are overheated, and the fixing belt 2 is heated. Temperature unevenness in which the temperature at both ends of the nip portion N increases. Alternatively, after a long standby state as described above, when temperature unevenness occurs in which both ends of the fixing belt 2 are lowered, when several sheets of the maximum size are passed, even after the end of the passing, Temperature unevenness in front of the paper is maintained, and temperature unevenness occurs in which the temperatures at both ends of the nip portion N of the fixing belt 2 are lowered.

  Accordingly, in order to eliminate such temperature unevenness of the fixing belt 2 after the completion of the sheet passing by using the belt fixing device 1 of the present invention, the fixing belt 2 is operated while the main motor 21 is operated after the end of the sheet passing. On / off control of the heater lamp 5a inside the heating roller 5 is performed based on the detected temperature of the non-contact thermistor provided at the center, and based on the detected temperature of the non-contact thermistor 7 provided at the center of the fixing belt 2. Then, the ON / OFF control of the first or second heater lamp 6a or 6b inside the internal heating roller 6 may be performed.

  For example, as shown in FIG. 8, after the continuous passage of A4 size paper in the vertical direction, the heater lamp 6a inside the internal heating roller 6 is detected by the non-contact thermistor 7 at the center (control temperature 170 ° C.). ON / OFF control based on the above is added.

  As a result, the temperature unevenness (broken line) of the belt temperature that occurs when the small-size paper is continuously passed and the temperature at both ends of the fixing belt 2 is higher than that at the center, and the light distribution is lower at both ends than at the center. Due to the operation of the first heater lamp 6a inside the internal heating roller 6 set to, a temperature difference (dotted line) in the temperature of the fixing roller 3 where the temperature at both ends is lower than that in the central part is generated, and this temperature difference is fixed. By adding to the fixing belt 2 via the roller 3, the temperature unevenness of the belt temperature can be quickly eliminated (solid line).

  In this case, the time for operating the main motor 21 can be determined by the contact type thermistor 8 provided outside the maximum sheet passing area of the fixing belt 2. For example, the main motor 21 is operated until the contact type thermistor 8 detects a predetermined temperature. By operating, the temperature unevenness of the fixing belt 2 can be solved efficiently.

  Similarly, when the temperature at both ends of the nip portion N of the fixing belt 2 is decreased, the light distribution is set to a value higher at both ends than at the center after the sheet passing. The temperature unevenness can be eliminated by turning on the heater lamp 6b 2 and rotationally driving the fixing belt 2.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the description has been given using the belt fixing device that conveys the paper in the substantially horizontal direction, but the same can be applied to the belt fixing device that conveys the paper in the substantially vertical direction. In addition, a contact / separation means such as a solenoid for separating / contacting the internal heating roller from the fixing roller may be provided as necessary.

  The present invention relates to a fixing device using a fixing belt, and can be used for an image forming apparatus such as a color laser printer.

These are explanatory drawings which show the structure of the outline of the belt fixing device which concerns on embodiment of this invention. These are schematic plan views showing the vicinity of the nip portion of the fixing belt for explaining the arrangement of the belt temperature detecting means and the thermometer. These are figures which show the light distribution in the axial direction of the heater lamp (a) inside a heating roller, and the heater lamp (b) inside an internal heating roller. These are sectional drawings which pass along the roller axis | shaft of the fixing roller of a belt fixing device, and a heating roller which shows the control system of the heater lamp inside a heating roller, and the heater lamp inside an internal heating roller. FIG. 3 shows a heater lamp inside a heating roller having a light distribution as shown in FIG. 3A when a B4 size paper on which a toner image is formed is passed vertically through a belt fixing device of the present invention. A first heater lamp inside the internal heating roller having a light distribution as shown in FIG. 3B, and a second heater lamp inside the internal heating roller having a light distribution as shown in FIG. It is an example of a timing chart of ON / OFF. 3A has a conventional belt fixing device (a) having only a heater lamp inside a heating roller having a light distribution as shown in FIG. 3 (a), and has a light distribution as shown in FIG. 3 (a). A heater lamp inside the heating roller, a first heater lamp inside the internal heating roller having a light distribution as shown in FIG. 3B, and an internal heating roller having a light distribution as shown in FIG. In the belt fixing device (b) of the present invention having an internal second heater lamp, after a long standby state, fixing B4 size paper on which a toner image is formed in the vertical direction at the start of continuous paper feeding It is a figure which shows an example of the result of having measured the temperature of the belt surface at a fixed point. 3A has a conventional belt fixing device (a) having only a heater lamp inside a heating roller having a light distribution as shown in FIG. 3 (a), and has a light distribution as shown in FIG. 3 (a). A heater lamp inside the heating roller, a first heater lamp inside the internal heating roller having a light distribution as shown in FIG. 3B, and an internal heating roller having a light distribution as shown in FIG. In the belt fixing device (b) of the present invention having an internal second heater lamp, before the B4 size paper on which the toner image is formed is continuously passed in the vertical direction and on the surface of the fixing belt during the continuous feeding. It is a figure which shows an example of the result of having measured temperature at fixed points. After the A4 size paper is continuously passed in the vertical direction, the temperature unevenness is eliminated by the internal heating roller having a light distribution (dotted line) opposite to the temperature unevenness (dashed line) on the surface of the fixing belt (solid line). FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Belt fixing device 2 Fixing belt 3 Fixing roller 4 Pressure roller 5 Heating roller 5a Heater lamp incorporated in the heating roller (heat source inside the heating roller)
6 Internal heating roller 6a First heater lamp built in the internal heating roller (first heat source inside the internal heating roller)
6b Second heater lamp built in the internal heating roller (second heat source inside the internal heating roller)
7 Non-contact thermistor (belt temperature detection means provided at the center of the fixing belt)
8 Contact type thermistor (belt temperature detection means provided outside the maximum belt feeding area)
9, 10, 11, 12, 13 Thermometer 13, 14, 15 Driver 16 Control unit 17 Power switch 18 Print switch 19 Registration switch 20 Eject switch 21 Main motor N Nip part P Paper T Toner image

Claims (5)

A pair of fixing rollers and a pressure roller disposed opposite to each other;
A heating roller with a built-in heat source;
A fixing belt comprising an endless belt that is stretched between the fixing roller and the heating roller;
A hollow portion formed inside the fixing belt, and an internal heating roller including first and second heat sources that are driven to rotate together with the fixing roller to heat the surface of the fixing roller;
Driving means for rotationally driving the fixing roller;
The fixing roller is driven to rotate by the driving means, and the fixing belt is heated by the heating roller, whereby a sheet carrying a fixing toner image is passed through a nip portion between the fixing belt and the pressure roller. In the belt fixing device that performs heat fixing,
The heat source inside the heating roller has an even light distribution at both ends and the center, and the first heat source inside the internal heating roller has a light distribution at which both ends are lower than the center. The belt fixing device, wherein the second heat source inside the heating roller has a light distribution in which both end portions are higher than the central portion.   At the start of continuous paper feeding after a long standby state, ON / OFF control of the heat source inside the heating roller is performed based on the temperature detected by the belt temperature detecting means provided at the center of the fixing belt while operating the driving means. At the same time, the heat source inside the heating roller and the second heat source inside the internal heating roller are ON / OFF controlled by alternately switching the heat sources based on the detected temperature of the belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt. The belt fixing device according to claim 1.   While continuously driving small-size paper, while operating the drive means, on and off control of the heat source inside the heating roller based on the temperature detected by the belt temperature detection means provided at the center of the fixing belt, and fixing The heat source inside the heating roller and the first heat source inside the internal heating roller are ON / OFF controlled by alternately switching the heat sources based on the temperature detected by the belt temperature detecting means provided outside the maximum sheet passing area of the belt. The belt fixing device according to claim 1 or 2.   After passing the paper, while operating the driving means, the heat source inside the heating roller is turned on / off based on the temperature detected by the belt temperature detecting means provided at the center of the fixing belt, and provided at the center of the fixing belt. 2. The belt fixing device according to claim 1, wherein ON / OFF control of the first or second heat source inside the internal heating roller is performed based on the detected temperature of the belt temperature detecting means.   5. The belt fixing device according to claim 4, wherein the driving means is operated until the belt temperature detecting means provided outside the maximum sheet passing area of the fixing belt detects a predetermined temperature.

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