JP2007334368A - Fixing device - Google Patents

Abstract

In an induction heating type fixing device incorporated in an image forming apparatus using toner, it is possible to suppress the generation of interference sound and to control the occurrence of flicker or the like less easily.
A fixing device 1 according to the present invention can independently raise the temperature of first and second thermistors 6a and 6b for detecting the temperature at a predetermined position in the longitudinal direction of a roller 2 and the center and end of a heating roller. First and second coils 11a and 11b, a drive circuit 33 for alternately supplying electric power to the respective coils, and first and second switching circuits 32a and 32b for supplying predetermined electric power to the individual coils, A CPU 34 and a temperature detection circuit 35 are included. The CPU 34, together with the main CPU 151 of the image forming apparatus 101, controls the power supplied to each coil based on the output of the temperature detection circuit.
[Selection] Figure 4

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device using induction heating, and more particularly to a fixing device for fixing toner that can be used in an electrophotographic copying machine or printer using a heat-meltable toner as a visualizing agent.

  A fixing device incorporated in a copying apparatus using an electrophotographic process heats and melts toner formed on a member to be fixed, and fixes the toner to the member to be fixed. As a method for heating toner usable in the fixing device, a method using radiant heat of a filament lamp, a flash heating method using a flash lamp as a heat source, and the like are widely known.

  However, a fixing device using a filament lamp radiates and heats a roller body surrounding the lamp by light and infrared rays generated by the filament lamp. Therefore, the heat conversion efficiency considering the loss when light is converted into heat and the efficiency when air heated in the roller transfers heat to the roller is 60 to 70%. For this reason, it is known that the time required for warming up becomes longer.

  From such a background, a fixing device using an induction heating device as a heat source is proposed in Japanese Patent Application Laid-Open Nos. 9-258586 and 8-76620.

  In Japanese Patent Laid-Open No. 9-258586, a current is passed through an induction coil in which a coil is wound around a core provided along the rotation axis of a metal roller to generate an induction current (eddy current) in the roller, thereby heating the roller. A fixing device is disclosed.

  In JP-A-8-76620, a conductive film containing magnetic field generating means and a pressure roller that is in close contact with the conductive film are arranged, and the conductive film is heated to convey between the conductive film and the pressure roller. A fixing device that fixes toner on a recording medium to the recording medium is disclosed.

  In order to prevent the temperature of the paper passage width from becoming uneven, an example in which a plurality of coils are arranged in accordance with the paper passage width along the axial direction of the fixing roller, and the power supplied to the coils is controlled. It is disclosed in Japanese Patent Laid-Open No. 2000-206913. In the fixing device disclosed in this publication, the temperature of the fixing roller is detected at a plurality of detection points, and the power supplied to each coil is controlled based on the temperature detected at each detection point.

  Japanese Patent Laid-Open No. 2001-31178 discloses an example in which power is independently supplied to each of a plurality of coils.

  In the coil driving method disclosed in Japanese Patent Application Laid-Open No. 2000-206813, the power supplied to the plurality of coils is changed simultaneously. For this reason, there is a problem that a difference occurs in the frequency of the electric power flowing through each coil and an interference sound (beat sound) is generated. In addition, there is a problem that a device for detecting the magnitude of the power supplied to each coil must be provided independently.

  The driving method disclosed in Japanese Patent Application Laid-Open No. 2001-31178 also has a problem that an apparatus for detecting the magnitude of the power supplied to each coil must be provided independently.

  That is, in any of the driving methods disclosed in the publications, it is necessary to manage the power of the entire fixing device while managing the amount of power with each coil. Necessary for coils.

  Further, when the coils are driven simultaneously, the amount of power generated in each coil is changed according to the temperature difference in the longitudinal direction of the roller. In this case, the frequency of the inverter circuit varies depending on the output. This means that there are a plurality of coils driven at different frequencies, and interference sound may occur. In particular, there is a problem that the greater the frequency difference, the greater the interference sound.

  In any of the publications, it is described that the temperature difference of the temperature detection means arranged at a position opposite to each coil is detected and electric power is distributed to each coil based on the temperature difference. However, when the power distribution is varied, voltage fluctuations, temperature ripples, and the like are different.

  Therefore, if the coil to be supplied with electric power is simply switched, there is a problem that flickering occurs in the surrounding lighting device, particularly the fluorescent lamp. Needless to say, if the temperature ripple is large, the variation in fixability is increased.

  An object of the present invention is to provide an induction heating type fixing device capable of suppressing the generation of interference sound and hardly causing flicker or the like in the surroundings.

  The present invention has been made on the basis of the above problems, and is arranged so as to be able to provide a predetermined pressure to the heat generating member having a cylindrical shape or a belt shape formed of a material that generates an induced current by electromagnetic induction. A pressure member that provides a predetermined pressure to the medium that is passed between the heat generating member and a first coil body that is supplied with predetermined power for generating an induced current in the heat generating member. And a second coil body that is arranged in a predetermined positional relationship with respect to each of the first coil body and the heat generating member, and is supplied with a predetermined power for generating an induced current in the heat generating member. And a first temperature detection that is provided in the vicinity of the first position where the heat generating member is heated by the induced current from the first coil body and detects the temperature at the first position of the heat generating member. Machine And a second temperature detection that is provided in the vicinity of the second position where the heat generating member is heated by the induced current from the second coil body and detects the temperature of the heat generating member at the second position. And a temperature at the first position of the heat generating member detected by the first temperature detecting mechanism and a temperature at the second position of the heat generating member detected by the second temperature detecting mechanism. In comparison, the temperature difference detection mechanism that outputs the temperature difference between the two and the first coil body and the second coil so that the temperature difference value output by the temperature difference detection mechanism is a predetermined value. A drive control mechanism that stops the supply of the predetermined power to one of the bodies and supplies the predetermined power to the other, and is output from the respective temperature detection mechanisms by the drive control mechanism From the temperature information to one of the coil bodies The temperature difference reference value held by the temperature difference detection mechanism when power is selectively supplied is set to be larger during standby than during fixing operation. .

  As described above, according to the present invention, in an image forming apparatus including an induction heating type fixing device, it is possible to suppress the occurrence of interference noise and to reduce the occurrence of flicker or the like in the surroundings.

  FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus to which an induction heating fixing device according to an embodiment of the present invention can be applied.

  As shown in FIG. 1, a digital copying apparatus (image forming apparatus) 101 forms an image corresponding to image data supplied from an image reading apparatus (scanner) 102 or from the scanner 102 or from the outside, and is to be fixed (object to be fixed). And an image forming unit 103 that outputs (fixes) the sheet P as a transfer material.

  When the image forming unit 103 is irradiated with light in a state where a predetermined potential is applied, the potential of the region irradiated with the light is changed and the change in the potential is held as an electrostatic image for a predetermined time. A photoconductor capable of being formed has a cylindrical photoconductor drum 105 formed on the outer peripheral surface.

  Image information is exposed on the photosensitive drum 105 from an exposure device 106 that can output a laser beam whose light intensity is changed in accordance with image data supplied from the scanner 102 or an external device. Accordingly, an electrostatic image, that is, an image is formed on the outer peripheral surface of the photosensitive drum 105. The image formed on the photosensitive drum 105 is visualized by selectively supplying toner as a visualization agent from the developing device 107.

  The toner aggregate, that is, the toner image on the photosensitive drum 105 developed (visualized) by the developing device 107 is fed by a paper feeding / conveying section by supplying a voltage for transfer from a transfer device (not described in detail). Is transferred to the paper P.

  The paper P on which the toner image is fixed by the fixing device 1 is discharged by a paper discharge roller 112 to a paper discharge tray 113 which is a space defined between the paper cassette 108 and the scanner 102 and is sequentially stacked.

  2 and 3 are schematic diagrams for explaining an example of a fixing device used in the image forming apparatus shown in FIG. 2 is a schematic cross-sectional view showing a state in which the fixing device 1 is cut at approximately the center in the long direction, and FIG. 3 is a plan view of the fixing device 1 in a state in which covers not described in detail are removed. It is a schematic plan view which shows the state seen.

  The fixing device 1 includes a heating (fixing) roller 2 having a diameter of approximately 50 mm and a pressure (pressing) roller 3 having a diameter of approximately 50 mm.

  The fixing roller 2 is a metal hollow cylinder having a thickness of about 1.5 mm. In this embodiment, iron is used, but stainless steel, aluminum, an alloy of stainless steel and aluminum, or the like can be used. Note that the length of the fixing roller 2 is approximately 340 mm in this example.

  On the surface of the fixing roller 2, a release layer (not shown) in which a fluorine resin typified by, for example, tetrafluoroethylene resin (Teflon (registered trademark)) is deposited to a predetermined thickness is formed.

  Instead of the fixing roller 2, a metal film having an endless belt shape formed by depositing a predetermined thickness of metal on the surface of a resin film having high heat resistance may be used.

  The pressure roller 3 is a roller in which an elastic body such as silicon rubber or fluorine rubber having a predetermined thickness is formed (coated) around an axis having a predetermined diameter. Note that the length of the pressure roller 3 is approximately 320 mm.

  The pressure roller 3 is arranged so that its own axis is substantially parallel to the axis of the fixing roller 2, and is pressed against the axis of the fixing roller 2 with a predetermined pressure via the pressure mechanism 4. Thereby, a part of the outer peripheral surface of the pressure roller 3 is elastically deformed, and a predetermined nip is defined between the two rollers. A separation claw 5 for separating the paper P passing through the nip from the fixing roller 2 is positioned at a predetermined position near the nip on the downstream side in the direction in which the fixing roller 2 rotates with respect to the nip. Yes. Further, when a metal film is used instead of the fixing roller 2, the nip may be formed on the film side.

  Although not shown, the fixing roller 2 is rotated in the direction of the arrow at a substantially constant speed by a driving force from a drum motor (or a fixing device (not shown) provided to rotate the fixing roller) for rotating the photosensitive drum 105. .

  Since the pressure roller 3 is in contact with the fixing roller 2 at a predetermined pressure by the pressure mechanism 4, the pressure roller 3 is rotated at a constant speed together with the fixing roller 2 by rotating the fixing roller 2.

  Around the fixing roller 2, at least two temperature detection elements 6 a and 6 b, a cleaner 7, and a heat generation abnormality detection element 8 are provided in order in the direction away from the peeling claw 5 along the direction in which the roller 2 is rotated. ing.

  The temperature detection elements 6 a and 6 b are, for example, thermistors for detecting the temperature of the outer peripheral surface of the fixing roller 2. At least one of the rollers 2 is positioned approximately in the center in the longitudinal direction. The other one is located at one end of the roller 2 in the longitudinal direction.

  Needless to say, three or more thermistors may be provided as necessary.

  The cleaner 7 removes toner that adheres to the fluororesin provided at a predetermined thickness on the outer periphery of the fixing roller 2, paper dust generated from the paper, or dust that floats inside the apparatus and adheres to the fixing roller 2. Remove. The cleaner 7 includes a cleaning member formed of a material that does not easily damage the fluororesin layer even if it comes into contact with the fixing roller 2, such as a felt or a fur brush, and a support member that supports the cleaning member. The cleaning member may be rotated in contact with the surface of the fixing roller 2 or may be pressed against the outer peripheral surface of the fixing roller 2 with a predetermined pressure.

  The heat generation abnormality detection element 8 is, for example, a thermostat, detects a heat generation abnormality in which the surface temperature of the fixing roller 2 is abnormally increased, and energizes a heating coil described below when a heat generation abnormality occurs. Used to shut off.

  Note that the order and position in which the temperature detection elements 6a and 6b, the cleaner 7 and the heat generation abnormality detection element 8 are arranged are not limited to the order and position shown in FIG.

  On the circumference of the pressure roller 3, a peeling claw 9 for peeling the paper P from the pressure roller 3 and a cleaning roller 10 for removing toner adhering to the circumferential surface of the pressure roller 3 are provided.

  Inside the fixing roller 2, an exciting coil 11 that generates eddy current is disposed on the material of the roller 2. In the example shown in FIG. 3, the exciting coil 11 includes a first coil 11 a located approximately in the center of the fixing roller 2 in the longitudinal direction, and second coils 11 b provided near both ends of the roller 2. Consists of.

  The second coil 11b is a coil obtained by winding a wire material having substantially the same resistivity and cross-sectional area (number of stranded wires) as the first coil 11a by the number of turns substantially equal to the number of turns of the first coil 11a. The second coil 11 b is located on both sides of the roller 2 in the axial direction with the first coil 11 a interposed therebetween in the longitudinal direction of the roller 2. In addition, the 2nd coil 11b is two parts located in the both sides of the 1st coil 11a, and is mutually connected in series. Therefore, the second coil 11b can output an output substantially equivalent to that of the first coil 11a (when it is necessary to identify individual coil portions, each portion is designated as the coil 11-1 or 11). -2).

  The first coil 11a is formed to have a length that can heat the width that contacts the outer peripheral surface of the roller 2 when, for example, A4 size paper is conveyed so that its short side is parallel to the axis of the fixing roller 2. Has been. Needless to say, the second coil 11 b is useful for heating the vicinity of both ends of the fixing roller 2.

  The first and second coils 11a and 11b are formed of litz wires twisted in an arbitrary number of wires obtained by covering a copper wire having a predetermined diameter with a heat-resistant material and insulating each other. In the embodiment of the present invention, the diameter of each wire rod of the litz wire is 0.5 mm, and the number of twists is 16. Polyamideimide is used as a covering material for insulating each wire. Thus, by using a litz wire for each of the coils 11a and 11b, the diameter of each wire can be made smaller than the penetration depth of the skin effect that occurs when the high-frequency current flows through each wire. The resistance value is reduced. Therefore, the power supplied to each coil can be used effectively.

  In the embodiment of the present invention, the coils 11a and 11b are wound around a magnetic core 12 formed in a predetermined shape as shown in FIG. By using the magnetic core 12, the magnetic flux generated from the coil is strengthened, and a predetermined output can be obtained even with a small number of turns.

  FIG. 4 is a schematic diagram illustrating an example of an excitation circuit that supplies a predetermined high-frequency current to the excitation coil shown in FIGS.

  As shown in FIG. 4, a first switching circuit (inverter circuit) 32a of the excitation unit 31 is connected to the central portion, that is, the first coil 11a. A second switching circuit (inverter circuit) 32b is connected to both ends, that is, the second coil 11b.

  Each inverter circuit 32a, 32b switches the DC voltage supplied from the power supply circuit 30 based on the drive frequency instruct | indicated by the drive circuit 33, and supplies it to each coil 11a, 11b. In addition, although the drive frequency instruct | indicated to each inverter circuit 32a, 32b is set by CPU34 based on the temperature conditions demonstrated below, it is the range of 20 kHz thru | or 50 kHz, for example. Accordingly, each of the coils 11a and 11b can output a high-frequency output of 700 W to 1.5 kW, for example, in terms of power in order to raise the temperature of the fixing roller 2 to a predetermined temperature.

  When the inverter circuit (first and second switching circuits 32a and 32b) is used, the power supplied to the coils (11a and 11b) incorporated in the circuit depends on the magnitude of the high-frequency current flowing through the coils. The magnitude of the high-frequency current is set by changing the ON time of the switching element of the inverter circuit. That is, the magnitude of the power supplied to each coil is changed based on the timing of the ON time and OFF time of the switching element instructed from the CPU 34 to the drive circuit 33, but is output to the coil thereafter. This will be described as electric power.

  The drive circuit 33 also alternately supplies the rectified output from the power supply circuit 30 to only one of the first and second inverter circuits 32a and 32b. That is, the drive circuit 33 also functions as a drive switching unit for supplying predetermined power to one of the two coils 11a and 11b. Note that the magnitude of the power applied to each of the coils 11a and 11b can be arbitrarily set by changing the ON time of the switching element input from the drive circuit 33 as described above. In the embodiment, the difference in power level is at most 30%, preferably not more than 20%, more preferably 10 so that no interference noise is generated or the surrounding lighting device is not affected when switching by the drive circuit 33. It is set to be within%.

  The drive frequency instructed to each of the inverter circuits 32a and 32b includes temperature data indicating the temperature near the center of the outer peripheral surface of the fixing roller 2 detected by the first thermistor 6a output from the temperature detection circuit 35 by the CPU 34 and the first frequency. 2 is set based on the temperature data indicating the temperatures of both ends of the roller 2 detected by the thermistor 6 b and is instructed to the drive circuit 33. Further, based on the temperature difference output from the temperature detection circuit 35, a motor pulse is supplied from the main CPU 151 on the copying apparatus 101 side to, for example, the fixing motor 123, that is, the motor driving circuit 153 for rotating the heating roller 2.

  Although the correspondence relationship between the temperature data and the output, the switching timing of energization to the first and second inverter circuits 32a and 32b by the drive circuit 33, etc. are not shown, for example, the data is stored in advance in a rewritable memory. ing. The data stored in the memory can be arbitrarily rewritten according to the power supply situation in the country or region where the copying apparatus 101 is installed or the maximum value of power that can be input to the copying apparatus 101.

  The main CPU 151 can detect an abnormality in, for example, the two thermistors 6 a and 6 b or the temperature detection circuit 35 based on the temperature difference output from the temperature detection circuit 35. That is, when any abnormality occurs in the individual thermistors 6a and 6b and the temperature detection circuit 35, or the energization to the coil for heating the heating roller 2 is interrupted due to factors such as paper jamming on the image forming unit 103 side. When it is necessary to do so, a control instruction for stopping a drive instruction from the drive circuit 33 to each switching circuit can be input to the CPU 34.

  As a method of supplying predetermined power to the first and second coils of the fixing roller of the fixing device using the excitation circuit shown in FIG. 4, basically, the first (center) coil 11a and the first coil 11a are used. Electric power is not simultaneously supplied to each of the two (end) coils 11b.

  That is, in the embodiment of the present invention, a method is used in which predetermined power is supplied to only one of the coils, or power is not temporarily supplied to any of the coils. In the embodiment of the present invention, the power supplied to the first coil 11a and the power supplied to the second coil 11b are set to be approximately equal. Roughly, when predetermined power is alternately supplied to the first and second coils 11a and 11b and the temperature near the center of the roller 2 reaches the set target temperature, the roller 2 temporarily The power supply to all the coils may be stopped until the temperature near the center becomes lower than the set target temperature by a predetermined temperature.

  Needless to say, it is possible to supply power to all the coils at the same time. In that case, however, the individual coils must be provided with a power detection mechanism for detecting the power output from the coils. As described above, it is preferable to supply power only to one of the coils. Note that if the difference in frequency of power supplied to each coil exceeds a predetermined range, not only the above-described interference sound is generated, but also within a specific range of the commercial power source to which the copying apparatus is connected. Since voltage fluctuations occur and flicker or the like occurs, when switching the coils to which power is supplied, it is preferable that the power supplied to each coil be substantially equal.

  Next, a method of selecting a coil to be supplied with predetermined power and raising the temperature of the heating roller will be described.

  As shown in FIG. 5, when a power switch (not shown) of the copying apparatus 101 is turned on, the temperature of the corresponding region of the fixing roller 2 is detected by the first and second thermistors (temperature detection mechanisms) 6a and 6b. . That is, the temperature around the center of the roller 2 in the longitudinal direction is detected by the thermistor 6a, and the temperature at the end of the roller 2 in the longitudinal direction is detected by the thermistor 6b. The detection outputs output from the thermistors 6a and 6b are input to the temperature detection circuit 35 (S1).

  The temperature data CT indicating the temperature near the center of the roller 2 and the temperature data ST indicating the temperature at the end of the roller 2 output from the temperature detection circuit 35 are output to the CPU 34 and the main CPU 151 of the image forming unit 103. First, the CPU 34 compares the temperature data CT with a set target temperature read from a memory (not shown). The set target temperature is, for example, 180 ° C. (S2).

  When the temperature data CT is lower than the set target temperature (S2-YES), energization of the first coil 11a is performed so that power of a predetermined frequency is supplied from the CPU 34 to the drive circuit 33 to the first coil 11a. Is instructed. When the temperature at the center of the roller 2 has already reached the set target temperature (S2-NO), as will be described later, the supply of power to the coil 11a is stopped and the standby state (warm-up end) is entered.

  On the other hand, when the temperature data CT is lower than the set target temperature, a predetermined drive frequency is input from the drive circuit 33 to the first inverter circuit 32a, so that the DC voltage from the power supply circuit 30 becomes the first voltage. 1 is switched by the inverter circuit 32a and supplied to the first coil 11a (S3).

  Next, it is checked whether or not the temperature near the center of the roller 2 (temperature data CT) is higher than the temperatures at both ends of the roller 2 (temperature data ST) (S4). If it is detected in step S4 that the temperature near the center of the roller 2 is lower than the temperature at the end (S4-NO), as will be described later, the power to the first coil 11a is Supply, i.e. heating in the middle of the roller, is temporarily stopped.

  When it is detected that the temperature at the center of the roller 2 is higher than the temperature at the end of the roller 2 (S4-YES), the temperature difference “CT-ST” in the longitudinal direction of the roller 2 is detected. Further, the temperature difference “CT-ST” is set to 5 ° C., for example (S5).

  In step S5, when it is detected that the difference between the temperature near the center of the roller 2 and the temperature at the end of the roller 2 is 5 ° C. or more (S5-YES), the power supplied to the coil 11a is It is shut off by a drive stop instruction from the CPU 34 to the drive circuit 33 (S6).

  On the other hand, if it is detected in step S5 that the difference between the temperature at the center of the roller 2 and the temperature at the end of the roller 2 is less than 5 ° C. (S5-NO), Electric power is supplied (the center of the roller 2 is heated).

  In step S6, when the supply of power to the first coil 11a is stopped, this time, the second coil 11b is supplied with power substantially equal to the power supplied to the first coil 11a. Is supplied by switching of the second inverter circuit 32b corresponding to the instruction (setting of the drive frequency) from (S7).

  Thereafter, it is checked whether or not the temperature at the end of the roller 2 (temperature data ST) is higher than the temperature near the center of the roller 2 (temperature data CT) (S8).

  If it is detected in step S8 that the temperature of the end of the roller 2 is higher than the temperature near the center (S8-YES), whether or not the temperature difference “ST-CT” between the two is greater than 5 ° C., for example. Is checked (S9).

  In step S9, when it is detected that the temperature of the end of the roller 2 is higher than the center temperature (S9-YES), the CPU 34 instructs the drive circuit 33 to stop the power to the coil 11b (S10). ). Therefore, when the temperature at the center of the roller 2 reaches 180 ° C. and the difference between the temperature at the end of the roller 2 and the temperature at the center of the roller 2 exceeds 5 ° C., the power supply to all the coils is Temporarily stopped.

  When it is detected in step S8 that the temperature of the end of the roller 2 is lower than the center temperature (S8-NO) and in step 8, the temperature difference “ST-CT” is less than 5 ° C. Needless to say, predetermined power is continuously supplied to the coil 11b in (S9-NO).

  In the driving method shown in FIG. 5, power is first supplied to the first coil 11a that heats up the center in the longitudinal direction of the roller 2, and the temperature in the center of the roller 2 causes the end of the roller in the longitudinal direction to move. When the temperature is raised to a temperature higher than the temperature of the end of the roller 2 detected at a position facing the second coil 11b to be raised, the power supply to the central coil 11a is stopped, and the end A predetermined power is supplied to the coil 11b. Further, when the temperature in the vicinity of the center in the longitudinal direction of the roller 2 reaches 180 ° C., the current supply to all the coils is temporarily interrupted without checking the temperature of the end portion.

  By repeating such control, the temperature of the center of the roller 2 and the end of the roller 2 can be made uniform. In the driving method described above, the set target temperature (180 ° C.) of the roller 2 can be controlled even if the supply of electric power is controlled based only on the detection result by the thermistor 6 a provided near the center of the roller 2. There is a feature that the temperature of the roller 2 can be raised to substantially the same temperature (180 ° C.) even if the supply of electric power is controlled based only on the detection result by the thermistor 6b provided at the end. In this case, the temperature at the end of the roller 2 may temporarily exceed 180 ° C., but the temperature difference between the temperature CT at the center of the roller and the temperature ST at the end of the roller does not exceed 5 ° C. Therefore, the temperature of a specific part of the roller does not rise extremely.

  Needless to say, when both the center and end of the roller 2 reach the target set temperature, power is supplied from the inverter circuits 32a and 32b to the corresponding coils, that is, from the drive circuit 33 to the inverter circuits 32a and 32b. Since the input of the driving frequency is stopped, the temperature of the entire area of the roller 2 is maintained substantially uniform.

  6 and 7 are schematic diagrams for explaining an example in which the switching timing when switching the coil for supplying power described with reference to FIG. 5 is adapted to the operation state of the copying apparatus.

  In the driving method shown in FIG. 6, when the temperature difference obtained from the temperature data CT at the center of the roller 2 output from the temperature detection circuit 35 and the temperature data ST at the end of the roller 2 reaches 3 ° C., the CPU 34 It is characterized by instructing the drive circuit 33 to switch the coil for supplying power. That is, when the temperature at the center of the roller 2 reaches 180 ° C., energization of all the coils is stopped, and the temperature difference between the temperature at the center of the roller 2 and the temperature at the end of the roller 2 reaches 3 ° C. At that time, predetermined power is supplied to one of the coils again. Therefore, the ripple (temperature unevenness) of the temperature distribution in the longitudinal direction of the roller 2 is suppressed to a small level.

  In this driving method, for example, the fixing roller 2 is heated up to the set target temperature from the time when the power of the copying apparatus 101 is turned on (during warm-up), or during the image forming operation by the copying apparatus 101. This is suitable when a sheet is passed between the roller 2 and the roller 3 (when the sheet is passed). For example, a large amount of energy is required to maintain the temperature of the roller 2 or to raise the temperature of the roller 2 to a predetermined temperature during paper feeding, that is, during image formation or warm-up. A lot of power close to the upper limit is required. Therefore, even if the control value (temperature difference) is set to 3 ° C., the power supply between the coil 11a and the coil 11b is often switched, but the power supply from the power supply circuit 30 is stopped by the drive circuit 33. There is little to be done.

  In addition, since the supply of power from the power supply circuit 30 is rarely stopped by the drive circuit 33, voltage fluctuations occur in the same commercial power supply circuit to which the copying apparatus 101 is connected, and fluorescent lamps in the same circuit are generated. Flicker is less likely to occur in (lighting). Naturally, since the temperature difference in the longitudinal direction of the roller 2 is small, it is difficult to cause a problem that the fixability is temporarily lowered.

  On the other hand, as is apparent from FIG. 6, the temperature difference (control value) between the center and the end of the roller 2 when switching the coil to which power is supplied is set to 3 ° C. It is clear that the coil to which power is supplied is frequently switched.

  In this case, as described above, the ripple of the temperature distribution of the roller can be reduced, and it is difficult to cause a problem that the fixing property is lowered. For example, the temperature at the center in the longitudinal direction of the roller 2 has reached 180 ° C. Thereafter, in a standby state in which an input for image formation is awaited, the number of times each inverter circuit is turned on / off is increased.

  Specifically, when the coils that supply power are alternately switched, if the temperature difference that is the control value for switching is managed at 3 ° C., the power is not supplied under conditions where the heat of the roller is difficult to decrease, such as in a standby state. Without switching the supplied coil, the input or blocking of the DC voltage from the power supply circuit 30 by the drive circuit 33 described with reference to FIG. 4 is repeated. Therefore, voltage fluctuation may occur in the commercial power supply circuit to which the copying apparatus 101 is connected, and flicker may occur in the fluorescent lamp (illumination) in the same circuit.

  Therefore, for example, in the standby state, as shown in FIG. 7, the timing for switching the coil to which power is supplied, that is, the control value (temperature difference) is set to 6 ° C.

  As shown in FIG. 7, when the timing of switching the coil to which power is supplied is, for example, 6 ° C. due to the temperature difference between the center and the end of the roller 2 in the longitudinal direction, the coil to which power is supplied continues. As a result, the time during which the electric power is supplied becomes longer, so that the ripple of the temperature distribution of the roller itself is increased.

  For example, when the temperature of the center of the roller reaches 180 ° C. while power is supplied to the coil 11a that raises the temperature of the center of the roller 2, the DC voltage input from the power supply circuit 30 to each of the coils 11a and 11b is cut off. Is done. Accordingly, the temperature at the end of the roller is maintained at a lower temperature than the temperature at the center of the roller.

  For this reason, when the CPU 34 detects that the temperature difference between the center and the end of the roller exceeds 6 ° C., power is supplied to the coil 11b in order to raise the temperature of the end of the roller 2. The

  As described above, according to the control shown in FIG. 7, the time during which power is supplied to the coil 11b is increased as compared with the control example in which the temperature difference described earlier with reference to FIG. 6 is small. Therefore, the timing at which the coil to which power is supplied is switched and the number of times the power supply is turned off when the drive circuit 33 does not supply the DC voltage of the power supply circuit 30 to any of the coils are reduced. This means that even if a voltage fluctuation occurs in the commercial power supply circuit to which the copying apparatus 101 is connected and flicker occurs in the fluorescent lamp (illumination) in the same circuit, the frequency (number of times) is set. Can be suppressed.

  According to the control shown in FIG. 7, compared to the control already described with reference to FIG. 6 (and FIG. 5), the ripple of the temperature distribution in the longitudinal direction of the roller and the center and end of the roller Any temperature difference between them is increased. However, in the standby state, the fixability does not have to be taken into consideration, so that an advantage of reducing flicker can be obtained. In addition, since it is sufficient that the ripple of the temperature distribution in the longitudinal direction of the roller 2 falls within a certain range between the time when the image formation is instructed and the sheet P is conveyed between the roller 2 and the roller 3, Power is also reduced.

  As described above, the power supplied to each of the central temperature raising coil 11a and the end temperature raising coil 11b for raising the temperature of the roller 2 of the fixing device 1 is switched according to the operating state of the copying apparatus 101. By changing the temperature difference (control value) for setting the timing, voltage fluctuation occurs in the commercial power supply circuit to which the copying apparatus 101 is connected, and flicker occurs in the fluorescent lamps in the same circuit. Can be deterred.

  In FIGS. 5 to 7, the example in which the operating state of the copying apparatus 101 is monitored and the coil to which power is supplied is switched has been described. However, for example, the timing of switching the coil that supplies power according to the temperature of the roller May be changed.

  As an example, when both the temperature at the center of the roller 2 and the temperature at the end of the roller 2 are significantly lower than the set target temperature (for example, 180 ° C.), the temperature raising operation is different from that during the image forming operation ( Therefore, the timing for switching the coil to which power is supplied may be roughly (large temperature difference).

  On the other hand, when the temperature detected by the thermistors 6a and 6b is near the set target temperature, it can be predicted that the fixing operation (image forming operation) is in progress. It is preferable to suppress the ripple of the temperature distribution in the longitudinal direction of the roller 2.

  FIG. 8 is a schematic diagram illustrating an example of temperature control different from the method of heating the heating roller described above with reference to FIGS. Note that the temperature control described below with reference to FIG. 8 includes a coil for raising the temperature of the roller already described with reference to FIG. 5 and a coil for raising the temperature of the end of the roller. The present invention relates to sampling of temperature information used when switching the timing of supplying predetermined power to each.

  As shown in FIG. 8, first, the operation state of the copying apparatus 101, that is, when a power switch (not shown) of the copying apparatus 101 is turned on or when a predetermined time elapses after the power switch is turned on, the initial operation is performed. The standby state that has been completed, or when the image formation is instructed and the sheet is conveyed between the heating roller and the pressure roller is checked (S21). It should be noted that during image formation, it can be divided into a fixing time in which paper is present between the rollers and a paper interval (interval) in which no paper is present between the rollers, but power is supplied to the coil to raise the temperature of the roller 2. In this case, it does not matter whether or not there is a sheet between the rollers at the time of image formation. Further, although not described in detail, the standby state includes a power saving mode in which the temperature of the roller is maintained at a temperature lower than that during normal standby.

  When the operation state of the copying apparatus 101 checked in step S21 is an image forming time or a warm-up time from when a power switch (not shown) is turned on to a standby state or an image forming ready state (S21-YES), the temperature The temperature information output from the first and second thermistors 6a and 6b input via the detection circuit 35 is captured (sampled) by the CPU 34 of the excitation unit 31 (and the main CPU 151 of the image forming unit 103). The interval is set to 0.3 seconds, for example (S22). Accordingly, the power supply (or drive stop) to each coil for raising the temperature of either the end or the center of the roller 2 and the switching timing of the energized coil are detected every 0.3 seconds. It is set based on the temperature difference in the direction. As a result, the temperature difference between the temperature at the center of the roller and the temperature at the end of the roller is made uniform to the extent that there is almost no difference when the sheet is not conveyed. Note that the interval at which the temperature information is sampled (taken in) is a predetermined time based on the characteristics of the coil (wire diameter, winding radius and number of windings, presence / absence of core material, etc.) and power supplied to the coil, For example, it may be set to about 0.5 seconds to 1 second.

  On the other hand, when the operation state of the copying apparatus 101 checked in step S21 is a standby state that does not belong to either the image formation time or the warm-up time (S21-NO), it is input via the temperature detection circuit 35. The interval at which the temperature information output from the first and second thermistors 6a and 6b is taken into the CPU 34 (main CPU 151) is set to 5 seconds, for example (S23). In this case, the temperature difference between the temperature at the center of the roller and the temperature at the end of the roller is larger than the case where the temperature difference is detected at a short interval described in step S22. Due to the reasons described above using, the fixing property need not be considered much. Therefore, there is an advantage that flicker is reduced. Further, the ripple of the temperature distribution of the roller is also increased, but it is sufficient that the ripple is within a certain range between the time when the image formation is instructed and the sheet is conveyed between the roller 2 and the roller 3. Power consumption is also reduced. The interval (time) at which the temperature information is sampled depends on the coil characteristics (wire diameter, winding radius and number of windings, presence or absence of core material, etc.), the material and thickness of the roller 2, and the power that can be supplied to the coil. Based on various parameters typified by the maximum value and the like, the temperature distribution in the longitudinal direction of the roller 2 is fixed from when the image formation is instructed until the sheet is conveyed between the roller 2 and the roller 3. It is set to such an extent that it can return to a temperature difference that does not affect the performance.

  As described above, changing the timing for sampling the temperature information from the first and second thermistors 6a and 6b shown in FIG. 8 is nothing other than changing the timing for supplying power to the coil.

  For example, when an amount of heat is required, such as during image formation or warm-up, the ripple generated in the temperature distribution in the longitudinal direction of the roller is reduced by shortening the interval for detecting the temperature difference in the longitudinal direction of the roller. it can. That is, the temperature distribution is made uniform over the entire area in the longitudinal direction of the roller, so that the fixability is improved.

  On the other hand, in the standby state and the power saving mode, by allowing the temperature distribution in the longitudinal direction of the roller to include ripples, the output fluctuates due to temporarily stopping energization of the coil. Even if flicker occurs in the lighting in the same circuit, the frequency (number of times) can be reduced.

  The reason for setting the shortest time (interval) of the timing for detecting the temperature difference to 0.3 seconds is from when power is supplied to the coil to which power is supplied until the output of the coil supplied with power is stabilized. This is because the time required (the time until the coil output reaches the target output) requires about 0.5 seconds. In other words, if the coil to which power is supplied is switched at a cycle shorter than 0.5 seconds, the output of the coil may not reach the target output. Switching should be avoided. In addition, 0.2 to 0.3 seconds are required to obtain a temperature difference from the temperatures detected by the first and second thermistors 6a and 6b and to feed back to the drive circuit 33. For this reason, in the present invention, the shortest interval (cycle) of the timing for detecting the temperature difference is set to 0.3 seconds.

  In FIG. 8, the example in which the coil to which power is supplied is switched in association with the operation state of the copying apparatus 101 has been described. However, for example, the switching timing of the coil to which power is supplied is changed according to the temperature of the roller. Also good.

  For example, when both the temperature at the center of the roller 2 and the temperature at the end of the roller 2 are significantly lower than the set target temperature (180 ° C. in the copying apparatus 101 of the present invention), the warm-up is in progress. Therefore, the timing for switching the coil to which power is supplied may be roughly.

  On the other hand, when the temperature detected by the first and second thermistors 6a and 6b is a temperature near the set target temperature, it can be predicted that the fixing operation is being performed. Therefore, the coil to which power is supplied is switched. It is preferable to make the timing small and suppress ripples in the temperature distribution in the longitudinal direction of the roller 2.

  FIG. 9 is a schematic diagram illustrating an example of a modification of the example in which the temperature of the heating roller described above is raised using FIG.

  As shown in FIG. 9, the operation state of the copying apparatus 101 is, for example, when a power switch (not shown) of the copying apparatus 101 is turned on, and the temperature of the heating roller 2 rises to a predetermined temperature after the power switch is turned on. Warm-up state until the initial operation is completed after being heated, when image formation is instructed and paper is conveyed between the heating roller and pressure roller, or when warm-up or image formation is completed If the image formation is in a standby state where no subsequent image formation is instructed, the temperatures of the center and the end of the roller 2 detected by the first and second thermistors 6a and 6b are used as temperature information. The data is continuously input to the main CPU 151 of the unit 103 at predetermined time intervals (S31). The timing at which the outputs of the thermistors 6a and 6b are taken into the CPU 34 and the main CPU 151 is about 0.1 second (100 msec), for example.

  In step S31, if the CPU 34 and the main CPU 151 are continuously input, the main CPU 151 causes the operation state of the copying apparatus 101, that is, whether or not the copying apparatus 101 is currently in the warm-up state (S32), and the image. It is checked whether or not formation is in progress (S33) and whether or not standby is in progress (S34). Needless to say, the order in which the operating states are checked is not governed by the order of the steps described above.

  If it is detected in step S32 that the copying apparatus 101 is currently warming up (S32—YES), the main CPU 151 instructs the CPU 34 of the excitation unit 31 to supply power to the coil to the drive circuit 33. It is instructed that the sampling interval for detecting the temperature difference is 0.3 seconds (S35).

  In step S33, if it is detected that the copying apparatus 101 is currently forming an image (S33-YES), the main CPU 151 transfers the coil to the drive circuit 33 from the main CPU 151 to the CPU 34 of the excitation unit 31, as in step S32-YES. In order to instruct power supply, the sampling interval for detecting the temperature difference is instructed to be 0.3 seconds (S35).

  In step S34, when it is detected that the copying apparatus 101 is on standby (S34-YES), a temperature difference is detected from the main CPU 151 to the CPU 34 in order to supply power to the coil to the drive circuit 33. It is instructed that the sampling interval is 5 seconds (S36). Similarly, when the copying apparatus 101 is not warming up (S32-NO) or when the copying apparatus 101 is not forming an image (S33-NO), the main CPU 151 transfers to the CPU 34 and the coil to the driving circuit 33 similarly. It is instructed that the sampling interval for detecting the temperature difference is 5 seconds in order to instruct power supply (S36).

  As described above, in the control shown in FIG. 9, the temperature information from the first and second thermistors 6 a and 6 b is sampled, and the timing for obtaining the temperature difference from the temperature information is determined according to the operating state of the copying apparatus 101. It is characterized by changing. Note that changing the timing for obtaining the temperature difference from the temperature information is nothing other than changing the timing for supplying power to the coil.

  For example, when an amount of heat is required, such as during image formation or warm-up, ripples generated in the temperature distribution in the longitudinal direction of the roller can be reduced by shortening the timing for detecting the temperature difference. That is, since the temperature in the longitudinal direction of the roller is made uniform, the fixability is improved.

  On the other hand, in the standby state or power saving mode, the temperature distribution in the longitudinal direction of the roller is allowed to include ripples by widening the interval for detecting the temperature difference, and energization to the coil is temporarily stopped. Even if the output fluctuates due to the above and flicker occurs in the illumination in the same circuit, the frequency (number of times) can be reduced.

  The reason for setting the shortest time (interval) of the timing for detecting the temperature difference to 0.3 seconds is from when power is supplied to the coil to which power is supplied until the output of the coil supplied with power is stabilized. This is because the time required (the time until the coil output reaches the target output) requires about 0.5 seconds. In other words, if the coil to which power is supplied is switched at a cycle shorter than 0.5 seconds, the output of the coil may not reach the target output. Switching should be avoided. In addition, 0.2 to 0.3 seconds are required to obtain a temperature difference from the temperatures detected by the first and second thermistors 6a and 6b and to feed back to the drive circuit 33. For this reason, in the present invention, the shortest interval (cycle) of the timing for detecting the temperature difference is set to 0.3 seconds.

  In FIG. 9, the example in which the coil to which power is supplied is switched in association with the operation state of the copying apparatus 101 has been described. However, for example, the timing for switching the coil that supplies power is changed in accordance with the temperature of the roller. Also good.

  As an example, when both the temperature at the center of the roller 2 and the temperature at the end of the roller 2 are significantly lower than the set target temperature (180 ° C. in the copying apparatus 101 of the present invention), the warm-up is being performed. Predictable. That is, the timing for switching the coil to which power is to be supplied may be approximate. Therefore, even if the timing for obtaining the temperature difference in the longitudinal direction of the roller from the temperature information output from the two thermistors is extended, there is little possibility that a problem occurs in the fixing property.

  On the other hand, when the temperature detected by the first and second thermistors 6a and 6b is a temperature near the set target temperature, it can be predicted that the fixing operation is being performed. Therefore, the coil to which power is supplied is switched. Therefore, it is preferable to suppress the temperature distribution in the longitudinal direction of the roller 2 from including ripples by shortening the interval for detecting the temperature difference as much as possible.

  FIG. 10 is a schematic diagram for explaining another example of temperature control of the method for heating the heating roller described above with reference to FIGS. Note that the temperature control of the roller 2 shown in FIG. 10 is mainly applied during an image forming operation or during warm-up until the temperature of the roller 2 reaches a set target temperature after the power is turned on. In this example, a predetermined amount of electric power is alternately supplied to the coil 11a for raising the temperature of the center of the roller 2 and the coil 11b for raising the temperature of the end of the roller 2 alternately for the same time. Shall. At this time, the time (interval) for detecting the temperature difference between the time at which power is supplied to the individual coils 11a and 11b and the temperature at the center of the roller 2 and the temperature at the end is set equal. And

  As shown in FIG. 10, at the time of warming up and image formation until the temperature of the roller 2 reaches the set target temperature, the first and second thermistors are sent to the CPU 34 at the timing described previously with reference to FIG. The temperature information output from 6a and 6b is input (S41).

  Next, the CPU 34 compares the temperature data CT indicating the temperature near the center of the roller with the temperature data ST indicating the temperature at the end of the roller (S42).

  In step S42, when it is detected that the temperature ST at the end of the roller is higher than the temperature CT at the center of the roller (S42-NO), the temperature ST at the end of the roller is compared with the temperature CT at the center of the roller. For example, it is checked whether the temperature is higher by 10 ° C. or more (S43).

  In step S43, when the temperature ST at the end of the roller is higher by 10 ° C. or more than the temperature CT at the center of the roller (S43—YES), the time during which power is supplied to the coil 11a that raises the temperature at the center of the roller. For example, in 1.2 seconds, the time during which power is supplied to the coil 11b that raises the temperature of the end of the roller is set to 0.3 seconds, for example (S46, S47).

  In step S43, if the temperature ST at the end of the roller is higher than the temperature CT at the center of the roller, but the difference is less than 10 ° C. (S43—NO), the coil 11a that raises the temperature at the center of the roller is applied. The time for supplying power is set to 1 second, for example, and the time for supplying power to the coil 11b for raising the temperature of the end of the roller is set to 0.5 seconds, for example (S44, S45).

  On the other hand, when it is detected in step S42 that the temperature CT at the center of the roller is higher than the temperature ST at the end of the roller (S42-YES), the temperature of the roller is compared with the temperature CT at the center of the roller. It is checked whether or not the temperature ST at the end is, for example, 10 ° C. or higher (S53).

  In step S53, when the temperature CT at the center of the roller is 10 ° C. or more higher than the temperature ST at the end of the roller (S53—YES), the time during which power is supplied to the coil 11b that raises the temperature of the end of the roller However, the time during which power is supplied to the coil 11a for raising the temperature of the center of the roller is set to, for example, 1.2 seconds, for example, 0.3 seconds (S54, S55).

  In step S53, if the temperature CT at the center of the roller is higher than the temperature ST at the end of the roller, but the difference is less than 10 ° C. (S53—NO), the coil 11b that raises the temperature of the end of the roller. Is set to 1 second, for example, and the time to supply power to the coil 11a for heating the center of the roller is set to 0.5 seconds, for example (S56, S57).

  More specifically, in the roller temperature control described above with reference to FIGS. 5 to 7, 8, and 9, the timing (period) at which a temperature difference is detected from the temperature at the center of the roller and the temperature at the end of the roller. However, in the case of 1.5 seconds, for example, power is supplied to the coil on the detected low temperature side, and power is supplied to the same coil during the period (interval) of detecting the temperature difference. Therefore, the longer the timing for switching the coil to which power is supplied, the greater the temperature difference in the longitudinal direction of the roller. On the other hand, as described above, in order to reduce the temperature difference in the longitudinal direction of the roller, it is effective to shorten the interval for switching the coil to which power is supplied.

  From this, in the power supply to the coil shown in FIG. 10, power is supplied to the coil on the detected low temperature side, but the supply time is set to be shorter than the timing for detecting the temperature difference.

  For example, as described in steps S44 and S45, when the temperature difference detection interval is 1.5 seconds, power is supplied to the coil 11a that raises the temperature for 1 second, and then the remaining 0.5 seconds. Is characterized in that electric power is supplied to the coil 11b for raising the temperature of the end portion.

  Thus, for example, predetermined power is supplied to either the coil 11a used for raising the temperature of the center of the roller 2 or the coil 11b used for raising the temperature of the end of the roller 2. The period of time is shorter than 1.5 seconds, which is the period for detecting the temperature difference (1 second in the above example), and the switching timing can be advanced. Therefore, the temperature difference in the longitudinal direction of the roller 2 can be reduced.

  In the above-described example, the interval for detecting the temperature difference is 1.5 seconds, and the time for supplying the predetermined power to each of the coils 11a and 11b is 1.0 seconds and 0.5 seconds. If the temperature difference between the center of the roller 2 and the end of the roller 2 still increases, the ratio of the time for supplying power to each coil is changed. The interval for detecting the temperature difference and the ratio of power supply to the coil 11a and the coil 11b within the interval are set, for example, in a service mode by a serviceman, for example, a predetermined input key (not shown) on the operation panel 141, for example, a copying magnification It can be changed with a key or the like. In addition, as long as the power supply ratio can be input to the main CPU 151, any method and configuration that can be implemented as the input method (form) can be used.

  For example, when the temperature difference exceeds 10 ° C., as shown in steps S46 and S47, when the temperature difference detection interval is 1.5 seconds, the coil 11a that raises the temperature in the center is 1.2 seconds. Electric power is supplied, and electric power is supplied to the coil 11b that raises the temperature of the end portion for the remaining 0.3 seconds. In addition, when switching the time when electric power is supplied to each coil 11a, 11b, it is only when the temperature difference detected in step S43 becomes larger than 10 ° C.

  In standby mode or power saving mode standby mode, the timing for switching the power supplied to the individual coils 11a and 11b is, for example, 2 seconds for the coil facing the low temperature position of the roller 2 and the remaining coils. Changed to 1 second. When the temperature exceeds the predetermined temperature, the power supply to each coil is temporarily stopped as in the other embodiments described above.

  According to this method, the switching interval can be extended without changing the ratio (switching timing) at which power is supplied to each coil. Therefore, the number of times the power supply to the respective switching circuits by the drive circuit is turned on / off (the number of times the output of the power supply circuit is connected to the switching circuit by the drive circuit) is reduced, and voltage fluctuation is suppressed. That is, for example, it is useful when flicker or the like is generated (or possibly generated). In addition, since the time during which power is continuously supplied to one coil (opposed to the higher temperature side) is shortened, the temperature distribution in the longitudinal direction of the roller 2 is made uniform. Further, the embodiment described with reference to FIG. 10 is particularly useful when, for example, the timing for detecting the temperature difference is relatively slow due to the constant of the temperature detection circuit or the like.

  The power supply switching shown in FIG. 10 has been described as an example in which the timing of supplying power to each coil is switched according to the operation mode of the copying apparatus 101. However, the power supply switching may be varied according to the temperature of the roller 2. Good. For example, when the temperature of the roller is significantly lower than a set target temperature (for example, 180 ° C.), the time for supplying power to any coil may be lengthened. On the contrary, after the thermistors 6a and 6b detect that the temperature of the roller has been raised to a temperature in the vicinity of the set target temperature, the switching timing at which predetermined power is supplied to the individual coils can be shortened. Good.

  Note that the power supply switching control shown in FIG. 10 and the control shown in FIG. 5 or FIG. 8 can be combined. Needless to say, the control method may be switched according to the operation mode of the copying apparatus.

  In the fixing device of the present invention described above, the temperature difference condition changing mechanism generates a temperature difference that is used to define the timing at which the drive control mechanism supplies predetermined power to the first and second coil bodies. During the operation in which the medium passes between the possible member and the pressure member, during the heating for heating the heat generating member, and for a predetermined time between the heat generating member and the pressure member, It can be changed according to the standby time when it is not conveyed.

  Further, in the above-described fixing device of the present invention, the temperature difference condition changing mechanism determines the temperature difference used for defining the timing at which the drive control mechanism supplies predetermined power to the first and second coil bodies. The temperature can be changed according to the temperature at the first position and the temperature at the second position of the heat generating member detected by the first temperature detection mechanism and the second temperature detection mechanism.

  Furthermore, in the above-described fixing device of the present invention, the temperature difference detection condition changing mechanism determines the temperature difference used by the drive control mechanism to define the timing at which predetermined power is supplied to the first and second coil bodies. The detection timing to detect is between the operation of the medium passing between the heat generating member and the pressurizing member, the heating of heating the heat generating member, and between the heat generating member and the pressure member. The medium can be changed according to the standby time during which the medium is not conveyed for a predetermined time.

  Furthermore, in the above-described fixing device of the present invention, the temperature difference detection condition changing mechanism determines the temperature difference used for defining the timing at which the drive control mechanism supplies predetermined power to the first and second coil bodies. The detection timing to be detected can be changed according to the temperature at the first position and the temperature at the second position of the heat generating member detected by the first temperature detection mechanism and the second temperature detection mechanism.

  Still further, in the above-described fixing device of the present invention, the drive switching condition changing mechanism has a timing at which the drive control mechanism supplies predetermined power to the first and second coil bodies at the heat generating member and the pressure member. During the operation in which the medium passes through, during the heating in which the heat generating member is heated, and in the standby time during which the medium is not conveyed for a predetermined time between the heat generating member and the pressure member. It can be changed accordingly.

  Furthermore, in the above-described fixing device of the present invention, the temperature difference detection condition changing mechanism is configured so that the timing at which the drive control mechanism supplies predetermined power to the first and second coil bodies is the same as the first temperature detection mechanism. It can be changed according to the temperature of the first position and the temperature of the second position of the heat generating member detected by the second temperature detection mechanism.

  Still further, in the above-described fixing device of the present invention, the temperature difference detection condition changing mechanism has a timing at which the drive control mechanism supplies predetermined power to the first and second coil bodies on the side to which power is supplied. The time until the coil output reaches a predetermined output (saturation) can be changed as the minimum period.

  Furthermore, in the above-described fixing device of the present invention, the power supply mechanism has a predetermined power supply for each of the first and second coil bodies when the temperature difference output from the temperature difference detection mechanism is larger than the predetermined temperature difference. It is possible to change the distribution ratio for supplying power of a magnitude of.

  Furthermore, in the above-described fixing device of the present invention, the distribution ratio at which the power supply mechanism supplies a predetermined amount of power to each of the first and second coil bodies can be changed from the outside.

  As described above, according to the fixing device of the present invention, the temperature of the heating roller in the longitudinal direction is alternately supplied to two coils provided so that the temperature and the center of the roller can be independently increased. However, the temperature difference in the longitudinal direction can be increased to substantially the same temperature.

  Further, according to the fixing device of the present invention, it is possible to suppress the occurrence of flicker in the illumination in the commercial power supply circuit in which the fixing device and the copying apparatus are incorporated.

1 is a schematic diagram illustrating an example of an image forming apparatus in which an induction heating type fixing device of the present invention is incorporated. FIG. 2 is a schematic cross-sectional view illustrating an example of an induction heating type fixing device that can be used in the image forming apparatus illustrated in FIG. 1. The schematic plan view which shows the state which looked at the fixing device shown in FIG. 2 from the plane direction in the state which removed the covers. FIG. 4 is a block diagram for explaining an example of an excitation unit (drive circuit) for driving the fixing device shown in FIGS. 2 and 3. 5 is a flowchart for explaining an example of a driving method of the fixing device of the present invention shown in FIGS. FIG. 5 is a schematic diagram illustrating changes in roller temperature by another driving method of the fixing device of the present invention shown in FIGS. 2 to 4. FIG. 5 is a schematic diagram for explaining changes in roller temperature by still another driving method of the fixing device of the present invention shown in FIGS. 2 to 4. 5 is a flowchart for explaining still another example of the driving method of the fixing device according to the present invention shown in FIGS. 6 is a flowchart for explaining still another example of the driving method of the fixing device according to the present invention shown in FIGS. 6 is a flowchart for explaining still another example of the driving method of the fixing device according to the present invention shown in FIGS.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fixing device, 2 ... Heating roller (heat generating member), 3 ... Pressure roller (pressing member), 6a ... 1st (central temperature detection) thermistor (1st temperature detection mechanism), 6b ... 1st 2 (for end temperature detection) thermistor (second temperature detection mechanism), 11 ... induction coil, 11a ... coil (first coil body), 11b ... coil (second coil body), 30 ... power supply circuit 32a ... first switching circuit, 32b ... second switching circuit, 33 ... drive circuit (drive control mechanism, power supply mechanism), 34 ... CPU (temperature difference detection mechanism, drive control mechanism, temperature difference detection condition change mechanism) , Drive switching condition changing mechanism), 35 ... temperature detection circuit, 101 ... copying apparatus, 141 ... operation panel, 151 ... main CPU.

Claims (3)

A cylindrical or belt-like heat generating member formed of a material that generates an induced current by electromagnetic induction;
A pressure member that is arranged to be able to provide a predetermined pressure to the heat generating member, and that provides a predetermined pressure to a medium that is passed between the heat generating member;
A first coil body to which a predetermined power for generating an induced current in the heat generating member is supplied;
A second coil body that is disposed in a predetermined positional relationship with respect to each of the first coil body and the heat generating member, and that is supplied with predetermined power for generating an induced current in the heat generating member;
A first temperature detection mechanism provided in the vicinity of a first position where the heat generating member is heated by an induced current from the first coil body and detecting a temperature at the first position of the heat generating member; ,
A second temperature detection mechanism provided in the vicinity of a second position where the heat generating member is heated by an induced current from the second coil body and detecting a temperature at the second position of the heat generating member; ,
The temperature of the first position of the heat generating member detected by the first temperature detection mechanism is compared with the temperature of the second position of the heat generating member detected by the second temperature detection mechanism. A temperature difference detection mechanism that outputs the temperature difference between the two,
The supply of the predetermined power to one of the first coil body and the second coil body is stopped so that the temperature difference value output by the temperature difference detection mechanism becomes a predetermined value, and the other A drive control mechanism for supplying the predetermined power to one side;
Have
The reference value of the temperature difference held by the temperature difference detection mechanism when power is selectively supplied to any one of the coil bodies from the temperature information output from the respective temperature detection mechanisms by the drive control mechanism, A fixing device characterized in that a standby time is set larger than that during a fixing operation. A cylindrical or belt-like heat generating member formed of a material that generates an induced current by electromagnetic induction;
A pressure member that is arranged to be able to provide a predetermined pressure to the heat generating member, and that provides a predetermined pressure to a medium that is passed between the heat generating member;
A first coil body to which a predetermined power for generating an induced current in the heat generating member is supplied;
A second coil body that is disposed in a predetermined positional relationship with respect to each of the first coil body and the heat generating member, and that is supplied with predetermined power for generating an induced current in the heat generating member;
A first temperature detection mechanism provided in the vicinity of a first position where the heat generating member is heated by an induced current from the first coil body, and detecting a temperature at the first position of the heat generating member; ,
A second temperature detection mechanism provided in the vicinity of a second position where the heat generating member is heated by an induced current from the second coil body and detecting a temperature at the second position of the heat generating member; ,
The temperature of the first position of the heat generating member detected by the first temperature detection mechanism is compared with the temperature of the second position of the heat generating member detected by the second temperature detection mechanism. A temperature difference detection mechanism that outputs the temperature difference between the two,
The first position and the second position of the heat generating member of the first coil body and the second coil body so that the temperature difference value output by the temperature difference detection mechanism becomes a predetermined value. A drive control mechanism for stopping the supply of the predetermined power to the coil generating an induced current on the higher temperature side at the position and supplying the predetermined power to the other one of the coils;
Have
The first temperature detection mechanism and the second temperature detection mechanism when power is selectively supplied to any one of the coil bodies from the temperature information output from the respective temperature detection mechanisms by the drive control mechanism. The fixing device is characterized in that the temperature detection sampling interval is set longer in the standby time than in the fixing operation.   The fixing device according to claim 2, wherein the reference value of the temperature difference to be compared by the temperature difference detection mechanism is set larger during standby than during fixing operation.

Images