Image heating device and image formation device

Abstract

To provide an image heating device and an image formation device capable of improving FPOT or reducing thermal stress applied to a substrate of a heater.SOLUTION: The image heating device comprises a fixation member, a heater heating the fixation member, and a heater control circuit for controlling the heater, and heats a toner image formed on a sheet. The heater includes a substrate and a heat generation unit provided on the substrate and generating heat by energization. The heater control circuit includes a first power feeding path for supplying first electrical power to the heat generation unit, a second power feeding path for supplying second electrical power smaller than the first electrical power to the heat generation unit, and a switch unit having a semiconductor switch including a plurality of semiconductors and selectively switching between the first power feeding path and the second power feeding path by operations of the semiconductor switch.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image heating device that heats a toner image formed on a sheet, and an image forming apparatus including the same. [Background technology]

[0002] Patent Document 1 discloses an image heating device that has a heater with multiple heating elements, and changes the resistance value of the entire heater by switching the power supply to the multiple heating elements with a relay. When this image heating device heats a fixing unit that is in a cold state, the relay is turned on and the power supplied to the heater is made relatively large. When the fixing unit warms up, the relay is turned off and the power supplied to the heater is made relatively small. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-138839 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the image heating device described in Patent Document 1, when the relay is opened and closed, the power supply to the heater is temporarily cut off, which causes a delay in the rise in temperature of the heater. As a result, the First Print Out Time (hereinafter referred to as FPOT), which is the time from when a print job is sent to image forming device 80 to when an image is printed on the first sheet, is reduced.

[0005] In addition, in the configuration of Patent Document 1, the heat distribution in the short-side direction of the heater is asymmetric, so the thermal stress of the heater substrate is likely to be large. In order to shorten the FPOT, it is necessary to increase the power supplied to the heater, so the thermal stress applied to the heater substrate also increases accordingly. In other words, in pursuit of shortening the FPOT, it is necessary to make the heat distribution of the heater as uniform as possible and reduce the thermal stress applied to the heater substrate.

[0006] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide an image heating device and an image forming apparatus capable of improving FPOT or reducing thermal stress applied to a heater substrate. [Means for solving the problem]

[0007] The present invention provides an image heating device that heats a toner image formed on a sheet, the image heating device comprising a fixing member, a heater that heats the fixing member, and a heater control circuit that controls the heater, the heater having a substrate and a heating unit that is provided on the substrate and generates heat when current is applied, the heater control circuit having a first power supply path that supplies a first power to the heating unit, a second power supply path that supplies a second power smaller than the first power to the heating unit, and a switch unit that includes a semiconductor switch having a plurality of semiconductors and selectively switches between the first power supply path and the second power supply path when the semiconductor switch is operated.

[0008] The present invention also provides an image heating device for heating a toner image formed on a sheet, the image heating device comprising a fixing member, a heater for heating the fixing member, and a heater control circuit for controlling the heater, the heater comprising a substrate and a heating unit provided on the substrate and generating heat when energized, the heating unit comprising a first heating element and a second heating element each extending in a longitudinal direction perpendicular to a short side direction parallel to a sheet transport direction and generating heat when energized, the first heating element comprising a first heating portion disposed at one end of the substrate in the short side direction and a second heating portion disposed at the other end of the substrate in the short side direction, the second heating element being disposed between the first heating portion and the second heating portion in the short side direction, the heater control circuit comprising a first power supply path for supplying a first power to the heating unit, a second power supply path for supplying a second power smaller than the first power to the heating unit, and a switch unit for selectively switching between the first power supply path and the second power supply path. Effect of the Invention

[0009] According to the present invention, it is possible to improve the FPOT or reduce the thermal stress applied to the heater substrate. [Brief description of the drawings]

[0010] [Figure 1] 1 is an overall schematic view showing an image forming apparatus according to a first embodiment. [Diagram 2] FIG. [Diagram 3] 3A is a diagram showing a heater control circuit and a heater, and FIG. 3B is a cross-sectional view showing the heater along 3B-3B. [Figure 4] (a) is a circuit diagram showing a first power supply path, (b) is a circuit diagram showing an equivalent circuit of the circuit shown in (a), (c) is a circuit diagram showing a second power supply path, and (d) is a circuit diagram showing an equivalent circuit of the circuit shown in (b). [Diagram 5] FIG. 4 is a diagram showing temperature control of the fixing unit. [Figure 6]FIG. 1A shows the steady-state heat distribution on the 3B-3B cross section of the heater when power is supplied through the first power supply path, and FIG. 1B shows the steady-state heat distribution on the 3B-3B cross section of the heater when power is supplied through the second power supply path. [Figure 7] 7A is a diagram showing a heater control circuit and a heater according to a second embodiment, and FIG. 7B is a cross-sectional view showing the heater along the line 7B-7B. [Figure 8] (a) is a circuit diagram showing a third power supply path, (b) is a circuit diagram showing an equivalent circuit of the circuit shown in (a), (c) is a circuit diagram showing a fourth power supply path, and (d) is a circuit diagram showing an equivalent circuit of the circuit shown in (b). [Figure 9] FIG. 4 is a diagram showing temperature control of the fixing unit. [Figure 10] 1A is a diagram showing the steady-state heat distribution on the 7B-7B cross section of the heater when power is supplied using the third power supply path, and FIG. 1B is a diagram showing the steady-state heat distribution on the 7B-7B cross section of the heater when power is supplied using the fourth power supply path. [Figure 11] 11A is a diagram showing a heater control circuit and a heater according to a third embodiment, and FIG. 11B is a cross-sectional view showing the heater along the line 11B-11B. [Figure 12] 1A is a circuit diagram showing a fifth power supply path, FIG. 1B is a circuit diagram showing an equivalent circuit of the circuit shown in FIG. 1A, FIG. 1C is a circuit diagram showing a sixth power supply path, and FIG. 1D is a circuit diagram showing an equivalent circuit of the circuit shown in FIG. [Figure 13] FIG. 4 is a diagram showing temperature control of the fixing unit. [Figure 14] 1A is a diagram showing the steady-state heat distribution in the 11B-11B cross section of the heater when power is supplied using the fifth power supply path, and FIG. 1B is a diagram showing the steady-state heat distribution in the 11B-11B cross section of the heater when power is supplied using the sixth power supply path. [Figure 15] 15A is a diagram showing a heater control circuit and a heater according to a fourth embodiment, and FIG. 15B is a cross-sectional view showing the heater along the line 15B-15B. [Figure 16] FIG. 4 is a diagram showing an image of temperature distribution in the longitudinal direction of a heater. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <First embodiment> [Overall structure] First, a first embodiment of the present invention will be described. An image forming apparatus 80 according to the first embodiment is an in-line (tandem) full-color laser beam printer.

[0012] The image forming apparatus includes printers, copiers, facsimiles, and multifunction machines, and refers to an apparatus that forms an image on a sheet used as a recording medium based on image information input from an external PC or image information read from a document. In addition to the main body having an image forming function, an image forming apparatus may be connected to auxiliary devices such as an optional feeder, an image reader, and a sheet processing device, and the entire system to which such auxiliary devices are connected is also a type of image forming apparatus. The sheets in this embodiment include paper such as paper and envelopes, plastic films such as overhead projector sheets (OHP), cloth, etc.

[0013] 1, the image forming apparatus 80 includes a sheet feeding section 60, an image forming section 50, a fixing unit 20, a reverse conveying section 70, and a control section 90. The control section 90 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), all of which are not shown. Various programs are stored in the ROM, and the CPU reads and executes the programs stored in the ROM. The RAM is used as a working area for the CPU.

[0014] When an image formation command is output to the image forming device 80, an image forming operation is started by the image forming section 50 based on image information input from an external computer or the like connected to the image forming device 80. The image forming section 50 includes four process cartridges 1a, 1b, 1c, and 1d that form images of four colors, yellow (Y), magenta (M), cyan (C), and black (Bk), exposure devices 5a, 5b, 5c, and 5d, and an intermediate transfer belt 8. The exposure devices 5a, 5b, 5c, and 5d correspond to the photosensitive drums of the process cartridges 1a, 1b, 1c, and 1d.

[0015] The four process cartridges 1a, 1b, 1c, and 1d have the same configuration except for the colors of the images they form. Therefore, only the image forming operation of the process cartridge 1a will be described, and descriptions of the process cartridges 1b, 1c, and 1d will be omitted.

[0016] The exposure device 5a corresponding to the process cartridge 1a irradiates a laser beam toward the photosensitive drum 2 of the process cartridge 1a based on the input image information. At this time, the photosensitive drum 2 is pre-charged by the charging roller 4, and an electrostatic latent image is formed on the photosensitive drum 2 by irradiating the photosensitive drum 2 with the laser beam. The photosensitive drum 2 as an image carrier is rotated at a predetermined process speed by a motor (not shown). Thereafter, the electrostatic latent image is developed by the developing roller 3, and a yellow (Y) toner image is formed on the photosensitive drum 2.

[0017] Similarly, magenta (M), cyan (C) and black (Bk) toner images are formed on the photosensitive drums of the process cartridges 1b, 1c and 1d. The toner images of each color formed on each photosensitive drum are transferred to the intermediate transfer belt 8 by primary transfer rollers 9a, 9b, 9c and 9d.

[0018] The toner image transferred to the intermediate transfer belt 8 is then transported to a secondary transfer roller 15, which serves as a transfer roller, by the intermediate transfer belt 8 which rotates in the direction of the arrow in Fig. 1. Note that the image forming operation for each color is performed at a timing to overlap the upstream toner image which has been primarily transferred onto the intermediate transfer belt 8.

[0019] The intermediate transfer belt 8 is wound around the assist roller 11, the drive roller 12, and the tension roller 13. In other words, the intermediate transfer belt 8 is stretched around the assist roller 11, the drive roller 12, and the tension roller 13. The intermediate transfer belt 8 rotates when the drive roller 12 is rotated by a motor (not shown). The drive roller 12 has a high friction rubber layer on its surface to drive the intermediate transfer belt 8, and this rubber layer has conductivity with a volume resistivity of 10.5 Ωcm or less. The drive roller 12 is disposed so as to sandwich the intermediate transfer belt 8 together with the secondary transfer roller 15. That is, the drive roller 12 faces the secondary transfer roller 15, and the intermediate transfer belt 8 is disposed between the drive roller 12 and the secondary transfer roller 15. The intermediate transfer belt 8 is sandwiched between the drive roller 12 and the secondary transfer roller 15. A transfer nip portion SN is formed between the intermediate transfer belt 8 and the secondary transfer roller 15.

[0020] The secondary transfer roller 15 is composed of an elastic roller having a volume resistivity of 107 to 109 Ωcm and a rubber hardness of 30° (Asker C hardness scale). The secondary transfer roller 15 is configured to press against the drive roller 12 via the intermediate transfer belt 8 with a total pressure of approximately 39.2 N. The secondary transfer roller 15 rotates following the intermediate transfer belt 8. Furthermore, a voltage of -2.0 to 7.0 kV can be applied to the secondary transfer roller 15 from a transfer power source (not shown).

[0021] In parallel with the above-mentioned image forming operation, a sheet S stored in a cassette 16 disposed in the lower part of the image forming apparatus 80 is fed by a pickup roller 17. The sheet S fed by the pickup roller 17 is conveyed to a registration roller pair 19 by a conveying roller pair 18.

[0022] The sheet S is corrected for skew by hitting the nip portion of the registration roller pair 19, which is in a stopped state. Then, the full-color toner image on the intermediate transfer belt 8 is transferred at the transfer nip portion SN to the first surface of the sheet S, which is conveyed at a predetermined conveying timing by the registration roller pair 19, by the secondary transfer bias applied to the secondary transfer roller 15. Residual toner remaining on the intermediate transfer belt 8 is collected by a cleaner 75.

[0023] The sheet S onto which the toner image has been transferred is applied with a predetermined heat and pressure by the fixing unit 20, so that the toner is melted and fixed. The sheet S that has passed through the fixing unit 20 is discharged onto the discharge tray 51 by the pair of discharge rollers 23 of the reverse conveying section 70.

[0024] The reverse conveying section 70 has a discharge roller pair 23, and a discharge sensor 30 and a reversing guide 24 provided between the fixing unit 20 and the discharge roller pair 23. The discharge sensor 30 can detect the position of the rear end of the sheet S, and is composed of, for example, a flag that moves when pressed by the sheet S, and an optical sensor that detects the movement of the flag. The reversing guide 24 guides the sheet S reversed by the discharge roller pair 23 to a double-sided conveying path 27 described later.

[0025] When forming images on both sides of the sheet S, the sheet S is first conveyed in a first direction D1 toward the outside of the machine by the fixing unit 20 and the discharge roller pair 23. When the rear end of the sheet S conveyed in the first direction D1 is detected by the discharge sensor 30, the discharge roller pair 23 reverses its rotation after the rear end of the sheet S passes a predetermined position. As a result, the sheet S is conveyed by the discharge roller pair 23 in a second direction D2 opposite to the first direction D1, and switches back.

[0026] The switched-back sheet S is guided to the double-sided conveying path 27 by the reversing guide 24, and is conveyed again to the registration roller pair 19 by the conveying roller pairs 25 and 26. A switching member movable between a first position and a second position may be provided between the discharge sensor 30 and the discharge roller pair 23. At the first position, the switching member guides the sheet S conveyed by the fixing unit 20 to the discharge roller pair 23. At the second position, the switching member guides the sheet S reversed by the discharge roller pair 23 toward the reversing guide 24. The switching member is moved from the first position to the second position based on the fact that the discharge sensor 30 detects the rear end of the sheet S conveyed in the first direction D1.

[0027] Then, a toner image is transferred at the transfer nip portion SN to the second surface of the sheet S. The toner image is fixed by the fixing unit 20, and the sheet S having the images formed on the first and second surfaces is discharged onto a discharge tray 51 by a pair of discharge rollers 23.

[0028] [Fuser unit] Next, the fixing unit 20 will be described in detail with reference to FIG. 2. The fixing unit 20, which serves as an image heating device for heating a toner image formed on a sheet S, includes a heating unit 21 and a pressure roller 22, as shown in FIG. 2. The heating unit 21 includes a heater 100 made of a plate-shaped ceramic heater, a holder 21b for holding the heater 100, and a fixing film 21c incorporating the heater 100 and the holder 21b. The fixing film 21c, which serves as a fixing member, is a cylindrical film. In addition, a thermistor 21d for controlling and regulating the temperature of the heater 100 is provided on the opposite side of the heater 100 from the pressure roller 22.

[0029] The pressure roller 22 as a pressure member is in pressure contact with the heater 100 and the holder 21b via the fixing film 21c to form a fixing nip portion N. In the fixing nip portion N, the sheet S is transported in the sheet transport direction CD. In the present embodiment, the pressure roller 22 is biased toward the heating unit 21, but the heating unit 21 may be biased toward the pressure roller 22.

[0030] The pressure roller 22 has an iron core 22a, an elastic layer 22b made of foamed silicone rubber provided on the core 22a, and a release layer 22c provided on the elastic layer 22b. The elastic layer 22b is located between the core 22a and the release layer 22c including the surface of the pressure roller 22 that contacts the sheet S.

[0031] The release layer 22c of the pressure roller 22 is made of perfluoroalkoxy resin (PFA). The release layer 22c is made of, for example, a tube that covers the elastic layer 22b or paint that is applied to the elastic layer 22b, but in this embodiment, it is made of a highly durable tube that covers the elastic layer 22b. In addition to PFA, the release layer 22c may be made of fluororesins such as polytetrafluoroethylene (PTFE) and perfluoroethylene-propylene copolymer (FEP), or fluororubber or silicone rubber that has good releasability.

[0032] The fixing film 21c of the heating unit 21 is rotated by the pressure roller 22. The sheet S is heated and pressurized by the heating unit 21 and the pressure roller 22 in the fixing nip portion N, and the toner image on the sheet S is fixed (bonded) to the sheet S. The sheet S is also transported to a pair of discharge rollers 23 by the heating unit 21 and the pressure roller 22.

[0033] [Heater control circuit and heater according to the first embodiment] Next, the first embodiment will be described with reference to Fig. 3(a) to Fig. 6(b). Fig. 3(a) is a diagram showing a heater control circuit 170 and a heater 100 included in the fixing unit 20 (see Fig. 2) of the present embodiment. Fig. 3(b) is a cross-sectional view showing the 3B-3B cross section of the heater 100.

[0034] The heater 100 shown in FIG. 3(b) is composed of heating elements 101 and 102, a conductor 103, contacts 106a to 106c, and insulating glass 105, which are formed on a ceramic substrate 104 as a substrate. The heating elements 101 and 102 constitute a heating unit 91 that generates heat when electricity is applied. The heating element 101 as a first heating element has two heating parts 101a and 101b that are arranged line-symmetrically in the short-side direction SD of the ceramic substrate 104, and is connected to the contacts 106a and 106c. That is, the heating part 101a as the first heating part is arranged at one end of the ceramic substrate 104 in the short-side direction SD, and the heating part 101b as the second heating part is arranged at the other end of the ceramic substrate 104 in the short-side direction SD.

[0035] The heating element 102 as the second heating element has two heating parts 102a and 102b arranged line-symmetrically in the short-side direction SD of the ceramic substrate 104, and is connected to the contact 106a and the contact 106b. The heating part 102a as the third heating part and the heating part 102b as the fourth heating part are arranged side by side in the short-side direction SD. The short-side direction SD is a direction parallel to the sheet conveying direction CD (see FIG. 2). The heating element 102 including the heating parts 102a and 102b is arranged between the heating parts 101a and 101b in the short-side direction SD of the ceramic substrate 104. The heating parts 101a, 101b, 102a, and 102b extend in the longitudinal direction LD perpendicular to the short-side direction SD, and are arranged side by side in the short-side direction SD. In this embodiment, the lengths of the heating elements 101 and 102 in the longitudinal direction LD are the same.

[0036] The resistance value of heating element 101 is set lower than that of heating element 102. For example, if the resistance value of heating element 101 is about 8 Ω, and if the voltage of commercial AC power supply 110 is 110 V, the maximum power applied to heating element 101 is about 1500 W (110 V × 110 V ÷ 8 Ω). Also, the resistance value of heating element 102 is, for example, about 24 Ω, and if the voltage of commercial AC power supply 110 is 110 V, the maximum power applied to heating element 102 is about 500 W (110 V × 110 V ÷ 24 Ω). Insulating glass 105 is provided to insulate the user from the heating element, which has approximately the same potential as commercial AC power supply 110.

[0037] The control circuit of the heater 100 shown in FIG. 3(a) is mainly composed of a commercial AC power supply 110, a current fuse 109, an electromagnetic relay 107, a noise filter 108, triacs 121 and 126, and a heater 100. The triacs 121 and 126 each have a main terminal T1, T2 and a gate terminal G between the main terminals T1 and T2, and the main terminals T1 and T2 are conductive when a gate voltage is applied to the gate terminal G. More specifically, each triac 121 and 126 is a circuit in which two thyristors are connected in parallel in the opposite directions, and when a gate voltage is applied, both positive and negative currents can flow and AC current can be controlled. A thyristor is a semiconductor in which p-type and n-type semiconductors are alternately stacked in four layers. In other words, the triacs 121 and 126 can be said to be semiconductor switches that have multiple semiconductors and can switch between conductive and non-conductive states of current. The triacs 121 and 126 form a switch unit 191 that selectively switches between a first power supply path PSC1 and a second power supply path PSC2, which will be described later.

[0038] The triac 121, which serves as a semiconductor switch and a first semiconductor switch, is controlled based on a control signal 125 from the control unit 90 (see FIG. 1), and a phototriac coupler 122 is used as a switch. When the triac 121 is turned on, the control signal 125 is set to a low level, causing a light-emitting diode 122a in the phototriac coupler 122 to emit light. A DC power supply Vcc is connected to the light-emitting diode 122a. The DC power supply Vcc is a power supply that shares a GND level with the control unit 90, and outputs a DC voltage such as 3.3V or 24V. The resistor 124 is a current-limiting resistor that serves to limit the current flowing through the light-emitting diode 122a in the phototriac coupler 122.

[0039] When the light-emitting diode 122a in the phototriac coupler 122 emits light, the triac section 122b in the phototriac coupler 122 becomes conductive. When the triac section 122b in the phototriac coupler 122 becomes conductive, a current is supplied from the commercial AC power supply 110 to the gate terminal G of the triac 121 via the resistor 123, and the triac 121 becomes conductive.

[0040] Here, the phototriac coupler 122 includes a zero-cross detection circuit 122c, which detects the zero-cross points of the commercial AC power supply 110, i.e., near phase angles 0° and 180°. That is, the zero-cross detection circuit 122c as a zero-cross detection unit detects the passage of the zero point of the voltage of the commercial AC power supply 110 as an AC power supply. Due to the function of the zero-cross detection circuit 122c, the triac unit 122b in the phototriac coupler 122 starts conducting only near the zero-cross points of the commercial AC power supply 110. Therefore, the triac 121 also starts conducting only near the zero-cross points of the commercial AC power supply 110. That is, the triac 121 can switch from a non-conductive state to a conductive state near phase angles 0° and 180° of the commercial AC power supply 110, but does not switch from a non-conductive state to a conductive state near phase angles 90° and 270° of the commercial AC power supply 110. The triac is an element that has the characteristic that once it is turned on, it maintains the conductive state until the commercial AC power supply 110 approaches the zero cross point.

[0041] Therefore, the triac 121 starts conducting near a zero cross point of the commercial AC power supply 110, and continues the conducting state until near the next zero cross point. That is, in this embodiment, the power supply from the commercial AC power supply 110 to the heating element 101 of the heater 100 is wave number controlled by the triac 121.

[0042] The operation of the triac 126 and its drive circuit is the same as that of the triac 121. That is, the light emitting diode 127a in the phototriac coupler 127 is switched between emitting and extinguishing light based on a control signal 130 from the control unit 90 (see FIG. 1). The light emitting diode 127a is connected to a DC power supply Vcc via a resistor 129. When the light emitting diode 127a in the phototriac coupler 127 emits light, the triac section 127b in the phototriac coupler 127 becomes conductive. When the triac section 127b in the phototriac coupler 127 becomes conductive, a current is supplied to the gate terminal G of the triac 126 from the commercial AC power supply 110 via the resistor 128, and the triac 126 becomes conductive.

[0043] The phototriac coupler 127 includes a zero-cross detection circuit 127c, the function of which is the same as that of the zero-cross detection circuit 122c. Therefore, the triac 126 starts conducting near a zero-cross point of the commercial AC power supply 110, and continues conducting until near the next zero-cross point. That is, in this embodiment, the power supply from the commercial AC power supply 110 to the heating element 102 of the heater 100 is wavenumber controlled by the triac 126.

[0044] The noise filter 108 is composed of, for example, a choke coil, a capacitor, etc., and serves to suppress noise terminal voltage by making it difficult for noise generated from the triacs 121 and 126 to be conducted to the commercial AC power supply 110 .

[0045] The current fuse 109 becomes non-conductive when an abnormal current flows through the heater control circuit 170 and the heater 100, and cuts off the power supply from the commercial AC power source 110 to the heater 100, thereby ensuring the safety of the fixing unit 20 (see FIG. 2).

[0046] The electromagnetic relay 107 plays a role in ensuring the safety of the fixing unit 20 by bringing the contacts into a non-conductive state and cutting off the power supply from the commercial AC power source 110 to the heater 100 if any abnormality occurs in the heater 100 .

[0047] Figures 4(a) to (d) show the power supply path of the heater control circuit 170. Figures 4(a) and 4(b) are circuit diagrams showing the first power supply path PSC1. Figure 4(a) shows only the parts necessary to explain the first power supply path PSC1 from Figure 3(a), with the first power supply path PSC1 shown in bold.

[0048] The first power supply path PSC1 is mainly composed of the commercial AC power supply 110, the heating element 101, and the triac 121. FIG. 4(b) is a circuit diagram showing an equivalent circuit of FIG. 4(a), and is a circuit diagram for making the first power supply path PSC1 easier to understand. As shown in FIG. 4(b), in this embodiment, the heating element 101 is connected in series to the triac 121, and the heating element 102 is connected in series to the triac 126. In addition, the heating element 101 and the triac 1021 are connected in parallel to the heating element 102 and the triac 126. In this embodiment, the triac 126 is always in a non-conductive state, and the triac 121 is in a conductive state, thereby selecting the first power supply path PSC1. In addition, in the first power supply path PSC1, the power supply from the commercial AC power supply 110 to the heating element 101 is controlled by switching the triac 121 between conductive and non-conductive states.

[0049] Fig. 4(c) and Fig. 4(d) are circuit diagrams showing the second power supply path PSC2. Fig. 4(c) shows the second power supply path PSC2 by extracting only the parts necessary for explaining the second power supply path PSC2 from Fig. 3(a) and using a thick line.

[0050] The second power supply path PSC2 is mainly composed of the commercial AC power supply 110, the heating element 102, and the triac 126. FIG. 4(d) is a circuit diagram showing the equivalent circuit of FIG. 4(c). In the second power supply path PSC2, the triac 121 is always kept in a non-conductive state and the triac 126 is kept in a conductive state, thereby selecting the second power supply path PSC2. In addition, in the second power supply path PSC2, the triac 126 is switched between conductive and non-conductive states to control the power supply from the commercial AC power supply 110 to the heating element 102. In this way, the first power supply path PSC1 and the second power supply path PSC2 are different from each other in at least some of the targets to which power is supplied, among the heating elements 101 and 102.

[0051] As described above, the resistance value of the heating element 101 is lower than the resistance value of the heating element 102. Therefore, the first power supply path PSC1 has a higher maximum power consumption than the second power supply path PSC2. In other words, it is assumed that the first power supply path PSC1 is used when a large amount of power is required for the fixing unit 20 (see FIG. 2), and the second power supply path PSC2 is used when a power as large as that of the first power supply path PSC1 is not required.

[0052] FIG. 5 shows how the temperature of the fixing unit 20 (see FIG. 2) of the present embodiment is controlled using the first power supply path PSC1 and the second power supply path PSC2. At time 0 (zero) in FIG. 5, the temperature of the heater 100 is sufficiently lower than the target temperature Ta and the predetermined temperature Tb. For example, the target temperature Ta is about 200° C., the predetermined temperature Tb is about 180° C., and the temperature of the heater 100 at time 0 (zero) is about 25° C. When the heater 100 is heated from this state, the triac 126 is put into a non-conductive state to form the first power supply path PSC1, and power is supplied from the commercial AC power supply 110 to the heating element 101. This state is continued until the temperature of the heater 100 reaches the predetermined temperature Tb. Period A shown in FIG. 5 corresponds to the period during which the heating element 101 is heated using the first power supply path PSC1.

[0053] During period A, the triac 121 is in a state where it can be switched between conductive and non-conductive in response to an instruction from the control unit 90 (see FIG. 1) based on the temperature of the heater 100. However, during period A, the temperature of the heater 100 deviates from the target temperature Ta, so the triac 121 is substantially always in a conductive state.

[0054] When the temperature of the heater 100 reaches a predetermined temperature Tb, the triac 121 is put into a non-conductive state to form the second power supply path PSC2, and power is supplied from the commercial AC power supply 110 to the heating element 102. This state continues until the temperature of the heater 100 reaches a target temperature Ta. Period B shown in FIG. 5 corresponds to a period in which the heating element 102 is heated using the second power supply path PSC1. It can be seen that the current supplied from the commercial AC power supply 110 to the heater 200 in period B is smaller than that in period A. This is because, as described above, the resistance value of the second power supply path PSC2 (the resistance value of the heating element 102) is larger than the resistance value of the first power supply path PSC1 (the resistance value of the heating element 101). Since the current supplied from the commercial AC power supply 110 to the heater 100 in period B is smaller than that in period A, the temperature rise of the heater 100 in period B is more gradual than that in period A.

[0055] The reason why power supply through the first power supply path PSC1 is not continued until the heater 100 reaches the target temperature Ta and power supply is switched to the second power supply path PSC2 at a predetermined temperature Tb is to prevent the temperature of the heater 100 from overshooting the target temperature Ta. However, if priority is given to quickly causing the heater 100 to reach the target temperature Ta rather than preventing the overshoot, power supply through the first power supply path PSC1 may be continued until the temperature of the heater 100 reaches the target temperature Ta. That is, the first power supply path PSC1 may be selected in period B and power may be supplied to the heating element 101 of the heater 100 from the first power supply path PSC1.

[0056] Once the temperature of the heater 100 reaches the target temperature Ta, the second power supply path PSC2 is used to control the temperature of the heater 100 to follow the target temperature Ta. Period C corresponds to the period during which the temperature of the heater 100 is controlled to the target temperature Ta using the second power supply path PSC1. In other words, the switch unit 191 (see FIG. 3(a)) selects the first power supply path PSC1 when the temperature of the heater 100 is lower than a predetermined temperature Tb, and selects the second power supply path PSC2 when the temperature of the heater 100 is higher than the predetermined temperature Tb.

[0057] 6(a) and (b) are diagrams showing an image of the heat distribution of the heater 100. FIG. 6(a) shows a steady heat distribution in the 3B-3B cross section of the heater 100 when power is supplied only to the heating element 101 using the first power supply path PSC1. Only the heating element 101 is heated in the first power supply path PSC1. In the center of the heater 100 in the short direction SD, the temperature rises due to heat from both of the two heating elements constituting the heating element 101, and as a result, the heat distribution of the heater 100 in the 3B-3B cross section becomes approximately uniform. In FIG. 6(a), the maximum temperature of the heater 100 is indicated by maximum temperature T5, and the minimum temperature of the heater 100 is indicated by minimum temperature T6. The temperature difference between the maximum temperature T5 and the minimum temperature T6 is temperature difference ΔT56.

[0058] FIG. 6(b) shows a steady heat distribution in the 3B-3B cross section of the heater 100 when power is supplied only to the heating element 102 using the second power supply path PSC2. Since the second power supply path PSC2 heats only the heating element 102, the temperature of the center of the heater 100 in the short-side direction SD becomes high. On the other hand, the temperature of both ends of the heater 100 in the short-side direction SD becomes relatively low because heat is easily dissipated therefrom. As a result, the heat distribution of the heater 100 in the 3B-3B cross section is such that the temperature of the center is high in the short-side direction SD and the temperature of the ends is low. In FIG. 6(b), the maximum temperature of the heater 100 is indicated by maximum temperature T7, and the minimum temperature of the heater 100 is indicated by minimum temperature T8. The temperature difference between the maximum temperature T7 and the minimum temperature T8 is temperature difference ΔT78.

[0059] Here, the smaller the temperature difference in the heat distribution on the 3B-3B cross section of the heater 100, the smaller the thermal stress acting on the ceramic substrate 104 of the heater 100. This is because when the temperature difference in the heater 100 is small, the ceramic substrate 104 expands almost uniformly in the longitudinal direction LD, and stress (distortion) due to the expansion difference in the ceramic substrate 104 is unlikely to occur.

[0060] Since the first power supply path PSC1 applies a larger power than the second power supply path PSC2, the temperature of the heater 100 rises faster and reaches the heat distribution shown in FIG. 6(a) in a short time. The temperature difference T56 in the heater 100 when power is supplied to the heater 100 using the first power supply path PSC1 is smaller than the temperature difference T78 in the heater 100 when power is supplied to the heater 100 using the second power supply path PSC2. Therefore, the thermal stress applied to the ceramic substrate 104 when power is supplied to the heater 100 using the first power supply path PSC1 is relatively smaller than that when power is supplied to the heater 100 using the second power supply path PSC2. This can improve the durability of the ceramic substrate 104.

[0061] That is, the first power supply path PSC1 has a relatively large power but a relatively small thermal stress on the ceramic substrate 104, and the second power supply path PSC2 has a relatively small power but a relatively large thermal stress on the ceramic substrate 104. Both of these prevent a large thermal stress from being applied to the ceramic substrate 104 in a short time, and even if an abnormality occurs in the heater control circuit 170 and the heater 100 overheats, the heater 100 can be easily protected by a safety device (not shown). In addition, by making the heat distribution of the heater 100 uniform, especially when the heater 100 is started up, the power supplied to the heater 100 can be increased, and the FPOT can be improved. If this were the case in the opposite case, that is, if the first power supply path PSC1 has a configuration with a large power and a large thermal stress, there is a risk that the heater 100 will be damaged before the safety device (not shown) is activated when an abnormality occurs in the first power supply path PSC1.

[0062] The effects obtained by the configuration of this embodiment are described below. First, the noise filter 108 can be made smaller. In all periods from period A to period C shown in Fig. 5, the triacs 121 and 126 perform wave number control, switching between conductive and non-conductive states in half-wave units of the commercial AC power supply 110. Wave number control can suppress the noise terminal voltage more effectively than phase control, so the configuration of this embodiment allows the noise filter 108 to be relatively smaller than in the case of phase control.

[0063] Secondly, flicker can be reduced. In principle, flicker is likely to occur in period C because a current change occurs due to switching of the triac 126 between conductive and non-conductive states. However, the peak current in period C is relatively small compared to the peak current in period A, so flicker can be reduced compared to when a current with a large peak is turned on and off as in period A. In addition, since a current basically flows constantly in period B, flicker hardly occurs. In period B, the current may be turned on and off at the timing when the temperature of the heater 100 approaches the target temperature Ta in FIG. 5, but the peak current in period B is smaller than the peak current in period A, just like period C. Therefore, flicker can be reduced compared to when a current with a large peak is turned on and off as in period A.

[0064] Although the peak current in period A is larger than in periods B and C, flicker is unlikely to occur because the current flows constantly and does not change. In this way, by controlling the temperature of the heater 100 by switching between the first power supply path PSC1 and the second power supply path PSC2 as shown in Fig. 5, flicker can be reduced in all periods from period A to period C compared to the heater control circuit 170 that has only the first power supply path PSC1.

[0065] Thirdly, even-order harmonic currents can be reduced. When wave number control is performed, even-order harmonic currents are generally observed. However, since wave number control is performed with a small current in period C, even-order harmonic currents can be reduced compared to when wave number control is performed with a large current such as in period A. Note that since current flows constantly in periods A and B, even-order harmonic currents are not observed.

[0066] Fourthly, the heater 100 can be heated in the shortest time without power loss. In FIG. 5, it can be seen that the current continues without interruption when transitioning from period A to period B. In other words, the switching from the first power supply path PSC1 to the second power supply path PSC2 can be performed seamlessly, and no power loss occurs. When the power supply path is switched using a mechanical switch such as an electromagnetic relay, a period in which the current is temporarily turned off occurs when the power supply path is switched. In contrast, when the triacs 121 and 126 are used as in this embodiment, the power supply path can be switched without power loss. Furthermore, by switching between the first power supply path PSC1 and the second power supply path PSC2 using the triacs 121 and 126, the risk of wear of the elements can be significantly reduced compared to the case of using a mechanical switch. As a result, there is also an effect that various restrictions such as a limit on the frequency of power supply path switching or a limit on the number of times the power supply path is switched do not need to be set.

[0067] Fifth, the temperature ripple of the heater 100 can be reduced. Generally, the smaller the change in the power current supplied to the heater, the smaller the temperature ripple of the heater. In the present embodiment, a small current is switched in period C, so the temperature ripple can be reduced compared to when a large current is switched as in period A. Since the sheet passes through the fixing unit 20 (see FIG. 2) during period C, a small temperature ripple during period C leads to improved quality of the fixing unit 20.

[0068] In this way, by using the configuration described in this embodiment, it is possible to provide a fixing unit 20 that does not cause adverse effects such as a noise filter size, flicker, harmonic current, power loss, and temperature ripple by shortening FPOT by supplying a large amount of power to the heater 100 in period A of Fig. 5, while reducing the current in periods B and C of Fig. 5. FPOT is an abbreviation for First Print Out Time, and refers to the time from when a print job is sent to the image forming apparatus 80 to when an image is printed on the first sheet.

[0069] <Second embodiment> [Heater control circuit and heater according to the second embodiment] Next, a second embodiment will be described with reference to Fig. 7(a) to Fig. 10(b). Fig. 7(a) is a diagram showing a heater control circuit 270 and a heater 200 included in a fixing unit 20 (see Fig. 2) of the present embodiment. Fig. 7(b) is a cross-sectional view showing a 7B-7B cross section of the heater 200.

[0070] The heater 200 shown in Figures 7(a) and (b) has the same shape as the heater 100 of the first embodiment, but differs from the heater 100 of the first embodiment only in the resistance value of the heating element. In this embodiment, the resistance value of the heating element 201 is about 24 Ω, and the resistance value of the heating element 202 is about 12 Ω. The heater control circuit 270 according to the second embodiment is also different from the heater control circuit 170 according to the first embodiment. Note that the same configuration as the first embodiment will be described with the same reference numerals assigned to the figures or omitted from the illustrations.

[0071] 7(a) is mainly composed of a commercial AC power supply 110, a current fuse 109, an electromagnetic relay 107, a noise filter 108, triacs 131 and 136, and a heater 200. The operations of the triacs 131 and 136 and their drive circuits are the same as those of the triacs 121 and 126 in the first embodiment, and therefore will not be described. The triacs 131 and 136 form a switch unit 192 that selectively switches between a third power supply path PSC3 and a fourth power supply path PSC4, which will be described later.

[0072] FIG. 8 shows the power supply path of the heater control circuit 270. FIG. 8(a) and FIG. 8(b) are circuit diagrams showing the third power supply path PSC3. FIG. 8(a) shows only the parts necessary for explaining the third power supply path PSC3 from FIG. 7(a) with the third power supply path PSC3 shown by a thick line. The heater 200 has a heating element 201 as a first heating element and a heating element 202 as a second heating element. The third power supply path PSC3 as the first power supply path is mainly composed of a commercial AC power supply 110, the heating element 201, and triacs 131 and 136. FIG. 8(b) is a circuit diagram showing an equivalent circuit of FIG. 8(a). As shown in FIG. 8(b), in this embodiment, the triac 136 as a semiconductor switch is connected in series to the heating element 202, and the heating element 201 is connected in parallel to the heating element 202 and the triac 136. In this embodiment, the third power supply path PSC3 is selected by constantly keeping the triac 136 in a conductive state, and the fourth power supply path PSC4 is selected by constantly keeping the triac 136 in a non-conductive state.

[0073] In the third power supply path PSC3, the triac 131 is switched between conductive and non-conductive states to control power supply from the commercial AC power supply 110 to the parallel heating element formed by the heating elements 201 and 202 connected in parallel.

[0074] 8(c) and 8(d) are circuit diagrams showing a fourth power supply path PSC4 as a second power supply path. In FIG. 8(c), only the parts necessary for explaining the fourth power supply path PSC4 are extracted from FIG. 7(a), and the fourth power supply path PSC4 is shown by a thick line. The fourth power supply path PSC4 is mainly composed of a commercial AC power source 110, a heating element 201, and a triac 131. FIG. 8(d) is a circuit diagram showing an equivalent circuit of FIG. 8(c). In the fourth power supply path PSC4, the triac 136 is always in a non-conducting state, and the power supply from the commercial AC power source 110 to the heating element 201 is controlled by switching the triac 131 between conductive and non-conductive states. In this way, the third power supply path PSC3 and the fourth power supply path PSC4 are different from each other in at least some of the targets to which power is supplied among the heating elements 201 and 202.

[0075] Here, in the third power supply path PSC3, heating element 201 and heating element 202 are connected in parallel, so that the combined resistance value is smaller than the resistance value of heating element 202 in the fourth power supply path PSC4. In this embodiment, the resistance value of heating element 201 is 24Ω, and the resistance value of heating element 202 is 12Ω, so that the combined parallel resistance is 8Ω. In other words, the resistance value of heating element 201 is larger than the resistance value of heating element 202. In this case, if the voltage of commercial AC power supply 110 is 110V, the maximum power applied to the parallel heating element formed by heating element 201 and heating element 202 is about 1500W (110V×110V÷8Ω). On the other hand, in the fourth power supply path PSC4, the resistance value of the heating element 202 is 24Ω, so if the voltage of the commercial AC power supply 110 is 110V, the maximum power applied to the heating element 202 is about 500W (110V×110V÷24Ω).

[0076] In this way, the third power supply path PSC3 has a higher maximum power consumption than the fourth power supply path PSC4. That is, it is assumed that the third power supply path PSC3 is used when a large amount of power is required for the fixing unit 20 (see FIG. 2), and the fourth power supply path PSC4 is used when a power as large as that of the third power supply path PSC3 is not required.

[0077] Fig. 9 shows how the temperature of the fixing unit 20 (see Fig. 2) of this embodiment is controlled using the third power supply path PSC3 and the fourth power supply path PSC4. At time 0 (zero) in Fig. 9, the temperature of the heater 200 is sufficiently lower than the target temperature Ta and the predetermined temperature Tb. For example, the target temperature Ta is about 200°C, the predetermined temperature Tb is about 180°C, and the temperature of the heater 200 at time 0 (zero) is about 25°C. When the heater 200 is heated from this state, power is first supplied to the heating element 201 via the fourth power supply path PSC4.

[0078] In reality, the temperature of the heater 200 would rise faster if a large amount of power were supplied to the heater 200 using the third power supply path PSC3, but in this embodiment, the triac 136 is driven by the triac 131. For this reason, the triac 136 cannot be made conductive from the beginning (from the first half wave of the commercial AC power supply 110). Therefore, it is necessary to start the flow of current using the fourth power supply path PSC4. Period D shown in FIG. 9 corresponds to the period during which the heating element 201 is heated using such a fourth power supply path PSC4.

[0079] After the triac 131 conducts for at least a half wave of the commercial AC power supply 110, the triac 136 is brought into a conductive state, and the heater 200 is heated using the third power supply path PSC3. In other words, when the temperature of the heater 200 is lower than a predetermined temperature Tb, the switch unit 192 (see FIG. 7(a)) selects the fourth power supply path PSC4 and then switches to the third power supply path PSC3. This state is maintained until the temperature of the heater 100 reaches the predetermined temperature Tb. A period E shown in FIG. 9 corresponds to a period during which the heating elements 201 and 202 connected in parallel are heated using the third power supply path PSC4. During the period E, the triac 131 is in a state in which it can be switched between conductive and non-conductive in response to an instruction from the control unit 90 (see FIG. 1) based on the temperature of the heater 200. However, in the period E, the temperature of the heater 200 deviates from the target temperature Ta, so that the triac 131 is substantially always in a conductive state.

[0080] 7(a) may be set to a logic that makes the triac 136 conductive at the same time as the start of period E, or may be set to that logic in advance from the beginning of period D. This is because even if the drive signal 140 for the triac 136 is set to a logic that makes the triac 136 conductive from the beginning of period D, the triac 136 will only be conductive at the first zero cross point after the triac 131 becomes conductive.

[0081] When the temperature of the heater 200 reaches a predetermined temperature Tb, the triac 136 is put into a non-conductive state to form the fourth power supply path PSC4, and power is supplied from the commercial AC power supply 110 to the heating element 201. This state is continued until the temperature of the heater 200 reaches the target temperature Ta. In other words, the switch unit 192 (see FIG. 7(a)) selects the fourth power supply path PSC4 when the temperature of the heater 200 is higher than the predetermined temperature Tb. A period F shown in FIG. 9 corresponds to a period in which the heating element 201 is heated using such a fourth power supply path PSC4. It can be seen that the current supplied from the commercial AC power supply 110 to the heater 200 is smaller in the period F than in the period E. This is because the resistance value of the fourth power supply path PSC4 (the resistance value of the heating element 201) is larger than the resistance value of the third power supply path PSC3 (the combined parallel resistance value of the heating elements 201 and 202) as described above. During period F, the current supplied from the commercial AC power supply 110 to the heater 200 is smaller than during period E, so the temperature of the heater 200 increases more slowly during period F than during period E.

[0082] The reason why the power supply through the third power supply path PSC3 is not continued until the heater 200 reaches the target temperature Ta and the power supply is switched to the fourth power supply path PSC4 at a predetermined temperature Tb is to prevent the temperature of the heater 200 from overshooting the target temperature Ta. However, if priority is given to quickly causing the heater 200 to reach the target temperature Ta rather than preventing the overshoot, the power supply through the third power supply path PSC3 may be continued until the temperature of the heater 200 reaches the target temperature Ta. That is, the third power supply path PSC3 may be selected in the period F and power may be supplied to the heating element 201 of the heater 200 from the third power supply path PSC3.

[0083] Once the temperature of the heater 200 reaches the target temperature Ta, the fourth power supply path PSC4 is used to control the temperature of the heater 200 to follow the target temperature Ta. A period Q shown in Fig. 9 corresponds to a period during which the temperature of the heater 200 is controlled to the target temperature Ta using such a fourth power supply path PSC4.

[0084] 10(a) and (b) are diagrams showing an image of heat distribution in the heater 200. FIG. 10(a) shows a steady heat distribution in the 7B-7B cross section of the heater 200 when power is supplied to the heat generating elements 201 and 202 connected in parallel using the third power supply path PSC3. In the third power supply path PSC3, the heat generating elements 201 and 202 are heated, and the temperature of the center of the heater 200 in the short direction SD where heat from all the heat generating elements is concentrated becomes the highest. In FIG. 10(a), the maximum temperature of the heater 200 is indicated by maximum temperature T9, and the minimum temperature of the heater 200 is indicated by minimum temperature T10. The temperature difference between the maximum temperature T9 and the minimum temperature T10 is temperature difference ΔT910.

[0085] FIG. 10(b) shows a steady heat distribution in the 7B-7B cross section of the heater 200 when power is supplied only to the heating element 201 using the fourth power supply path PSC4. In the fourth power supply path PSC4, only the heating element 201 is heated, but in the center part in the short direction SD of the heater 200, the temperature rises due to heat from both of the two heating elements constituting the heating element 101. As a result, the heat distribution in the 7B-7B cross section becomes approximately uniform. In FIG. 10(b), the maximum temperature of the heater 200 is indicated by maximum temperature T11, and the minimum temperature of the heater 200 is indicated by minimum temperature T12. The temperature difference between the maximum temperature T11 and the minimum temperature T12 is temperature difference ΔT1112.

[0086] Here, the smaller the temperature difference in the thermal distribution on the 7B-7B cross section of the heater 200, the smaller the thermal stress applied to the ceramic substrate 104 of the heater 200. This is because when the temperature difference in the heater 200 is small, the ceramic substrate 104 expands almost uniformly in the longitudinal direction LD, and stress (distortion) due to the expansion difference in the ceramic substrate 104 is unlikely to occur.

[0087] A temperature difference T1112 in the heater 200 when power is supplied to the heater 200 using the fourth power supply path PSC4 is smaller than a temperature difference T910 in the heater 200 when power is supplied to the heater 200 using the third power supply path PSC3. Therefore, the thermal stress applied to the ceramic substrate 104 when power is supplied to the heater 200 using the fourth power supply path PSC4 is relatively smaller than that when power is supplied to the heater 200 using the third power supply path PSC3.

[0088] Comparing the time when the third power supply path PSC3 is selected and the time when the fourth power supply path PSC4 is selected, the time when the fourth power supply path PSC4 is selected is longer. When only one sheet is passed through the fixing unit 20 (see FIG. 2), the time when the fourth power supply path PSC4 is selected is about 2 to 3 times longer, and when multiple sheets are passed through the fixing unit 20, the time when the fourth power supply path PSC4 is selected is tens or thousands of times longer. Therefore, in this embodiment, the stress applied to the ceramic substrate 104 is set to be small in the fourth power supply path PSC4, which is selected for a long time, to improve the reliability of the fixing unit 20. Also, by making the heat distribution of the heater 200 uniform, especially during the period F, the power supplied to the heater 200 can be increased, and the FPOT can be improved.

[0089] In the configuration of this embodiment, assuming a failure in which the triacs 131 and 136 are simultaneously shorted, current is passed through the third power supply path PSC3, and a maximum of 1500 W is supplied to the heater 200. That is, even in the case of an abnormal situation in which the plurality of triacs 131 and 136 are simultaneously shorted, one of the power supply paths used during normal operation is selected.

[0090] On the other hand, if the triacs 121 and 126 simultaneously short-circuit in the configuration of the first embodiment, a large power of 2016 W (110 V×110 V÷6 Ω) will be supplied to the parallel heating element (e.g., 6 Ω) formed by the heating elements 101 and 102. In this way, assuming a simultaneous short-circuit failure of multiple triacs 131 and 136, it can be said that the present embodiment is a safer configuration than the first embodiment.

[0091] In this embodiment, the same effects as those of the first embodiment can be achieved. That is, by using the configuration of this embodiment, firstly, the noise filter 108 can be made smaller, secondly, flicker can be reduced, and thirdly, even-order harmonics can be reduced. In addition, fourthly, the heater can be heated in the shortest time possible without power loss, and fifthly, the temperature ripple of the heater 200 can be reduced.

[0092] In this embodiment, the resistance value of heating element 201 (about 24 Ω) is greater than the resistance value of heating element 202 (about 12 Ω), but this relationship does not necessarily have to be the case. In the configuration of this embodiment, the effect is greater if the resistance value of heating element 201 is greater than the resistance value of heating element 202 (contributing more to shortening FPOT). However, the effect of the present invention can be obtained even when the resistance values ​​of heating element 201 and heating element 202 are equal or when the resistance value of heating element 201 is less than the resistance value of heating element 202. Therefore, the relationship in the resistance values ​​of heating elements 201 and 202 does not limit the configuration of this embodiment.

[0093] <Third embodiment> [Heater control circuit and heater according to the third embodiment] Next, a third embodiment will be described with reference to Fig. 11(a) to Fig. 14(b). Fig. 11(a) is a diagram showing a heater control circuit 370 and a heater 300 included in the fixing unit 20 (see Fig. 2) of the present embodiment. Fig. 11(b) is a cross-sectional view showing the 11B-11B cross section of the heater 300.

[0094] The heater 300 shown in Figures 11(a) and (b) has the same shape as the heater 100 of the first embodiment, but differs from the heater 100 of the first embodiment only in the resistance value of the heating element. In this embodiment, the resistance value of the heating element 301 is about 8 Ω, and the resistance value of the heating element 302 is about 16 Ω. The heater control circuit 370 according to the third embodiment is also different from the heater control circuit 170 according to the first embodiment. Note that the same configurations as those in the first embodiment will be described with the same reference numerals assigned to them or will not be shown in the figures.

[0095] 11(a), a heater control circuit 370 of a heater 300 is mainly composed of a commercial AC power supply 110, a current fuse 109, an electromagnetic relay 107, a noise filter 108, triacs 111 and 116, and a heater 300. The heater 300 has a heating element 301 as a first heating element and a heating element 302 as a second heating element. The operations of the triacs 111 and 116 and their drive circuits are the same as those of the triacs 121 and 126 in the first embodiment, and therefore will not be described. The triacs 121 and 126 form a switch unit 193 that selectively switches between a fifth power supply path PSC5 and a sixth power supply path PSC6, which will be described later.

[0096] FIG. 12 shows the power supply path of the heater control circuit 270. FIG. 12(a) and FIG. 12(b) are circuit diagrams showing the fifth power supply path PSC5. FIG. 12(a) shows only the parts necessary for explaining the fifth power supply path PSC5 from FIG. 11(a) and shows the fifth power supply path PSC5 with a thick line. The fifth power supply path PSC5 as the first power supply path is mainly composed of the commercial AC power supply 110, the heating element 301, and the triacs 111 and 116. FIG. 12(b) is a circuit diagram showing an equivalent circuit of FIG. 12(a). As shown in FIG. 12(b), in this embodiment, the triac 116 is connected in parallel to the heating element 302, and the heating element 301 is connected in series to the triac 116 and the heating element 302 connected in parallel. In this embodiment, the fifth power supply path PSC5 is selected by always keeping the triac 116 in a conductive state. Moreover, power is supplied only to the heating element 301 by shorting the heating element 302 with the triac 116. In the fifth power supply path PSC5, the power supply from the commercial AC power supply 110 to the heating element 301 is controlled by switching the triac 111 between conductive and non-conductive states.

[0097] 12(c) and 12(d) are circuit diagrams showing a sixth power supply path PSC6 as a second power supply path. In FIG. 12(c), only the parts necessary for explaining the sixth power supply path PSC6 are extracted from FIG. 11(a), and the sixth power supply path PSC6 is shown by a thick line. The sixth power supply path PSC6 is mainly composed of a commercial AC power supply 110, a heating element 301, a heating element 302, and a triac 111. FIG. 12(d) is a circuit diagram showing an equivalent circuit of FIG. 12(c). In this embodiment, the sixth power supply path PSC6 is selected by always keeping the triac 116 in a non-conducting state. In the sixth power supply path PSC6, the power supply from the commercial AC power supply 110 to the heating elements 301 and 302 connected in series is controlled by switching the triac 111 between conductive and non-conductive states. In this manner, the fifth power supply path PSC5 and the sixth power supply path PSC6 are different from each other in at least some of the targets, among the heating elements 301 and 302, to which power is supplied.

[0098] Here, in the sixth power supply path PSC6, the heating element 301 and the heating element 302 are connected in series, so that the combined resistance value is larger than that of the heating element 301 in the fifth power supply path PSC5. In this embodiment, the resistance value of the heating element 301 is 8Ω, and the resistance value of the heating element 302 is 16Ω, so that the combined series resistance is 24Ω. If the voltage of the commercial AC power supply 110 is 110V, the maximum power applied to the entire heating elements 301 and 302 connected in series is about 500W (110V×110V÷24Ω). That is, the resistance value of the heating element 301 is smaller than that of the heating element 302. On the other hand, in the fifth power supply path PSC5, the resistance value of the heating element 301 is 8Ω, so that if the voltage of the commercial AC power supply 110 is 110V, the maximum power applied to the heating element 301 is about 1500W (110V×110V÷8Ω).

[0099] In this way, the sixth power supply path PSC6 has a smaller maximum power consumption than the fifth power supply path PSC5. That is, it is assumed that the fifth power supply path PSC5 is used when a large amount of power is required for the fixing unit 20 (see FIG. 2), and the sixth power supply path PSC6 is used when a power as large as that of the fifth power supply path PSC5 is not required.

[0100] Fig. 13 shows how the temperature of the fixing unit 20 (see Fig. 2) of this embodiment is controlled using the fifth power supply path PSC5 and the sixth power supply path PSC6. At time 0 (zero) in Fig. 13, the temperature of the heater 300 is sufficiently lower than the target temperature Ta and the predetermined temperature Tb. For example, the target temperature Ta is about 200°C, the predetermined temperature Tb is about 180°C, and the temperature of the heater 300 at time 0 (zero) is about 25°C. When the heater 300 is heated from this state, first, power is supplied to the heating elements 301 and 302 connected in series by the sixth power supply path PSC6.

[0101] Normally, the temperature of the heater 300 would rise faster if a large amount of power were supplied to the heater 300 using the fifth power supply path PSC5, but in this embodiment, the triac 116 is driven by the triac 111. For this reason, the triac 116 cannot be made conductive from the beginning (from the first half-wave of the commercial AC power supply 110). Therefore, it is necessary to start the flow of current using the sixth power supply path PSC6. Period H shown in FIG. 13 corresponds to the period during which the heating elements 301 and 302 connected in series are heated using such a sixth power supply path PSC6.

[0102] After the triac 111 conducts for at least a half wave of the commercial AC power supply 110, the triac 116 is brought into a conductive state, and the heater 300 is heated using the fifth power supply path PSC5. In other words, when the temperature of the heater 300 is lower than a predetermined temperature Tb, the switch unit 193 (see FIG. 11(a)) selects the sixth power supply path PSC6 and then switches to the fifth power supply path PSC5. It can also be said that there is a period I during which the switch unit 193 selects the fifth power supply path PSC5 when the temperature of the heater 300 is lower than the predetermined temperature Tb. This state is continued until the temperature of the heater 300 reaches the predetermined temperature Tb. The period I shown in FIG. 13 corresponds to the period during which the heating element 301 of the heater 300 is heated using such a third power supply path PSC4. During period I, the triac 111 is in a state in which it can be switched between conductive and non-conductive in response to an instruction from the control unit 90 (see FIG. 1) based on the temperature of the heater 300. However, during period I, the temperature of the heater 300 deviates from the target temperature Ta, so the triac 111 is essentially in a constant conductive state.

[0103] 11(a) may be set to a logic that makes the triac 116 conductive at the same time as the start of period I, or may be set to that logic in advance from the beginning of period H. This is because even if the drive signal 120 for the triac 116 is set to a logic that makes the triac 116 conductive from the beginning of period H, the triac 116 will only be conductive at the first zero cross point after the triac 111 becomes conductive.

[0104] When the temperature of the heater 300 reaches a predetermined temperature Tb, the triac 116 is turned off to form the sixth power supply path PSC6, and power is supplied from the commercial AC power supply 110 to the heating elements 301 and 302. This state is maintained until the temperature of the heater 300 reaches the target temperature Ta. In other words, the switch unit 193 (see FIG. 11(a)) selects the sixth power supply path PSC6 when the temperature of the heater 300 is higher than the predetermined temperature Tb. A period J shown in FIG. 13 corresponds to a period during which the heating elements 301 and 302 are heated using such a sixth power supply path PSC6. It can be seen that the current supplied from the commercial AC power supply 110 to the heater 300 during the period J is smaller than that during the period I. This is because, as described above, the resistance value of the sixth power supply path PSC6 (the combined series resistance value of the heating element 301 and the heating element 302) is greater than the resistance value of the fifth power supply path PSC5 (the resistance value of the heating element 301). Since the current supplied from the commercial AC power supply 110 to the heater 300 in period J is smaller than that in period I, the temperature rise of the heater 300 in period J is more gradual than that in period I.

[0105] The reason why the power supply through the fifth power supply path PSC5 is not continued until the heater 300 reaches the target temperature Ta and the power supply is switched to the sixth power supply path PSC6 at a predetermined temperature Tb is to prevent the temperature of the heater 300 from overshooting the target temperature Ta. However, if priority is given to quickly causing the heater 300 to reach the target temperature Ta rather than preventing the overshoot, the power supply through the fifth power supply path PSC5 may be continued until the temperature of the heater 300 reaches the target temperature Ta. That is, the fifth power supply path PSC5 may be selected in the period J and power may be supplied to the heating element 301 of the heater 300 from the fifth power supply path PSC5.

[0106] Once the temperature of the heater 300 reaches the target temperature Ta, the sixth power supply path PSC6 is used to control the temperature of the heater 300 to follow the target temperature Ta. A period K shown in Fig. 13 corresponds to a period during which the sixth power supply path PSC6 is used to control the temperature of the heater 300 to the target temperature Ta.

[0107] 14(a) and (b) are diagrams showing an image of the heat distribution of the heater 300. FIG. 14(a) shows the steady heat distribution of the heater 300 in the 11B-11B cross section when power is supplied only to the heat generating element 301 using the fifth power supply path PSC5. In the fifth power supply path PSC5, only the heat generating element 301 is heated, but the center part of the heater 300 in the short direction SD receives heat from both of the two heat generating elements constituting the heat generating element 301 and the temperature rises, so that the heat distribution in the 11B-11B cross section becomes approximately uniform. In FIG. 14(a), the maximum temperature of the heater 300 is indicated by maximum temperature T13, and the minimum temperature of the heater 300 is indicated by minimum temperature T14. The temperature difference between the maximum temperature T13 and the minimum temperature T14 is temperature difference ΔT1314.

[0108] Fig. 14(b) shows a steady heat distribution in the 11B-11B cross section of the heater 300 when power is supplied to the heating elements 301 and 302 connected in series using the sixth power supply path PSC6. In the sixth power supply path PSC6, the heating elements 301 and 302 are heated, and the temperature of the center of the heater 300 in the short direction SD where heat from all the heating elements is concentrated becomes the highest. In Fig. 14(b), the maximum temperature of the heater 300 is indicated by maximum temperature T15, and the minimum temperature of the heater 300 is indicated by minimum temperature T16. The temperature difference between the maximum temperature T15 and the minimum temperature T16 is temperature difference ΔT1516.

[0109] Here, the smaller the temperature difference in the 11B-11B cross section of the heater 300, the smaller the thermal stress applied to the ceramic substrate 104 of the heater 300. This is because when the temperature difference in the heater 300 is small, the ceramic substrate 104 expands almost uniformly in the longitudinal direction LD, and stress (distortion) due to the expansion difference in the ceramic substrate 104 is unlikely to occur.

[0110] A temperature difference T1314 in the heater 300 when power is supplied to the heater 300 using the fifth power supply path PSC5 is smaller than a temperature difference T1516 in the heater 300 when power is supplied to the heater 300 using the sixth power supply path PSC6. Therefore, the thermal stress applied to the ceramic substrate 104 when power is supplied to the heater 300 using the fifth power supply path PSC5 is relatively smaller than that when power is supplied to the heater 300 using the sixth power supply path PSC6. This can improve the durability of the ceramic substrate 104.

[0111] That is, the fifth power supply path PSC5 has a relatively large power but the thermal stress applied to the ceramic substrate 104 is relatively small, and the sixth power supply path PSC6 has a relatively small power but the thermal stress applied to the ceramic substrate 104 is relatively large. Both of these prevent a large thermal stress from being applied to the ceramic substrate 104 in a short period of time, and even if an abnormality occurs in the heater control circuit 370 and the heater 300 overheats, it becomes easier to protect the heater 300 with a safety device (not shown) or the like. Furthermore, by making the heat distribution of the heater 300 uniform, particularly when the heater 300 is started up, the power supplied to the heater 300 can be increased, and the FPOT can be improved.

[0112] In the configuration of this embodiment, assuming a failure in which the triacs 111 and 116 are simultaneously shorted, current is passed through the fifth power supply path PSC5, and a maximum of 1500 W is supplied to the heater 300. In other words, even in the case of an abnormal situation in which a plurality of triacs 111 and 116 fail, only one of the power supply paths used during normal operation is selected.

[0113] On the other hand, if the triacs 121 and 126 in the configuration of the first embodiment simultaneously short-circuit, a large power of 2016 W (110 V×110 V÷6 Ω) will be supplied to the parallel heating elements (e.g., 6 Ω) of the heating elements 101 and 102. In this way, assuming simultaneous failure of multiple triacs 121 and 126, it can be said that the configuration of this embodiment is safer than the configuration of the first embodiment.

[0114] Furthermore, the second embodiment and the present embodiment are compared with respect to simultaneous short-circuit failures of the triacs 121 and 126. When a simultaneous short-circuit failure occurs in the triacs 121 and 126 in the present embodiment, power is supplied to the heater 300 through the fifth power supply path PSC5, and the temperature difference in the heater 300 becomes the temperature difference Δ1314 shown in FIG. 14(a). On the other hand, when a simultaneous short-circuit failure occurs in the triacs 111 and 116 in the second embodiment, power is supplied to the heater 200 through the third power supply path PSC3, and the temperature difference in the heater 200 becomes the temperature difference Δ910 shown in FIG. 10(a). Between the temperature difference Δ1314 and the temperature difference Δ910, the temperature difference Δ1314 is smaller. Therefore, when a simultaneous short-circuit failure of the triacs 121 and 126 is assumed, the thermal stress applied to the ceramic substrate 104 is smaller in the present embodiment than in the second embodiment. In this way, the configuration of this embodiment is superior to the first and second embodiments in terms of safety when simultaneous short-circuit failures of multiple triacs are assumed.

[0115] In this embodiment, it is possible to achieve the same effects as those of the first and second embodiments, namely, firstly, the noise filter 108 can be made smaller, secondly, flicker can be suppressed, thirdly, even-order harmonics can be reduced, fourthly, the heater can be heated in the shortest time without power loss, and fifthly, the temperature ripple of the heater 300 can be reduced.

[0116] In this embodiment, the resistance value of heating element 301 (about 8 Ω) is less than the resistance value of heating element 302 (about 16 Ω), but this relationship does not necessarily have to be the case. In the configuration of this embodiment, the effect is greater when the resistance value of heating element 301 is less than the resistance value of heating element 302 (contributing to shortening FPOT). However, the effect of the present invention can be obtained even when the resistance values ​​of heating element 301 and heating element 302 are equal or when the resistance value of heating element 301 is greater than the resistance value of heating element 302. Therefore, the relationship in the resistance values ​​of heating elements 301 and 302 does not limit the configuration of this embodiment.

[0117] <Fourth embodiment> [Heater control circuit and heater according to the fourth embodiment] Next, a fourth embodiment will be described with reference to Figs. 15(a) to 16. Fig. 15(a) is a diagram showing a heater control circuit 470 and a heater 400 included in the fixing unit 20 (see Fig. 2) of the present embodiment. Fig. 15(b) is a cross-sectional view showing a 15B-15B cross section of the heater 400. Fig. 16 is a diagram showing an image of temperature distribution in the longitudinal direction LD of the heater 400.

[0118] The heater 400 shown in Fig. 15(a) is almost the same as the heater 300 of the third embodiment, but differs from the configuration of the third embodiment only in the length of the heating element. Also, the heater control circuit 470 according to the fourth embodiment is similar to the heater control circuit 370 according to the third embodiment. Therefore, the contents of the third embodiment described using Figs. 12(a) to 14(b) are common to the fourth embodiment, and the description thereof will be omitted.

[0119] 15(a) and 15(b) mainly comprises a commercial AC power supply 110, a current fuse 109, an electromagnetic relay 107, a noise filter 108, triacs 111 and 116, and a heater 400. The heater 400 has a heating element 401 as a first heating element, and a heating element 402 as a second heating element. The operations of the triacs 111 and 116 and their drive circuits are the same as those of the triacs 121 and 126 in the first embodiment, and therefore will not be described.

[0120] 16, the length of the heat generating element 401 in the longitudinal direction LD is about 2 mm longer than the LTR paper width (215.9 mm). The length of the heat generating element 402 in the longitudinal direction LD is set to be about 2 mm shorter than the A4 paper width (210 mm). That is, in the present embodiment, the heat generating element 401 is longer than the heat generating element 402 in the longitudinal direction LD.

[0121] In the process of heating the fixing unit 20 (see FIG. 2) in a cold state (see, for example, period I in FIG. 13), the fifth power supply path PSC5 shown in FIG. 12(a) is used, and power is supplied only to the heating element 401. Therefore, as shown by the solid line in the graph of FIG. 16, the temperature is high up to the end of the heater 400 in the longitudinal direction LD. In the process of heating the fixing unit 20 in a cold state, heat is dissipated from the ceramic substrate 104 and the pressure roller 22 (see FIG. 2) in the range L shown in FIG. 16. Therefore, the temperature does not rise sufficiently at the end of the heater 400 in the longitudinal direction LD, and fixing failure may occur at the end of the sheet in the longitudinal direction LD that has passed through the fixing unit 20.

[0122] For this reason, in the process of heating the fixing unit 20, it is desirable to heat as wide an area as possible in the longitudinal direction LD of the heater 400. In the present embodiment, this is achieved by making the length of the heating element 401 about 2 mm longer than the LTR paper width, which is the maximum width of the sheet that can be conveyed to the fixing unit 20, to prevent poor fixing at the edges of the LTR paper.

[0123] On the other hand, in this embodiment, when the fixing unit 20 (see FIG. 2) is near the target temperature Ta shown in FIG. 13, the sixth power supply path PSC6 is used, and power is supplied to the heat elements 401 and 402 connected in series. Since the heat element 402 has a higher resistance value than the heat element 401, the power (voltage) applied to the heat element 402 is greater than the power (voltage) applied to the heat element 401. For this reason, as shown by the dashed line in the graph of FIG. 16, the temperature of the end portion of the heater 400 in the longitudinal direction LD is slightly lower than when the heater 400 is heated using the fifth power supply path PSC5.

[0124] When the fixing unit 20 (see FIG. 2) is sufficiently warmed up (for example, see period K in FIG. 13), in the area where the area where the heating elements (401, 402) of the heater 400 generate heat does not overlap with the paper width, the heating elements become in a dry-fire state, and temperature rise in non-paper passing areas becomes a problem. Therefore, when the fixing unit 20 is sufficiently warmed up, the length in the longitudinal direction LD of the heating element 402 is optimized by being slightly shorter than the A4 paper width so that temperature rise in non-paper passing areas does not become a problem even when A4 paper is passed through.

[0125] In this way, by using the configuration of this embodiment, in addition to the effects described in the third embodiment, it is possible to achieve both the suppression of poor fixing performance at the ends of the heater 400 in the longitudinal direction LD and the suppression of temperature rise in non-paper passing areas.

[0126] In this embodiment, the heating elements 401 and 402 are configured so that the length of the heating element 401 in the longitudinal direction LD is greater than the length of the heating element 402 in the longitudinal direction LD, but the specific dimensions are not particularly limited.

[0127] <Other embodiments> In any of the above-described embodiments, the heaters 100, 200, 300, and 400 are in direct contact with the fixing film 21c, but this is not limiting. For example, the heaters 100, 200, 300, and 400 may be in contact with the fixing film 21c via a sheet material having high thermal conductivity, such as an iron alloy or aluminum. Even if such a sheet material is provided between the heaters 100, 200, 300, and 400 and the fixing film 21c, the pressure roller 22 sandwiches the fixing film 21c together with the heaters 100, 200, 300, and 400.

[0128] In addition, in any of the above-described embodiments, a triac is used as a semiconductor switch for switching the power supply path, but the present invention is not limited to this. For example, a transistor such as a bipolar transistor may be used as the semiconductor switch.

[0129] In addition, in any of the above-described embodiments, the heater substrate is made of a ceramic substrate having a ceramic base material, but is not limited thereto. For example, instead of the ceramic substrate, a metal substrate made of a combination of a metal and an insulating member may be used.

[0130] Moreover, the above-mentioned first to fourth embodiments may be arbitrarily combined. For example, the heat generating element 101 in the first embodiment may be formed to be longer than the heat generating element 102.

[0131] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0132] The disclosure of the present embodiment also includes the following configuration examples and method examples. (Configuration 1) An image heating device for heating a toner image formed on a sheet, the image heating device comprising: a fixing member; a heater for heating the fixing member; and a heater control circuit for controlling the heater, The heater includes a substrate and a heating unit that is provided on the substrate and generates heat when electricity is applied thereto; the heater control circuit includes a first power supply path that supplies a first power to the heat generating unit, a second power supply path that supplies a second power smaller than the first power to the heat generating unit, and a switch unit including a semiconductor switch having a plurality of semiconductors, the switch unit selectively switching between the first power supply path and the second power supply path by operation of the semiconductor switch. 1. An image heating apparatus comprising: (Configuration 2) The semiconductor switch is a triac. 2. An image heating apparatus according to configuration 1, (Configuration 3) the heater control circuit includes a zero-cross detection unit that detects a passage of a zero point of a voltage of an AC power supply connected to the first power supply path and the second power supply path, the switch unit selectively switches between the first power supply path and the second power supply path at a timing when the zero-cross detection unit detects a passage of a zero point of the voltage of the AC power supply. 3. An image heating apparatus according to configuration 2. (Configuration 4) the heater control circuit has a phototriac coupler that switches the triac between a conductive state and a non-conductive state, The phototriac coupler has a zero-cross detection circuit as the zero-cross detection unit. 4. An image heating apparatus according to configuration 3. (Configuration 5) the switch unit selectively switches between the first power supply path and the second power supply path when a phase angle of an AC power source connected to the first power supply path and the second power supply path is 0° or 180°; 5. The image heating apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. (Configuration 6) The heating unit includes a first heating element and a second heating element that generate heat when electricity is applied thereto, The first power supply path and the second power supply path are different from each other in at least a part of targets to which power is supplied among the first heating element and the second heating element. 6. An image heating apparatus according to any one of configurations 1 to 5. (Configuration 7) the first heating element and the second heating element extend in a longitudinal direction perpendicular to a short-side direction parallel to a sheet conveying direction, the first heating element has a first heating portion disposed at one end of the substrate in the short side direction and a second heating portion disposed at the other end of the substrate in the short side direction, The second heat generating element is disposed between the first heat generating portion and the second heat generating portion in the short side direction. 7. The image heating apparatus according to configuration 6, (Configuration 8) The second heating element has a third heating portion and a fourth heating portion each extending in the longitudinal direction and aligned in the lateral direction. 8. An image heating apparatus according to configuration 7. (Configuration 9) the semiconductor switch is a first semiconductor switch, the switch unit includes a second semiconductor switch having a plurality of semiconductors; the first heating element is connected in series with the first semiconductor switch; the second heating element is connected in series with the second semiconductor switch; the first heating element and the first semiconductor switch are connected in parallel to the second heating element and the second semiconductor switch; the switch unit selects the first power supply path by putting the first semiconductor switch in a conductive state and the second semiconductor switch in a non-conductive state, and selects the second power supply path by putting the first semiconductor switch in a non-conductive state and the second semiconductor switch in a conductive state. 9. The image heating apparatus according to configuration 7 or 8, (Configuration 10) The resistance value of the first heating element is smaller than the resistance value of the second heating element. 10. An image heating apparatus according to configuration 9. (Configuration 11) the switch unit selects the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature. 11. The image heating apparatus according to configuration 9 or 10. (Configuration 12) the semiconductor switch is connected in series with the second heating element; the first heating element is connected in parallel to the second heating element and the semiconductor switch; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state. 9. The image heating apparatus according to configuration 7 or 8, (Configuration 13) The resistance value of the first heating element is greater than the resistance value of the second heating element. 13. An image heating apparatus according to configuration 12, (Configuration 14) the switch unit selects the second power supply path and then switches to the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature. 14. The image heating apparatus according to configuration 12 or 13, (Configuration 15) the semiconductor switch is connected in parallel to the second heating element; the first heating element is connected in series with the semiconductor switch and the second heating element which are connected in parallel; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state. 9. The image heating apparatus according to configuration 7 or 8, (Configuration 16) The resistance value of the first heating element is smaller than the resistance value of the second heating element. 16. An image heating apparatus according to configuration 15, (Configuration 17) the switch unit selects the second power supply path and then switches to the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature. 17. The image heating apparatus according to configuration 15 or 16, (Configuration 18) The lengths of the first heating element and the second heating element in the longitudinal direction are the same. 18. The image heating apparatus according to any one of configurations 7 to 17. (Configuration 19) In the longitudinal direction, the first heating element is longer than the second heating element. 18. The image heating apparatus according to any one of configurations 7 to 17. (Configuration 20) The substrate is a ceramic substrate based on ceramic. 20. An image heating apparatus according to any one of configurations 1 to 19. (Configuration 21) An image heating device for heating a toner image formed on a sheet, the image heating device comprising: a fixing member; a heater for heating the fixing member; and a heater control circuit for controlling the heater, The heater includes a substrate and a heating unit that is provided on the substrate and generates heat when electricity is applied thereto; The heating unit includes a first heating element and a second heating element, each of which extends in a longitudinal direction perpendicular to a short-side direction parallel to a sheet conveying direction and generates heat when electricity is applied thereto; the first heating element has a first heating portion disposed at one end of the substrate in the short side direction and a second heating portion disposed at the other end of the substrate in the short side direction, the second heat generating element is disposed between the first heat generating portion and the second heat generating portion in the short side direction, the heater control circuit includes a first power supply path that supplies a first power to the heat generating unit, a second power supply path that supplies a second power smaller than the first power to the heat generating unit, and a switch unit that selectively switches between the first power supply path and the second power supply path; 1. An image heating apparatus comprising: (Configuration 22) the switch unit selects at least the first power supply path during a period when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path during a period when the temperature of the heater is higher than the predetermined temperature. 22. An image heating apparatus according to configuration 21, (Configuration 23) The second heating element has a third heating portion and a fourth heating portion each extending in the longitudinal direction and aligned in the lateral direction. 23. The image heating apparatus according to configuration 21 or 22. (Configuration 24) The switch unit includes a first semiconductor switch and a second semiconductor switch, each of which includes a plurality of semiconductors; the first heating element is connected in series with the first semiconductor switch; the second heating element is connected in series with the second semiconductor switch; the first heating element and the first semiconductor switch are connected in parallel to the second heating element and the second semiconductor switch; the switch unit selects the first power supply path by putting the first semiconductor switch in a conductive state and the second semiconductor switch in a non-conductive state, and selects the second power supply path by putting the first semiconductor switch in a non-conductive state and the second semiconductor switch in a conductive state. 24. The image heating apparatus according to any one of configurations 21 to 23. (Configuration 25) the first power supply path supplies the first power to the first heating element and does not supply power to the second heating element; the second power supply path supplies the second power to the second heating element and does not supply power to the first heating element; 25. An image heating apparatus according to configuration 24. (Configuration 26) The resistance value of the first heating element is smaller than the resistance value of the second heating element. 26. The image heating apparatus according to configuration 24 or 25. (Configuration 27) the switch unit includes a semiconductor switch having a plurality of semiconductors and connected in series to the second heating element, the first heating element is connected in parallel to the second heating element and the semiconductor switch; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state. 24. The image heating apparatus according to any one of configurations 21 to 23. (Configuration 28) the first power supply path supplies the first power to the first heating element and the second heating element; the second power supply path supplies the second power to the first heating element and does not supply power to the second heating element; 28. An image heating apparatus according to configuration 27, (Configuration 29) The resistance value of the first heating element is greater than the resistance value of the second heating element. 29. The image heating apparatus according to configuration 27 or 28. (Configuration 30) the switch unit includes a semiconductor switch having a plurality of semiconductors and connected in parallel to the second heating element, the first heating element is connected in series with the semiconductor switch and the second heating element which are connected in parallel; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state. 24. The image heating apparatus according to any one of configurations 21 to 23. (Configuration 31) the first power supply path supplies the first power to the first heating element and does not supply power to the second heating element; the second power supply path supplies the second power to the first heating element and the second heating element; 31. The image heating apparatus according to configuration 30, (Configuration 32) The resistance value of the first heating element is smaller than the resistance value of the second heating element. 32. The image heating apparatus according to configuration 30 or 31, (Configuration 33) the switch unit selects the second power supply path and then switches to the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature. 33. The image heating apparatus according to any one of configurations 30 to 32. (Configuration 34) The lengths of the first heating element and the second heating element in the longitudinal direction are the same. 34. The image heating apparatus according to any one of configurations 21 to 33. (Configuration 35) In the longitudinal direction, the first heating element is longer than the second heating element. 34. The image heating apparatus according to any one of configurations 21 to 33. (Configuration 36) The substrate is a ceramic substrate based on ceramic. 36. An image heating apparatus according to any one of configurations 21 to 35. (Configuration 37) The fixing member is a cylindrical film. 37. The image heating apparatus according to any one of configurations 1 to 36, (Configuration 38) an image forming unit that forms a toner image on a sheet; An image heating apparatus according to any one of configurations 1 to 37, a pressure member that heats and presses the sheet together with the image heating device to fix the toner image on the sheet, 1. An image forming apparatus comprising: [Explanation of symbols]

[0133] 20: image heating device (fixing unit) / 21c: fixing member (fixing film) / 22: pressure member (pressure roller) / 50: image forming section / 80: image forming device / 91: heat generating unit / 100, 200, 300, 400: heater / 101, 201, 203, 401: first heat generating element (heat generating element) / 101a: first heat generating section (heat generating section) / 101b: second heat generating section (heat generating section) / 102, 202, 302, 402: second heat generating element (heat generating element) / 102a: third heat generating section (heat generating section) / 102b: fourth heat generating section (heat generating section) / 104: substrate (ceramic substrate) / 110: AC power power source (commercial AC power source) / 121: semiconductor switch, first semiconductor switch (triac) / 122: phototriac coupler / 122c: zero-cross detection unit, zero-cross detection circuit / 136: semiconductor switch (triac) / 170, 270, 370, 470: heater control circuit / 191, 192, 193: switch unit / PSC1, PSC3, PSC5: first power supply path (first power supply path, third power supply path, fifth power supply path) / PSC2, PSC4, PSC6: second power supply path (second power supply path, fourth power supply path, sixth power supply path)

Claims

1. An image heating device for heating a toner image formed on a sheet, the image heating device comprising: a fixing member; a heater for heating the fixing member; and a heater control circuit for controlling the heater, The heater includes a substrate and a heating unit that is provided on the substrate and generates heat when electricity is applied thereto; the heater control circuit includes a first power supply path that supplies a first power to the heat generating unit, a second power supply path that supplies a second power smaller than the first power to the heat generating unit, and a switch unit that includes a semiconductor switch having a plurality of semiconductors and selectively switches between the first power supply path and the second power supply path by operation of the semiconductor switch; 1. An image heating apparatus comprising:

2. The semiconductor switch is a triac.

2. An image heating apparatus according to claim 1, wherein the image heating apparatus comprises:

3. the heater control circuit includes a zero-cross detection unit configured to detect a passage of a zero point of a voltage of an AC power supply connected to the first power supply path and the second power supply path, the switch unit selectively switches between the first power supply path and the second power supply path at a timing when the zero-cross detection unit detects a passage of a zero point of the voltage of the AC power supply; 3. The image heating apparatus according to claim 2,

4. the heater control circuit has a phototriac coupler that switches the triac between a conductive state and a non-conductive state, The phototriac coupler has a zero-cross detection circuit as the zero-cross detection unit.

4. The image heating apparatus according to claim 3.

5. the switch unit selectively switches between the first power supply path and the second power supply path when a phase angle of an AC power source connected to the first power supply path and the second power supply path is 0° or 180°; 2. An image heating apparatus according to claim 1, wherein the image heating apparatus comprises:

6. The heating unit includes a first heating element and a second heating element that generate heat when electricity is applied thereto, The first power supply path and the second power supply path are different from each other in at least a part of targets to which power is supplied among the first heating element and the second heating element.

2. An image heating apparatus according to claim 1, wherein the image heating apparatus comprises:

7. the first heating element and the second heating element extend in a longitudinal direction perpendicular to a short side direction parallel to a sheet conveying direction, the first heating element has a first heating portion disposed at one end of the substrate in the short side direction and a second heating portion disposed at the other end of the substrate in the short side direction, The second heat generating element is disposed between the first heat generating portion and the second heat generating portion in the short side direction.

7. An image heating apparatus according to claim 6.

8. The second heating element includes a third heating portion and a fourth heating portion each extending in the longitudinal direction and aligned in the lateral direction.

8. An image heating apparatus according to claim 7.

9. the semiconductor switch is a first semiconductor switch, The switch unit includes a second semiconductor switch having a plurality of semiconductors, the first heating element is connected in series with the first semiconductor switch; the second heating element is connected in series with the second semiconductor switch; the first heating element and the first semiconductor switch are connected in parallel to the second heating element and the second semiconductor switch; the switch unit selects the first power supply path by putting the first semiconductor switch in a conductive state and the second semiconductor switch in a non-conductive state, and selects the second power supply path by putting the first semiconductor switch in a non-conductive state and the second semiconductor switch in a conductive state.

8. An image heating apparatus according to claim 7.

10. The resistance value of the first heating element is smaller than the resistance value of the second heating element.

10. An image heating apparatus according to claim 9.

11. the switch unit selects the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature.

10. An image heating apparatus according to claim 9.

12. the semiconductor switch is connected in series with the second heating element; the first heating element is connected in parallel to the second heating element and the semiconductor switch; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state.

8. An image heating apparatus according to claim 7.

13. The resistance value of the first heating element is greater than the resistance value of the second heating element.

13. The image heating apparatus according to claim 12.

14. the switch unit selects the second power supply path and then switches to the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature.

13. The image heating apparatus according to claim 12.

15. the semiconductor switch is connected in parallel to the second heating element; the first heating element is connected in series with the semiconductor switch and the second heating element which are connected in parallel; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state.

8. An image heating apparatus according to claim 7.

16. The resistance value of the first heating element is smaller than the resistance value of the second heating element.

16. An image heating apparatus according to claim 15.

17. the switch unit selects the second power supply path and then switches to the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature.

16. An image heating apparatus according to claim 15.

18. The lengths of the first heating element and the second heating element in the longitudinal direction are the same.

8. An image heating apparatus according to claim 7.

19. In the longitudinal direction, the first heating element is longer than the second heating element.

8. An image heating apparatus according to claim 7.

20. The substrate is a ceramic substrate based on ceramic.

2. An image heating apparatus according to claim 1, wherein the image heating apparatus comprises:

21. An image heating device for heating a toner image formed on a sheet, the image heating device comprising: a fixing member; a heater for heating the fixing member; and a heater control circuit for controlling the heater, The heater includes a substrate and a heating unit that is provided on the substrate and generates heat when electricity is applied thereto; the heating unit includes a first heating element and a second heating element, each of which extends in a longitudinal direction perpendicular to a short-side direction parallel to a sheet conveying direction and generates heat when electricity is applied thereto; the first heating element has a first heating portion disposed at one end of the substrate in the short side direction and a second heating portion disposed at the other end of the substrate in the short side direction, the second heat generating element is disposed between the first heat generating portion and the second heat generating portion in the short side direction, the heater control circuit includes a first power supply path that supplies a first power to the heat generating unit, a second power supply path that supplies a second power smaller than the first power to the heat generating unit, and a switch unit that selectively switches between the first power supply path and the second power supply path.

1. An image heating apparatus comprising:

22. the switch unit selects at least the first power supply path during a period when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path during a period when the temperature of the heater is higher than the predetermined temperature.

22. An image heating apparatus according to claim 21.

23. The second heating element includes a third heating portion and a fourth heating portion each extending in the longitudinal direction and aligned in the lateral direction.

22. An image heating apparatus according to claim 21.

24. The switch unit includes a first semiconductor switch and a second semiconductor switch, each of which includes a plurality of semiconductors; the first heating element is connected in series with the first semiconductor switch; the second heating element is connected in series with the second semiconductor switch; the first heating element and the first semiconductor switch are connected in parallel to the second heating element and the second semiconductor switch; the switch unit selects the first power supply path by putting the first semiconductor switch in a conductive state and the second semiconductor switch in a non-conductive state, and selects the second power supply path by putting the first semiconductor switch in a non-conductive state and the second semiconductor switch in a conductive state.

22. An image heating apparatus according to claim 21.

25. the first power supply path supplies the first power to the first heating element and does not supply power to the second heating element; the second power supply path supplies the second power to the second heating element and does not supply power to the first heating element; 25. An image heating apparatus according to claim 24.

26. The resistance value of the first heating element is smaller than the resistance value of the second heating element.

25. An image heating apparatus according to claim 24.

27. the switch unit includes a semiconductor switch having a plurality of semiconductors and connected in series to the second heating element, the first heating element is connected in parallel to the second heating element and the semiconductor switch; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state.

22. An image heating apparatus according to claim 21.

28. the first power supply path supplies the first power to the first heating element and the second heating element; the second power supply path supplies the second power to the first heating element and does not supply power to the second heating element; 28. An image heating apparatus according to claim 27.

29. The resistance value of the first heating element is greater than the resistance value of the second heating element.

28. An image heating apparatus according to claim 27.

30. the switch unit includes a semiconductor switch having a plurality of semiconductors and connected in parallel to the second heating element, the first heating element is connected in series with the semiconductor switch and the second heating element which are connected in parallel; the switch unit selects the first power supply path by bringing the semiconductor switch into a conductive state, and selects the second power supply path by bringing the semiconductor switch into a non-conductive state.

22. An image heating apparatus according to claim 21.

31. the first power supply path supplies the first power to the first heating element and does not supply power to the second heating element; the second power supply path supplies the second power to the first heating element and the second heating element; 31. The image heating apparatus according to claim 30.

32. The resistance value of the first heating element is smaller than the resistance value of the second heating element.

31. The image heating apparatus according to claim 30.

33. the switch unit selects the second power supply path and then switches to the first power supply path when the temperature of the heater is lower than a predetermined temperature, and selects the second power supply path when the temperature of the heater is higher than the predetermined temperature.

31. The image heating apparatus according to claim 30.

34. The lengths of the first heating element and the second heating element in the longitudinal direction are the same.

22. An image heating apparatus according to claim 21.

35. In the longitudinal direction, the first heating element is longer than the second heating element.

22. An image heating apparatus according to claim 21.

36. The substrate is a ceramic substrate based on ceramic.

22. An image heating apparatus according to claim 21.

37. The fixing member is a cylindrical film.

37. An image heating apparatus according to claim 1, wherein the image heating apparatus is a heater.

38. an image forming unit that forms a toner image on a sheet; An image heating apparatus according to any one of claims 1 to 36, a pressure member that heats and presses the sheet together with the image heating device to fix the toner image on the sheet, 1. An image forming apparatus comprising:

Images