JP5556615B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a technique for detecting abnormal heat generation in a resistance heating element type fixing device and determining the cause thereof.

  In an electrophotographic image forming apparatus, various fixing devices have been developed for melting and pressure-bonding toner carried on a recording sheet, and one of them is a resistance heating element type fixing device. The resistance heating element type fixing device melts the toner by supplying power to the resistance heating element layer provided on the fixing belt to generate Joule heat. Since the fixing belt has a low heat capacity and is in close contact with the recording sheet, the heat efficiency is very high, and quick warm-up can be realized with low power consumption.

  In the resistance heating element system, the resistance heating element layer is covered with an insulating layer in order to prevent leakage and electric shock. However, if foreign matter enters from the outside of the fixing device or the insulating layer deteriorates due to long-term use, the live part may be exposed. Further, when the resistance heating element layer is damaged, the current distribution is biased and there is a risk of causing uneven fixing and abnormal heat generation. When the damage is large, the resistance heating element layer may be heated from the fixing temperature (for example, 180 ° C.) to 300 ° C. or more in a short time (for example, about 3 minutes), and the silicon constituting the fixing roller There is a risk of rubber melting.

  For such a problem, for example, a countermeasure has been proposed in which abnormal heat generation is detected using a temperature detection element such as a thermistor or a thermostat to stop power supply to the resistance heating element layer. However, abnormal heat generation due to damage to the resistance heating element layer locally occurs around the damaged site. Thermistors and thermostats can only detect local temperatures around the element. For this reason, if the damaged part of the resistance heating element layer is out of the detection position of the temperature detection element, abnormal heat generation cannot be detected.

  Therefore, it is conceivable to monitor the entire resistance heating element layer by connecting temperature detection elements in series and arranging them in an array along the resistance heating element layer.

JP 2000-109997 A Japanese Patent Laid-Open No. 9-281845

However, abnormal heat generation of the resistance heating element layer also occurs due to causes other than damage. For example, when small-size paper is continuously fixed, if an excessive temperature rise (hereinafter referred to as “edge excessive temperature rise”) occurs in the non-sheet passing region, it is also detected by the temperature detection element.
When the resistance heating element layer is damaged, it is necessary to immediately stop the image formation and replace the fixing roller. On the other hand, when the end portion is excessively heated, image formation can be normally continued by adjusting the temperature by temporarily interrupting the power supply and cooling the resistance heating element layer. Therefore, when abnormal heat generation is detected, it is not appropriate to take the same measures uniformly, and the measures to be taken differ depending on the cause of abnormal heat generation. In particular, since abnormal heat generation due to damage may cause damage to the apparatus, it is important to detect the presence or absence.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device and an image forming apparatus that detect abnormal heat generation due to damage to a resistance heating element layer.

In order to achieve the above object, a fixing device according to the present invention is a fixing device that fixes a toner image on a recording sheet by causing Joule heating of a resistance heating element layer provided in an endless fixing belt, and the rotation of the fixing belt. A pair of temperature detection means for detecting the temperature of the fixing belt portion in a symmetric area with respect to the center in the axial direction, and abnormal heat generation for detecting abnormal heat generation of the fixing belt from the respective detection results of the pair of temperature detection means A temperature difference is detected by the temperature difference detecting means when the abnormal heat generation is detected by the detecting means, the temperature difference detecting means for detecting the temperature difference detected by the pair of temperature detecting means, and the abnormal heat detecting means. When it is, provided with a determination means the resistance heating layer is damaged, and the symmetrical region, as a whole, over the entire in the rotation axis direction of the fixing belt Lever, it is possible to detect abnormal heating without omission.
Further, the fixing device fixes the toner image on the recording sheet by causing Joule heating of the resistance heating element layer provided in the endless fixing belt, the regions being symmetrical with respect to the center in the rotation axis direction of the fixing belt, Plural pairs of temperature detection means for detecting the temperature of the fixing belt portion, abnormal heat generation detection means for detecting abnormal heat generation of the fixing belt from the detection results of the pair of temperature detection means, and the pair of temperature detection means If the temperature difference is detected by the temperature difference detection means that detects the temperature difference detected by the temperature difference detection means and the abnormal heat generation detection means, the resistance heating element layer is damaged. comprising a a determination means that, the, each other said pair of temperature detecting means detects the temperature of the different areas from each other, are the different regions, as a whole, a fixing base If not over the entire of the bets in the rotation axis direction, it is possible to more precisely identify the damage location of the resistive heating element layer.

Further, the fixing device fixes the toner image on the recording sheet by causing Joule heating of the resistance heating element layer provided in the endless fixing belt, the regions being symmetrical with respect to the center in the rotation axis direction of the fixing belt, Detected by a pair of temperature detection means for detecting the temperature of the fixing belt portion, an abnormal heat detection means for detecting abnormal heat generation of the fixing belt from the detection results of the pair of temperature detection means, and the pair of temperature detection means. If the temperature difference is detected by the temperature difference detection means for detecting the temperature difference and the abnormal heat generation detection means by the temperature difference detection means, the resistance heating element layer is damaged. a determination unit, in addition to the pair of temperature detecting means, in the direction of the axis of rotation center of the fixing belt, the smallest among the plurality of types of recording sheets to be center fed A center temperature detecting means for detecting the temperature of the portion of the recording sheet that is equal to or smaller than the sheet passing width; and a center abnormal heat detecting means for detecting abnormal heat generation of the fixing belt from the electrical resistance value of the center temperature detecting means, and the pair of temperatures The detecting means may detect the temperature in a region other than the region where the center temperature detecting means in the rotation axis direction of the fixing belt detects the temperature. In this way, since the end portion overheating cannot occur within the sheet passing range of the recording sheet having the smallest sheet passing width, damage to the resistance heating element layer can be detected with a simpler apparatus configuration.

In this case, the pair of temperature detecting means multiple pairs with, each other said pair of temperature detecting means detects the temperature of the different areas from each other, the different regions are, as a whole, in the rotation axis direction of the fixing belt If the center temperature detection means covers the entire region other than the region where the temperature is detected, the damage position of the resistance heating element layer can be specified with higher accuracy.
An image forming apparatus according to the present invention includes the fixing device according to the present invention. As a result, the above-described effects of the fixing device according to the present invention can be obtained.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a partially cutaway perspective view showing a main configuration of a fixing device 115. FIG. 2 is a cross-sectional perspective view showing a configuration of a fixing belt 201. FIG. It is a figure which shows the main structures of the control part. It is a figure which shows the structure of an abnormal heat generation detection mechanism. 6 is a cross-sectional view showing the arrangement of an abnormal heat generation detection mechanism 400. FIG. It is a flowchart which shows the detection and discrimination | determination operation | movement of abnormal heat generation. It is a figure which shows the structure of the abnormal heat generation detection mechanism which concerns on the modification of this invention. It is a figure which shows the structure of the abnormal heat generation detection mechanism which concerns on another modification. It is a flowchart which shows the detection and discrimination | determination operation | movement of abnormal heat generation which concern on a modification. It is a figure which shows the structure of the abnormal heat generation detection mechanism which concerns on this modification which concerns on another modification.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings.
[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.
FIG. 1 is a diagram illustrating a main configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a document reading unit 100, an image forming unit 110, and a paper feeding unit 120. The document reading unit 100 optically reads a document placed on a platen tray with an automatic document feeder (ADF) and generates image data. The image data is stored in the control unit 112 described later.

  The image forming unit 110 includes image forming units 111Y to 111K, a control unit 112, an intermediate transfer belt 113, a secondary transfer roller pair 114, a fixing device 115, a paper discharge roller pair 116, a paper discharge tray 117, a cleaner 118, and a timing roller pair 119. It has. The image forming unit 110 is equipped with toner cartridges 101Y to 101K that supply toners of Y (yellow), M (magenta), C (cyan), and K (black) colors.

  Upon receipt of toner from the toner cartridges 101Y to 101K, the image forming units 111Y to 111K form toner images of each color of YMCK under the control of the control unit 112, and the intermediate transfer belt so that these toner images overlap each other. Electrostatic transfer (primary transfer) 113 is performed. The intermediate transfer belt 113 is an endless rotator, and rotates in the direction of arrow A to convey the primary transferred toner image to the secondary transfer roller pair 114.

  The paper feeding unit 120 includes a paper feeding cassette 121 that stores the recording paper P for each paper size, and supplies the recording paper P to the image forming unit 110. The supplied recording paper P is unloaded one by one in parallel with the intermediate transfer belt 113 conveying the toner image, and is conveyed to the secondary transfer roller pair 114 via the timing roller pair 119. The timing roller pair 119 includes a pair of rollers, and adjusts the timing at which the recording paper P reaches the secondary transfer roller pair 114.

  The secondary transfer roller pair 114 is composed of a pair of rollers having a potential difference, and these roller pairs are pressed against each other to form a transfer NIP portion. In the transfer NIP portion, the toner image on the intermediate transfer belt 113 is electrostatically transferred (secondary transfer) onto the recording paper P. The recording paper P to which the toner image has been transferred is conveyed to the fixing device 115. Further, the residual toner remaining on the intermediate transfer belt 113 after the secondary transfer is further conveyed in the direction of arrow A, and then scraped off by the cleaner 118 and discarded.

  The fixing device 115 is a resistance heating element type fixing device, which heats and melts the toner image and presses the toner image onto the recording paper P. The recording paper P to which the toner image has been fused is discharged onto the paper discharge tray 117 by the paper discharge roller pair 116. The control unit 112 controls the operation of the image forming apparatus 1 including the above. The control unit 112 also transmits / receives image data to / from other devices such as a personal computer (PC) and accepts print jobs.

In transferring the toner image, a transfer charger or a transfer belt may be used instead of the transfer roller. Further, when the residual toner on the intermediate transfer belt 113 is removed, a cleaning brush, a cleaning roller, or the like may be used instead of the cleaner 118 (cleaning blade).
[2] Configuration of Fixing Device 115 Next, the configuration of the fixing device 115 will be described.

  FIG. 2 is a partially cutaway perspective view showing the main configuration of the fixing device 115. As shown in FIG. 2, the fixing device 115 is brought into pressure contact with the fixing roller via an endless fixing belt 201 that can be elastically deformed, a fixing roller 210 in which the fixing belt 201 is loosely fitted, and the fixing belt 201. A pressure roller 220 and a power supply member 230 that supplies power for heat generation to the fixing belt 201 are provided. The fixing device 115 also includes a meandering restricting plate that restricts the meandering of the fixing belt. However, in FIG. 2, the meandering restricting plate is not shown in order to make the device configuration easy to see.

  The fixing belt 201 has a cylindrical shape before assembly, but elastically deforms when a certain amount of external force is applied in the radial direction, and returns to a lower state by its own restoring force when the application of the external force is stopped from the deformed state. What can hold a shape is used. The dimension of the fixing belt 201 in the radial direction is, for example, an inner diameter of 30 [mm]. The configuration of the fixing belt 201 will be described in detail later.

  The fixing roller 210 is formed by laminating an elastic layer 213 around a long cored bar 212, and a circulation path of the fixing belt 201 (a travel path when the fixing belt 201 travels around. Hereinafter, “belt circulation path”). It is arranged inside. The cored bar 212 as the shaft portion is made of, for example, aluminum or stainless steel having a diameter of 18 [mm]. The elastic layer 213 is made of heat-resistant rubber such as silicone rubber or fluororubber, or a foamed material thereof (which may be laminated), and has a thickness of, for example, 5 [mm].

The outer diameter of the fixing roller 210 is smaller than the inner diameter of the fixing belt 201 (for example, 28 [mm]), and the fixing roller 210 and the fixing belt 201 are in contact with each other at the fixing nip N. A gap (space) is provided between them.
With such a configuration, the area of heat transfer from the fixing belt 201 to the fixing roller 210 is smaller than the configuration in which the fixing belt 201 is in close contact with the fixing roller 210, and the heat generated from the fixing belt 201 is reduced. The heat transfer loss such as the part being transferred to the housing of the fixing device 115 that rotatably supports the shafts 211 at both ends of the cored bar 212 via the cored bar 212 of the fixing roller 210 is reduced to achieve high thermal efficiency. be able to.

  The pressure roller 220 is formed by laminating a release layer 224 around an elongated cored bar 222 via an elastic layer 223, and is disposed outside the belt circulation path. The pressure roller 220 is urged by an urging mechanism (not shown) and presses the fixing roller 210 from the outside of the fixing belt 201 via the fixing belt 201 to secure a fixing nip N between the surface of the fixing belt 201. To do. The outer diameter of the pressure roller 220 is desirably in the range of 20 to 100 [mm], and is 35 [mm] in the present embodiment.

The cored bar 222 has a hollow pipe shape made of, for example, aluminum or iron and has an outer diameter of, for example, 30 [mm]. The thickness is preferably in the range of 0.1 to 10 [mm], and in the present embodiment, it is 2 [mm]. Note that a solid cylindrical shape or a cross-sectional shape such as a three-pointed shape may be used.
The elastic layer 223 is made of, for example, heat-resistant rubber such as silicone rubber or fluorine rubber, or a foamed material thereof, and the thickness is preferably within a range of 1 to 20 [mm]. 2.5 [mm].

The release layer 224 may be made of a fluororesin tube such as PFA (PerFluoroAlkoxy), a fluororesin coating, or the like, and may be provided with conductivity in order to prevent toner offset due to charging. The thickness of the release layer 224 is preferably in the range of 5 to 100 [μm], and in the present embodiment, it is 20 [μm].
In the fixing roller 210, shaft portions 211 at both ends in the axial direction of the cored bar 212 are rotatably supported by a housing of the fixing device 115 via a bearing member (not shown). Similarly, in the pressure roller 220, the shaft portions 221 at both ends in the axial direction of the cored bar 222 are rotatably supported by the housing via a bearing member (not shown).

The pressure roller 220 is rotationally driven in the direction of arrow A by transmission of driving force from a driving motor (not shown). Following the rotation of the pressure roller 220, the fixing belt 201 runs around in the direction of the arrow B, and the fixing roller 210 is driven to rotate in the same direction. The fixing roller 210 may be the driving side, and the fixing belt 201 and the pressure roller 220 may be the driven side.
Electrodes 202 are provided over the entire outer peripheral surface of both ends sandwiching the sheet passing region in the axial direction of the fixing roller 210 (hereinafter referred to as “roller axial direction”) on the outer peripheral surface of the fixing belt 201. The pair of power supply members 230 receive a biasing force in the direction from the outside to the inside of the fixing belt 201 and are pressed against the electrodes 202, respectively. Details will be described later.

The power supply member 230 is a rectangular parallelepiped block having a size of, for example, 10 [mm] in length, 5 [mm] in width, and 7 [mm] in height, and is made of copper graphite or carbon having slidability and conductivity. These are so-called carbon brushes made of a material such as graphite, and each is electrically connected to a power source 232 via a conductive wire (harness) 231.
A meandering restricting plate is attached to the shaft portion 211 at both ends of the fixing roller 210 in the rotation axis direction. The meandering restriction plate rotates together with the fixing roller 210 to restrict the meandering of the fixing belt 201. As will be described later, the fixing device 115 includes an abnormal heat detection mechanism for detecting abnormal heat generation of the fixing belt 201.

[3] Configuration of Fixing Belt 201 Next, the configuration of the fixing belt 201 will be described.
FIG. 3 is a cross-sectional perspective view showing the configuration of the fixing belt 201. In FIG. 3, the alternate long and short dash line indicates the center line of the shaft portion 211, and the illustration below the center line is omitted. FIG. 3 is a view focusing on one end of the fixing belt 201 in the rotation axis direction, but the fixing belt 201 has the same configuration at the other end. In addition, in order to make a figure legible, the dimension of each member differs from the dimension illustrated below.

As shown in FIG. 3, the fixing belt is formed by sequentially laminating a resistance heating element layer 302, an elastic layer 303, and a release layer 304 on an insulating layer 301. An electrode 202 is attached on the resistance heating element layer 302 in the direction of the rotation axis of the fixing roller 210 and outside the elastic layer 303.
The resistance heating element layer 302 receives power from the electrode 202 and generates Joule heat. The resistance heating element layer 302 is adjusted to a predetermined electrical resistivity by dispersing a conductive filler in the resin. As the resin material, it is desirable to use a heat resistant resin such as PI (Poly Imide), PPS (Poly Phenilene Sulfide), and PEEK (Poly Ether Ether Ketone).

Conductive fillers include metals such as silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), and carbon-based carbon nanotubes, carbon nanofibers, carbon microcoils, etc. A material may be used, and two or more of these may be mixed and dispersed. As the shape of the conductive filler, a fibrous shape is desirable in order to increase the probability that the fillers are in contact with each other with the same content. The thickness of the conductive filler is preferably about 5 to 100 [μm]. Needless to say, the electrical resistivity of the conductive filler should be determined according to the voltage to be applied, the current, the thickness of the resistance heating element layer 302, and the diameter and length of the fixing belt 201. 1.0 × 10 ^{−6 to} 9.9 × 10 ⁻³ [Ωm], and 1.0 × 10 ^{−5 to} 5.0 × 10 ⁻³ [Ωm]. More preferably.

  The release layer 304 is provided with release properties such as fluorine tubes such as PFA (Tetra Fluoro Ethylene-Perfluoro Alkyl Vinyl Ether Copolymer), PTFE (Poly Tetra Fluoro Ethylene), ETFE (Ethylene Tetra Fluoro Ethlylene), and fluorine coating. The configuration is desirable and may be conductive. Examples of the fluorine-based tube include products such as PFA350-J, 451HP-J, and 951HP Plus manufactured by Mitsui DuPont Fluorochemical Co., Ltd.

The contact angle between the release layer 304 and water may be 90 ° or more, and more preferably 110 ° or more. The surface roughness of the release layer 304 is preferably such that the center line average roughness (Ra) is within a range of 0.01 to 50 [μm]. The thickness of the release layer 304 is preferably in the range of 5 to 100 [μm], for example.
The release layer 304 may have a configuration of three or more layers reinforced and insulated by laminating a resin such as PI or PPS on the elastic layer of fluororubber.

The electrodes 202 are laminated over the entire circumference of the fixing belt 201 at both ends of the fixing belt 201 in the rotation axis direction. By adopting such a shape, when the electrode 202 is energized, a uniform current distribution can be realized in the entire resistance heating element layer 302, so that uniform heat generation can be obtained.
Further, meandering restricting members 301 are disposed outside both ends of the fixing belt 201, and the fixing belt 201 can be prevented from meandering.

  The material of the electrode 202 is preferably a metal with low electrical resistivity, such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), zinc (Zn), tungsten (W), nickel (Ni), Brass is good. In addition, when laminating the electrode 202 on the resistance heating element layer 302, it is desirable to use a method such as fixing with a conductive adhesive material or plating.

The insulating layer 301 is made of a heat-resistant insulating resin such as PI, PPS, or PEEK, and the thickness is preferably in the range of 5 to 100 [μm]. The entire outer peripheral surface of the insulating layer 301 is covered with a resistance heating element layer 302.
[4] Configuration of Control Unit 112 Next, the configuration of the control unit 112 will be described.

  FIG. 4 is a diagram illustrating a main configuration of the control unit 112. As shown in FIG. 4, the control unit 112 includes a CPU (Central Processing Unit) 401, a ROM (Read Only Memory) 402, a RAM (Random Access Memory) 403, and an ADC (Analogue to Digital Converter) 404. When the CPU 401 reads the program from the ROM 402 after being automatically reset when the power is turned on, the CPU 401 uses the RAM 403 as a working storage area and operates according to the program.

Further, the CPU 401 converts the analog detection value generated by the abnormal heat generation detection mechanism 400 into a digital value through the ADC 404 and acquires it. As a result, processing such as stopping of the image forming processing when abnormal heat generation is detected is performed.
[5] Abnormal Heat Generation Detection Mechanism Next, a mechanism for detecting abnormal heat generation of the fixing belt 201 will be described.

  The fixing device 115 includes an abnormal heat generation detection mechanism in order to detect abnormal heat generation of the fixing belt 201. FIG. 5 is a diagram illustrating a configuration of the abnormal heat generation detection mechanism. As shown in FIG. 5, the abnormal heat detection mechanism 400 includes thermistor arrays 501a and 501b, resistance value detection circuits 502a and 502b, a comparison circuit 503, and abnormal heat detection circuits 504a and 504b.

  The thermistor arrays 501a and 501b are serially connected thermistors arranged in the direction of the rotation axis of the fixing belt 201 along the outer peripheral surface of the fixing belt 201, respectively. The thermistor arrays 501a and 501b are configured symmetrically with respect to the center of the fixing belt 201 in the rotation axis direction of the fixing belt 201, and both the thermistors are arranged from the center to the end of the fixing belt 201. It is installed. Both the thermistor arrays 501 a and 501 b change the electric resistance value due to the influence of heat from the fixing belt 201.

  Resistance value detection circuits 502a and 502b detect electric resistance values of the thermistor arrays 501a and 501b, respectively. The comparison circuit 503 compares the electric resistance values detected by the resistance value detection circuits 502a and 502b, and determines whether or not the abnormal heat generation is caused by a flaw based on the magnitude of the difference value. Specifically, in most cases, the damage that occurs in the resistance heating element layer occurs in one of the region facing the thermistor array 501a and the region facing the thermistor array 501b, or across both regions. Even in this case, it is almost biased to either one.

  For this reason, the change in the electrical resistance value caused by abnormal heat generation due to damage differs between the thermistor arrays 501a and 501b. Therefore, the comparison circuit 503 compares the thermistor arrays 501 a and 501 b to determine whether or not the abnormal heat generation is due to damage, and outputs the determination result to the control unit 211. However, since the comparison circuit 503 does not detect the magnitude of the electrical resistance value itself between the thermistor arrays 501a and 501b, the presence or absence of abnormal heat generation is detected by the abnormal heat detection circuits 504a and 504b.

Abnormal heat detection circuits 504a and 504b detect the presence or absence of abnormal heat generation by comparing the electrical resistance values detected by the resistance value detection circuits 502a and 502b with reference values, respectively.
FIG. 6 is a cross-sectional view showing the arrangement of the abnormal heat detection mechanism 400. As shown in FIG. 6, the abnormal heat generator detection mechanism 400 includes a thermistor array 501 mounted on a substrate 600, and is disposed so that the thermistor array 501 is close to and faces the outer peripheral surface of the fixing belt 201. .

  The thermistor array 501 may be made of a PTC (Positive Temperature Coefficient) material or an NTC (Negative Temperature Coefficient) material. In this embodiment, the PTC material, that is, the temperature is high. A material having a higher electrical resistance value is used. Therefore, when the thermistor array 501 has an electric resistance value larger than the predetermined reference value, it is determined that abnormal heat is generated. On the other hand, when NTC material is used, it may be determined that abnormal heat is generated when the electrical resistance value of the thermistor array 501 is smaller than a predetermined reference value.

[6] Abnormal Heat Generation Detection and Discrimination Operation Next, abnormal heat generation detection and discrimination operation will be described.
FIG. 7 is a flowchart showing the abnormal heat generation detection and determination operation according to the present embodiment. The control unit 112 refers to the output signals of the abnormal heat detection circuits 504a and 504b (S701), and if the electrical resistance value of any of the thermistor arrays 501a and 501b is not greater than or equal to the reference value (threshold value) Ta (S702). : NO), since it is determined that no abnormal heat generation has occurred, the process proceeds to step S701, and the output signals of the abnormal heat detection circuits 504a and 504b are continuously monitored.

  If the electrical resistance value of either the thermistor array 501a or 501b is greater than or equal to the reference value Ta (S702: YES), it is determined that abnormal heat generation has occurred, so the output signal of the comparison circuit 503 is referred to (S703). . If the difference in electrical resistance value between the thermistor arrays 501a and 501b is smaller than the predetermined threshold value Tb (S704: NO), the end excessive temperature rise caused by the continuous passage of small-size paper is caused. Since it is determined that the image has occurred, the image forming process is temporarily stopped (S705), and the output signals of the abnormal heat generation detection circuits 504a and 504b are monitored while cooling the excessively heated portion (S706). Thereafter, when the electrical resistance values of the thermistor arrays 501a and 501b become smaller than the predetermined threshold value Tc (S707: YES), it is determined that the fixing belt 201 has been sufficiently cooled, so the image forming process is resumed (S708). .

  On the other hand, when the difference in electrical resistance value between the thermistor arrays 501a and 501b is larger than the predetermined threshold value Tb (S704: YES), the resistance heating element layer 302 is damaged and the image forming process is continued. Since it is determined to be dangerous, image formation is prohibited (S709) and the user of the image forming apparatus 1 is left with a notice that damage has occurred in the resistance heating element layer 302 (S710). This notification may be performed, for example, by displaying an error message on the operation panel or generating an alarm sound.

[7] Modifications Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .
(1) In the above embodiment, the case where the presence or absence of damage to the resistance heating element layer 302 is determined by comparing the electrical resistance values of the pair of thermistor arrays 501a and 501b has been described, but the present invention is not limited to this. Needless to say, it may be as follows.

  FIG. 8 is a diagram showing a configuration of an abnormal heat generation detection mechanism according to this modification. As shown in FIG. 8, in the abnormal heat detection mechanism 800 according to this modification, the thermistor arrays 801a and 801d are paired and the thermistor arrays 801b and 801c are paired. The resistance value detection circuits 802a to 802d detect the electrical resistance values of the thermistor arrays 801a to 801d, respectively. Detect whether or not.

The comparison circuit 803a detects the difference in electrical resistance value between the thermistor arrays 801a and 801d, and the comparison circuit 803b detects the difference in electrical resistance value between the thermistor arrays 801b and 801c. Further, output signals from the abnormal heat detection circuits 804 a to 804 d and the comparison circuits 803 a and 803 b are output to the control unit 211.
Thus, as the number of thermistor arrays is increased, the range of the fixing belt 201 monitored by each thermistor array is narrowed. Therefore, the position where abnormal heat generation occurs, in other words, the position where the resistance heating element layer 302 is damaged becomes more accurate. Can be specified. Therefore, if a thermistor array pair having a symmetrical structure is provided at a symmetrical position with respect to the center of the fixing belt 201 in the rotation axis direction, the effects of the present invention can be obtained regardless of the number of the pairs.

(2) In the above embodiment, the case where the cause of abnormal heat generation of the fixing belt 201 is determined using the pair of thermistor arrays 501a and 501b has been described, but the present invention is not limited to this. You may do as follows.
FIG. 9 is a diagram showing a configuration of an abnormal heat generation detection mechanism according to this modification. As shown in FIG. 9, the abnormal heat generation detection mechanism 900 according to the present modification includes three thermistor arrays 901a to 901c, and the electric resistance values are detected and detected by the resistance value detection circuits 902a to 902c, respectively. Based on the electrical resistance value, the presence or absence of abnormal heat generation is determined by the abnormal heat detection circuits 904a to 904c. The comparison circuit 903 detects a difference in electrical resistance value between the thermistor arrays 901a and 901c. Output signals from the abnormal heat detection circuits 904a to 904c and the comparison circuit 903 are input to the control unit 211.

  In the thermistor array 901b, the range of the fixing belts 201 facing each other is equal to or smaller than the sheet passing width of the smallest size recording sheet among the recording sheets fixed by the fixing device 115. The thermistor arrays 901a and 901c are disposed on both ends of the fixing belt 201 with the thermistor array 901b interposed therebetween. Since the range facing the thermistor array 901b is equal to or smaller than the minimum sheet passing width, the range facing the thermistor arrays 901a and 901c includes the non-sheet passing area of all the recording sheets fixed by the fixing device 115.

  Therefore, the abnormal heat generation due to the end excessive temperature rise does not occur in the range where the thermistor array 901b is opposed, in other words, the abnormal heat detection detected by the thermistor array 901b is all due to the resistance heating element layer 302 being damaged. It can be determined that it is a thing. On the other hand, in the range where the thermistor arrays 901a and 901c face each other, both abnormal heat generation due to excessive temperature rise at the end and abnormal heat generation due to damage to the resistance heating element layer 302 can occur. Determine the cause.

  FIG. 10 is a flowchart showing an abnormal heat generation detection and determination operation according to this modification. As shown in FIG. 10, the control unit 112 refers to the output signal of the abnormal heat detection circuit 904b (S1001), and if the electrical resistance value of the thermistor array 901b is equal to or greater than the reference value (threshold value) Ta (S1002). : YES), since it is determined that abnormal heat generation due to damage to the resistance heating element layer 302 has occurred, image formation is prohibited (S1011) and the occurrence of damage is notified (S1012). If the electrical resistance value of the thermistor array 901b is not equal to or greater than the reference value (threshold value) Ta (S1002: NO), the same operation as in the above embodiment is executed, and thus the description is omitted.

Even in this case, it is possible to know the damage position in more detail while suppressing the complexity of the apparatus configuration to determine the cause of abnormal heat generation.
Even in the case where the thermistor array 901b is provided, the damage position can be detected with high accuracy by providing a plurality of thermistor array pairs for detecting end excessive temperature rise. FIG. 11 is a diagram illustrating a configuration of an abnormal heat generation detection mechanism according to the present modification example. As shown in FIG. 11, two thermistor array pairs for detecting end excessive temperature rise may be provided.

  That is, a pair of thermistor arrays 1101a and 1101e and a pair of thermistor arrays 1101b and 1101d. In this way, the damage position of the resistance heating element layer 302 can be specified in more detail. Including the modification (1), the number of thermistor array pairs may be three or more. The effects of the present invention can be obtained regardless of the number of thermistor array pairs.

(3) In the above embodiment, the case where the comparison circuit and the abnormal heat generation detection circuit are used has been described. However, it goes without saying that the present invention is not limited to this, and the detection is performed by the resistance value detection circuit instead. The controller 112 may refer to the electrical resistance value of the thermistor array to determine the presence or absence of abnormal heat generation and the cause of heat generation.
(4) Although the case where a plurality of thermistors are connected in series has been described in the above embodiment, the number of thermistors connected in series may be appropriately selected according to the size of the fixing belt. A single thermistor may be used instead of the thermistor array. The effect of the present invention can be obtained regardless of the number of thermistors used.

  (5) Although not particularly mentioned in the above embodiment, the image forming apparatus 1 may be a copying machine or a facsimile machine. Also, it may be a printer device or a multi-function machine (MFP: Multi Function Peripheral) that combines these functions. If the device has a resistance heating element type fixing device, the present invention is applied, The effect can be obtained.

  The fixing device and the image forming apparatus according to the present invention are useful as a technique for detecting abnormal heat generation in a resistance heating element type fixing device and determining the cause thereof.

1 …………………………………………………… Image forming device 115 ……………………………………………… Fusing device 201 …… ……………………………………………… Fixing belt 302 ………………………………………………… resistance heating element layer 400, 800, 900, 1100 ............ Abnormal heat generation detection mechanisms 501a, 501b, 801a to 801d... Thermistor arrays 901a to 901c, 1101a to 1101e. 1102a to 1102e ... Resistance value detection circuits 503, 803a, 803b, 903 ..... Comparison circuits 1103a, 1103b ........... Comparison circuits 504a, 504b, 804a to 804d ..... Abnormal Heat detection circuit 904a~904c, 1104a~1104e ... abnormal heat detection circuit

Claims (5)

A fixing device for fixing a toner image to a recording sheet by causing Joule heating of a resistance heating element layer provided in an endless fixing belt,
A pair of temperature detection means for detecting the temperature of the fixing belt portion in a region symmetrical to each other about the center in the rotation axis direction of the fixing belt;
Abnormal heat detection means for detecting abnormal heat generation of the fixing belt from the respective detection results of the pair of temperature detection means;
Temperature difference detection means for detecting a temperature difference detected by the pair of temperature detection means;
A determination means for determining that the resistance heating element layer is damaged if a temperature difference is detected by the temperature difference detection means when abnormal heat generation is detected by the abnormal heat detection means;
The symmetrical region as a whole, that the entire area in the rotation axis direction of the fixing belt you said fixing device. A fixing device for fixing a toner image to a recording sheet by causing Joule heating of a resistance heating element layer provided in an endless fixing belt,
A plurality of pairs of temperature detection means for detecting the temperature of the fixing belt portion in a region symmetrical to each other about the center in the rotation axis direction of the fixing belt,
Abnormal heat detection means for detecting abnormal heat generation of the fixing belt from the respective detection results of the pair of temperature detection means;
Temperature difference detection means for detecting a temperature difference detected by the pair of temperature detection means;
A determination means for determining that the resistance heating element layer is damaged if a temperature difference is detected by the temperature difference detection means when abnormal heat generation is detected by the abnormal heat detection means;
The pair of temperature detection means detect temperatures in different regions,
The different regions as a whole, a fixing device you characterized in that over the entire in the rotation axis direction of the fixing belt. A fixing device for fixing a toner image to a recording sheet by causing Joule heating of a resistance heating element layer provided in an endless fixing belt,
A pair of temperature detection means for detecting the temperature of the fixing belt portion in a region symmetrical to each other about the center in the rotation axis direction of the fixing belt;
Abnormal heat detection means for detecting abnormal heat generation of the fixing belt from the respective detection results of the pair of temperature detection means;
Temperature difference detection means for detecting a temperature difference detected by the pair of temperature detection means;
A determination means for determining that the resistance heating element layer is damaged if a temperature difference is detected by the temperature difference detection means when the abnormal heat generation is detected by the abnormal heat detection means;
In addition to the pair of temperature detecting means, a center temperature detecting means for detecting a temperature of a portion of the center of the fixing belt in the rotation axis direction that is equal to or smaller than the paper passing width of the smallest recording sheet among a plurality of types of recording sheets passed through the center. When,
A center abnormal heat detection means for detecting abnormal heat generation of the fixing belt from the electrical resistance value of the center temperature detection means,
It said pair of temperature detecting means, the center temperature detection means in the rotation axis direction of the fixing belt you and detects the temperature of a region other than the region for detecting the temperature fixing device. It said pair of temperature detecting means multiple pairs comprising,
The pair of temperature detection means detect temperatures in different regions,
4. The fixing device according to claim 3 , wherein the different areas cover the entire area other than the area where the center temperature detecting means in the rotation axis direction of the fixing belt detects the temperature as a whole. An image forming apparatus comprising: a fixing device according to any one of claims 1 to 4.

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