JP2014085594A - Image heating device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device and an image forming apparatus capable of reducing load on a power source when a temperature in an end part is raised while a temperature of a paper passing part is maintained to be a setting temperature.SOLUTION: An image heating device (114) includes: first temperature detection means (11) for detecting a temperature of a paper passing part (P2) on a surface of an image heating member (3), which a recording material (P) of a prescribed size passes; and second temperature detection means (12) for detecting a temperature of a non paper passing part (P3) outside the paper passing part on the surface of the image heating member. The image heating device further includes control means (104) for controlling a power source (116) so as to make a detection result of the first temperature detection means a first temperature lower than a prescribed Curie temperature. When a detection result of the second temperature detection means reaches a second temperature which is equal to or lower than the prescribed Curie temperature but higher than the first temperature, the control means decreases a maximum power amount of the power supply lower than the maximum power amount before the detection result of the second temperature detection means reaches the second temperature.

Description

  The present invention relates to an image heating apparatus such as a fixing device that heats an image formed on a recording material, and an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine including these image heating apparatuses. Relates to the device.

  Conventionally, an induction heating type fixing device has been proposed as a fixing device. In this fixing device, an induction coil is concentrically disposed inside a hollow fixing roller made of a metal conductor, and an induction eddy current is generated in the fixing roller by a high frequency magnetic field generated by flowing a high frequency current through the induction coil. And a configuration in which Joule heat is generated by the skin resistance of the fixing roller. According to this induction heating type fixing device, since the electric-heat conversion efficiency is improved, the warm-up time can be shortened (see Patent Document 1).

  In such a fixing device, when temperature control is performed based on the temperature detection of the sheet passing area, when continuously fixing a recording material having a size smaller than the heating area of the fixing roller, A so-called non-sheet-passing portion temperature rise occurs in which no electric power is supplied to a non-sheet-passing portion area to increase the temperature. When such non-sheet passing portion temperature rise occurs, various problems such as temperature rise in the apparatus and thermal deterioration of the fixing device constituent members occur.

  As a countermeasure, for example, a method has been proposed in which the Curie temperature of a magnetic shunt alloy as a heating element (the transition temperature at which a ferromagnetic material changes to a paramagnetic material) is adjusted near the fixing temperature. That is, according to this method, when the fixing roller temperature reaches the Curie temperature, the magnetism of the fixing roller rapidly decreases, so that the fixing roller temperature does not easily exceed the Curie temperature. When the fixing roller as the image heating member reaches the Curie temperature, the power factor is reduced, and accordingly, the power consumption of the induction coil is reduced and the heat generation is suppressed, so that self-temperature control is possible.

Japanese Patent Laying-Open No. 2005-250012

  According to the above adjustment method, the fixing roller temperature does not easily rise beyond the Curie temperature, so that the temperature rise of the non-sheet passing portion can be suppressed. However, when the fixing roller as the image heating member approaches the Curie temperature, the impedance of the fixing roller decreases, and the power source supplying the high frequency current to the induction coil consumes the power consumed inside the power source trying to supply the same power. May increase. For this reason, if measures are not taken against this problem, the load on the power supply increases.

  Further, in the configuration in which the temperature control is performed so that the temperature of the sheet passing portion area becomes a preset temperature, it may be possible to set the temperature at the time of adjusting the temperature of the fixing roller to a temperature lower than the Curie temperature.

  However, even if it is attempted to control the temperature of the fixing roller at a temperature lower than the Curie temperature, if the temperature is detected only in the sheet passing area, if the temperature rise in the non-sheet passing area occurs, In the partial area, the Curie temperature may be reached. If the Curie temperature is reached in the non-sheet passing portion region, the load on the power supply may increase as in the above adjustment method.

  The present invention provides an image heating apparatus and an image forming apparatus capable of reducing a load on a power source when the temperature of an end portion rises while the temperature of a sheet passing portion is maintained at a set temperature. With the goal.

  The present invention relates to an image heating apparatus, a magnetic flux generating means for generating a magnetic flux based on a supplied current, a power supply capable of variably adjusting a maximum power amount and supplying a current to the magnetic flux generating means, a predetermined curie An image heating member that is made of a magnetic shunt alloy adjusted to a temperature, generates heat by the magnetic flux generated by the magnetic flux generation means, and heats the image on the recording material, and has a predetermined size among the surfaces of the image heating member First temperature detecting means for detecting the temperature of the paper passing portion through which the recording material passes, and second temperature detecting means for detecting the temperature of the non-paper passing portion outside the paper passing portion of the surface of the image heating member. And a control means for controlling the power supply so that a detection result of the first temperature detection means becomes a first temperature lower than the predetermined Curie temperature, and the control means includes the second temperature detection. The detection result of the means is the predetermined A maximum electric energy of the power source is made lower than a maximum electric energy before reaching the second temperature when the second temperature is lower than the temperature of the temperature and higher than the first temperature. To do.

  According to the present invention, when the detection result of the second temperature detecting means for detecting the temperature of the non-sheet passing portion reaches the second temperature that is lower than the predetermined Curie temperature and higher than the first temperature, the maximum power of the power supply The amount can be controlled to be lower than the maximum amount of power before reaching the second temperature. As a result, it is possible to reduce the load on the power supply when the temperature of the end portion rises while the temperature of the sheet passing portion is maintained at the set temperature.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a front view illustrating a main part of the fixing device according to the present exemplary embodiment. FIG. 2 is a side cross-sectional view illustrating a main part of the fixing device in the present embodiment. FIG. 10 is a flowchart for explaining the operation of the fixing device in the present embodiment.

  Embodiments according to the present invention will be described below with reference to FIGS. In this embodiment, the image heating device is described as a configuration applied to a fixing device that fixes an unfixed toner image on a recording material. However, the present invention heats a recording material carrying a fixed image or a semi-fixed image. It can also be implemented as a heat treatment apparatus for adjusting the surface properties of the image. FIG. 1 is a schematic configuration diagram showing an image forming apparatus 100 including an electromagnetic induction heating type fixing device 114 to which the present invention is applied.

[Image forming apparatus]
The image forming apparatus 100 of this example is an image forming apparatus using a transfer type electrophotographic process and using a laser scanning exposure method (a copying machine, a printer, a facsimile, a composite function machine thereof). As shown in FIG. 1, 101 is a document reading device (image scanner), and 102 is an area designating device (digitizer), both of which are arranged on the upper surface side of the image forming apparatus 100.

  The document reading apparatus 101 scans a document by a scanning illumination optical system including a light source or the like provided inside a document surface placed on the document table of the apparatus, and reflects reflected light from the document surface to light from a CCD line sensor or the like. It is read by a sensor, and image information is converted into a time series electric digital electric signal.

  The area designating apparatus 102 sets a document reading area and outputs a signal. A control unit (CPU) 104 receives signals from the document reading device 101, the area designating device 102, the print controller 103, and the like, and performs signal processing for sending commands to each unit of the image output mechanism and various image forming sequence controls. is there. The control unit 104 comprehensively controls the operation of each unit in the image forming apparatus 100.

  The following is a description of the image output mechanism unit (image forming mechanism unit). Reference numeral 105 denotes a rotating drum electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) serving as an image carrier, which is driven to rotate in the clockwise direction indicated by an arrow at a predetermined peripheral speed. In the rotation process, the photosensitive drum 105 is uniformly charged with a predetermined polarity and potential by the charging device 106, and the uniformly charged surface is subjected to image exposure (L) by the image writing device 107. As a result, the potential of the exposed bright portion of the uniformly charged surface declines, and an electrostatic latent image corresponding to the exposure pattern is formed on the surface of the photosensitive drum 105.

  In this example, the image writing device 107 is a laser scanner, outputs laser light L modulated in accordance with the image data signal-processed by the control unit 104, and scans and exposes the uniformly charged surface of the rotating photosensitive drum 105. Thus, an electrostatic latent image corresponding to the document image information is formed.

  Next, the electrostatic latent image is developed as a toner image by the developing device 108. The toner image is a material to be heated that is fed at a predetermined control timing from the sheet feeding mechanism unit to the transfer unit T that is a portion opposite to the photosensitive drum 105 and the transfer charging device 106 at the position of the transfer charging roller 109. It is electrostatically transferred to a certain recording material P from the surface of the photosensitive drum 105.

  In the case of this example, the sheet feeding mechanism section includes a cassette sheet feeding section 111 in which a large size recording material P is stacked and accommodated, and a cassette sheet feeding section 110 in which a small size recording material P is loaded and accommodated. . The paper feed mechanism unit has a recording material conveyance path 112 that conveys the recording material P separated and fed from the cassette paper feeding unit 111 or 110 to the transfer unit T at a predetermined timing. The photosensitive drum 105, the developing device 108, the transfer unit T, and the like constitute an image forming unit that forms a toner image on the recording material.

  The recording material P that has received the transfer of the toner image from the surface of the photosensitive drum 105 at the transfer portion T is fixed from the surface of the photosensitive drum 105 and is transferred to the fixing device (image heating device) 114. And is discharged onto a paper discharge tray 115 outside the image forming apparatus.

  On the other hand, the surface of the photosensitive drum 105 after separation of the recording material is cleaned by the cleaning device 113 after removal of adhering contaminants such as transfer residual toner, and images are formed repeatedly.

[Fixing device]
Next, the fixing device 114 as an image heating device will be described in detail with reference to FIGS. 2 is a front view showing the main part of the fixing device 114, and FIG. 3 is a side sectional view showing the main part of the fixing device 114.

  The fixing device 114 shown in FIGS. 2 and 3 is a heating roller type, electromagnetic induction heating type heat fixing device. The fixing device 114 fixes the unfixed toner image t formed on the recording material P by the image forming unit including the photosensitive drum 105, the developing device 108, the transfer unit T, and the like to the recording material P.

  The fixing device 114 includes a fixing roller (image heating member) 1 and a pressure roller 2 that are pressed against each other with a predetermined pressing force to form a fixing nip portion N having a predetermined nip length (nip width). The fixing roller 1 and the pressure roller 2 are arranged in the width direction (the left-right direction in FIG. 2, the front-back direction in FIG. 3) orthogonal to the conveyance direction of the recording material P (the front-back direction in FIG. 2, the left-right direction in FIG. 3). ) Are supported so as to extend parallel to each other.

  The fixing roller 1 is elongated in the width direction (left and right direction in FIG. 2) orthogonal to the conveyance direction (front side to back direction in FIG. 2) of the recording material P, and generates heat by the magnetic flux generated in the coil assembly 3. Thus, an image heating member for heating the toner image (image) t on the recording material is configured. That is, the fixing roller 1 is a magnetic shunt alloy adjusted to a predetermined Curie temperature, and constitutes an image heating member that heats the toner image (image) t on the recording material by heat generated by the magnetic flux generated from the induction coil 6. To do. The coil assembly 3 constitutes magnetic flux generating means for generating a magnetic flux based on the supplied current.

  A fixing roller 1 as an image heating member is a roller having a hollow (cylindrical) metal layer (conductive layer, cored bar) 1b, and a heat-resistant release layer coated with a fluororesin or the like on its outer peripheral surface. (Heat transfer material) 1a is formed.

  The metal layer 1b, which is an induction heating element, is composed of a magnetic shunt alloy whose Curie temperature is adjusted as desired (see JP 2000-39797 A). Examples of the magnetic shunt alloy include magnetic metals (conductors, magnetic bodies) such as iron, nickel, SUS430, iron-nickel alloys, iron-nickel-chromium alloys, and nickel-cobalt alloys. The magnetic shunt alloy has a large electric resistance and a large amount of heat generation below the Curie point, but when it exceeds the Curie point, it loses its magnetism and the electric resistance decreases and the heat generation amount decreases.

  The fixing roller 1 (metal layer 1b) is made of a magnetic shunt alloy adjusted to a predetermined Curie temperature. Heat. That is, the thickness of the metal layer 1b of the fixing roller 1 is set to 0.05 to 1.5 mm, for example, and the Curie temperature of the metal layer 1b can fix the unfixed toner image t to the recording material P. It is set to be higher than the fixing temperature and lower than the heat resistance temperature of the induction coil 6 as a coil. Specifically, the fixing temperature is set to 195 ° C., the heat resistant temperature is set to 230 ° C., and the Curie temperature is set to 205 ° C.

  The fixing roller 1 is rotatably supported at both end portions between front and back side plates (fixing unit frames) 21 and 22 of the fixing device 114 via bearings 23 and 23, respectively. Inside the hollow cylindrical metal layer 1b, a coil assembly 3 as magnetic flux generating means is inserted and arranged. The coil assembly 3 generates a high frequency magnetic field that induces an induced current (eddy current) in the fixing roller 1 to generate Joule heat.

  The pressure roller 2 is composed of a shaft core 2a, and an elastic body layer 2b that is a surface releasable heat-resistant rubber layer (silicone rubber layer or the like) formed in a roller shape integrally with the outer periphery of the shaft core 2a. Laura. The pressure roller 2 is arranged in parallel to the lower side of the fixing roller 1, and bearings 26, 26 are provided between the side plates 21, 22 on the front side and the back side of the fixing device 114 on both ends of the shaft core 2 a, respectively. It is rotatably supported via.

  The pressure roller 2 is pressed against the lower surface of the fixing roller 1 with a predetermined pressing force against the elasticity of the elastic layer 2b by a biasing means (not shown). As a result, a fixing nip portion N having a predetermined nip length and nip width as a heating portion is formed. The nip length of the fixing nip N is a dimension in the width direction perpendicular to the recording material conveyance direction, and the nip width is a dimension in the recording material conveyance direction.

  The coil assembly 3 is an assembly of a bobbin 4, a core (core material) 5 made of a magnetic material, an induction coil (excitation coil, induction heat source) 6, a stay 7 made of an insulating member, and the like. The core 5 is inserted into a through hole formed in the bobbin 4, and the induction coil 6 is formed by winding a copper wire around the bobbin 4. The bobbin 4, core 5, and induction coil 6 unit are fixedly supported by the stay 7. The coil assembly 3 is fixed to a stay 7 formed separately from the bobbin 4 and stored so as not to be exposed to the outside of the fixing roller 1.

  The core 5 is preferably made of a material having a high magnetic permeability and a small self-loss. For example, ferrite, permalloy, sendust and the like are suitable. The bobbin 4 also functions as an insulating part that insulates the core 5 from the induction coil 6.

  Reference numeral 13 in FIG. 3 denotes a separation claw. The separation claw 13 prevents the recording material P introduced into the fixing nip portion N and exiting the fixing nip portion N from being wound around the fixing roller 1. Serves to separate. The bobbin 4, stay 7, and separation claw 13 described above can be formed from heat-resistant and electrically insulating engineering plastic such as liquid crystal polymer, polyimide, polyphenylene sulfide, and the like.

  In order to generate an alternating magnetic flux that enables sufficient heating, the induction coil 6 should have a low resistance component and a high inductance (a higher coefficient is preferable. A higher number of coil turns). is necessary. As the core wire of the induction coil 6, a litz wire in which about 80 to 160 fine wires having a diameter of 0.1 to 0.3 are bundled is used. Insulated coated electric wires are used for the thin wires.

  An induction coil 6 is formed on the bobbin 4 that supports the magnetic core 5 by winding the coil a plurality of times in a horizontal boat shape along the longitudinal direction of the fixing roller 1 according to the shape of the bobbin 4. The horizontal boat shape means a substantially semi-cylindrical cross-sectional shape (a substantially semi-circular cross-sectional shape) to appropriately follow the inner shape of the metal layer 1b.

  As shown in FIG. 2, two outward lead wires (coil supply wires) 6 a and 6 b of the induction coil 6 are drawn from one end portion of the fixing roller 1. The round shaft portion 7a on the near side of the stay 7 is formed in a hollow shaft shape. Outer lead wires 6 a and 6 b drawn out from the hollow portion of the round shaft-shaped portion 7 a are connected to a coil power source 116 as an energization portion for energizing the induction coil 6.

  The coil power supply 116 is configured as a current supply unit that supplies a high-frequency current to the induction coil 6, a constant-current unit that supplies a constant current, and a frequency variable control unit that variably controls the frequency. In addition, the coil power source 116 can adjust the maximum power amount variably, and constitutes the power source of the present invention that supplies current to the coil assembly 3 as magnetic flux generating means.

  In addition, a thermostat 15 is disposed above the fixing roller 1 as a countermeasure mechanism when the fixing roller temperature rises abnormally. The thermostat 15 is in contact with the surface of the fixing roller 1, and when the temperature reaches a preset temperature, the contact is opened to cut off the energization to the induction coil 6, and the fixing roller 1 becomes a high temperature equal to or higher than a predetermined temperature. To prevent.

  As shown in FIG. 3, a fixing roller cleaner 14 is disposed above the fixing roller 1. The fixing roller cleaner 14 includes a web feeding shaft portion 14b that holds the cleaning web 14a in a roll form, and a web winding shaft portion 14c.

  A pressing roller 14d that presses the web portion between the shaft portions 14b and 14c against the outer surface of the fixing roller 1 is provided. The toner offset to the surface of the fixing roller 1 is wiped by the web portion pressed against the fixing roller 1 by the pressing roller 14d, whereby the surface of the fixing roller is cleaned. The web portion pressed against the fixing roller 1 is gradually renewed by gradually feeding the web 14a from the feeding shaft portion 14b side to the winding shaft portion 14c side.

  As shown in FIG. 2, in this embodiment, the sheet passing is performed with a central reference. C indicated by a one-dot chain line in FIG. 2 is the center reference. That is, for any size recording material, the central portion of the recording material passes through the axial central portion of the fixing roller 1. Accordingly, in the image forming apparatus 100 of the present embodiment, the maximum size of the recording material that can be passed is A3, and the heating area is designed to be 297 mm, which is the width of the A3 recording material.

  Further, the minimum size of the recording material that can be passed is postcard size vertical feed. In the present embodiment, a size smaller than A3 which is a large size paper is referred to as a small size paper. In this case, since the width of the recording material is narrower than the heating width, there is a possibility that the non-sheet passing portion temperature rises when the non-sheet passing portion of the recording material is heated.

  The first thermistor 11 and the second thermistor 12 are pressed against the surface of the fixing roller 1 by an elastic member so as to face the induction coil 6 across the fixing roller 1 (metal layer 1b) and are elastically pressed against each other. Yes.

  The first thermistor 11 serves as a central temperature detection device for the fixing roller 1 in contact with the central portion of the fixing roller corresponding to the substantially central portion of the paper passing portion area (paper passing portion) P2 of small size paper (postcard size paper). Yes. The first thermistor 11 is a sheet passing area (sheet passing section) through which a recording material of a predetermined size (small size paper: B5 size paper, postcard size paper, etc.) passes among the surface of the fixing roller 1 as an image heating member. ) The first temperature detecting means of the present invention for detecting the temperature of P2 is constituted. In other words, the first thermistor 11 passes the sheet through which the recording material of the minimum size (small size paper: B5 size paper, postcard size paper, etc.) that can be passed in the direction orthogonal to the conveyance direction of the recording material P passes. 1st temperature detection means which detects the temperature of a part is comprised.

  When the recording material P to be passed is a small size paper (postcard size paper), a large size paper (A3 size paper) passage area P1 and a small size paper passage area P2 in the fixing nip N The difference area is a non-sheet passing area (non-sheet passing area, non-sheet passing area) P3.

  The second thermistor 12 detects the non-sheet passing portion temperature when the fixing roller 1 passes the small size paper, and the small size paper (postcard). (Size paper) is in contact with the non-sheet passing portion region P3 which is a difference region from the sheet passing portion region P2. The second thermistor 12 detects the temperature of the non-sheet passing portion region (non-sheet passing portion) P3 out of the sheet passing portion region (sheet passing portion) P2 on the surface of the fixing roller 1 as the image heating member. It constitutes the second temperature detection means of the invention.

  The fixing roller temperature detection signals of the first and second thermistors 11 and 12 are input to a control unit (CPU) 104 provided in the image forming apparatus 100. The control unit 104 activates the apparatus by turning on a main power switch (not shown) of the apparatus, and starts predetermined image forming sequence control. The fixing device 114 starts the rotation of the fixing roller 1 when a drive source (not shown) is activated. Following the rotation of the fixing roller 1, the pressure roller 2 is also rotated (rotatingly rotated).

  The control unit 104 controls the coil power supply so that the detection result of the first thermistor (first temperature detecting means) 11 becomes a first temperature (for example, 195 ° C. at the fixing temperature) lower than a predetermined Curie temperature (for example, 205 ° C.). The control means for controlling 116 is configured. When the detection result of the second thermistor 12 reaches a second temperature that is lower than a predetermined Curie temperature (for example, 205 ° C.) and higher than the first temperature (for example, 195 ° C.), the control unit 104 Is made lower than the maximum power amount before reaching the second temperature. In the present embodiment, the second temperature is, for example, 205 ° C. for A3 size paper and 200 ° C. for postcard size paper.

  As the second temperature, the control unit 104 uses a recording material having a smaller width than the second temperature (for example, 205 ° C.) of a recording material having a large width orthogonal to the recording material passing direction (large size paper: A3 size paper). It sets so that the 2nd temperature (for example, 200 degreeC) of small size paper: postcard size paper may become lower.

  The control unit 104 activates a coil power supply 116 for driving the induction coil 6 and supplies a high-frequency current (for example, 10 to 500 kHz) from the coil power supply 116 to the induction coil 6. As a result, a high-frequency alternating magnetic flux is generated around the induction coil 6, and the fixing roller 1 generates heat by electromagnetic induction to increase the temperature toward the fixing temperature (predetermined temperature), that is, 195 ° C. in this embodiment. . The temperature rise of the fixing roller 1 is detected by the first and second thermistors 11 and 12, and the detected temperature information is input to the control unit 104.

  The control unit 104 is guided from the coil power supply 116 so that the detected temperature of the fixing roller 1 input from the first and second thermistors 11 and 12 is maintained at the first temperature (fixing temperature), for example, 195 ° C. The power supplied to the coil 6 is controlled to raise the temperature of the fixing roller 1. As a result, temperature adjustment is performed so that the fixing roller 1 has a fixing temperature of 195 ° C.

  In this state, the recording material P carrying the unfixed toner image t is introduced from the image forming unit side to the fixing nip portion N, and is nipped and conveyed through the fixing nip portion N. The unfixed toner image t is heated and fixed on the surface of the recording material P by the pressure applied at the fixing nip N.

  For example, when small-size paper is continuously passed, the temperature of the fixing roller portion corresponding to the small-size paper passing area P2 that is the paper passing area is the first temperature (fixing temperature). Maintained at 195 ° C. In this case, the temperature of the fixing roller portion corresponding to the non-sheet passing portion region (non-sheet passing portion) P3 exceeds the fixing temperature of 195 ° C. because the heat of the fixing roller portion is not consumed for heating the recording material or the toner image. The temperature rises.

  In this embodiment, when returning the reduced maximum electric energy, it controls as follows. That is, the control unit 104 reduces the maximum power amount of the coil power supply 116 and then the detection result (non-sheet passing portion temperature) by the second thermistor 12 becomes the first temperature or lower (the fixing temperature or lower). Then, the maximum power amount of the coil power source 116 is returned to the maximum power amount before being lowered. That is, control is performed so that the maximum power amount is restored. In the present embodiment, the term “below the first temperature” means, for example, a case where the temperature is 195 ° C. or lower than 195 ° C.

  In addition, the present embodiment includes a fixing device 114 as an image heating device, and a photosensitive drum 105 and a transfer charging roller 109 as conveying means for conveying a recording material to the fixing device 114. Further, the image forming apparatus includes a print controller 103 as an adjusting unit that controls the photosensitive drum 105 and the transfer charging roller 109 to adjust the interval (paper interval) between recording materials sequentially conveyed to the fixing device 114 (FIG. 1). reference).

  In the print controller 103, when the maximum power amount of the coil power supply 116 is lowered, the interval between the recording materials (so-called “paper interval”) is made longer than before the maximum power amount of the coil power supply 116 is lowered. To control. Thereby, it is possible to satisfactorily perform the fixing by the fixing roller 1 when the reduced maximum power amount is supplied.

  Here, a mechanism that makes it difficult for the fixing roller 1 to increase in temperature near the Curie temperature will be described.

  That is, the heat generation amount P of the electromagnetic induction heating is proportional to the skin resistance Rs of the metal layer 1b of the fixing roller 1 and proportional to the square of the eddy current i, and is expressed by the following formula (1).

  The skin resistance Rs is expressed by the following formula (2).

  The eddy current i is proportional to the magnetic field H generated by the induction coil 6.

  Further, since the magnetic field H is proportional to the number of turns N of the coil and the coil current I, the heat generation amount P when the fixing roller 1 is less than the Curie temperature is expressed by the following equation (3).

  From the above formula (3), it can be seen that when the temperature of the fixing roller 1 increases and the magnetic permeability μ decreases, the heat generation amount P decreases.

  Here, the number of sheets leading to the temperature rise in the non-sheet passing portion will be described. In this embodiment, for example, 75 sheets of A4 size recording material can be passed in one minute at a process speed of 350 mm / s. . At this speed, when the B5 size is continuously fed by a fixing roller using a general iron cored bar instead of the fixing roller 1 using a member (Curie material) in which the Curie point is set according to the present invention. 150 sheets, the heat resistance temperature 230 ° C., which is the upper limit of the temperature of the non-sheet passing portion, has been reached.

  Here, the temperature rise of the components of the coil power supply 116 will be described. That is, from the above equation (2), when the temperature of the fixing roller 1 increases and the magnetic permeability μ decreases, the skin resistance Rs of the fixing roller 1 decreases, so that the impedance of the fixing roller 1 decreases. At this time, when the power control is performed by constant power control, when the impedance of the fixing roller 1, which is an external resistance viewed from the coil power supply 116 side, is reduced, the power not consumed by the fixing roller 1 is the internal resistance of the coil power supply 116. Must be consumed.

  In general, the temperature adjustment control of the fixing roller is generally performed by constant power control so that the power that can be used by the fixing device can be used to the maximum. Therefore, in the conventional fixing device that does not perform the control according to the present invention, when the fixing roller is close to the Curie temperature, the power consumption due to the internal resistance of the coil power supply increases and the power supply by the high frequency power supply may become unstable. .

  Even if the target temperature at the time of adjusting the temperature of the fixing roller 1 is set to be equal to or lower than the Curie temperature, the cause of the temperature increase of the fixing roller 1 near the Curie temperature is due to the temperature increase of the non-sheet passing portion described above. The width at which the temperature rises at the non-sheet passing portion is determined by the width of the recording material in the width direction (left and right direction in FIG. 2) orthogonal to the recording material conveyance direction. Hereinafter, the “width of the recording material” indicates the width of the recording material in the width direction orthogonal to the conveyance direction of the recording material.

  Since the impedance of the fixing roller 1 varies depending on the length of the temperature rise of the non-sheet passing portion, in this embodiment, the temperature of the non-sheet passing portion is detected by the second thermistor 12 and corresponds to the width of the recording material. Then, control is performed so as to reduce the maximum amount of power supplied to the fixing roller 1.

  In other words, when the size of the recording material is small and the length of temperature rise at the non-sheet passing portion is long, the maximum amount of power supplied to the fixing roller 1 is reduced at a low temperature. More specifically, in the A3 size, the determination of the temperature increase in the non-sheet-passing portion is set to reduce the maximum electric energy at the set Curie temperature of 205 ° C., and in the postcard size, at 200 ° C. before the Curie temperature. The maximum amount of power is reduced. For other sizes, the temperature at which the maximum amount of power is reduced is determined by proportional calculation.

  As described above, when the maximum power amount is lowered, the temperature of the fixing roller 1 is lowered as a result, and it becomes difficult to maintain the fixing temperature (image heating temperature). Therefore, when the fixing temperature becomes the minimum temperature necessary for fixing the toner, control is performed so that the temperature of the fixing roller 1 is not lowered as much as possible by lengthening the sheet passing interval (inter-sheet) of the recording material. Do.

  That is, the productivity may decrease as a result of lowering the maximum power amount with respect to the temperature increase of the non-sheet passing portion. Therefore, in order to maintain the productivity as much as possible, it is possible to delay the detection of the temperature rise of the non-sheet passing portion as much as possible, delay the timing of lowering the maximum power amount, and suppress the decrease in productivity. By performing such control, when the number of images formed is not so large, the temperature at the edge is not increased, so that productivity can be prevented from being affected.

  The maximum power amount when the non-sheet passing portion is not heated is, for example, 1000 W, while the A3 size is fixed with the non-sheet passing portion at the Curie temperature of 205 ° C. If so, change to about 900W. In the case of postcard size, it is changed to about 300W.

  When the maximum power amount of the coil power source 116 is reduced, the control unit 104 has a recording material having a smaller width than a recording material having a large width orthogonal to the sheet passing direction (large size paper (A3 size paper)). Control is performed so that the maximum amount of electric power after reduction is smaller for small-size paper (postcard-size paper).

  The electric power Ps supplied from the coil power supply 116 to the induction coil 6 of the fixing roller 1 is expressed by the following formula (4). However, L in Formula (4) shows the width | variety (thrust width: mm) of the width direction of a recording material.

  Here, the operation using the fixing device 114 of the present embodiment will be described with reference to the flowchart of FIG.

  That is, when the process starts, a print job is input to the image forming apparatus 100 in step S1. In step S2, the control unit 104 determines whether or not the temperature detected by the first thermistor 11 has reached a first temperature (eg, 195 ° C.) lower than a predetermined Curie temperature (eg, 205 ° C.). As a result, if the detected temperature of the first thermistor 11 is not the first temperature, step S2 is repeated.

  On the other hand, when it is determined in step S2 that the detected temperature of the first thermistor 11 has reached the first temperature, the control unit 104 starts fixing by the fixing device 114 in step S3.

  Subsequently, in step S4, the control unit 104 determines that the temperature detected by the second thermistor 12 is equal to or lower than a predetermined Curie temperature and higher than the first temperature (for example, 205 ° C. for large size paper, In the case of small size paper, it is determined whether or not the temperature has reached 200.degree. As a result, if the detected temperature is not higher than the predetermined Curie temperature and does not reach the second temperature higher than the first temperature, step S3 is repeated.

  On the other hand, if it is determined in step S4 that the detected temperature has reached the second temperature that is equal to or lower than the predetermined Curie temperature and is higher than the first temperature, the control unit 104 determines the maximum power of the coil power supply 116 in step S5. The amount is controlled to be lower than the maximum amount of power before reaching the second temperature.

  Subsequently, in step S6, the control unit 104 determines whether or not the second temperature has become equal to or lower than the first temperature based on the temperature detection of the second thermistor 12. As a result, if the second temperature is not lower than the first temperature, step S5 is repeated.

  On the other hand, when determining in step S6 that the second temperature has become equal to or lower than the first temperature, in step S7, the control unit 104 sets the maximum power amount of the coil power supply 116 to the maximum power amount before reduction in step S5. Return.

  In step S8, the control unit 104 determines whether or not there is a remaining print job. If it is determined that there is a remaining print, the process is repeated from step S3. On the other hand, if it is determined that there is no print residue, the job is terminated.

  In the present embodiment described above, the control unit 104 determines the maximum power amount of the coil power supply 116 when the detection result of the second thermistor 12 reaches a second temperature that is lower than a predetermined Curie temperature and higher than the first temperature. , And control to lower than the maximum amount of power before reaching the second temperature. Thereby, the temperature increase of the non-sheet passing portion in the fixing roller 1 can be effectively suppressed. Furthermore, it is possible to reduce the load on the coil power supply 116 when the temperature of the end portion rises while the temperature of the paper passing portion is maintained at the set temperature.

  In the present embodiment, even if the fixing roller 1 tries to exceed the heat resistance temperature, the thermostat 15 that contacts the upper portion of the fixing roller 1 opens the contact when the temperature exceeds the heat resistance temperature, thereby inducing the induction coil. Ensure that power to 6 is cut off. As a result, the fixing roller 1 can be reliably prevented from reaching a high temperature exceeding the heat resistance temperature.

  As described above, in this embodiment, the Curie temperature is set to a temperature higher than the fixing temperature (image heating temperature) at which the image is heated by the fixing roller 1 and lower than the heat resistance temperature of the fixing device 114. Here, the control unit 104 that controls energization of the induction coil 6 so that the temperature detected by the first thermistor 11 becomes the fixing temperature, the temperature detected by the second thermistor 12 is lower than the Curie temperature and higher than the fixing temperature. When the second temperature (set temperature) is reached, the following can be performed. That is, the control unit 104 sets the maximum power amount applied to the induction coil 6 to be smaller than the maximum power amount applied to the induction coil 6 before the temperature detected by the second thermistor 12 reaches the second temperature. The temperature detected by the thermistor 11 can be controlled to be the fixing temperature.

  Then, it is possible to reduce the load on the coil power supply 116 when the temperature of the end portion rises while the temperature of the sheet passing portion region (sheet passing portion) P2 is maintained at the fixing temperature. In this embodiment, the set temperature of the fixing temperature is the same before and after the maximum amount of power applied to the induction coil 6 is reduced. Note that when the control to reduce the maximum electric energy is performed, the set temperature of the fixing temperature is not changed, but after that, the setting temperature of the fixing temperature is set lower than the setting temperature before the control to reduce the maximum electric energy. Also good. Even in this case, for example, the fixing property can be ensured by performing control such as reducing the process speed.

  In the present embodiment, the first and second thermistors 11 and 12 are used as the first and second temperature detection means. However, instead of the second thermistor 12, a magnetic coil 12A as a magnetic flux detection means (shown by a broken line in FIG. 2). It is also possible to use That is, it is also possible to detect the leakage magnetic flux that changes when the temperature of the non-sheet passing portion region (non-sheet passing portion) P3 of the fixing roller 1 approaches the Curie point as an eddy current flowing in the magnetic coil 12A. Alternatively, it is possible to use means for detecting a change in the current value or power consumption supplied to the exciting coil (not shown) with the magnetic change.

  In the electromagnetic induction heating type fixing device 114 of the present embodiment, the form of the image heating member is not limited to the fixing roller 1, and may be a form of another rotating body such as an endless belt body. In addition, the image heating member can be configured as a member of the induction heating element alone, or as a composite layer member of two or more layers including other material layers such as a heat resistant resin and ceramics, including the layer of the induction heating element. It can also be configured.

  The induction heating of the induction heating element by the magnetic flux generation means described above is not limited to the internal heating method, and an external heating type apparatus configuration in which the magnetic flux generation means is disposed outside the induction heating element may be employed.

  The temperature detecting means is not limited to the first and second thermistors 11 and 12 and may be any other temperature detecting element. The temperature detecting means is not limited to the contact type but may be a non-contact type.

  Further, in the present embodiment, the recording medium has been described as being transported based on the central reference. However, the present invention is not limited to this, and it is needless to say that the present invention can be effectively applied to an apparatus configured to transport based on one side. .

  DESCRIPTION OF SYMBOLS 1 ... Image heating member (fixing roller), 3 ... Magnetic flux generation means (coil assembly), 6 ... Coil (induction coil), 11 ... 1st temperature detection means (1st thermistor), 12 ... 2nd temperature detection means ( (Second thermistor), 100 ... image forming apparatus, 103 ... adjusting means (print controller), 104 ... control means (control section), 105,109 ... conveying means (photosensitive drum, transfer charging roller), 114 ... image heating apparatus (Fixing device) 116 ... power source, energizing part (coil power source), P ... recording material, P2 ... paper passing part (paper passing part area), P3 ... non-paper passing part (non-paper passing part area)

Claims (6)

Magnetic flux generating means for generating magnetic flux based on the supplied current;
A power source capable of variably adjusting the maximum power amount and supplying a current to the magnetic flux generating means;
An image heating member that is made of a magnetic shunt alloy adjusted to a predetermined Curie temperature, heats an image on a recording material that passes by being heated by the magnetic flux generated by the magnetic flux generation means,
A first temperature detecting means for detecting a temperature of a paper passing portion through which a recording material of a predetermined size passes among the surface of the image heating member;
A second temperature detecting means for detecting a temperature of a non-sheet passing portion out of the sheet passing portion of the surface of the image heating member;
Control means for controlling the power supply so that a detection result of the first temperature detection means becomes a first temperature lower than the predetermined Curie temperature,
The control means, when the detection result of the second temperature detection means reaches a second temperature lower than the predetermined Curie temperature and higher than the first temperature, the maximum power amount of the power supply, Lower than the maximum amount of power before reaching the second temperature,
An image heating apparatus. The second temperature is set to be lower for a recording material having a small width than a recording material having a large width orthogonal to the sheet passing direction of the recording material.
The image heating apparatus according to claim 1. When the control unit reduces the maximum power amount of the power source, the recording material with the small width is less than the recording material with the large width perpendicular to the sheet passing direction of the recording material. Set the value lower,
The image heating apparatus according to claim 1, wherein the apparatus is an image heating apparatus. The control means reduces the maximum power amount of the power source when the detection result by the second temperature detection means becomes equal to or lower than the first temperature after reducing the maximum power amount of the power source. To restore the maximum amount of power,
The image heating apparatus according to claim 1, wherein the image heating apparatus is an image heating apparatus. An image heating apparatus according to any one of claims 1 to 4,
Conveying means for conveying a recording material to the image heating device;
Adjusting means for controlling the conveying means to adjust the interval between the recording materials sequentially conveyed to the image heating device,
The adjusting means makes the interval between the recording materials longer when the maximum power amount of the power source is reduced than before the maximum power amount of the power source is reduced.
An image forming apparatus. Coils,
An energization section for energizing the coil;
A magnetic shunt alloy adjusted to a predetermined Curie temperature, an image heating member for heating an image on a recording material by heat generated by magnetic flux generated from the coil;
First temperature detecting means for detecting a temperature of a paper passing portion through which a recording material having a minimum size capable of passing paper in a direction orthogonal to the conveyance direction of the recording material passes;
A second temperature detecting means for detecting the temperature of the non-sheet passing area through which the recording material to be passed does not pass;
Control means for controlling energization to the coil so that the temperature detected by the first temperature detection means becomes an image heating temperature for heating the image by the image heating member,
In the image heating apparatus, wherein the Curie temperature is higher than the image heating temperature and lower than the heat resistant temperature of the image heating apparatus.
The control means includes
When the temperature detected by the second temperature detection means is lower than the Curie temperature and reaches a set temperature higher than the image heating temperature, the maximum power amount applied to the coil is detected by the second temperature detection means. And the temperature detected by the first temperature detection means is controlled to be the image heating temperature by making the temperature lower than the maximum amount of power applied to the coil before reaching the set temperature.
An image heating apparatus.

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