JP2012108412A - Image forming apparatus and fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent an erroneous determination of abnormal heat generation in an image forming apparatus that determines the presence/absence of the abnormal heat generation of a resistance heating element layer by detecting the amount of powdery smoke.SOLUTION: This image forming apparatus includes a fixing device that thermally fixes an unfixed image onto a recording sheet using a resistance heating element that generates heat by Joule heat through energization. This image forming apparatus monitors the amount of powdery smoke generated in the fixing device, and determines the presence/absence of the abnormal heat generation of the resistance heating element by whether the amount of the powdery smoke in the fixing device exceeds a predetermined threshold or not. In not printing, this image forming apparatus sets the threshold used for determining the presence of the abnormal heat generation to a first threshold, however, in printing, for avoiding an erroneous determination due to powdery smoke generated irrelevant to the abnormal heat generation, sets the threshold used for determining the presence of the abnormal heat generation, to a second threshold (S802) that is higher than the first threshold by an amount equivalent to the amount of the powdery smoke.

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine, and more particularly to a technique for detecting abnormal heat generation of a resistance heating element in an image forming apparatus that thermally fixes an unfixed image using a resistance heating element.

In recent years, as a fixing device of an image forming apparatus such as a printer or a copying machine, a fixing device using a layer of a resistance heating element that generates Joule heat upon energization has been used. In this fixing device, since the heating element generates heat by directly supplying power to the resistance heating element layer, the thermal efficiency can be increased and the warm-up time can be shortened.
For this reason, even when the power supply to the resistance heating element is stopped (sleep state) when the image forming apparatus is in a print job input waiting state, the fixing device can perform the heat fixing operation in a short time. It can be returned to the state. Therefore, when the input waiting state continues for a long period of time, the power consumption can be reduced by putting the fixing device in the sleep state.

This resistance heating element layer is generally formed by dispersing a conductive material such as a metal in an insulating material such as a heat resistant resin, and is covered with an insulating layer. Since there is a danger of electric shock if the resistance heating element layer that is energized is touched directly, the electric shock is prevented by covering with an insulating layer.
On the other hand, since the thickness of the insulating layer is as thin as several hundred μm, the insulating layer is damaged due to 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 portion of the resistance heating element layer where the current density is increased abnormally generates heat at a high temperature.

If this abnormal heat generation is left unattended, the fixing device will be seriously damaged and the surrounding devices will be affected. Therefore, the fixing device is provided with measures such as detecting it early and shutting off the power supply to the fixing device. It is necessary to prevent the damage from becoming serious.
As a means for detecting this abnormal heat generation, it is possible to use a temperature detection element such as a thermistor or a thermostat provided in the fixing device, but since the detection range is narrow, depending on the position of the resistance heating element layer where the abnormal heat generation occurs. May cause the occurrence of abnormal heat generation to be overlooked.

  Patent Document 1 discloses a technique for detecting abnormal heat generation by detecting, with a fine particle sensor, dust generated from an insulating layer or the like when abnormal heat generation occurs in a resistance heating element layer. Thereby, the detection range of abnormal heat generation can be widened, and it is possible to effectively prevent the abnormal heat generation from being overlooked.

JP 2000-155495 A

  However, since dust is generated at times other than when the resistance heating element layer is abnormally heated, if the amount of dust that is not caused by abnormal heat generation is large, the dust may be erroneously detected. In particular, when printing processing is performed in the image forming apparatus, the amount of paper dust and toner scattered from the fed paper increases, and these are detected as dust by the fine particle sensor. As a result, in fact, abnormal heat generation may be erroneously determined even though abnormal heat generation has not occurred.

  The present invention has been made in view of the above-described problems. In an image forming apparatus that determines the presence or absence of abnormal heat generation in a resistance heating element layer by detecting the amount of powder smoke, An object of the present invention is to provide an image forming apparatus capable of effectively preventing erroneous determination.

  In order to achieve the above object, an image forming apparatus according to an aspect of the present invention includes an image fixing apparatus that heat-fixes an unfixed image on a recording sheet using heat generated by a resistance heating element that generates Joule heat when energized. A resistance heating element according to a monitoring device for monitoring the amount of smoke generated in the fixing device and whether or not the amount of dust in the fixing device exceeds a set threshold value. The abnormal heat generation determination means for determining the presence or absence of abnormal heat generation and the threshold value used for determining the presence or absence of abnormal heat generation during non-printing are set to the first threshold value, and are independent of the abnormal heat generation during printing. In order to avoid misjudgment due to the smoke generated in the case, the threshold used for the determination of the presence or absence of abnormal heat generation is set to a second threshold that is higher than the first threshold by an amount corresponding to the amount of dust And control means .

Here, the monitoring unit is configured to measure the number of times the value of the measured smoke concentration is higher than a reference value within a predetermined period, and the measurement unit that repeatedly measures the concentration of the smoke in the fixing device. And a threshold value used for determining the presence or absence of abnormal heat generation may be a threshold value for the number of times.
Further, the monitoring means monitors the amount of the smoke by measuring the smoke density in the fixing device, and the threshold used for determining the presence or absence of abnormal heat generation is a threshold for the smoke density. Can be.

Further, the image forming apparatus may include a stopping unit that stops power supply to the fixing device when the abnormal heat generation is detected. Further, the image forming apparatus may include a notifying unit for notifying that when the abnormal heat generation is detected.
A fixing device according to another aspect of the present invention is a fixing device that thermally fixes an unfixed image on a recording sheet using heat generated by a resistance heating element that generates Joule heat when energized. Monitoring means for monitoring the amount of smoke generated in the apparatus and abnormal heat generation determination for determining whether the resistance heating element has abnormal heat generation based on whether or not the amount of powder smoke in the device exceeds a predetermined threshold And a threshold value used for determining whether or not there is abnormal heat generation at the time of non-printing, is set as a first threshold value, and at the time of printing, erroneous determination due to dust generated regardless of the abnormal heat generation during printing is performed. In order to avoid this, a threshold control means is provided for setting a threshold used for determining whether or not there is abnormal heat generation to a second threshold that is higher than the first threshold by an amount corresponding to the amount of the smoke.

  By providing the above configuration, when printing, the threshold for the amount of powder smoke used for determining whether or not the resistance heating element has abnormal heat generation is generated without the smoke generated by abnormal heat generation during printing (paper The resistance is set to be higher than the non-printing threshold by the amount corresponding to the amount of dust (dust from powder, toner, etc.), so the resistance heating element malfunctions due to dust generated regardless of the abnormal heating of the resistance heating element. It is possible to effectively prevent erroneous determination of heat generation.

  In addition, when the amount of smoke generated regardless of abnormal heat generation is small, the amount of smoke generated regardless of the abnormal heat generation during printing is lower than the threshold during printing. Since abnormal heating of the resistance heating element is detected using a correspondingly low threshold value, in order to avoid false detection, when the threshold value is uniformly set higher than a predetermined value regardless of printing or non-printing Compared to the above, the detection timing when abnormal heat generation occurs can be advanced. As a result, it is possible to effectively prevent the damage to the fixing device from spreading by delaying the detection timing of abnormal heat generation during non-printing.

1 is a diagram illustrating a configuration of a printer. 3 is a perspective view illustrating a configuration of a main part of the fixing device 5. FIG. 2 is a cross-sectional view illustrating an overall configuration of a fixing device 5. FIG. 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 a fixing device abnormal heat generation detection process performed by a control unit 60. It is a flowchart which shows the operation | movement of the abnormal heat generation detection process (step S603) at the time of warm-up which the control part 60 performs. It is a flowchart which shows the operation | movement of the abnormal heat generation detection process at the time of printing (step S605) which the control part 60 performs. It is a flowchart which shows operation | movement of the standby abnormal heat generation detection process (step S607) which the control part 60 performs.

(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 D. 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 main part of the fixing device 5. FIG. 3 is a cross-sectional view showing the overall configuration of the fixing device 5. Hereinafter, the configuration of the fixing device 5 will be described with reference to both the drawings.

  As shown in FIG. 2, the fixing device 5 includes a heating rotator 51, a fixing roller 52, a pressure roller 53, and the like. As shown in FIG. 3, the heating rotator 51, the fixing roller 52, and the pressure roller 53 are covered with a frame body 56. The apparatus covered with the frame 56 by the pressure roller 53 rotating in the rotation direction indicated by the arrow B and the heating rotating body 51 following the rotation direction indicated by the arrow A along with the rotation of the pressure roller 53. Inside, airflow is generated along the rotation direction. An arrow C in FIG. 3 indicates an air flow generated by the rotation of the heating rotator 51.

2, as in FIG. 3, the arrow A indicates the rotation direction of the heating rotator 51, the arrow B indicates the rotation direction of the pressure roller 53, and the arrow C indicates the heating rotator 51. The airflow generated by rotation is shown.
Returning to the description of FIG. 3, the recording sheet is guided into the apparatus by the upper and lower guide plates 561 and 562 in the direction of the white arrow indicated by the symbol S and enters the fixing nip 59, and is thermally fixed by the fixing nip 59. After that, it is guided to the discharge roller pair 565 by the guide plates 563 and 564 and discharged out of the apparatus.

Returning to the description of FIG. 2, the heating rotator 51 is an endless belt, and power supply electrodes 511 and 512 are provided at both ends thereof, and power supply brushes 501 and 502 are supplied from the power supply unit 500 to both electrodes. Power is supplied through the cable. Thereby, an electric current flows between both electrodes, and the heating rotator 51 generates heat.
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. Further, in the region of the heating rotator 51 excluding the end portion, as shown in the figure, an insulating layer 513, a resistance heating element layer 514, an elastic layer 515, and a release layer 516 are laminated in this order. .

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 for reinforcing the strength of the heating rotator 51. As a material of the insulating layer 513, 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 × It is desirable to be within the range of 10 ^{−5 to} 5.0 × 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 an insulating layer for improving the releasing property 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 a driving force from a pressure roller drive motor (not shown) 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 59 having a predetermined width in the circumferential direction between the outer periphery 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 516, 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 516. it can.
Further, as shown in FIGS. 2 and 3, a particulate sensor 54 is arranged in the vicinity of the heating rotator 51 at a predetermined position on the inlet side of the fixing nip 59, and in the vicinity of the outer peripheral surface of the heating rotator 51. A temperature sensor 55 is disposed at a predetermined position (here, near the center in the direction of the rotation axis).

As shown in FIG. 2, the fine particle sensor 54 is a transmission type sensor composed of a light emitting element (for example, LED) 54a and a light receiving element (for example, phototransistor) 54b. Time and the amount of smoke per unit volume) is detected and output to the control unit 60.
The dust detected by the fine particle sensor 54 includes fine particles such as dust in the fixing device 5, paper dust on the recording sheet, toner, and smoke generated when the resistance heating element layer 514 abnormally generates heat. It is. The fine particle sensor 54 utilizes the fact that the amount of received light that reaches the light receiving element 54b from the light emitting element 54a varies according to the concentration of the smoke generated in the fixing device 5, and detects the amount of variation to thereby detect the dust. Detect concentration.

The arrangement position of the particulate sensor 54 is not limited to the predetermined position as long as it is a position along the flow path of the air flow in the fixing device 5 and in the vicinity of the heating rotator 51.
The temperature sensor 55 detects the surface temperature 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. As the temperature sensor 55, 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 via the power supply control unit 6 described later, and the surface temperature is a predetermined temperature (for example, the fixing temperature). (About 160 ° C. to 180 ° C.)).

[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, 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 executes a program for controlling the image processing unit 3, the paper feeding unit 4, the power supply control unit 6, the fine particle sensor 54, the temperature sensor 55, the operation panel 7, and the like, and a fixing device abnormal heat generation detection process to be described later. This program is stored.
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 controls the image processing unit 3, the paper feeding unit 4, the power supply control unit 6, the particulate sensor 54, the temperature sensor 55, the operation panel 7, and the like by executing various programs stored in the ROM 603. A fixing device abnormal heat generation detection process to be described later is executed.

The parameter storage unit 606 stores various threshold values, reference values, and the like used in the fixing device abnormal heat generation detection process described later. Specifically, the parameter storage unit 606 stores a reference number threshold, an abnormal heat generation reference value, and the like.
Here, the “reference number threshold value” is a threshold value for the number of times that the smoke density in the fixing device 5 exceeds the abnormal heat generation reference value within a predetermined period, and is a determination criterion for occurrence of abnormal heat generation. Refers to the threshold value.

  As the reference number threshold, it is predicted that the generation of powder smoke not caused by abnormal heat generation in the fixing device 5 is expected to be small. There are two reference frequency thresholds for high sensitivity, which are judgment criteria for heat generation, and reference frequency threshold values for low sensitivity, which are judgment criteria for abnormal heat generation of the resistance heating element layer 514 during printing. The reference frequency threshold for high sensitivity is a threshold corresponding to the amount of powder smoke generated from the heating rotator 51 when abnormal heat generation occurs in the resistance heating element layer 514, and is determined in advance by experiments or the like.

  The reference frequency threshold for low sensitivity is a resistance heating element caused by dust smoke (dust from recording sheet paper dust or toner scattered during printing) generated regardless of abnormal heating of the resistance heating element layer 514 that occurs during printing. In order to avoid erroneous detection of abnormal heat generation in the layer 514, the threshold value is set to be higher than the reference frequency threshold value for high sensitivity by an amount corresponding to the amount of powder smoke generated regardless of the above. About how much the threshold value is set to be higher than the reference number threshold value for high sensitivity, for example, the manufacturer of the printer 1 performs an experiment or the like in advance and determines the amount of powder smoke generated independently, The determined threshold value is stored in the parameter storage unit 606.

Here, the reference frequency threshold value for high sensitivity is set to 5 times, and the reference frequency threshold value for low sensitivity is set to 1 time. Further, the “abnormal heat generation reference value” refers to a reference value of the dust concentration that serves as an index for estimating the occurrence of abnormal heat generation in the fixing device 5. As the abnormal heat generation reference value, for example, the concentration of powder smoke generated from the heating rotator 51 when the abnormal heat generation in the resistance heat generating layer 514 is in the early stage of generation can be used. Here, the abnormal heat generation reference value is set to 5 mg / m ³ · h.

The power supply control unit 6 performs control for switching on / off of energization to the power supply unit 500 of the fixing device 5 based on a control signal input from the control unit 60.
The operation panel 7 includes a liquid crystal display, a touch panel stacked on the liquid crystal display, operation buttons for inputting various instructions, and the like, and receives input of various instructions from the user through operations of the touch panel, operation buttons, and the like. Various display information such as an operation screen such as a print setting screen and a print result is displayed on the liquid crystal display.

[4] Fixing Device Abnormal Heat Generation Detection Process FIG. 6 is a flowchart showing the operation of the fixing device abnormal heat generation detection process performed by the control unit 60. When the power is turned on (step S601), the control unit 60 starts monitoring the detection value of the smoke density by the particulate sensor 54 at a predetermined interval (for example, an interval of 10 milliseconds) (step S602), which will be described later. An abnormal heat generation detection process during warm-up is performed (step S603).

Next, the control unit 60 determines whether or not a print job waiting for printing is accepted (step S604). If the print job is accepted (step S604: YES), execution of all print jobs waiting for printing is executed. Until printing is completed, the abnormal heat generation detection process described later is repeated (step S605, step S606: YES).
In step S604, when a print job is not accepted (step S604: NO), or when execution of all print jobs waiting for printing is completed (step S606: NO), detection of abnormal heat generation during standby described later is performed. Processing is performed (step S607).

  When a predetermined time (for example, 30 minutes) elapses after the transition to the standby state (step S608: YES), the control unit 60 waits until a new print job is received. Then, the power supply to the power supply unit 500 of the fixing device 5 is stopped, and the fixing device 5 is shifted to a sleep state that is a power saving (low power) state (step S609, step S610: NO, step S611).

When a new print job is received (step S610: YES), the control unit 60 proceeds to the process of step S603.
Next, the operation of the warm-up abnormal heat generation detection process (step S603) will be described. FIG. 7 is a flowchart showing the above operation. The control unit 60 supplies power to the power supply unit 500 of the fixing device 5 via the power supply control unit 6 to start warming up the fixing device 5, and the smoke density detected by the particulate sensor 54 is the abnormal heat generation reference value. A variable t indicating the number of times exceeding the number is initialized to 0 (step S701).

Then, the control unit 60 sets the reference number threshold value to the high sensitivity reference number threshold value (here, one time) stored in the parameter storage unit 606 (step S702).
Next, every time a detection value (smoke density) is input from the particulate sensor 54, the control unit 60 determines whether or not the detection value exceeds the abnormal heat generation reference value stored in the parameter storage unit 606. (Step S703), if exceeding (Step S703: YES), the variable t is changed to a value obtained by adding 1 to t (Step S704), and t is the reference number threshold for high sensitivity set in Step S702. Is determined (step S705).

On the other hand, if the detected value does not exceed the abnormal heat generation reference value in step S703 (step S703: NO), the time until the surface temperature of the heating rotator 51 of the fixing device 5 reaches the fixing temperature that is the target temperature. (Step S706: During NO), the processing after Step S703 is repeated.
In step S705, when t has reached the reference count threshold value for high sensitivity (step S705: YES), the control unit 60 stops power supply to the power supply unit of the fixing device 5 via the power supply control unit 6. (Step S707), and a warning message indicating that “the fixing device 5 is abnormally heated” is displayed on the liquid crystal display unit of the operation panel 7 (Step S708).

  Next, the operation of the abnormal heating detection process during printing (step S605) will be described. FIG. 8 is a flowchart showing the above operation. The control unit 60 starts execution of the accepted print job waiting for printing, initializes the variable t to 0 (step S801), and further sets the reference number threshold value to the low sensitivity stored in the parameter storage unit 606. Is set to a reference frequency threshold value (here, 5 times) (step S802).

  Next, every time a detection value (smoke density) is input from the particulate sensor 54, the control unit 60 determines whether or not the detection value exceeds the abnormal heat generation reference value stored in the parameter storage unit 606. (Step S803), if exceeding (step S803: YES), the variable t is changed to a value obtained by adding 1 to t (step S804), and t is a reference count threshold value for low sensitivity set in step S802. Is determined (step S805).

On the other hand, in step S803, if the detected value does not exceed the abnormal heat generation reference value (step S803: NO), until the print job being executed is completed (during step S806: NO), the steps after step S803 are performed. Repeat the process.
In step S805, when t reaches the reference count threshold value for low sensitivity during execution of the print job (step S805: YES), the control unit 60 supplies power to the fixing device 5 via the power control unit 6. The power supply to the printer is stopped (step S807), and a warning message indicating that “the fixing device 5 is abnormally generating heat” is displayed on the liquid crystal display of the operation panel 7 (step S808).

  Next, the operation of the standby abnormal heat generation detection process (step S607) will be described. FIG. 9 is a flowchart showing the above operation. The controller 60 sets the surface temperature of the heating rotator 51 of the fixing device to a predetermined temperature (for example, a fixing temperature (about 160 to 180 ° C.) at which the heat fixing can be performed immediately, or 10 to 20 from the fixing temperature. The process shifts to a state maintained at a temperature lower by about 0 ° C. (hereinafter referred to as “standby state”), and the variable t is initialized to 0 (step S901).

Then, the control unit 60 sets the reference number threshold value to the high sensitivity reference number threshold value (here, one time) stored in the parameter storage unit 606 (step S902).
Next, every time a detection value (smoke density) is input from the particulate sensor 54, the control unit 60 determines whether or not the detection value exceeds the abnormal heat generation reference value stored in the parameter storage unit 606. (Step S803), if exceeding (step S903: YES), the variable t is changed to a value obtained by adding 1 to t (step S904), and t is the reference number threshold for high sensitivity set in step S902. Is determined (step S905).

On the other hand, in step S903, when the detected value does not exceed the abnormal heat generation reference value (step S903: NO), until a new print instruction is input (step S906: during NO), the steps after step S903 are performed. Repeat the process.
In step S905, when t reaches the reference number threshold for high sensitivity (step S905: YES), the control unit 60 stops the power supply to the power supply unit of the fixing device 5 via the power supply control unit 6. (Step S907), a warning message indicating that “the fixing device 5 is abnormally generating heat” is displayed on the liquid crystal display unit of the operation panel 7 (Step S908).
(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 fixing device abnormal heat generation detection process of the present embodiment, the number of times that the smoke density detected by the fine particle sensor 54 exceeds the abnormal heat generation reference value is counted, and the counted number becomes the reference number threshold value. Although the abnormal heat generation of the resistance heating element layer 514 is detected depending on whether or not it is reached, the abnormal heat generation of the resistance heating element layer 514 may be detected by directly comparing the smoke concentration with the threshold value.

Specifically, in the parameter storage unit 606, instead of the high-sensitivity and low-sensitivity frequency thresholds, a smoke density threshold (for example, 1 mg / m ³ · h as a high-sensitivity threshold is set as a low-sensitivity threshold). 5 mg / m ³ · h) is stored as a threshold value, and the resistance heating element layer 514 is determined depending on whether the smoke density detected by the fine particle sensor 54 has reached the high sensitivity threshold value or the low sensitivity threshold value. Abnormal heat generation may be detected.

(2) In the present embodiment, the control unit 60 performs the fixing device abnormal heat generation detection process. However, a separate control unit including a CPU or the like is provided in the fixing device 5, and the control unit Alternatively, the fixing device abnormal heat generation detection process may be performed.
(3) In the present embodiment, in the abnormal heat generation detection process during printing, the criterion for detecting abnormal heat generation of the resistance heating element layer 514 is the same regardless of the quality and size of the printed recording sheet. However, since the amount of paper dust generated at the time of printing differs according to the quality and size of the recording sheet, the determination criterion may be changed according to the quality and size of the recording sheet.

  For example, the reference count threshold is 4 times when the recording sheet is fine paper, 5 times when it is plain paper, and 6 times when it is recycled paper, depending on the paper quality of the recording sheet to be printed. The determination criterion may be changed. Alternatively, the reference number threshold is set to 6 times when the recording sheet size is A3, 5 times when the recording sheet size is A4, and 4 times when the recording sheet size is A5, depending on the size of the recording sheet to be printed. The determination criterion may be changed. Similarly, in the case of the modification (1), the determination criteria may be changed according to the quality and size of the recording sheet.

As a result, abnormal heat generation criteria are adjusted so as to correspond to the amount of paper dust corresponding to the quality and size of the printed recording sheet, so even if the quality or size of the printed recording sheet changes. Thus, the detection accuracy of abnormal heat generation can be prevented from deteriorating.
(4) In the present embodiment, in the abnormal heat generation detection process during printing, the criterion for detecting abnormal heat generation of the resistance heating element layer 514 is the same regardless of the degree of toner deterioration. Since the amount tends to increase as the toner deteriorates, the determination criterion may be changed according to the degree of deterioration of the toner used for printing.

Specifically, the degree of toner deterioration is estimated by counting the number of days that have elapsed from the date of manufacture of the toner, and the criterion is such that the reference number threshold increases stepwise as the number of days elapsed increases. It is good also as setting. In the case of the modified example (1), the determination criterion may be set in the same manner.
As a result, the abnormal heat generation criterion is adjusted so that the influence of the increase in the amount of toner scattering accompanying the progress of toner deterioration is offset, so that the detection accuracy of abnormal heat generation does not decrease due to the progress of toner deterioration. Can be.

(5) In the present embodiment, the fine particle sensor 54 is arranged in the vicinity of the heating rotator 51 to measure the amount of dust, but the airflow in the fixing device 5 near the heating rotator 51 is measured. It is good also as arrange | positioning a duct in the position along a flow path, arrange | positioning the particulate sensor 54 in the said duct, and measuring the amount of dust using the particulate sensor 54, after guiding dust in the duct.
(6) In the fixing device abnormal heat generation detection process of the present embodiment, when there is abnormal heat generation in the resistance heating element layer 514, a warning message indicating that is displayed. It is good also as sending a voice message instead. Moreover, it is good also as warning by making light etc. light-emit.

  The present invention relates to an image forming apparatus such as a printer or a copying machine, and can be used as a technique for detecting abnormal heat generation of a resistance heating element in an image forming apparatus in which an unfixed image is thermally fixed using a resistance heating element.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y-3K Image forming part 4 Paper feed part 5 Fixing device 6 Power supply control part 7 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 Conveying path 44 Timing roller 45 Secondary transfer roller 46 Secondary transfer position 51 Heating rotary member 52 Fixing roller 53 Pressure roller 54 Particulate sensor 55 Temperature sensor 56 Frame 59 Fixing nip 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 metal 523 Heat insulation layer

Claims (6)

An image forming apparatus having a fixing device that thermally fixes an unfixed image on a recording sheet using heat generated by a resistance heating element that generates Joule heat when energized,
Monitoring means for monitoring the amount of dust generated in the fixing device;
Abnormal heat generation determination means for determining the presence or absence of abnormal heat generation of the resistance heating element depending on whether or not the amount of powder smoke in the fixing device exceeds a set threshold value;
At the time of non-printing, the threshold value used for the determination of the presence or absence of abnormal heat generation is set as the first threshold value,
At the time of printing, in order to avoid erroneous determination due to dust generated regardless of the abnormal heat generation, the threshold value used for the determination of the presence or absence of abnormal heat generation is set to the first threshold corresponding to the amount of the powder smoke. Threshold control means for setting a higher second threshold;
An image forming apparatus comprising: The monitoring means includes
Measuring means for repeatedly measuring the smoke density in the fixing device;
Counting means for counting the number of times the measured smoke density value is higher than a reference value within a predetermined period as the amount of the dust,
Have
The image forming apparatus according to claim 1, wherein the threshold used for determining whether or not there is abnormal heat generation is a threshold for the number of times. The monitoring means monitors the amount of the smoke by measuring the smoke density in the fixing device,
The image forming apparatus according to claim 1, wherein the threshold value used for determining whether or not there is abnormal heat generation is a threshold value for smoke density. The image forming apparatus according to claim 1, further comprising: a stopping unit that stops power supply to the fixing device when the abnormal heat generation is detected. 5. The image forming apparatus according to claim 1, further comprising a notification unit configured to notify when the abnormal heat generation is detected. A fixing device that heat-fixes an unfixed image on a recording sheet using heat generated by a resistance heating element that generates Joule heat when energized,
Monitoring means for monitoring the amount of smoke generated in the device;
Abnormal heat generation determination means for determining the presence or absence of abnormal heat generation of the resistance heating element depending on whether or not the amount of smoke in the apparatus exceeds a predetermined threshold;
At the time of non-printing, the threshold value used for the determination of the presence or absence of abnormal heat generation is set as the first threshold value,
At the time of printing, in order to avoid erroneous determination due to smoke generated regardless of the abnormal heat generation at the time of printing, the threshold used for the determination of the presence or absence of abnormal heat generation is set to the first corresponding to the amount of the powder smoke. Threshold control means for setting a second threshold higher than the threshold of
A fixing device comprising:

Images