Image heating device and heater for use in image heating device

Abstract

To provide a heater and an image heating device capable of suppressing temperature rising at a non-paper feed part when subjecting heating treatment to an image formed on recording material with small size.SOLUTION: A heater includes a plurality of heating blocks, in a longitudinal direction, which can be independently controlled and includes a pair of a first conductor, a second conductor, and a heating element. At least one of electrodes corresponding to the respective heating blocks is disposed, in a longitudinal direction, in a region disposed with the heating elements.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image heating device such as a fixing device mounted in an electrophotographic image forming apparatus such as a copying machine or a printer, or a gloss imparting device that improves the glossiness of a toner image fixed on a recording material by reheating the toner image, and also to a heater used in such an image heating device. [Background technology]

[0002] One image heating device has an endless belt (also called an endless film), a heater that contacts the inner surface of the endless belt, and a roller that forms a nip with the heater via the endless belt. When small-size paper is continuously printed on an image forming device equipped with this image heating device, a phenomenon occurs in which the temperature of the area in the longitudinal direction of the nip where the paper does not pass gradually rises (non-paper-passing area temperature rise). If the temperature of the non-paper-passing area becomes too high, it can damage various parts within the device, and if large-size paper is printed on while the non-paper-passing area temperature rise has occurred, toner can be high-temperature offset onto the endless belt in the area corresponding to the non-paper-passing area of ​​the small-size paper.

[0003] One method for suppressing the temperature rise in the non-paper-passing areas is to form the heating resistor (hereinafter referred to as the heating element) on the heater substrate from a material with a positive resistance-temperature characteristic. It has been considered to arrange two conductors at both ends of the substrate's short side so that current flows to the heating element in the short side direction of the heater (the paper transport direction) (hereinafter referred to as transport direction power supply) (Patent Document 1). The idea is that when the temperature of the non-paper-passing areas rises, the resistance value of the heating element in the non-paper-passing areas rises, suppressing the current flowing to the heating element in the non-paper-passing areas and thereby suppressing heat generation in the non-paper-passing areas. The positive resistance-temperature characteristic is a characteristic in which resistance increases as temperature rises, and is hereinafter referred to as PTC (Positive Temperature Coefficient). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-151003 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even in such a heater, current flows through the heating element located in the non-paper passing area.

[0006] An object of the present invention is to provide a heater and an image heating device that can further suppress temperature rise in non-sheet passing areas while preventing an increase in the size of the heater. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention provides: an endless belt; a heater provided in the internal space of the endless belt, the heater having a long, narrow substrate and a plurality of heat-generating blocks arranged on the substrate in the longitudinal direction of the substrate and generating heat when power is supplied thereto; and a roller in contact with the outer surface of the endless belt, the roller sandwiching the endless belt together with the heater and forming a nip portion between the heater and the endless belt to sandwich and transport a recording material; wherein the heat generation distribution of the heater in the longitudinal direction can be switched by controlling the power supplied to the plurality of heat-generating blocks, and the image heating device heats an image formed on the recording material while sandwiching and transporting the recording material in the nip portion; the plurality of heat-generating blocks include a first heat-generating block located at a position including a reference position for transporting the recording material in the longitudinal direction, and a second heat-generating block located adjacent to the first heat-generating block in the longitudinal direction; and the fixing device further includes a temperature detection element for detecting the temperature of the second heat-generating block, the temperature detection element being located in an area farther from the first heat-generating block than the center of the second heat-generating block in the longitudinal direction.

[0008] The present invention also provides a heater having a substrate, a first conductor arranged on the substrate along the longitudinal direction of the substrate, a second conductor arranged on the substrate along the longitudinal direction at a different position in the short direction of the substrate from the first conductor, and a heating element arranged between the first conductor and the second conductor and generating heat using power supplied via the first conductor and the second conductor, wherein the heater has a plurality of independently controllable heating blocks in the longitudinal direction, each consisting of a set of the first conductor, the second conductor, and the heating element, and at least one of the electrodes corresponding to each of the heating blocks is arranged within the area in the longitudinal direction where the heating element is provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. [Figure 2] FIG. 1 is a cross-sectional view of an image heating apparatus according to a first embodiment. [Figure 3] FIG. 2 is a diagram showing the heater configuration of the first embodiment. [Figure 4] FIG. 2 is a diagram of a heater control circuit according to the first embodiment. [Figure 5]3 is a flowchart of heater control according to the first embodiment. [Figure 6] 5A and 5B are diagrams illustrating the effect of suppressing the temperature rise of non-sheet passing portions of the heater in the first embodiment. [Figure 7] FIG. 10 is a diagram showing the heater configuration of the second embodiment. [Figure 8] FIG. 10 is a diagram of a heater control circuit according to a second embodiment. [Figure 9] 10 is a flowchart of heater control according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing the heater configuration of the third embodiment. [Figure 11] FIG. 10 is a diagram showing the heater configuration of the fourth embodiment. [Figure 12] FIG. 10 is a diagram showing the heater configuration of the fifth embodiment. [Figure 13] FIG. 10 is a diagram showing the heater configuration of the sixth embodiment. [Figure 14] FIG. 13 is a diagram for explaining the effect of the seventh embodiment. [Figure 15] FIG. 13 is a diagram showing the heater configuration of the seventh embodiment. [Figure 16] FIG. 13 is a diagram showing the heater configuration of a modified example of the seventh embodiment. [Figure 17] FIG. 13 is a diagram showing the heater configuration of the eighth embodiment. [Figure 18] FIG. 13 is a diagram showing the heater configuration of the ninth embodiment. [Figure 19] FIG. 20 is a diagram showing the heater configuration of the tenth embodiment. [Figure 20] FIG. 20 is a diagram showing the heater configuration of the eleventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Example 1 1 is a cross-sectional view of a laser printer (image forming apparatus) 100 that uses electrophotographic recording technology. When a print signal is generated, a scanner unit 21 emits laser light modulated according to image information, and the laser light scans a photosensitive member 19 that has been charged to a predetermined polarity by a charging roller 16. As a result, an electrostatic latent image is formed on the photoreceptor 19. Toner is supplied from the developing device 17 to this electrostatic latent image, and a toner image corresponding to the image information is formed on the photoreceptor 19. Meanwhile, recording materials (recording sheets) P ​​loaded in the paper feed cassette 11 are fed one by one by the pickup roller 12 and transported toward the registration rollers 14 by rollers 13. The recording material P is then transported from the registration rollers 14 to the transfer position in time with the toner image on the photoreceptor 19 reaching the transfer position formed by the photoreceptor 19 and the transfer roller 20. As the recording material P passes the transfer position, the toner image on the photoreceptor 19 is transferred to the recording material P. The recording material P is then heated by the image heating device 200, and the toner image is thermally fixed to the recording material P. The recording material P bearing the fixed toner image is then ejected by rollers 26 and 27 onto a tray at the top of the laser printer 100. Reference numeral 18 denotes a cleaner that cleans the photosensitive member 19, and 28 denotes a paper feed tray (manual feed tray) that has a pair of recording material regulating plates whose width can be adjusted according to the size of the recording material P. The paper feed tray 28 is provided to accommodate recording materials P of sizes other than standard sizes. 29 denotes a pickup roller that feeds the recording material P from the paper feed tray 28, and 30 denotes a motor that drives the image heating device 200 and the like. Power is supplied to the image heating device 200 from a control circuit 400 that is connected to a commercial AC power source 401. The photosensitive member 19, charging roller 16, scanner unit 21, developing device 17, and transfer roller 20 described above constitute an image forming unit that forms an unfixed image on the recording material P.

[0011] The laser printer 100 of this embodiment is compatible with multiple recording material sizes. The paper feed cassette 11 can accommodate Letter paper (approximately 216 mm x 279 mm), Legal paper (approximately 216 mm x 356 mm), A4 paper (210 mm x 297 mm), and Executive paper (approximately 184 mm x 267 mm). It can also accommodate JIS B5 paper (182 mm x 257 mm) and A5 paper (148 mm x 210 mm).

[0012] In addition, non-standard size paper, including DL envelopes (110 mm x 220 mm) and COM10 envelopes (approximately 105 mm x 241 mm), can be fed from the paper feed tray 28 and printed on. The printer in this example is a laser printer that basically feeds paper vertically (conveys the paper with the long side parallel to the transport direction). The widest (largest) standard widths of recording materials (catalog widths) compatible with the device are Letter paper and Legal paper, which are approximately 216 mm wide. In this example, recording material P with a paper width smaller than the maximum size compatible with the device is defined as small size paper.

[0013] FIG. 2 is a cross-sectional view of image heating apparatus 200. Image heating apparatus 200 has a cylindrical film (endless belt) 202, a heater 300 in contact with the inner surface of film 202, and a pressure roller (nip portion forming member) 208 that forms a fixing nip portion N with heater 300 via film 202. The base layer of film 202 is made of a heat-resistant resin such as polyimide or a metal such as stainless steel. An elastic layer such as heat-resistant rubber may also be provided on the surface of film 202. Pressure roller 208 has a core metal 209 made of a material such as iron or aluminum, and an elastic layer 210 made of a material such as silicone rubber. Heater 300 is held by holding member 201 made of heat-resistant resin. Holding member 201 also has a guide function for guiding the rotation of film 202. Pressure roller 208 receives power from motor 30 and rotates in the direction of the arrow. As pressure roller 208 rotates, film 202 rotates accordingly. The recording material P bearing the unfixed toner image is heated and fixed while being nipped and conveyed through the fixing nip N.

[0014] As shown in Fig. 3(A), the heater 300 is heated by a heating element provided on a ceramic substrate 305. Thermistors TH1, TH2, TH3, and TH4 serving as temperature detection elements are in contact with the back side of the substrate 305 in the paper passage area of ​​the laser printer 100. A safety element 212 such as a thermoswitch or thermal fuse that is activated in the event of abnormal heat generation in the heater 300 to cut off power supplied to the heater 300 is also in contact with the back side of the substrate 305. Reference numeral 204 denotes a metal stay for applying pressure from a spring (not shown) to the holding member 201.

[0015] 3 shows a configuration diagram of the heater 300 of the embodiment 1. The configuration of the heater 300 and the effect of suppressing the temperature rise in the non-sheet passing portion will be described with reference to FIGS.

[0016] 3A shows a cross section of the heater 300 in the width direction. A first conductor 301 is provided on a substrate 305 in a layer 1 on the back surface of the heater 300 (the surface opposite to the surface that contacts the endless belt) along the longitudinal direction of the heater 300. Furthermore, a second conductor 303 is provided on the substrate 305 along the longitudinal direction of the heater 300 at a position different from the first conductor 301 in the width direction of the heater 300. The first conductor 301 is separated into a conductor 301a arranged on the upstream side in the conveying direction of the recording material P and a conductor 301b arranged on the downstream side.

[0017] Furthermore, the heater 300 is provided between a first conductor 301 and a second conductor 303, and has a heating element 302 that generates heat by power supplied via the first conductor 301 and the second conductor 303. The heating element 302 is separated into a heating element 302a arranged on the upstream side in the conveying direction of the recording material P, and a heating element 302b arranged on the downstream side.

[0018] If the heat generation distribution in the short side direction of the heater 300 (the conveying direction of the recording material) becomes asymmetric, the stress generated in the substrate 305 when the heater 300 generates heat increases. If the stress generated in the substrate 305 increases, cracks may occur in the substrate 305. For this reason, the heat generation element 302 is separated into a heat generation element 302a arranged on the upstream side in the conveying direction and a heat generation element 302b arranged on the downstream side, so that the heat generation distribution in the short side direction of the heater 300 becomes symmetric.

[0019] Additionally, layer 2 on the rear surface of heater 300 is provided with insulating (glass in this embodiment) surface protection layer 307 that covers heating element 302, conductor 301, and conductor 303. Additionally, layer 1 on the sliding surface of heater 300 (the surface that comes into contact with the endless belt) has surface protection layer 308 made of sliding glass or polyimide coating.

[0020] FIG. 3(B) shows a plan view of each layer of the heater 300. The heater 300 has, on the backside layer 1, a plurality of heat generating blocks arranged in the longitudinal direction of the heater 300, each of which is made up of a set of a first conductor 301, a second conductor 303, and a heat generating element 302. As an example, the heater 300 of this embodiment has a total of three heat generating blocks, located in the center and both ends of the heater 300 in the longitudinal direction. The first heat generating block 302-1 is made up of heat generating elements 302a-1 and 302b-1, which are formed symmetrically in the short direction of the heater 300. Similarly, the second heat generating block 302-2 is made up of heat generating elements 302a-2 and 302b-2, and the third heat generating block 302-3 is made up of heat generating elements 302a-3 and 302b-3.

[0021] The first conductor 301 is provided along the longitudinal direction of the heater 300. The first conductor 301 is composed of conductor 301a connected to the heating elements (302a-1, 302a-2, 302a-3) and conductor 301b connected to the heating elements (302b-1, 302b-2, 302b-3).

[0022] The second conductor 303 provided along the longitudinal direction of the heater 300 is divided into three conductors 303-1, 303-2, and 303-3.

[0023] Electrodes E1, E2, E3, E4-1, and E4-2 are connected to electrical contacts for supplying power from a control circuit 400 of the heater 300, which will be described later. Electrode E1 is an electrode for supplying power to heat generating block 302-1 via conductor 303-1. Similarly, electrode E2 is an electrode used for supplying power to heat generating block 302-2 via conductor 303-2. Electrode E3 is an electrode for supplying power to heat generating block 302-3 via conductor 303-3. Electrodes E4-1 and E4-2 are electrodes connected to a common electrical contact for supplying power to the three heat generating blocks 302-1 to 303-3 via conductor 301a and conductor 301b.

[0024] However, the resistance value of the conductor is not zero, which affects the heat generation distribution in the longitudinal direction of the heater 300. Therefore, electrodes E4-1 and E4-2 are provided at both ends of the heater 300 in the longitudinal direction so that a symmetrical heat generation distribution in the longitudinal direction of the heater 300 can be obtained even when affected by the electrical resistance of the conductors 303-1, 303-2, 303-3, 301a, and 301b.

[0025] Furthermore, the surface protection layer 307 of layer 2 on the back surface of the heater 300 is formed except for the electrodes E1, E2, E3, E4-1, and E4-2, allowing electrical contacts to be connected to each electrode from the back surface of the heater 300. In this embodiment, electrodes E1, E2, E3, E4-1, and E4-2 are provided on the back surface of the heater 300, allowing power to be supplied from the back surface of the heater 300. Furthermore, the ratio of power supplied to at least one of the multiple heat generating blocks to the other heat generating blocks can be changed. Providing electrodes on the back surface of the heater 300 eliminates the need for wiring using a conductive pattern on the substrate 305, allowing the width of the substrate 305 in the short direction to be shortened. This reduces the material cost of the substrate 305 and shortens the warm-up time required for the heater 300 to heat up by reducing the thermal capacity of the substrate 305. The electrodes E1, E2, and E3 are provided in the region where the heating element is provided in the longitudinal direction of the substrate. The surface protection layer 308 of the sliding surface layer 1 of the heater 300 is provided in the region where it slides against the film 202.

[0026] 3(C), holes are provided in the holding member 201 of the heater 300 for electrical contacts of thermistors (temperature detection elements) TH1 to TH4, the safety element 212, and electrodes E1, E2, E3, E4-1, and E4-2. HTH1 to HTH4, H212, HE1 to HE3, HE4-1, and HE4-2 are the holes.

[0027] Between the stay 204 and the holding member 201 are provided the aforementioned thermistors (temperature detection elements) TH1 to TH4, the safety element 212, and electrical contacts in contact with the electrodes E1, E2, E3, E4-1, and E4-2. C1 to C3, C4-1, and C4-2 are electrical contacts. In FIG. 3C, the dashed lines connecting the electrical contacts C1 to C3, C4-1, and C4-2 and the dashed line connecting the safety element 212 all indicate power supply cables (AC lines). The dashed lines connecting the temperature detection elements TH1 to TH4 indicate signal lines (DC lines). These elements and electrical contacts are disposed facing the back surface of the heater 300. The electrical contacts in contact with the electrodes E1, E2, E3, E4-1, and E4-2 are electrically connected to the heater electrodes by spring biasing, welding, or other methods. Each electrical contact is connected to a control circuit 400 of the heater 300, which will be described later, via a cable (shown by the broken line above) or a conductive material such as a thin metal plate provided between the stay 204 and the holding member 201.

[0028] Power control for heater 300 is performed based on the output of thermistor TH1, which is located near the center of the sheet passing section (near transport reference position X, described later). Thermistor TH4 detects the temperature at the end of the heat generation area of ​​heat generation block 302-2 (the temperature at the end of the heat generation area in the state of FIG. 6(B)). Thermistor TH2 detects the temperature at the end of the heat generation area of ​​heat generation block 302-1 (the temperature at the end of the heat generation area in the state of FIG. 6(A)). Thermistor TH3 detects the temperature at the end of the heat generation area of ​​heat generation block 302-3 (the temperature at the end of the heat generation area in the state of FIG. 6(A)).

[0029] Furthermore, in the device of this embodiment, one or more thermistors are provided in each of the three heat generating blocks to detect a state in which power is supplied to only one heat generating block due to a malfunction or other reason, thereby enhancing the safety of the device. If only malfunctions of triac 416 and triac 426 are considered, at least one thermistor may be provided for each of the multiple independently controllable heat generating blocks (for example, in FIG. 3, only thermistors TH1 and TH2 are provided). In this embodiment, in addition to malfunctions of triac 416 and triac 426, one or more thermistors are provided in each of the three heat generating blocks to consider faults in the electrical contacts to each electrode. For example, if there is a fault in the electrical contact to electrode E1, power may not be supplied to heat generating block 302-1, but may be supplied to heat generating block 302-3. For this reason, both the heat generating block 302-1 and the heat generating block 302-3 are provided with thermistors TH2 and TH3.

[0030] In order to prevent malfunction due to a rise in temperature in non-paper passing areas, safety element 212 abuts against a portion of the paper passing area for the smallest size paper available and set in laser printer 100 (near the center of heat generating block 302-2), which is less affected by a rise in temperature in non-paper passing areas. This reduces the temperature of safety element 212 during normal operation, so the operating temperature of safety element 212 can be set low and the safety of image heating device 200 can be increased.

[0031] Next, the effect of suppressing temperature rise in non-paper passing areas of the heater 300 will be described using Figure 6. Figure 6(A) is a diagram explaining temperature rise in non-paper passing areas when power is supplied to all three heat generating blocks. This shows an example in which B5 paper is transported in the vertical direction with the center of the heat generating area as the reference. The reference position when transporting the recording material P is defined as the recording material P transport reference position X.

[0032] The paper feed cassette 11 has a position regulation plate that regulates the position of the recording material P, and feeds the recording material P from a predetermined position for each size of the loaded recording material P, and transports the recording material P so that it passes a predetermined position in the image heating device 200. Similarly, the paper feed tray 28 has a position regulation plate that regulates the position of the recording material P, and transports the recording material P so that it passes a predetermined position in the image heating device 200.

[0033] The heater 300 has a heating area length of 220 mm for a paper width of approximately 216 mm to accommodate letter paper being transported vertically. When B5 paper, 182 mm wide, is transported vertically through the heater 300 with a heating area length of 220 mm, 19 mm non-paper-passing areas are created at both ends of the heating area. Power control to the heater 300 is performed so that the detected temperature of the thermistor TH1 located near the center of the paper-passing area maintains the target temperature. However, because the paper does not absorb heat in the non-paper-passing areas, the temperature in the non-paper-passing areas is higher than in the paper-passing areas. As shown in Figure 6(A), for B5-sized paper, the edge of the recording material P passes through a portion of the heating blocks 302-1 and 302-3 at both ends, creating 19 mm non-paper-passing areas at each end. However, because the heating element 302 is a PTC, the resistance of the heating element in the non-paper-passing areas is higher than that of the heating element in the paper-passing areas, making it difficult for current to flow. This principle prevents the temperature from rising in the non-paper-passing areas.

[0034] FIG. 6B illustrates the temperature rise in the non-paper-passing area when power is supplied only to the central heat-generating block 302-2 of the heater 300. This figure shows an example of a 110 mm-wide DL-size envelope being conveyed vertically, based on the center of the heat-generating area. The heat-generating block 302-2 of the heater 300 has a heat-generating area length of 157 mm for a paper width of 148 mm to accommodate A5 paper being conveyed vertically. When a 110 mm-wide DL-size envelope is conveyed vertically on the heater 300 with the central heat-generating block 302-2 having a length of 157 mm, a 23.5 mm non-paper-passing area is created at both ends of the central heat-generating block 302-2. The heater 300 is controlled based on the output of the thermistor TH1 located near the center of the paper-passing area. Because the paper does not absorb heat in the non-paper-passing area, the temperature in the non-paper-passing area rises compared to the paper-passing area. In the state shown in Figure 6(B), the impact of the non-paper passing area can be reduced by first supplying power only to heat generating block 302-2. Generally, the longer the non-paper passing area, the worse the temperature rise in the non-paper passing area. Therefore, the effect of supplying power to PTC heat generating element 302 in the conveyance direction alone may not be enough to suppress the temperature rise in the non-paper passing area. Therefore, as shown in Figure 6(B), it is effective to shorten the length of the non-paper passing area as much as possible. Furthermore, the temperature rise in the non-paper passing area of ​​23.5 mm at both ends of the central heat generating block 302-2 can be suppressed using the same principle as in Figure 6(A).

[0035] 6B, the effect of suppressing the temperature rise in the non-sheet-passing area when power is supplied only to the heat generating block 302-2 in the center of the heater 300 can be obtained even when the heat generating element 302 does not have a positive resistance temperature coefficient (PTC). Therefore, this embodiment is not limited to the use of a PTC for the heat generating element 302. Furthermore, the configuration of this embodiment can also be applied to the case where the heat generating element 302 does not have a resistance temperature coefficient or has a negative resistance temperature coefficient (NTC).

[0036] FIG. 4 shows a circuit diagram of the control circuit 400 of the heater 300 in the first embodiment. Reference numeral 401 denotes a commercial AC power supply connected to the laser printer 100. Power control of the heater 300 is performed by turning on and off triacs 416 and 426. By controlling triacs 416 and 426, heat generating blocks 302a-1 and 302a-3 and heat generating block 302a-2 can be controlled independently. Power is supplied to the heater 300 via electrodes E1 to E3, E4-1, and E4-2. In this embodiment, the resistance values ​​of heat generating blocks 302a-1 and 302b-1 are assumed to be 140 Ω, the resistance values ​​of heat generating blocks 302a-2 and 302b-2 are assumed to be 28 Ω, and the resistance values ​​of heat generating blocks 302a-3 and 302b-3 are assumed to be 140 Ω.

[0037] The zero-cross detection unit 430 is a circuit that detects the zero-cross of the AC power supply 401, and outputs a ZEROX signal to the CPU 420. The ZEROX signal is used to control the heater 300. The relay 440 is used as a means for cutting off power to the heater 300, and is activated by outputs from thermistors TH1 to TH4 (cutting off the power supply to the heater 300) when the heater 300 becomes overheated due to a malfunction or the like.

[0038] When the RLON440 signal goes high, the transistor 443 goes on, current is passed from the power supply voltage Vcc2 to the secondary coil of the relay 440, and the primary contact of the RLON440 goes on. When the RLON440 signal goes low, the transistor 443 goes off, the current flowing from the power supply voltage Vcc2 to the secondary coil of the relay 440 is cut off, and the primary contact of the RLON440 goes off.

[0039] Next, we will explain the operation of the safety circuit using relay 440. When any one of the temperatures detected by thermistors TH1 to TH4 exceeds a predetermined value set for that temperature, comparison unit 441 activates latch unit 442, and latch unit 442 latches the RLOFF signal in a low state. When the RLOFF signal goes low, even if CPU 420 sets the RLON440 signal to a high state, transistor 443 is maintained in an off state, so relay 440 can be maintained in an off state (safe state).

[0040] If the temperatures detected by the thermistors TH1 to TH4 do not exceed the respective predetermined values, the RLOFF signal of the latch unit 442 is in an open state. Therefore, when the CPU 420 sets the RLON440 signal to a high state, the relay 440 can be turned on, and power can be supplied to the heater 300.

[0041] Next, the operation of the triac 416 will be described. Resistors 413 and 417 are bias resistors for the triac 416, and the phototriac coupler 415 is a device for ensuring a creepage distance between the primary and secondary. The triac 416 is turned on by passing current through the light-emitting diode of the phototriac coupler 415. Resistor 418 is a resistor for limiting the current flowing from the power supply voltage Vcc to the light-emitting diode of the phototriac coupler 415, and transistor 419 turns the phototriac coupler 415 on and off. The transistor 419 operates in accordance with the FUSER1 signal from the CPU 420.

[0042] When triac 416 is energized, power is supplied to heating elements 302a-2 and 302b-2, and power is supplied to a resistor with a combined resistance of 14 Ω. By controlling the power control by triac 416 and triac 426 at a power ratio of 1:0, power is supplied only to heating elements 302a-2 and 302b-2, resulting in the state described in FIG. 6B.

[0043] The circuit operation of triac 426 is the same as that of triac 416, so a description thereof will be omitted. Triac 426 operates in accordance with the FUSER2 signal from CPU 420. When triac 426 is energized, power is supplied to heating elements 302a-1, 302b-1, 302a-3, and 302b-3. These four heating elements 302a-1, 302b-1, 302a-3, and 302b-3 are connected in parallel, so power is supplied to resistors with a combined resistance of 35 Ω.

[0044] In the state shown in FIG. 6A, power is supplied using triacs 416 and 426. That is, when triacs 416 and 426 are energized, power is supplied to heating elements 302a-1, 302b-1, 302a-2, 302b-2, 302a-3, and 302b-3. Because these six heating elements 302a-1, 302b-1, 302a-2, 302b-2, 302a-3, and 302b-3 are connected in parallel, power is supplied to resistors with a combined resistance of 10 Ω. By controlling the power by triacs 416 and 426 at a conduction ratio of 1:1, the state described in FIG. 6A is achieved.

[0045] The total resistance of the heater 300 is often designed to accommodate the power required for the maximum recording material P width (in this embodiment, Letter and Legal paper). In the configuration of this embodiment, the total resistance in the state shown in FIG. 6B is 14 Ω, which is higher than the 10 Ω total resistance in the state shown in FIG. 6A. This is advantageous in terms of harmonic standards, flicker, and heater 300 safety protection (which generally worsens as the resistance value decreases). For example, consider a heater in which three heat generating blocks (302-1, 302-2, and 302-3) are connected in series and adjusted to 10 Ω. In this configuration, if power is supplied only to the heat generating block 302-2 in the center of the heater, the total resistance of the heater will decrease, which is unfavorable in terms of harmonic standards, flicker, and heater 300 safety protection. In the configuration of this embodiment, multiple heat generating blocks (three heat generating blocks in this embodiment) divided along the heater's longitudinal direction are connected in parallel, which is advantageous in suppressing harmonics, flicker, and other issues.

[0046] Next, a temperature control method for the heater 300 will be described. The temperature detected by thermistor TH1 is divided by a resistor (not shown) and detected by the CPU 420 as a TH1 signal (thermistors TH2 to TH4 are detected by the CPU 420 in a similar manner). The CPU (controller) 420 performs internal processing to calculate the power to be supplied, for example, by PI control, based on the temperature detected by thermistor TH1 and the set temperature of the heater 300. This is then converted into control levels for the phase angle (phase control) and wave number (wave number control) corresponding to the power to be supplied, and the triacs 416 and 426 are controlled according to these control conditions. In this embodiment, the temperature of the heater 300 is controlled based on the heater temperature detected by thermistor TH1. However, the temperature of the film 202 may be detected by a thermistor or thermopile, and the temperature of the heater 300 may be controlled based on this detected temperature.

[0047] 5 is a flowchart illustrating the control sequence of image heating device 200 by CPU 420. When a print request occurs in S501, relay 440 is turned ON in S502. Next, in S503, it is determined whether the width of the recording material is 157 mm or more. In laser printer 100 of this embodiment, the process proceeds to S504 in the case of Letter paper, Legal paper, A4 paper, Executive paper, B5 paper, or non-standard size paper with a width of 157 mm or more fed from paper feed tray 28. Then, the conduction ratio of triac 416 to triac 426 is set to 1:1 (the state of FIG. 6(A)).

[0048] If the width of the recording material is narrower than 157 mm (in this embodiment, A5 paper, DL envelopes, COM10 envelopes, and non-standard size paper narrower than 157 mm), the process proceeds to S505. Then, the energization ratio of triac 416 to triac 426 is set to 1:0 (the state in FIG. 6B).

[0049] The method for determining the width of the recording material in S503 may be any method, such as using a paper width sensor provided in the paper feed cassette 11 or the paper feed tray 28, or using a sensor such as a flag provided on the transport path of the recording material P. Other methods include a method based on width information of the recording material P set by the user, a method based on image information for forming an image on the recording material P, etc.

[0050] In S506, the image forming process speed is set to full speed using the set current supply ratio, and fixing is performed at the target temperature of 200° C. set for thermistor TH1.

[0051] In S507, it is determined whether the maximum temperature TH2Max of thermistor TH2, the maximum temperature TH3Max of thermistor TH3, and the maximum temperature TH4Max of thermistor TH4 set in the CPU 420 have been exceeded. If it is detected based on the thermistor signals TH2 to TH4 that the temperature rise in the non-paper passing area has worsened and the temperature at the edge of the heat generating area has exceeded a predetermined upper limit, the process proceeds to S509, the image formation process speed is set to half speed, and fixing is performed at the target temperature set for thermistor TH1 of 170°C. The process proceeds to S509 and continues fixing until the end of the print job is detected in S510. Setting the image formation process speed to half speed allows for fixation at a lower temperature than at full speed, so the target fixing temperature can be reduced and the temperature in the non-paper passing area can be suppressed. If the temperatures of the thermistors do not exceed the maximum temperature in S507, the process proceeds to S508. In S508, the process proceeds to S506 and continues fixing until the end of the print job.

[0052] The above process is repeated, and when the end of the print job is detected in S508 and S510, the relay 440 is turned off in S511, and the image formation control sequence is ended in S512.

[0053] In the control of this embodiment, the power distribution ratio between the triac 416 and the triac 426 is set based on width information about the recording material P, and the heat generation distribution in the longitudinal direction of the heater 300 is controlled. Alternatively, a method of controlling the heat generation distribution in the longitudinal direction of the heater 300 based on the temperature detection results of the thermistors corresponding to each heating block may be considered. As a specific example, the control of the heating block 302-2 may be performed by power control using PI control or the like using the triac 416 based on the temperature detection results of thermistor TH1. The control of the heating blocks 302-1 and 302-3 may be performed by power control using PI control or the like using the triac 426 based on the temperature detection results of thermistor TH2 or thermistor TH3. The optimum control method can be used depending on the configuration of the image heating device 200 (the number of divisions of the heating blocks of the heater 300, the positions of the thermistors, etc.) and the specifications of the image forming apparatus 200 (the type of recording material supported, etc.).

[0054] As described above, by using the heater 300 and image heating apparatus 200 of this embodiment 1, it is possible to suppress temperature rise in non-sheet-passing areas when printing sizes smaller than the maximum size supported by the apparatus. Furthermore, the symmetry of the heat generation distribution in the short-side direction of the heater 300 is improved, reducing thermal stress on the substrate 305. Furthermore, the symmetry of the heat generation distribution in the long-side direction of the heater 300 is improved, reducing unevenness in the heat generation distribution in the long-side direction of the heater 300. Furthermore, in the heater 300 of this embodiment, by providing electrodes on the back surface of the heater 300, it is not necessary to provide wiring using a conductive pattern on the substrate 305. Therefore, it is possible to increase the number of heat generation blocks in the long-side direction of the heater 300, the number of electrodes, and the number of triacs that control the heat generation distribution in the long-side direction of the heater 300, without increasing the short-side width of the heater 300. Furthermore, by increasing the number of stages for switching the heat generation distribution in the long-side direction of the heater, it is possible to obtain a heat generation distribution in the long-side direction of the heater that is optimized for a wider range of recording material P widths. Therefore, in heater 300, the width of substrate 305 in the short direction can be shortened, which has the effect of reducing the material cost of substrate 305 and shortening the start-up time of image heating apparatus 200 by reducing the heat capacity of substrate 305. Furthermore, by providing one or more thermistors in each of the multiple heat generating blocks, safety in the event of a failure of image heating apparatus 200 can be improved.

[0055] Example 2 Next, a second embodiment will be described in which the heater 300, the holding member 201 for the heater 300, and the heater control circuit 400 described in the first embodiment and mounted on the image heating device 200 of the laser printer 100 are modified. The same components as those in the first embodiment will be designated by the same symbols and will not be described again. The heater 700 of the second embodiment is configured to be able to switch the heat generation distribution in the longitudinal direction of the heater 700 between four stages. Figure 7 shows a configuration diagram of the heater 700 of the second embodiment. Figure 7(A) shows a cross section of the heater 700 in the short direction.

[0056] The heater 700 has a first conductor 701 provided on the substrate 305 along the longitudinal direction of the heater 700, and a second conductor 703 provided on the substrate 305 along the longitudinal direction of the heater 700 at a position different from the first conductor 701 in the short direction of the heater 700. The first conductor 701 is separated into a conductor 701a arranged on the upstream side in the conveying direction of the recording material P and a conductor 701b arranged on the downstream side.

[0057] Furthermore, the heater 700 is provided between a first conductor 701 and a second conductor 703, and has a heating element 702 that generates heat by power supplied via the first conductor 701 and the second conductor 703. The heating element 702 is separated into a heating element 702a disposed on the upstream side in the conveying direction of the recording material P, and a heating element 702b disposed on the downstream side.

[0058] 7(B) shows a plan view of each layer of the heater 700. Layer 1 on the back surface of the heater 700 has a plurality of heat generating blocks arranged in the longitudinal direction of the heater 700, each of which is made up of a set of a first conductor 701, a second conductor 703, and a heat generating element 702. The heater 700 of this embodiment has a total of seven heat generating blocks 702-1 to 702-7 at the center and both ends in the longitudinal direction of the heater 700. BL1 to BL7 in the figure indicate the individual blocks.

[0059] Heat generating blocks 702-1 to 702-7 are respectively composed of heat generating elements 702a-1 to 702a-7 and heat generating elements 702b-1 to 702b-7, which are formed symmetrically in the short direction of heater 700. First conductor 701 is composed of conductor 701a connected to the heat generating elements (702a-1 to 702a-7) and conductor 701b connected to the heat generating elements (702b-1 to 702b-7). Similarly, second conductor 703 is divided into seven conductors 703-1 to 703-7.

[0060] Electrodes E1 to E7, E8-1, and E8-2 are used to connect to electrical contacts used to supply power from a control circuit 800 of the heater 700, which will be described later. Electrodes E1 to E7 are electrodes used to supply power to heat generating blocks 702-1 to 702-7 via conductors 703-1 to 703-7, respectively. Electrodes E8-1 and E8-2 are electrodes used to connect to a common electrical contact used to supply power to the seven heat generating blocks 702-1 to 702-7 via conductors 701a and 701b.

[0061] Furthermore, the surface protection layer 707 of layer 2 on the rear surface of the heater 700 is formed except for the locations of electrodes E1, E2, E3, E4, E5, E6, E7, E8-1, and E8-2, and is configured so that electrical contacts can be connected to each electrode from the rear surface side of the heater 700.

[0062] In this embodiment, electrodes E1, E2, E3, E4, E5, E6, E7, E8-1, and E8-2 are provided on the rear surface of the heater 700, and power can be supplied from the rear surface side of the heater 700. In addition, the ratio of power supplied to at least one of the heat generating blocks and power supplied to the other heat generating blocks can be controlled.

[0063] As shown in FIG. 7(C), the holding member 712 of the heater 700 has holes for the electrical contacts of the thermistor (temperature detection element) TH1, the safety element 212, and the electrodes E1, E2, E3, E4, E5, E6, E7, E8-1, and E8-2.

[0064] The aforementioned thermistor (temperature detection element) TH1, safety element 212, and electrical contacts of electrodes E1, E2, E3, E4, E5, E6, E7, E8-1, and E8-2 are provided between stay 204 and holding member 712 and abut against the rear surface of heater 700. The configuration of the electrical contacts that come into contact with electrodes E1, E2, E3, E4, E5, E6, E7, E8-1, and E8-2 is the same as in Example 1, so a description thereof will be omitted.

[0065] Figure 8 shows a circuit diagram of a control circuit 800 for a heater 700 in a second embodiment. Figure 4 in the first embodiment describes a method of using two triacs to control power and the heat generation distribution in the longitudinal direction of the heater 300. In the second embodiment, a method of using one triac to control power and three relays 851 to 853 to control the heat generation distribution in the longitudinal direction of the heater 700 is described. In this example, the relays 851 to 853 are controlled to select a heat generation block to which power is supplied from among a plurality of heat generation blocks, that is, heat generation blocks to which power is supplied and heat generation blocks to which power is not supplied are formed, and this is expressed as being independently controllable.

[0066] The relays 851 to 853 operate in accordance with the RLON851 to 853 signals from the CPU 420. When the RLON851 to 853 signals are in a high state, the transistors 861 to 863 are turned on, current is passed from the power supply voltage Vcc2 to the secondary coils of the relays 851 to 853, and the primary contacts of the relays 851 to 853 are turned on. When the RLON851 to 853 signals are in a low state, the transistors 861 to 863 are turned off, the current flowing from the power supply voltage Vcc2 to the secondary coils of the relays 851 to 853 is cut off, and the primary contacts of the relays 851 to 853 are turned off.

[0067] Next, the relationship between the states of relays 851 to 853 and the heat generation distribution in the longitudinal direction of heater 700 will be described. When relays 851 to 853 are all OFF, power is supplied to heat generation block 702-4, and a 115 mm width of heater 700 generates heat, resulting in a heat generation distribution for DL ​​and COM10 envelopes, as shown in Figure 7(B). When relay 851 is ON and relays 852 to 853 are OFF, power is supplied to heat generation blocks 702-3 to 702-5, and a 157 mm width of heater 700 generates heat, as shown in Figure 7(B), resulting in a heat generation distribution for A5 paper. When relays 851 to 852 are ON and relay 853 is OFF, power is supplied to heat generation blocks 702-2 to 702-6, and a 190 mm width of heater 700 generates heat, as shown in Figure 7(B), resulting in a heat generation distribution for Executive and B5 paper. When relays 851 to 853 are all ON, power is supplied to heat generating blocks 702-1 to 702-7, and the heater 700 generates heat over a width of 220 mm, resulting in heat distributions for letter paper, legal paper, and A4 paper, as shown in Figure 7(B). In this way, by using three relays 851 to 853, the control circuit 800 of this embodiment can control the heat distribution in the longitudinal direction of the heater 700 in four stages.

[0068] Power to the heater 700 is controlled by turning on / off the triac 816. The circuit operation of the triac 816 is the same as that of the triac 416 described in the first embodiment, so a description thereof will be omitted. The triac 816 is provided on a common current path for current flowing through all of the heat generating blocks 702-1 to 702-7. Therefore, in any of the four stages of heat distribution control of the heater 700 described above, the power supplied to the heater 700 can be controlled by turning on / off the triac 816.

[0069] Next, a temperature control method for heater 700 will be described. The temperature detected by thermistor TH1 is divided by a resistor (not shown) and detected by CPU 420 as a TH1 signal. Internal processing in CPU (controller) 420 calculates the power to be supplied, for example by PI control, based on the temperature detected by thermistor TH1 and the set temperature of heater 700. This is then converted into control levels for the phase angle (phase control) and wave number (wave number control) corresponding to the power to be supplied, and triac 816 is controlled according to these control conditions.

[0070] Furthermore, since the heat generating block 702-4 is provided with a temperature detection element that is connected to the power supply without passing through the relays 851 to 853, it is possible to detect the temperature of the heater 700 regardless of the operating state of the relays 851 to 853. Note that, as in the first embodiment, control may be performed according to the film temperature rather than the heater temperature.

[0071] The configuration described in the second embodiment can prevent a state in which power is supplied only to the heat generating blocks 702-1 to 702-3 and 702-5 to 702-7 at both ends of the heater 700, regardless of the operating states (assuming short circuit failure and open circuit failure states) of the relays 851 to 853. When power is supplied to the heat generating blocks 702-1 to 702-3 and 702-5 to 702-7 at both ends of the heater 700, power is also supplied to the heat generating block 702-2 at the center of the heater 700, regardless of the operating states of the relays 851 to 853. Therefore, in this embodiment, the thermistor TH1 and the safety element 212 are brought into contact with the heat generating block 702-4, so that the safety circuit (the safety circuit of the relay 440 and the safety element 212) functions regardless of the operating states of the relays 851 to 853.

[0072] 9 is a flowchart illustrating the control sequence of image heating apparatus 200 by CPU 420. When a print supply request occurs in S901, relay 440 is turned on in S902.

[0073] In S903, it is determined whether the width of the recording material P is 115 mm or more. If the width of the recording material P is 115 mm or more, the process proceeds to S904, where the relay 851 is held in the ON state. If the width of the recording material P is less than 115 mm, the process proceeds to S905, where the relay 851 is held in the OFF state. In S906, it is determined whether the width of the recording material P is 157 mm or more.

[0074] If the width of the recording material P is 157 mm or more, the process proceeds to S907, where the relay 852 is maintained in the ON state. If the width of the recording material P is less than 157 mm, the process proceeds to S908, where the relay 852 is maintained in the OFF state.

[0075] In S909, it is determined whether the width of the recording material P is 190 mm or more. If the width of the recording material P is 190 mm or more, the process proceeds to S910, where the relay 853 is held in the ON state. If the width of the recording material P is less than 190 mm, the process proceeds to S911, where the relay 853 is held in the OFF state.

[0076] In S912, the image formation process speed is set to full speed while maintaining the set states of relays 851 to 853, and image formation is performed at the target temperature set for thermistor TH1 of 200° C. In S913, the process returns to S912 and the fixing process continues until the print job is completed. The above process is repeated, and when the end of the print job is detected in S913, the relay 440 is turned off in S914, and the image formation control sequence is ended in S915.

[0077] The heater 700 of this embodiment can also increase the number of stages for switching the heat generation distribution in the longitudinal direction of the heater 700 without increasing the width of the heater 700 in the lateral direction.

[0078] The control circuit 800 described in the second embodiment can be applied to the heater 300 by matching the number of relays that control the heat generation distribution to that of the heater 300 (using one relay to switch the heat generation distribution in the heater's longitudinal direction between two stages). Similarly, the control circuit 400 described in the first embodiment can be applied to the heater 700 by matching the number of triacs that control the heat generation distribution in the heater's longitudinal direction to that of the heater 700 (using four triacs to switch the heat generation distribution in the heater's longitudinal direction between four stages). For the heaters shown in FIGS. 10 to 13, which will be described in the following embodiments, either the control method of the control circuit 400 or the control circuit 800 may be used.

[0079] Example 3 Fig. 10 is a diagram for explaining the configuration of a heater 1000 applicable to the third embodiment. The same components as those in the first embodiment are designated by the same symbols and will not be described again. The heater 1000 shown in Fig. 10 is characterized by a method of supplying power from an electrode on the rear surface of the heater 1000 to a heating element 302 arranged on the sliding surface side of a substrate 305 via a through hole T.

[0080] 10(A) shows a cross section in the short direction of the heater 1000. As shown in Fig. 10(A), the heater 1000 has a first conductor 301, a second conductor 303, and a heating element 302 on a layer 1 on the sliding surface side of a substrate 305.

[0081] FIG. 10B shows a plan view of each layer of the heater 1000. Electrode E1, formed on the back surface of the heater 1000, is connected to conductor 303-1 via conductor 1004-1 and through-hole T1. Similarly, electrode E2 is connected to conductor 303-2 via conductor 1004-2 and through-holes T2-1 and T2-2. Electrode E3 is connected to conductor 303-3 via conductor 1004-3 and through-hole T3. Electrode E4-1 is connected to conductors 301a and 301b via conductor 1004-4-1 and through-holes T4-1a and T4-1b. Electrode E4-2 is connected to conductors 301a and 301b via conductor 1004-4-2 and through-holes T4-2a and T4-2b.

[0082] Furthermore, the surface protection layer 1008 of the layer 2 on the sliding surface of the heater 1000 is an insulating glass used to protect the first conductor 301, the second conductor 303 and the heating element 302 and to improve sliding properties with the film 202.

[0083] As shown in the heater 1000, the effect of this proposal can also be obtained with a configuration in which the heating element 302 is formed on the sliding surface side of the substrate 305.

[0084] Example 4 11 is a diagram for explaining the configuration of a heater 1100 applicable to the fourth embodiment. The same components as those in the first and third embodiments are designated by the same reference numerals and will not be described again.

[0085] 11 is characterized in that heat generating blocks 1102-1 to 1102-3 are not divided in the short side direction of the heater 1100, and similarly, the first conductor 1101 is not divided in the short side direction of the heater 1101. Also, compared to the heater 300 and the heater 1000, the heater 1100 is characterized in that the electrodes E1 and E3 are connected on the substrate 305, and the electrodes E4-1 and E4-2 are connected on the substrate 305, thereby reducing the number of electrodes.

[0086] Fig. 11(A) shows a cross section in the short direction of the heater 1100. Fig. 11(B) shows a plan view of each layer of the heater 1100.

[0087] Electrode E1 formed on the back surface of heater 1100 and conductor 1103-1 are connected via conductor 1104-1 and through-hole T1. Similarly, electrode E2 and conductor 1103-2 are connected via conductor 1104-2 and through-holes T2-1 and T2-2. Electrode E4 and conductor 1101 are connected via conductor 1104-4 and through-hole T4. Conductor 1103-3 is connected to electrode E1 via conductor 1104-1 and through-hole T3. While the control circuit 400 shown in FIG. 4 requires electrodes E1 and E3 to be connected outside of heater 300, this configuration does not require electrodes E1 and E3 to be connected outside of heater 300. Similarly, electrodes E4-1 and E4-2 do not need to be connected outside of heater 400. Therefore, a protective layer 1107 is provided on the layer 2 on the rear surface of the heater 1100 except for the areas where the electrodes E1, E2, and E4 are located.

[0088] In the heater 1100 of this embodiment, the electrode E3 is omitted by connecting the second conductor connected to the heat generating blocks (heat generating blocks 1102-1 and 1102-3) that do not need to be controlled independently on the substrate 305. In addition, one of the electrodes (E4-1 and E4-2 in FIG. 3) connected to the first conductor and provided on the left and right sides of the substrate 305 is omitted. This makes it possible to reduce the number of electrodes required. Furthermore, as shown in the heater 1100, the effect of this proposal can be obtained even in a configuration in which the heat generating element 1102 is not divided in the short direction of the heater 1100.

[0089] Example 5 12 is a diagram for explaining the configuration of a heater 600 applicable to the fifth embodiment. The same components as those in the first embodiment are designated by the same reference numerals and will not be described again.

[0090] The heater 600 shown in FIG. 12 is characterized in that the heating elements 602a-1, 602b-1, 602a-2, 602b-2, 602a-3, and 602b-3 are further divided into a plurality of heating elements connected in parallel.

[0091] Fig. 12(A) shows a cross section in the short direction of the heater 600. Fig. 12(B) shows a plan view of each layer of the heater 600.

[0092] Heating element 602a-1, which is divided into multiple parts, is connected between conductor 603-1 and conductor 601a and receives power from there. Heating elements 602b-1, 602a-2, 602b-2, 602a-3, and 602b-3 have the same configuration as heating element 602a-1, and therefore their explanation will be omitted.

[0093] The parallel-connected heating elements of the heating element 602a-1 are arranged at an angle with respect to the longitudinal and lateral directions of the heater 600, and overlap in the longitudinal direction. This reduces the effect of gaps between the heating elements, improving the uniformity of the heat generation distribution in the longitudinal direction of the heater 600. Furthermore, in the heater 600 of this embodiment, the endmost heating elements of adjacent heating blocks overlap in the longitudinal direction even in the gaps between the heating blocks, making the heat generation distribution more uniform. The endmost heating elements of adjacent heating blocks are the rightmost heating element of the heating element 602a-1 and the leftmost heating element of the heating element 602a-2, and the rightmost heating element of the heating element 602a-2 and the leftmost heating element of the heating element 602a-3.

[0094] Alternatively, the resistance values ​​of the parallel-connected heating elements 602a-1 to 602a-3 and 602b-1 to 602b-3 may be adjusted individually to uniform the temperature distribution within one heating block. Similarly, the resistance values ​​of the parallel-connected heating elements 602a-1 to 602a-3 and 602b-1 to 602b-3 may be adjusted individually to uniform the heat distribution in the longitudinal direction of the heater 600 across the multiple heating blocks (heat generating blocks 602-1 to 602-3).

[0095] The resistance values ​​of the parallel-connected heating elements 602a-1 to 602a-3 and 602b-1 to 602b-3 can be adjusted by adjusting the width, length, spacing, inclination, etc. By using the heater 600 of this embodiment, it is possible to suppress temperature unevenness in the gaps between the multiple heating blocks.

[0096] Example 6 13 is a diagram for explaining the configuration of a heater 1300 applicable to Example 6. The same components as those in Examples 1 and 3 are designated by the same reference numerals and will not be described again.

[0097] The heater 1300 shown in FIG. 13 is characterized in that power is supplied to the heat generating block via electrodes on the rear surface of the heater 1300 only for some of the electrodes.

[0098] 13(A) shows a cross section in the short direction of the heater 1300. As shown in Fig. 13(A), the heater 1300 has a first conductor 1301, a second conductor 1303, and a heating element 302 on a layer 1 on the sliding surface side of a substrate 305.

[0099] FIG. 13B shows a plan view of each layer of the heater 1300. Electrode E2, formed on layer 1 on the back surface of the substrate 305, and conductor 1303-2, formed on layer 1 on the sliding surface side, are connected via conductor 1304 and through holes T2-1 and T2-2. Electrode E1 is connected to conductor 1303-1, electrode E3 is connected to conductor 1303-3, and electrodes E4-1 and E4-2 are connected to conductors 1301a and 1301b. Electrodes E1, E3, E4-1, and E4-2 are located outside the areas where the heater 1300 slides over the film 202 at both ends in the longitudinal direction. Therefore, electrical contacts can be provided on the sliding surface side at both ends in the longitudinal direction of the heater 1300 to connect to electrodes E1, E3, E4-1, and E4-2. Therefore, the holding member 1312 used in the heater 1300 does not have holes for the electrodes E1, E3, E4-1, and E4-2.

[0100] In the heater 1300, power is supplied only to some of the heat generating blocks (302-2) via electrodes on the back surface. In order to supply power from both longitudinal ends of the heater 1300 to the heat generating blocks that are not in contact with both longitudinal ends of the heater 1300, it is necessary to widen the width of the heater 1300 in the short direction and add conductors to the substrate 305. The heat generating blocks that are not in contact with both longitudinal ends of the heater are heat generating block 302-2 in the heater 1300 of this embodiment and heat generating blocks 702-2 to 702-6 in the heater 700 described in Example 2. Therefore, it is sufficient to provide electrodes on the second conductor or to configure the heater 1300 so that power can be supplied from electrodes connected via through holes T to at least one or more heat generating blocks that are not in contact with both longitudinal ends of the heater 1300.

[0101] Example 7 15A and 15B are diagrams illustrating the configuration of a heater 1500 applicable to the seventh embodiment. The heater 1500 shown in Fig. 15A is configured such that the positions of the electrodes E1, E2, E4, and E5 are closer to the center of the heater longitudinal direction (dashed line X in Fig. 15) within each heat generating block. This configuration can suppress uneven heat generation by the heater. The effects thereof will be described below.

[0102] First, the heat generation unevenness that occurs in a heater in which current flows parallel to the conveyance direction of the recording material will be described using a heater 1400 for explaining heat generation unevenness shown in FIG. 14. FIG. 14(A) is a plan view of the back surface layer 1 of the heater 1400. The cross-sectional configuration of the heater, i.e., the back surface layer, sliding surface layer, and substrate, is the same as in Example 1. For ease of understanding, the heater 1400 has a first conductor (1401, 1402), a second conductor 1403, and heating resistors (1404, 1405) that are not divided in the heater's longitudinal direction. Furthermore, the first and second conductors and heating resistors have uniform resistance values. Electrodes E1, E2a, and E2b are connected to electrical contacts for supplying power. Electrode E1 is located at the longitudinal center, and applying a voltage between electrodes E1 and E2 causes the heating elements (1404, 1405) to generate heat.

[0103] Figure 14(B) shows the potential distribution of conductors 1401 and 1403 in the longitudinal direction of the heater when a voltage of +100 V is applied to electrode E1 and 0 V to electrode E2. Conductor 1402 has the same potential distribution as 1401, so it is not shown. The potential of conductor 1403 is greatest at the center in the longitudinal direction and decreases toward both ends. This is a voltage drop due to the electrical resistance of the conductor itself. The magnitude of this voltage drop varies depending on the ratio of the resistance values ​​of conductor 1403 and heating element 1404. Similarly, the potential distribution of conductor 1401 also causes a voltage drop from the center toward the ends. This also varies depending on the ratio of the resistance values ​​of conductor 1401 and heating element 1405.

[0104] The conductor and heating element of the heater 1400 are formed on a ceramic substrate by screen printing, and the thickness of each is within the range of 4 to 10 μm. The material of the conductors (1401, 1402, 1403) is Ag, and the specific resistance is 2×10 ―8 The material of the heating elements (1404, 1405) is RuO2, and the resistivity is 3×10 -2 The value was set to Ωm.

[0105] Here, the voltage applied to the heating element 1404 is the potential difference between the conductor 1403 and the conductor 1401, and so is distributed as shown by the dashed line in Figure 14(B). In other words, the voltage applied to the heating element 1404 is non-uniform in the longitudinal direction, and therefore the heat distribution of the heating element 1404 is also non-uniform. Similarly, the heat distribution of the heating element 1405 is also non-uniform. This causes uneven heat generation from the heater.

[0106] Next, the configuration of a heater 1500 of Example 7 will be described. Fig. 15(A) is a plan view of the back surface layer 1 of the heater 1500, and the cross-sectional configuration of the heater, that is, the configuration of the back surface layer 2, sliding surface layer, and substrate, is the same as that of Example 1. Note that only the configurations of the back surface layer 1 and electrodes are different from those of Examples 8 and onwards, which will be described later, and therefore descriptions of layers other than the back surface layer 1 will be omitted.

[0107] The conductor 1503 and heating elements (1504, 1505) are divided into five blocks in the heater longitudinal direction, and power is supplied to each block via electrodes E1, E2, E3, E4, and E5. In addition, electrodes E1, E2, E4, and E5 are located closer to the center of the heater (dashed line X) than the center of each block in the heater longitudinal direction.

[0108] FIG. 15B shows the potential distribution of conductors 1501 and 1503 when a voltage of +100 V is applied to electrodes E1, E2, E3, E4, and E5 of heater 1500, and 0 V is applied to electrodes E6a and E6b. The potential distribution of conductor 1502 is similar to that of conductor 1501, so it is not shown. The potential of the conductor decreases from each electrode position toward the longitudinal end of the block. This is a similar phenomenon to the voltage drop described for heater 1400 in FIG. 14. The distribution of the potential difference between conductors 1503 and 1501 is shown by the dashed line in FIG. 15B, and the maximum value of this potential difference is 97 V and the minimum value is 92 V. In other words, the range of the voltage applied to the heating elements (1504 and 1505) is 5 V.

[0109] 16 shows an example in which the positions of the electrodes are different from those of the heater 1500. The heater 1600 has a structure in which the electrodes E1, E2, E4, and E5 are positioned closer to the end of the heater than the center of each block.

[0110] 16(B) shows the potential distribution of conductors 1601 and 1603 when a voltage of +100 V is applied to electrodes E1, E2, E3, E4, and E5 of heater 1600, and 0 V is applied to electrodes E6a and E6b. The potential distribution of conductor 1602 is the same as that of conductor 1601, so it is not shown. The distribution of the potential difference between conductors 1603 and 1601 is shown by the dashed line in FIG. 16(B), and the maximum value of this potential difference is 99 V and the minimum value is 90 V. In other words, there is a 9 V unevenness in the voltage applied to the heating elements (1604 and 1605).

[0111] Table 1 shows the maximum and minimum values ​​of the potential difference between the conductors of heater 1500 and heater 1600, as well as the range of the potential difference.

[0112] [Table 1]

[0113] Therefore, to suppress uneven heat generation in the heater's longitudinal direction, it is preferable to position the electrodes of each block closer to the center of the heater (dashed line X) than the center of each block in the heater's longitudinal direction, as in heater 1500.

[0114] Example 8 17 is a diagram for explaining the configuration of a heater 1700 applicable to Example 8. The heater 1700 has a plurality of electrodes arranged on each heat generating block.

[0115] 17(A) is a plan view of the back surface layer 1 of the heater 1700. The conductor 1703 and the heating elements (1704, 1705) are divided into three parts in the longitudinal direction of the heater. Power is supplied to the heating elements 1704a and 1705a from electrodes E1 and E2, to the heating elements 1704b and 1705b from electrodes E3 and E4, and to the heating elements 1704c and 1705c from electrodes E5 and E6.

[0116] Electrodes E1, E2, E3, E4, E5, and E6 are all at the same potential, as are electrodes E11, E12, E13, E14, E21, E22, E23, and E24. Figure 17(B) shows the potential distributions of conductors 1701 and 1703 when a voltage of +100 V is applied to electrodes E1, E2, E3, E4, E5, and E6, and 0 V is applied to electrodes E11, E12, E13, E14, E21, E22, E23, and E24. The potential distribution of conductor 1702 is similar to that of conductor 1701, so it is not shown. The potential distribution of conductor 1703 is highest at the six electrodes E1 through E6, and the potential is lower between the electrodes. However, the potential drop is smaller than that of the heater shown in Figure 16(A). This is because, for example, when considering the path of current flowing from electrode E1 to E11, arranging two electrodes E1 and E2 in the block of conductor 1703a shortens the distance between electrodes E1 and E11. In other words, the apparent resistance value of conductor 1703a in the current path between electrodes E1 and E11 decreases, thereby reducing the amount of potential drop across conductor 1703a. Similarly, arranging multiple electrodes (E11, E12, E13, E14) on conductor 1701 reduces unevenness in the potential of conductor 1701.

[0117] Therefore, the potential difference between conductors 1703 and 1701, shown by the dashed line in Figure 17(B), is a maximum of 99 V and a minimum of 98 V, and the range of the potential difference is also small. In this way, by providing multiple electrodes of the same potential on one heat generating block, it is possible to suppress unevenness in the potential difference in the longitudinal direction of the heater. This makes the voltage applied to heating elements 1704 and 1705 uniform in the longitudinal direction of the heater, thereby suppressing uneven heat generation by the heater.

[0118] Example 9 18 is a diagram illustrating the configuration of a heater 1800 applicable to Example 9. Heat generating elements 1804 and 1805 of the heater 1800 are continuous (not divided) in the longitudinal direction of the heater.

[0119] 18(A) is a plan view of the back surface layer 1 of the heater 1800. The conductor 1803 is divided into three parts in the longitudinal direction, and power is supplied to the conductor 1803a from the electrode E1, to the conductor 1803b from the electrode E2, and to the conductor 1803c from the electrode E3.

[0120] 18B shows the potential distribution of heating elements 1804 and 1805 and conductors 1801 and 1802 when a voltage of +100 V is applied to electrodes E1, E2, and E3 of heater 1800 and 0 V is applied to electrodes E4a and E4b. The potential distribution of heating elements 1804 and 1805 is the potential distribution at the positions of dashed lines A and B in FIG. 18A. In this embodiment, heating elements 1804 and 1805 are not divided, so the potential at the positions of heating elements 1804 and 1805 corresponding to the divided positions of conductor 1803 does not become 0 V. Therefore, heating elements 1804 and 1805 generate heat continuously in the longitudinal direction, and there is no region where the heat generation amount becomes 0, resulting in a more uniform heat generation distribution of the heater.

[0121] Example 10 Figure 19 is a diagram illustrating the configuration of heaters 1900A and 1900B applicable to embodiment 10. Figure 19(A) shows the back surface layer 1 of heater 1900A, and conductor 1903A is divided in the heater longitudinal direction. The boundary between conductors 1903Aa and 1903Ab is oblique to the heater longitudinal direction and the recording material conveyance direction. In addition, the boundary between conductors 1903Ab and 1903Ac is also oblique to the heater longitudinal direction and the recording material conveyance direction.

[0122] Here, heating elements 1904A and 1905A are not divided in the longitudinal direction. However, as explained in Example 9, the heat generation amount decreases at the contact points between the heating elements and the gap areas where conductor 1903A is divided. However, the positions of the portions of heating elements 1904A and 1905A where the heat generation amount decreases are offset in the heater longitudinal direction. This is because the dividing line of conductor 1903A is oblique.

[0123] Therefore, by shifting the portions of heating element 1904A and heating element 1905A where the heat generation amount decreases in the longitudinal direction, the heat generation distribution of the entire heater can be made more uniform.

[0124] As shown in Fig. 19(B), the conductor 1903B may be divided into hook shapes. The configuration other than the shape of the conductor 1903B is the same as in Fig. 19(A), so detailed description will be omitted.

[0125] Example 11 Fig. 20 is a diagram for explaining the configuration of a heater 2000 applicable to Example 11. The heater 2000 shown in Fig. 20 is the same as Example 10 in that the heating element is not divided, but each block is formed by dividing the conductor. However, it differs in that an electrode is provided outside the area where the heating element is provided in the longitudinal direction of the heater (the area where maximum size paper passes).

[0126] 20(A) is a cross-sectional view of a heater 2000. As shown in Fig. 20(A), the heater 2000 has a first conductor 2001, a second conductor 2003, and a heating element 2004 in a layer 1 on the sliding surface side of a substrate 2010.

[0127] FIG. 20B shows a plan view of the sliding surface layer 1. As shown in this figure, the heating elements 2004 and 2005 are not divided in the heater longitudinal direction. The conductors 2001 and 2002 are divided into three in the heater longitudinal direction. The electrodes E1, E2, E3, and E4 connected to the conductors 2001, 2002, and 2003 are located outside the recording material passage area. The direction of the current flowing through the heating elements in this heater is also parallel to the recording material conveyance direction. The sliding surface layer 2 (surface protection layer 2012) is an insulating glass layer that protects the conductors and heating elements and improves sliding performance with the film 202. The dividing positions of the conductors 2001a and 2001b and the dividing positions of the conductors 2002a and 2002b may be different in the heater longitudinal direction. The same applies to the relationship between the dividing positions of the conductors 2001b and 2001c and the dividing positions of the conductors 2002b and 2002c. [Explanation of symbols]

[0128] 300 heater 301(301a, 301b) First conductor 302 Heating element 302-1 (302a-1, 302b-1) First heat generating block 302-2 (302a-2, 302b-2) Second heating block 302-3 (302a-3, 302b-3) Third heating block 303 (303-1, 303-2, 303-3) Second conductor E4-1, E4-2 Electrodes of the first conductor E1, E2, E3 Second conductor electrodes 200 Image heating device 400 Control circuit

Claims

1. An endless belt; a heater provided in an internal space of the endless belt, the heater including a long and narrow substrate and a plurality of heat generating blocks arranged on the substrate in a longitudinal direction of the substrate, the heat generating blocks generating heat when supplied with power; a roller that contacts the outer peripheral surface of the endless belt, the roller sandwiching the endless belt together with the heater and forming a nip portion between the endless belt and the roller for sandwiching and conveying a recording material; an image heating device that can switch a heat generation distribution of the heater in the longitudinal direction by controlling power supplied to the plurality of heat generation blocks, and heats an image formed on a recording material while nipping and conveying the recording material at the nip portion, the plurality of heat generating blocks include a first heat generating block disposed at a position including a recording material conveyance reference position in the longitudinal direction, and a second heat generating block disposed adjacent to the first heat generating block in the longitudinal direction, The fixing device further has a temperature detection element that detects the temperature of the second heat generation block, and the temperature detection element is provided in an area farther from the first heat generation block than the center of the second heat generation block in the longitudinal direction.

2. An image heating device as described in Claim 1, characterized in that each of the multiple heat generating blocks has a heat generating element with a positive resistance temperature characteristic.

Images