JP2015132701A - image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device which accurately detects a break of a film over the longitudinal direction thereof, and prohibits image heating processing.SOLUTION: An image heating device includes: a film (42) which is for heating an image on a sheet at a nip part, has an insulation layer, has an endless shape, and rotates; an abutting rotator (41) which has a conductive abutting layer abutting the outer surface of the film and forms the nip part in cooperation with the film; a pressing member (47) which presses the film from the internal surface thereof toward the abutting rotator to form the nip part, and has a conductive contact layer in contact with the internal surface of the film; detection means (60) which detects the conduction between the abutting layer and the contact layer caused by a break of the film; and control means (121) for controlling whether or not image heating processing is prohibited on the basis of the detection result of the detection means.

Description

  The present invention relates to an image heating apparatus for heating an image on a sheet. This image heating apparatus is used in an image forming apparatus such as a copying machine, a printer, a fax machine, and a multifunction machine having a plurality of these functions.

  2. Description of the Related Art Conventionally, in an image forming apparatus, an image of a toner is formed on a sheet by an image forming unit, and then an image is fixed on the sheet by applying heat and pressure at a nip portion of a fixing device (image heating device). . In the fixing device used in this manner, in order to stably secure the width of the nip portion, a fixing device that forms a nip portion using a belt-like heating member is used recently.

  In the fixing device described in Patent Document 1, a nip portion is formed between the fixing film and the pressure roller. More specifically, a nip portion having a desired width is formed by pressing a thin fixing film having a low heat capacity from its inner surface against a pressure roller by a pressure plate.

  In the fixing device described in Patent Document 1, a temperature sensor is provided so as to face the surface of the fixing film, and a periodic temperature change accompanying rotation of the surface of the fixing film is detected.

  By the way, in a fixing device using a thin fixing film as in Patent Document 1, a part of the fixing film may be torn due to the mixing of foreign matter, fatigue due to use, or the like. Such a torn fixing film causes poor contact with the sheet during the fixing process, so that heat cannot be properly transmitted to the image on the sheet, and image defects such as gloss unevenness occur. There is a fear.

JP 2011-28088 A

  In view of this, for such a problem, a temperature sensor such as that provided in the fixing device described in Patent Document 1 detects a temperature drop at a broken portion of the fixing film to detect the break. Can think.

  However, such a countermeasure has a problem that the detection range of the temperature sensor is narrower than the longitudinal region used for heating the image on the sheet of the fixing film. For this reason, in order to detect breakage in the entire area of the fixing film, it is necessary to arrange a plurality of temperature sensors, which may lead to an increase in cost.

  Therefore, a fixing device that can detect tears occurring in a longitudinal region used for heating an image on a sheet of a fixing film with a simple configuration is desired.

  An object of the present invention is to provide an image heating apparatus that detects the tearing of the film with accuracy over the longitudinal direction and prohibits the image heating process.

  The present invention provides an image heating apparatus comprising: an endless rotating film having an insulating layer, which is a film that heats an image on a sheet at a nip portion; and a conductive contact layer that contacts an outer surface of the film. A contact rotating body provided with a contact rotating body that cooperates with the film to form a nip portion, and a pressing member that presses the film from the inner surface toward the contact rotating body, and contacts the inner surface of the film. A pressing member having a conductive contact layer, a detecting means for detecting conduction between the contact layer and the contact layer due to film tearing, and whether image heating processing is prohibited based on a detection result of the detecting means And a control means for controlling the above.

  According to the present invention, in the image heating apparatus, it is possible to accurately detect the film tearing in the longitudinal direction and prohibit the image heating process.

1 is a cross-sectional view of an image forming apparatus in an embodiment. It is explanatory drawing for demonstrating the flow of the image heating process by the image heating apparatus in an Example. It is a front view of the image heating apparatus in an Example. It is a block diagram which shows the relationship of each structure of the image heating apparatus in an Example. An equivalent circuit diagram (a) shows a conduction detection circuit when the heating film is in a normal state, and an equivalent circuit diagram (b) shows a conduction detection circuit when the heating film is in a torn state. It is a flowchart of prohibition control of image heating processing.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to examples. In the following embodiments, an image forming apparatus will be described by taking a laser beam printer using an electrophotographic process as an example. Hereinafter, this laser beam printer is referred to as a printer 1.

(Image forming device)
FIG. 1 is a cross-sectional view of a printer 1 that is an image forming apparatus according to the present exemplary embodiment. The printer 1 transfers the toner image formed on the photosensitive drum 3 (hereinafter referred to as the drum 3) in the image forming unit 2 to the sheet P, and the fixing device 40 fixes the image transferred on the sheet P. Device. Hereinafter, the configuration will be described in detail with reference to the drawings.

  As shown in FIG. 1, an image forming unit 2 for forming an image is disposed in the center of the inside of the printer 1. In the image forming unit 2, a charger 4, a developing device 5, and a cleaning device 6 are installed around a drum 3 that is a drum-type electrophotographic photosensitive member, and an exposure device 7 is disposed above the image forming unit 2. Is installed. The developing device 5 stores single color toner (black toner).

  The drum 3 is a negatively charged OPC photoreceptor having a photoconductive layer on an aluminum drum base, and is driven to rotate at a predetermined process speed in the direction of the arrow (clockwise) by a driving device (not shown). . The charger 4 uniformly charges the surface of the drum 3 to a predetermined negative potential with a charging bias applied from a charging bias power source (not shown). The developing device 5 attaches black toner to each electrostatic latent image formed on the drum 3 and develops the toner image (visible image). The cleaning device 6 removes and collects the toner remaining on the surface of the drum 3 after the transfer. In the exposure device 7, a laser beam modulated in accordance with the image information is output to expose the surface of the drum 3. Thus, an electrostatic latent image corresponding to the image information is formed on the surface of the drum 3 charged by the charger 4.

  The transfer roller 31 is pressed against the drum 3 to form a nip portion Te. The toner image T carried on the drum 3 is transferred at a nip portion Te to a sheet P conveyed as described later by a transfer roller 31 to which a transfer bias is applied.

  The sheet P sent out from the cassette 21 by the feeding roller pair 22 passes through the conveyance guide 23 and abuts against the registration roller pair 24. Then, the sheet P is passed through the pre-transfer conveyance guide 25 by the registration roller pair 24 and is fed to the nip portion Te so as to be synchronized with the toner image T conveyed by the drum 3. The sheet P to which the toner image T is transferred at the nip portion Te and separated from the drum 3 is conveyed to the fixing device 40. The fixing device 40 heats and presses the unfixed toner image T on the sheet to fix it on the sheet P. The sheet P on which the toner image T is fixed passes through the discharge guide 51 and is discharged and stacked on the discharge tray 53 on the housing by the discharge roller 52. In this way, a series of image forming processes is completed.

(Fixing device)
Next, the fixing device 40 that is an image heating device used in the printer 1 will be described.

  FIG. 2 is an explanatory diagram for explaining the flow of image heating processing by the fixing device 40. FIG. 3 is a front view of the fixing device 40.

  The fixing device 40 is a belt-type image heating device that heats a cylindrical film (belt) having a small heat capacity from the inside by radiation of a halogen heater. Since the fixing device 40 has a small heat capacity and a high temperature increase rate, the fixing device 40 can be immediately subjected to a fixing process simply by energizing it during use. Therefore, there is an advantage that the power consumption at the time of printing standby is very small. Hereinafter, the configuration of the fixing device 40 will be described in detail with reference to the drawings.

  As shown in FIG. 2, when a heating film 42 (hereinafter referred to as film 42) is sandwiched between a pad 47 (hereinafter referred to as pad 47) and a pressure roller 41 (hereinafter referred to as roller 41), a nip portion N is obtained. Is formed. The film 42 rotates in the direction of arrow B, and the roller 41 rotates in the direction of arrow A. The sheet P conveyed to the nip portion N is nipped and conveyed in the direction of arrow C. At this time, since the film 42 and the pad 47 are heated by the heater 45, the unfixed toner image on the sheet P is heated and pressed to fix the image on the sheet P. In the fixing device 40, the image heating process is performed as described above.

  The film 42 is a flexible cylindrical (endless) belt (film) based on metal or resin, and is an electrically insulating belt in the thickness direction. The film 42 is constituted by providing a release layer 42c on at least a heat-resistant resin such as polyimide, polyamideimide, PEEK, or a metal base layer 42a such as nickel or SUS (stainless steel). For the release layer 42c, a material having good release properties and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, PTFE, and FEP can be selected.

  PTFE is polytetrafluoroethylene. PFA is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer. FEP is a tetrafluoroethylene hexafluoropropylene copolymer. PEEK is polyetheretherketone.

  The film 42 of this embodiment is provided with a silicone rubber layer having a thickness of about 300 μm as an elastic layer 42 b on a polyimide material base layer 42 a having a thickness of about 50 μm, a diameter of about φ25 mm, and a length of about 300 mm. . Further, the surface of the elastic layer 42b is covered with a fluororesin tube having a thickness of about 20 μm as the release layer 42c. In this embodiment, the film 42 has insulating properties in all layers, but the elastic layer 42b mainly functions as an insulating layer for giving the film 42 electrical insulation in the thickness direction. Further, a black paint having heat resistance is applied to the inner surface of the film 42 so that the light emitted from the heater 45 is efficiently absorbed. The film 42 only needs to have insulating properties in the thickness direction, and is not limited to the layer configuration described above. For example, the base layer 42a and the release layer 42c may serve as an insulating layer, and an insulating layer may be provided separately from these.

  The pad 47 is a pressing member for making the nip portion N have a desired width by pressing the film 42 against the roller 41. As the pad 47, a plate-like member made of a conductive material having a width of 5 to 20 mm, a length of about 300 mm, and a thickness of 0.5 to 2 mm is used. The conductive material is, for example, a single material selected from iron, copper, stainless steel, carbon, or the like, or a composite material containing or laminating these materials. When a plate-like member formed of a plurality of layers is used as the pad 47, a conductive material layer is disposed on the contact layer that contacts the inner surface of the film. The pad 47 in this example uses an aluminum flat plate having a width of about 10 mm and a thickness of about 1 mm. Therefore, the entire aluminum flat plate plays a role as a contact layer. Note that the pressing member is not necessarily a plate-like member. The pressing member may be a roller-shaped member as long as it has conductivity and can press the film 42 toward the roller 41 in the region along the longitudinal direction. The longitudinal length of the contact layer is not necessarily the same as the longitudinal length of the pad 47. However, it is desirable to provide at least a length corresponding to the maximum area of the image formed on the maximum size sheet P that can be introduced into the fixing device 40 (a length longer than the maximum area of the image). Further, it is desirable that the pad 47 and the contact layer are provided at a length and a position that do not protrude from the end portion in the longitudinal direction of the film 42 so as not to contact the roller 41 at the end portion.

  The pad holder 43 (hereinafter referred to as the holder 43) is a member that holds the pad 47 in a state of being pressed toward the roller 41. The holder 43 is preferably made of a material with low heat conduction to surrounding members from the viewpoint of energy saving. For example, heat resistant glass, polycarbonate, liquid crystal polymer, or other heat resistant resin is used. Further, it is desirable to provide insulation so that a current flowing through the pad 47 does not flow into a support stay 46 described later. In this example, Sumika Super E5204L manufactured by Sumitomo Chemical Co., Ltd. was used.

  The holder 43 holds only the both end portions in the width direction of the pad 47 so that the pad 47 is radiantly heated by the heater 45, and the center portion in the width direction secures a slit (gap) along the longitudinal direction. . The holder 43 also has a guide function for securing the rotation trajectory of the film 42. The support stay 46 supports the pad 47 through the holder 43. The support stay 46 is preferably made of a material that is not easily bent even when a high pressure is applied. In this embodiment, SUS304 is used.

  As shown in FIG. 3, the support stay 46 is supported by the flange 111a on one end side in the longitudinal direction and by the 111b on the other end side.

  The flange 111 (111a, 111b) regulates the movement of the film 42 in the longitudinal direction and the shape in the circumferential direction. The flange 111 holds the heater 45 so as to bridge between the flange 111a and the flange 111b. The flanges 111a and 111b are formed of a heat resistant resin such as a liquid crystal polymer or a phenol resin. In this example, PPS (polyphenylene sulfide) was used.

  A pressure spring 115a is contracted between the flange 111a and the pressure arm 114a. A pressure spring 115b is contracted between the flange 111b and the pressure arm 114b. With this configuration, the film 42 is pressed against the upper surface of the roller 41 with a predetermined pressing force by the elastic force of the pressurizing spring 115 (115a, 115b) via the flange 111, the support stay 46, and the pad 47. A fixing nip N having a width is formed. In this embodiment, the applied pressure is 156.8 N on one end side, and the total applied pressure is 313.6 N (32 kgf).

  In the present embodiment, the width of the nip portion N is set to be in the range of 8 mm to 9 mm. The length of the nip portion N in the longitudinal direction is set to be about 300 mm. Therefore, heat treatment can be performed on an image in a range narrower than the length of the nip portion N in the longitudinal direction. At this time, in the longitudinal direction of the film 42, the relationship of the length of the nip portion N> the sheet P size ≧ the image region is satisfied. In this embodiment, heat treatment can be performed on an image formed on a sheet P having an A4 size or less. The sheet P having an A4 size or smaller is, for example, a postcard, A5, B4, or A4 size.

  The roller 41 as a contact rotating body is a roller member that forms a nip portion N in cooperation with the film 42 by contacting the outer surface of the film 42. The roller 41 is configured by providing an elastic layer 41b and a release layer 41c on a cored bar 41a, and the size of the portion having the elastic layer 41b is about φ24 mm in diameter and about 300 mm in length. The cored bar 41a and the elastic layer 41b are firmly bonded with an adhesive made of silicone resin. Moreover, the roller 41 is comprised so that the whole may have electroconductivity, and the metal core 41a and the mold release layer 41c can be electrically connected through the elastic layer 41b. The release layer 41 c functions as a contact layer that contacts the outer surface of the film 42. Further, the length of the contact layer is not necessarily the same as the length of the pad 47 in the longitudinal direction, but at least corresponds to the maximum area of the image formed on the maximum size sheet P that can be introduced into the fixing device 40. It is desirable to provide it with a length that is longer than the maximum area of the image. Further, the release layer 41c and the contact layer are desirably provided at a length and a position that do not protrude from the end portion in the longitudinal direction of the film 42 so as not to contact the pad 47 at the end portion.

  The elastic layer 41a of the roller 41 is a conductive rubber layer formed on the basis of elastic solid rubber, elastic sponge rubber, elastic foam rubber or the like. In this embodiment, conductive silicone rubber having a thickness of about 3 mm, in which carbon particles are dispersed in silicone rubber, is used. The hardness of the conductive silicone rubber is 20 degrees as measured with an Asker rubber hardness meter C type (ASKER), and the electrical resistivity is 5.0 [Ω · cm].

The release layer 41c of the roller 41 is a layer for improving the separation property of the sheet P from the roller 41, and a resin having excellent release property such as PFA is used. In this embodiment, a PFA tube having a volume resistivity of 5.0 × 10 ² [Ω · cm] is used with a thickness of about 50 μm. Note that a PFA coat may be used as the release layer 41c, and the PFA tube and the PFA coat can be used properly according to the required thickness, mechanical and electrical strength.

  The hardness of the roller 41 is 65 degrees as measured by an Asker rubber hardness meter C type (ASKER). In order to reduce the heat capacity and improve the quick start property, the thickness of the elastic layer 41b is preferably 1 to 3 mm, and the release layer 41c may be used within a range of 20 to 50 μm.

  The metal core 41a of the roller 41 is a stainless steel shaft member having a diameter of about 18 mm. The cored bar 41a is rotatably held by an insulating bearing 112a on one end side in the axial direction and an insulating bearing 112b on the other end side. The bearings 112 (112 a and 112 b) are provided on the frame body 113 of the fixing device 40. Further, as shown in FIG. 3, a gear G is provided at one end in the axial direction of the cored bar 41a, and the driving of the motor M as driving means is transmitted.

  As shown in FIG. 2, the roller 41 is rotationally driven in the direction of arrow A by the motor M, and transmits the drive to the film 42 at the nip portion N, whereby the film 42 is driven to rotate in the direction of arrow B.

  The heater 45 generates heat when energized, and heats the film 42 and the pad 47 with radiant heat. As shown in FIG. 2, the heater 45 is provided at a position separated from the film 42, preferably near the center. As the heater 45, a lamp heater, a heating wire, or the like is used. In this embodiment, a cylindrical halogen lamp having a length of about 300 mm in the longitudinal direction is used.

  As shown in FIG. 2, the thermistor 118 is provided in contact with the surface side of the film 42, and detects the surface temperature of the film 42. By outputting an output corresponding to the temperature detected by the thermistor 118 to the control circuit 121 described later, the energization to the heater 45 is controlled, and the film 42 is maintained at a predetermined temperature (160 to 190 ° C.).

(Detection of tearing of heated film)
Next, a configuration for detecting film breakage will be described. FIG. 4 is a block diagram showing the relationship between the components of the fixing device 40. FIG. 5 shows an equivalent circuit diagram (a) of the conduction detection circuit 60 when the film 42 is in a normal state (hereinafter referred to as the detection circuit 60), and an equivalent circuit diagram of the detection circuit 60 when the film 42 is in a torn state. b).

In this embodiment, the tearing of the film 42 is detected by detecting conduction between the pad 47 and the roller 41. The conduction in the description of the present embodiment means that the pad 47 and the roller 41 are electrically connected. For example, when the pad 47 and the roller 41 are in physical contact, the pad 47 and the roller 41 are electrically connected. Alternatively, when the film 42 has a conductive layer, the pad 47 and the roller 41 are electrically connected when the pad 47 and the roller 41 are pressed through the conductive layer of the film 42. . In this embodiment, the continuity is determined based on whether or not a current flows in a circuit including the pad 47 and the roller 41 as a part of the circuit. As described above, the pad 47 and the roller 41 have conductivity, and the insulating film 42 is sandwiched between them. If the film 42 is in a normal state (unbreakable state), even if a voltage is applied between the pad 47 and the roller 41, the film 42 is insulated by the film 42. No current flows. However, when the film 42 is torn, the pad 47 and the roller 41 are in contact with each other at the torn portion, and an electric current flows (conducts) by being electrically connected. In the present embodiment, the tearing of the film 42 means that a part of the film 42 is damaged due to the mixing of foreign matter into the nip portion N, external force at the time of jamming, and fatigue accompanying use. The tearing of the film 42 can occur at any position in the longitudinal direction of the film 42 such as an end portion or a central portion thereof. In the present embodiment, by aligning the longitudinal direction length of the film 42 and the longitudinal direction length of the nip portion N and the end positions thereof, not only the range that affects the image heating process but also the entire region of the film 42 is affected. It is possible to detect tears. The longitudinal length of the film 42, the longitudinal length of the nip portion N, and the positions of these end portions are not necessarily aligned. This is because if the longitudinal length of the nip portion N is a few millimeters shorter than the longitudinal length of the film 42, conduction can be detected by the progress of the belt breakage.
Hereinafter, it explains in detail using a drawing.

  As shown in FIG. 4, the brush 61 is a member that makes electrical connection with the cored bar 41 a of the roller 41. The brush 61 has a configuration in which fiber materials having conductive properties are bundled, and the tip of the brush 61 is provided so as to be slidably pressed against the cored bar 41a. With such a configuration, even when the roller 41 is rotating, it can be electrically connected. The brush 61 is not limited to the above-described configuration as long as it can be electrically connected to the rotating roller 41. For example, the brush 61 may be a leaf spring-shaped member made of a conductive metal material.

  Further, the object with which the brush 61 is brought into contact is not limited to the cored bar 41a. For example, the brush 61 may be pressed against the release layer 41 c of the roller 41. At this time, the elastic layer 41b of the roller 41 is preferably non-conductive. Even with such a configuration, the conduction between the pad 47 and the roller 41 can be detected. However, when the brush 61 is pressed against the release layer 41c, a contact line is formed on the surface of the roller 41, which may affect the image quality. Therefore, the contact with the cored bar 41a as in the present embodiment. A configuration is preferred.

  As shown in FIG. 4, the detection circuit 60 as detection means electrically connects the pad 47 and the brush 61 by a conducting wire 62 with an insulating coating. More specifically, the conducting wire 62 extending from one end side of the detection circuit 60 is soldered to a surface opposite to the contact surface of the pad 47 on one end side in the longitudinal direction of the pad 47. A conducting wire 62 extending from the other end of the detection circuit 60 is connected to the brush 61 with a connector. In addition, the connection position of the conducting wire 62 to the pad 47 is not limited to the position described above. As long as it is electrically conductive and can be electrically connected to the layer in contact with the film 42, it may be the side surface of the end of the pad 47. You may connect the conducting wire 62 to. Moreover, the connection method of the conducting wire 62 is not limited to the above-described method, and can be appropriately designed as long as the connection with the target member is performed.

  The detection circuit 60 is a circuit that detects conduction between the contact layer of the pad 47 and the contact layer of the roller 41. The detection circuit 60 includes a power source 60a for generating a potential difference between the pad 47 and the roller 41, and an ammeter 60b for detecting a current flowing through the circuit. When the ammeter 60 b detects the current flowing through the circuit, the ammeter 60 b outputs a signal corresponding to the detected current value to the control circuit 121. A constant voltage of 5 [V] is applied to the detection circuit 60 of the present embodiment, and the in-circuit resistance R is 1 [MΩ]. That is, when it is conducted, a current of 5 [μA] flows in the circuit. Note that the detection circuit 60 is not limited to the above-described configuration as long as it can detect conduction between the contact layer of the pad 47 and the contact layer of the roller 41. For example, the power source 60a may apply an AC voltage instead of a constant voltage between the contact layer of the pad 47 and the contact layer of the roller 41. However, if the applied voltage is large, the toner image T on the sheet P may be affected due to discharge, so the voltage applied between the contact layer and the contact layer is several [mV] to several tens of mV. [V] is desirable. Further, a voltmeter may be used in place of the ammeter 60b, and various ICs as alternatives can be used. The conductivity in the present embodiment refers to a property that generates a current that can be detected by the ammeter 60a when a voltage is applied to the power supply 60a.

  Next, the operation of the detection circuit 60 will be described using an equivalent circuit. As shown in FIG. 5, the equivalent circuit has a configuration corresponding to a power source 60 a, an ammeter 60 b, and an in-circuit resistance R in the detection circuit 60. In this equivalent circuit, wiring corresponding to the conductive wire 62 extends from both ends of the detection circuit 60 and is connected to the terminal of the switch unit. At this time, one terminal corresponds to the pad 47 and the other terminal corresponds to the roller 41. Whether the switch portion of the equivalent circuit is in the “open” state or the “conducting” state is related to the state of the film 42 in the nip portion N.

  When the film 42 is not torn in the nip portion N, the pad 47 and the roller 41 are insulated from each other by the film 42, so that they are not electrically connected. Therefore, as shown in FIG. 5A, the switch portion of the equivalent circuit is “open”, and no current flows in the circuit. On the other hand, when the film 42 is torn at the nip portion N, the pad 47 and the roller 41 are electrically connected through the torn portion. Therefore, as shown in FIG. 5B, a current of 5 [μA] flows (conducts) in the equivalent circuit in which the current path is formed. In this embodiment, a state where no current flows between the pad 47 and the roller 41 is referred to as an insulated state.

(Control of image heating device)
Next, control of the operation of the fixing device 40 when the tearing of the film 42 is detected will be described. FIG. 6 is a flowchart of image heating processing inhibition control. The control circuit 121 performs control to prohibit execution of the image heating process when the detection circuit 60 detects that the film 42 is torn. If the image is fixed while the film 42 is torn, contact failure occurs at the torn portion, so that proper fixing is not performed and a defective image is generated. Therefore, in this embodiment, the above-described control is performed to prevent the output of a defective image. In this embodiment, the process of fixing the image T on the sheet P by heating and pressurizing the toner image T on the sheet P is referred to as an image heating process. The image heating process is not limited to the process of fixing the unfixed toner image T to the sheet P. For example, a process for fixing a semi-fixed image on the sheet P or a process for performing a heating process on the fixed image may be used. In this embodiment, in order to prohibit the image heating process described above, the energization to the heater 45 and the energization to the motor M are cut off. Hereinafter, it explains in detail using a drawing.

  The control circuit 121 as a control means is a circuit that includes, for example, a CPU that performs calculations associated with various controls, and a non-volatile medium such as a ROM that stores various programs. A program corresponding to the flowchart shown in FIG. 6 is stored in the ROM, and the CPU reads and executes the program, thereby controlling the image heating process of the fixing device 40. Note that the control circuit 121 may be an integrated circuit such as an ASIC as long as it performs the same function.

  As shown in FIG. 4, the control circuit 121 is electrically connected so that the outputs of the thermistor 118 and the detection circuit 60 can be detected. The control circuit 121 is electrically connected so that the energization contents of the motor M and the heater 45 can be controlled.

  The control circuit 121 samples the output from the thermistor 118 at a predetermined period (about 100 μs in this embodiment), and reflects the obtained temperature information in the energization control to the heater 45. That is, the control circuit 121 controls energization supplied to the heater 45 based on the output of the thermistor 118. In the present embodiment, the temperature of the film 42 is controlled to be constant at a predetermined temperature (160 to 190 ° C.) during the job in accordance with the job execution instruction received by the control circuit 121.

  Further, the control circuit 121 controls the energization contents of the motor M as a driving means. When energization is performed, the motor M starts driving. The motor M is mechanically connected to the gear G, drives the roller 41 via the gear G, and rotates the film 42 following the roller 41. With such a configuration, the sheet P sandwiched between the roller 41 and the film 42 is conveyed at a predetermined process speed (about 250 mm / sec in this embodiment).

  The control circuit 121 samples the output from the detection circuit 60 at a predetermined period (about 10 μs in this embodiment), and controls the energization to the heater 45 and the motor M based on the obtained output. In this embodiment, when the ammeter 60b detects the presence of a current, that is, when the input to the ammeter 60b is not 0 [μA], the control circuit 121 determines that there is conduction and inhibits the image heating process. That is, the control circuit 121 performs control to interrupt energization to the heater 45 and the motor M if the job is in progress, and does not execute the subsequent job if the job is not in progress. Depending on the circuit configuration of the continuity detection circuit 60 and the specifications of the ammeter 60b, the ammeter 60b may detect a current regardless of whether the film 42 is broken. In that case, a control circuit is provided based on a comparison between the threshold value and the detected value of the ammeter 60 b by providing a threshold value for the current magnitude so that the image heating process can be appropriately prohibited based on the current accompanying the breakage of the film 42. 121 may determine the presence or absence of conduction. For example, the control circuit 121 sets the threshold value X to 4 [μA], determines that there is continuity when the value detected by the ammeter 60 b is 4 [μA] or more, and prohibits image heating processing. . As described above, in this embodiment, in both cases where the value detected by the ammeter 60b is not 0 [μA] and when the value is greater than or equal to the predetermined value X, these are in a state of being conductive. Call.

  The fixing device 40 operates as follows when the control circuit 121 executes a program corresponding to the flowchart shown in FIG.

  The control circuit 121 receives a job execution instruction (STEP1, hereinafter, STEP is abbreviated as S as in S1). Next, the control circuit 121 performs a warm-up operation of the fixing device 40 by the pre-rotation (S2). In the warm-up operation, the control circuit performs control so that the heater 45 is energized until the temperature detected by the thermistor 118 reaches a predetermined target temperature T1 (160 ° C. in this embodiment). When the detected temperature of the thermistor 118 reaches the target temperature T1, the control circuit 121 energizes the motor M to drive it. The roller 41 is rotationally driven by the driving of the motor M, and the film 42 is rotated by the roller 41.

  With the warm-up operation described above, the control circuit 121 starts sampling the output of the ammeter 60b (S3). At this time, while the film 42 rotates at least once, the control circuit 121 samples the output of the ammeter 60b, so that the tearing of the film 42 can be detected over the entire circumference. The control circuit 121 determines the detection result of the detection circuit 60 (S4). When the control circuit 121 detects the conduction of the detection circuit 60 (detection current I ≠ 0 [μA]), the control circuit 121 determines that the film 42 is torn and proceeds to S7. If the detection circuit 60 does not detect continuity (detection current I = 0 [μA]), the control circuit 121 determines that the film 42 is normal and proceeds to S5.

  When it is determined that the film 42 is torn, the control circuit 121 prohibits the image heating process of the fixing device 40, and thus interrupts the energization of the heater 45 and the motor M during the execution of the job (S7). Then, the control circuit 121 displays an error on the operation unit (not shown) of the printer 1 (S8). The error display is not limited to that performed by the operation unit of the printer 1 main body, but may be performed on a display screen of a printer driver of an information terminal (not shown) connected to the printer 1.

  When the error is displayed once, the control circuit 121 performs control for prohibiting the execution of the job until the fixing device 40 is replaced or repaired by a service person.

  When the control circuit 121 determines that the film 42 is normal, the control circuit 121 energizes the heater 45 so that the detected temperature becomes T2 (165 ° C. in this embodiment), and reaches the end condition of the received job execution instruction. The image heating process is performed until (S5, S6). While the job is being executed, the output of the detection circuit 60 is continuously sampled (S3). By performing such control, it becomes possible to detect the tearing of the film 42 that occurs during execution of the job, particularly the tearing of the film 42 that occurs from the end side. When the end condition of the received job execution instruction is reached, the control circuit 121 stops energization of the heater 45 and the motor M, and normally stops the fixing device 40 (S9).

According to the present embodiment, the detection circuit 60 is provided in the fixing device 40 that heats the image on the sheet using the film 42. Then, by detecting the conduction between the contact layer of the pad 47 and the release layer 41 c of the roller 41, it is possible to detect the occurrence of tearing of the film 42.
According to this embodiment, the control circuit 121 samples the output of the ammeter 60b during at least one rotation of the film 42, so that the tearing of the film 42 can be detected over the entire circumference.

  According to the present embodiment, it is possible to prevent the output of a defective image by prohibiting the image heating process when the film 42 is detected to be broken.

(Other examples)
As mentioned above, although the Example which can apply this invention was described, the numerical value illustrated by each Example mentioned above is an example, Comprising: It is not limited to this numerical value. Numerical values can be selected as appropriate. In addition, the configurations described in the embodiments may be changed as appropriate within the scope where the present invention can be applied.

  The film 42 is not limited to the on-demand configuration supported by the pad 47 and the holder 43, and may be, for example, a belt unit method spanning a plurality of rollers. At that time, the film 42 may be rotationally driven by the plurality of rollers. However, an on-demand configuration as in the above-described embodiment is desirable from the viewpoint of reducing the heat capacity.

  The heating method of the film 42 is not limited to the method of heating the film 42 by radiation like the heater 45. For example, a method may be used in which a ceramic heater is bonded to the upper surface of the pad 47 and the film 42 is heated via the pad 47 by the heat generated by the ceramic heater. Further, a heat generating belt that generates heat by energizing the resistance heat generating layer may be used. In that case, it is good to comprise so that the alternating current which flows through a resistance heating layer may not flow into the detection circuit 60. FIG. For example, the layer structure of the film 42 is preferably provided in an insulating layer so as to sandwich the resistance heating layer. In addition, during the image heating process in which an alternating current flows through the resistance heating layer, the conductive wire 62 extending from the detection circuit 60 is preferably separated from the pad 47 and the brush 61. Then, in a preparatory operation for an image heating process in which an alternating current is not passed through the resistance heating layer, the conductor 62 is connected to the pad 47 and the brush 61, the heating belt is rotated, and the detection circuit 60 is operated. Alternatively, the detection circuit 60 may be configured not to provide a reference potential. For example, the power source 60a may be configured to use a battery and not be grounded. Further, the ammeter 60b may transmit an output corresponding to the detected current value to the control circuit 121 by an optical relay or the like without performing electrical connection.

  What forms the nip portion N with the film 42 is not limited to a roller member such as the roller 41. For example, a pressure belt unit that is a unit in which a belt is bridged by a plurality of rollers may be used.

  The image forming apparatus described using the printer 1 as an example is not limited to an image forming apparatus that forms a monochrome image, but may be an image forming apparatus that forms a full-color image. Further, the image forming apparatus can be implemented in various applications such as a copying machine, a fax machine, and a multifunction machine in addition to necessary equipment, equipment, and a housing structure.

  The image heating apparatus in the above description is not limited to an apparatus that fixes an unfixed toner image on the sheet P. For example, a device that fixes a semi-fixed toner image on the sheet P or a device that heats a fixed image may be used. Therefore, the fixing device 40 as the image heating device may be a surface heating device that adjusts the gloss and surface properties of the image, for example.

41 Pressure roller 42 Heated film 43 Pad holder 47 Nip pad 60 Continuity detection circuit 121 Control circuit M Motor P Sheet

Claims (4)

A film for heating an image on a sheet at a nip portion, an endless rotating film provided with an insulating layer;
A contact rotating body having a conductive contact layer that contacts the outer surface of the film, the contact rotating body forming the nip portion in cooperation with the film;
A pressing member that presses the film from the inner surface thereof toward the contact rotating body, the pressing member having a conductive contact layer that contacts the inner surface of the film;
Detection means for detecting conduction between the contact layer and the contact layer due to the tearing of the film;
Control means for controlling whether to prohibit the image heating process based on the detection result of the detection means;
An image heating apparatus comprising: The image forming apparatus according to claim 1, wherein the control unit controls whether to prohibit image heating processing based on a detection result of the detection unit during at least one rotation of the film.   The image heating apparatus according to claim 1, wherein the pressing member presses the film in the entire region in the longitudinal direction.   The image heating apparatus according to claim 1, further comprising a driving unit that rotationally drives the contact rotating body, wherein the film is driven to rotate by the contact rotating body.

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