JP2005173446A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain fixing temperature at the time of standby while dissolving faults such as noise and wear of components at the time of standby for fixation. <P>SOLUTION: Length of width (heater lamp heating width) which becomes equal to or more than predetermined reference temperature with width of a fixing roller in the axis direction on the surface of the fixing roller by heating of a heater lamp is longer than length of the width (maximum paper feed width) of a medium with the maximum width of the fixing roller in the axis direction among media used for the fixing device. In addition, it is shorter than length of width (electromagnetic induction heating width) which becomes equal to or more than the reference temperature with width of the fixing roller in the axis direction on the surface of the fixing roller by heating of an induction heating apparatus. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device used for electrophotographic image formation and an image forming apparatus including the fixing device.

  In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers, copiers, and facsimiles. In order to achieve these required performances, it is important to improve the thermal efficiency of the fixing device used in the image forming apparatus.

  In an image forming apparatus, an unfixed toner image is transferred to a recording material sheet, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. Formed on recording material. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

  Among these, as an electromagnetic induction heating type fixing device, in the technique disclosed in Patent Document 1, Joule heat is generated by an eddy current generated in a magnetic metal member by an alternating magnetic field, and a heating body including the magnetic metal member is heated by electromagnetic induction. Means to make it have been proposed.

  Hereinafter, the configuration of the electromagnetic induction heating type fixing device will be described with reference to FIG. FIG. 11 is an explanatory view showing a conventional fixing device using an electromagnetic induction heating method. As shown in FIG. 11, the conventional fixing device has a film inner surface guide 221 on which a heating body 220 including an exciting coil unit 218 and a magnetic metal member 219 as a heating unit is mounted, and a magnetic metal member 219 against the inner wall. The fixing roller 201 having a heat-resistant cylindrical film 217 that wraps the film inner surface guide 221 in contact with the film 217 is pressed against the film 217 at the position of the magnetic metal member 219. A pressure roller 222 that forms the fixing nip N and rotates the film 217 is formed.

  The film 217 has a heat resistance of 100 μm or less, ideally 50 μm or less and 20 μm or more, and is a single layer film such as PTFE, PFA, FEP or the like, or a film such as polyimide, polyamideimide, PEEK, PES, PPS, etc. A composite layer film in which PTFE, PFA, FEP or the like is coated on the outer peripheral surface is used.

  The film inner surface guide 221 is made of a member having rigidity and heat resistance formed of a resin such as PEEK or PPS, and the heating body 220 is fitted in the substantially central portion of the film inner surface guide 221 in the longitudinal direction. Yes.

  The pressure roller 222 includes a core 222a and a heat-resistant rubber layer 222b having a good releasability such as silicone rubber provided around the core 222a. The pressure roller 222 has a predetermined bearing and biasing means (both not shown). The film 217 is sandwiched with a pressing force so as to be in pressure contact with the magnetic metal member 219 of the heating body 220. The pressure roller 222 is driven to rotate counterclockwise by a driving means (not shown).

  By the rotational driving of the pressure roller 222, a frictional force is generated between the pressure roller 222 and the film 217, and the rotational force acts on the film 217. The film 217 is in close contact with the magnetic metal member 219 of the heating body 220. While sliding.

  A medium having an unfixed toner image T formed by a printer engine (not shown) between the film 217 and the pressure roller 222 in the fixing nip N in a state where the heating body 220 has reached a predetermined temperature. A medium 211 is introduced. The medium 211 is sandwiched between the pressure roller 222 and the film 217 and conveyed through the fixing nip portion N, so that the heat of the magnetic metal member 219 is applied to the medium 211 via the film 217, and the unfixed toner image T Is melt-fixed on the medium 211. At the exit of the fixing nip N, the medium 211 that has passed is separated from the surface of the film 217 and conveyed to a paper discharge tray (not shown).

  As described above, in the electromagnetic induction heating type fixing device, the magnetic metal member 219 serving as the induction heating means is disposed close to the toner image T of the medium 11 through the film 217 by utilizing the generation of eddy current. Therefore, the heating efficiency is further improved as compared with the fixing device of the film heating type.

  Among image forming apparatuses, a fixing device in a full-color image forming apparatus is required to have a capability of sufficiently heating and melting a toner particle layer having a thickness of four or more layers. In order to achieve this requirement, an electromagnetic induction heating type fixing device requires a rubber elastic layer of about 200 μm on the surface of the film 217 in order to sufficiently enclose the toner image and uniformly heat and melt it.

JP-A-8-22206

  The electromagnetic induction heating type fixing device as described above generates heat directly from a heat generating member such as a fixing roller or a fixing belt by electromagnetic induction. Therefore, the heat conversion efficiency is higher and smaller than that of the heater lamp heating method. The surface of the fixing roller and the fixing belt can be quickly raised to the fixing temperature with electric power.

  However, in the electromagnetic induction heating type fixing device, if the electromagnetic induction heating is performed in a state where the heat generating member is stopped, the heat generating member becomes locally extremely high temperature. For this reason, when performing electromagnetic induction heating, it is necessary to rotate the heating member. At that time, there is no problem in rotating the heating member when heating is started and when the medium on which the toner image is formed is passed, but the image can be immediately formed in the standby state when the image is not formed. In order to maintain the heat generating member at the temperature, the heat generating member must always be rotated during standby, and the heat generating member is always in operation even though the device is not used. Rotation causes noise, and the heat generating member rotates even when not in use, so that wear of parts (for example, bearings, rollers, etc. when rotating the heat generating member) increases, and the life of the parts is the device life. There is a problem that it becomes shorter.

  In order to avoid these problems, it may be possible to maintain the temperature without rotating the heat generating member by considerably reducing the input power in the induction heating method, but if the heat generating member is not rotated, it is heated only locally. The temperature of the pressure roller or the like decreases, and the temperature of the heat generating member drops due to the pressure roller being deprived of the temperature when the paper is passed, causing problems such as poor fixing.

  An object of the present invention is to eliminate the problems such as noise and wear of parts during standby for fixing, and to maintain the fixing temperature during standby.

  Another object of the present invention is to minimize the amount of heat escaped from the end of the fixing roller and to form an effective heat distribution, thereby realizing downsizing of the apparatus and improvement in efficiency. .

  The present invention provides a fixing device for fixing a toner image on the medium by heating and pressing a medium on which a toner image is formed at a nip portion formed between a fixing roller and a pressure roller. An induction heating device that heats the fixing roller, a driving source that rotationally drives the fixing roller, a heater that is provided inside the fixing roller or the pressure roller, and that heats the fixing roller or the pressure roller, and the fixing When performing the above, the heating by the induction heating device and the rotational drive are performed, and when waiting for the execution of the new fixing, the heating by the induction heating device or the heating amount is reduced, the rotational drive is stopped, and the Control means for performing the heating by a heater, and a predetermined width of the fixing roller surface in the axial direction of the fixing roller by the heating of the heater. The length of the width equal to or higher than the reference temperature is longer than the maximum sheet passing width which is the length of the medium having the maximum axial width among the media used in the fixing device, and the fixing by heating of the induction heating device. In the fixing device, the width of the roller surface in the axial direction is shorter than the length of the width that is equal to or higher than the reference temperature.

  Therefore, the rotation of the fixing roller can be stopped during standby to eliminate problems such as noise and component wear, while the heater can maintain the fixing temperature during standby. Further, the amount of heat escaped from the end of the fixing roller can be minimized, and an effective heat generation distribution can be formed, so that the induction heating device can be reduced in size and improved in efficiency.

  The best mode for carrying out the present invention will be described.

  FIG. 1 is a longitudinal sectional view of a digital copying machine 100 according to the present embodiment. The digital copying machine 100 implements the image forming apparatus of the present invention, and is a so-called multifunction machine. That is, the digital copying machine 100 has a copying function and other functions, for example, a printer function and a facsimile function, and the copying function, the printer function, and the facsimile are operated by operating an application switching key of an operation unit (not shown). It is possible to select the functions by switching them sequentially. Thus, the copy mode is selected when the copy function is selected, the print mode is selected when the printer function is selected, and the facsimile mode is selected when the facsimile mode is selected.

  Next, the schematic configuration of the digital copying machine 100 and the operation in the copy mode will be described. In FIG. 1, in an automatic document feeder (hereinafter referred to as ADF) 101, a document placed on a document table 102 with an image surface facing upward is pressed when a start key on an operation unit (not shown) is pressed. Then, the sheet is fed to a predetermined position on the document table 102 made of contact glass by the feeding belt 104. The ADF 101 has a count function that counts up the number of documents every time a document is fed. After the image information is read by the image reading device 106, the document on the contact glass 105 is discharged onto the paper discharge tray 108 by the feeding belt 104 and the discharge roller 107.

  When the document set detector 109 detects that the next document is present on the document table 102, the lowermost document on the document table 102 is similarly contacted by the feed roller 103 and the feed belt 104. It is fed to a predetermined position on the glass 105. After the image information is read by the image reading device 106, the original on the contact glass 105 is discharged onto the paper discharge tray 108 by the feeding belt 104 and the discharge roller 107. Here, the feeding roller 3, the feeding belt 4, and the discharging roller 7 are driven by a conveyance motor.

  When selected, the first paper feeding device 110, the second paper feeding device 111, and the third paper feeding device 112 feed the stacked transfer paper, and the transfer paper is photosensitized by the vertical conveyance unit 116. It is transported to a position where it contacts the body 117. For example, a photosensitive drum is used as the photosensitive member 117, and is rotated by a main motor (not shown).

  Image data read from the document by the image reading device 106 is subjected to predetermined image processing by an image processing device (not shown) and then converted into optical information by a writing unit 118, and a charging device (not shown) is provided on the photosensitive drum 117. Are uniformly charged and then exposed to light information from the writing unit 118 to form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 117 is developed by the developing device 119 to become a toner image. A printer engine that forms an image on a medium such as paper by an electrophotographic system is configured by the writing unit 118, the photosensitive drum 117, the developing device 119, and other well-known devices around the photosensitive drum 117 (not shown). .

  The conveyance belt 120 serves as a sheet conveyance unit and a transfer unit, and a transfer bias is applied from a power source. The conveyance belt 120 is conveyed on the photosensitive drum 117 while conveying the transfer sheet from the vertical conveyance unit 116 at a constant speed with the photosensitive drum 117. The toner image is transferred onto the transfer paper. The transfer paper is fixed with a toner image by a fixing device 121 and is discharged to a paper discharge tray 123 by a paper discharge unit 122. The photosensitive drum 117 is cleaned of residual toner by a cleaning device (not shown) after the toner image is transferred.

  The above operation is an operation for copying an image on one side of a sheet in a normal mode. When an image is copied on both sides of a transfer sheet in a duplex mode, one of the paper feed trays 113 to 115 is copied. The transfer paper that is further fed and has an image formed on the surface as described above is switched to the double-sided paper feed path 124 side by the paper discharge unit 122 instead of the paper discharge tray 123 side, and switched back by the reversing unit 125 Then, the front and back sides are reversed and conveyed to the duplex conveying unit 126.

  The transfer paper transported to the double-sided transport unit 126 is transported to the vertical transport unit 116 by the double-sided transport unit 126, transported to the position where it abuts on the photoconductive drum 117 by the vertical transport unit 116, and is transferred onto the photoconductive drum 117. The toner image formed in the same manner as above is transferred to the back surface, and the toner image is fixed by the fixing device 121, whereby double-sided copying is performed. This double-sided copy is discharged to the paper discharge tray 123 by the paper discharge unit 122.

  Further, when the transfer paper is reversed and discharged, the transfer paper that is switched back by the reversing unit 125 and turned upside down is not conveyed to the duplex conveying unit 126 but is discharged via the reverse discharge conveyance path 127. The paper is discharged to the paper discharge tray 123 by the unit 122.

  In the print mode, image data from the outside is input to the writing unit 118 instead of the image data from the above-described image processing apparatus, and an image is formed on the transfer paper as described above.

  Further, in the facsimile mode, the image data from the image reading device 106 is transmitted to the other party by a facsimile transmission / reception unit (not shown), and the image data from the other party is received by the facsimile transmission / reception unit, instead of the image data from the image processing device described above. As a result, the image is formed on the transfer paper as described above.

  The digital copying machine 100 includes a large-sized sheet supply device (hereinafter referred to as LCT), a finisher 12 that performs sorting, punching, stapling, and the like, a mode for reading a document, setting of a copy magnification, and supply. And an operation unit for setting the paper tray, setting the post-processing by the finisher 12, and displaying to the operator.

  Next, the configuration of the fixing device 121 will be described with reference to FIG.

  A fixing device 121 shown in FIG. 2 includes an induction heating device 6, a heating roller 1 heated by electromagnetic induction of the induction heating device 6, a fixing roller 2 arranged in parallel with the heating roller 1, and the heating roller 1 and fixing. An endless belt-like heat-resistant belt (toner heating body) 3 that is stretched between the rollers 2 and heated by the heating roller 1 and rotated in the direction of arrow A by at least one of these rollers, and a belt 3 And a pressure roller 4 that is pressed against the fixing roller 2 and rotates in the forward direction with respect to the belt 3. The fixing device 121 heats and presses the medium 11 on which the toner image T is formed at a nip portion formed between the fixing roller 2 and the pressure roller 4 to fix the toner image T on the medium 11.

  The heating roller 1 is made of, for example, a hollow cylindrical magnetic metal member such as iron, cobalt, nickel, or an alloy of these metals, and has a low heat capacity and a high temperature rise.

  The fixing roller 2 includes, for example, a metal core 2a made of stainless steel or the like, and an elastic member 2b in which a heat-resistant silicone rubber is solid or foamed and covered with the core 2a. A contact portion having a predetermined width is formed between the pressure roller 4 and the fixing roller 2 by the pressing force from the pressure roller 4. The belt 3 stretched between the heating roller 1 and the fixing roller 2 generates heat at a contact portion W1 with the heating roller 1 heated by the induction heating device 6. Then, the inner surface of the belt 3 is continuously heated by the rotation of the heating roller 1 and the fixing roller 2, and as a result, the entire belt is heated.

As shown in FIGS. 2 and 3, the induction heating device 6 that heats the heating roller 1 by electromagnetic induction includes an exciting coil 7 that is a magnetic field generating means and a coil guide plate 8 around which the exciting coil 7 is wound. Have. The coil guide plate 8 has a semi-cylindrical shape arranged close to the outer peripheral surface of the heating roller 1. As shown in FIG. 3B, the excitation coil 7 is composed of a single long excitation coil wire. The coil is alternately wound along the coil guide plate 8 in the axial direction of the heating roller 1.
The exciting coil 7 is connected to an induction heating drive circuit 51 (FIG. 4) whose oscillation circuit has a variable frequency.

  Outside the excitation coil 7, a semi-cylindrical excitation coil core 9 made of a ferromagnetic material such as ferrite is fixed to the excitation coil core support member 10 and is disposed close to the excitation coil 7. In the present embodiment, the exciting coil core 9 has a relative permeability of, for example, 2500.

  The exciting coil 7 is fed with a high-frequency alternating current of 10 kHz to 1 MHz, preferably a high-frequency alternating current of 20 kHz to 800 kHz, thereby generating an alternating magnetic field. The alternating magnetic field acts on the heat generating layer of the heating roller 1 and the belt 3 in the contact area W1 between the heating roller 1 and the heat-resistant belt 3 and the vicinity thereof, and in the direction B that prevents the change of the alternating magnetic field inside these. Eddy current flows.

  This eddy current generates Joule heat according to the resistance of the heating roller 1 and the heat generating layer, and the belt 3 having the heating roller 1 and the heat generating layer mainly in the contact area between the heating roller 1 and the belt 3 and its vicinity. Is heated by electromagnetic induction.

  In the induction heating device 6 of the present embodiment, as shown in FIG. 2, a heater lamp 30 is provided inside the pressure roller 4, and the fixing roller 2 can be heated from the inside.

  FIG. 4 is a block diagram of a control system of the fixing device 121.

  This control system implements control means. A CPU 41 that centrally controls the fixing device 121, a ROM 42 that stores predetermined control programs and fixed data, and a RAM 43 that serves as a work area for the CPU 41 are connected via a bus 44. The microcomputer 45 is connected. The microcomputer 45 operates in accordance with control of a host microcomputer (not shown) that controls the entire copying machine 100 in a centralized manner.

  In the bus 44, an induction heating drive circuit 51 that drives the induction heating device 6 by energizing the induction heating device 6 (excitation coil 7 thereof), and a heater drive circuit 52 that drives the heater lamp 30 by energizing the heater lamp 30. A motor driving circuit 54 for driving a motor 53 that is a driving source for driving the belt 3 by rotating the heating roller 1 or the fixing roller 2, a temperature sensor 55 for detecting the temperature of the belt 3, and a heater lamp 30. A temperature sensor 56 for detecting the surface temperature of the pressure roller 4 (or the fixing roller 2) is connected.

  Next, the contents of the control operation executed by the CPU 41 based on the control program stored in the ROM 42 will be described.

  FIG. 5 shows the relationship between the temperature of the belt 3 (belt temperature), electromagnetic induction ON / OFF (a), heater lamp 30 ON / OFF (b), and belt 3 rotation ON / OFF (c). It is description explaining. In the following description, the CPU 41 determines whether it is at the time of start-up, paper-feeding, or standby, according to a command from the host microcomputer.

(1) At startup When the main power supply of the copying machine 100 is turned on, the CPU 41 turns on the induction heating device 6 and heats the belt 3 until the surface temperature of the belt 3 reaches a predetermined set temperature (electromagnetic induction ON). . At this time, the rotation of the motor 53 is started simultaneously with the turning on of the main power supply, and the driving of the belt 3 is started (belt rotation ON). Such an operation is a startup operation for starting up the fixing device 121 so that an image can be formed when the main power supply of the copying machine 100 is turned on.

(2) When paper is passed (when fixing is performed)
Due to the start-up operation, the belt 3 reaches a predetermined set temperature so that an image can be formed. When the image forming operation is started and fixing is performed, the belt 3 is further heated by electromagnetic induction heating (electromagnetic induction ON). . The driving of the belt 3 is also maintained (belt rotation ON).

(3) During standby When the image forming operation is completed and the next image formation is in a standby state waiting for an instruction from the user, the rotation of the belt 3 is stopped (belt rotation OFF), and heating by electromagnetic induction heating is also stopped. (Electromagnetic induction OFF). When the temperature of the belt 3 falls below a predetermined set temperature in this standby state, the heater lamp 30 inside the pressure roller 4 (or the fixing roller 2) is turned on to heat the pressure roller 4 (or the fixing roller 2). To do. Based on the temperature detected by the temperature sensor 56, the CPU 41 performs ON / OFF control of the heater lamp 30 (heater lamp ON / OFF) in order to keep the surface temperature of 4 (or the fixing roller 2) at a constant temperature. For example, the heater lamp 30 is turned off when the temperature detected by the temperature sensor 56 is higher than the first reference temperature, and the heater lamp 30 is turned on when the temperature is lower than the second reference temperature lower than the first reference temperature. This can be realized by doing so.

  Further, if the power of the heater lamp 30 in the pressure roller 4 (or the fixing roller 2) is set low in advance, the temperature of the pressure roller 4 (or the fixing roller 2) is constant even when the heater lamp 30 is fully lit. Since the temperature does not rise above the temperature, ON / OFF control of the heater lamp 30 becomes unnecessary.

  FIG. 6 is an explanatory diagram for explaining another example of the control operation.

  The control operation of FIG. 6 differs from that of FIG. 5 in that the belt 3 is continuously heated by electromagnetic induction heating even during standby (electromagnetic induction ON). However, in this case, the power supplied to the induction heating device 6 (excitation coil 7 thereof) is reduced and the amount of heat generated by electromagnetic induction heating is reduced as compared to when starting up and when passing paper. Even in this case, the heater lamp 30 is ON / OFF controlled in the same manner as in FIG. 5 to maintain the heating of the pressure roller 4 (or the fixing roller 2).

  In this case, if the power supplied to the heater lamp 30 is reduced, the temperature of the pressure roller 4 (or the fixing roller 2) exceeds a certain temperature even if the heater lamp 30 is fully lit without ON / OFF control. Therefore, the above-described ON / OFF control based on the temperature detected by the temperature sensor 56 is not necessary.

  FIG. 7 is a timing chart of the contents of the control operation described above with reference to FIGS. That is, the CPU 41 determines whether the current time is a start-up time, a paper passing time, or a standby time according to a command from a host microcomputer, and performs the following control. First, at the time of start-up or paper passing (Y in step S1), electromagnetic induction is turned on to perform induction heating by the induction heating device 6, and belt rotation is turned on to drive the belt 3 ( Step S2). When it is a standby time (Y in Step S3), the electromagnetic induction is turned off (or the supply power is reduced and turned on), the belt rotation is turned off, and the heater lamp 30 is turned on and off (Step S4).

  With the above control operation, the pressure roller 4 (or the fixing roller 2) is heated from the inside during standby to maintain the surface temperature of the pressure roller 4 (or the fixing roller 2) at the set temperature, so that the belt 3 is electromagnetic. By local heating of only the heated portion by induction heating, it is possible to prevent heat from being taken away by the pressure roller 4 at the time of paper passing and the temperature of the belt to drop, thereby causing a fixing failure.

  Since the driving of the belt 3 is stopped during standby, it is possible to prevent the occurrence of problems such as noise and wear of parts caused by continuing to drive the belt 3 during standby.

  Here, the arrangement of the heater lamp 30 arranged in the pressure roller 4 will be described. As shown in FIGS. 2 and 3B, the excitation coil 7 of the induction heating device 6 is wound around a position facing the heating roller 1 and has a curved shape along the outer peripheral surface of the heating roller 1. ing. At this time, the heat generation distribution of the heating roller 1 generates heat in the hatched portion E shown in FIG. On the other hand, since the number of turns at the end of the excitation coil 7 cannot be increased and the magnetic flux density is low, the amount of heat generation is low, and even if the temperature at both ends of the heating roller 1 and the belt 3 is increased, the temperature is hardly increased. Therefore, the length of the exciting coil 7 parallel to the heating roller 1 in FIG. 3 is set to the fixing roller when the medium 11 passes through the fixing device 121 among the media 11 such as paper of various sizes used in the copying machine 1. 2. It is necessary to take longer than the width length (maximum sheet passing width) of the pressure roller 4 having the maximum width in the axial direction. The length of the exciting coil 7 is made longer than the maximum sheet passing width, the width of the shaded portion E (heating width) of the heating roller 1, the width of the belt 3 that receives heat from the shaded portion E, and consequently the fixing roller 2 is the belt. 3, the width of the range in which the fixing roller 2 is heated by induction heating (the surface temperature of the fixing roller 2 when there is no heating by the induction heating device 6 and the heater lamp 30) The width of the range (heat generation width) that is higher than the reference temperature (however, a predetermined temperature higher than this temperature may be used as the reference temperature) is longer than the maximum sheet passing width, and the width direction of the medium 11 having the maximum sheet passing width size. It is possible to sufficiently heat both ends of the.

  However, unnecessarily lengthening the exciting coil 7 may increase the size of the fixing device 121, and the length of the fixing device 121 may be limited by the length. For this reason, the fixing roller 2 during standby is heated by the heater lamp 30 having a heat generation width that is wider than the maximum sheet passing width in the pressure roller 4 (or the fixing roller 2) and narrower than the heat generation width by the induction heating device 6. And the pressure roller 4 are configured to assist heating to a substantially maximum sheet passing width. At this time, if the range of the heat generation by the induction heating device 6 is equal to or longer than the heat generation width of the heater lamp 30, the heating area other than the sheet passing range is heated, and the heat generation amount per unit length. As a result, the efficiency is lowered. Therefore, the heat generation width by the heater lamp 30 is set narrower than the heat generation width by the induction heating device 6. FIG. 9 shows the position of the fixing roller 2 in the axial direction on the horizontal axis and the surface temperature of the fixing roller 2 at each position on the horizontal axis, and shows the maximum sheet passing width at the axial position of the fixing roller 2. Each heating range is also shown.

  In addition, the heater lamp 30 may be set so that the amount of heat generated at both ends thereof is larger than that at the center. This can be realized by making the filaments at both ends of the heater lamp 30 thicker than the central portion thereof (the heater lamp 30 having such a configuration is well known and will not be described in detail). FIG. 10 is an explanatory diagram corresponding to FIG. 8 in this case. According to such a configuration, it is effective when the temperature at both ends of the pressure roller 4 decreases due to heat transfer from the support shaft of the pressure roller 4 during standby. By making the temperature of the end of the nip portion with the pressure roller 4 higher than the central portion, the same effect as in FIG. 9 can be obtained without unnecessarily increasing the size of the induction heating device 6.

  With this configuration, the heat generation width of the heater lamp 30 disposed in the pressure roller 4 (fixing roller 2) is wider than the maximum sheet passing width and shorter than the heat generation width by the induction heating device 6, and the fixing roller Thus, the amount of heat escape from the end portion of 2 can be minimized, an effective heat distribution can be formed, and the induction heating device 6 can be reduced in size and improved in efficiency.

1 is a longitudinal sectional view of a digital copying machine according to an embodiment of the present invention. FIG. 3 is an explanatory diagram of a configuration of a fixing device. It is explanatory drawing of a structure of an induction heating apparatus. It is a block diagram of a control system. It is explanatory drawing explaining the control content. It is explanatory drawing explaining another control content. It is a flowchart explaining the control content. It is explanatory drawing of an effect | action of an induction heating apparatus. It is explanatory drawing explaining the temperature in each position of the width direction of a fixing roller. FIG. 6 is an explanatory diagram for explaining temperatures at respective positions in the width direction of the fixing roller when the heat generation amount at both end portions in the axial direction of the heater lamp is larger than the heat generation amount at the central portion. It is explanatory drawing of the conventional fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating roller 2 Fixing roller 3 Belt 4 Pressure roller 6 Induction heating apparatus 11 Medium 100 Image forming apparatus 121 Fixing apparatus T Toner image

Claims (5)

In a fixing device for fixing the toner image on the medium by heating and pressing the medium on which the toner image is formed at a nip portion formed between the fixing roller and the pressure roller.
An induction heating device for heating the fixing roller by electromagnetic induction;
A drive source for rotationally driving the fixing roller;
A heater provided inside the fixing roller or the pressure roller and heating the fixing roller or the pressure roller;
When the fixing is performed, the induction heating device performs the heating and the rotational driving, and when waiting for a new fixing, the induction heating device stops the heating or reduces the heating amount, and stops the rotational driving. And control means for performing the heating by the heater;
With
The width of the fixing roller surface that is equal to or higher than a predetermined reference temperature in the axial direction of the fixing roller due to the heating of the heater is that of the medium used in the fixing device having the maximum axial width. Longer than the maximum sheet passing width that is the length of the width, and shorter than the length of the width that becomes equal to or higher than the reference temperature in the axial width of the surface of the fixing roller by heating of the induction heating device,
A fixing device.   The fixing device according to claim 1, wherein the reference temperature is a surface temperature of the fixing roller when the heating by the heater and the induction heating device is not performed.   The fixing device according to claim 1, wherein the heater has a heat generation amount at both end portions in the axial direction larger than a heat generation amount at a central portion. A heating roller that receives the heating by the induction heating device;
A belt stretched between the heating roller and the fixing roller;
With
The drive source drives the belt by rotationally driving the heating roller or the fixing roller to rotationally drive the heating roller and the fixing roller.
The fixing device according to claim 1, wherein In an electrophotographic image forming apparatus,
An image forming apparatus comprising the fixing device according to claim 1.

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