JP2008275873A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of fixing a toner image of excellent image quality and also with excellent heat energy efficiency by reducing temperature unevenness more surely than in a conventional manner, and also, suppressing the outflow of the heat energy to an area, where a recording medium does not pass, of a fixing belt or to a heat equalizing means. <P>SOLUTION: The fixing device 14 for the image forming apparatus 100 includes: a fixing roller 21; a heat roller 22 equipped with first to third heaters 24a to 24c; a fixing belt 25; a pressure roller 51; temperature detecting sensors 61a to 61c; the heat equalizing roller 62; and a solenoid 63. Upon continuous printing, when a temperature T in the non recording paper passing area of the fixing belt 25 becomes equal to or higher than a prescribed temperature T1, heating the non-passing area is stopped, further, when the temperature T detected in the non passing area becomes equal to or higher than a prescribed temperature T2, the heat equalizing roller 62 is brought in contact with the inside surface of the fixing belt 25. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, a sheet carrying an unfixed toner image is inserted into a nip of a heated roller pair, such as an electrophotographic copying machine, a facsimile machine, or a printer, and the unfixed toner is heated and melted and fixed on the sheet. The present invention relates to an image forming apparatus equipped with the apparatus.

  In an electrophotographic image forming apparatus, a heat source is incorporated in at least one roller of a roller pair forming a nip, and a sheet carrying an unfixed toner image is inserted into the nip of the roller pair heated by the heat source. Thus, a heat roller fixing method for fixing toner onto a sheet is widely used.

  In such a heat roller fixing method, the efficiency of heat transfer from the heat source such as a halogen lamp built in the fixing roller to the roller surface is low, and it takes a long time to transfer the heat to the roller surface. .

  Therefore, an endless fixing belt is bridged between the fixing roller and the heating roller, the fixing belt generates heat by the heat source of the heating roller, and the unfixed toner image is applied to the sheet at the nip between the fixing roller and the pressure roller via the fixing belt. By using the fixing method, the heating efficiency is improved, and the warm-up time until the fixing belt reaches a fixing temperature is shortened.

  However, in such a fixing method, when narrow paper is continuously printed, heat is taken away in a portion where the paper passes on the fixing belt, but heat is not taken away in a portion where the paper does not pass. In some cases, the temperature at both ends of the width becomes high, and uneven temperature distribution occurs in the paper width direction. As a result, there is a possibility that the toner image has uneven fixing property or glossiness.

Therefore, in order to improve such a problem, a technique for improving the temperature unevenness of the fixing belt has been proposed. For example, Patent Document 1 discloses an endless belt, a heating unit that heats the endless belt, a pressing unit that pressurizes the outer periphery of the endless belt to form a fixing nip, and a temperature in the belt width direction in contact with the endless belt. Using a fixing device having a temperature-uniforming means for equalizing, and when the width of the print medium is smaller than a predetermined size, or the temperature difference between the central portion in the belt width direction and one predetermined end is not less than a predetermined value. In some cases, a technique has been disclosed in which the temperature unevenness is brought into contact with the endless belt and separated at other times so that the heat of the endless belt is evenly distributed in the width direction and temperature unevenness is eliminated.
Japanese Patent Laying-Open No. 2005-77880

  However, in the technique of Patent Document 1, the temperature equalizing means is brought into contact with and separated from the endless belt based on the temperature difference at a predetermined position in the belt width direction. There is a risk that a temperature change caused by a standby time associated with an image quality maintenance operation such as toner replenishment or calibration performed during a printing operation may be erroneously detected as temperature unevenness due to paper passing. Such erroneous detection may cause malfunction in contact and separation of the temperature equalizing means with the endless belt.

  Further, even after the excessive temperature rise in the non-sheet passing area, the heating of the area continues, and the temperature rise due to the heating is reduced by the contact of the temperature-uniforming means, so that the heating energy flows out to the atmosphere through the non-sheet passing area. There is a risk of causing. Furthermore, the heating energy flows out to the temperature-equalizing means through the non-sheet passing region, and in addition, the contact frequency of the temperature-equalizing means may increase. If the heating of the non-sheet passing area is continued and the temperature-equalizing means is positively contacted as described above, heat may flow out to the non-sheet passing area and the temperature equalizing member, and the energy efficiency may be reduced.

  The present invention has been made in view of the above circumstances, and in an image forming apparatus equipped with a fixing device for fixing an unfixed toner image carried on a recording medium, temperature unevenness is more reliably reduced than before. At the same time, by suppressing the outflow of thermal energy to the non-passage area of the recording medium and the temperature-equalizing means on the fixing belt, the image enables fixing of the toner image having excellent image quality and excellent thermal energy efficiency. An object is to provide a forming apparatus.

  In order to achieve the above object, the present invention contacts a fixing roller, a heating roller, an endless fixing belt stretched between the fixing roller and the heating roller, and the fixing roller via the fixing belt. A pressure roller that forms a nip portion through which the recording medium is inserted, and an image forming apparatus equipped with a fixing device that fixes a toner image carried on the recording medium at the nip portion. A plurality of heat generating means disposed on the fixing belt and capable of separately heating a passing area and a non-passing area of the recording medium; a temperature detecting means for detecting a temperature of the non-passing area; and the fixing belt When the detection result of the temperature detecting means becomes equal to or higher than a predetermined temperature T1, the temperature generating means for temperature-uniforming the fixing belt in the width direction by contacting and separating from the inner surface of the fixing belt Heating control for controlling the lighting of the means to stop the heating of the non-passing area, and temperature equalization control for bringing the temperature equalizing means into contact with the fixing belt when the temperature becomes equal to or higher than a predetermined temperature T2 higher than T1. And a control means capable of executing the above.

  According to the present invention, the plurality of heat generating means inside the heating roller includes a first heat generating means for heating at least a central portion and a second heat generating means for heating both ends in the width direction of the recording medium. And the energization to the second heat generating means is stopped when the heating control is executed.

  Further, the present invention provides the control means for fixing a plurality of the recording medium when fixing a recording medium having a predetermined width smaller than the maximum width of the insertable recording medium and fixing a recording medium larger than the predetermined width. The heat generating means is selectively used.

  According to the first configuration of the present invention, when an excessive temperature rise occurs in the non-passing area of the fixing belt, first, heating of the non-passing area of the fixing belt by the heating roller is stopped, and even after the heating control, When the excessive temperature rises, the temperature-uniforming means is inscribed in the fixing belt, thereby suppressing the excessive temperature increase in the non-passing area and reducing the temperature unevenness of the fixing belt, as well as the non-passing area and the equalizing area. The release of thermal energy to the heating means can be suppressed. Therefore, it is possible to fix a toner image having excellent image quality and thermal energy efficiency.

  Further, by performing heating control and soaking control using a predetermined threshold temperature, it is possible to avoid erroneous detection and malfunction. Accordingly, the heating control and the soaking control can be performed more reliably, and the excellent toner image can be fixed more reliably.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the first heat generating means for heating the central portion and both ends are heated inside the heating roller in the width direction of the recording paper. The heating control can be performed by stopping the energization of the second heat generating means when the non-passage region is overheated. Therefore, heating control and soaking control can be performed with a simpler configuration of stopping energization of the second heat generating means, and the complexity of the apparatus can be further avoided.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, a recording medium having a predetermined width or less passes among the plurality of heat generating units provided in the heating roller. By selectively using the heat generating means when the recording medium larger than the predetermined width passes, it is possible to perform heating control and soaking control of the fixing nip according to the width of the inserted recording medium. Accordingly, it is possible to further avoid the heating of the non-passing area, and it is possible to perform the heating control and the soaking control excellent in thermal energy efficiency and the fixing of the toner image.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a fixing device mounted on an image forming apparatus according to an embodiment of the present invention. The fixing device 14 includes a fixing unit 20 and a pressure unit 50.

  The fixing unit 20 is roughly composed of a fixing roller 21, a heating roller 22, and a fixing belt 25. The fixing roller 21 is mainly composed of a core metal 21a made of stainless steel, and a sponge silicon rubber constituting an elastic member layer 21b is provided outside the core metal 21a. The fixing roller 21 is driven by a driving device (not shown) and rotates so that its peripheral speed is the same as the conveyance speed of the recording paper (recording medium).

  The heating roller 22 is formed of a cylindrical member 23 made of metal such as thin Al (aluminum), Fe (iron), SUS (stainless steel), and the like, and rotates together with the fixing belt 25 described later according to the rotation of the fixing roller 21. The cylindrical member 23 can be molded using a glass material such as quartz or borosilicate, or a resin material such as polyimide or polyamide, in addition to the metal material.

  Inside the heating roller 22, a first heater 24a, a second heater 24b, and a third heater 24c (heat generating means) are respectively provided from the center in the belt width direction toward both outer sides. The first heater 24a, the second heater 24b, and the third heater 24c are halogen lamps having different light emission (heating) widths.

  FIG. 2 is a temperature distribution diagram in the belt width direction of each fixing belt 25 by the light emission of the first heater 24a and the second heater 24b, and FIG. 3 is the light emission of the first heater 24a and the third heater 24c. FIG. 6 is a temperature distribution diagram in the belt width direction of each fixing belt 25. 2 and 3, the horizontal axis indicates the belt width direction, and the vertical axis indicates the belt surface temperature. In FIG. 2, the A3 vertical size recording paper width (297 mm, solid line) and the A4 vertical size recording paper width (210 mm, broken line) are shown as references, and in FIG. 3, the A4 vertical size recording paper width (solid line) and A5 vertical size are shown. The recording paper width (148 mm, broken line) is shown as a reference.

  As shown in FIGS. 2 and 3, the first heater 24a has an effective light emission width equal to or larger than the recording paper width sufficient to fix the recording paper width of A4 vertical size (hereinafter referred to as “A4”). The width portion of the fixing belt 25 is designed to be heated. The light emitted from the first heater 24a can fix the recording paper up to A4 width.

  As shown in FIG. 2, the second heater 24 b has an effective light emission width from the periphery of both ends of the first heater 24 a to the outside, and emits light together with the second heater 24 a, thereby A3 vertical size (hereinafter referred to as “A3”). ), Which has an effective light emission width equal to or greater than the width of the recording paper, and is designed to heat the portion of the fixing belt 25. That is, the second heater 24b has an effective light emission width in a portion from the periphery of both ends of the A3 width to the outside, and is designed to heat both ends of the fixing belt 25 with the A3 width. Then, by combining the first heater 24a and the second heater 24b to emit light, the first heater 24a heats the central portion of the A3 recording paper width, the second heater 24b heats both end portions of the A3 recording paper width, and A3 Recording paper up to the width can be fixed.

  As shown in FIG. 3, the third heater 24c is designed to have an effective light emission width smaller than the A4 recording paper width. As will be described later, it is used for control during continuous printing of A4 recording paper. Here, the third heater 24c has an effective light emission width equal to or greater than the width of the recording paper sufficient to fix the recording paper of A5 vertical size (hereinafter referred to as “A5”), and the width of the fixing belt 25. Designed to heat the part. This makes it possible to fix recording paper up to A5 width.

  Light emitted from the first to third heaters 24 a to 24 c is located at a position of the periphery of the first to third heaters 24 a to 24 c that faces the portion where the fixing belt 25 contacts the heating roller 22. A reflecting plate 24 (not shown) is provided so as to direct the light. The first to third heaters 24a to 24c may be electric heaters in addition to the halogen lamp, and are not particularly limited.

  The fixing belt 25 is an endless belt in which an elastic layer made of silicon rubber, fluororesin, or the like is formed on the surface of a rolled metal substrate such as Ni (nickel) or SUS (stainless steel). In addition, the fixing belt 25 is formed, for example, by forming a metal oxide layer such as carbon black or iron black on the back surface of the metal base to absorb light from a halogen lamp and convert it into heat. For example, it may be a single layer made of a heat-resistant resin such as polyimide, and is not particularly limited. The fixing belt 25 is wound around the fixing roller 21 and the heating roller 22 and given a predetermined tension.

  The pressure unit 50 includes a pressure roller 51. As with the fixing roller 21, the pressure roller 51 is provided with a sponge silicon rubber constituting the elastic member layer 51 b on the outside of the core metal 51 a made of stainless steel. The pressure roller 51 is brought into contact with the fixing roller 21 via the fixing belt 25, thereby forming a nip portion through which the recording paper is inserted. The pressure roller 51 is brought into contact with the fixing roller 21 via the fixing belt 25, and rotates according to the rotation of the fixing roller 21.

  As shown in FIG. 1, temperature detection sensors 61 a, 61 b, and 61 c (temperature detection means) are in contact with the surface of the fixing belt 25 on the outer side and in the immediate vicinity of the downstream side of the portion where the fixing belt 25 contacts the heating roller 21. Is provided. The temperature detection sensors 61a to 61c are thermistors, and as shown in FIG. 2, the temperature detection sensor 61a is located in the center with respect to the width direction of the fixing belt 25, and is in the recording paper passage area on the belt surface. Perform temperature detection. The detection sensor 61b is located near the outside of the A3 width, and the detection sensor 61c is located near the outside of the A4 width, respectively, and detects the temperature of the non-passing area on the surface of the fixing belt 25 when each recording sheet is used. Do.

  The temperature detection sensors 61a to 61c transmit an output signal corresponding to the detection result to the control unit 35 described later. The temperature detection result of the passage area by the temperature detection sensor 61a is used for the control to maintain the fixing temperature of the fixing nip portion, which will be described later, to maintain the fixing temperature substantially constant. On the other hand, the temperature detection result of the non-passing region by the temperature detection sensors 61b and 61c is used for the soaking control described later. In addition to the above, the temperature detection sensors 61a to 61c may be thermocouples, for example, and are not particularly limited. In addition, since the temperature of the fixing belt 25 immediately after heating can be measured by disposing the detection position immediately downstream of the heating roller 22 as in the present embodiment, the surrounding environment affecting the detection result Although the influence of the factor can be reduced, the detection position can be, for example, outside and upstream of the portion where the fixing belt 25 contacts the fixing roller 21, and is not particularly limited.

  Then, between the fixing roller 21 and the heating roller 22, on the inner surface side of the fixing belt 25 on the upstream side with respect to the recording paper conveyance direction, and at a position where the inner surface of the fixing belt 25 can be contacted and separated. A soaking roller 62 (soaking means) is provided. The temperature-uniforming roller 62 is in contact with the inner surface of the fixing belt 25 to absorb the heat of the high-temperature portion in the belt width direction and transmit a part of the heat to the low-heat portion to thereby gradient the temperature distribution in the belt width direction. Is to make it smaller. That is, by absorbing the heat of the overheated portion generated in the non-passing area of the recording paper in the fixing belt 25 during continuous printing and transmitting a part thereof to the passing area, the width of the fixing belt 25 is increased. It is intended to make the surface temperature uniform.

  The soaking roller 62 is a member having good thermal conductivity, and is made of a metal roller, a heat pipe, or the like. If the thermal conductivity of the temperature-uniforming roller 62 is large, temperature transfer from the non-passing area to the passing area is performed quickly, and the temperature drop of the fixing belt 25 can be suppressed. From this viewpoint, it is preferable to use, for example, Al (aluminum) as the soaking roller 62. In addition, by using a member having a large heat capacity in addition to thermal conductivity as the temperature equalizing roller 62, it is possible to prevent the temperature equalizing roller 62 itself from rising in temperature and to suppress a decrease in heat absorption in the non-passing area. . From this viewpoint, for example, it is more preferable to use Cu (copper) as the metallic roller.

  From this point of view, the soaking roller 62 may be a two-layer member composed of a highly heat conductive surface layer member such as Al and Cu and a high heat capacity core member capable of storing heat inside. More preferred. Examples of the high heat capacity core member include a member made of a porous material such as sponge or a heat conductive gel. In addition, a fluorine-based resin layer such as a Teflon (registered trademark) coat may be provided on the surface of the temperature-uniforming roller 62 in consideration of slidability with the fixing belt 25.

  In addition, by arranging the temperature-uniforming roller 62 on the downstream side of the temperature detection sensors 61a to 61c and the upstream side of the fixing roller 21, the detection results of the temperature detection sensors 61a to 61c can be favorably reflected. It becomes. From this point of view, it is preferable that the soaking roller 62 is disposed on the downstream side of the temperature detection sensors 61a to 61c and close to the sensor.

  A solenoid 63 is provided to bring the temperature-uniforming roller 62 into contact with and away from the inner surface of the fixing belt 25. The solenoid 63 operates so that the temperature-uniforming roller 62 is inscribed in the fixing belt 25 and separated from the fixing belt 25 by a control signal from the control unit 35 described later. As a means for contacting / separating the temperature-uniforming roller 62 with respect to the fixing belt 25, for example, a cam can be used and is not particularly limited. In the present embodiment, the soaking roller 62 is used. However, for example, a plate-like soaking plate may be used instead of the soaking roller 62, and there is no particular limitation.

  FIG. 4 is a block diagram illustrating an example of a control mechanism of the image forming apparatus according to the present embodiment. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image forming unit 3, a fixing device 14, an image input unit 32, an AD conversion unit 33, a storage unit 34, a control unit 35, and an operation panel 36.

  When the image forming apparatus 100 is a copying machine, the image input unit 32 includes a scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of reflected light from the document, and reflected light from the document. An image reading unit 6 (not shown) including a condensing lens that collects and forms an image and a CCD that converts the imaged image light into an electrical signal. The image forming apparatus 100 is a printer. In some cases, the receiving unit receives image data transmitted from a personal computer or the like. The image signal input from the image input unit 32 is sent to the control unit 35, appropriately performs image processing such as gradation processing, and after being converted into a digital signal by the AD conversion unit 33, an image in the storage unit 34 to be described later. It is sent to the memory 40.

  The image forming unit 3 includes a photosensitive drum 5, a charging unit 4, an exposure unit 7, a developing unit 8, a transfer roller 13, and the like. Based on the image data converted by the AD conversion unit 33 and stored in the image memory 40. Then, an electrostatic latent image is formed on the photosensitive drum 5. The photosensitive drum 5, the transfer roller 13, and the fixing roller 21 (see FIG. 1) in the fixing device 14 are rotationally driven by a main motor (not shown), and the control unit 35 transmits a control signal to the main motor. The rotation and stop of the photosensitive drum 5, the transfer roller 13, and the fixing roller 21 are controlled.

  The storage unit 34 includes an image memory 40, a RAM 41, and a ROM 42, and the image memory 40 stores an image signal input by the image input unit 32 and digitally converted by the AD conversion unit 33, and is stored in the control unit 35. Send it out. The RAM 41 and ROM 42 store an image processing program, processing contents, and the like of the control unit 35. In addition, a control program for the first to third heaters 24a to 24c of the heating roller 22 and a fixing control temperature as a reference for the control for maintaining the fixing nip portion at a substantially constant predetermined temperature that can be fixed are also stored. .

  Further, a control program (described later) for controlling the first and third heaters 24a to 24c and the temperature equalizing roller 62 for contacting and separating the temperature equalizing roller 62 with respect to the fixing belt 25 to equalize the temperature of the fixing belt 25; Threshold temperatures T1 and T2 (described later) serving as control standards are also stored.

  The control unit 35 is, for example, a central processing unit (CPU), and generally controls the image input unit 32, the image forming unit 3, the fixing device 14 and the like according to a set program, and is input from the image input unit 32. The image signal is converted into image data by scaling processing or gradation processing as necessary. The exposure unit 7 irradiates a laser beam based on the processed image data, and forms a latent image on the photosensitive drum 5. Further, the control unit 35 also controls each part of the image forming apparatus such as the image input unit 32, the charging unit 4, the exposure unit 7, and the developing unit 8 in accordance with the set program.

  Further, the control unit 35 receives an output signal from the temperature detection sensor 61a, and based on the fixing control temperature stored in the storage unit 34, turns on and off the first to third heaters 24a to 24c. The output signals from the temperature detection sensors 61b and 61c are received, and the first and third heaters 24a to 24c are turned on and off based on the threshold temperatures T1 and T2 stored in the storage unit 34, and the solenoid 63 is averaged. It has a function of separating and contacting the heat roller 62.

  The operation panel 36 includes an operation unit composed of a plurality of operation keys and a display unit (none of which is shown) for displaying setting conditions, apparatus statuses, and the like. For example, when the image forming apparatus 100 has a facsimile function, it is also used for various settings such as registering a facsimile transmission destination in the storage unit 34 and further reading and rewriting the registered transmission destination. Is done.

  Next, an example (control example 1) of heating control and soaking control of the image forming apparatus according to the present embodiment will be described.

  Here, A3 width recording paper is printed. In this case, as shown in FIG. 2, the first heater 24 a (first light emitting means) and the second heater 24 b (second light emitting means) are turned on so that the effective light emission width is equal to or greater than the A3 width. Heat. By such heating, the passage area of the A3 recording paper in the fixing nip portion is set to a predetermined fixing temperature, the toner image is transferred, and the A3 recording paper passing through the fixing nip is fixed. Then, the temperature detection sensor 61a disposed in the passage area detects the temperature of the passage area of the fixing belt 25. Based on the detection result, the control unit 35 sets the fixing control temperature as a reference value and the first heater. The fixing temperature is kept substantially constant by performing ON / OFF control of the 24a and the second heater 24b.

  Further, the temperature detection sensor 61b disposed in the non-passing area of the A3 recording paper detects the temperature of the non-passing area on the surface of the fixing belt 25. FIG. 5 is a temperature distribution diagram in the width direction of the fixing belt 25 when the A3 recording paper is continuously printed, and the A3 recording paper width is indicated by a one-dot chain line. As shown in FIG. 5, when A3 recording paper is continuously printed, the temperature detected by the temperature detection sensor 61b in the non-passing area becomes high, and the non-passing area of the fixing belt 25 becomes overheated with respect to the passing area.

  When the non-passing area detection temperature T becomes equal to or higher than the predetermined threshold temperature T1, the control unit 35 turns off the second heater 24b that heats both ends of the A3 recording paper width and stops heating the non-passing area. However, as described above, the passing region of the fixing nip portion is maintained at a substantially constant temperature in order to maintain the fixing property. For this reason, the heat used for maintaining the temperature of the passing area may move to the non-passing area on the belt surface by the continuous printing, and the excessive temperature rise state of the non-passing area may further progress.

  The temperature detection results by the temperature detection sensors 61a and 61b at this time are shown in FIG. FIG. 6 is a temperature distribution diagram in the width direction of the fixing belt 25 when the A3 recording paper is continuously printed after the second heater 24b is turned off, and the A3 recording paper width is indicated by a one-dot chain line. As shown in FIG. 6, the overheated state further proceeds after the second heater 24b is turned off.

  As described above, when the non-passing region on the belt surface is further overheated and the non-passing region detection temperature T by the temperature detection sensor 61b is equal to or higher than the predetermined threshold temperature T2, the control unit 35 activates the solenoid 63. Then, the temperature-uniforming roller 62 is brought into contact with the inner surface of the fixing belt 25 to prevent temperature rise at both ends of the fixing belt 25.

  In this control example, control is performed using the threshold temperatures T1 and T2, for example, immediately after a temperature rise or during a standby time associated with an image quality maintenance operation such as toner supply or calibration performed during a printing operation. It is possible to further avoid erroneously detecting a temperature change or the like as temperature unevenness due to paper passing. After the second heater 24b is turned off, the control unit 35 performs ON / OFF control of only the heater 24a based on the detection result of the passage region temperature by the temperature detection sensor 61a, so that the fixing temperature is kept substantially constant. .

  In this control example, when the first heater 24a and the second heater 24b among the first to third heaters 24a to 24c are used, the non-passage region detection temperature T becomes equal to or higher than the threshold temperature T1. The overheating of the non-passing region can be suppressed with a simple configuration in which the second heater 24b is turned off, that is, the energization to the second heater 24b is stopped. it can.

  FIG. 7 is a flowchart showing a control procedure of this control example. The control will be described according to the steps in FIG. 7 with reference to FIG. 2 and FIGS.

  First, the image forming apparatus 100 is turned on (step S1). The soaking roller 62 is separated from the fixing belt 25. After the printing conditions such as the number of prints and the printing magnification are manually set by the user through the operation panel 36 or an input operation from the personal computer, and the paper size is manually set by the input operation or automatically set by the document reading operation, the start button is turned on. Thus, a print start instruction (print signal) is input (step S2).

  When the print signal is input, the first heater 24a and the second heater 24b are turned on by the control unit 35 (step S3). Then, the temperature detection sensor 61a and the temperature detection sensor 61b start the temperature detection of the passing area and the non-passing area of the fixing belt 25 (step S4), and the printing process is started.

  Next, the control unit 35 reads a predetermined threshold temperature T1 stored in the storage unit 34, and first determines whether or not the non-passage region detection temperature T by the temperature detection sensor 61b is equal to or higher than the threshold temperature T1. (Step S5). When T1 ≦ T, the second heater 24b is turned off (step S6), thereby preventing excessive temperature rise in the non-passing area on the surface of the fixing belt 25.

  Further, the printing process is continued, and the control unit 35 further increases the non-passage area detection temperature T by the temperature detection sensor 61b to a predetermined threshold temperature T2 stored in the storage unit 34 or higher. It is determined whether or not (step S7). When T2 ≦ T, the temperature equalizing roller 62 is brought into contact with the inner surface of the fixing belt 25 by the solenoid 63 (step S8), thereby preventing excessive temperature rise in the non-passing area on the surface of the fixing belt 25. . In such a state, the printing process is performed up to the predetermined number of prints set in step S <b> 2 while keeping the soaking roller 62 in contact with the fixing belt 25.

  If T1> T in step S5, the control unit 35 performs the printing process with the second heater 24b turned on. Further, when T2> T in step S7, the control unit 35 performs the printing process with the second heater 24b turned off and the heat equalizing roller 62 being separated.

  Then, it is determined whether or not a predetermined number of printing processes have been completed (step S9). If printing is continuing, the process returns to step S5 and the same control is performed (steps S5 to S8). If the number of printed sheets set in step S2 has ended, the control unit 35 determines whether or not the soaking roller 62 is in contact with the fixing belt 25 (step S10). If the soaking roller 62 is in contact, it is separated from the fixing belt 25 (step S11), and all the processes are completed. On the other hand, if the soaking roller 62 is separated in step S10, all the processes are finished as it is.

  FIG. 8 shows a control result according to this control example. FIG. 8 is a temperature distribution diagram in the width direction of the fixing belt 25, showing the temperature distribution when the heating control and the soaking control according to this control example are not performed, and when the heating control is performed, and shows the A3 recording paper width with a dotted line. Show. The fixing control temperature is also shown. As shown in FIG. 8, according to this control example, the second heater 24b is turned off when the non-passing region detection temperature T by the temperature detection sensor 61b is equal to or higher than T1 among the first heater 24a and the second heater 24b. Further, when the non-passage area detection temperature T is equal to or higher than T2, the temperature equalizing roller 62 is brought into contact with the inner surface of the fixing belt 25, thereby suppressing the temperature increase in the non-sheet passing area on the surface of the fixing belt 25.

  That is, when the detection result (temperature T) of the non-passing region by the temperature detection sensor 61b is equal to or higher than the threshold temperature T1, the second heater 24b is controlled to stop heating of the non-heating region, and the heating control. After that, when the detection result (temperature T) of the non-passage region of the sensor 61b becomes a threshold temperature T2 higher than T1, the temperature equalization control for bringing the temperature equalization roller 62 into contact with the fixing belt 25 is executed. As a result, the temperature rise in the non-sheet passing region on the surface of the fixing belt 25 is suppressed.

  Thus, by stopping the heating of the non-passing area of the fixing belt 25, the release of heat energy from the non-passing area to the atmosphere can be suppressed. Prior to the contact of the temperature-uniforming roller 62, the heating of the non-sheet passing area is stopped and the temperature rise in the area is temporarily suppressed, so that the subsequent temperature-uniforming roller 62 is brought into contact with the fixing belt 25. And the release of heat energy to the temperature-uniforming roller 62 due to the contact can be suppressed.

  Accordingly, the fixing device 14 can suppress a decrease in thermal energy due to contact with the non-passing region of the fixing belt 25 and the temperature-uniforming roller 62, and is excellent in energy efficiency. Further, since the threshold temperatures T1 and T2 are used, malfunction can be avoided more. Furthermore, when the non-passage area detection temperature T is equal to or higher than T1, it is only necessary to turn off the second heater 24b, so that the configuration is further simplified.

  Next, another heating control and soaking control (control example 2) of the image forming apparatus according to the present embodiment will be described.

  In this control example, A4 width recording paper is printed. Therefore, among the first to third heaters 24a to 24c, the first heater 24a and the third heater 24c are used, and the temperature detection sensor 61c is used instead of the temperature detection sensor 61b, so that the non-passing area on the surface of the fixing belt 25 is used. Since the temperature is detected and the heating control and the temperature equalization control are performed, the description is omitted.

  As shown in FIG. 3, the first heater 24a is turned on to heat the fixing belt 25 so that the effective light emission width is equal to or larger than the A4 width, and the A4 recording paper passing through the fixing nip is fixed. Then, the temperature detection sensor 61c disposed in the non-sheet passing area of the fixing belt 25 detects the temperature of the non-sheet passing area.

  Further, when the A4 recording paper is continuously printed and the non-passage region detection temperature T at the temperature detection sensor 61c becomes equal to or higher than the predetermined threshold temperature T1, the control unit 35 turns off the first heater 24a, and instead uses the third heater. The heater 24c is turned on. Thereby, heating of the non-passing area on the surface of the fixing belt 25 can be stopped. Thereafter, when the non-passage region detection temperature T in the temperature detection sensor 61c becomes equal to or higher than a predetermined threshold temperature T2 by continuous printing, the control unit 35 activates the solenoid 63, and the temperature equalizing roller is formed on the inner surface of the fixing belt 25. 62 abuts to prevent a temperature rise in the non-passing area of the fixing belt 25.

  At this time, the temperature detection sensor 61a detects the passing region temperature of the fixing belt 25, and based on the detection result, the fixing control temperature is used as a reference value, and the control unit 35 controls the first heater 24a while the heater 24a is lit. During the lighting of the third heater 24c, ON / OFF control of the third heater 24c is performed, and the temperature of the passing region in the fixing nip portion is maintained at a substantially constant temperature at which fixing is possible.

  FIG. 9 is an example of a control procedure in this control example. In this control example, the first heater 24a is turned on in step 3, and in steps S4, S5, and S6, the temperature detection of the non-passing region of the fixing belt 25 is performed using the temperature detection sensor 61c. When T1 ≦ T in step S5, the first heater 24a is turned off and the third heater 24c is turned on (step 6). The other steps are the same as in FIG.

  In this control example, the first heater 24a capable of fixing A4 recording paper and the third heater 24c capable of fixing A5 recording paper are used. However, in continuous printing of A4 recording paper, other than that, for example, there is an effective light emission width at both ends of the third heater 24c, and it is sufficient to fix the A4 recording paper by emitting light together with the third heater 24c. Using another heater (not shown) designed to have an effective light emission width equal to or larger than the recording paper width, the other heater and the third heater 24c are turned on to start continuous printing, and the temperature detection sensor 61c does not pass. When the area detection temperature T is equal to or higher than T1, the heating control for turning off the other heater may be performed.

  According to such a configuration, since it is only necessary to turn off the other heater, heating control can be performed with a simple configuration as described above.

  As described above, with the configuration of the present invention, heating of the non-passing area of the fixing belt 25 is stopped, so that release of thermal energy from the non-passing area to the atmosphere can be suppressed. Moreover, since the contact time can be shortened by bringing the temperature equalizing roller 62 into contact with the fixing belt 25 after the heating is stopped, the release of heat energy to the temperature equalizing roller 62 due to such contact can also be suppressed. . Furthermore, the temperature gradient of the temperature distribution in the width direction of the fixing belt 25 can be reduced while suppressing the decrease of the heat energy to the non-passing region and the temperature-uniforming roller 62, and the temperature unevenness can be reduced. .

  Therefore, it is possible to fix a toner image having excellent image quality and thermal energy efficiency. Moreover, malfunctioning can be avoided by performing soaking control using predetermined threshold temperatures T1 and T2. Furthermore, in the heating control, if the second heater 24b (or the other heater) is turned off when the non-passage region detection temperature T is equal to or higher than T1, the configuration is simplified.

  In each of the above embodiments, A3 recording paper and A4 recording paper are respectively printed. However, it is possible to selectively print A3 width recording paper and A4 width recording paper. Examples of such a configuration include the following configuration.

  That is, in the flowchart (FIGS. 7 and 9) of each of the above embodiments, whether or not the set recording paper is a predetermined recording paper size (A4 recording paper size) by the control unit 35 after step S2. Is inserted, and if the size is larger than the predetermined size, the processing after step S3 in the control example 1 is performed. On the other hand, when it is determined that the recording sheet is equal to or smaller than the predetermined size, the processing after step S3 in the control example 2 is performed.

  Thus, of the first to third heaters 24a to 24c, the first heater 24a and the second heater 24b are used when printing A3 recording paper, and the first heater 24a is used when printing A4 recording paper. And the third heater 24c, that is, by selectively using the first to third heaters 24a to 24c, the fixing nip heating control and the temperature equalization control according to the width of the inserted recording medium are performed. It can be carried out. Accordingly, heating of the non-passing area of the fixing belt 25 can be further avoided, and further, heating control and soaking control excellent in thermal energy efficiency and toner image fixing can be performed.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the A3 and A4 width recording sheets have been described, but other sheets and combinations thereof can be applied in exactly the same manner. In this case, for example, a plurality of heaters corresponding to the width of the recording paper to be printed are provided on the heating roller 22 and a temperature detection sensor for the non-passing area of the fixing belt 25 corresponding to each recording paper is provided. When the temperature exceeds the predetermined threshold temperature T1, heating of the non-passing area is stopped, and when the non-passing area detection temperature T further rises and exceeds the predetermined threshold temperature T2, the temperature equalizing roller 62 is moved to the fixing belt 25. Inscribed in

  The present invention includes a fixing roller, a heating roller, an endless fixing belt stretched between the fixing roller and the heating roller, and a nip for inserting a recording medium into contact with the fixing roller via the fixing belt. A fixing roller for fixing a toner image carried on a recording medium at the nip portion. The fixing belt is disposed inside the heating roller, and is provided with a fixing roller. A plurality of heat generating means capable of separately heating the passing area and the non-passing area of the recording medium, temperature detecting means for detecting the temperature of the non-passing area, and contacting and separating from the inner surface of the fixing belt. Therefore, when the detection result of the temperature detecting means becomes equal to or higher than a predetermined temperature T1, the lighting of the heat generating means is controlled and controlled in advance. Control means capable of executing heating control for stopping heating of the non-passing region and temperature equalization control for bringing the temperature equalization means into contact with the fixing belt when the temperature becomes equal to or higher than a predetermined temperature T2 higher than T1; , With.

  Accordingly, by stopping heating of the non-passing area of the fixing belt, release of heat energy from the non-passing area to the atmosphere is suppressed, and after the heating is stopped, the soaking roller is brought into contact with the fixing belt. Thus, the contact time can be shortened, and the temperature unevenness in the width direction of the fixing belt can be reduced while suppressing the release of thermal energy to the temperature-uniforming roller. Therefore, it is possible to fix a toner image having excellent image quality and thermal energy efficiency. And malfunction can be avoided more by performing heating control and soaking | uniform-heating control using predetermined threshold temperature T1 and T2.

  Further, in the heating control described above, if the non-passage area detection temperature is equal to or higher than a predetermined temperature, the configuration is simpler if the power supply to the heating means is stopped. Further, by selectively using the heat generating means according to the widths of a plurality of recording media, it is possible to further avoid the heating of the non-passing area and to fix the toner image with excellent thermal energy efficiency.

1 is a schematic cross-sectional view showing a fixing device according to an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a temperature distribution diagram in the belt width direction of each fixing belt 25 by light emission of the first heater and the second heater according to the present embodiment. FIG. 6 is a temperature distribution diagram in the belt width direction of each fixing belt 25 by light emission of the first heater and the third heater according to the present embodiment. FIG. 3 is a block diagram illustrating an example of a control mechanism of the image forming apparatus according to the present embodiment. FIG. 6 is a temperature distribution diagram in the width direction of the fixing belt when A3 recording paper is continuously printed. FIG. 6 is a temperature distribution diagram in the width direction of the fixing belt when A3 recording paper is further continuously printed after the second heater is turned off. These are flowcharts showing an example (control example 1) of the control procedure of the image forming apparatus according to the present embodiment. These are temperature distribution diagrams which show the control result by this control example. These are flowcharts showing another control procedure example (control example 2) of the image forming apparatus according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 14 Fixing device 20 Fixing part 21 Fixing roller 22 Heating roller 24a 1st heater (1st heat generating means)
24b Second heater (second heating means)
24c Third heater (heat generating means)
25 Fixing belt 35 Control section (control means)
50 pressure part 51 pressure roller 61a temperature detection sensor 61b temperature detection sensor (temperature detection means for non-passing region)
61c Temperature detection sensor (temperature detection means for non-passing area)
62 Soaking roller (Soaking means)
63 Solenoid 100 Image forming apparatus

Claims (3)

A fixing roller, a heating roller, an endless fixing belt spanned between the fixing roller and the heating roller, and a nip portion that contacts the fixing roller through the fixing belt and allows the recording medium to pass therethrough are formed. An image forming apparatus equipped with a fixing device that fixes a toner image carried on a recording medium at the nip portion.
A plurality of heat generating means disposed inside the heating roller and capable of separately heating a passing area and a non-passing area of the recording medium in the fixing belt;
Temperature detecting means for detecting the temperature of the non-passing region;
Soaking means for soaking the fixing belt in the width direction by contacting and separating from the inner surface of the fixing belt; and
When the detection result of the temperature detection means becomes equal to or higher than the predetermined temperature T1, the heating control for controlling the lighting of the heat generation means to stop the heating of the non-passing region, and the predetermined temperature T2 higher than the T1. Control means capable of performing soaking control to bring the soaking means into contact with the fixing belt;
An image forming apparatus comprising:   The plurality of heat generating means inside the heating roller includes a first heat generating means for heating at least a central portion and a second heat generating means for heating both ends in the width direction of the recording medium, and the heating control is performed. The image forming apparatus according to claim 1, wherein energization of the second heat generating unit is stopped when executing.   The control means selectively selects the plurality of heating means when fixing a recording medium having a predetermined width smaller than a maximum width of the insertable recording medium or fixing a recording medium having a width larger than the predetermined width. The image forming apparatus according to claim 1, wherein the image forming apparatus is used in an image forming apparatus.

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