JP2011253140A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that uses a resistance heating layer as a heating element and can detect occurrence of heating abnormality in high probability.SOLUTION: The fixing device heat-fixes an unfixed image on a recording sheet by using Joule heat generation, and includes a cylindrical heating roller 51 having a resistance heating layer where a plurality of elongated resistive thin pieces are arranged in a circumferential direction of the roller with a gap between the adjacent resistive thin pieces and with their longitudinal ends connected to feeding electrodes formed on the whole circumferences at both ends of the roller. The fixing device further includes a temperature sensor 54 for monitoring temperatures of the resistive thin pieces respectively. Presence or absence of heating abnormality is detected based on the monitoring result of the temperature sensor 54.

Description

  The present invention relates to a fixing device provided in an image forming apparatus such as a printer or a copying machine, and more particularly to a technique for detecting a heat generation abnormality in a fixing device using a resistance heating element layer as a heating layer.

  In recent years, as a fixing device for an image forming apparatus such as a printer or a copying machine, a fixing device using a resistance heating element layer that generates Joule heat upon energization as a heat generating layer has been used. This resistance heating element layer is configured by dispersing a conductive material such as a metal in an insulating material such as a heat resistant resin. Since there is a risk of electric shock if the resistance heating element layer that is energized is touched directly, the resistance heating element layer is generally covered with an insulating layer in order to prevent electric shock.

  Patent Document 1 discloses a fixing device using a resistance heating element layer covered with an insulating layer as a heating layer. In the fixing device, since the heating element generates heat by supplying power directly to the resistance heating element layer, the thermal efficiency of the fixing device can be increased and the warm-up time can be shortened.

JP 2009-109997 A

  Since the resistance heating element layer is covered with an insulating layer, it is not usually touched directly. However, since the thickness of the insulating layer is as thin as about several hundred μm, the insulating layer is scratched by contact with foreign matter or a recording sheet mixed from the outside, and the scratch extends to the resistance heating element layer. The current density locally increases around the edge, and the part of the resistance heating element layer where the current density is increased heats up to a high temperature, or a temperature difference occurs between the periphery of the scratch and the other part. In some cases, temperature unevenness may occur and the quality of the fixed image may deteriorate.

Although it is possible to detect this heat generation abnormality using a temperature sensing element such as a thermistor or thermostat provided in the fixing device, the detection range is narrow, so depending on the location of the resistance heating element layer where the heat generation abnormality occurs In some cases, the occurrence of abnormal heating is overlooked.
The present invention has been made in view of the above-described problems, and in a fixing device using a resistance heating element layer as a heat generation layer, the fixing device capable of detecting the occurrence of heat generation abnormality with high probability and the An object of the present invention is to provide an image forming apparatus including a fixing device.

  In order to achieve the above object, a fixing device according to an aspect of the present invention is a fixing device that thermally fixes an unfixed image on a recording sheet using Joule heat generation, on an insulating peripheral surface, A cylindrical rotating body having a resistance heating element layer in which a plurality of elongated resistance thin pieces are arranged at intervals in the circumferential direction of the rotating body with both ends in the longitudinal direction connected to power supply electrodes at both ends of the rotating body Monitoring means for monitoring the temperature of each resistance flake, and estimation means for estimating the presence or absence of heat generation abnormality of the resistance heating element layer based on the monitoring result by the monitoring means.

The estimation means can estimate that the heat generation abnormality has occurred when any of the temperatures of the resistance slices is higher than an upper limit value or lower than a lower limit value. Further, the estimation means can estimate that the heat generation abnormality has occurred when a difference between a maximum value and a minimum value of the temperature of each resistance slice exceeds a threshold value.
Furthermore, the cylindrical rotating body can be an endless belt. The interval may be less than 1 cm. The image forming apparatus according to an aspect of the present invention may be an image forming apparatus including the fixing device.

  By providing the above configuration, each of the plurality of resistance thin pieces of the resistance heating element layer is arranged at intervals in the circumferential direction of the rotating body on the insulating peripheral surface. When the size of the scratch on the resistance thin piece extends over the entire width in the circumferential direction of the resistance thin piece, no current flows through the resistance thin piece, so the resistance thin piece does not generate heat and the resistance thin piece. By monitoring this temperature, it is possible to easily detect that a heat generation abnormality has occurred in the resistance heating element layer.

  In addition, even when the scratch on the resistance thin piece is small and does not reach the entire circumferential width of the resistance thin piece, the resistance heating element layer is compared with the case where the resistance heating element layer is configured as one layer covering the entire insulating peripheral surface. The rate of increase in resistance due to scratches increases, the rate of decrease in current amount increases accordingly, and the current density flowing through the resistance slices decreases, so the amount of decrease in temperature due to scratches in one resistance slice increases. As a result, the temperature difference between the case where there is a scratch and the case where there is no scratch can be increased, and detection of abnormal heat generation in the resistance heating element layer can be facilitated accordingly.

Here, the monitoring means is disposed at a predetermined position in the vicinity of the cylindrical rotating body, and each time the resistance thin pieces pass through the vicinity of the predetermined position by rotating the cylindrical rotating body, The temperature of the resistance thin piece is detected, the position obtaining means for obtaining the relative position of the detected resistance thin piece from the reference position in the rotation direction of the cylindrical rotating body, and the temperature detected by the monitoring means is an upper limit value. A relative position storage means for storing the relative position of the resistance flake when it is higher or lower than a lower limit;
It is good also as providing.

Thereby, since the relative position in the cylindrical rotating body of the resistance flake in which the heat generation abnormality is estimated can be stored, the user can easily read the relative position and the position of the resistance flake having the heat generation abnormality easily. Can be specified.
Here, when a heat generation abnormality is estimated, power supply control means for stopping power supply to each of the resistance heating elements may be provided.

As a result, when a heat generation abnormality is estimated, the power supply to each resistance flake is stopped, so that the user can continue the heat fixing of the recording sheet in a state where the heat generation abnormality occurs, and the fixing failure It is possible to prevent problems such as these from occurring.
Here, when a heat generation abnormality is estimated, a notification means for notifying that may be provided.

  As a result, when a heat generation abnormality is estimated, a notification to that effect is made, so that the user can quickly take necessary measures such as repair.

1 is a diagram illustrating a configuration of a printer. 2 is a perspective view illustrating a configuration of a fixing device 5. FIG. 3 is a cross-sectional view showing a detailed structure in a region excluding both ends of a heating rotator 51. FIG. 4 is a cross-sectional view in the direction of the rotation axis around one end of the heating rotator 51 (the end on the side where the electrode 511 is present). 3 is a diagram illustrating a relationship between a configuration of a control unit 60 and main components that are controlled by the control unit 60. FIG. 6 is a flowchart illustrating an operation of belt temperature abnormality detection processing performed by a control unit 60. It is a figure which shows the modification of operation | movement of a belt temperature abnormality detection process.

(Embodiment)
Hereinafter, an embodiment of an image forming apparatus according to an embodiment of the present invention will be described with reference to an example in which the image forming apparatus is applied to a tandem color digital printer (hereinafter simply referred to as “printer”).
[1] Configuration of Printer First, the configuration of the printer 1 according to the present embodiment will be described. FIG. 1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing device 5, and a control unit 60.

When the printer 1 is connected to a network (for example, a LAN) and receives a print instruction from an external terminal device (not shown) or an operation panel (not shown), toner images of each color of yellow, magenta, cyan, and black are received based on the instruction. , And multiple transfer of these to form a full-color image, thereby executing a printing process on a recording sheet.
Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are expressed as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K, an exposure unit 10, an intermediate transfer belt 11, a secondary transfer roller 45, and the like.
Since the image forming units 3Y, 3M, 3C, and 3K have the same configuration, the configuration of the image forming unit 3Y will be mainly described below.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, and a cleaner 35Y for cleaning the photosensitive drum 31Y. A Y-color toner image is formed on the photosensitive drum 31Y.

The developing device 33Y faces the photosensitive drum 31Y and conveys charged toner to the photosensitive drum 31Y.
The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is driven to rotate in the direction of arrow C. The exposure unit 10 includes a light emitting element such as a laser diode, emits laser light L for forming images of Y to K colors in response to a drive signal from the control unit 60, and each of the image forming units 3Y, 3M, 3C, and 3K. The photosensitive drum is exposed and scanned.

By this exposure scanning, an electrostatic latent image is formed on the photosensitive drum 31Y charged by the charger 32Y. Similarly, electrostatic latent images are formed on the photosensitive drums of the image forming units 3M, 3C, and 3K.
The electrostatic latent image formed on each photoconductor drum is developed by each developing unit of the image forming units 3Y, 3M, 3C, and 3K, and a toner image of a corresponding color is formed on each photoconductor drum.

  The formed toner image is shifted on the intermediate transfer belt 11 so that the toner image is superimposed on the same position on the intermediate transfer belt 11 by the primary transfer rollers of the image forming units 3Y, 3M, 3C, and 3K. After the primary transfer sequentially, the toner images on the intermediate transfer belt 11 are secondarily transferred onto the recording sheet collectively by the action of electrostatic force by the secondary transfer roller 45. The recording sheet on which the toner image is secondarily transferred is further conveyed to the fixing device 5, and the toner image (unfixed image) on the recording sheet is heated and pressed in the fixing device 5 and thermally fixed on the recording sheet. Thereafter, the paper is discharged onto a paper discharge tray 72 by a discharge roller 71.

  The paper feed unit 4 includes a paper feed cassette 41 that stores recording sheets (denoted by reference numeral S in FIG. 1), a feed roller 42 that feeds the recording sheets in the paper feed cassette 41 one by one onto the transport path 43, and a feed roller 42. A timing roller 44 and the like for taking the timing of sending the recorded sheet to the secondary transfer position 46 are provided. The number of paper feed cassettes is not limited to one and may be plural.

As the recording sheet, paper sheets (plain paper, thick paper) having different sizes and thicknesses, and film sheets such as an OHP sheet can be used. When there are a plurality of paper feed cassettes, recording sheets of different sizes, thicknesses or materials may be stored in the paper feed cassettes.
Each of the rollers such as the feeding roller 42 and the timing roller 44 is driven to rotate by a conveyance motor (not shown) as a power source through a power transmission mechanism (not shown) such as a gear or a belt. As this conveyance motor, for example, a stepping motor capable of controlling the rotational speed with high accuracy is used.

The recording sheet is conveyed from the paper feeding unit 4 to the secondary transfer position 46 in accordance with the movement timing of the toner image on the intermediate transfer belt 11, and the toner images on the intermediate transfer belt 11 are collectively collected by the secondary transfer roller 45. Secondary transfer is performed on the recording sheet.
[2] Configuration of Fixing Device FIG. 2 is a perspective view showing the configuration of the fixing device 5. As shown in the figure, the fixing device 5 includes a heating rotator 51, a fixing roller 52, and a pressure roller 53. The heating rotator 51 is an endless belt, and power supply electrodes 511 and 512 are provided at both ends thereof. Power is supplied to both electrodes from the power supply unit 500 through power supply brushes 501 and 502. Thereby, an electric current flows between both electrodes, and the heating rotator 51 generates heat. Further, a temperature sensor 54 is disposed at a predetermined position in the vicinity of the outer peripheral surface of the heating rotator 51 (here, in the vicinity of the central portion in the rotation axis direction), and one end side of the heating rotator 51 (FIG. 2). The phase detection sensor 55 is arranged at a position facing the inner peripheral surface of the heating rotator 51 on the left end side).

  FIG. 3 is a cross-sectional view showing a detailed structure in a region excluding both ends of the heating rotator 51. As shown in the figure, in the region excluding both ends, the heating rotator 51 is configured by laminating an insulating layer 513, a resistance heating element layer 514, an elastic layer 515, and a release layer 516 in this order. The resistance heating element layer 514 is divided into a plurality of elongated layers in the circumferential direction of the heating rotator 51 (here, equally divided), and is divided into elongated layers (hereinafter referred to as “divided layers”). ) Are arranged so as to circulate on the insulating layer 513 at equal intervals in the circumferential direction. A gap between adjacent divided layers is filled with an insulating elastic layer 515 so that the adjacent divided layers are in an insulating state. In order to prevent temperature unevenness in the fixing temperature in the paper passing region of the heating rotator 51, it is desirable that the distance between adjacent divided layers be as close as possible, and be several mm or less (less than 1 cm). It is desirable.

  Thus, the resistance heating element layer 514 is not integrally disposed as a single layer on the entire peripheral surface of the insulating layer 513, but is divided into a plurality of divided layers and disposed in the insulating layer 513. When the resistance heating element layer 514 is damaged, and as a result, a heat generation abnormality occurs, a change in resistance value or current can be easily detected as a temperature change. For example, as indicated by reference numeral 201 in FIG. 2, when the circumferential length of the scratch extends over the entire circumferential width of one divided layer of the resistance heating element layer 514, the divided layer includes Since no current flows as indicated by an arrow marked with × at 202, the divided layer does not generate heat. Therefore, by detecting the surface temperature of the region corresponding to the divided layer on the outer peripheral surface of the heating rotator 51, it is possible to easily detect an abnormal heat generation. On the other hand, when the resistance heating element layer is configured as one layer covering the entire peripheral surface of the insulating layer without being divided, the temperature of the entire resistance heating element layer is locally increased even if the temperature rapidly increases. However, it is difficult to detect a temperature change in a region other than the local area where the scratch is generated, with little change, and there is a high possibility that the heat generation abnormality due to the generation of the scratch is overlooked.

  Furthermore, as indicated by reference numeral 203 in FIG. 2, even when the scratch is small and does not reach the entire width in the circumferential direction of one divided layer of the resistance heating element layer 514, it is caused by the scratch as compared with the case where the entire layer is a single layer. The rate of increase in resistance increases, the rate of decrease in current amount increases accordingly, and the current density flowing through one divided layer decreases accordingly, so that the amount of decrease in temperature in the divided layer increases. As a result, the temperature difference between when there is a flaw and when there is no flaw can be increased, and it becomes easier to detect an abnormal heat generation as a temperature change.

The greater the number of divided layers of the resistance heating element layer 514 that is equally divided, the smaller the circumferential width of the divided layer, and accordingly, the heat generation abnormality caused by small scratches is efficiently detected. be able to.
FIG. 4 is a cross-sectional view in the rotation axis direction around one end of the heating rotator 51 (the end on the side where the electrode 511 is present). As shown in the drawing, an insulating layer 513, a resistance heating element layer 514, and an electrode 511 are laminated in this order at the end of the heating rotator 51. The electrode 511 is made of a conductive material. As a material of the electrode 511, for example, a metal such as copper (Cu), aluminum (Al), nickel (Ni), brass, phosphor bronze, or the like can be used. The insulating layer 513 is a layer that reinforces the strength of the heating rotator 51 and insulates between the adjacent resistance heating element layers 514. For example, a polyimide resin can be used.

  The resistance heating element layer 514 is a layer that is electrically connected to the electrodes 511 and 512 and generates Joule heat when supplied with power through the electrodes 511 and 512. The resistance heating element layer 514 is configured by dispersing a conductive material in an insulating material such as a heat resistant resin. The electric resistance value (or volume resistivity) of the resistance heating element layer 514 is adjusted to a predetermined electric resistance value (or volume resistivity) by adjusting the amount of the conductive material.

  Examples of heat-resistant resins include polyimide resins, polyethylene sulfide resins, polyether ether ketone resins, polyaramid resins, polysulfone resins, polyimide amide resins, polyester-imide resins, polyphenylene oxide resins, poly-p-xylylene resins, polybenzimidazole resins, etc. Can be used. As the heat-resistant resin used for the resistance heating element layer 514, it is desirable to use a polyimide resin that exhibits excellent characteristics such as heat resistance, insulation, and mechanical strength.

  As the conductive material, metals such as silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), carbon nanotubes, carbon nanofibers, carbon nanocoils, etc. can be used. Two or more kinds of conductive materials (for example, carbon nanomaterial and metal) may be used. In this case, the metal is preferably needle-like or flaky silver (Ag) or nickel (Ni), and the particle size is preferably 0.01 to 10 μm. Thereby, the resistance heating element layer 514 having a uniform electric resistance can be molded by being intertwined with the carbon nanomaterial linearly. When the metal is in the form of particles, powders, or lumps, the resistance heating element layer has a uniform electric resistance because it is not entangled with the carbon nanomaterial mixed in the resistance heating element layer 514 and is in point contact with the carbon nanomaterial. 514 is difficult to obtain.

The thickness of the resistance heating element layer 514 is arbitrary, but is preferably about 5 to 100 μm. The electric resistance value of the resistance heating element layer 514 can be set in a range of about 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻² Ω · m, but the electric resistance value is 1.0 × 10 ^{−5 to} 5.0 ×. It is desirable to be within the range of 10 ⁻³ Ω · m.
The elastic layer 515 is a layer for transferring heat uniformly and flexibly to the toner image on the recording sheet. By providing the elastic layer 515, the toner image can be prevented from being crushed or the toner image can be melted non-uniformly, and image noise can be prevented from being generated. As a material of the elastic layer 515, an insulating rubber material or resin material having heat resistance and elasticity is used. For example, silicone rubber can be used.

  The thickness of the elastic layer 515 is 10 to 800 μm, more preferably 100 to 300 μm. If the thickness of the elastic layer 515 is less than 10 μm, it is difficult to obtain sufficient elasticity in the thickness direction. On the other hand, if the thickness exceeds 800 μm, it is difficult to cause the heat generated in the resistance heating element layer 514 to reach the outer peripheral surface of the heating rotator 51 and the heat transfer efficiency is poor.

  The release layer 516 is an outermost layer of the heating rotator 51 and is a layer for improving the releasability between the heating rotator 51 and the recording sheet. As a material for the release layer 516, a material that can withstand use at a fixing temperature and has excellent release properties with respect to toner can be used. For example, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), PFEP (tetrafluoroethylene / hexafluoroethylene) A fluororesin such as a propylene fluoride copolymer) can be used. The thickness of the release layer 516 is 5 to 100 μm, desirably 10 to 50 μm.

  Returning to the description of FIG. 2, the fixing roller 52 and the pressure roller 53 are axially supported at both end portions 521 and 531 in the axial direction of the core bars 522 and 532 so as to be rotatable on a bearing portion of a frame (not shown). The pressure roller 53 is rotationally driven in the direction of arrow B when the driving force from the pressure roller driving motor 56 is transmitted. As the pressure roller 53 rotates, the heating rotator 51 and the fixing roller 52 are driven to rotate in the direction of arrow A.

The fixing roller 52 is formed by covering the circumference of a long cylindrical cored bar 522 with a heat insulating layer 523, and is disposed inside the circulation path of the heating rotator 51. The metal core 522 is a member that supports the fixing roller 52 and is made of a material having heat resistance and strength. As a material of the core metal 522, for example, aluminum, iron, stainless steel, or the like can be used.
The heat insulating layer 523 is a layer for preventing the heat generated by the heating rotator 51 from escaping to the cored bar 522. As a material for the heat insulating layer 523, it is desirable to use a sponge (heat insulating structure) made of a rubber material or a resin material having low thermal conductivity and heat resistance and elasticity. This is because the heating rotator 51 can be bent and the nip width can be widened. The heat insulating layer 523 may have a two-layer structure of a solid body and a sponge body. In the case where a silicon sponge material is used as the heat insulating layer 522, the thickness is desirably 1 to 10 mm. More preferably, it is 2-7 mm.

  The pressure roller 53 is formed by laminating a release layer 534 around a cylindrical cored bar 532 via an elastic layer 533, and is disposed outside the circulation path of the heating rotator 51. Then, the fixing roller 52 is pressed through the heating rotator 51 to form a fixing nip having a predetermined width in the circumferential direction between the outer peripheral surface of the heating rotator 51. The metal core 532 is a member that supports the pressure roller 53 and is made of a material having heat resistance and strength. As a material of the core metal 532, for example, aluminum, iron, stainless steel, or the like can be used.

The elastic layer 533 is an elastic body such as silicone rubber or fluororubber and is made of a material having high heat resistance within a thickness range of 1 to 20 mm. Similar to the release layer 515, the release layer 534 is a layer for improving the release property between the pressure roller 53 and the recording sheet, and may be composed of the same material and thickness as the release layer 515. it can.
The temperature sensor 54 detects the surface temperature (t) in the circumferential direction of the outer peripheral surface of the heating rotator 51 that is driven to rotate, and outputs a detection result to the control unit 60. The time interval to be detected is set in advance to a time interval at which the surface temperature in the region on the outer peripheral surface of the heating rotator 51 corresponding to each resistance heating element layer 514 divided and arranged in the circumferential direction during the circular drive can be detected. . As the temperature sensor 54, for example, an infrared detection type thermopile can be used. Based on the detection result of the surface temperature, the control unit 60 controls on / off of energization to the heating rotator 51 so that the surface temperature becomes a predetermined temperature (for example, a fixing temperature).

The phase detection sensor 55 is an optical photosensor including a light emitting element and a light receiving element, and is provided on the inner peripheral surface on the end side of the heating rotator 51 when the heating rotator 51 is driven around. When the reflecting plate reaches a position facing the phase detection sensor 55, the light reflected from the reflecting plate is detected by the light receiving element, and a detection signal is output to the control unit 60.
Each time the detection signal is output, the control unit 60 starts time measurement, and resets the measurement value when the next detection signal is input. Since the time from when the detection signal is input to when the next detection signal is input is a fixed time, based on the measured value, the current rotation phase of the heating rotator 51 (the reflector is the phase detection sensor 55). The amount of movement in the circumferential direction from the current reference position) in the case where the position at the opposite position is set as the reference position can be calculated. For example, if the time required for the heating rotator 51 to make one rotation is 2 seconds, when the measured value is 1 second, the heating rotator 51 moves in the circumferential direction by a half rotation from the reference position. Will be.

[3] Configuration of Control Unit FIG. 5 is a diagram illustrating a relationship between the configuration of the control unit 60 and main components to be controlled by the control unit 60. The control unit 60 is a so-called computer, and as shown in the figure, a CPU (Central Processing Unit) 601, a communication interface (I / F) unit 602, a ROM (Read Only Memory) 603, a RAM (Random Access Memory). 604, an image data storage unit 605, a parameter storage unit 606, a phase counter 607, and the like.

The communication I / F unit 602 is an interface for connecting to a LAN such as a LAN card or a LAN board. The ROM 603 stores a program for controlling the image processing unit 3, the paper feeding unit 4, the fixing device 5, and the operation panel 6.
The RAM 604 is used as a work area when the CPU 601 executes a program.
The image data storage unit 605 stores image data for printing input via the communication I / F unit 602 or an image reading unit (not shown). The CPU 601 executes various programs stored in the ROM 603 to control the image processing unit 3, the paper feeding unit 4, and the operation panel 6, and further includes a power supply unit 500, a temperature sensor 54, a phase detection sensor 55, and an additional sensor. The functions of the entire fixing device 5 are controlled by the control of the pressure roller drive motor 56, and the belt temperature abnormality detection process described later is executed in the fixing device 5.

  The parameter storage unit 606 stores various threshold values used in belt temperature abnormality detection processing described later. Specifically, an abnormal threshold value (for example, 200 ° C.) indicating a high-temperature side threshold value for determining whether or not the surface temperature of the heating rotator 51 is abnormally heated, generation of scratches in the resistance heating element layer 514 A normal lower limit threshold (for example, a lower limit temperature of the fixing temperature is set as a normal lower limit threshold) indicating a threshold for detecting a decrease in the resulting surface temperature, and a count threshold (for example, a threshold of the number of times the normal temperature lower limit threshold is exceeded) (for example, 2 times) etc. The phase counter 607 starts time measurement every time a detection signal is input from the phase detection sensor 55, and resets the measurement value when the next detection signal is input.

[4] Belt Temperature Abnormality Detection Processing FIG. 6 is a flowchart showing an operation of belt temperature abnormality detection processing performed by the control unit 60. When an instruction for starting the belt temperature abnormality detection process is input from the operation panel 6 and a program for executing the belt temperature abnormality detection process is started, the control unit 60 sets a variable K indicating the number of times that the normal lower limit threshold is exceeded to 0. Initialization is performed (step S601), and the detection result of the surface temperature (t) in the circumferential direction of the heating rotator 51 is received from the temperature sensor 54 at predetermined time intervals (step S602).

  Each time an input of the detection result of the surface temperature (t) is received, the control unit 60 determines whether t exceeds the abnormal threshold value stored in the parameter storage unit 606, and whether t is below the normal lower limit threshold value. (Step S603, Step S604). When t exceeds the abnormal threshold value (step S603: YES), the control unit 60 acquires a measurement value via the phase counter 607, calculates a rotation phase based on the measurement value, and stores it in the parameter storage unit 606. The calculated rotation phase is stored (step S605), the energization to the fixing device 5 is turned off, the heating and rotation of the heating rotator 51 are stopped, and an abnormality indicating occurrence of heat generation abnormality on the display unit of the operation panel 6 is detected. A message is displayed (step 606). Note that. The abnormal message may be notified by a method other than display, for example, by voice.

  When t is below the normal lower limit threshold (step S603: NO, step S604: YES), the control unit 60 adds 1 to the variable K (step S608), and K is stored in the parameter storage unit 606. It is determined whether or not the number of times threshold has been exceeded (step S609). When t is not less than the normal lower limit threshold (step S603: NO, step S604: NO), the control unit 60 initializes the variable K to 0 (step S607).

  When t exceeds the number-of-times threshold (step S609: YES), the control unit 60 proceeds to the processing of step S605 and step S606. When t does not exceed the number of times threshold (step S609: NO), the control unit 60 is instructed until an instruction to end the belt temperature abnormality detection process is input from the operation panel 6 (step S610: YES) The transition to the process of step S602 is repeated.

  As described above, when a local flaw occurs in the divided layer of the resistance heating element layer 514 at a position where detection by the temperature sensor 54 is possible, abnormal heat generation around the end of the flaw is caused by the processing in step S603. By detecting, it is possible to directly detect the heat generation abnormality in the divided layer. Further, when a local flaw occurs in the divided layer of the resistance heating element layer 514 outside the range that can be detected by the temperature sensor 54, the temperature of the divided layer at which the flaw has occurred is determined by the divided layer due to the flaw. As a result of the increase in resistance, the current is less likely to flow than in a normal state where no scratch has occurred, and as a result, the current density flowing through the divided layer decreases, and the temperature of the divided layer decreases as a whole. The temperature decrease can be detected by the process of step S604, and the heat generation abnormality in the divided layer can be estimated.

Therefore, by performing the belt temperature abnormality detection process as described above, there is a risk of overlooking the heat generation abnormality due to the occurrence of scratches in the resistance heating element layer, compared to the case where the resistance heating element layer is divided into one layer. The heat generation abnormality can be detected more reliably, and it is possible to effectively prevent the heat fixing operation from being continued in a state where the heat generation abnormality has occurred. As a result, it is possible to prevent a situation in which the thermal fixing operation of the unfixed image is continued and the image quality of the fixed image is deteriorated in a state where temperature unevenness occurs, and the user can It is possible to prevent the occurrence of a serious situation such as a burn or other injury caused by touching a portion that generates heat in the vicinity of the head.
(Modification)
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

  (1) In the present embodiment, in the belt temperature abnormality detection process, whether the surface temperature (t) of the heating rotator 51 exceeds the abnormality threshold is determined as a heat generation abnormality caused by the occurrence of scratches in the resistance heating element layer 514. No, whether it is less than the normal lower limit threshold or not, but by detecting the temperature difference between the surface temperatures (t) of the heating rotator 51 caused by the occurrence of scratches, the occurrence of scratches May be estimated.

  FIG. 7 is a diagram showing a modification of the operation of the belt temperature abnormality detection process in the above case. When an instruction to start the belt temperature abnormality detection process is input from the operation panel 6 and a program for executing the belt temperature abnormality detection process is started, the control unit 60 sets the maximum value of the surface temperature (t) of the heating rotator 51. Tmin indicating Tmin and Tmin indicating the minimum value of t are respectively set to initial values (step S701).

  Here, the initial value of Tmax is T0, the initial value of Tmin is T1, T0 and T1 are T0> T1, and the difference between them (T0−T1) is smaller than the threshold value of the difference between Tmax and Tmin. It is assumed that it is set in advance. Note that the threshold value is determined by obtaining a difference between the maximum value and the minimum value of t, which is detected when a flaw is actually generated in the resistor heating layer 514 by performing an experiment or the like in advance. And

Each time the controller 60 receives an input of the detection result of the surface temperature (t) of the heating rotator 51 at a predetermined time interval from the temperature sensor 54 (step S702), whether t exceeds Tmax or not. It is determined whether it is below Tmin (step S703, step S704).
When t exceeds Tmax (step S703: YES), the control unit 60 updates the value of Tmax to t (step S705), and when t is lower than Tmin (step S703: NO). Step S704: YES), the value of Tmin is updated to t (Step S706).

  Next, the control unit 60 determines whether or not the difference between Tmax and Tmin (Tmax−Tmin) exceeds a threshold value (step S707). If the difference exceeds the threshold value (step S707: YES), the phase counter 607 is set. The measurement value is obtained through the calculation, the rotation phase is calculated based on the measurement value, the calculated rotation phase is stored in the parameter storage unit 606 (step S708), the energization to the fixing device 5 is turned off, and the heating is performed. The heating and rotation of the rotating body 51 are stopped, and an abnormal message indicating the occurrence of an abnormal heat generation is displayed on the display unit of the operation panel 6 (step 709). Note that. The abnormal message may be notified by a method other than display, for example, by voice.

When the determination result in step S707 is negative (step S707: NO), the control unit 60 performs control until an instruction to end the belt temperature abnormality detection process is input from the operation panel 6 (step S710: YES). The unit 60 repeats the transition to the process of step S702.
(2) In this embodiment, the belt heating type fixing device is used. However, the effect of this embodiment is that the fixing device using the resistance heating element layer is a fixing device other than the belt heating type. Can also be realized. For example, a divided layer of the plurality of resistance heating element layers 514 may be provided directly on the fixing roller, and the fixing device may be configured by a fixing roller and a pressure roller.

  (3) In the belt temperature abnormality detection process of this embodiment and the modification of (1), a heat generation abnormality is estimated in the resistance heating element layer 514 based on the detection result (t) of the surface temperature of the heating rotator 51. In this case, an abnormality message is displayed on the display unit of the operation panel (step 606 in FIG. 6 and step S709 in FIG. 7). At this time, information on the rotational phase stored in the parameter storage unit 606 is also displayed. It may be displayed together.

  (4) In the belt temperature abnormality detection processing of this embodiment and the modification of (1), the surface temperature (t) is directly detected by the temperature sensor 54, and the presence or absence of occurrence of heat generation abnormality is estimated based on the detection result. However, another parameter indicating the surface temperature, for example, a change in the amount of current flowing through each divided layer of the resistance heating element layer 514 is detected, and the presence or absence of the occurrence of heat generation is estimated based on the detection result. It is good as well.

(5) In the present embodiment, the resistance heating element layer 514 is equally divided into a plurality of divided layers at equal intervals in the circumferential direction, but the way of division is not limited to equal division. For example, the widths in the circumferential direction of the respective divided layers may be different lengths, and the circumferential distance between the divided layers may not be equal as long as it does not exceed 1 cm.
(6) In the present embodiment, the shape of each divided layer of the resistance heating element layer 514 is an elongated shape, but the shape of the divided layer is not limited to an elongated shape. The shape may be any shape as long as the peripheral surface of the insulating layer 513 can be covered with an interval close to the circumferential direction (an interval shorter than 1 cm).

  The present invention relates to a fixing device provided in an image forming apparatus such as a printer or a copying machine, and more particularly to a technique for detecting a heat generation abnormality in a fixing device using a resistance heating element as a resistance heating element layer.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y-3K Image forming part 4 Paper feed part 5 Fixing device 6 Operation panel 10 Exposure part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 31Y Photosensitive drum 32Y Charger 33Y Developer 34Y Primary transfer roller 35Y cleaner 41 paper feed cassette 42 feed roller 43 transport path 44 timing roller 45 secondary transfer roller 46 secondary transfer position 51 heating rotator 52 fixing roller 53 pressure roller 54 temperature sensor 55 phase detection sensor 56 pressure roller drive motor 60 Control unit 71 Discharge roller 72 Discharge tray 500 Power supply unit 501, 502 Power supply brush 511, 512 Electrode 513 Insulating layer 514 Resistance heating element layer 515, 533 Elastic layer 516, 534 Release layer 521, 531 Core metal end 522, 532 Core 523 Heat insulation layer

Claims (9)

A fixing device that heat-fixes an unfixed image on a recording sheet using Joule heating,
Resistive heat generation in which a plurality of elongated strips of resistive strips are arranged at intervals in the circumferential direction of the rotating body, with the longitudinal ends connected to the feeding electrodes at both ends of the rotating body on the insulating peripheral surface A cylindrical rotating body having a body layer;
Monitoring means for monitoring the temperature of each resistance flake;
Based on the monitoring result by the monitoring means, estimating means for estimating the presence or absence of abnormal heating of the resistance heating element layer;
A fixing device comprising: The estimation means estimates that the heat generation abnormality has occurred when any of the temperatures of the resistance slices is higher than an upper limit value or lower than a lower limit value. The fixing device according to 1. The fixing device according to claim 1, wherein the estimation unit estimates that the heat generation abnormality has occurred when a difference between a maximum value and a minimum value of the temperature of each resistance flake exceeds a threshold value. The monitoring means is disposed at a predetermined position in the vicinity of the cylindrical rotating body, and each time the resistance thin pieces pass through the vicinity of the predetermined position as the cylindrical rotating body rotates, the resistance thin pieces Detect the temperature of
Position acquisition means for acquiring a relative position of the detected resistance flake from a reference position in the rotation direction of the cylindrical rotating body;
When the temperature detected by the monitoring means is higher than the upper limit value or lower than the lower limit value, relative position storage means for storing the relative position of the resistance slice,
The fixing device according to claim 2, further comprising: The fixing device according to claim 1, further comprising: a power supply control unit that stops power supply to each of the resistance heating elements when a heat generation abnormality is estimated. 6. The fixing device according to claim 5, further comprising notification means for notifying that a heat generation abnormality is estimated. The fixing device according to claim 1, wherein the cylindrical rotating body is an endless belt. The fixing device according to claim 1, wherein the interval is less than 1 cm.   An image forming apparatus comprising the fixing device according to claim 1.

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