Image heating apparatus and heater for use in image heating apparatus

Abstract

The present disclosure relates to an image heating apparatus and a heater used in the image heating apparatus. In the image heating apparatus having a plurality of heating blocks independently controllable in a long side direction of the heater, the size of the heater can be suppressed from increasing, and the temperatures of the plurality of heating blocks can be detected. The heater has a first temperature sensor corresponding to a first heating block, a second temperature sensor corresponding to a second heating block, a first electric conductor electrically coupled to the first temperature sensor, a second electric conductor electrically coupled to the second temperature sensor, and a common electric conductor electrically coupled to the first temperature sensor and the second temperature sensor.

Description

[0001] This application is a divisional application of the Chinese Invention Patent Application No. 201680052256.4, filed on August 12, 2016, entitled "Image Heating Apparatus and Heater Used in Image Heating Apparatus". TECHNICAL FIELD

[0002] The present invention relates to an image heating apparatus, such as a fuser installed in an image forming apparatus for electrophotographic recording, such as a copier and a printer, or a gloss providing apparatus that re-heats a toner image fixed to a recording material to improve the glossiness of the toner image. The present invention further relates to a heater used in the image heating apparatus. BACKGROUND

[0003] The image heating apparatus includes a tubular film, a heater in contact with an inner surface of the film, and a roller that forms a nip portion together with the heater through the film. When continuous printing is performed on a small-sized sheet using an image forming apparatus having the image heating apparatus, a phenomenon in which the temperature of a region in which paper does not pass in the longitudinal direction of the nip portion gradually increases (temperature rise in a non-passing paper portion) can occur. Excessive temperature rise of the non-passing paper portion can damage parts within the apparatus. In a case where printing is performed on a large-sized sheet while the temperature in the non-passing paper portion is rising, toner heat offset can be caused in a region on the film corresponding to the non-passing paper portion of the small-sized sheet.

[0004] One of the solutions for suppressing such temperature rise in the non-passing paper portion, an apparatus in which a plurality of longitudinal heating resistor groups (heating blocks) are included in the heater has been proposed, in which the heating distribution of the heater is changed according to the size of the recording material (PLT1).

[0005] BIBLIOGRAPHIC LIST

[0006] PATENT LITERATURE

[0007] PTL 1: Japanese Patent Publication No. 2014-59508 SUMMARY

[0008] In view of the occurrence of a failure in such an apparatus, the apparatus can be configured to monitor the temperature of each heating block. Even when one of the plurality of heating blocks is uncontrollable and abnormal heating occurs, power supply can be quickly stopped based on the result of temperature monitoring of each heating block.

[0009] However, as the number of heating blocks increases, the number of temperature sensors each for monitoring the temperature also increases. Providing many temperature sensors within the area of the substrate of the heater can increase the size of the heater.

[0010] SOLUTION TO THE PROBLEM

[0011] An aspect of the present application provides a heater for use in an image heating apparatus, the heater including a substrate, a first heating block, a second heating block, a first temperature sensor, a second temperature sensor, a first conductive pattern, a second conductive pattern, and a common conductive pattern, the first heating block being disposed on the substrate and configured to generate heat from power supplied thereto, the second heating block being disposed at a position different from that of the first heating block in a longitudinal direction of the substrate and configured to individually control the first heating block, the first temperature sensor being disposed at a position corresponding to the first heating block, the second temperature sensor being disposed at a position corresponding to the second heating block, the first conductive pattern being electrically coupled to the first temperature sensor, the second conductive pattern being electrically coupled to the second temperature sensor, and the common conductive pattern being electrically coupled to the first temperature sensor and the second temperature sensor.

[0012] Another aspect of the present application provides a heater usable in an image heating apparatus, the heater including a substrate, a heat generating member, a temperature sensor, and an electrode in contact with an electrical contact for supplying power to the heat generating member, the heat generating member being disposed on one surface of the substrate and configured to generate heat from power supplied thereto, the temperature sensor being disposed on the other surface of the substrate opposite to the one surface and configured to detect a temperature of the heater, wherein the electrode is placed on the one surface of the substrate within a region of the heat generating member in a longitudinal direction of the heater.

[0013] Further features of the present application will become apparent from the following description of example embodiments with reference to the drawings.

[0014] Advantages of the present application

[0015] According to the present application, an increase in size of the heater can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a sectional view of an image forming apparatus.

[0017] Figure 2 is a sectional view of an image heating apparatus.

[0018] Figure 3A The configuration of the heater according to the first example embodiment is exemplarily illustrated.

[0019] Figure 3B The configuration of the heater according to the first example embodiment is exemplarily illustrated.

[0020] Figure 3C The configuration of the heater according to the first example embodiment is exemplarily illustrated.

[0021] Figure 4A heater control circuit according to the first example embodiment is illustrated.

[0022] Figure 5 A heater control flowchart according to the first example embodiment is illustrated.

[0023] Figure 6A A configuration of a heater according to the second example embodiment is illustrated.

[0024] Figure 6B A configuration of a heater according to the second example embodiment is illustrated.

[0025] Figure 7 A heater control circuit according to the second example embodiment is illustrated.

[0026] Figure 8 A heater control flowchart according to the second example embodiment is illustrated.

[0027] Figure 9A A variation of a heater is illustrated.

[0028] Figure 9B A variation of a heater is illustrated.

[0029] Figure 10A A variation of a heater is illustrated.

[0030] Figure 10B Another variation of a heater is illustrated.

[0031] Figure 11A A power-on control mode of a heater is illustrated.

[0032] Figure 11B Another power-on control mode of a heater is illustrated. DETAILED DESCRIPTION

[0033] First Embodiment

[0034] Figure 1is a cross-sectional view of a laser printer (image forming apparatus) 100 that applies an electrophotographic recording technique. In response to the occurrence of a print signal, a scanner unit 21 emits laser light modulated based on image information so that a photosensitive member 19 that is electrostatically charged to a predetermined polarity by a charging roller 16 can be scanned. Thereby, an electrostatic latent image is formed on the photosensitive drum 19. A toner is supplied to the electrostatic latent image from a developing unit 17 so that a toner image according to the image information is formed on the photosensitive member 19. On the other hand, recording materials (recording paper) P stacked in a paper cassette 11 are fed one by one by a pick-up roller 12, and are conveyed toward a resistance roller 14 by a roller 13. In synchronization with the arrival of the toner image on the photosensitive member 19 at a transfer position formed by the photosensitive member 19 and a transfer roller 20, each recording material P is conveyed from the resistance roller 14 to the transfer position. During the passage of the recording material P through the transfer position, the toner image on the photosensitive member 19 is transferred to the recording material P. Thereafter, the recording material P is heated by an image heating apparatus (fixing apparatus) 200 so that the toner image is heated and fixed to the recording material P. The recording material P bearing the fixed toner image is output to a tray in an upper portion of the laser printer 100 by rollers 26 and 27. A cleaner 18 cleans the photosensitive member 19. A motor 30 drives the image heating apparatus 200 and the like. Electric power is supplied to the image heating apparatus 200 from a control circuit 400 connected to a commercial alternating current (AC) power source 401. The photosensitive member 19, the charging roller 16, the scanner unit 21, the developing unit 17, and the transfer roller 20 are components of an image forming unit configured to form an unfixed image on the recording material P. A cartridge 15 is a replaceable unit. The laser printer 100 further includes a light source 22, a polygon mirror 23, and a mirror 24.

[0035] The laser printer 100 according to this example embodiment supports a plurality of sizes of recording materials. Letter paper (about 216 mm x 279 mm) and Legal paper (about 216 mm x 356 mm) can be set in the paper cassette 11. In addition, A4 paper (210 mm x 297 mm), Executive paper (about 184 mm x 267 mm), JIS B5 paper (182 mm x 257 mm), and A5 paper (148 mm x 210 mm) can be set therein.

[0036] The printer in this embodiment is a laser printer configured to feed paper vertically (or can feed paper in such a manner that the long side of the paper can be parallel to the conveying direction). This configuration is also applicable to a printer that feeds paper horizontally. Letter paper and legal paper are the largest (widest) among the regular recording materials supported by the apparatus (based on the width of the recording materials on the catalog), and have a width of about 216 mm. In the following description of this exemplary embodiment, a paper width smaller than the maximum size of the recording material P supported by the apparatus will be referred to as a small-size paper.

[0037] Figure 2 is a cross-sectional view of the image heating apparatus 200. The image heating apparatus 200 has a tubular film 202, a heater 300 in contact with the inner surface of the film 202, and a pressure roller (nipping portion forming member) 208 that forms a fixing nipping portion N together with the heater 300 through the film 202. The film 202 has a base layer made of a heat-resistant resin such as polyimide or a metal such as stainless steel. The film 202 can have an elastic layer of heat-resistant rubber. The pressure roller 208 has a core bar 209 made of iron, aluminum, or the like, and an elastic layer 210 made of silicone rubber. The heater 300 is held by a holding member 201 of a heat-resistant resin such as liquid crystal polymer. The holding member 201 has a guide function for guiding the rotation of the film 202. The pressure roller 208 is rotated in the direction indicated by the arrow as shown in Figure 2 , by receiving power from a motor 30. The rotation of the pressure roller 208 is followed by the rotation of the film 202. The recording material P carrying an unfixed toner image is pinched and conveyed by the fixing nipping portion N to be heated and fixed. The apparatus 200 as described above has the tubular film 202 and the heater 300 in contact with the inner surface of the film 202, and the image formed on the recording material is heated by the heater 300 through the film 202.

[0038] The heater 300 has a ceramic substrate 305 and a heating resistor (heat generating member) (see Figures 3A to 3C ) provided on the substrate 305 for generating heat from the supplied electric power. A surface protective layer 308 of glass for providing the film 202 with slidability is provided on the surface (first surface) of the substrate 305 close to the fixing nipping portion N. A surface protective layer 307 of glass for insulating the heating resistor is provided on the opposite surface (second surface) of the substrate 305 close to the fixing nipping portion N. The second surface has an exposed electrode (indicated representatively by E4), and when an electric contact (indicated representatively by C4) for feeding electric power touches this electrode, the heating resistor is electrically coupled to an AC power source 401. Details of the heater 300 will be described below.

[0039] A protection element 212 such as a temperature control switch and a temperature fuse is configured to block the supply of electric power to the heater 300 in response to abnormal heating of the heater 300. The protection element 212 can be placed in close proximity to the heater 300 or can be placed in a gap of the heater 300. A metal support 204 for applying pressure (not illustrated) to the holding member 201 for sprinting functions to reinforce the holding member 201 and the heater 300.

[0040] Figure 3A and 3B The configuration of the heater 300 according to the first exemplary embodiment will be illustrated. Figure 3A The configuration of the heater 300 according to the first exemplary embodiment will be illustrated. Figure 3B A cross-sectional view of the heater 300 near the transfer reference position X on the recording material P shown in Fig. 1. Figure 3B is a plan view of each layer of the heater 300. Figure 3C is a plan view of a holding member configured to hold the heater 300.

[0041] The printer according to this embodiment is a center reference printer configured to transfer a recording material by placing the center of the recording material in the width direction (orthogonal to the transfer direction) at the transfer reference position X.

[0042] Next, details of the configuration of the heater 300 will be described. The back surface layer 1 of the heater 300, which is the heater surface on the opposite side of the heater surface in contact with the film 202, has a plurality of heating blocks each having a set of a first electric conductor 301, a second electric conductor 303, and a heating resistor (heat generating member) 302 in the long side direction of the heater 300. The heater 300 of this exemplary embodiment has a total of seven heating blocks HB1 to HB7. Assuming that one of the seven heating blocks is a first heating block and another heating block is a second heating block, the heater 300 has the following configuration. That is, the heater 300 has a substrate and a first heating block provided on the substrate, the first heating block for generating heat by receiving an electric power supply. The heater 300 further has a second heating block provided at a position different from that of the first heating block in the long side direction of the substrate and controlled independently of the first heating block. Independent control of the heating blocks will be described below.

[0043] Each of the heating blocks has a first electric conductor 301 and a second electric conductor 303. The first electric conductor 301 is provided along the long side direction of the substrate, and the second electric conductor 303 is provided at a position different from that of the first electric conductor 301 in the short side direction of the substrate along the long side direction of the substrate. Each of the heating blocks further has a heating resistor 302 provided between the first electric conductor 301 and the second electric conductor 303, the heating resistor 302 being used to generate heat from electric power supplied through the first electric conductor 301 and the second electric conductor 302.

[0044] The heating resistors 302 in the heating blocks can be divided into heating resistors 302a and heating resistors 302b at positions symmetrical to each other with respect to the center of the substrate in the short side direction of the heater 300. The first electric conductors 301 can be divided into electric conductors 301a connected to the heating resistors 302a and electric conductors 301b connected to the heating resistors 302b. Because the heating resistors 302a and the heating resistors 302b are placed at positions symmetrical to each other with respect to the center of the substrate, the substrate is not easily broken even when heat is generated by the heater and thermal stress occurs in the substrate.

[0045] Because the heater 300 has seven heating blocks HB1 to HB7, the heating resistors 302a include seven heating resistors 301a-1 to 302a-7. In the same manner, the heating resistors 302b include seven 302b-1 to 302b-7. The second electric conductors 303 include seven electric conductors 303-1 to 303-7. The heating resistors 302a-1 to 302a-7 are placed on the upstream side in the conveyance direction of the recording material P within the substrate 305, and the heating resistors 302b-1 to 302b-7 are placed on the downstream side in the conveyance direction of the recording material P within the substrate 305.

[0046] The back surface layer 2 of the heater 300 has an insulating surface protective layer 307 (glass in this example embodiment) covering the heating resistors 302, the first electric conductors 301, and the second electric conductors 303. In this case, the surface protective layer 307 does not cover the electrodes E1 to E7 and E8-1 and E8-2, which are in contact with the electric contacts C1 to C7 and C8-1 and C8-2 for feeding electric power. The electrodes E1 to E7 supply electric power to the heating blocks HB1 to HB7 through the second electric conductors 303-1 to 303-7, respectively. The electrodes E8-1 and E8-2 feed electric power to the heating blocks HB1 to HB7 through the first electric conductors 301a and 301b.

[0047] Because the resistance values of the conductive bodies are not equal to zero, the resistance has an influence on the heating distribution in the long side direction of the heater 300. Therefore, the electrodes E8-1 and E8-2 are separated at both ends in the long side direction of the heater 300 so as to prevent unevenness of the heating distribution even when influenced by the resistance of the first conductive bodies 301a and 301b and the second conductive bodies 303-1 to 303-7.

[0048] As shown in FIG. 8, the safety element 212 and the electrical contacts C1 to C7, C8-1 and C8-2 are placed between the support 204 and the holding member 201. As shown in FIG. 9, the holding member 201 has holes HC1 to HC7, HC8-1 and HC8-2 through which the electrical contacts C1 to C7, C8-1 and C8-2 connected to the electrodes E1 to E7, E8-1 and E8-2 extend. The holding member 201 further has a hole H212 through which the heat-sensitive portion of the safety element 212 extends. The electrical contacts C1 to C7, C8-1 and C8-2 are electrically coupled to the corresponding electrodes by pushing by a spring, soldering or other schemes. The safety element 212 is also pushed by a spring, and the heat-sensitive portion is in contact with the surface protection layer 307. The electrical contacts are connected to the control circuit 400 in the heater 300 through a cable or a conductive member such as a thin metal plate provided between the support 204 and the holding member 201, which will be described below. Figure 2 Figure 3C Providing the electrodes on the back surface of the heater 300 can eliminate the necessity of an area for providing wiring for electrically connecting the second conductive bodies 303-1 to 303-7 on the substrate 305, so that the width in the short side direction of the substrate 305 can be reduced. Therefore, the size of the heater can be prevented from increasing. As shown in FIG. 10, the electrodes E2 to E6 are provided within the area having the heating resistors in the long side direction of the substrate.

[0049] Providing the electrodes on the back surface of the heater 300 can eliminate the necessity of an area for providing wiring for electrically connecting the second conductive bodies 303-1 to 303-7 on the substrate 305, so that the width in the short side direction of the substrate 305 can be reduced. Therefore, the size of the heater can be prevented from increasing. As shown in FIG. 10, the electrodes E2 to E6 are provided within the area having the heating resistors in the long side direction of the substrate. Figure 3B

[0050] The heater 300 of this embodiment individually controls the plurality of heating blocks so that various heating distributions can be formed, which will be described below. For example, a heating distribution according to the size of the recording material can be defined. Further, the heating resistors 302 can be formed of a material having PTC (positive temperature coefficient). The use of the material having PTC can suppress the temperature rise of the non-passing paper portion even in the case where the end portion of the recording material does not match the boundary of the heating block.

[0051] ​​The heater 300 has a plurality of thermistors (temperature sensors) T1-1 to T1-4 and T2-4 to T2-7 on the sliding surface layer 1 closer to the sliding surface (contacting the film), which are configured to sense the temperature of the heating blocks HB1 to HB7. The thermistors can be made of a material having a large TCR (temperature coefficient of resistance) in a positive or negative direction. According to this embodiment, the thermistors are formed by thinly printing a material having an NTC (negative temperature coefficient) on a substrate. One or more thermistors provided for each of the heating blocks HB1 to HB7 can sense the temperature of all the heating blocks.

[0052] Assuming that one of the thermistors T1-1 to T1-4 is a first temperature sensor and another of the thermistors T1-1 to T1-4 is a second temperature sensor, the heater 300 has the following configuration. That is, the heater 300 has the first temperature sensor at a position corresponding to the first heating block and the second temperature sensor at a position corresponding to the second heating block.

[0053] The thermistors T1-1 to T1-4 are electrically coupled to conductive patterns ET1-1 to ET1-4, respectively, on the substrate 305. Assuming that the conductive pattern of the conductive patterns ET1-1 to ET1-4 to be connected to the first temperature sensor is a first conductive pattern and the conductive pattern connected to the second temperature sensor is a second conductive pattern, the heater 300 has the following configuration. That is, the heater 300 has the first conductive pattern electrically coupled to the first temperature sensor and the second conductive pattern electrically coupled to the second temperature sensor. The heater 300 further has a common conductive pattern EG1 electrically coupled to the first temperature sensor and the second temperature sensor. Hereinafter, the group of the thermistors T1-1 to T1-4, the conductive patterns ET1-1 to ET1-4, and the common conductive pattern EG1 will be referred to as a thermistor group TG1.

[0054] The heater 300 further has a thermistor group TG2 of the thermistors T2-4 to T2-7, the conductive patterns ET2-4 to ET2-7, and a common conductive pattern EG2. The thermistor groups TG1 and TG2 are provided on the substrate surface of the substrate 305 on opposite sides of the substrate surface having the first heating block and the second heating block.

[0055] According to this example, at least one corresponding thermistor is provided for each of the heating blocks HB1 to HB7. However, providing one corresponding thermistor for at least two heating blocks can also improve the reliability of the device. However, as in this embodiment, at least one corresponding thermistor can be provided for all the heating blocks.

[0056] By treating the first temperature sensor and the second temperature sensor as one group using the common conductive patterns EG1 and EG2 as in this embodiment, the following effects can be provided. That is, compared to a case where two conductive patterns are connected to each of the thermistors T1-1 to T1-4 without using the common conductive patterns, the cost for the conductive patterns can be reduced, and the size of the heater can be prevented from increasing.

[0057] In order to obtain the slidability of the film 202, the surface of the substrate 305 near the fixing nip portion N (sliding surface layer 2) is coated with an insulating surface protective layer 308 (glass in this embodiment). The surface protective layer 308 covers the thermistors T1-1 to T1-4 and T2-4 to T2-7, the conductive patterns ET1-1 to ET1-4 and ET2-4 to ET2-7, and the common conductive patterns EG1 and EG2. However, in order to obtain connection with the electrical contacts, as shown in FIG. 6, a part of the conductive patterns ET1-1 to ET1-4 and ET2-4 to ET2-7 and a part of the common conductive patterns EG1 and EG2 are exposed at both ends of the heater 300. Figure 3B

[0058] Figure 4 is a circuit diagram of the control circuit 400 in the heater 300. A commercial AC power source 401 is connected to the laser printer 100. The power control to the heater 300 is performed by the energization / non-energization of triacs 411 to 414. The triacs 411 to 414 operate in accordance with FUSER1 to FUSER4 signals from a CPU 420. Figure 4 The drive circuit for the triacs 411 to 414 is not illustrated in FIG. 4.

[0059] From Figures 3A to 3C and Figure 4 It is understood that the seven heating blocks HB1 to HB7 are divided into four groups (group 1: HB4, group 2: HB3 and HB5, group 3: HB2 and HB6, group 4: HB1 and HB7). The control circuit 400 in the heater 300 has a circuit configuration capable of controlling the four groups independently of each other. The triac 411, the triac 412, the triac 413, and the triac 414 can control the group 1, the group 2, the group 3, and the group 4, respectively.

[0060] The zero-crossing detection unit 421 is a circuit configured to detect the zero-crossing of the AC power source 401, and outputs a ZEROX signal to the CPU 420. The ZEROX signal can be used as a reference signal for controlling the phase of the triacs 411 to 414, for example.

[0061] ​Next, a method for detecting the temperature of the heater 300 will be described. The thermistor group TG1 will be described first. The CPU 420 receives signals (Th1-1 to Th1-4) obtained by dividing the voltage Vcc by the resistance values of the thermistors (T1-1 to T1-4) and the resistance values of the resistors (451 to 454). For example, the signal Th1-1 is a signal obtained by dividing the voltage Vcc by the resistance value of the thermistor T1-1 and the resistance value of the resistor 451. Because the thermistor T1-1 has a resistance value that varies according to temperature, when the temperature of the heating block HB1 changes, the level of the signal Th1-1 input to the CPU also changes. The CPU 420 converts the input signal Th1-1 to a temperature according to the level. Because the same processing is performed on the signals Th1-2 to Th1-4 corresponding to the other thermistors T1-2 to T1-4 in the thermistor group TG1, any repetitive description will be omitted.

[0062] Next, the thermistor group TG2 will be described. In the thermistor group TG2, like the thermistor group TG1, the CPU 420 receives signals (Th2-4 to Th2-7) obtained by dividing the voltage Vcc by the resistance values of the thermistors (T2-4 to T2-7) and the resistance values of the resistors (464 to 467). Because the method applied by the CPU 420 for conversion to temperature is the same as the method for conversion to temperature used for the thermistor group TG1, any repetitive description will be omitted.

[0063] Next, power control (temperature control of the heater) of the heater 300 will be described. During the fixing process, the heating blocks HB1 to HB7 are controlled in such a manner that the temperatures sensed by the thermistors (T1-1 to T1-4) in the thermistor group TG1 can be maintained at a set temperature (control target temperature). More specifically, the power to be supplied to group 1 (the heating block HB4) is controlled by controlling the drive of the bidirectional thyristor 411 in such a manner that the temperature sensed by the thermistor T1-4 can be maintained at a set temperature. The power to be supplied to group 2 (the heating blocks HB3 and HB5) is controlled by controlling the drive of the bidirectional thyristor 412 in such a manner that the temperature sensed by the thermistor T1-3 can be maintained at a set temperature. The power to be supplied to group 3 (the heating blocks HB2 and HB6) is controlled by controlling the drive of the bidirectional thyristor 413 in such a manner that the temperature sensed by the thermistor T1-2 can be maintained at a set temperature. The power to be supplied to group 4 (the heating blocks HB1 and HB7) is controlled by controlling the drive of the bidirectional thyristor 414 in such a manner that the temperature sensed by the thermistor T1-1 can be maintained at a set temperature. The thermistors in the thermistor group TG1 are used to perform control for maintaining the heating blocks at a predetermined temperature.

[0064] The CPU 420 calculates the power supply amount by performing PI control based on, for example, the set temperature (control target temperature) of the heating block and the temperature sensed by the thermistors (T1-1 to T1-4) within the thermistor group TG1. Further, the power supply amount is converted into a control time for the corresponding phase angle (phase control) or wave number (wave number control), and the bidirectional thyristors 411 to 414 are controlled based on the control time. For fixing ordinary paper having the largest size, the set temperature of each group in the device of this embodiment is 250°C. For fixing ordinary paper having a smaller size, the set temperature of group 1 is 250°C, and the set temperatures of the other groups are lower than 250°C. The set temperature of each group can be defined in accordance with information such as the size, type, and surface properties of the recording material.

[0065] The relay 430 and the relay 440 are installed as units for shutting off the power to the heater 300 when the temperature of the heater 300 excessively rises due to, for example, a failure in the device. Next, the circuit operation of the relay 430 and the relay 440 will be described.

[0066] When the RLON signal output from the CPU 420 becomes the high state, the transistor 433 becomes the conductive state, and energizes the secondary coil of the relay 430 from the direct current power source (voltage Vcc). The primary side contact of the relay 430 becomes the ON state. When the RLON signal becomes the low state, the transistor 433 becomes the non-conductive state. The current fed from the power source (voltage Vcc) to the secondary coil of the relay 430 is blocked, and the primary side contact of the relay 430 becomes the OFF state. Further, when the RLON signal becomes the high state, the transistor 443 becomes the conductive state. The secondary coil of the relay 440 is energized from the power source (voltage Vcc), and the primary side contact of the relay 440 becomes the ON state. When the RLON signal becomes the low state, the transistor 443 becomes the non-conductive state. The current fed from the power source (voltage Vcc) to the secondary coil of the relay 440 is blocked, and the primary side contact of the relay 440 becomes the OFF state.

[0067] Next, the operation of the protection circuit using the relay 430 and the relay 440 (or the hardware circuit not passing through the CPU 420) will be described. When the level of one of the signals Th1-1 to Th1-4 exceeds the predetermined value set within the comparison unit 431, the comparison unit 431 causes the latch unit 432 to operate, and the latch unit 432 latches the RLOFF1 signal to the low state. When the RLOFF1 signal becomes the low state, the transistor 433 remains in the non-conductive state even if the CPU 420 changes the RLON signal to the high state. Therefore, the relay 430 can remain in the OFF state (or the safe state). The latch unit 432 outputs the RLOFF1 signal for the ON state in the non-latch mode.

[0068] Furthermore, when the level of any one of signals Th2-4 to Th2-7 exceeds the predetermined value set in comparison unit 441, comparison unit 441 activates latch unit 442, and latch unit 442 latches the RLOFF2 signal to a low state. When the RLOFF2 signal goes low, because even if CPU 420 goes high, transistor 443 remains off, relay 440 can remain in the closed state (or safe state). In the non-latched state, latch unit 442 outputs the RLOFF signal for the open state. Both the predetermined value set in comparison unit 431 and the predetermined value set in comparison unit 441 are equivalent to 300°C.

[0069] Next, the protection operation of the circuit utilizing two thermistor groups TG1 and TG2 will be described. For example... Figures 3A to 3C and Figure 4 As shown, one thermistor from thermistor group TG1 and one thermistor from thermistor group TG2 are provided for each of the four groups (groups 1 to 4). At least one thermistor is provided for each of the heating blocks HB1 to HB7. More specifically, for group 1 (HB4), thermistor T1-4 from thermistor group TG1 and thermistor T2-4 from thermistor group TG2 are placed accordingly. For group 2 (HB3 and HB5), thermistor T1-3 from thermistor group TG1 and thermistor T2-5 from thermistor group TG2 are placed accordingly. For group 3 (HB2 and HB6), thermistor T1-2 from thermistor group TG1 and thermistor T2-6 from thermistor group TG2 are placed accordingly. For groups 4 (HB1 and HB7), thermistors T1-1 from thermistor group TG1 and T2-7 from thermistor group TG2 are placed accordingly. For each of the heating blocks HB1 to HB7, at least one of the eight thermistors is placed accordingly. This arrangement of the thermistors improves the reliability of the protective operations performed by the circuit in the event of a device failure. This will be described below.

[0070] For example, suppose one of the thermistors T1-1 to T1-4 in the thermistor group TG1 fails. Even if the group including the heating block corresponding to the failed thermistor becomes uncontrollable due to the failed thermistor, the group with the heating block containing the failed thermistor also includes the thermistors (one of T2-4 to T2-7) in the thermistor group TG2. Therefore, the protection circuit operates through the thermistor in the thermistor group TG2 (its power supply is stopped).

[0071] Next, an advantage of the configuration in which at least one of the eight thermistors is placed corresponding to one of the heating blocks HB1 to HB7.

[0072] For example, assume a case where the thermistor T2-5 corresponding to group 2 is placed at a position corresponding to the heating block HB3 in the same group 2 as the heating block HB5, instead of a position corresponding to the heating block HB5. In this case, the thermistors T1-3 in the thermistor group TG1 and the thermistor T2-5 in the thermistor group TG2 are placed at positions corresponding to the heating block HB3, and no thermistor is placed at a position corresponding to the heating block HB5. In this configuration as well, the temperature of group 2 can be monitored. However, when the electrode E3 and the electrical contact C3 in this configuration have a contact failure, there is a possibility that the heating block HB3 can not be heated, while the heating block HB5 in the same group 2 as the heating block HB3 can be heated. Even when the heating block HB5 of group 2 abnormally generates heat, the two thermistors T1-3 and T2-5 corresponding to group 2 cannot monitor it, and the protection circuit does not work.

[0073] On the other hand, according to this embodiment, the thermistor T1-3 in the thermistor group TG1 is placed at a position corresponding to the heating block HB3, and the thermistor T2-5 in the thermistor group TG2 is placed at a position corresponding to the heating block HB5. Therefore, even when the electrode E3 and the electrical contact C3 have a contact failure and only the heating block HB5 in group 2 generates heat, the temperature can be monitored with the thermistor T2-5, and the protection circuit can be made to operate. As described above, because at least one of the eight thermistors is placed corresponding to one of the heating blocks HB1 to HB7, the reliability of the apparatus can be improved.

[0074] Figure 5 is a flowchart illustrating a control sequence of the control circuit 400 in the CPU 420. If a print request occurs in S100, the relays 430 and 440 are made to be in an on state in S101.

[0075] In S102, the triac 414 is subjected to PI control so that the temperature sensed by the thermistor T1-1 (signal Th1-1) can reach a control target temperature to control the power to be supplied to the heating blocks HB1 and HB7.

[0076] In S103, the triac 413 is subjected to PI control so that the temperature sensed by the thermistor T1-2 (signal Th1-2) can reach a control target temperature to control the power to be supplied to the heating blocks HB2 and HB6.

[0077] In S104, the triac 412 is subjected to PI control so that the temperature sensed by the thermistor T1-3 (signal Th1-3) can reach the control target temperature to control the power to be supplied to the heating blocks HB3 and HB5.

[0078] In S105, the triac 411 is subjected to PI control so that the temperature sensed by the thermistor T1-4 (signal Th1-4) can reach the control target temperature to control the power to be supplied to the heating block HB4.

[0079] As described above, the control target temperature of each heating block is set based on information about the size of a given recording material. In the apparatus according to this embodiment, the control target temperature of the heating block HB4 including the conveyance reference X is set to one temperature regardless of the size of the recording material, while the control target temperatures of the other heating blocks are changed based on the size of the recording material. As the size of the recording material decreases, the control target temperatures set for the heating blocks other than the heating block HB4 are lowered.

[0080] In S106, it is determined whether the temperature rise in the non-passing paper portion is equal to or lower than a predetermined threshold temperature (margin temperature) Tmax. According to this embodiment, Tmax is set to be higher than the control target temperature of 250°C of the heating block HB4, and is set to 280°C which is a temperature lower than the predetermined value of 300°C set for the comparison units 431 and 441. The positional relationship between the thermistors in the thermistor group TG1 and the reference X is different from the positional relationship between the thermistors in the thermistor group TG2 and the reference X. The thermistors in the thermistor group TG2 are placed on the outer side in the long side direction of the heater 300 with respect to the conveyance reference position X, compared to the thermistors in the thermistor group TG1. As shown in FIG. 6, the relationship can be easily understood by comparing the distance from the reference X to the thermistor T1-4 corresponding to the heating block HB4 and the distance from the reference X to the thermistor T2-4 corresponding to the heating block HB4. Because of this arrangement, the thermistors in the thermistor group TG2 can detect the temperature rise in the non-passing paper portion, if any, occurring within one heating block. Figure 3B

[0081] When it is determined in S106 that the temperatures sensed by the thermistors T2-4 to T2-7 are equal to or lower than the threshold temperature Tmax, the process moves to S108. The control in S102 to S106 is repeated until it is detected in S108 that the print job ends.

[0082] ​If it is determined in S106 that the temperature of the thermistors T2-4 to T2-7 is higher than the threshold temperature Tmax, the processing speed of image formation of the image forming apparatus 100 is reduced in S107, and the control target temperature of the thermistors T1-1 to T1-4 is reduced so that the fixing processing can then be performed. The reduced processing speed of image formation can provide fixing properties even at a lower temperature compared to full speed processing. Thus, the temperature rise in the non-paper passing portion can be suppressed.

[0083] The above processing is repeated, and if it is detected in S108 that the print job is ended, the relay 430 and the relay 440 are turned off in S109. Then, the control sequence for image formation is ended in S110.

[0084] Second Exemplary Embodiment

[0085] Next, a second exemplary embodiment will be described in which the heater 300 and the control circuit 400 for the heater according to the first exemplary embodiment are changed to a heater 600 and a control circuit 700. Similar numbers refer to similar parts in the description of the first exemplary embodiment and the second exemplary embodiment, and any repetitive description will be omitted. The heater 600 according to the second exemplary embodiment differs from the heater 300 in the configuration of the sliding surface layer 1. The control circuit 700 has heating blocks HB1 to HB7 all of which are independently controlled.

[0086] Figure 6A And 6B The configuration of the heater 600 according to the second exemplary embodiment will be illustrated. Since the configuration other than the sliding surface layer 1 is the same as the heater 300, any repetitive description will be omitted.

[0087] The sliding surface layer 1 of the heater 600 has thermistors T3-1a to T3-4a, T3-1b to T3-3b, T4-4a to T4-7a, T4-5b to T4-7b, and T5 configured to detect the temperature of the heating blocks HB1 to HB7. Since two or more thermistors are associated with all of the heating blocks HB1 to HB7, the temperature of all of the heating blocks can be detected even when one of the thermistors fails.

[0088] The thermistor group TG3 has seven thermistors T3-1a to T3-4a and T3-1b to T3-3b, conductive patterns ET3-1a to ET3-4a and ET3-3b, ET3-12b, a common conductive pattern EG3.

[0089] Further, the thermistor group TG4 has seven thermistors T4-4a to T4-7a and thermistors T4-5b to T4-7b, conductive patterns ET4-4a to ET4-7a, ET4-5b and ET4-67b, and a common conductive pattern EG4.

[0090] First, the thermistor group TG3 will be described. The thermistors T3-1b and T3-2b are configured to detect the temperatures of the heating blocks HB1 and HB2, and these two thermistors are connected in parallel between the conductive pattern ET3-12b and the common conductive pattern EG3. As one of the heating blocks HB1 and HB2 increases in temperature, one of the resistance values of the thermistors T3-1b and T3-2b greatly decreases. Therefore, the temperatures of both of the heating blocks HB1 and HB2 can be detected with the conductive pattern ET3-12b configured to detect the resistance values of the thermistors. Therefore, compared to the case where the conductive patterns are connected and wired to the thermistors T3-1b and T3-2b, the cost of the wiring for forming the conductive patterns can be reduced. The width in the short side direction of the substrate 305 can be reduced. Further, the thermistors T4-6b and T4-7b can be connected in parallel.

[0091] The common conductive patterns EG3 and EG4 are connected on the substrate 305 by the conductive pattern EG34 for disconnection detection as shown in Figure 7 Performing such disconnection detection can improve the level of safety when a disconnection failure occurs.

[0092] The two thermistors T3-3a and T3-3b are provided for one heating block HB3, and the conductive patterns ET3-3a and ET3-3b configured to detect resistance values and the common conductive pattern EG3 provide a configuration that can detect the temperature.

[0093] Within the range of the heating block HB3, the thermistor T3-3b placed at a position apart from the conveyance reference position X is configured to detect the temperature of the edge, and the thermistor T3-3a placed at a position close to the conveyance reference position X is configured for temperature adjustment. A plurality of thermistors can be provided for one heating block as needed.

[0094] Because the configuration and operation of the thermistor group TG4 are the same as those of the thermistor group TG3, any repetitive description will be omitted.

[0095] The thermistor T5 is a single thermistor provided between the conductive patterns ET5 and EG5 for detecting resistance values. The single thermistor can be combined with a thermistor group as needed.

[0096] Figure 7 is a circuit diagram of a control circuit 700 for the heater 600 according to the second exemplary embodiment. The power control to the heater 600 is performed by the on / off of the thyristors 711 to 717. The thyristors 711 to 717 operate according to the FUSER1 to FUSER7 signals from the CPU 420. The control circuit 700 for the heater 600 has the circuit configuration of seven thyristors 711 to 717 for independently controlling the seven heating blocks HB1 to HB7.

[0097] Next, how to detect the temperature of the heater 600 will be described. The CPU 420 receives signals (Th3-1a to Th3-4a, Th3-3b, Th3-12b) obtained by dividing the voltage Vcc by the resistance values of the thermistors T3-1a to T3-4a, T3-1b and T3-2b in the thermistor group TG3 and the resistance values of the resistors 751 to 756. The CPU 420 further receives signals obtained by dividing the voltage Vcc by the resistance values of the thermistors T4-4a to T4-7a, T4-5b to T4-7b in the thermistor group TG4 and the resistance values of the resistors 771 to 776. These signals are indicated by Th4-4a to Th4-7a, Th4-5b and Th4-67b in Figure 7 . The CPU further receives a signal (Th5) obtained by dividing the voltage Vcc by the resistance value of the thermistor T5 and the resistance value of the resistor 761. The CPU 420 converts the received signals to temperatures based on the levels of the signals.

[0098] The CPU 420 calculates the power supply amount by performing the PI control, for example, based on the set temperature (control target temperature) of the heating block and the temperature sensed by the thermistors. The calculated power supply amount is converted to the control time for the corresponding phase angle (phase control) or wave number (wave number control), and the thyristors 711 to 717 are controlled based on the control time.

[0099] Next, the operation of the protection circuit using the relays 430 and 440 will be described. Based on the Th3-1a to Th3-4a signals of the thermistor group TG3 and the Th4-5b and Th4-67b signals of the thermistor group TG4, the comparison unit 431 causes the latch unit 432 to operate if one of the sensed temperatures exceeds a predetermined value set respectively.

[0100] Further, based on the Th4-4a to Th4-7a signals of the thermistor group TG4 and the Th3-3b and Th3-12b signals of the thermistor group TG3, the comparison unit 441 causes the latch unit 442 to operate if one of the sensed temperatures exceeds a predetermined value set respectively.

[0101] Next, the disconnection detection circuit 780 will be described. The disconnection detection circuit 780 is a circuit that can be used to improve safety in the case where the common conductive patterns EG3 and EG4 are disconnected.

[0102] The circuit operation of the disconnection detection circuit 780 will be described. When the common conductive patterns EG3 and EG4 are disconnected, the pull-up of the resistors 781 and 782 to the power supply voltage Vcc causes the disconnection detection signal ThSafe to become a high state. The resistors 781 and 782 are provided in consideration of a failure due to a resistor short circuit. When the disconnection detection signal ThSafe becomes a high state, the latch units 432 and 442 are caused to operate.

[0103] Next, the effects of the disconnection detection circuit 780 and the conductive pattern EG34 will be described. First, a case where the common conductive pattern EG3 and the common conductive pattern EG4 are connected to GND as in the configuration of the first exemplary embodiment, without both the conductive pattern EG34 and the disconnection detection circuit 780, will be described. In this case, when the common conductive pattern EG3 is disconnected, all of the thermistors of the thermistor group TG3 are disabled. Therefore, the protection circuit configured to terminate the supply of power to the heating blocks HB1 to HB3 does not operate. Further, when the common conductive pattern EG4 is disconnected, all of the thermistors of the thermistor group TG4 are disabled. Therefore, the protection circuit configured to terminate the heating blocks HB5 to HB7 does not operate.

[0104] Next, a case where, although the conductive pattern EG34 that connects the common conductive patterns EG3 and EG4 is provided, the common conductive patterns EG3 and EG4 are connected to GND as in the configuration of the first exemplary embodiment, without the disconnection detection circuit 780, will be described. In this case, because of the effect of the conductive pattern EG34, one of the common conductive patterns EG3 and EG4 is connected to GND through the conductive pattern EG34 even when the other is disconnected. Therefore, temperature detection can be performed by the thermistor groups TG3 and TG4. However, the conductive patterns (ET3-1a to ET3-4a and ET3-12b, ET3-3b, and EG3) configured to connect the thermistor group TG3 and the connector (not illustrated) of the control circuit 700 are disconnected, all of the thermistors of the thermistor group TG3 are disabled. Therefore, the protection circuit configured to terminate the supply of power to the heating blocks HB1 to HB3 does not operate. Further, the conductive patterns (ET4-4a to ET4-7a and ET4-67b, ET4-5b, and EG4) configured to connect the thermistor group TG4 and the connector of the control circuit 700 are disconnected, all of the thermistors of the thermistor group TG4 are disabled. Therefore, the protection circuit configured to terminate the supply of power to the heating blocks HB5 to HB7 does not operate.

[0105] On the other hand, the device of this embodiment has the conductive pattern EG34 and the disconnection detection circuit 780. Thus, it is possible to detect the failure state of both the cases where the common conductive pattern EG3 and EG4 are disconnected and where the connector connecting the thermistor groups TG3 and TG4 and the control circuit 700 is disconnected.

[0106] Figure 8 is a flowchart illustrating a control sequence on the control circuit 700 to be executed by the CPU 420. Like numerals refer to like components in Figure 5 and Figure 8 , and any repetitive description will be omitted.

[0107] In S201, the triac 711 is subjected to PI control so that the temperature sensed by the thermistor T3-1a (signal Th3-1a) can reach a predetermined target temperature to control the power to be supplied to the heating block HB1.

[0108] In S202, the triac 712 is subjected to PI control so that the temperature sensed by the thermistor T3-2a (signal Th3-2a) can reach a predetermined target temperature to control the power to be supplied to the heating block HB2.

[0109] In S203, the triac 713 is subjected to PI control so that the temperature sensed by the thermistor T3-3a (signal Th3-3a) can reach a predetermined target temperature to control the power to be supplied to the heating block HB3.

[0110] In S204, the triac 714 is subjected to PI control so that the temperature sensed by the thermistor T5 (signal Th5) can reach a predetermined target temperature to control the power to be supplied to the heating block HB4.

[0111] In S205, the triac 715 is subjected to PI control so that the temperature sensed by the thermistor T4-5a (signal Th4-5a) can reach a predetermined target temperature to control the power to be supplied to the heating block HB5.

[0112] In S206, the triac 716 is subjected to PI control so that the temperature sensed by the thermistor T4-6a (signal Th4-6a) can reach a predetermined target temperature to control the power to be supplied to the heating block HB6.

[0113] In S207, the triac 717 is subjected to PI control so that the temperature sensed by the thermistor T4-7a (signal Th4-7a) can reach a predetermined target temperature to control the power to be supplied to the heating block HB7.

[0114] In S208, it is determined whether the temperature rise in the non-paper passing portion is equal to or lower than a predetermined threshold temperature (tolerance temperature) Tmax.

[0115] When it is determined in S208 that the temperatures sensed by the thermistors T3-4a, T4-4a, T3-3b, and T4-5b are equal to or lower than the threshold temperature Tmax, the process moves to S108. Then, the control in S201 to S208 is repeated until it is detected in S108 that the print job ends.

[0116] Third Exemplary Embodiment

[0117] Figure 9A And 9B The heater 800 in the third exemplary embodiment has a heating resistor 802 near the fixing nip portion N and a thermistor group TG6 on the opposite side of the fixing nip portion N. Like numbers refer to like parts in the description of the first and third exemplary embodiments, and any description will be omitted.

[0118] Figure 9A is a cross-sectional view of the central region (near the conveyance reference position X) of the heater 800. The back surface layer 1 has only the conductive pattern, and a chip thermistor T6-2 is incorporated thereon. The heater 800 further has electrodes 810 and 811 for the chip thermistor T6-2. The chip thermistor T6-2 is connected to the conductive pattern EG6 and the conductive patterns ET6-2 through the electrode 810 and the electrode 811. Placing the thermistor group TG6 on the opposite side of the fixing nip portion N as in the heater 800 can eliminate the necessity of flatness of its sliding surface layer, so that a thick chip thermistor T6-2 can be installed.

[0119] The thermistor group TG6 provided in the back surface layer 1 of the heater 800 has three chip thermistors T6-1 to T6-3, conductive patterns ET6-1 to ET6-3 configured to detect the resistance values of the thermistors, and a common conductive pattern EG6.

[0120] The sliding surface layer 1 of the heater 800 has three heating blocks HB1 to HB3. The heating resistor 802 is divided into three, 802-1 to 802-3, and receives a power supply through the first electric conductor 801 and three second electric conductors 803-1 to 803-3. The second electric conductors 803-1 to 803-3 are connected to the electrodes E1 to E3, and the first electric conductor 801 is connected to the electrode E8. A switching element such as a bidirectional thyristor is provided for each of the electrodes E1 to E3, and the electrode E8 is provided as a common electrode, so that the three heating blocks HB1 to HB3 can be controlled independently of each other. The sliding surface layer 2 of the heater 800 has a protective layer 808 of glass having sliding properties and insulating properties.

[0121] In the heater 800, the first electric conductor 801 and the second electric conductors 803 can be connected through wiring at both ends of the heater in the short side direction for supplying power to the heating blocks HB1 to HB3. Because of this necessity, when the number of heating blocks is particularly increased, the area for wiring the first electric conductor 801 and the second electric conductors 803 can increase, thereby increasing the size of the heater.

[0122] The electrodes E2 to E6 can be provided within the heating region as in the heater 300 according to the first exemplary embodiment and the heater 600 according to the second exemplary embodiment, so that the area required for wiring the first electric conductor 301 and the second electric conductor 303 is not required. Thus, the size of the heater does not increase while the number of heating blocks can be increased. In the configuration having the electrodes E2 to E6 in the heating region, it can be necessary to provide the electrodes E2 to E6 on the opposite side of the fixing nip N for connecting the electric contacts C2 to C6. For this purpose, the heating blocks (HB1 to HB7) can be provided on the opposite side of the fixing nip N, and the thermistor groups (TG1, TG2, TG3, and TG4) can be formed close to the fixing nip N.

[0123] When a smaller number of heating blocks is provided, as in the heater 800 according to this embodiment, the thermistor group TG6 having a plurality of sheet-shaped thermistors can be placed on the opposite side of the fixing nip N.

[0124] Fourth Exemplary Embodiment

[0125] Figure 10A and 10B The heater according to the fourth exemplary embodiment illustrated in the above-described (1) differs from the heaters according to the first exemplary embodiment and the second exemplary embodiment in the shape of the heating resistor. Figure 10A The heating resistors 902a and 902b in the illustrated heater 900 are continuous (or not divided) in the long side direction.

[0126] Figure 10A is a plan view of the back surface layer 1 of the heater 900. Because the electrically conductive body 303 is divided into seven in the long side direction, the heating resistors 902a and 902b are independently temperature-controlled in the regions of the heating blocks HB1 to HB7. Because the heating resistors 902a and 902b are not divided, the heater 900 continuously generates heat in the long side direction even in the gap regions in which the electrically conductive body 303 is divided. Therefore, there is no region in which the heating value is equal to 0 (zero), and the heater can thereby uniformly generate heat in the long side direction.

[0127] Figure 10B The illustrated heater 1000 has heating resistors 1002a and 1002b that are further divided into a plurality of heating resistors connected in parallel.

[0128] Figure 10B is a plan view of the back surface layer 1 of the heater 1000. The heating resistor 1002a is divided into a plurality of heating resistors connected in parallel between the connected electrically conductive body 303 and the electrically conductive body 301a. Further, the heating resistor 1002b is divided into a plurality of heating resistors connected in parallel between the electrically conductive body 303 and the electrically conductive body 301a.

[0129] The heating resistors obtained by dividing the heating resistors 1002a and 1002b are inclined in the long side direction and the short side direction of the heater 1000, and overlap each other in the long side direction of the heater 1000. This can reduce the influence of the gaps between the plurality of divided heating resistors, and thereby can improve the uniformity of the heating distribution in the long side direction of the heater 1000. In the heater 1000, because the divided heating resistors at the edges of adjacent heating blocks overlap each other in the long side direction, a more uniform heating distribution can be provided in the long side direction of the heater 1000 even in the gaps between the heating blocks. The heating resistors at the edges of adjacent heating blocks can be, for example, the heating resistor at the right end of the heating block HB1 and the heating resistor at the left end of the heating block HB2.

[0130] The uniformity of the heating distribution of the heating resistors 1002a and 1002b can be obtained by adjusting the width, length, interval, inclination, and the like of the divided heating resistors. The adoption of the configuration of the heater 900 or the heater 1000 can suppress temperature unevenness in the gaps between the plurality of heating blocks.

[0131] Fifth Exemplary Embodiment

[0132] Figure 11A and 11B The waveform of the current fed to the heating blocks in the control circuit 400 according to the first exemplary embodiment is illustrated. Figure 11AThe table illustrates the driving modes for the bidirectional thyristor 411 (or a table of waveforms of the current to be fed to the heating block HB4), these waveforms being defined for each duty cycle of the power to be supplied to the heater 300. Furthermore, Figure 11B Examples illustrate the driving modes for bidirectional thyristors 412 to 414 (or a table showing the waveforms of the currents fed to heating blocks HB1 to HB3 and HB5 to HB7).

[0133] The CPU 420 calculates the level (duty cycle) of the power to be supplied to the heater in each control cycle, and then selects a waveform according to the duty cycle for each heating block to be supplied with that power. In the control method according to this exemplary embodiment, four half-waves are defined as a control cycle to set the energizing control mode for each bidirectional thyristor, thereby controlling the power supplied to the heater 300.

[0134] An example of a power-on control mode for a bidirectional SCR 411 will be described, in which the duty cycle is equal to 25%. According to Figure 11A The power-on control mode A shown for the bidirectional SCR 411, where the first half-wave transitions to the second half-wave at 90°... ° Phase angle control supplies 50% power and shuts off the power during the third to fourth half-wave. Therefore, an average of 25% power is supplied to the heating block HB4 of heater 300. In power-on control mode A, phase control is performed during the first to second half-wave.

[0135] exist Figure 11B In the power-on control modes shown for bidirectional thyristors 412 to 414, the third half-wave to the fourth half-wave uses 90°. ° Phase angle control supplies 50% of the power, and the power is switched off during the first half-wave to the second half-wave. Therefore, an average of 25% of the power is supplied to the heating blocks HB1 to HB3 and HB5 to HB7 of heater 300. Power-on control mode B performs phase control during the third half-wave to the fourth half-wave.

[0136] Because the resistance of heating element HB4 in heater 300 is lower than that of other heating elements, the current variation during phase control is larger compared to other heating elements. According to this embodiment, the period for feeding the phase control current to heating element HB4 (from the first half-wave to the second half-wave) differs from the periods for feeding the phase control current to other heating elements HB1 to HB3 and HB5 to HB7 (from the third half-wave to the fourth half-wave). Therefore, fluctuations in the current fed to the entire heater 300 under phase control can be suppressed. The same applies to duty cycles other than 25%.

[0137] like Figure 11A and 11BAs shown, the control periods for the plurality of triacs can be synchronized for control (this is referred to as synchronized control over the plurality of triacs) so that harmonic current in the image heating apparatus 200 can be reduced. Figure 11A and 11B The example synchronized control is illustrated, and for example, synchronized control can be performed over the plurality of triacs to reduce flicker.

[0138] The same method can be applied to the triacs 711 to 717 in the control circuit 700 to perform synchronized control over the plurality of triacs.

[0139] Synchronized control over the plurality of triacs can advantageously reduce harmonic current and flicker, and even when the total resistance value of the heater 300 is set to be low, standards for preventing harmonic current and flicker can be further satisfied. When a lower resistance value can be set to the heater 300, the maximum power that can be supplied from the AC power source 401 to the heater 300 can be increased.

[0140] In the plurality of example embodiments described above, a center reference printer is used in which a center of a recording material in a width direction is placed at a conveyance reference position X to convey the recording material. However, the present application is also applicable to a one-side reference printer in which one end in a long side direction of a heater is defined as a conveyance reference position, and one end of a recording material in a width direction is placed at the conveyance reference position to convey the recording material.

[0141] While the present application has been described with reference to example embodiments, it is to be understood that the application is not limited to the disclosed example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all the

[0142] This application claims the benefit of Japanese Patent Application No. 2015-179567, filed September 11, 2015, which is hereby incorporated by reference in its entirety.

[0143] List of Reference Signs

[0144] 200 image heating apparatus

[0145] 300 heater

[0146] 301 first electric conductor

[0147] 302 heating resistor

[0148] 303 second electric conductor

[0149] 305 substrate

[0150] E1-E7, E8-1, E8-2 electrode

[0151] HB1-HB7 heating block

Claims

1. A heater for use in an image heating apparatus, the heater comprising: a substrate; a plurality of heating blocks disposed on the substrate and configured to generate heat from power supplied to the plurality of heating blocks, the plurality of heating blocks including: a first heating block placed at one end of the plurality of heating blocks with respect to a long side direction of the substrate; a second heating block placed at a position different from the position at which the first heating block is disposed with respect to the long side direction; a third heating block placed at the other end of the plurality of heating blocks with respect to the long side direction; and a fourth heating block placed at a position different from the positions at which the first, second, and third heating blocks are disposed with respect to the long side direction; a first electrode in contact with a first electrical contact provided on the image heating apparatus to supply power to the first heating block; a second electrode in contact with a second electrical contact provided on the image heating apparatus to supply power to the second heating block; a third electrode in contact with a third electrical contact provided on the image heating apparatus to supply power to the third heating block; a fourth electrode in contact with a fourth electrical contact provided on the image heating apparatus to supply power to the fourth heating block; and a common electrode in contact with a common electrical contact to supply power to the first to fourth heating blocks, wherein the first to fourth electrodes are electrically independent of each other, each of the first to fourth heating blocks has a first conductive body disposed along the long side direction, a second conductive body disposed at a position different from the position of the first conductive body in a short side direction of the substrate along the long side direction, and a heat generating member disposed between the first and second conductive bodies and configured to generate heat from power supplied through the first and second conductive bodies, the first conductive bodies of the first to fourth heating blocks are connected to each other, the common electrode is connected to the first conductive bodies and is disposed outside a region in which the plurality of heating blocks are disposed with respect to the long side direction, the second electrode is connected to the second conductive body of the second heating block and is disposed within a region in which the second heating block is disposed with respect to the long side direction and within a region in which the second conductive body of the second heating block is disposed with respect to the short side direction, the fourth electrode is connected to the second conductive body of the fourth heating block and is disposed within a region in which the fourth heating block is disposed with respect to the long side direction and within a region in which the second conductive body of the fourth heating block is disposed with respect to the short side direction, the first electrode is connected to the second conductive body of the first heating block, the third electrode is connected to the second conductive body of the third heating block, the first electrode is disposed outside the region in which the plurality of heating blocks are disposed with respect to the long side direction and within the region in which the second conductive body of the first heating block is disposed with respect to the short side direction, and the second electrode is disposed outside the region in which the plurality of heating blocks are disposed with respect to the long side direction and within the region in which the second conductive body of the second heating block is disposed with respect to the short side direction, and the third electrode is disposed outside the region in which the plurality of heating blocks are disposed with respect to the long side direction and within the region in which the second conductive body of the third heating block is disposed with respect to the short side direction, and the fourth electrode is disposed outside the region in which the plurality of heating blocks are disposed with respect to the long side direction and within the region in which the second conductive body of the fourth heating block is disposed with respect to the short side direction. The third electrode is provided outside a region in which the plurality of heating blocks are arranged with respect to the long-side direction and within a region in which the second electrically conductive body of the third heating block is arranged with respect to the short-side direction.

2. The heater of claim 1, wherein, The length of the first heating block with respect to the long-side direction is shorter than the length of the second heating block, and the length of the third heating block with respect to the long-side direction is shorter than the length of the fourth heating block.

3. The heater of claim 1, further comprising: The second common electrode is in contact with another common electric contact to supply electric power to the first heating block to the fourth heating block, The second common electrode is provided outside a region in which the plurality of heating blocks are arranged with respect to the long-side direction.

4. An image heating apparatus that heats an image formed on a recording material, the image heating apparatus comprising: a tubular film; a heater provided inside a space of the film; a first electric contact; a second electric contact; a third electric contact; a fourth electric contact; and a common electric contact, The heater includes: a substrate, a plurality of heating blocks arranged on the substrate and configured to generate heat from electric power supplied to the plurality of heating blocks, the plurality of heating blocks including: a first heating block placed at one end of the plurality of heating blocks with respect to a long-side direction of the substrate; a second heating block placed at a position different from the position at which the first heating block is arranged with respect to the long-side direction; a third heating block placed at the other end of the plurality of heating blocks with respect to the long-side direction; and a fourth heating block placed at a position different from the positions at which the first heating block, the second heating block, and the third heating block are arranged with respect to the long-side direction, a first electrode in contact with the first electric contact to supply electric power to the first heating block, a second electrode in contact with the second electric contact to supply electric power to the second heating block, a third electrode in contact with the third electric contact to supply electric power to the third heating block, a fourth electrode in contact with the fourth electric contact to supply electric power to the fourth heating block, and a common electrode in contact with the common electric contact to supply electric power to the first heating block to the fourth heating block, The first electrode to the fourth electrode are electrically independent of each other, Each of the first heating block to the fourth heating block has a first electrically conductive body arranged along the long-side direction, a second electrically conductive body arranged at a position different from the position of the first electrically conductive body in a short-side direction of the substrate along the long-side direction, and a heat generating member arranged between the first electrically conductive body and the second electrically conductive body and configured to generate heat from electric power supplied through the first electrically conductive body and the second electrically conductive body, The first electrically conductive bodies of the first heating block to the fourth heating block are connected to each other, the common electrode is connected to the first electrically conductive bodies, and the common electrode is provided outside a region in which the plurality of heating blocks are arranged with respect to the long-side direction. The second electrode is connected to the second electrically conductive body of the second heating block, and the second electrode is provided within a region in which the second heating block is arranged with respect to the long-side direction and within a region in which the second electrically conductive body of the second heating block is arranged with respect to the short-side direction. ​ The fourth electrode is connected to the second conductive body of the fourth heating block, and the fourth electrode is disposed in a region in which the fourth heating block is disposed with respect to the long-side direction and in a region in which the second conductive body of the fourth heating block is disposed with respect to the short-side direction, The first electrode is connected to the second conductive body of the first heating block, The third electrode is connected to the second conductive body of the third heating block, The first electrode is disposed outside a region in which the plurality of heating blocks are disposed with respect to the long-side direction and in a region in which the second conductive body of the first heating block is disposed with respect to the short-side direction, and The third electrode is disposed outside a region in which the plurality of heating blocks are disposed with respect to the long-side direction and in a region in which the second conductive body of the third heating block is disposed with respect to the short-side direction.

5. The image heating apparatus according to claim 4, wherein The length of the first heating block with respect to the long-side direction is shorter than the length of the second heating block, and the length of the third heating block with respect to the long-side direction is shorter than the length of the fourth heating block.

6. The image heating apparatus of claim 4, further comprising: A second common electrode that is in contact with another common electrical contact to supply power to the first heating block to the fourth heating block, The second common electrode is disposed outside a region in which the plurality of heating blocks are disposed with respect to the long-side direction.

7. The image heating apparatus of claim 4, further comprising: A roller configured to form a press-bonding portion with the heater through the film to press-bond the recording material.

Images