JP7639110B2 - Image heating apparatus and heater for use in image heating apparatus - Google Patents

Description

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

As an image heating device, there is a device having a cylindrical film, a heater that contacts the inner surface of the film, and a roller that forms a nip portion with the heater via the film. When small size paper is continuously printed by an image forming device equipped with this image heating device, a phenomenon occurs in which the temperature of an area in the longitudinal direction of the nip where the paper does not pass gradually increases (non-paper passing area temperature increase).
If the temperature of the non-paper passing areas becomes too high, it can damage various parts inside the device, and when printing on large-sized paper while the temperature of the non-paper passing areas is rising, the toner can be high-temperature offset onto the film in the area corresponding to the non-paper passing areas of the small-sized paper.

As one method for suppressing this temperature rise in non-paper passing areas, a device has been proposed in which the heat generating resistor on the heater is divided into multiple groups (heat generating blocks) in the heater's longitudinal direction, and the heater's heat distribution is switched according to the size of the recording material (Patent Document 1).

JP 2014-59508 A

When considering equipment failure, it is preferable to configure the device to monitor the temperature of each heat generating block. Even if one of the multiple heat generating blocks becomes uncontrollable and generates abnormal heat, if the temperature of each heat generating block is monitored, power supply can be stopped quickly.

However, as the number of heat generating blocks increases, the number of temperature detection elements for monitoring the temperature also increases. If many temperature detection elements are provided within the area of the heater substrate, the heater will become larger.

The present invention for solving the above-mentioned problems includes a cylindrical film, a heater provided in an internal space of the film, the heater having a substrate, a first heat generating block provided on the substrate and generating heat when supplied with electric power, and a second heat generating block provided at a position in the longitudinal direction of the substrate different from the position at which the first heat generating block is provided and generating heat when supplied with electric power, a roller that contacts an outer peripheral surface of the film, the roller sandwiching the film between the heater and the heater to form a nip portion for sandwiching and conveying a recording material between the heater and the film, a first switch element for controlling the electric power supplied to the first heat generating block, a second switch element for controlling the electric power supplied to the second heat generating block, and a switch between the first switch element and the second switch element. and a control unit that controls a nip element, and heats and fixes a toner image formed on a recording material onto the recording material while nipping and transporting the recording material at the nip portion, wherein a region in the longitudinal direction in which the first heat generating block is provided has a plurality of temperature sensors, the outputs of which are input to the control unit , and the plurality of temperature sensors include a first sensor, a second sensor and a third sensor, the first sensor being provided near a reference position for transporting the recording material in the longitudinal direction, the second sensor being provided at one end position in the region in which the first heat generating block is provided, and the third sensor being provided at the other end position in the longitudinal direction in the region in which the first heat generating block is provided.

The present invention makes it possible to prevent the heater from becoming too large.

FIG. FIG. FIG. 2 is a diagram showing the heater configuration of the first embodiment. FIG. 2 is a diagram of a heater control circuit according to the first embodiment. 4 is a flowchart of heater control according to the first embodiment. FIG. 11 is a diagram showing a heater configuration according to a second embodiment. FIG. 11 is a diagram of a heater control circuit according to a second embodiment. 10 is a flowchart of a heater control according to the second embodiment. FIG. 13 is a diagram showing a modified example of the heater. FIG. 13 is a diagram showing a modified example of the heater. FIG. 4 is a diagram showing a heater current control pattern.

Example 1
FIG. 1 is a cross-sectional view of a laser printer (image forming apparatus) 100 using electrophotographic recording technology. When a print signal is generated, a scanner unit 21 emits a laser beam modulated according to image information, and scans a photoconductor 19 charged to a predetermined polarity by a charging roller 16. As a result, an electrostatic latent image is formed on the photoconductor 19. Toner is supplied from a developing device 17 to this electrostatic latent image, and a toner image according to the image information is formed on the photoconductor 19. Meanwhile, recording materials (recording paper) P loaded in a paper feed cassette 11 are fed one by one by a pickup roller 12 and conveyed toward a registration roller 14 by a roller 13. Furthermore, the recording material P is conveyed from the registration roller 14 to a transfer position in accordance with the timing when the toner image on the photoconductor 19 reaches a transfer position formed by the photoconductor 19 and a transfer roller 20. The toner image on the photoconductor 19 is transferred to the recording material P while the recording material P passes through the transfer position.
Thereafter, the recording material P is heated by an image heating device (fixing device) 200, and the toner image is heat-fixed to the recording material P. The recording material P carrying the fixed toner image is discharged to a tray at the top of the laser printer 100 by rollers 26 and 27. Reference numeral 18 denotes a cleaner for cleaning the photoconductor 19. Reference numeral 30 denotes a motor for driving the image heating device 200 and the like. Power is supplied to the image heating device 200 from a control circuit 400 connected to a commercial AC power source 401. The above-mentioned photoconductor 19, charging roller 16, scanner unit 21, developing device 17, and transfer roller 20 constitute an image forming section for forming an unfixed image on the recording material P. Reference numeral 15 denotes a cartridge as a replaceable unit. Reference numeral 22 denotes a light source, 23 denotes a polygon mirror, and 24 denotes a reflecting mirror.

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

The printer in this example is a laser printer that basically feeds paper vertically (transports the paper so that the long side is parallel to the transport direction). The configuration proposed here can also be applied to printers that feed paper horizontally. The largest (widest) recording materials among the standard recording material widths (catalog recording material widths) that the device supports 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 that the device supports is defined as small size paper.

FIG. 2 is a cross-sectional view of the image heating device 200. The image heating device 200 has a cylindrical film 202, a heater 300 that contacts the inner surface of the film 202, and a pressure roller (nip portion forming member) 208 that forms a fixing nip portion N with the heater 300 via the film 202. The material of the base layer of the film 202 is a heat-resistant resin such as polyimide, or a metal such as stainless steel. The film 202 may also be provided with an elastic layer such as heat-resistant rubber. The 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. The heater 300 is held by a holding member 201 made of a heat-resistant resin such as a liquid crystal polymer. The holding member 201 also has a guide function for guiding the rotation of the film 202. The pressure roller 208 receives power from a motor 30 and rotates in the direction of the arrow. The film 202 rotates in response to the rotation of the pressure roller 208. The recording material P carrying the unfixed toner image is heated and fixed while being nipped and conveyed through the fixing nip N.
Thus, the device 200 has a cylindrical film 202 and a heater 300 in contact with the inner surface of the film 202 , and heats the image formed on the recording material with heat from the heater 300 via the film 202 .

The heater 300 has a ceramic substrate 305 and a heating resistor (heating element) (see FIG. 3) that is provided on the substrate 305 and generates heat when power is supplied. A glass surface protection layer 308 is provided on the surface (first surface) of the substrate 305 on the side of the fixing nip N to ensure the sliding properties of the film 202. A glass surface protection layer 307 is provided on the surface (second surface) opposite the surface on the fixing nip N side of the substrate 305 to insulate the heating resistor. An electrode (E4 is shown here as a representative) is exposed on the second surface, and the heating resistor is electrically connected to the AC power source 401 by contacting an electrical contact (C4 is shown here as a representative) for power supply. A detailed description of the heater 300 will be given later.

Number 202 is a protective element 212 such as a thermoswitch or a temperature fuse that is activated when the heater 300 generates abnormal heat and cuts off the power supplied to the heater 300. The protective element 212 is disposed in contact with the heater 300 or with a slight gap from the heater 300. Number 204 is a metal stay that applies pressure from a spring (not shown) to the holding member 201, and also serves to reinforce the holding member 201 and the heater 300.

FIGS. 3A and 3B show the configuration of the heater 300 of the first embodiment. FIG. 3A shows a cross-sectional view of the heater 300 near the transport reference position X of the recording material P shown in FIG. 3B. FIG. 3B shows a plan view of each layer of the heater 300. FIG. 3C is a plan view of a holding member that holds the heater 300.

The printer in this example is a center-based printer that aligns the center of the recording material in the width direction (the direction perpendicular to the transport direction) with the transport reference position X.

Next, the configuration of the heater 300 will be described in detail. On the back surface layer 1 of the heater 300, which is the heater surface opposite to the heater surface in contact with the film 202, a plurality of heat generating blocks each consisting of a first conductor 301, a second conductor 303, and a heat generating resistor (heat generating element) 302 are provided in the longitudinal direction of the heater 300. The heater 300 of this embodiment has a total of seven heat generating blocks HB1 to HB7. If one of the seven heat generating blocks is the first heat generating block and the other heat generating block is the second heat generating block, the heater 300 has the following configuration. That is, the heater 300 has a substrate and a first heat generating block formed on the substrate and generating heat when power is supplied. In addition, the heater 300 has a second heat generating block formed at a position different from the position where the first heat generating block is formed in the longitudinal direction of the substrate and controlled independently of the first heat generating block. The independent control of the heat generating blocks will be described later.

Each heating block has a first conductor 301 arranged along the longitudinal direction of the substrate, and a second conductor 303 arranged along the longitudinal direction of the substrate at a different position in the short direction of the substrate from the first conductor 301. Each heating block further has a heating resistor 302 arranged between the first conductor 301 and the second conductor 303, which generates heat by power supplied via the first conductor 301 and the second conductor 303.

The heating resistor 302 of each heating block is divided into heating resistor 302a and heating resistor 302b formed at mutually symmetrical positions with respect to the center of the substrate in the short direction of the heater 300. The first conductor 301 is also divided into conductor 301a connected to heating resistor 302a and conductor 301b connected to heating resistor 302b. Since heating resistor 302a and heating resistor 302b are formed at mutually symmetrical positions with respect to the center of the substrate, the substrate is less likely to crack even if the heater generates heat and thermal stress is generated in the substrate.

The heater 300 has seven heat generating blocks HB1 to HB7, so the heat generating resistor 302a is divided into seven parts, 302a-1 to 302a-7. Similarly, the heat generating resistor 302b is divided into seven parts, 302b-1 to 302b-7. Furthermore, the second conductor 303 is also divided into seven parts, 303-1 to 303-7. Note that the heat generating resistors 302a-1 to 302a-7 are arranged upstream of the conveying direction of the recording material P within the substrate 305, and the heat generating resistors 302b-1 to 302b-7 are arranged downstream of the conveying direction of the recording material P within the substrate 305.

The back surface layer 2 of the heater 300 is provided with an insulating (glass in this embodiment) surface protection layer 307 that covers the heating resistor 302 , the first conductor 301 , and the second conductor 303 .
However, the surface protective layer 307 does not cover the electrodes E1 to E7, E8-1, and E8-2 with which the electrical contacts C1 to C7, C8-1, and C8-2 for power supply come into contact. The electrodes E1 to E7 are electrodes for supplying power to the heat generating blocks HB1 to HB7 via the second conductors 303-1 to 303-7, respectively. The electrodes E8-1 and E8-2 are electrodes for supplying power to the heat generating blocks HB1 to HB7 via the first conductors 301a and 301b.

However, the resistance value of the conductor is not zero, and therefore affects the heat generation distribution in the longitudinal direction of the heater 300. Therefore, to prevent the heat generation distribution from becoming uneven even when affected by the electrical resistance of the first conductors 301a, 301b and the second conductors 303-1 to 303-7, the electrodes E8-1 and E8-2 are provided separately at both ends of the heater 300 in the longitudinal direction.

As shown in FIG. 2, the space between the stay 204 and the holding member 201 is provided with a safety element 212 and electrical contacts C1 to C7, C8-1, and C8-2. As shown in FIG. 3(C), the holding member 201 is provided with holes HC1 to HC7, HC8-1, and HC8-2 through which the electrical contacts C1 to C7, C8-1, and C8-2 that are connected to the electrodes E1 to E7, E8-1, and E8-2 pass. The holding member 201 also has a hole H212 through which the heat-sensing portion of the protective element 212 passes. The electrical contacts C1 to C7, C8-1, and C8-2 are electrically connected to the corresponding electrodes by a spring bias or welding or other techniques. The protective element 212 is also biased by a spring, and its heat-sensing portion is in contact with the surface protective layer 307. Each electrical contact is connected to the heater 300 control circuit 400 (described later) via a conductive member such as a cable or a thin metal plate provided in the space between the stay 204 and the holding member 201.

By providing electrodes on the back surface of the heater 300, there is no need to provide an area on the substrate 305 for wiring that electrically connects to each of the second conductors 303-1 to 303-7, and the width of the substrate 305 in the short direction can be shortened. This prevents the heater from becoming too large. As shown in FIG. 3B, the electrodes E2 to E6 are provided within the area in the longitudinal direction of the substrate where the heating resistors are provided.

As will be described later, the heater 300 of this example is capable of forming various heat distributions by independently controlling multiple heat generating blocks. For example, it is possible to set a heat distribution according to the size of the recording material. Furthermore, the heating resistor 302 is formed of a material that has a positive temperature coefficient (PTC). By using a material that has a PTC, it is possible to suppress the temperature rise of non-paper passing areas even in cases where the edge of the recording material and the boundary of the heat generating block do not coincide.

On the sliding surface layer 1 on the sliding surface side (the surface in contact with the film) of the heater 300, multiple thermistors (temperature detection elements) T1-1 to T1-4 and T2-4 to T2-7 are formed to detect the temperature of each of the heat generating blocks HB1 to HB7. The material of the thermistors may be any material that has a large positive or negative TCR (Temperature Coefficient of Resistance). In this example, the thermistors are constructed by thinly printing a material with a NTC (Negative Temperature Coefficient) on the substrate. Since one or more thermistors are provided corresponding to all of the heat generating blocks HB1 to HB7, the temperatures of all of the heat generating blocks can be detected.

If one of the thermistors T1-1 to T1-4 is a first temperature detection element, and the other one of the thermistors T1-1 to T1-4 is a second temperature detection element, the heater 300 has the following configuration. That is, the heater 300 has a first temperature detection element provided at a position corresponding to the first heat generation block, and a second temperature detection element provided at a position corresponding to the second heat generation block.

The thermistors T1-1 to T1-4 are electrically connected to the conductive patterns ET1-1 to ET1-4 provided on the substrate 305, respectively. If the conductive pattern connected to the first temperature detection element among the conductive patterns ET1-1 to ET1-4 is called the first conductive pattern, and the conductive pattern connected to the second temperature detection element is called the second conductive pattern, the heater 300 has the following configuration. That is, the heater 300 has a first conductive pattern electrically connected to the first temperature detection element, and a second conductive pattern electrically connected to the second temperature detection element. The heater 300 further has a common conductive pattern EG1 electrically connected to the first and second temperature detection elements. Hereinafter, the set of thermistors T1-1 to T1-4, conductive patterns ET1-1 to ET1-4, and common conductive pattern EG1 will be referred to as thermistor group TG1.

The heater 300 is also provided with a thermistor group TG2 consisting of a set of thermistors T2-4 to T2-7, conductive patterns ET2-4 to ET2-7, and a common conductive pattern EG2. Thermistor groups TG1 and TG2 are formed on the substrate surface opposite to the substrate surface on which the first and second heat generating blocks of the substrate 305 are formed.

In this example, at least one corresponding thermistor is provided for each of the heat generating blocks HB1 to HB7, but the reliability of the device can be improved by providing only one corresponding thermistor for at least two heat generating blocks. However, it is preferable to provide at least one corresponding thermistor for all heat generating blocks, as in this example.

As in this example, by using common conductive patterns EG1 and EG2 to combine the first and second temperature detection elements into one pair, the following effects can be achieved. That is, compared to connecting two conductive patterns to each of the thermistors T1-1 to T1-4 without using a common conductive pattern, the cost of the conductive patterns can be reduced and the size of the heater can be prevented from increasing.

To ensure the sliding properties of the film 202, an insulating (glass in this example) surface protection layer 308 is formed by coating on the surface (sliding surface layer 2) of the substrate 305 on the side of the fixing nip portion N. The surface protection layer 308 covers the thermistors T1-1 to T1-4, T2-4 to T2-7, the conductive patterns ET1-1 to ET1-4, ET2-4 to ET2-7, and the common conductive patterns EG1 and EG2. However, to ensure connection with the electrical contacts, parts of the conductive patterns ET1-1 to ET1-4, ET2-4 to ET2-7, and parts of the common conductive patterns EG1 and EG2 are exposed at both ends of the heater 300, as shown in FIG. 3B.

Figure 4 is a circuit diagram of the control circuit 400 of the heater 300. Reference numeral 401 denotes a commercial AC power source connected to the laser printer 100. Power control of the heater 300 is performed by turning on/off the triacs 411-414. The triacs 411-414 operate according to the FUSER1-FUSER4 signals from the CPU 420, respectively. Note that the drive circuits for the triacs 411-414 have been omitted from Figure 4.

As can be seen from Figures 3 and 4, the seven heat generating 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 of the heater 300 has a circuit configuration that can independently control the four groups. Triac 411 can control group 1, triac 412 can control group 2, triac 413 can control group 3, and triac 414 can control group 4.

The zero-cross detection unit 421 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 as a reference signal for phase control of the triacs 411 to 414, etc.

Next, the method of detecting the temperature of the heater 300 will be described. First, the thermistor group TG1 will be described. 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 resistors (451 to 454) are input to the CPU 420. For example, the signal Th1-1 is a signal obtained by dividing the voltage Vcc by the resistance value of thermistor T1-1 and the resistance value of resistor 451. Since the thermistor T1-1 has a resistance value according to the temperature, when the temperature of the heat generating 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 into a temperature according to its level. The processing of the signals Th1-2 to Th1-4 corresponding to the other thermistors T1-2 to T1-4 of the thermistor group TG1 is similar, so a description will be omitted.

Next, the thermistor group TG2 will be described. As with TG1, the thermistor group TG2 receives signals (Th2-4 to Th2-7) that are the result of dividing the voltage Vcc by the resistance values of the thermistors (T2-4 to T2-7) and resistors (464 to 467) as input to the CPU 420. The method of conversion to temperature by the CPU 420 is the same as for the thermistor group TG1, so a description will be omitted.

Next, the power control to the heater 300 (heater temperature control) will be described. During the fixing process, each of the heat generating blocks HB1 to HB7 is controlled so that the detected temperature of the thermistors (T1-1 to T1-4) in the thermistor group TG1 is maintained at the set temperature (control target temperature). Specifically, the power supplied to group 1 (heat generating block HB4) is controlled by controlling the drive of triac 411 so that the detected temperature of thermistor T1-4 is maintained at the set temperature. The power supplied to group 2 (heat generating blocks HB3 and HB5) is controlled by controlling the drive of triac 412 so that the detected temperature of thermistor T1-3 is maintained at the set temperature. The power supplied to group 3 (heat generating blocks HB2 and HB6) is controlled by controlling the drive of triac 413 so that the detected temperature of thermistor T1-2 is maintained at the set temperature. The power supplied to group 4 (heat generating blocks HB1 and HB7) is controlled by controlling the driving of triac 414 so that the temperature detected by thermistor T1-1 is maintained at the set temperature. In this way, each thermistor in thermistor group TG1 is used to perform control to keep each heat generating block at a constant temperature.

The CPU 420 calculates the supply power, for example by PI control, based on the set temperature (control target temperature) of each heat generating block and the detected temperature of each thermistor (T1-1 to T1-4) in thermistor group TG1. The calculated supply power is then converted into control timing such as the corresponding phase angle (phase control) and wave number (wave number control), and the triacs 411 to 414 are controlled with this control timing. Note that the set temperature of each group in this example device when fixing the largest size plain paper is 250°C. When fixing small size plain paper, 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 may be set appropriately according to information such as the size, type, and surface properties of the recording material.

Relay 430 and relay 440 are installed as a means for cutting off power to heater 300 if heater 300 becomes overheated due to factors such as equipment failure. Next, the circuit operation of relay 430 and relay 440 will be described.

When the RLON signal output from the CPU 420 goes high, the transistor 433 goes on, current flows from the DC power supply (voltage Vcc) to the secondary coil of the relay 430, and the primary contact of the relay 430 goes on. When the RLON signal goes low, the transistor 433 goes off, current flows from the power supply (voltage Vcc) to the secondary coil of the relay 430, and the primary contact of the relay 430 goes off. Similarly, when the RLON signal goes high, the transistor 443 goes on, current flows from the power supply (voltage Vcc) to the secondary coil of the relay 440, and the primary contact of the relay 440 goes on. When the RLON signal goes low, the transistor 443 goes OFF, the current flowing from the power supply (voltage Vcc) to the secondary coil of the relay 440 is cut off, and the primary contact of the relay 440 goes OFF.

Next, the operation of the protection circuit (hardware circuit that does not go through CPU 420) using relay 430 and relay 440 will be described. When the level of any one of signals Th1-1 to Th1-4 exceeds a predetermined value set inside comparison unit 431, comparison unit 431 operates latch unit 432, which latches the RLOFF1 signal in a low state. When the RLOFF1 signal goes low, even if CPU 420 sets the RLON signal to a high state, transistor 433 is maintained in an OFF state, so relay 430 can be maintained in an OFF state (safe state). Note that in the non-latching state, latch unit 432 outputs the RLOFF1 signal in an open state.

Similarly, when the level of any one of signals Th2-4 to Th2-7 exceeds a predetermined value set in comparison unit 441, comparison unit 441 operates latch unit 442, which latches the RLOFF2 signal in a low state. When the RLOFF2 signal is in a low state, even if CPU 420 sets the RLON 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). In a non-latching state, latch unit 442 outputs the RLOFF signal in an open state. In this example, the predetermined value set in comparison unit 431 and the predetermined value set in comparison unit 441 are both set to values equivalent to 300°C.

Next, the circuit protection operation using the two thermistor groups TG1 and TG2 will be described. As shown in Figures 3 and 4, one thermistor in the thermistor group TG1 and one thermistor in the thermistor group TG2 are arranged in correspondence with each of the four groups (groups 1 to 4) described above. Furthermore, at least one thermistor is arranged in correspondence with each of all of the heat generating blocks HB1 to HB7.
Specifically, thermistor T1-4 in thermistor group TG1 and thermistor T2-4 in thermistor group TG2 are arranged in correspondence with group 1 (HB4). Thermistor T1-3 in thermistor group TG1 and thermistor T2-5 in thermistor group TG2 are arranged in correspondence with group 2 (HB3 and HB5). Thermistor T1-2 in thermistor group TG1 and thermistor T2-6 in thermistor group TG2 are arranged in correspondence with group 3 (HB2 and HB6). Thermistor T1-1 in thermistor group TG1 and thermistor T2-7 in thermistor group TG2 are arranged in correspondence with group 4 (HB1 and HB7). At least one of the eight thermistors is arranged in correspondence with each of all heat generating blocks HB1 to HB7. Such a thermistor layout improves the reliability of the circuit protection operation in the event of a device failure, as will be explained below.

For example, consider the case where one of the thermistors T1-1 to T1-4 in thermistor group TG1 fails. Even if the group containing the heating block corresponding to the failed thermistor becomes uncontrollable due to the thermistor failure, the group of the heating block containing the failed thermistor also contains a thermistor in thermistor group TG2 (any of T2-4 to T2-7). Therefore, the protection circuit will operate (stopping the power supply) via the thermistor in thermistor group TG2.

Next, we will explain the advantages of a configuration in which at least one of the eight thermistors is arranged to correspond to each of the heat generating blocks HB1 to HB7.

For example, suppose the thermistor T2-5 corresponding to group 2 is placed in a position corresponding to heat generating block HB3, which is in the same group 2 as heat generating block HB5, rather than in a position corresponding to heat generating block HB5. In this case, thermistor T1-3 of thermistor group TG1 and thermistor T2-5 of thermistor group TG2 are placed in a position corresponding to heat generating block HB3, and there is no thermistor in a position corresponding to heat generating block HB5. Even with this configuration, the temperature of group 2 can be monitored. However, in this configuration, if there is poor contact between electrode E3 and electrical contact C3, heat generating block HB3 will not generate heat, but heat generating block HB5, which is in the same group 2 as heat generating block HB3, may be generating heat. And even if heat generating block HB5 in group 2 generates abnormal heat, the two thermistors T1-3 and T2-5 corresponding to group 2 cannot monitor this, and the protection circuit will not work.

In contrast, in this example, thermistor T1-3 of thermistor group TG1 is placed in a position corresponding to heat generating block HB3, and thermistor T2-5 of thermistor group TG2 is placed in a position corresponding to heat generating block HB5. Therefore, even if poor contact occurs between electrode E3 and electrical contact C3 and only heat generating block HB5 in group 2 generates heat, this temperature can be monitored by thermistor T2-5 and the protection circuit can be operated. In this way, at least one of the eight thermistors is placed in correspondence with each of the heat generating blocks HB1 to HB7, improving the reliability of the device.

Figure 5 is a flow chart explaining the control sequence of the control circuit 400 by the CPU 420. When a print request occurs in S100, relays 430 and 440 are turned on in S101.

In S102, the triac 414 is PI controlled to control the power supplied to the heat generating blocks HB1 and HB7 so that the temperature detected by thermistor T1-1 (signal Th1-1) reaches the control target temperature.

In S103, the triac 413 is PI controlled to control the power supplied to the heat generating blocks HB2 and HB6 so that the temperature detected by thermistor T1-2 (signal Th1-2) reaches the control target temperature.

In S104, the triac 412 is PI controlled to control the power supplied to the heat generating blocks HB3 and HB5 so that the temperature detected by thermistor T1-3 (signal Th1-3) reaches the control target temperature.

In S105, the triac 411 is PI controlled to control the power supplied to the heat generating block HB4 so that the temperature detected by thermistor T1-4 (signal Th1-4) reaches the control target temperature.

As described above, the control target temperature of each heat generating block is set according to the recording material size information. In this example, the device sets the control target temperature of heat generating block HB4, which includes the transport reference X, to the same temperature regardless of the recording material size, and the control target temperatures of the other heat generating blocks are changed according to the recording material size. The smaller the recording material size, the lower the control target temperatures of heat generating blocks other than heat generating block HB4 are set.

In S106, it is determined whether the temperature rise of the non-sheet passing portion of the heater 300 is equal to or lower than a predetermined threshold temperature (allowable temperature) Tmax. In this example, Tmax is set to 280°C, which is higher than the control target temperature 250°C of the heat generating block HB4 and lower than the predetermined value 300°C set in the comparison unit 431 and comparison unit 441. In addition, the positional relationship between the thermistor in the thermistor group TG1 and the reference X is different from the positional relationship between the thermistor in the thermistor group TG2 and the reference X. Compared to the thermistor in the thermistor group TG1, the thermistor in the thermistor group TG2 is disposed outside the conveying reference position X in the longitudinal direction of the heater 300 in each heat generating block. As shown in FIG. 3B, this relationship can be easily understood by comparing the distance from the reference X of the thermistor T1-4 corresponding to the heat generating block HB4 and the distance from the reference X of the thermistor T2-4 corresponding to the heat generating block HB4. This layout allows the thermistors in thermistor group TG2 to detect any temperature rise in non-paper passing areas within one heat generating block.

If the temperatures of thermistors T2-4 to T2-7 are equal to or lower than the threshold temperature Tmax in S106, the process proceeds to S108, and the controls in S102 to S106 are repeated until the end of the print job is detected in S108.

If the temperatures of thermistors T2-4 to T2-7 exceed the threshold temperature Tmax in S106, the image formation process speed of image forming apparatus 100 is reduced in S107, and fixing process is performed with the control target temperatures of thermistors T1-1 to T1-4 reduced. By reducing the image formation process speed, fixing can be ensured even at a lower temperature compared to full speed, and the temperature rise in non-paper passing areas can also be suppressed.

The above process is repeated, and when the end of the print job is detected in S108, relays 430 and 440 are turned OFF in S109, and the image formation control sequence ends in S110.

Example 2
Next, a second embodiment will be described in which the heater 300 and the heater control circuit 400 described in the first embodiment are replaced with a heater 600 and a control circuit 700. The same components as those in the first embodiment are designated by the same symbols and will not be described. The heater 600 of the second embodiment has a different configuration of the slide surface layer 1 compared to the heater 300. The control circuit 700 is configured to be able to independently control all of the heat generating blocks HB1 to HB7.

Figure 6 shows a configuration diagram of a heater 600 of Example 2. The configuration other than the sliding surface layer 1 is the same as that of the heater 300, so a description is omitted.

Thermistors T3-1a to T3-4a, T3-1b to T3-3b, T4-4a to T4-7a, T4-5b to T4-7b, and T5 are arranged on the sliding surface layer 1 of the heater 600 to detect the temperature of each of the heat generating blocks HB1 to HB7. Since two or more thermistors are associated with each of the heat generating blocks HB1 to HB7, the temperature of all of the heat generating blocks can be detected even if one thermistor breaks down.

Thermistor group TG3 has seven thermistors T3-1a to T3-4a and T3-1b to T3-3b, conductive patterns ET3-1a to ET3-4a, ET3-3b, and ET3-12b, and a common conductive pattern EG3.

Similarly, 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.

First, the thermistor group TG3 will be described. Thermistor T3-1b and thermistor T3-2b are thermistors for detecting the temperatures of heat generating blocks HB1 and HB2, and are configured to be connected in parallel between conductive pattern ET3-12b and common conductive pattern EG3. Even if the temperature of either heat generating block HB1 or HB2 rises, the resistance value of either thermistor T3-1b or thermistor T3-2b drops significantly. For this reason, the temperature detection of both heat generating blocks HB1 and HB2 can be performed by a single conductive pattern ET3-12b for detecting the resistance value of the thermistor. Therefore, the cost of forming the wiring of the conductive pattern can be reduced compared to the case where a conductive pattern is connected and wired to each of thermistors T3-1b and T3-2b. In addition, the width of the short side of the substrate 305 can be shortened. Similarly, thermistor T4-6b and thermistor T4-7b are also connected in parallel.

The common conductive patterns EG3 and EG4 are connected on the substrate 305 by the conductive pattern EG34, and are used for disconnection detection, which will be described in FIG. 7. By detecting disconnection, safety can be improved in the event of a disconnection failure.

Two thermistors, T3-3a and T3-3b, are installed for each heat generating block HB3, and the temperature can be detected by conductive patterns ET3-3a and ET3-3b for resistance value detection, and a common conductive pattern EG3.

Within the range of the heat generating block HB3, the thermistor T3-3b located far from the transport reference position X is a thermistor for detecting the end temperature, and the thermistor T3-3a located closer to the transport reference position X is a thermistor for temperature control. If necessary, multiple thermistors may be provided in one heat generating block.

The explanation for thermistor group TG4 is the same as for thermistor group TG3, so it will be omitted.

Thermistor T5 is a standalone thermistor formed between conductive patterns ET5 and EG5 for detecting resistance values. If necessary, a standalone thermistor may be used in combination with a thermistor group.

Figure 7 shows a circuit diagram of the control circuit 700 of the heater 600 of the second embodiment. Power control of the heater 600 is performed by turning on/off the triacs 711 to 717. The triacs 711 to 717 operate according to the FUSER1 to FUSER7 signals from the CPU 420, respectively. The control circuit 700 of the heater 600 has a circuit configuration that allows the seven heat generating blocks HB1 to HB7 to be independently controlled by the seven triacs 711 to 717.

Next, a method for detecting the temperature of the heater 600 will be described. Signals (Th3-1a to Th3-4a, Th3-3b, Th3-12b) obtained by dividing voltage Vcc by the resistance values of thermistors T3-1a to T3-4a, T3-1b, and T3-2b in thermistor group TG3 and resistors 751 to 756 are input to the CPU 420. Similarly, signals obtained by dividing voltage Vcc by the resistance values of thermistors T4-4a to T4-7a, T4-5b to T4-7b in thermistor group TG4 and resistors 771 to 776 are input to the CPU 420. These signals are shown as Th4-4a to Th4-7a, Th4-5b, and Th4-67b. Similarly, a signal (Th5) obtained by dividing the resistance of thermistor T5 and resistor 761 is input to the CPU. The CPU 420 converts each input signal into a temperature according to its level.

The CPU 420 calculates the supply power, for example by PI control, based on the set temperature (control target temperature) of each heat generating block and the detected temperature of each thermistor. Furthermore, the calculated supply power is converted into control timing such as the corresponding phase angle (phase control) and wave number (wave number control), and the triacs 711 to 717 are controlled with this control timing.

Next, the operation of the protection circuit using relays 430 and 440 will be described. When any one of the detected temperatures exceeds a predetermined value set based on the Th3-1a to Th3-4a signals of thermistor group TG3 and the Th4-5b and Th4-67b signals of thermistor group TG4, the comparator 431 operates the latch unit 432.

Similarly, when any one of the detected temperatures exceeds a predetermined value set based on the Th4-4a to Th4-7a signals of thermistor group TG4 and the Th3-3b and Th3-12b signals of thermistor group TG3, the comparator 441 activates the latch unit 442.

Next, we will explain the disconnection detection circuit 780. The disconnection detection circuit 780 is a circuit used to increase safety in the event that the common conductive patterns EG3 and EG4 are disconnected.

The circuit operation of the disconnection detection circuit 780 will be described. If the connection between the common conductive patterns EG3 and EG4 is broken, the disconnection detection signal ThSafe goes to a high state because it is pulled up to the power supply voltage Vcc by resistors 781 and 782. Note that resistors 781 and 782 are provided as two resistors in consideration of resistor short failures. When the disconnection detection signal ThSafe goes to a high state, it activates latch units 432 and 442.

Next, the effects of the disconnection detection circuit 780 and the conductive pattern EG34 will be described. First, a case will be described in which neither the conductive pattern EG34 nor the disconnection detection circuit 780 is provided, and the common conductive patterns EG3 and EG4 are each connected to GND, as in the configuration of the first embodiment. In this case, if the common conductive pattern EG3 is disconnected, all the thermistors in the thermistor group TG3 will no longer function, and the protection circuit that stops the supply of power to the heat generating blocks HB1 to HB3 will no longer function. Similarly, if the common conductive pattern EG4 is disconnected, all the thermistors in the thermistor group TG4 will no longer function, and the protection circuit that stops the supply of power to the heat generating blocks HB5 to HB7 will no longer function.

Next, a case will be described in which, although there is a conductive pattern EG34 connecting the common conductive patterns EG3 and EG4, there is no disconnection detection circuit 780, and the common conductive patterns EG3 and EG4 are each connected to GND, as in the configuration of Example 1. In this case, due to the effect of the conductive pattern EG34, even if one of the common conductive patterns EG3 and EG4 is disconnected, it is connected to GND via the conductive pattern EG34. Therefore, temperature detection by the thermistor groups TG3 and TG4 is possible. However, if a connector (not shown) that connects the conductive patterns (ET3-1a to ET3-4a, ET3-12b, ET3-3b, EG3) of the thermistor group TG3 to the control circuit 700 is disconnected, all the thermistors of the thermistor group TG3 will no longer function. Therefore, the protection circuit that stops the power supply to the heat generating blocks HB1 to HB3 will no longer work. Similarly, if the connector connecting the conductive patterns of thermistor group TG4 (ET4-4a to ET4-7a, ET4-67b, ET4-5b, EG4) to the control circuit 700 is unplugged, all the thermistors in thermistor group TG4 will no longer function. As a result, the protection circuit that stops the power supply to heat generating blocks HB5 to HB7 will no longer function.

In contrast, the device of this example has a conductive pattern body EG34 and a disconnection detection circuit 780. This makes it possible to detect both fault conditions, such as a disconnection of the common conductive patterns EG3 and EG4, and a disconnection of the connector connecting the thermistor groups TG3 and TG4 to the control circuit 700.

Figure 8 is a flowchart explaining the control sequence of the control circuit 700 by the CPU 420. The same symbols are used for configurations similar to those in Figure 5, and the explanation is omitted.

In S201, the triac 711 is PI controlled to control the power supplied to the heat generating block HB1 so that the temperature detected by thermistor T3-1a (signal Th3-1a) reaches a predetermined target temperature.

In S202, the triac 712 is PI controlled to control the power supplied to the heat generating block HB2 so that the temperature detected by thermistor T3-2a (signal Th3-2a) reaches a predetermined target temperature.

In S203, the triac 713 is PI controlled to control the power supplied to the heat generating block HB3 so that the temperature detected by thermistor T3-3a (signal Th3-3a) reaches a predetermined target temperature.

In S204, triac 714 is PI controlled to control the power supplied to heat generating block HB4 so that the temperature detected by thermistor T5 (signal Th5) reaches a predetermined target temperature.

In S205, the triac 715 is PI controlled to control the power supplied to the heat generating block HB5 so that the temperature detected by thermistor T4-5a (signal Th4-5a) reaches a predetermined target temperature.

In S206, the triac 716 is PI controlled to control the power supplied to the heat generating block HB6 so that the temperature detected by thermistor T4-6a (signal Th4-6a) reaches a predetermined target temperature.

In S207, triac 717 is PI controlled to control the power supplied to heat generating block HB7 so that the temperature detected by thermistor T4-7a (signal Th4-7a) reaches a predetermined target temperature.

In S208, a determination is made as to whether the temperature rise in the non-paper passing area of the heater 300 is equal to or lower than a predetermined threshold temperature (allowable temperature) Tmax.

If in S208 the temperatures of thermistors T3-4a, T4-4a, T3-3b, and T4-5b are equal to or lower than the threshold temperature Tmax, the process proceeds to S108, and the control of S201 to S208 is repeated until the end of the print job is detected in S108.

Example 3
9 is an example in which a heating resistor 802 is disposed on the side of the fixing nip portion N, and a thermistor group TG6 is disposed on the opposite side of the fixing nip portion N. Configurations similar to those in the first embodiment are designated by the same symbols and will not be described.

Figure 9 (A) shows a cross-sectional view of the center of heater 800 (near transport reference position X). Only a conductive pattern is formed on back surface layer 1, and chip thermistor T6-2 is adhered from above. 810 and 811 are electrodes of chip thermistor T6-2. Conductive patterns EG6 and ET6-2 are connected to chip thermistor T6-2 via electrodes 810 and 811. By arranging thermistor group TG6 on the opposite side of fixing nip portion N as in heater 800, the flatness required for the sliding surface layer is not required, and a thick chip thermistor T6-2 can be installed.

The thermistor group TG6 provided on 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 for detecting the resistance values of the thermistors, and a common conductive pattern EG6.

The heater 800 has three heat generating blocks HB1 to HB3 on the sliding surface layer 1. The heating resistor 802 is divided into three parts 802-1 to 802-3, and power is supplied via the first conductor 801 and the three divided second conductors 803-1 to 803-3. The second conductors 803-1 to 803-3 are connected to the electrodes E1 to E3, and the first conductor 801 is connected to the electrode E8. The three heat generating blocks HB1 to HB3 can be controlled independently by providing switching elements such as triacs on the electrodes E1 to E3, with the electrode E8 as a common electrode. The heater 800 has a protective layer 808 made of glass having both sliding and insulating properties.

In the heater 800, in order to supply power to the heat generating blocks HB1 to HB3, it is necessary to wire the first conductor 801 and the second conductor 803 to both ends of the heater in the short direction. Therefore, particularly when the number of heat generating blocks increases, the area for wiring the first conductor 801 and the second conductor 803 increases, and the heater becomes larger.

When electrodes E2 to E6 are provided within the heat generating region, as in heater 300 described in Example 1 and heater 600 described in Example 2, the area required for wiring first conductor 301 and second conductor 303 is not required, so the number of heat generating blocks can be increased without increasing the size of the heater. In a configuration in which electrodes E2 to E6 are provided within the heat generating region, electrodes E2 to E6 must be provided on the opposite side of the fixing nip N to connect electrical contacts C2 to C6. For this reason, it is effective to form the heat generating blocks (HB1 to HB7) on the opposite side of the fixing nip N and form the thermistor group (TG1, TG2, TG3, TG4) on the fixing nip N side.

When the number of heat generating blocks is small, a method can be applied in which a thermistor group TG6 using multiple chip thermistors is placed on the opposite side of the fixing nip portion N, as in the heater 800 described in this embodiment.

Example 4
The heater of Example 4 shown in Fig. 10 has a different shape of the heating resistor from the heaters of Examples 1 and 2. Heating resistors 902a and 902b of a heater 900 shown in Fig. 10(A) are continuous (not divided) in the longitudinal direction.

Figure 10 (A) is a plan view of the back surface layer 1 of the heater 900. The conductor 303 is divided into seven parts in the longitudinal direction, so that the heating elements 902a and 902b are configured to be able to control the temperature independently in the regions of the heat generating blocks HB1 to HB7. As the heating elements 902a and 902b of the heater 900 are not divided, the heater generates heat continuously in the longitudinal direction even in the gap regions where the conductor 303 is divided, and there is no region where the heat generation amount becomes 0 (zero), so the heater can generate heat more uniformly in the longitudinal direction.

The heater 1000 shown in FIG. 10(B) is one in which the heating resistors 1002a and 1002b are further divided into multiple heating resistors connected in parallel.

Figure 10 (B) is a plan view of the back surface layer 1 of the heater 1000. The heating resistor 1002a is divided into multiple parts and connected in parallel between the conductor 303 and the conductor 301a. Similarly, the heating resistor 1002b is divided into multiple parts and connected in parallel between the conductor 303 and the conductor 301a.

The divided heating resistors of the heating resistors 1002a and 1002b are arranged at an angle to the longitudinal and lateral directions of the heater 1000, and overlap in the longitudinal direction of the heater 1000. This reduces the effect of the gaps between the divided heating resistors, and improves the uniformity of the heat distribution in the longitudinal direction of the heater 1000. In addition, in the heater 1000, the divided heating resistors at the extreme ends of adjacent heating blocks overlap in the longitudinal direction even in the gaps between the heating blocks, so that the heat distribution in the longitudinal direction of the heater 1000 can be made more uniform. The extreme end heating resistors of adjacent heating blocks are, 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.

The heat distribution of the heating resistors 1002a and 1002b can be adjusted by adjusting the width, length, spacing, inclination, etc. of the divided heating resistors. By adopting the configuration of heater 900 or heater 1000, it is possible to suppress temperature unevenness in the gaps between multiple heating blocks.

Example 5
Fig. 11 shows the waveforms of currents passed through each heat generating block in the control circuit 400 shown in the first embodiment. Fig. 11(A) shows the drive patterns of the triac 411 (a table of the waveforms of currents passed through the heat generating block HB4) set for each duty ratio of the power supplied to the heater 300. Similarly, Fig. 11(B) shows the drive patterns of the triacs 412 to 414 (a table of the waveforms of currents passed through the heat generating blocks HB1 to HB3, HB5 to HB7).

The CPU 420 calculates the level of power (duty ratio) to be supplied to the heater for each control cycle, and selects a waveform corresponding to the duty ratio for each heat generating block to be supplied. In the control method of this embodiment, four half waves constitute one control cycle, and the current control pattern for each triac is set to control the power supplied to the heater 300.

Below, an example of the current control pattern of the triac 411 when the duty ratio is 25% is described. In the current control pattern A of the triac 411 shown in FIG. 11(A), the first half wave to the second half wave are controlled at a phase angle of 90° to supply 50% power, and the third half wave to the fourth half wave are turned off. Therefore, an average of 25% power is supplied to the heat generating block HB4 of the heater 300. Current control pattern A is a current control pattern that performs phase control on the first half wave to the second half wave.

In addition, in the current control pattern of triacs 412-414 shown in FIG. 11(B), the third to fourth half waves are controlled at a phase angle of 90° to supply 50% power, and the first to second half waves are turned off. Therefore, an average of 25% power is supplied to the heat generating blocks HB1-HB3 and HB5-HB7 of the heater 300. Current control pattern B is a current control pattern that performs phase control on the third to fourth half waves.

The heat generating block HB4 of the heater 300 has a lower resistance than the other heat generating blocks, and therefore experiences a larger fluctuation in current during phase control than the other heat generating blocks. Therefore, in this example, the timing at which the phase control current flows through the heat generating block HB4 (1 half wave to 2 half wave) is shifted from the timing at which the phase control current flows through the other heat generating blocks HB1 to HB3 and HB5 to HB7 (3 half wave to 4 half wave). This makes it possible to suppress the fluctuation in the phase control current flowing through the entire heater 300. The same applies for duty ratios other than 25%.

As shown in FIG. 11, in this example, the harmonic current of the image heating device 200 can be reduced by synchronizing the control timing of multiple triacs (synchronous control of multiple triacs). FIG. 11 is an example of synchronous control, and synchronous control of multiple triacs may be performed to reduce flicker, for example.

Furthermore, the same method can be used to synchronously control multiple triacs 711 to 717 in the control circuit 700.

The advantage of synchronous control of multiple triacs is that harmonic currents and flicker can be reduced, and standards for harmonic currents and flicker can be satisfied even if the total resistance value of the heater 300 is set low. If the resistance value of the heater 300 can be set low, the maximum power that can be supplied from the AC power source 401 to the heater 300 can be increased.

The above-mentioned embodiments have been described using a center-based printer that aligns the center of the recording material in the width direction with the transport reference position X. However, the present invention can also be applied to a one-sided printer that uses one end of the heater in the longitudinal direction as the transport reference position and transports the recording material such that one end of the recording material in the width direction is aligned with the transport reference position.

200 Image heating device 300 Heater 301 First conductor 302 Heating resistor 303 Second conductor 305 Substrate E1 to E7, E8-1, E8-2 Electrodes HB1 to HB7 Heating block

Claims (2)

A cylindrical film;
a heater provided in an internal space of the film, the heater having a substrate, a first heat generating block provided on the substrate and generating heat when supplied with electric power, and a second heat generating block provided at a position different from the position at which the first heat generating block is provided in the longitudinal direction of the substrate and generating heat when supplied with electric power;
a roller that contacts an outer peripheral surface of the film, the roller sandwiching the film between the roller and the heater to form a nip portion for sandwiching and conveying a recording material between the roller and the film;
a first switch element for controlling power supplied to the first heat generating block;
a second switch element for controlling power supplied to the second heat generating block;
a control unit that controls the first switch element and the second switch element;
a fixing device for fixing a toner image formed on a recording material by heat to the recording material while nipping and conveying the recording material at the nip portion,
a plurality of temperature sensors are provided in the region in which the first heat generating block is provided in the longitudinal direction , the plurality of temperature sensors each having an output input to the control unit ;
the plurality of temperature sensors includes a first sensor, a second sensor, and a third sensor;
the first sensor is provided near a reference position for conveying the recording material in the longitudinal direction,
the second sensor is provided at one end position in the longitudinal direction within a region in which the first heat generating block is provided,
the third sensor is provided at the other end position in the longitudinal direction within the region in which the first heat generating block is provided;
A fixing device comprising: an image forming unit for forming a toner image on a recording material;
A fixing unit that heats and fixes a toner image formed on a recording material to the recording material,
2. An image forming apparatus, comprising: a fixing section comprising the fixing device according to claim 1.

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