JP2019012113A - Fixation device and image formation device - Google Patents

Abstract

To suppress increase in power and suitably heat various sizes of sheets without a complicated structure.SOLUTION: A fixation device 13 of a printer comprises: a heat resistant film 22; a heating body 23 for heating one surface side of the heat resistant film 22, and heating a toner image on a sheet which passes on the other surface side of the heat resistant film 22; and a current detection part 38 for detecting a current amount I of current flowing to the heating body 23. The heating body 23 comprises: a heat element 32 which is provided over the whole region in a width direction orthogonal to a passage direction of the sheet and generates heat by electrification; and a temperature sensitive resistor 33 provided on a part in the width direction and electrically connected to the heat element 32. A control device of the fixation device 13 performs voltage control for lowering voltage applied to the heating body 23 by a voltage application part 37 to a target voltage based on a total resistance of the heating body and a prescribed target power or a lower voltage, when the current amount I exceeds a prescribed current threshold, caused by reduction of the total resistance of the heating body 23.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet, and an image forming apparatus including the fixing device.

  The image forming apparatus includes a fixing device that heats and fixes a toner image formed on a sheet. The fixing device includes a heating member that heats the toner image and a pressure member that pressurizes the toner image against the paper. The heating member is configured, for example, by fixing and supporting a heating body in a hollow portion of a cylindrical member such as a belt or a film. By applying a film member such as a heat resistant film as the cylindrical member and applying a low heat capacity heating body as the heating body, it becomes possible to save power and shorten the warm-up time compared to the roller type heating member. .

  By the way, in the fixing device, when heat-fixing is continuously performed on a small-sized sheet, the film member and the pressure member are not in contact with the part (sheet passing area) where the sheet is in contact (non-sheet passing area). ) And the amount of heat release. Then, in the non-sheet passing area, the temperature of the film member and the pressure member is higher in the non-sheet passing area than in the sheet passing area.

  On the other hand, for example, Patent Document 1 uses a heating resistor in which a heating resistor having a negative temperature change coefficient (TCR) is formed in a strip shape on an insulating substrate. When the temperature of the non-sheet passing area is higher than the temperature of the sheet passing area, the resistance value of the heating resistor is smaller in the non-sheet passing area than in the sheet passing area. Can also be suppressed.

  Further, in Patent Document 2, the heating element is composed of an energization heating element sandwiched between at least one pair of electrodes, and has an energization path that branches from the middle in the direction perpendicular to the heating element traveling direction of the energization heating element. A resistor in which at least one resistor having a negative TCR is connected is used. When the temperature of the non-sheet-passing area where the resistor is arranged increases, the resistance value of the resistor decreases, and the energization heating element in the non-sheet-passing area is cut off. It is suppressed.

  Further, in Patent Document 3, as a heating element, a resistance heating element having a plurality of small heating elements electrically connected in parallel to each other arranged in a direction orthogonal to the moving direction of the fixing belt, and a small heating element from the power source A device including a PTC element connected in series with a small heating element and having a resistance value rising at a predetermined temperature or higher is used. When the temperature of the non-sheet-passing area where the PTC element is disposed becomes equal to or higher than a predetermined temperature, the resistance value of the PTC element increases, and the current supplied to the small heating element is suppressed. The

Japanese Patent Laid-Open No. 08-64350 Japanese Patent Laid-Open No. 06-283254 JP 2009-244595 A

  However, in the case of a heating element in which a TCR has a negative heating resistor, if the heating resistor is continuously energized without passing paper for some reason, the temperature of the entire heating resistor increases. As a result, the resistance value of the entire heating resistor is lowered, so that the power is greatly increased and the temperature of the heating resistor is rapidly increased.

  In addition, in a heating element in which a resistor or a PTC element having a negative TCR is connected to the energization path, it is necessary to connect the resistor and the PTC element with a certain interval, so it is difficult to support all sizes of paper. Moreover, there is a problem that the configuration becomes more complicated as the number of resistors and PTC elements is increased.

  By the way, with respect to the heating resistor sandwiched between a pair of electrodes, the heating body is partly with respect to the direction perpendicular to the moving direction of the heat resistant film, and with respect to the moving direction of the heat resistant film. In some cases, a temperature-sensitive resistor (CTR) whose resistance value decreases at a predetermined temperature or higher is provided so as to be in contact with the entire surface. When the temperature of the non-sheet-passing area where the temperature-sensitive resistor is placed exceeds a predetermined temperature, the resistance value of the temperature-sensitive resistor decreases and the current flowing to the heating resistor is suppressed. The rise is suppressed.

  However, in this heating element, when a constant power supply voltage is applied, the resistance value of the entire heating element decreases as the area where the resistance value of the temperature-sensitive resistor decreases, and the current flowing through the heating element decreases. It gets bigger. Then, the allowable current of devices such as a heating body and a low voltage substrate to which voltage is applied may be exceeded, and these devices may be damaged. In addition, since the power consumption is excessively increased and the power supply voltage is lowered, there is a possibility that a problem that flicker occurs or the breaker falls occurs.

  In view of the above circumstances, an object of the present invention is to appropriately heat sheets of various sizes without complicating the configuration while suppressing an increase in power.

  The fixing device according to the present invention includes a film member, a heating body that heats one side of the film member and heats a toner image on a sheet that passes the other side of the film member, and a current that flows through the heating body. An electric current detector for detecting the amount of the heating element, and the heating element is provided over the entire area in the width direction orthogonal to the sheet passing direction, and generates a heating resistor that generates heat when energized; and A temperature-sensitive resistor that is provided in part and electrically connected to the heating resistor, and the amount of current exceeds a predetermined current threshold due to a decrease in the total resistance of the heater In this case, voltage control is performed to lower the voltage applied to the heating body to a target voltage or lower based on the total resistance of the heating body and a predetermined target power.

  In the fixing device, as the voltage control, the voltage applied to the heating body is turned on and off in the cycle so that an average voltage in a half-wave control period having a predetermined number of cycles is equal to or lower than the target voltage. It is recommended to perform half-wave control that switches in half-wave units.

  In the fixing device, as the voltage control, the voltage applied to the heating body is turned on and off in time units within the phase control period so that an average voltage in a predetermined phase control period is equal to or lower than the target voltage. It is recommended to perform phase control to be switched with.

  The fixing device may control the amplitude so that the voltage applied to the heating body is equal to or lower than the target voltage as the voltage control.

  The fixing device may apply a voltage lower than the maximum voltage during normal operation to the heating body at the time of startup.

  The fixing device further includes a temperature detection unit that detects the temperature of the heating resistor at a position where the temperature sensitive resistor is not provided in the width direction, and a temperature detected by the temperature detection unit is a predetermined temperature threshold value. When it is above, it is good to apply a voltage lower than the maximum voltage during normal operation to the heating element.

  The image forming apparatus of the present invention includes the above-described fixing device.

  According to the present invention, it is possible to appropriately heat various sizes of paper without complicating the configuration while suppressing an increase in power.

1 is a cross-sectional view illustrating a printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device of a printer according to an embodiment of the present invention. It is a bottom view showing a heating element of a fixing device of a printer according to an embodiment of the present invention. It is a bottom view side view showing a heating body of a fixing device of a printer according to an embodiment of the present invention. FIG. 2 is a circuit diagram illustrating a heating body and its periphery of a fixing device of a printer according to an embodiment of the present invention. 1 is a block diagram illustrating an electrical configuration of a fixing device of a printer according to an embodiment of the present invention. 6 is a graph illustrating an example of a voltage applied to a heating body during normal operation in the fixing device of the printer according to the embodiment of the present invention. 6 is a graph illustrating an example of a voltage applied to a heating body by half-wave control in a fixing device of a printer according to an embodiment of the present invention. 6 is a graph illustrating an example of a voltage applied to a heating body by half-wave control in a fixing device of a printer according to an embodiment of the present invention. 6 is a graph illustrating an example of a voltage applied to a heating body during normal operation in the fixing device of the printer according to the embodiment of the present invention. 5 is a graph showing an example of a voltage applied to a heating body by phase control in the printer fixing device according to the embodiment of the present invention. 5 is a graph showing an example of a voltage applied to a heating body by phase control in the printer fixing device according to the embodiment of the present invention.

  First, the overall configuration of a printer 1 (image forming apparatus) according to an embodiment of the present invention will be described with reference to FIG. Hereinafter, for convenience of explanation, the front side of the sheet in FIG. Arrows L, R, U, Lo, Fr, and Rr appropriately attached to the drawings indicate the left side, right side, upper side, lower side, front side, and rear side of the printer 1, respectively.

  The printer 1 includes a substantially box-shaped printer main body 2. A paper feed cassette 3 for storing paper (recording medium) is provided at a lower portion of the printer main body 2. A paper discharge tray 4 is provided at the upper portion of the printer main body 2. Provided.

  An exposure unit 5 composed of a laser scanning unit (LSU) is disposed below the discharge tray 4 in the upper part of the printer main body 2, and an image forming unit 6 is provided below the exposure unit 5. . The image forming unit 6 is rotatably provided with a photosensitive drum 7 as an image carrier. Around the photosensitive drum 7, a charger, a developing device connected to a toner container, a transfer roller, A cleaning device is arranged along the rotation direction of the photosensitive drum 7.

  In addition, a paper conveyance path 10 is provided inside the printer main body 2. A paper feeding unit 11 is provided in the vicinity of the paper feeding cassette 3 at the upstream end of the conveyance path 10, and a transfer unit 12 including a photosensitive drum 7 and a transfer roller is provided in the middle part of the conveyance path 10. A fixing device 13 is provided in the downstream portion of the transport path 10, and a paper discharge unit 14 is provided in the vicinity of the paper discharge tray 4 at the downstream end of the transport path 10. In addition, a control device 15 that controls the fixing device 13 is provided inside the printer body 2.

  Next, an image forming operation of the printer 1 having such a configuration will be described. The printer 1 starts an image forming operation when image data is input from an external computer or the like and an instruction to start printing is given. First, after the surface of the photosensitive drum 7 is charged by the charger of the image forming unit 6, the photosensitive drum 7 is exposed in accordance with the image data by the laser beam from the exposure unit 5, and the photosensitive drum. An electrostatic latent image is formed on the surface 7. Next, the electrostatic latent image is developed into a toner image by the developer of the image forming unit 6 using toner.

  On the other hand, the paper stored in the paper feed cassette 3 is taken out by the paper feed unit 11 and transported on the transport path 10. The sheet on the conveyance path 10 is conveyed to the transfer unit 12 at a predetermined timing, and the toner image on the photosensitive drum 7 is transferred to the sheet by the transfer unit 12. The sheet on which the toner image has been transferred is conveyed to the fixing device 13 and the toner image is fixed on the sheet by the fixing device 13. The paper on which the toner image is fixed is discharged from the paper discharge unit 14 to the paper discharge tray 4.

  Next, the configuration of the fixing device 13 will be described with reference to FIGS. The fixing device 13 includes a heating member 20 and a pressure member 21. The heating member 20 includes an endless belt-shaped heat resistant film 22 (film member) and a heating body 23 disposed in a hollow portion of the heat resistant film 22. The heating member 20 and the pressure member 21 are disposed to face and contact each other with the conveyance path 10 interposed therebetween, and a fixing nip is formed between the heating member 20 and the pressure member 21.

  The heat resistant film 22 of the heating member 20 is formed in a cylindrical shape longer than the width of the maximum size sheet in the width direction orthogonal to the sheet conveyance direction along the conveyance path 10. The heat resistant film 22 is formed of a material having high heat resistance, releasability, durability, and strength. For example, the material of the heat resistant film 22 is a single layer film of PTFE (polytetrafluoroethylene) or PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), or a film surface of polyimide, polyamideimide, PEEK, PESPPS, or the like. Alternatively, a composite layer film coated or coated with PTFE or PFA may be used. In order to reduce the heat capacity and shorten the warm-up time, the heat-resistant film 22 is formed with a film thickness of, for example, 100 μm or less, preferably 20 μm or more and 40 μm or less.

  The heat resistant film 22 is rotatably supported at both ends in the width direction, and rotates along the paper transport direction. The inner surface of the heat resistant film 22 is in contact with the heating body 23 and slides relative to the heating body 23 by rotating. In addition, the heat resistant film 22 has an outer peripheral surface that is in contact with the pressure member 21 and contacts a sheet that passes through the fixing nip when rotating.

  The heating member 23 of the heating member 20 has a longer shape than the width of the maximum size sheet in the width direction, and is fixedly supported by the holder 24. The holder 24 is longer than the heating element 23 in the width direction and is formed of a heat insulating material, and both ends in the width direction are fixed to a fixing frame (not shown) of the fixing device 13.

  As shown in FIGS. 3A and 3B, the heating body 23 includes a substrate 30, a pair of power supply electrodes 31 provided on one surface of the substrate 30, and a heating resistor 32 (electric heating element) provided on one surface of the substrate 30. A temperature sensitive resistor 33 (CTR: Critical Temperature Resistor) provided between the heating resistor 32 and the substrate 30, an overcoat 34 provided on the surface of the heating resistor 32, and the other surface of the substrate 30. A thermistor 35 (temperature detection unit) and a thermostat 36 are included. The heating body 23 is disposed in contact with the inner peripheral surface of the heat resistant film 22 with the one surface side of the substrate 30 on which the heating resistor 32 is provided facing the pressing member 21.

The substrate 30 is a plate-like member that is longer than the width of the maximum size sheet in the width direction, and has a predetermined length along the transport direction. The substrate 30 is formed of a material having high electrical insulation, heat resistance, and low heat capacity. As a material for the substrate 30, ceramics such as Al ₂ O ₃ (alumina), AlN, and SiC may be used.

  The pair of power supply electrodes 31 are provided at both ends of the substrate 30 in the width direction. As shown in FIG. 4, one power supply electrode 31 a is connected to a voltage application unit 37, and the other power supply electrode 31 b is grounded via a current detection unit 38.

  The heating resistor 32 is a heat generation source that generates heat when power is supplied, and the heating body 23 is heated when the heating resistor 32 generates heat. The heating resistor 32 is made of a material such as silver palladium (Ag / Pd), for example. The heating resistor 32 is provided in a linear or strip shape along the width direction between the pair of power supply electrodes 31, and both ends in the width direction are respectively connected to the pair of power supply electrodes 31 as shown in FIG. Yes. The heating resistor 32 generates heat when a current flows through the pair of power supply electrodes 31.

  When the temperature sensitive resistor 33 is heated to a predetermined temperature (for example, 150 ° C. to 200 ° C.) or higher, the resistance value decreases. The temperature sensitive resistor 33 is formed of, for example, ceramics such as barium titanate, a conductive polymer, or the like. The temperature sensitive resistor 33 is provided along the width direction in the non-sheet passing region R2 at both ends of the sheet passing region R1 of the minimum size sheet in the width direction (see FIG. 3B). Further, the temperature-sensitive resistor 33 has a length equal to or longer than that of the heat generating resistor 32 in the transport direction. In other words, in the non-sheet passing region R2, the heat resistor 32 is entirely covered in the transport direction. It is provided as follows. Therefore, in the width direction, a layer of only the heating resistor 32 is formed in the sheet passing region R1, and a composite layer of the heating resistor 32 and the temperature sensitive resistor 33 is formed in the non-sheet passing region R2. The temperature sensitive resistor 33 is in contact with the heat generating resistor 32 and is electrically connected in parallel with the non-sheet passing region R2 portion of the heat generating resistor 32 as shown in FIG.

  The overcoat 34 covers and protects the heating resistor 32 across the width direction and the conveyance direction between the pair of power supply electrodes 31. The overcoat 34 is made of, for example, glass having electrical insulation.

  The thermistor 35 and the thermostat 36 are attached to a portion corresponding to the paper passing area R1. The thermistor 35 is a control temperature sensor for controlling the fixing temperature of the heating member 20, detects the temperature of the substrate 30, and the control device 15 controls the fixing temperature based on the detected temperature. The thermistor 35 is also used for voltage control of a voltage application unit 37 described later. The thermostat 36 is a safety temperature sensor for preventing an excessive temperature rise of the heating member 20, detects the temperature of the substrate 30, and when an abnormal temperature rise is predicted from the detected temperature, to the heating body 23. Is forcibly cut off.

  The pressure member 21 is a cylindrical pressure roller that is longer than the width of the maximum size sheet in the width direction. The pressure member 21 includes, for example, a cylindrical cored bar, an elastic layer provided around the cored bar, and a release layer that covers the elastic layer. The elastic layer is made of, for example, silicon rubber, and the release layer is made of, for example, PTFE or PFA. The pressurizing member 21 is supported so as to be rotatable in the conveying direction, and is pressed toward the heating member 20 by a pressing member (not shown). In other words, the pressure member 21 is pressed toward the heating body 23 with the heat resistant film 22 interposed therebetween. Further, for example, the pressure member 21 is connected to a drive source 41 (see FIG. 5) such as a motor, and is rotated by a driving force from the drive source 41, and the heating member 20 is rotated by the rotation of the pressure member 21. Followed rotation.

  Next, the electrical configuration of the control device 15 that controls the fixing device 13 will be described with reference to FIG. The control device 15 is composed of a CPU or the like, and is connected to a storage device 40 such as a ROM or a RAM. In addition, as the control device 15 and the storage device 40, a main control device and a main storage device that collectively control each unit of the printer 1 may be applied.

  The control device 15 controls each unit connected to the control device 15 based on a control program and control data stored in the storage device 40. For example, the control device 15 is connected to the thermistor 35, the voltage application unit 37, the current detection unit 38, and the drive source 41.

  The voltage application unit 37 is controlled by the control device 15 to apply a voltage to the heating body 23. The voltage control of the voltage application unit 37 will be described later.

  The current detection unit 38 detects a current flowing through the heating body 23 when the heating body 23 is energized by voltage application of the voltage application unit 37. For example, as illustrated in FIG. 4, the current detection unit 38 includes a fixed resistor 38 a connected in series with the heating body 23, and detects a detection voltage V between the fixed resistor 38 a and the ground. The current detection unit 38 detects the current amount I flowing through the heating body 23 by converting the detection voltage V into a current, and inputs the detected current amount I to the control device 15. Or the electric current detection part 38 is not limited to the detection of the electric current amount I using the fixed resistance 38a, For example, you may be comprised so that an electric current may be measured directly.

  Next, voltage control of the voltage application unit 37 will be described. For example, when the current amount I detected by the current detection unit 38 exceeds a predetermined current threshold value (for example, 10 A) due to a decrease in the total resistance of the heating body 23, the control device 15 performs heating element 23. The voltage application unit 37 is controlled so that the voltage applied to is lower than the target voltage based on the current amount I and a predetermined target power (for example, 1000 W). The target voltage is calculated backward from the current amount I and the target power.

  When the fixing device 13 is in a normal operation, the voltage application unit 37 applies an AC normal operation voltage having a predetermined amplitude A and a predetermined period T1 to the heater 23 as shown in FIG. 6A. For example, when the target power of the heating body 23 is set to 1000 W and the voltage application unit 37 applies a normal operating voltage having an effective value of 100 V to the heating body 23 when the total resistance of the heating body 23 is 10Ω, A current of 10 A (current amount I) flows through the heating element 23 and 1000 W of power is generated. At this time, when the temperature of the heating body 23 (temperature sensitive resistor 33) rises and the total resistance of the heating body 23 falls to 5Ω, the voltage application unit 37 applies a normal operating voltage of an effective value of 100V to the heating body 23. Then, a current of 20 A (current amount I) flows through the heating body 23, and 2000 W of power is generated.

  Therefore, the control device 15 controls the voltage application unit 37 so that a voltage of 70.71% (about 70%) of the normal operating voltage is applied to the heating body 23 as a target voltage. As a result, a current of about 14.14 A is passed through the heating element 23 having a total resistance of 5Ω, and the target electric power (1000 W) is generated in the heating element 23.

  As voltage control for lowering the voltage applied to the heating body 23 as described above, the voltage application unit 37 is, for example, in a half-wave control period T2 having a predetermined number (for example, 5) of periods T1 of AC normal operating voltages. Then, half-wave control is performed to switch on and off the voltage applied to the heating body 23 in half-wave units (half-cycle units) of the period T1 so that the average voltage (average voltage of effective values) is equal to or lower than the target voltage. .

  For example, when the voltage that is 100% of the normal operating voltage is set as the target voltage, the voltage applying unit 37, as shown in FIG. The applied voltage is controlled so that all of the 10 half-waves) are turned on (solid line). Further, when the voltage of 50% of the normal operating voltage is set as the target voltage, the voltage application unit 37 includes a half wave included in the half wave control period T2, as shown in FIG. 6B (for example, included in the five cycles T1). The applied voltage is controlled so that half of the half waves (5 half waves) are turned on (solid line) and the other half waves are turned off (dotted line). Furthermore, when the voltage 20% of the normal operating voltage is set as the target voltage, the voltage application unit 37, as shown in FIG. 6C, has half the number of half of the half waves included in the half wave control period T2. The applied voltage is controlled so that the wave (two half waves) is turned on (solid line) and the other half wave is turned off (dotted line). The half wave control period T2 is not limited to 10 half waves, and may be set to include 20 or other numbers of half waves. As the number of half waves included in the half wave control period T2 increases, the applied voltage can be controlled more finely.

  Or as voltage control which makes the voltage applied to the heating body 23 low, the voltage application part 37 sets the average voltage (average voltage of an effective value) as the phase control period T3 for one period T1 of the normal operating voltage of alternating current, for example. ) Is controlled so as to switch on and off the voltage applied to the heater 23 in units of time (predetermined time intervals) within the phase control period T3 so that the voltage is less than or equal to the target voltage.

  For example, when the voltage that is 100% of the normal operating voltage is set as the target voltage, the voltage application unit 37 sets the applied voltage to be on (solid line) at all times in the phase control period T3 as shown in FIG. 7A. Control. Further, when 50% of the normal operating voltage is set as the target voltage, the voltage application unit 37 is turned on (solid line) in half time in the phase control period T3 and turned off in other times as shown in FIG. 7B. The applied voltage is controlled to be (dotted line). Furthermore, when the voltage 20% of the normal operating voltage is set as the target voltage, the voltage application unit 37 is turned on (solid line) at the time of 1/5 in the phase control period T3 for another time as shown in FIG. 7C. Then, the applied voltage is controlled so as to be turned off (dotted line). The phase control period T3 is not limited to one cycle T1, and may be set to a half cycle of the cycle T1. As the phase control period T3 is shorter, the applied voltage can be corrected at shorter intervals.

  Alternatively, as voltage control for lowering the voltage applied to the heater 23, the voltage application unit 37 controls, for example, the amplitude A of the AC normal operating voltage so that the applied voltage (effective value) is equal to or lower than the target voltage. To control.

  In the fixing device 13, the temperature of the heating body 23 is already high and the total resistance of the heating body 23 is reduced before the temperature detection of the heating body 23 by the current detection unit 38, that is, at the start of the fixing process. Have For example, the temperature of the temperature-sensitive resistor 33 may become high immediately after the fixing device 13 is started after continuously fixing small-size sheets.

  Therefore, the control device 15 has a limit voltage lower than the normal operating voltage (maximum voltage during normal operation) at the start (starting time) of the fixing process of the fixing device 13 for which the total resistance of the heating body 23 has not been calculated. The voltage application unit 37 is controlled so as to be applied to the heating body 23. For example, the limit voltage is set to a voltage (for example, several V) that is allowed even when the total resistance of the heating body 23 is the lowest. For example, when the total resistance of the heating body 23 is the highest, the heating body It is set so as not to exceed the electric power generated in the heating body 23 when a normal operating voltage is applied to the heater 23. Note that, after a predetermined time has elapsed since the previous fixing process until the temperature of the heating element 23 has sufficiently decreased, the voltage application unit 37 is controlled so that the normal operating voltage is applied even when the fixing device 13 is activated. Good.

  Alternatively, when the temperature detected by the thermistor 35 (temperature detection unit) is equal to or higher than a predetermined temperature threshold (for example, 150 ° C.), the control device 15 applies a voltage so as to apply the above-described limiting voltage to the heating body 23. The unit 37 is controlled.

  Note that the voltage application unit 37 may be controlled to apply the normal operating voltage after the fixing device 13 is activated or when the temperature detected by the thermistor 35 is lower than a predetermined temperature threshold. Or you may control the voltage application part 37 so that an applied voltage may be raised from said limit voltage to a normal operating voltage gradually. Thereby, the heating body 23 can be heated efficiently.

  According to the present embodiment, as described above, the fixing device 13 of the printer 1 (image forming apparatus) heats the heat-resistant film 22 (film member) and the one surface side of the heat-resistant film 22 to thereby heat-resistant film. 22 includes a heating body 23 that heats the toner image on the paper that passes the other surface side of the paper 22 and a current detection unit 38 that detects a current amount I flowing through the heating body 23. The heating element 23 is provided over the entire region in the width direction orthogonal to the sheet passing direction, and the heating resistor 32 generates heat by energization, and is provided in a part of the width direction. It is comprised from the temperature sensitive resistor 33 electrically connected. The control device 15 of the fixing device 13 determines the voltage applied to the heating body 23 by the voltage application unit 37 when the current amount I exceeds a predetermined current threshold due to a decrease in the total resistance of the heating body 23. Voltage control is performed to lower the voltage to a target voltage or less based on the total resistance of the heating element 23 and a predetermined target power.

  Thereby, when the temperature of the non-sheet-passing region R2 where the temperature sensitive resistor 33 is provided becomes higher than a predetermined temperature, the resistance value of the temperature sensitive resistor 33 is reduced, and the current supplied to the heating resistor 32 is suppressed. The Therefore, the temperature rise in the non-sheet passing region R2 can be suppressed. On the other hand, by providing a portion that does not contact the temperature sensitive resistor 33, even if the heating resistor 32 is continuously energized without passing paper for some reason, the resistance value of the entire heating resistor 32 is a predetermined value. It does not drop below. Therefore, the electric power of the heating body 23 does not increase beyond a predetermined amount, and a rapid temperature increase of the heating resistor 32 can be suppressed. Furthermore, when the current amount I detected by the current detection unit 38 exceeds a predetermined current threshold, the current flowing through the devices such as the heating body 23 and the voltage application unit 37 is reduced in order to reduce the voltage applied to the heating body 23. Can be prevented from exceeding the allowable current, and stable electric power can be generated in the heater 23. Therefore, damage to these devices can be suppressed, power consumption is excessively increased, power supply voltage is prevented from dropping, and problems such as occurrence of flicker and breaker can be suppressed. As described above, according to the present invention, the fixing device 13 can appropriately heat sheets of various sizes without complicating the configuration while suppressing an increase in power.

  Further, as the voltage control, the control device 15 turns on and off the voltage applied to the heating body 23 so that the average voltage in the half-wave control period T2 having a predetermined number of periods T1 is equal to or lower than the target voltage. You may perform the half wave control switched by the half wave unit of the period T1. Thereby, the voltage applied to the heating body 23 can be precisely controlled.

  Alternatively, as the voltage control, the control device 15 turns on and off the voltage applied to the heating body 23 within the phase control period T3 so that the average voltage in the predetermined phase control period T3 is equal to or lower than the target voltage. Phase control that switches in time units may be performed. Thereby, the voltage applied to the heating body 23 can be precisely controlled.

  Or the control apparatus 15 may control the amplitude A so that the voltage applied to the heating body 23 may become below a target voltage as said voltage control. Thereby, the voltage applied to the heating body 23 can be precisely controlled.

Further, the control device 15 may perform control such that a voltage lower than the maximum voltage during normal operation is applied to the heating body 23 when the fixing device 13 is started.
Thereby, even when the total resistance of the heating body 23 is reduced when the fixing device 13 is started, an excessive voltage application to the heating body 23 can be suppressed and an increase in power can be suppressed.

  Alternatively, the fixing device 13 further includes a thermistor 35 (temperature detection unit) that detects the temperature of the heating resistor 32 at a position where the temperature sensitive resistor 33 is not provided in the width direction, and the control device 15 includes the thermistor 35. Control may be performed so that a voltage lower than the maximum voltage during normal operation is applied to the heater 23 when the detected temperature is equal to or higher than a predetermined temperature threshold. Thereby, even when the total resistance of the heating body 23 is reduced due to the temperature rise of the heating body 23, an excessive voltage application to the heating body 23 can be suppressed and an increase in power can be suppressed.

  In the present embodiment, the case where the configuration of the present invention is applied to the monochrome printer 1 has been described. However, in another different embodiment, the present invention is applied to other image forming apparatuses such as a color printer, a copier, a facsimile machine, and a multifunction machine. It is also possible to apply this configuration.

1 Printer (image forming device)
DESCRIPTION OF SYMBOLS 2 Printer main body 6 Image forming part 10 Conveyance path 13 Fixing device 15 Control device 20 Heating member 21 Pressure member 22 Heat resistant film 23 Heating body 30 Substrate 31, 31a, 31b Feeding electrode 32 Heating resistor 33 Temperature sensitive resistor 34 Over Coat 35 Thermistor 36 Thermostat 37 Voltage application unit 38 Current detection unit

Claims (7)

A film member;
A heating body that heats one surface side of the film member and heats a toner image on a sheet passing through the other surface side of the film member;
A current detector for detecting the amount of current flowing through the heating body,
The heating body is
A heating resistor that is provided over the entire region in the width direction perpendicular to the paper passing direction, and generates heat when energized;
It is provided in a part of the width direction, and is composed of a temperature sensitive resistor that is electrically connected to the heating resistor,
When the amount of current exceeds a predetermined current threshold due to a decrease in the total resistance of the heating body, the voltage applied to the heating body is based on the total resistance of the heating body and a predetermined target power A fixing device that performs voltage control to lower the voltage to a target voltage or lower.   As the voltage control, the voltage applied to the heating body is switched on and off in units of half-waves of the cycle so that the average voltage in the half-wave control period having a predetermined number of cycles is equal to or less than the target voltage. The fixing device according to claim 1, wherein wave control is performed.   As the voltage control, phase control is performed in which the voltage applied to the heating body is turned on and off in units of time within the phase control period so that the average voltage in a predetermined phase control period is equal to or less than the target voltage. The fixing device according to claim 1.   The fixing device according to claim 1, wherein as the voltage control, an amplitude is controlled so that a voltage applied to the heating body is equal to or lower than the target voltage.   5. The fixing device according to claim 1, wherein a voltage lower than a maximum voltage during normal operation is applied to the heating body at startup. A temperature detector for detecting the temperature of the heating resistor at a position where the temperature sensitive resistor is not provided in the width direction;
The voltage lower than the maximum voltage during normal operation is applied to the heating body when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature threshold value. The fixing device according to 1.   An image forming apparatus comprising the fixing device according to claim 1.

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