Image heating apparatus and image forming apparatus

Abstract

To manage the heat generation distribution of a rotary heating element with high accuracy.SOLUTION: The image heating apparatus includes a rotary heat generation member having a heat generation layer, a magnetic field generation unit that generates an induced current in the heat generation layer of the rotary heat generation member by generating an alternating magnetic flux in accordance with supplied AC power, an inverter that controls the AC power supplied to the magnetic field generation unit, a control unit that controls the inverter, and a detection unit that detects a change in electrical resistance of the heat generation layer. The control means changes the drive frequency of the inverter according to the electric resistance of the heat generation layer based on the detection result of the detection means.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an image heating device that heats an image formed on a recording material, and an image forming apparatus. [Background technology]

[0002] In recent years, image heating devices using an electromagnetic induction heating method that can directly generate heat in the heat-generating layer of a rotary heating element have become known. In a conventional image heating device using an electromagnetic induction heating method, it has been proposed to change the heat generation distribution in the longitudinal direction of the rotary heating element by changing the drive frequency of the current flowing through the excitation coil (see Patent Document 1). Specifically, the image heating device described in Patent Document 1 proposes a configuration in which a drive frequency and target temperature corresponding to a desired heat generation distribution are stored in advance in a storage device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-129816 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the conveying distance of the recording material of the rotary heating element becomes long, the electrical resistance value of the heating layer may fluctuate. When the electrical resistance value of the heating layer changes, the relationship between the drive frequency and the temperature distribution of the rotary heating element fluctuates, so with the method described in Patent Document 1, the rotary heating element may not achieve the desired heat distribution.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image heating device and an image forming apparatus that are capable of managing the heat distribution of a rotary heating element with high precision. [Means for solving the problem]

[0006] One aspect of the present invention is an image heating device that heats an image formed on a recording material, comprising: a rotary heating element having a heat-generating layer; magnetic field generating means that generates an alternating magnetic flux in response to supplied AC power to generate an induced current in the heat-generating layer of the rotary heating element; an inverter that controls the AC power supplied to the magnetic field generating means; control means that controls the inverter; and detection means that detects changes in the electrical resistance of the heat-generating layer, wherein the control means changes the drive frequency of the inverter in response to the electrical resistance of the heat-generating layer based on the detection result of the detection means. [Effects of the Invention]

[0007] According to the present invention, the heat generation distribution of the rotary heating element can be controlled with high precision. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of an image forming apparatus according to a first embodiment. [Figure 2] 1 is a cross-sectional view of an image heating apparatus according to a first embodiment. [Figure 3] FIG. 1 is a schematic front view of an image heating apparatus according to a first embodiment. [Figure 4] 1 is a circuit configuration diagram of a high-frequency inverter according to a first embodiment. [Figure 5] FIG. 2 is a schematic configuration diagram of a core unit according to the first embodiment. [Figure 6] FIG. 4 is a diagram showing the heat distribution in the longitudinal direction of the fixing film with respect to the drive frequency according to the first embodiment. [Figure 7] FIG. 4 is a diagram showing the relationship between the electrical resistance value and heat distribution of the heat generating layer of the fixing film. [Figure 8] FIG. 10 is a diagram showing the relationship between the conveyance distance of the fixing film and the amount of change in the electrical resistance of the heat generating layer. [Figure 9] FIG. 4 is a diagram showing the relationship between the electrical resistance value of the heat generating layer and the driving frequency at which the heat generation distribution becomes uniform according to the first embodiment. [Figure 10]FIG. 4 is a flowchart of drive frequency correction control according to the first embodiment. [Figure 11] FIG. 10 is a diagram showing the relationship between the conveyance distance of the fixing film and the amount of change in the electrical resistance of the heat generating layer according to the second embodiment. [Figure 12] FIG. 10 is a diagram showing the transport distance of the fixing filter and the drive frequency corresponding to the transport distance. DETAILED DESCRIPTION OF THE INVENTION

[0009] First Embodiment (Outline of image forming apparatus) A fixing device as an image heating device according to an embodiment of the present invention and an image forming apparatus 100 equipped with the same will be described below with reference to the drawings. As shown in Fig. 1, the image forming apparatus 100 is equipped with a paper feed section 102 on which recording material P is stacked, an image forming means 103 that forms an image on the recording material P conveyed from the paper feed section 102, and an image heating device 200. In this image forming apparatus 100, the recording material P stacked in the paper feed section 102 is conveyed to the image forming means 103 at a predetermined timing.

[0010] Image forming means 103 in this embodiment is an electrophotographic image forming means, and includes a charging means, an exposure means, a developing means, a cleaning means, a photosensitive drum, and a transfer means, all of which are not shown. Image forming means 103 performs a series of processes in an electrophotographic process, forms a toner image on the photosensitive drum, and transfers an unfixed toner image to a recording material P being conveyed. The recording material P with the unfixed toner image transferred thereto is conveyed to image heating device 200, where it is heated and pressurized, thereby fixing the unfixed toner image transferred onto the recording material P. Thereafter, the recording material P with the fixed toner image is discharged outside image forming apparatus 100. This series of controls is performed by control circuit 10, which serves as control means and is equipped with CPU (calculation means) 110.

[0011] (Configuration of image heating device) Next, the configuration of the image heating device 200 will be described with reference to FIGS. 2 and 3. In this embodiment, the image heating device 200 is an electromagnetic induction heating type image heating device. As shown in FIG. 2, the image heating device 200 includes a fixing film 1, which is a rotary heating element, and a pressure roller 8, which is a pressure rotating element, and forms a fixing nip N between the fixing film 1 and the pressure roller 8, which pressurizes and heats the recording material P. Also, inside the fixing film 1, a film guide member 6, a pressure rigid stay 5, and a core unit 4 are provided. The film guide member 6 is made of a heat-resistant PPS (polyphenylene sulfide) resin or the like, and is pressed downward via the pressure rigid stay 5. Furthermore, a sliding member 7 is formed on the underside of the film guide member 6, and the shape of the fixing nip N is determined by this sliding member 7.

[0012] The core unit 4 has an exciting coil 3 wound around a magnetic core 2 serving as a magnetic core material (see FIG. 5), and is inserted into the fixing film 1 between the film guide member 6 and the pressure rigid stay 5. The magnetic core 2 and the exciting coil 3 wound around the outer periphery of the magnetic core 2 serve as magnetic field generating means that generate an alternating magnetic flux (alternating magnetic field) in response to AC power supplied from a high-frequency inverter 11, thereby generating an induced current in the heat generating layer of the rotary heating element.

[0013] The pressure roller 8 is disposed opposite the film guide member 6 with the fixing film 1 sandwiched therebetween, and forms a fixing nip N of a predetermined width between the pressure roller 8 and the film guide member 6 by pressing the pressure roller 8 against the film guide member 6. The pressure roller 8 is driven to rotate counterclockwise by a driving means M, and the fixing film 1 is rotated by the frictional force between the pressure roller 8 and the fixing film 1.

[0014] Fig. 3 is a schematic front view of image heating apparatus 200. As shown in Fig. 3, pressure springs 17a and 17b are arranged between both ends of pressure rigid stay 5 and spring receiving members 18a and 18b formed on the chassis of image heating apparatus 200, and film guide member 6 is urged downward by the urging forces of pressure springs 17a and 17b. In addition, fixing film flanges 12a and 12b are provided on both ends of fixing film 1, and these fixing film flanges 12a and 12b, together with film guide member 6, regulate the rotational trajectory of fixing film 1.

[0015] Furthermore, a temperature detection element 9 is provided in the center of the fixing film 1 in the longitudinal direction, and this temperature detection element 9 serves as a temperature detection means for detecting the surface temperature of the fixing film 1. A signal from the temperature detection element 9 is input to a control circuit 10, and the control circuit 10 is configured to control a high-frequency inverter 11 based on the temperature detected by the temperature detection element 9.

[0016] The memory 14 is a storage means that stores the frequencies and other information required to control the high-frequency inverter 11, and the control circuit 10 can access the memory 14 to write and read data. The high-frequency inverter 11 supplies a switching current with a frequency and amplitude based on a control signal from the control circuit 10 to the excitation coil via a power supply contact (not shown). As a result, the heat-generating layer 1a (see FIG. 2) of the fixing film 1 is heated by electromagnetic induction, and the surface temperature is controlled to a predetermined target temperature (approximately 150°C to 200°C).

[0017] In this embodiment, the fixing film 1 is a cylindrical rotating body with a composite structure including the heat-generating layer 1a, a base layer made of a conductive material and having a diameter of 10 to 50 mm, an elastic layer 1b laminated on the outer surface of the heat-generating layer 1a, and a release layer 1c laminated on the outer surface of the elastic layer 1b. The heat-generating layer 1a is a metal film with a thickness of 10 to 50 μm, and the elastic layer 1b is a silicone rubber with a hardness of 20 degrees (JIS-A, 1 kg load) and a thickness of 0.3 to 0.1 mm. The surface layer 1c (release layer) is a fluororesin tube with a thickness of 50 μm to 10 μm. When an alternating magnetic flux acts on the heat-generating layer 1a, an induced current is generated and the heat is generated. This heat is transferred to the elastic layer 1b and the release layer 1c, heating the entire fixing film 1. When a recording material P passes through the fixing nip N, the toner image T on the recording material P is heated and fixed.

[0018] (Configuration of high frequency inverter) Next, the configuration of the high-frequency inverter 11 will be described with reference to FIG. 4. FIG. 4 is a circuit diagram of the high-frequency inverter 11 according to this embodiment. In this circuit diagram, reference numeral 21 denotes a commercial AC power supply, 22 denotes a diode bridge, which is one of the rectifying means, 23, 27, 30, and 31 denote capacitors, 26 and 35 denote inductances, 24, 28, and 29 denote switching elements, 25 denotes a diode, and 34 denotes a resistor. The fixing film 1 and the core unit 4 are replaced by a resistor 34 and an inductance 35 as an equivalent circuit. Reference numeral 19 denotes a step-down converter circuit, and 20 denotes a half-bridge inverter circuit, which also functions as a current resonant circuit. Reference numeral 32 denotes a first drive circuit that controls the output voltage of the step-down converter circuit 19. Reference numeral 33 denotes a second drive circuit that controls the drive frequency of the half-bridge inverter circuit 20.

[0019] An AC voltage input from a commercial AC power supply 21 is rectified by a diode bridge 22 and input to a step-down converter circuit 19. A signal from a temperature detection element 9, which detects the temperature of the fixing film 1, is input to a control circuit 10, which then outputs a PWM signal 36, the duty of which corresponds to the detected temperature, to the step-down converter circuit 19. The step-down converter circuit 19 controls the voltage amplitude in accordance with the duty-controlled PWM signal 36, and the controlled voltage is input to a half-bridge inverter circuit 20. A switching signal 37, which alternately switches the open and closed states of a switch element 28 and a switch element 29, is input from the control circuit 10 to a drive circuit 33 of the half-bridge inverter circuit 20. The switching signal 37 is driven at a frequency approximately equal to the resonant frequency of a series resonant circuit formed by a capacitor 31 and an inductance 35. This switching signal 37 inputs an AC voltage V1 of a predetermined frequency to the excitation coil of the core unit 4. Here, if the effective voltage of the commercial AC power supply 21 is Vac_rms (V), the effective voltage of the AC voltage V1 is V1_rms (V), and the duty of the PWM signal 36 is Dpwm (%), the following relationship holds: However, the high-frequency inverter 11 is not limited to this circuit configuration, and other methods may be used.

[0020]

number

[0021] In FIG. 4, 39 denotes a voltage detection circuit for detecting the voltage rectified by the diode bridge 22. The voltage detection circuit 39 transmits a signal corresponding to the voltage applied to the high-frequency inverter 11 to the control circuit 10 via a voltage detection signal 40 using a voltage dividing resistor (not shown). Also, 41 denotes a current detection circuit for detecting the current supplied to the high-frequency inverter 11, and is composed of a current transformer and a detection resistor (not shown). The detection resistor converts the current flowing through the current transformer into a voltage, and a voltage signal corresponding to the amount of current is transmitted to the control circuit 10 via a current detection signal 42. As will be described in detail later, in this embodiment, the voltage detection circuit 39 and the current detection circuit 41 function as detection means for detecting the electrical resistance of the heat generating layer 1a. The voltage detection circuit 39 and the current detection circuit 41 can also be considered detection means for detecting changes in the electrical resistance of the heat generating layer 1a.

[0022] (Explanation of core unit configuration and heating principle) Next, the configuration and heating principle of the core unit 4 as a magnetic field generating means will be explained using FIG. 5. FIG. 5 is a schematic diagram of the core unit 4. The magnetic core 2 is, for example, a rod-shaped ferrite core. More specifically, this magnetic core 2 is formed from a material that has a high saturation magnetic flux density around 150°C to 200°C, small hysteresis loss, and high relative permeability. For example, the magnetic core 2 is formed from a ferromagnetic material made of an oxide or alloy material with high permeability, such as sintered ferrite, ferrite resin, amorphous alloy, or permalloy.

[0023] As shown in the figure, an excitation coil 3 is wound circumferentially around the magnetic core 2 from one end to the other. In some cases, multiple excitation coils 3 are wound in parallel, taking into account the current rating. As described above, the fixing film 1 is provided with a heat-generating layer 1a, which generates heat when a current flows through it.

[0024] A switching current corresponding to the AC voltage V1 generated by the high-frequency inverter 11 flows in the direction of arrow I1 through the excitation coil 3. By passing a switching current through the excitation coil 3, it forms an alternating magnetic field in the direction of the rotation axis of the fixing film 1, and functions as a magnetic field generating means that generates an induced current in the circumferential direction of the fixing film 1. The magnetic core 2 also functions as a member that induces the magnetic field lines generated by the excitation coil 3 and forms a magnetic path. In the figure, S is a diagram of a circuit that simulates only a portion of the fixing film 1. The heat generation principle of the fixing film 1 follows Faraday's law. Faraday's law states that "when the magnetic field in circuit S is changed, an induced electromotive force that tries to flow current in the circuit is generated, and the induced electromotive force is proportional to the time change in the magnetic flux that penetrates the circuit perpendicularly."

[0025] Consider the case where circuit S is placed in the center of the magnetic core 2 in the longitudinal direction shown in Figure 5 and a switching current is passed through the exciting coil 3. When a switching current is passed, an alternating magnetic field (alternating magnetic flux) is formed inside the magnetic core 2. At that time, the induced electromotive force generated in circuit S is proportional to the time change in the magnetic flux Φ that penetrates perpendicularly, according to the following equation.

[0026]

number

[0027] This induced electromotive force V causes an induced electromotive force (circulating current) I2 to flow in the circumferential direction of the heat generating layer 1a of the fixing film 1, generating Joule heat.

[0028] (Relationship between driving frequency and heat distribution) FIG. 6 shows the relationship between the drive frequency of the half-bridge inverter circuit 20 and the heat generation distribution in the longitudinal direction of the fixing film 1. In the following description, the drive frequency of the half-bridge inverter circuit 20 is also simply referred to as the drive frequency of the inverter 11. The amount of heat generated at the longitudinal ends decreases as the drive frequency of the power supplied from the half-bridge inverter circuit 20 to the excitation coil 3 decreases from 50 kHz to 44 kHz, 36 kHz, and 20 kHz. By utilizing this characteristic, the drive frequency is controlled to be lower as the recording material passing width narrows, thereby suppressing temperature rise in non-paper passing areas. The relationship between the drive frequency and the heat generation distribution fluctuates, for example, when the electrical resistance of the heat-generating layer 1a of the fixing film 1 changes.

[0029] (Relationship between the electrical resistance of the heating layer and heat distribution) Next, the relationship between the electrical resistance value of the heat-generating layer and the heat generation distribution will be explained. Figure 7 shows the heat generation distributions when fixing films with heat-generating layer electrical resistance values ​​a to f are operated at a drive frequency of 50 kHz. When the heat-generating layer is thick, the cross-sectional area of ​​the heat-generating layer increases, resulting in a lower electrical resistance value of the heat-generating layer. The heat generation distribution for electrical resistance values ​​a to c, which have low electrical resistance values, tends to have higher heat generation temperatures at the edges, as shown in the figure. On the other hand, when the heat-generating layer is thin, the cross-sectional area of ​​the heat-generating layer decreases, resulting in a higher electrical resistance value of the heat-generating layer. The heat generation distribution for electrical resistance values ​​d to f, which have high electrical resistance values, tends to have lower heat generation temperatures at the edges, as shown in the figure. The heat generation distribution of fixing films varies due to manufacturing variations in the electrical resistance value of the heat-generating layer, resulting in fluctuating heat generation distribution. Therefore, using the aforementioned characteristic of changing the heat generation distribution depending on the drive frequency, the drive frequency is adjusted during the assembly process of the image heating device 200 to achieve a uniform heat generation distribution.

[0030] For example, in the case of a fixing film with a high heat generation temperature at the edges, such as a heat generation distribution of electrical resistance values ​​a to c, the drive frequency is adjusted to an optimum frequency band lower than 50 kHz to achieve a uniform heat generation distribution. On the other hand, in the case of a fixing film with a low heat generation temperature at the edges, such as a heat generation distribution of electrical resistance values ​​d to f, the drive frequency is adjusted to an optimum frequency band higher than 50 kHz to achieve a uniform heat generation distribution. In this way, in the assembly process, the drive frequency adjusted for each paper size is stored in memory 14 as a reference frequency.

[0031] (Variation in the electrical resistance of the heating layer due to increased transport distance) Next, the relationship between the conveyance distance of the fixing film 1 and the change in the electrical resistance of the heat-generating layer 1a will be explained with reference to FIG. 8. Note that FIG. 8 shows the characteristics of three fixing films (a), (b), and (c). The fixing film 1 is formed with a predetermined curve in the fixing nip portion, and as this curve is repeated with rotation, fine cracks tend to occur. These fine cracks hinder the flow of current in the heat-generating layer 1a, so the more fine cracks there are, the higher the electrical resistance of the heat-generating layer 1a. Therefore, as the conveyance distance of the fixing film increases, the electrical resistance of the heat-generating layer 1a also increases.

[0032] Therefore, if the film continues to be driven at the drive frequency adjusted during the assembly process, the heat generation distribution after the conveyance distance is increased may result in a lower heat generation temperature at the edges, as shown in the heat generation distribution for electrical resistance values ​​d to f in Figure 7. The occurrence of these fine cracks is affected by factors such as the thickness of the heat generation layer 1a, resulting in variations in characteristics, as shown in fixing films (a), (b), and (c). In order to obtain a uniform heat generation distribution even for such a fixing film after the conveyance distance is increased, it is necessary to correct the drive frequency according to the electrical resistance value of the heat generation layer 1a at that time.

[0033] (Method for detecting the electrical resistance of the heating layer and method for correcting the driving frequency) Next, a method for detecting the electrical resistance of the heat generating layer 1a will be described. In this embodiment, the driving frequency (reference frequency) fa that provides a uniform heat distribution as described above and the electrical resistance (reference resistance) Ra of the heat generating layer 1a at that frequency are measured in advance during the assembly process and stored in memory 14.

[0034] The CPU 110 mounted on the control circuit 10 also functions as a resistance calculation means, and calculates the electrical resistance of the heat generating layer 1a after the conveyance distance has increased from the voltage information detected by the voltage detection circuit 39 and the current information detected by the current detection circuit 41. When the electrical resistance of the heat generating layer 1a after the conveyance distance has increased is Rd, the electrical resistance Rd of the heat generating layer 1a when driven at the drive frequency fa can be calculated from Equation 3.

[0035]

number

[0036] Next, a method for correcting the drive frequency will be described. FIG. 9 is a table showing the drive frequencies at which the heat distribution becomes uniform when five fixing films with different electrical resistance values ​​of the heat-generating layer 1a are each heated. The magnitude relationship of the electrical resistance values ​​of the fixing films is R1>R2>R3>R4>R5. The magnitude relationship of the drive frequencies is f1>f2>f3>f4>f5. It is assumed that it is known in advance that the fluctuation in the electrical resistance of the heat-generating layer 1a due to an increase in the conveying distance falls within the range of R1 to R5. The drive frequency is corrected using this table.

[0037] The CPU 110 mounted on the control circuit 10 also functions as heat distribution changing means. After calculating Rd using Equation 3, the CPU 110 performs linear interpolation on the table in Fig. 9 using Equation 4 to calculate the drive frequency fd corresponding to the electrical resistance Rd after the conveying distance has increased. That is, the drive frequency of the high-frequency inverter 11 is calculated based on the detection results of the detection means 39, 41 when power is supplied to the magnetic field generating means 3, 4 with the drive frequency of the high-frequency inverter 11 set to the reference frequency.

[0038]

number

[0039] The value n in Equation 4 is determined by the electrical resistance closest to the detected Rd among the electrical resistances shown in Figure 9. For example, if the detected Rd is within the range between R2 and R3 and closest to R2, n = 2, and the drive frequency fd to be applied after the conveyance distance is increased can be calculated. For example, if the electrical resistance of the fixing film 1 increases from the reference resistance due to a crack in the fixing film 1, the CPU 110 corrects the drive frequency of the inverter 11 to be higher than the reference frequency. Furthermore, for example, if the heat-generating layer 1a is formed on the polyimide base layer of the fixing film 1 using ink containing metal particles, the crystalline structure of the metal particles may change depending on the time the heat-generating layer 1a is exposed to high temperatures, causing the electrical resistance of the heat-generating layer 1a to decrease. In this case, the CPU 110 controls the drive frequency of the inverter 11 to be corrected lower.

[0040] (Control flow chart) Next, the drive frequency correction control after the conveyance distance has increased will be described using the flowchart in Figure 10. When the image forming apparatus 100 receives a print job, the CPU 110 of the control circuit 10 determines whether the current conveyance distance of the fixing film 1 exceeds a predetermined distance N (S101). If it is less than the predetermined distance N, it determines that the influence of heat distribution on the image is small, and starts normal print control without correcting the drive frequency (S120).

[0041] On the other hand, if CPU 110 of control circuit 10 determines that it has exceeded predetermined distance N, it corrects the drive frequency. Specifically, first, CPU 110 of control circuit 10 drives and rotates image heating apparatus 200 to start printing, and starts temperature adjustment control at drive frequency fa (S102). However, unlike normal print operation, although temperature adjustment control of image heating apparatus 200 is started, image formation operation is put on hold and does not start until correction of the drive frequency is complete.

[0042] When the temperature of the fixing film 1 is controlled to the target temperature (S103: No to YES), the CPU 110 of the control circuit 10 calculates the electrical resistance Rd from the voltage information and current information (S104), and calculates the drive frequency fd (S105). Then, when the calculation of the drive frequency fd is completed, the CPU 110 stores the calculated drive frequency fd in the memory 14 (S106), and the drive frequency fd is used in the next and subsequent print control. The CPU 110 also changes the currently used drive frequency fa to the drive frequency fd (S107). After the change, image formation is resumed and the print operation is started (S108).

[0043] In the above embodiment, step S107 is performed before image formation, but S107 may be skipped and the corrected drive frequency may be applied when the next print starts. In the present embodiment, the heat generating layer 1a may have a large TCR (Temperature Coefficient of Resistance) characteristic, so the electrical resistance of the heat generating layer 1a is detected when the temperature control is complete and the temperature is near the target temperature. However, this is not limiting. The temperature control may be extended after printing is completed, the electrical resistance of the heat generating layer 1a at that time may be detected, and the corrected drive frequency may be applied when the next print starts.

[0044] On the other hand, if the TCR characteristic of the heat generating layer 1a is sufficiently small, there is little impact in detecting the electrical resistance of the heat generating layer 1a regardless of the temperature, so the electrical resistance of the heat generating layer 1a may be detected between the start of temperature control and the time when the target temperature is reached.

[0045] Furthermore, in this embodiment, the drive frequency correction control is performed for each predetermined conveyance distance, but this is not limited to this. The drive frequency correction control may be performed for each predetermined cumulative number of rotations of the fixing film 1, rather than for each distance the sheet is conveyed by the fixing film 1. Also, the electrical resistance of the heat-generating layer 1a may be detected for each print, and the drive frequency may be corrected if the variation in electrical resistance from the reference electrical resistance is greater than or equal to a predetermined value. In addition, the drive frequency correction control may be performed for each predetermined number of prints or for each predetermined driving time of the image heating device 200. In other words, any value related to the rotation distance of the fixing film 1 may be used for timing control of the drive frequency correction control.

[0046] As described above, according to this embodiment, by detecting the electrical resistance of the heat-generating layer 1a in the fixing film after the conveying distance has increased and correcting the drive frequency, even if the electrical resistance value of the heat-generating layer 1a fluctuates, the heat generation distribution can be corrected to the desired value, thereby preventing fixing defects. That is, in this embodiment, the drive frequency of the inverter 11 is changed according to the electrical resistance of the heat-generating layer 1a based on the detection results of the detection means 39 and 41. This makes it possible to accurately manage the heat generation distribution of the fixing film (heating film), which is a rotating heat generating element.

[0047] <Second embodiment> Next, a second embodiment will be described with reference to Figures 11 and 12. In this embodiment, a method of correcting the drive frequency different from that of the first embodiment will be described when a fixing film is installed in which the increase in the electrical resistance value of the heat generating layer 1a relative to the transport distance is constant. In the following description, only the differences from the first embodiment will be described, and the same reference numerals will be used for the other components, and their description will be omitted.

[0048] 11 shows the relationship between the conveyance distance of the fixing film 1 and the amount of change in electrical resistance of the heat-generating layer 1a in the second embodiment. As shown in FIG. 11, the characteristic of the amount of change in resistance with respect to the conveyance distance is constant, regardless of the fixing film. Therefore, in this embodiment, it is possible to correct the heat distribution by changing the drive frequency according to the conveyance distance of the fixing film 1 without calculating the value of the electrical resistance of the heat-generating layer 1a.

[0049] FIG. 12 is a table showing drive frequencies corresponding to the conveyance distance of the fixing film 1. As mentioned above, the electrical resistance of the heat-generating layer 1a of the fixing film 1 changes at a constant rate depending on the conveyance distance. The drive frequencies shown in FIG. 12 indicate drive frequencies at which the heat generation distribution is uniform, with the electrical resistance of the heat-generating layer 1a changing every 5,000 meters of conveyance distance. In this embodiment, printing at the corresponding drive frequency within the conveyance distance range shown in FIG. 12 does not affect the image due to the heat generation distribution. A table of drive frequencies corresponding to these conveyance distances is stored in memory 14. Note that in this embodiment, the rotation sensor for detecting the conveyance distance of the fixing film 1 functions as a detection means for detecting changes in the electrical resistance of the heat-generating layer. As such, the detection means does not necessarily have to be able to directly detect the electrical resistance of the heat-generating layer; it may be composed of any sensor or information processing unit that can detect a value correlated with changes in the electrical resistance of the heat-generating layer.

[0050] Next, a method for controlling the drive frequency will be explained. When the CPU 110 of the control circuit 10 receives a print job, it reads from the memory 14 the drive frequency corresponding to the current fixing film transport distance, and starts printing at that corresponding drive frequency. Initially, the drive frequency is fa measured in the assembly process, and every time the fixing film transport distance reaches 5,000 meters, the drive frequency is changed in sequence from drive frequency fa to drive frequency fa1, drive frequency fa2, etc. The drive frequency is changed in sequence according to the transport distance up to drive frequency faN, which is the frequency to be changed to by the time the fixing film 1 reaches the end of its life. The high-low relationship of the drive frequencies is determined by the drive frequency fa1. <fa2<···<faNとなっている。

[0051] In this embodiment, the characteristic of the resistance change amount with respect to the conveying distance is a characteristic that changes according to a linear function, but this is not limited to this. If it changes according to an exponential function, the drive frequency may be corrected in accordance with this change.

[0052] As described above, according to the present invention, by using a predetermined driving frequency depending on the transport distance of the fixing film, even if fluctuations in the electrical resistance value of the heat-generating layer 1a occur, the heat generation distribution can be corrected to the desired one, thereby preventing poor fixing.

[0053] That is, in this embodiment, information defining the relationship between a value relating to the rotation distance of the rotary heating element, such as the conveyance distance of the fixing film 1, and the drive frequency of the inverter is stored in memory 14. Then, a value relating to the rotation distance of the rotary heating element is actually determined, and an appropriate drive frequency of the inverter is determined based on this detected value and the information stored in memory. By correcting the drive frequency of inverter 11 to the determined frequency, it is possible to manage the heat distribution of the fixing film 1 so as to be uniform. Note that, as described above, the value relating to the rotation distance of the rotary heating element may be, in addition to the conveyance distance of the fixing film 1, the cumulative number of rotations of the fixing film 1, the number of prints, the drive time of the image heating device 200, etc.

[0054] <Third embodiment> Next, a third embodiment will be described. In this embodiment, a configuration is described in which the drive frequency is calculated from the rate of change in the electrical resistance of the heat generating layer 1a after the conveying distance is increased. In the following explanation, only the differences from the first embodiment will be explained, and the other components will be assigned the same reference numerals and their explanation will be omitted.

[0055] A method for correcting the drive frequency in this embodiment will be described. As in the first embodiment, in this embodiment, the drive frequency fa that provides a uniform heat distribution and the electrical resistance Ra of the heat-generating layer 1a at that frequency are measured during the assembly process and stored in memory 14. In this embodiment, the rate of change A of the drive frequency (correction value) of the high-frequency inverter 11 with respect to fluctuations in the electrical resistance value of the heat-generating layer 1a is also stored in memory 14.

[0056] The CPU 110 installed in the control circuit 10 compares the electrical resistance value Rd of the heating layer 1a calculated using Equation 3 with the electrical resistance Ra of the heating layer 1a read from the memory 14, and corrects the drive frequency if the amount of variation is greater than a predetermined value. The drive frequency fd corresponding to the electrical resistance Rd of the heating layer 1a after the conveyance distance has increased can be calculated using Equation 5. That is, the CPU 110 calculates the electrical resistance value Ra of the heating layer 1a based on the detection results of the detection means when power is supplied to the magnetic field generating means 3 and 4 with the drive frequency of the high-frequency inverter 11 set to the reference frequency. Then, the drive frequency of the high-frequency inverter 11 is changed based on the difference between the calculated electrical resistance value Ra and the reference resistance value Rd, the rate of change A, and the reference frequency fa.

[0057]

number

[0058] In this way, by storing in memory 14 the slope, which is the rate of change in the electrical resistance of heat generating layer 1a with respect to the transport distance of the fixing film, a table like that in the first embodiment can be prepared, and the drive frequency can be corrected without occupying storage space in memory 14.

[0059] As described above, according to this embodiment, the desired heat generation distribution can be corrected by correcting the drive frequency according to the electrical resistance of the heat generation layer 1a in the fixing film after the conveying distance has increased, without occupying memory storage area, thereby preventing fixing failures.

[0060] <Summary> [Configuration 1] An image heating device that heats an image formed on a recording material, a rotating heating element having a heating layer; a magnetic field generating means for generating an alternating magnetic flux in response to supplied AC power to induce an induced current in the heat generating layer of the rotary heating element; an inverter for controlling AC power supplied to the magnetic field generating means; a control means for controlling the inverter; a detection means for detecting a change in the electrical resistance of the heat generating layer, The control means changes the drive frequency of the inverter in accordance with the electrical resistance of the heat generating layer based on the detection result of the detection means. An image heating apparatus characterized by:

[0061] [Configuration 2] The detection means a current detection means for detecting a current supplied to the inverter; a voltage detection means for detecting a voltage applied to the inverter, the control means determines the value of the electrical resistance of the heat generating layer based on the detection results of the current detection means and the voltage detection means. 2. The image heating apparatus according to configuration 1,

[0062] [Configuration 3] a reference frequency of the drive frequency and a storage means for storing the reference frequency; the control means changes the drive frequency of the inverter based on the detection result of the detection means when power is supplied to the magnetic field generating means with the drive frequency of the inverter set to the reference frequency. 3. The image heating apparatus according to configuration 1 or 2.

[0063] [Configuration 4] the storage means stores a reference resistance value of the electric resistance of the heating layer corresponding to the reference frequency, the control means determines the electrical resistance value of the heat generating layer based on the detection result of the detection means when power is supplied to the magnetic field generating means with the drive frequency of the inverter set to the reference frequency, and if the electrical resistance value of the heat generating layer is higher than the reference resistance value, corrects the drive frequency of the inverter to be higher than the reference frequency. 4. The image heating apparatus according to configuration 3,

[0064] [Configuration 5] the storage means stores a plurality of electrical resistance values ​​of the heat generating layer and a plurality of drive frequency values ​​corresponding to the plurality of electrical resistance values, the control means performs linear interpolation based on the determined electrical resistance value of the heat generating layer and the relationship between the electrical resistance values ​​of the plurality of heat generating layers stored in the storage means and the values ​​of the plurality of drive frequencies to determine the value of the drive frequency corresponding to the determined electrical resistance value of the heat generating layer, and changes the drive frequency of the inverter to the determined value. 5. An image heating apparatus according to configuration 4, wherein:

[0065] [Configuration 6] the detection means detects a value related to a rotation distance of the rotary heating element, a storage means for storing information defining a relationship between a value relating to a rotation distance of the rotary heating element and a drive frequency of the inverter, the control means determines a drive frequency value of the inverter from the detection value detected by the detection means based on the information stored in the storage means, and changes the drive frequency of the inverter to the determined value. 2. The image heating apparatus according to configuration 1,

[0066] [Configuration 7] the storage means stores a reference resistance value of the electric resistance of the heating layer corresponding to the reference frequency, and a rate of change of a correction value of the drive frequency of the inverter with respect to a fluctuation in the electric resistance value of the heating layer; the control means determines the electrical resistance value of the heat generating layer based on the detection result of the detection means when power is supplied to the magnetic field generating means with the drive frequency of the inverter set to the reference frequency, and changes the drive frequency of the inverter based on the difference between the determined electrical resistance value and the reference resistance value, the rate of change, and the reference frequency. 4. The image heating apparatus according to configuration 3,

[0067] [Configuration 8] the magnetic field generating means comprises: a magnetic core material that is inserted through the rotary heating element and arranged in the direction of the rotation axis of the rotary heating element; and an excitation coil that is wound around the outer periphery of the magnetic core material in a circumferential direction and generates an alternating magnetic flux in the direction of the rotation axis of the rotary heating element; supplying AC power to the excitation coil to generate an induced current in the circumferential direction of the heat generating layer of the rotary heating element; 8. An image heating apparatus according to any one of configurations 1 to 7.

[0068] [Configuration 9] an image forming means for forming an image on a recording material; an image heating apparatus according to any one of configurations 1 to 8; the image heating device heats the image formed on the recording material by the image forming means; An image forming apparatus characterized by: [Explanation of symbols]

[0069] 1: Rotary heating element (fixing film) / 1a: Heat generation layer / 3, 2: Magnetic field generating means (excitation coil, magnetic core) / 10: Control means (control circuit) / 11: Inverter (high frequency inverter) / 39, 41: Detection means (voltage detection circuit, current detection circuit) / 200: Image heating device

Claims

1. An image heating device that heats an image formed on a recording material, a rotating heating element having a heating layer; a magnetic field generating means for generating an alternating magnetic flux in response to supplied AC power to induce an induced current in the heat generating layer of the rotary heating element; an inverter for controlling AC power supplied to the magnetic field generating means; a control means for controlling the inverter; a detection means for detecting a change in the electrical resistance of the heat generating layer, The control means changes the drive frequency of the inverter in accordance with the electrical resistance of the heat generating layer based on the detection result of the detection means. An image heating apparatus characterized by:

2. The detection means a current detection means for detecting a current supplied to the inverter; a voltage detection means for detecting a voltage applied to the inverter, the control means determines the value of the electrical resistance of the heat generating layer based on the detection results of the current detection means and the voltage detection means.

2. An image heating apparatus according to claim 1.

3. a reference frequency of the drive frequency and a storage means for storing the reference frequency; the control means changes the drive frequency of the inverter based on the detection result of the detection means when power is supplied to the magnetic field generating means with the drive frequency of the inverter set to the reference frequency.

2. An image heating apparatus according to claim 1.

4. the storage means stores a reference resistance value of the electric resistance of the heating layer corresponding to the reference frequency, the control means determines the electrical resistance value of the heat generating layer based on the detection result of the detection means when power is supplied to the magnetic field generating means with the drive frequency of the inverter set to the reference frequency, and if the electrical resistance value of the heat generating layer is higher than the reference resistance value, corrects the drive frequency of the inverter to be higher than the reference frequency.

4. An image heating apparatus according to claim 3.

5. the storage means stores a plurality of electrical resistance values ​​of the heat generating layer and a plurality of drive frequency values ​​corresponding to the plurality of electrical resistance values, the control means performs linear interpolation based on the determined electrical resistance value of the heat generating layer and the relationship between the electrical resistance values ​​of the plurality of heat generating layers stored in the storage means and the values ​​of the plurality of drive frequencies to determine the value of the drive frequency corresponding to the determined electrical resistance value of the heat generating layer, and changes the drive frequency of the inverter to the determined value.

5. An image heating apparatus according to claim 4.

6. the detection means detects a value related to a rotation distance of the rotary heating element, a storage means for storing information defining a relationship between a value relating to a rotation distance of the rotary heating element and a drive frequency of the inverter, the control means determines a drive frequency value of the inverter from the detection value detected by the detection means based on the information stored in the storage means, and changes the drive frequency of the inverter to the determined value.

2. An image heating apparatus according to claim 1.

7. the storage means stores a reference resistance value of the electric resistance of the heating layer corresponding to the reference frequency, and a rate of change of a correction value of the drive frequency of the inverter with respect to a fluctuation in the electric resistance value of the heating layer; the control means determines the electrical resistance value of the heat generating layer based on the detection result of the detection means when power is supplied to the magnetic field generating means with the drive frequency of the inverter set to the reference frequency, and changes the drive frequency of the inverter based on the difference between the determined electrical resistance value and the reference resistance value, the rate of change, and the reference frequency.

4. An image heating apparatus according to claim 3.

8. the magnetic field generating means comprises: a magnetic core material that is inserted through the rotary heating element and arranged in the direction of the rotation axis of the rotary heating element; and an excitation coil that is wound around the outer periphery of the magnetic core material in a circumferential direction and generates an alternating magnetic flux in the direction of the rotation axis of the rotary heating element; supplying AC power to the excitation coil to generate an induced current in the circumferential direction of the heat generating layer of the rotary heating element; 2. An image heating apparatus according to claim 1.

9. an image forming means for forming an image on a recording material; an image heating apparatus according to any one of claims 1 to 8, the image heating device heats the image formed on the recording material by the image forming means; An image forming apparatus characterized by:

Images