JP7622118B2 - Image heating device, image forming device - Google Patents

Description

The present invention relates to an image heating device, particularly an image heating device used in image forming devices such as copying machines and printers that use electrophotographic or electrostatic recording methods.

Conventionally, among image heating devices used in electrophotographic and other image forming devices, a film heating type image heating device that excels in on-demand capability and power saving has been known.

An image heating device that uses a film heating method has a ceramic heater or halogen lamp in the internal space of a heat-resistant, endless fixing film. The unfixed toner image on the recording material is heated and fixed while the recording material is sandwiched and transported between the fixing film and the pressure roller.

When small-sized recording materials are continuously printed on an image forming apparatus using such an image heating device, a non-paper passing area temperature rise occurs in the direction of the rotation axis of the fixing film, where the temperature of the area through which the recording material does not pass gradually increases. If the temperature of the non-paper passing area becomes too high, it may damage various parts inside the device, and if a large-sized recording material is printed in a state in which a non-paper passing area temperature rise has occurred, there is a risk that the toner will be offset to the fixing film at a high temperature in the area corresponding to the non-paper passing area of the small-sized recording material.

As one method for suppressing the temperature rise in non-paper passing areas, Patent Document 2 describes a configuration in which the heater is divided into multiple heat generating blocks in the longitudinal direction and the heat distribution of the heater is switched according to the width of the recording material.

Patent Publication 2014-59508

Temperature detection elements are arranged in the areas of the multiple heat generating blocks arranged in the longitudinal direction, corresponding to each heat generating block. The power supplied to each heat generating block is controlled according to the detection results of the temperature detection elements. However, if there are individual differences in the temperature detection elements, there is a risk that the detection results detected by each temperature detection element will vary. This may result in variation in the temperature in each heat generating block.

The invention of this application was made in consideration of the above situation, and aims to suppress temperature variation in each heat generating block.

In order to achieve the above object, an image heating device is provided that includes a first rotating body, a heater disposed in the internal space of the first rotating body, a second rotating body that contacts the outer circumferential surface of the first rotating body and forms a nip portion that sandwiches and conveys a recording material together with the heater via the first rotating body, a memory, and a control unit, and a recording material on which an image has been formed is sandwiched and conveyed in the nip portion and heated, and the heater includes a long and narrow substrate, a plurality of heating resistors arranged in a line in the longitudinal direction of the substrate, a first heating block including a heating resistor disposed in the central region of the substrate in the longitudinal direction, a second heating block including a heating resistor disposed on the end side of the heating resistor included in the first heating block in the longitudinal direction, a first temperature detection element disposed in an area corresponding to the first heating block and detecting a temperature, and a second temperature detection element disposed in an area corresponding to the second heating block and detecting a temperature. and a second temperature detection element that detects the first heat generation block, the memory stores first correction information for correcting the target temperature of the first heat generation block and second correction information for correcting the target temperature of the second heat generation block, the control unit determines a first target temperature of the first heat generation block based on the detection result of the first temperature detection element and the first correction information, controls the power supplied to the first heat generation block based on the first target temperature, determines a second target temperature of the second heat generation block based on the detection result of the second temperature detection element and the second correction information, controls the power supplied to the second heat generation block based on the second target temperature, and the second correction information is determined by the difference between the surface temperature of the first region of the first rotating body corresponding to the first heat generation block and the surface temperature of the second region of the first rotating body corresponding to the second heat generation block.

The present invention makes it possible to suppress temperature variations in each heat generating block.

Schematic diagram of an image forming apparatus Schematic diagram of an image heating device Heater schematic diagram Heater control circuit diagram Schematic diagram of thermal characteristic measurement jig Graph showing temperature transitions measured using a thermal characteristic measuring tool Film surface temperature and film temperature difference of each heat generating block measured by a thermal characteristic measuring jig Flowchart showing correction control of target temperature Film surface temperature of each heat generating block in the examples Film surface temperature of each heat generating block in the comparative example

The following describes embodiments of the present invention with reference to the drawings. Note that the following embodiments do not limit the invention as claimed, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

Example 1
(Image forming apparatus)
1 is a schematic diagram of an electrophotographic image forming apparatus. A video controller 120 receives image information and print instructions sent from an external device such as a personal computer and performs image processing, etc. A control unit 113 includes a CPU, ROM, RAM, etc., and is capable of communicating with the video controller 120. In response to print commands and image information sent from the video controller 120, the control unit 113 controls each unit constituting the image forming apparatus 100 and forms an image.

The image forming operation will be described below. The recording material P loaded in the paper feed cassette is fed by the feed roller 102. The control unit 113 manages the conveyance status of the recording material P using a conveyance sensor 114, a registration sensor 115, a pre-fixing sensor 116, and a fixing discharge sensor 117 arranged on the conveyance path.

The photosensitive drum 104 is rotated counterclockwise at a predetermined speed by the power transmitted from a drive motor (not shown). The charger 105 uniformly charges the surface of the photosensitive drum 104 as it is rotated. The laser beam scanner 106 irradiates the charged surface of the photosensitive drum 104 with laser light that is modified according to an image signal, forming an electrostatic latent image on the photosensitive drum 104.

The developing unit 107 visualizes the electrostatic latent image formed on the photosensitive drum 104 as a toner image (image) by attaching toner, which is a developer. The toner image formed on the photosensitive drum 104 is primarily transferred onto the intermediate transfer body 103 by applying a primary transfer bias to the primary transfer roller. The photosensitive drum 104, charger 105, laser beam scanner 106, and developing unit 107 are arranged for four colors, yellow (Y), magenta (M), cyan (C), and black (K).

A toner image of each color is formed on each photosensitive drum 104 and sequentially transferred (primary transfer) onto the intermediate transfer body 103, forming a color image on the intermediate transfer body 103. The image transferred (primary transfer) onto the intermediate transfer body 103 is secondarily transferred (secondary transfer) onto the recording material P at a secondary transfer section formed by the intermediate transfer body 103 and the secondary transfer roller 108 by applying a secondary transfer bias to the secondary transfer roller 108. The image heating device 200 fixes the image onto the recording material P by applying heat and pressure to the image transferred (secondary transfer) onto the recording material P. The recording material P with the fixed image is discharged to a paper discharge tray.

The image forming apparatus 100 of this embodiment is capable of forming images on recording materials of multiple sizes. Specifically, it is possible to print on recording materials of the following sizes: Letter paper (approximately 216 mm x 279 mm), Legal paper (approximately 216 mm x 356 mm), A4 paper (210 mm x 297 mm), Executive paper (approximately 184 mm x 267 mm). B5 paper (182 mm x 257 mm), A5 paper (148 mm x 210 mm). It is also possible to form images on non-standard paper, including DL envelopes (110 mm x 220 mm) and COM10 envelopes (approximately 105 mm x 241 mm).

The image forming device 100 basically feeds paper vertically (conveys the paper so that the long side is parallel to the transport direction). In addition, among the standard recording materials (compatible recording materials in the catalog) that can be transported by the image forming device 100, the widest in the direction perpendicular to the transport direction is Letter paper and Legal paper, which are approximately 216 mm wide.

In the image forming apparatus 100, a control circuit 400 connected to a commercial AC power source 401 supplies power to the image heating device 200. In addition, the control unit 113 stores a temperature control program and a temperature control table for the image heating device 200 in memory. The control unit 113 controls the temperature of the image heating device 200 based on image information received from the video controller 120 using a method described below.

(Image heating device)
FIG. 2 is a schematic diagram of the image heating device 200. The image heating device 200 has the following members. A fixing film 202 as a first rotating body, a heater 300 arranged in the internal space of the fixing film 202, a pressure roller 208 as a second rotating body forming a fixing nip portion N together with the heater 300 via the fixing film 202, and a metal stay 204. The fixing film 202 is a multi-layer heat-resistant film formed in a cylindrical shape, and a heat-resistant resin such as polyimide having a thickness of about 50 to 100 μm, or a metal such as stainless steel having a thickness of about 20 to 50 μm can be used as a base layer. In addition, a heat-resistant resin having excellent releasability such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) having a thickness of about 10 to 50 μm is coated on the surface of the fixing film 202 to form a release layer. This makes it possible to prevent toner adhesion and ensure separation from the recording material P. Furthermore, particularly in devices that form color images, in order to improve image quality, a heat-resistant rubber such as silicone rubber having a thickness of about 100 to 400 μm and a thermal conductivity of about 0.2 to 3.0 W/m·K may be provided as an elastic layer between the base layer and the release layer.

In this embodiment, from the viewpoints of thermal responsiveness, image quality, durability, etc., a 60 μm thick polyimide base layer, a 300 μm thick silicone rubber elastic layer with a thermal conductivity of 1.6 W/m·K, and a 30 μm thick PFA release layer are used.

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 heater holding member 201 made of heat-resistant resin, and heats the fixing film 202. The heater holding member 201 also has a guide function for guiding the rotation of the fixing film 202. The metal stay 204 receives a biasing force from a biasing member (not shown) and biases the heater holding member 201 toward the pressure roller 208. The pressure roller 208 receives power from a motor and rotates in the direction of arrow R1. The pressure roller 208 rotates, and the fixing film 202 rotates in the direction of arrow R2. The unfixed toner image on the recording material P is fixed by applying heat from the fixing film 202 while nipping and conveying the recording material P in the fixing nip portion N.

The heater 300 has a heating resistor disposed on a ceramic substrate 305. The heater 300 has a surface protection layer 308 disposed on the side of the fixing nip N and a surface protection layer 307 disposed on the opposite side of the fixing nip N. An electrode (electrode E4 is shown here as an example) and a plurality of electrical contacts (electrical contact C4 is shown here as an example) are provided on the opposite side of the fixing nip N, and power is supplied from each electrical contact to each electrode. The heater 300 will be described in detail later with reference to FIG. 3. In addition, a safety element 212 such as a thermoswitch or a temperature fuse that operates to cut off the power supplied to the heater 300 when the heater 300 generates abnormal heat is disposed so as to abut directly on the heater 300 or indirectly via the holding member 201.

The image heating device 200 is provided with memories M1 to M7 as storage areas. The memories M1 to M7 store individual information (unique information) related to the image heating device 200. The image heating device 200 is detachable from the image forming device 100. Therefore, the memories M1 to M7 in this embodiment are capable of communicating with the control unit 113 of the image forming device 100 when the image heating device 200 is attached to the image forming device main body 100. This allows the control unit 113 to grasp the individual information of the image heating device 200. In this embodiment, the memories M1 to M7 are non-volatile memories such as NVRAM, but may also be in the form of an IC tag such as RFID, or a QR code (registered trademark).

(heater)
3A and 3B are schematic diagrams of the heater 300. FIG. 3A is a cross-sectional view in the vicinity of the transport reference position X shown in FIG. 3B. The transport reference position X is a reference position when the recording material P is transported. In this embodiment, the recording material P is transported so that the center part in the direction perpendicular to the transport direction is along the transport reference position X. Note that the direction of the long side of the elongated heater 300 in FIG. 3A is also referred to as the longitudinal direction (the front-rear direction in FIG. 3A), and the direction of the short side of the heater 300 perpendicular to the longitudinal direction is also referred to as the transverse direction (the left-right direction in FIG. 3A). Furthermore, the thickness direction of the heater 300 perpendicular to the longitudinal direction and the transverse direction is also referred to as the thickness direction (the up-down direction in FIG. 3A).

The heater 300 has a first conductor 301 (301a, 301b) arranged along the longitudinal direction of the heater 300 on the surface of the back layer side of the substrate 305. In addition, a second conductor 303 (303-4 near the transport reference position X) is arranged along the longitudinal direction of the heater 300 on the substrate 305 at a different position in the short direction of the heater 300 from the first conductor 301. The first conductor 301 is separated into a conductor 301a arranged on the upstream side in the transport direction of the recording material P and a conductor 301b arranged on the downstream side. Between the first conductor 301 and the second conductor 303, there is a heating resistor 302 that generates heat by power supplied via the first conductor 301 and the second conductor 303.

In this embodiment, the heating resistor 302 is separated into heating resistor 302a (302a-4 near the transport reference position X) arranged upstream in the transport direction of the recording material P, and heating resistor 302b (302b-4 near the transport reference position X) arranged downstream. In addition, an insulating surface protection layer 307 is provided on the back surface layer 2 of the heater 300 to cover the heating resistor 302, the first conductor 301, and the second conductor 303 (303-4 near the transport reference position X), avoiding the electrode portion (E4 near the transport reference position X). In this embodiment, as an example, the surface protection layer 307 is glass.

Figure 3(b) shows a plan view of each layer of the heater 300. A plurality of heat generating blocks each consisting of a set of a first conductor 301, a second conductor 303, and a heating resistor 302 are provided in the longitudinal direction of the heater 300 on the back surface layer 1 of the heater 300. The heater 300 of this embodiment has heat generating blocks HB1 to HB7 corresponding to a total of seven heating regions in the longitudinal direction of the heater 300. The heat generating blocks HB1 to HB7 are respectively composed of heating resistors 302a-1 to 302a-7 and heating resistors 302b-1 to 302b-7 formed symmetrically in the short direction of the heater 300. The first conductor 301 is composed of a conductor 301a connected to the heating resistors 302a-1 to 302a-7 and a conductor 301b connected to the heating resistors 302b-1 to 302b-7. Similarly, the second conductor 303 is divided into seven conductors 303-1 to 303-7 to correspond to the seven heat generating blocks HB1 to HB7. Heat generating block HB4 is a heat generating block that includes the central region in the longitudinal direction of the heater 300. Heat generating blocks HB1 to 3 and HB5 to 7 are heat generating blocks that are closer to the ends of the heater 300 than heat generating block HB4 in the longitudinal direction.

In this embodiment, the width of the heat generating blocks HB1 to HB7 is 220 mm, and each of the heat generating blocks HB1 to HB7 is divided into seven equal parts with a width of 31.4 mm. Electrodes E8-1 and E8-2 are connected to a common electrical contact used to supply power to the seven heat generating blocks HB1 to HB7 via conductors 301a and 301b. In this embodiment, electrodes E8-1 and E8-2 are provided at both ends in the longitudinal direction, but for example, only electrode E8-1 may be provided on one side, or separate electrodes may be provided upstream and downstream in the recording material transport direction.

The surface protection layer 307 of the back surface layer 2 of the heater 300 is formed except for the locations of the electrodes E1 to E7, E8-1, and E8-2, and is configured so that power can be supplied from the back surface layer side of the heater 300. In addition, the power supplied to each heat generating block is configured so that it can be controlled independently.

Thermistors Th1 to Th7 are arranged as temperature detection elements on the sliding surface layer 1 on the sliding surface side of the heater 300 to detect the temperature of each of the heat generating blocks HB1 to HB7. Thermistors Th1 to Th7 are formed by forming a thin layer of material with PTC or NTC characteristics (NTC characteristics in this embodiment) on a substrate. As the thermistors are arranged in areas corresponding to each of the heat generating blocks HB1 to HB7, the temperature of each heat generating block can be detected by detecting the resistance value of each thermistor.

To energize the four thermistors Th1 to Th4, conductors ET1-1 to ET1-4 for detecting the resistance values of the thermistors and a common conductor EG1 for the thermistors are formed. The thermistors Th1 to Th4 form a thermistor block TB1. Similarly, to energize the three thermistors Th5 to Th7, conductors ET2-5 to ET2-7 for detecting the resistance values of the thermistors and a common conductor EG2 for the thermistors are formed. The thermistors Th5 to Th7 form a thermistor block TB2.

A surface protection layer 308 (glass in this embodiment) with slidability is formed on the sliding surface layer 2 on the sliding surface side of the heater 300. Note that the surface protection layer 308 is not formed on both ends of the heater 300 in the longitudinal direction because electrical contacts corresponding to the conductors ET1-1 to ET1-4, ET2-5 to ET2-7, and the common conductors EG1 and EG2 are disposed on both ends.

Figure 3(c) shows the contact surface of the holding member 201 with the heater 300. As shown in Figure 3(c), the holding member 201 has holes for connecting the electrodes E1 to E7, E8-1, and E8-2 with the electrical contacts C1 to C7, C8-1, and C8-2. The electrical contacts C1 to C7, C8-1, and C8-2 that contact the electrodes E1 to E7, E8-1, and E8-2 are electrically connected to the electrodes of the heater by spring biasing, welding, or other methods. Each electrical contact is connected to a control circuit 400 of the heater 300, which will be described later, via a conductive material such as a cable or a thin metal plate. In addition, the electrical contacts provided on the conductors ET1-1 to ET1-4, ET2-5 to ET2-7 for detecting the resistance value of the thermistor, and the common conductors EG1 and EG2 of the thermistor, are also connected to the control circuit 400, which will be described later.

(Control circuit)
4 is a circuit diagram of a control circuit 400 that controls the heater 300. A commercial AC power source 401 is connected to the image forming apparatus 100. Power control of the heater 300 is performed by turning on/off triacs 411 to 417. The triacs 411 to 417 operate according to FUSER1 to FUSER7 signals output from the control unit 113. The drive circuits for the triacs 411 to 417 are omitted here. The control circuit 400 has a circuit configuration that allows seven heat generating blocks HB1 to HB7 to be independently controlled by the seven triacs 411 to 417.

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 control unit 113. The ZEROX signal is used for phase control of the triacs 411 to 417, timing detection of wave number control, etc.

Next, a method for detecting the temperature of the heater 300 will be described. Thermistors Th1 to Th4 in thermistor block TB1 detect the temperature by outputting the partial voltages between thermistors Th1 to Th4 and resistors 451 to 454 as Th1 to Th4 signals to the control unit 113. Similarly, thermistors Th5 to Th7 in thermistor block TB2 detect the temperature by outputting the partial voltages between thermistors Th5 to Th7 and resistors 465 to 467 as Th5 to Th7 signals to the control unit 113.

The control unit 113 controls the power supplied to each heat generating block, for example by PI control, based on the difference between the current temperature detected by the thermistor that detects the temperature of each heat generating block and the target temperature (hereinafter also referred to as the control temperature) of each heat generating block. The control unit 113 converts the power supplied into a control level of the phase angle (phase control) and wave number (wave number control) of the AC power supply, and controls the energization/cutoff of the triacs 411-417. The control unit 113 also communicates with memories M1-M7 in the image heating device 200, and corrects the target temperature of each heat generating block based on the individual information stored in M1-M7. The specific correction content will be described later.

The relay 430 and the relay 440 are used as a means for cutting off power to the heater 300 when the heater 300 becomes overheated due to a malfunction or the like. The operation of the relay 430 and the relay 440 will be described. When the RLON signal becomes high, the transistor 433 becomes ON, current is passed from the power supply voltage Vcc to the secondary coil of the relay 430, and the primary contact of the relay 430 becomes ON. When the RLON signal becomes low, the transistor 433 becomes OFF, the current flowing from the power supply voltage Vcc to the secondary coil of the relay 430 is cut off, and the primary contact of the relay 430 becomes OFF. Similarly, when the RLON signal becomes high, the transistor 443 becomes ON, current is passed from the power supply voltage Vcc to the secondary coil of the relay 440, and the primary contact of the relay 440 becomes 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 safety circuit using relay 430 and relay 440 will be described. When any one of the temperatures detected by thermistors Th1 to Th4 exceeds the corresponding threshold value, comparison unit 431 operates latch unit 432, which latches the RLOFF1 signal in the Low state. When the RLOFF1 signal is in the Low state, even if control unit 113 sets the RLON signal to the High state, transistor 433 is maintained in the OFF state, so relay 430 can be maintained in the OFF state (safe state). In addition, when in the non-latching state, latch unit 432 outputs the RLOFF1 signal in the open state. Similarly, when any one of the temperatures detected by thermistors Th5 to Th7 exceeds the corresponding threshold value, comparison unit 441 operates latch unit 442, which latches the RLOFF2 signal in the Low state. When the RLOFF2 signal goes low, even if the control unit 113 sets the RLON signal to high, the transistor 443 is kept in the OFF state, so the relay 440 can be kept in the OFF state (safe state). Similarly, in the non-latching state, the latch unit 442 outputs the RLOFF2 signal in an open state.

(Heater Control Method)
For the sake of simplicity, hereinafter, each heat generating block HB1 to HB7 will be referred to as HBi (i=1 to 7). In this embodiment, the power supplied to the thermistors Th1 to Th7 that detect the temperature of each heat generating block HBi is controlled so that the thermistors reach the target temperature Ttgti. However, depending on the width of the recording material P, the heat generating block corresponding to the non-paper passing area is controlled to have a temperature 10° C. lower than the target temperature Ttgti in order to suppress a temperature rise in the non-paper passing area. Whether or not the heat generating block corresponds to the non-paper passing area is determined by the control unit 113 based on size information of the recording material P.

In this embodiment, the target temperature Ttgti for each heat generating block HBi is obtained by correction based on the target base temperature Tb and the individual information stored in memories M1 to M7 in the image heating device 200. As the first correction, the target base temperature Tb is corrected using the target temperature correction value B stored in memory M4. The target temperature correction value B is a value obtained by converting the heat transfer performance of the fixing nip portion of the specific image heating device 200 into a correction temperature.

The heat transfer performance of the fixing nip may vary from one image heating device 200 to another, mainly due to the following factors. Examples of factors include the elastic layer thickness and surface layer thickness of the fixing film 202, and the pressure applied to the pressure roller 208. By correcting the target basic temperature Tb with the target temperature correction value B, the individual variation in heat transfer performance can be suppressed, and the quality of the image heating device 200 can be stabilized. Note that the elastic layer thickness and surface layer thickness of the fixing film 202, and the pressure applied to the pressure roller 208 do not vary significantly depending on the position in the longitudinal direction. Therefore, in this embodiment, it is assumed that the heat transfer performance of the fixing nip does not vary significantly depending on the position in the longitudinal direction, and the target temperature correction value B is not stored in each heat generating block. However, if it is desired to control the correction value by changing it depending on the position in the longitudinal direction, the target temperature correction value B corresponding to each heat generating block may be stored in memory.

As the second correction, the target temperature Ttgti of each heat generating block is corrected based on the film temperature difference ΔTfsi stored in memories M1 to M3 and M5 to M7 (i = 1 to 3, 5 to 7). In this embodiment, heat generating block HB4 is the reference region. The film temperature difference ΔTfsi represents the difference in the temperature of the fixing film of each heat generating block HBi (i = 1 to 3, 5 to 7) relative to the reference heat generating block HB4 when all heat generating blocks are uniformly temperature-controlled. The film temperature difference ΔTfsi is caused by the occurrence of variations in the temperatures detected by thermistors Th1 to Th7. A correction is performed to suppress the variation in the temperature of the fixing film in the longitudinal direction due to this difference. Specific methods for calculating the correction value and the correction method will be described later.

(Calculation method of correction value and storage in memory area)
The target temperature correction value B and the film temperature difference ΔTfsi are measured by a thermal characteristic measuring tool (external measuring device) 500 in the final step of the manufacturing process of the image heating apparatus 200 and stored in memory. In other words, the thermal characteristic measuring tool 500 measures the image heating apparatus 200 in an initial state. FIG. 5 is a configuration diagram of the thermal characteristic measuring tool 500. The thermal characteristic measuring tool 500 can drive the image heating apparatus 200 as a single unit. Also, the power supplied to each of the heat generating blocks HB1 to HB7 can be controlled according to the values detected by each of the thermistors Th1 to Th7. The thermal characteristic measuring tool 500 has a control circuit section 511, a motor control section 532, a motor 536, and a power supply section 537. The control circuit section 511 controls the power supply from the power supply section 537, and the motor control section 532 controls the driving of the motor 536.

The pressure roller 208 attached to the thermal characteristic measuring jig 500 is driven to rotate in the same manner as the fixing operation described above by the driving force of the motor 536 being transmitted via a drive transmission mechanism (not shown). In addition, the heater 300 is supplied with power from the power supply unit 537, so that the heater 300 heats the fixing film 202 from the inside in the same manner as the fixing operation described above.

The thermal characteristic measuring tool 500 outputs values detected by thermistors Th1 to Th7 to the control circuit section 511. Seven contact temperature sensors (hereinafter also referred to as film surface temperature sensors) 530-1 to 530-7 are arranged in the longitudinal direction of the fixing film 202. In synchronization with the temperature detection by thermistors Th1 to TH7, the film surface temperature sensors 530-1 to 530-7 measure the surface temperature of the fixing film 202. The film surface temperature sensors 530-1 to 530-7 are each arranged at a position in the longitudinal direction that coincides with the arrangement of thermistors Th1 to Th7. The film surface temperature sensors 530-1 to 530-7 measure the surface temperature of each area of the fixing film 202 that corresponds to the heat generating blocks HB1 to HB7.

The surface temperature of the pressure roller 208 is measured by non-contact temperature sensors (hereinafter also referred to as pressure roller surface temperature sensors) 540-1 to 540-7. Like the film surface temperature sensors 530-1 to 530-7, the pressure roller surface temperature sensors 540-1 to 540-7 are also arranged in positions that coincide with the arrangement of the thermistors Th1 to Th7 in the longitudinal direction. The pressure roller surface temperature sensors 540-1 to 540-7 measure the surface temperature of the pressure roller 208 corresponding to the heat generating blocks HB1 to HB7. Hereinafter, the temperatures detected by thermistors Th1 to Th7 are also referred to as Tth1 to Tth7. The temperatures detected by the film surface temperature sensors 530-1 to 530-7 are also referred to as Tf1 to Tf7, and the temperatures detected by the pressure roller surface temperature sensors 540-1 to 540-7 are also referred to as Tpr1 to Tpr7.

Figure 6 is a graph showing the temperature transition of an example of measurement of the image heating device 200 using the thermal characteristic measuring tool 500. The graph shows the temperature transitions of the detected temperature Tth4 of thermistor Th4, the detected temperature Tf4 of the film surface temperature sensor 530, and the detected temperature Tpr4 of the pressure roller surface temperature sensor 540. A method for calculating the target temperature correction value B will be explained using Figure 6.

The control circuit section 511 judges whether the temperatures detected by the thermistors Th1 to Th7, the film surface temperature sensors 530-1 to 530-7, and the pressure roller surface temperature sensors 540-1 to 540-7 are all 25±4°C. If the temperatures are within the range, temperature measurement by each sensor is started. First, a fixed power of 400W is supplied to the heater 300 for 10 seconds to drive the image heating device 200. Then, the temperature control is started according to the detection results of thermistors Th1 to Th7. In the measurement with the thermal characteristic measuring tool 500, the target temperature for temperature control using thermistors Th1 to Th7 is set to 200°C. For 60 seconds from the start of measurement, the temperatures Tth1 to Tth7 detected by the thermistors, the temperatures Tf1 to Tf7 detected by the film surface temperature sensors, and the temperatures Tpr1 to Tpr7 detected by the pressure roller surface temperature sensors are measured.

The control circuit section 511 calculates the amounts of increase ΔTf1 to ΔTf7, which are the differences between the initial temperature and the temperatures Tf1 to Tf7 detected by the film surface temperature sensor 530 at the timing t when the integrated power reaches 3600 J. The control circuit section 511 also calculates the amounts of increase ΔTpr1 to ΔTpr7, which are the differences between the initial temperature and the temperatures Tf1 to Tf7 detected by the pressure roller surface temperature sensor 540. The control circuit section 511 then calculates the target temperature correction value B using the amounts of increase ΔTf4 and ΔTpr4 in the reference heat generation block HB4 according to the following formula (1). In this embodiment, the coefficient a is set to 0.175, the coefficient b to -0.3, and the constant term c to 5.4. The calculated target temperature correction value B is rounded down to one decimal place.
Target temperature correction value B=a*ΔTf4+b*ΔTpr4+c (1)
The calculated target temperature correction value B is stored in memory M4. The target temperature correction value B stored in memory M4 is used as a temperature adjustment control correction value for all heat generating blocks when image heating apparatus 200 is installed in image forming apparatus 100 and operated. The method for this will be described later.

In the image heating device 200 in this embodiment, ΔTf4 = 115 and ΔTpr4 = 75, as shown in FIG. 6. Therefore, from equation (1), the target temperature correction value B = 0.175 * 115 + (-0.3) * 75 + 5.4 = 3.025 can be obtained, and the target temperature correction value B is set to +3.0.

The control circuit 511 also calculates the average Tfavei of the temperatures Tfi detected by the film surface temperature sensor for 5 seconds from 55 seconds to 60 seconds after the start of startup (i=1 to 7). The control circuit 511 also calculates the difference ΔTfsi of Tfavei from the average Tfave4 detected by the film surface temperature sensor for each heat generation block HBi except for the reference heat generation block HB4 using the following formula (2) (i=1 to 3, 5 to 7).
ΔTfsi=Tfavei-Tfave4...(2)
Fig. 7(a) is a graph showing the average Tfavei of the temperatures detected by the film surface temperature sensors in each heat generation block in image heating apparatus 200. Fig. 7(b) is a graph showing the difference ΔTfsi of Tfavei with respect to Tfave4. Control circuit section 511 stores the differences ΔTfsi in the corresponding memories M1-3, M5-7. Table 1 shows the items stored in each memory M1-M7, their contents, and the stored information values (correction information) in image heating apparatus 200.

(Temperature control correction method and effect during image formation)
Memories M1 to M7 of image heating device 200 store information on the heat transfer performance of the fixing nip portion in reference heat generating block HB4 acquired under predetermined conditions in advance as described above, and information on temperature variation in the longitudinal direction for reference heat generating block HB4. Correction control of the target temperature of image heating device 200 using this information will be explained using the flowchart in FIG. 8. Note that the image heating device 200 will be explained under the above-mentioned conditions. Control unit 113 determines target temperature Ttgti of each heat generating block HBi (i=1 to 7) based on information on recording material P received from video controller 120, image information to be printed, and information stored in memories M1 to M7.

At S1, the control unit 113 receives an image formation signal from the video controller 120. At S2, the control unit 113 sets the print mode. Here, the control unit 113 determines the target base temperature Tb and the print speed S, which is the recording material transport speed per unit time, from an internal table based on information (type, basis weight, size) related to the recording material P used in image formation and image information (monochrome mode/color mode). For example, in the case of 80g plain paper, letter size, and color mode, Tb = 230.0°C and S = 220 mm/sec are set.

In S3, control unit 113 reads out target temperature correction value B specific to image heating apparatus 200 from memory M4 of image heating apparatus 200. Here, target temperature correction value B=+3.0 is read out as shown in Table 1. In S4, control unit 113 finds target temperature Ttgt4 in reference heat generation block HB4 using target base temperature Tb, target temperature correction value B, and the following equation (3).
Ttgt4=Tb+B...(3)
In this embodiment, it can be determined that Ttgt4=230.0+3.0=233.0.

In S5, the control unit 113 reads out the difference ΔTfsi in the detected temperatures of the film surface temperature sensors from memories M1 to M3 and M5 to M7 of the image heating device 200 (i = 1 to 3, 5 to 7).

In S6, the control unit 113 uses the target temperature Ttgt4 in the reference heat generation block HB4, the read ΔTfsi, the coefficient k, and the following formula (4) to determine a target temperature Ttgti other than the target temperature Ttgt4. In this embodiment, the coefficient k is set to 1.5. The coefficient k is a coefficient for converting the difference ΔTfsi in the film surface temperature into a correction amount based on the thermistor temperature. The target temperature Ttgti is calculated by rounding up to one decimal place.
Ttgti=Ttgt4-k*ΔTfsi...(4)
As an example, a case will be described where the target temperature Ttgt1 of the heat generating block HB1 is calculated. ΔTfs1 read out in S5 is -1.0 by referring to Table 1. Furthermore, since the target temperature Ttgt4=233.0, it is possible to calculate Ttgt1=233.0-1.5*(-1.0)=234.5 using the above formula (4). The target temperatures Ttgti corresponding to each heat generating block HBi are shown in Table 2.

Image formation is performed by controlling thermistors TH1 to TH7 based on the target temperature Ttgti shown in Table 2.

Figure 9 shows the film surface temperature in each heat generating block when printing is performed for 2 minutes using the image heating device 200 in this embodiment under the following conditions: color mode, environmental temperature 25°C, and 80g Letter-size plain paper. The film surface temperature is experimentally measured by lightly contacting a thermocouple with the surface of the fixing film 202. The thermocouple is attached at a position in the longitudinal direction equivalent to the placement of thermistors TH1 to TH7.

As shown in Figure 9, the temperature variation in the longitudinal direction of the film surface is Δ1.0°C or less, including measurement error. Similarly, film surface temperatures were measured using this evaluation method using multiple image heating devices 200. It was confirmed that the temperature variation in the longitudinal direction of the film surface was within a range of Δ1.0°C or less for all image heating devices 200.

Thus, even if the detection values of each temperature detection element are controlled to the same temperature, there is a risk of temperature variation occurring between each heat generation block, but by performing temperature correction as in this embodiment, it is possible to suppress the variation. This makes it possible to suppress the occurrence of differences in the heating state of the image due to temperature differences on the film surface, which leads to uneven fixability and uneven gloss. It is also possible to suppress the occurrence of differences in thermal expansion of the fixing film due to temperature differences between each heat generation block. This makes it possible to suppress the occurrence of differences in outer diameter in the longitudinal direction of the fixing film, which in turn causes twisting in the fixing film in the longitudinal direction due to differences in the rotation distance.

Comparative Example
A comparative example will be shown in which the correction control of this embodiment is not applied, using the same apparatus as the above-described image heating apparatus 200. Fig. 10 shows the film surface temperature of the comparative example.

In the comparative example, no correction is made to suppress the difference between the film temperature of the reference heat generating block HB4 and the film temperature in each heat generating block. In other words, the process of reading out the film temperature difference ΔTfsi in S5 of FIG. 8 and the process of calculating a target temperature Ttgti other than the target temperature Ttgt4 in S6 are not performed. Therefore, the target temperature is set to the same value as Ttgt4 for all thermistors TH1 to TH7, which is 233.0°C. This results in a difference between each heat generating block and the reference heat generating block HB4, that is, a difference between Tfavei and Tfave4, as shown in FIG. 7(b). And, as shown in FIG. 10, there is variation in the temperature of the film surface in each heat generating block.

As shown in FIG. 10, the temperature in the longitudinal direction of the film surface varies within a range of Δ3.6°C. In this embodiment, as described above, the temperature difference is suppressed to Δ1.0°C or less. In other words, the temperature difference in the longitudinal direction of the film surface is suppressed more effectively than in the comparative example.

In this embodiment, the temperature difference ΔTfsi with respect to the reference heat generating block after power is supplied to the heater 300 for a certain time (predetermined period) is calculated and stored in memory. However, this is not limited to this, and for example, a certain amount of power (predetermined amount of power) may be supplied to the heater 300, and the temperature difference ΔTfsi with respect to the reference heat generating block may be calculated when the fixing film reaches a predetermined temperature.

In addition, in this embodiment, a thermistor structure is described in which a material having TCR characteristics is thinly printed on a substrate and integrated with the heater, but this is not limited to this. A temperature detection element that is a separate component from the heater may also be used. The same effect can be obtained by using the control of this embodiment even when using a thermistor that detects by contacting the heater, a thermistor that detects by contacting the inner circumferential surface of the fixing film, or a thermopile that detects without contacting the outer circumferential surface of the fixing film.

In this embodiment, the target temperature correction value B is calculated only for the reference heat generating block HB4, but the present invention is not limited to this. For example, the target temperature correction value Bi may be calculated for each heat generating block and stored in memory. In this case, the target temperature correction value Bi for each heat generating block is calculated by the following formula (5).
Bi=a*ΔTfi+b*ΔTpri+c (i=1 to 7)...(5)
In this case, it is desirable to switch between a control in which the target basic temperature Tb is added to the target temperature correction value Bi in each heat generating block and set as the final target temperature, and a control in which the target temperature Ttgti is set as in this embodiment, as necessary. In the control in which Tb+Bi in each heat generating block is set as the final target temperature, the target temperature can be set according to the heat transfer performance of the fixing nip of each heat generating block. This makes it possible to suppress unevenness in the fixing property of the toner image in the longitudinal direction. On the other hand, the temperature difference in the longitudinal direction of the film surface is not necessarily optimized. Therefore, in a mode in which the fixing film is less likely to twist at a low speed and in which uniform fixing property in the longitudinal direction is prioritized, such as a glossy paper compatible mode, Tb+Bi in each heat generating block is set as the final target temperature. In other modes, it is preferable to set the target temperature using the control of this embodiment.

113 Control unit 200 Image heating device 300 Heater

Claims (8)

A first rotating body;
a heater disposed in an internal space of the first rotating body;
a second rotating body that contacts an outer circumferential surface of the first rotating body and forms a nip portion that sandwiches and conveys a recording material together with the heater via the first rotating body;
Memory,
a control unit, and a recording material on which an image is formed is nipped and conveyed in the nip portion and heated,
The heater is
A thin board and
A plurality of heating resistors arranged in a line in the longitudinal direction of the substrate;
a first heat generating block including a heat generating resistor disposed in a central region of the substrate in the longitudinal direction;
a second heat generating block including a heat generating resistor disposed on an end side of the first heat generating block in the longitudinal direction;
a first temperature detection element that is disposed in an area corresponding to the first heat generating block and detects a temperature;
a second temperature detection element that is disposed in an area corresponding to the second heat generating block and detects a temperature;
the memory stores first correction information for correcting a target temperature of the first heat generating block and second correction information for correcting a target temperature of the second heat generating block;
the control unit determines a first target temperature of the first heat generation block based on a detection result of the first temperature detection element and the first correction information, and controls power supplied to the first heat generation block based on the first target temperature, determines a second target temperature of the second heat generation block based on a detection result of the second temperature detection element and the second correction information, and controls power supplied to the second heat generation block based on the second target temperature,
an image heating apparatus characterized in that the second correction information is obtained from the difference between the surface temperature of a first region of the first rotating body corresponding to the first heat generating block and the surface temperature of a second region of the first rotating body corresponding to the second heat generating block. The image heating device according to claim 1, characterized in that the second correction information is obtained from the difference between the surface temperature of the first region of the first rotating body and the surface temperature of the second region of the first rotating body when the image heating device is in an initial state and power is supplied to the heater for a predetermined period of time. a first surface temperature sensor that contacts an outer circumferential surface of the first rotating body and detects a surface temperature of the first area when the image heating apparatus is in an initial state;
3. The image heating apparatus according to claim 2, further comprising: a second surface temperature sensor that, in an initial state of the image heating apparatus, contacts an outer circumferential surface of the first rotating body and detects the surface temperature of the second area. The image heating device according to claim 1, characterized in that the second correction information is obtained from the difference between the surface temperature of the first region of the first rotating body and the surface temperature of the second region of the first rotating body when the image heating device is in an initial state and a predetermined amount of power is supplied to the heater. a first surface temperature sensor that contacts an outer circumferential surface of the first rotating body and detects a surface temperature of the first area when the image heating apparatus is in an initial state;
5. The image heating apparatus according to claim 4, further comprising: a second surface temperature sensor that, in an initial state of the image heating apparatus, contacts an outer circumferential surface of the first rotating body and detects the surface temperature of the second area. a third heat generating block including a heat generating resistor disposed on an end side of the first heat generating block in the longitudinal direction;
a third temperature detection element that is disposed in an area corresponding to the third heat generating block and detects a temperature;
the memory stores third correction information for correcting a target temperature of the third heat generating block;
the control unit determines a third target temperature of the third heat generating block based on a detection result of the third temperature detection element and the third correction information, and controls power supplied to the third heat generating block based on the third target temperature;
2. An image heating apparatus according to claim 1, wherein the third correction information is obtained from a difference between a surface temperature of a first region of the first rotating body corresponding to the first heat generating block and a surface temperature of a third region of the first rotating body corresponding to the third heat generating block. the first rotating body is a film,
the second rotating body is a pressure roller,
2. The image heating device according to claim 1, wherein the heater is disposed in an internal space of the film, the film is sandwiched between the heater and the pressure roller, and the image formed on the recording material is heated through the film in the nip portion. an image forming means for forming an image on a recording material;
2. An image forming apparatus comprising: an image heating device according to claim 1 for fixing an image formed on a recording material.

Images