JP5183366B2 - Image heating device - Google Patents

Description

  The present invention is an electromagnetic (magnetism) suitable for use as an image heating and fixing apparatus mounted on an image forming apparatus such as a copying machine, a printer, or a facsimile machine that forms an image by an electrophotographic system, an electrostatic recording system, a magnetic recording system, or the like. The present invention relates to an induction heating type image heating apparatus.

  Examples of the image heating device include a fixing device that fixes or presupposes an unfixed image on the recording material, and a gloss increasing device that increases the gloss of the image by heating the image fixed on the recording material. In addition, an image heating apparatus or the like may be used to quickly dry ink in an image forming apparatus that forms an image with a liquid containing a dye or a pigment, such as an ink jet method.

  Conventionally, as a fixing device for heating and fixing an unfixed image on a recording material, a contact heating method device such as a heat roller method or a belt (film) heating method has been widely used. Such a device uses a halogen lamp or a heating resistor as a heating source for the heating member, and generates heat by passing an electric current through the halogen lamp or a heating resistor, and the heat is heated via a roller or a belt (film) as a heat transfer member. An unfixed image is heat-fixed by being applied to a recording material as a material.

  An electromagnetic induction heating type fixing device is also known. In this apparatus, a magnetic flux is generated by a magnetic field generating means and applied to a metal substrate of a fixing roller as a heating member (fixing member). That is, an eddy current is generated in the metal substrate of the fixing roller to generate heat by Joule heat. Thus, by directly heating the metal substrate of the fixing roller by the generation of eddy current, the efficiency of energy consumption can be increased compared to the heat roller using a halogen lamp.

  In addition to a fixing roller, an endless fixing belt (heating belt) having a low heat capacity is generally used as a fixing member to be heated by electromagnetic induction. The fixing member has a pressing member inside, and the fixing belt is not stretched. There has already been proposed a type of driving in a circular manner (Patent Document 1). In the system in which the low heat capacity fixing belt is heated by electromagnetic induction, the fixing belt can be directly heated locally, so that it can be heated to a predetermined temperature in a short time. Japanese Patent Application Laid-Open No. H10-228688 describes that the fixing belt can be heated efficiently by preventing the leakage of magnetic flux by bringing the second magnetic body close to the inside of the fixing belt.

On the other hand, since local and steep temperature changes occur, it is necessary to accurately detect and control the temperature of the fixing belt. Therefore, a fixing device as in Patent Document 2 has been proposed. According to this patent document 2, the temperature of the fixing belt is accurately detected and the fixing belt is heated uniformly by arranging the magnetic body arranged inside the fixing belt and the magnetic body of the coil so as to face each other. I can do it.
Japanese Patent Laid-Open No. 2002-148983 JP 2006-267332 A

  However, the fixing device as described above has the following problems. That is, in the fixing device described in Patent Document 2, the magnetic bodies are arranged at intervals. For this reason, the magnetic coupling is weaker than that in the case where the magnetic body is disposed on the entire surface, and a power supply having a larger capacity is required.

  In addition, the pressure-opposing member that is arranged in the fixing belt and presses in the direction of the pressure roller needs to have sufficient rigidity in order to obtain a uniform fixing property and glossiness in the longitudinal direction. Therefore, the pressure facing member is often made of metal. However, if the pressure facing member is not partially covered with the core in the fixing belt, a demagnetizing field is generated by the eddy current flowing in the pressure facing member, and the magnetic field on the fixing belt is weakened to reduce the heat generation amount. As a result, temperature unevenness occurs.

  On the other hand, if the signal line of the temperature detection element is arranged close to the inner surface of the fixing belt, noise or temperature rise occurs due to the induced current caused by the coil, and accurate measurement cannot be performed. In addition, there are problems such as rubbing against the inner surface of the fixing belt and heat resistance of signal lines.

  The present invention has been proposed in view of the above-described conventional problems with an electromagnetic induction heating type image heating apparatus using a heating belt. The purpose is to prevent the noise of the signal line of the temperature detection element, etc., even when a magnetic substance is provided close to the inner surface of the heating belt to strengthen the magnetic coupling, and the heating belt is heated efficiently, and the surface temperature of the heating belt is increased. An object of the present invention is to provide an image heating apparatus capable of accurately controlling the image.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a rotatable heating belt having a conductive layer, and a pressure member that can rotate in pressure contact with the outer peripheral surface of the heating belt. A metal stay inside the heating belt that presses the heating belt in the direction of the pressure member, and covers the heating belt inner peripheral surface side of the metal stay and is close to the inner surface of the heating belt. A heating means having a magnetic core and an internal magnetic member disposed; a coil disposed outside the heating belt and generating an induced current in the conductive layer of the heating belt; A heating means configured to wind a part of the body core; a temperature detection element that detects a temperature of the heating belt; and a temperature control unit that performs temperature control of the heating belt based on a detection value of the temperature detection element. And an image heating apparatus that heats a recording material carrying an image at a nip portion between the heating belt and the pressure member, wherein the temperature detection element is in contact with the inner surface of the heating belt, The signal line of the temperature detecting element is connected to the internal magnetic member and the metal stay through an opening provided at a position facing a part of the magnetic core around which the coil is wound. It is wired inside and is pulled out from the end of the metal stay).

  According to the present invention, it is possible to provide an image heating apparatus capable of preventing noise of a signal line of a temperature detection element, heating the heating belt efficiently, and controlling the surface temperature of the heating belt accurately and uniformly.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

[Example]
(1) Example of Image Forming Apparatus FIG. 11 is a schematic configuration model diagram of the image forming apparatus of this embodiment. The image forming apparatus according to the present exemplary embodiment includes an image forming unit that forms an unfixed image on a recording material, and an image heating apparatus that uses an electromagnetic induction heating method as a fixing device that fixes the unfixed image on the recording material. Device. The image forming apparatus forms an image corresponding to electrical image information input from an external apparatus 200 such as a host computer to a control circuit unit 100 (control means: CPU) of the image forming apparatus on a recording material and outputs the image. This is a photographic full-color laser printer. The control circuit unit 100 is an electric circuit that comprehensively controls the operation of the image forming apparatus, and starts image forming operation sequence control when an image forming operation start signal is input. The image forming apparatus of this embodiment has a process speed of 180 mm / sec, and can form 40 sheets of A4 size (210 mm × 297 mm) recording material per minute with horizontal paper feed (transverse feed). Device.

  Y, M, C, and K are first to fourth toner image forming units (image forming units) arranged in a line from the left to the right in the drawing, and yellow (Y), magenta (M), and magenta, respectively. This is an electrophotographic process mechanism for forming toner images of four colors of cyan (C) and black (K).

  Each toner image forming unit is provided with a photosensitive drum 2 (Y, M, C, K) as an image carrier. Around each photosensitive drum, a charging roller 3 (Y / M / C / K), a developing device 4 (Y / M / C / K), and a primary transfer roller 5 (Y / M / C / K) are installed. Has been. Further, an exposure device (laser beam scanning exposure device) 6 (Y, M, C, K) is installed above the charging roller and the developing device of each toner image forming unit.

  In this embodiment, the photosensitive drum 2 is a negatively chargeable organic photosensitive drum having an OPC photosensitive layer, and is driven to rotate in a direction indicated by an arrow (counterclockwise) by a driving device (not shown) at a predetermined speed. The charging roller 3 contacts the photosensitive drum with a predetermined pressure contact force, and uniformly charges the surface of the photosensitive drum to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). The exposure device 6 outputs a laser beam modulated in accordance with the time-series electric digital pixel signal of the image information input from the external device 200 to the control circuit unit 100, and the uniform charging processing surface of the corresponding photosensitive drum 2 is output. Scan exposure. Thereby, an electrostatic latent image corresponding to the exposed image information is formed on the surface of each photosensitive drum. Each of the developing devices 4 (Y, M, C, and K) is a two-component developing system in this embodiment, and stores Y, C, M, and K color toners, respectively. Each developing device applies toner to the electrostatic latent image formed on the photosensitive drum by a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum, which is applied to the developing roller from a developing bias power source (not shown). Then, the electrostatic latent image is reversely developed as a toner image. The primary transfer roller 5 is in contact with the surface of each photosensitive drum with a predetermined pressing force via an intermediate transfer belt 1 as an intermediate transfer member. The intermediate transfer belt 1 is stretched between a driving roller 8, a secondary transfer counter roller 7, and a driven roller 9, and an arrow is synchronized with the rotation of the photosensitive drum 2 by the rotation of the driving roller 8. It is rotationally driven in the direction (clockwise).

  In each toner image forming portion, the contact portion between the photosensitive drum and the intermediate transfer belt is a primary transfer portion, and the primary transfer roller power supply (not shown) has a polarity opposite to that of the toner from the primary transfer roller. A next transfer bias is applied at a predetermined control timing. As a result, the toner images formed on the surfaces of the respective photosensitive drums 2 are sequentially superimposed and preliminarily transferred onto the intermediate transfer belt 1 that is driven to rotate and is primarily transferred. That is, on the intermediate transfer belt 1, a multicolor image toner image is formed by superimposing Y color, C color, M color, and K color toner images.

  A secondary transfer roller 10 is brought into pressure contact with the secondary transfer counter roller 7 through the intermediate transfer belt 1. A contact portion between the intermediate transfer belt 1 and the secondary transfer roller 10 is a secondary transfer portion. A secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 10 from a secondary transfer bias power source (not shown) at a predetermined control timing. The multi-color toner images on the intermediate transfer belt 1 are secondarily transferred collectively to the recording material 13 conveyed from the paper feeding unit to the secondary transfer unit at a predetermined control timing.

  The recording material 13 that has exited the secondary transfer portion is separated from the surface of the intermediate transfer belt 1 and introduced into the fixing device 12, where the toner image of the multicolor image is heated and pressed and fixed at the fixing nip portion. Then, the recording material 13 is discharged to the outside as a multicolor image formed product (full color image formed product). Further, the surface of the intermediate transfer belt 1 after separation of the recording material is cleaned by a cleaner 11.

  Reference numeral 14 denotes a cassette paper supply unit, and 15 denotes a manual paper supply unit (multipurpose tray). By driving the paper feed roller 16 or 17 at a predetermined control timing, one sheet of recording material 13 is separated and fed from the cassette paper feed unit 14 or the manual paper feed unit 15, and is transferred to the secondary transfer unit by the sheet path 18. It is conveyed toward. Then, the sheet is fed by the registration roller 19 to the secondary transfer unit at a predetermined control timing. That is, the recording material 13 is introduced into the secondary transfer portion in accordance with the timing at which the leading end of the multicolor image toner image on the intermediate transfer belt 1 is moved to the secondary transfer portion.

  In the image forming apparatus of the present embodiment, the sheet passing standard of the recording material 13 is the center of the recording material width center for both the paper feeding / conveyance from the cassette paper feeding unit 14 and the paper feeding / conveyance from the manual paper feeding unit 15. It is a standard.

(2) Fixing device 12
FIG. 1 is a front model diagram of the main part of the fixing device 12, FIG. 2 is a longitudinal front model diagram, and FIG. 3 is an enlarged cross-sectional model diagram along line (3)-(3) in FIG.

  In the following description, regarding the fixing device, the front refers to the surface of the device viewed from the recording material inlet side, the rear surface refers to the opposite surface (recording material outlet side), and the left and right refers to the left or right when the device is viewed from the front. is there. The upstream side and the downstream side are the upstream side and the downstream side with respect to the recording material conveyance direction or the fixing belt rotation direction (heating belt rotation direction). Further, the longitudinal direction of the fixing device or a member constituting the fixing device is a direction orthogonal to the recording material conveyance direction in the recording material conveyance path surface or a direction parallel to the rotation axis direction of the fixing belt (heating belt rotation axis direction). is there. The short direction is a direction parallel to the recording material conveyance direction. The sheet passing width of the recording material is a recording material dimension in a direction orthogonal to the recording material conveyance direction on the recording material surface.

  The fixing device 12 includes a belt unit 21, a pressure roller 22 having elasticity as a rotatable pressure member, and a heating unit between left and right side plates 50L and 50R of a fixing device frame (chassis, frame). Coil unit (magnetic field generating means) 31 is provided. In the present embodiment, the recording material P is fed by so-called center reference conveyance, and O is the center reference line (virtual line). W is the sheet passing width (maximum sheet passing width) of the recording material P having the maximum sheet width that is used in the apparatus.

a: Belt unit 21
The belt unit 21 has a flexible fixing belt having a cylindrical shape (endless belt shape, sleeve shape) as a rotatable heating belt having a conductive layer (induction heating element: a rotatable heating member that generates heat by magnetic flux). 23. Further, it includes a pressure pad 24, a pressure stay (metal stay) 25 as a pressing member, and an inner core 26 as an internal magnetic member, which are disposed inside the fixing belt 23. The pressure stay 25 is a gold member that is inside the fixing belt 23 and presses the fixing belt 23 toward the pressure roller 22. Further, end holders 27 </ b> L and 27 </ b> R attached to both left and right ends of the pressure stay 25 are provided. Further, it has a temperature detecting element 28 and a safety element 29. The pressure pad 24 is located below the pressure stay 25, and the inner core 26 is located above the pressure stay 25. The longitudinal dimensions of the pressure pad 24 and the pressure stay 25 are longer than the longitudinal dimension of the fixing belt 23, and both left and right ends protrude outward from the left and right ends of the fixing belt 23. In this embodiment, the length of the pressure pad 24 and the pressure stay 25 is 360 mm. End holders 27L and 27R are attached to the left and right ends of the pressure stay 25, respectively. FIG. 4 is an exploded perspective view of the pressure pad 24, the pressure stay 25, the inner core 26, the end holders 27L and 27R, the temperature detection element 28, and the security element 29 described above.

  FIG. 5 is a model diagram of the layer structure of the fixing belt 23 in this embodiment. The fixing belt 23 includes a cylindrical base layer 23a, an inner surface coat layer 23b provided on the inner peripheral surface of the base layer 23a, an elastic layer 23c provided in order on the outer peripheral surface of the base layer 23a, and a release layer. It is a member having a composite layer structure of the layer 23d, and has flexibility as a whole.

  The base layer 23 a is a conductive layer (conductive member), and is an electromagnetic induction heating layer that generates an induced current (eddy current) by the action of magnetic flux of the coil unit 31 and generates heat due to Joule heat. In this example, a cylindrical nickel electroformed belt having an inner diameter of about 30 mm and a thickness of about 30 μm was used as the base layer 23a. The base layer 23 a may be configured to be heated by the magnetic flux of the coil unit 31. If it is a nickel electroformed belt, the thickness should just be about 20-100 micrometers. Moreover, as the base layer 23a, a layer in which a thin metal film such as copper or silver is laminated on polyimide having a thickness of about 90 μm may be used. The inner surface coating layer 23b was provided with 20 μm of polyimide in order to reduce sliding friction with the fixing belt inclusion. In addition, you may provide 10-50 micrometers of resin layers, such as a fluororesin, polyamideimide, and a polyimide. Further, a layer in which fine particles are dispersed may be used to increase the surface roughness of the inner surface of the belt and further reduce the sliding friction with the fixing belt inclusion. As the elastic layer 23c, silicone rubber having a thickness of about 300 μm was used. As the release layer 23d, a PFA (perfluoroalkoxy) or PTFE coating layer having a thickness of about 30 μm was used. Alternatively, a PFA tube can be used.

  The pressure pad 24 is a member having a composite layer structure of a pedestal 24a, an elastic layer 24b, and a pad cover 24c. The pad cover 24 c side faces the inner surface of the fixing belt 23. In this embodiment, silicone rubber as the elastic layer 24b is formed on the iron base 24a with a thickness of 3t. As the pad cover 24c, in order to improve the slidability with the inner surface of the fixing belt 23, a polyimide base material coated with PTFE was used. Further, in order to improve the slidability, silicon oil or grease may be applied to the pad cover 24c.

  The pressure stay 25 is a U-shaped rigid member having a downward cross section and is responsible for supporting the inner core 26 and pressing the pressure pad 24. Considering the maintenance of the gap between the inner core 26 and the fixing belt 23 and the strength against the pressure of the pressure pad 24, it is preferable to be made of metal such as iron or SUS.

  The inner core 26 is a magnetic member that covers the fixing belt inner peripheral surface side (heating belt inner peripheral surface side) of the metal pressure stay (metal stay) 25 and is disposed close to the inner surface of the fixing belt 23. . That is, it is a U-shaped member having a downward cross-sectional configuration configured to cover the surface of the pressure stay 25 (on the inner peripheral surface side of the heating belt). The inner core 26 prevents the magnetic flux (inductive magnetic field) of the coil unit 31 from acting on the metal pressure stay 25 and generating an induced current in the pressure stay 25. between. The inner core 26 is disposed close to the inner surface of the fixing belt 23 so as to cover the surface of the pressure stay 25. The inner core 26 is preferably made of a material having a high magnetic permeability and a small self-loss. For example, ferrite, permalloy, sendust, or the like is suitable.

b: Pressure roller 22
The pressure roller 22 as a rotatable pressure member of the present embodiment is configured as a soft roller having an outer diameter of about 30 mm. More specifically, for example, a cylindrical metal pipe having a thickness of about 2 mm using a steel material such as STKM (carbon steel pipe for mechanical structure) or an aluminum material is used as the core metal 22a, and the outer peripheral surface of the core metal 22a is thick. A 3 mm silicone rubber layer 22b is provided. Further, a release layer 22c using a PFA (perfluoroalkoxy) tube having a thickness of about 50 μm is provided outside the silicone rubber layer 22b.

  The pressure roller 22 is disposed such that the left and right end portions of the cored bar 22a are rotatably held between the left and right side plates 50L and 50R of the fixing device frame via bearing members 51L and 51R, respectively. . A drive gear G is concentrically attached to one end (left side) of the cored bar 22a.

  The belt unit 21 is arranged in parallel above the pressure roller 22 with the pressure pad 24 facing downward. The left end holder 27L and the right end holder 27R are respectively engaged with vertical guide slits 52L and 52R provided on the left side plate 50L and the right side plate 50R of the fixing device frame. . Then, the upper surface of the left end holder 27L and the upper surface of the right end holder 27R are respectively pressed and urged downward with a predetermined pressure F by a pressurizing mechanism (not shown). In this embodiment, the pressure is urged with a total pressure of about 400 N. Due to this pressing force, a downward pressing force is applied to the stay 25, and the lower surface of the pressure pad 24 is pressed against the upper surface of the pressure roller 22 against the elasticity of the elastic layer 22 b with the fixing belt 23 interposed therebetween. As a result, a fixing nip portion N having a predetermined width is formed between the fixing belt 23 and the pressure roller 22 in the recording material conveyance direction a necessary for heat fixing.

c: Coil unit 31
The coil unit 31 as a magnetic field generating unit is a heating unit that is disposed outside the fixing belt 23 and includes a coil 32 and a magnetic core 33 that generate an induced current in the conductive layer 23 a of the fixing belt 23. The coil 32 is configured to wind a part 33 a of the magnetic core 33. More specifically, the coil unit 31 is curved in a cross section so as to correspond to the outer peripheral surface of the cylindrical fixing belt 23. Then, on the upper side of the belt unit 21 (on the side opposite to the pressure roller 22 side), the longitudinal direction is parallel to the longitudinal direction of the belt unit 21 and a predetermined gap is provided between the outer surface of the fixing belt 23. It is arranged in a face-to-face state. That is, the coil unit 31 is fixed and supported between the left and right side plates 50L and 50R of the fixing device frame body via the left and right brackets 53L and 53R.

  The coil unit 31 has a coil (excitation coil) 32 for supplying current from the excitation circuit (external power supply unit) 101 (FIG. 7) and generating an induced current in the base layer (conductive layer) 23a of the fixing belt 23. . In this embodiment, a high frequency voltage of about 25 kHz is supplied from the excitation circuit 101 to the coil 32. The coil unit 31 has a magnetic core 33 for concentrating the magnetic flux generated from the coil 32 and a coil cover 34 for preventing the fixing belt 23 and the coil 32 from coming into direct contact. The coil 32 is a bundle of a plurality of Litz wires coated with polyimide, and is wound around the core 33a (the magnetic core at the center of the coil 32) a plurality of times as shown in FIG. It is wound around a horizontally long and flat sheet-like spiral coil. The magnetic core 33 covers the side opposite to the fixing belt 23 side of the coil 32 so that the magnetic flux generated by the coil 32 does not substantially leak to other than the base layer 23 a that is the conductive layer of the fixing belt 23. The magnetic core 33 is preferably made of a material having a high magnetic permeability and a small self-loss. For example, ferrite, permalloy, sendust and the like are suitable.

d: Fixing Operation Based on the image formation start signal, the control circuit unit 100 (FIG. 7) turns on the fixing driving device M and turns on the excitation circuit 101 at least during execution of image formation. When the fixing driving device M is turned on, a driving force is transmitted to the driving gear G of the pressure roller 22, and the pressure roller 22 is rotationally driven in a counterclockwise direction indicated by an arrow in FIG. Due to the rotation of the pressure roller 22, a rotational force acts on the fixing belt 23 by the frictional force between the surface of the pressure roller 22 and the surface of the fixing belt 23 in the fixing nip portion N. The inner surface of the fixing belt 23 is in close contact with the lower surface of the pressure pad 24 in the fixing nip portion N and slides outwardly around the pressure pad 24, the pressure stay 25, and the inner core 26 in the clockwise direction indicated by the arrow. 2 is rotated at the same speed as the rotational speed of 2. In this embodiment, the fixing belt 23 rotates at a surface rotation speed of 180 mm / sec, and 40 full-color images can be fixed in one A40 size per minute. The pressure pad 24 also serves as a guide member for the rotating fixing belt 23. Further, when the rotating fixing belt 23 moves to the left or right along the longitudinal direction of the pressure pad, the inner surface of the flange portion 27L-a provided on the left end holder 27L or the right end holder 27R. Is regulated by the inner surface of the flange portion 27R-a.

  Further, when the excitation circuit 101 is turned on, a high frequency current is applied to the coil 32 of the coil unit 31, and the base layer 23 a of the fixing belt 23 is inductively heated by the magnetic field generated by the coil 32. The heat of the base layer 23a raises the temperature of the rotating fixing belt 23. The temperature control function unit (temperature control unit) of the control circuit unit 100 performs temperature control so that the temperature becomes substantially constant at a predetermined target temperature (fixing temperature) of the fixing belt 23. That is, the power input to the coil 23 is controlled by changing the frequency of the high-frequency current based on the detection value of a temperature detection element (hereinafter referred to as a temperature sensor) 28 that detects the temperature of the fixing belt 23. Temperature control. The temperature sensor 28 is a thermistor, for example. In this embodiment, the temperature is controlled so that the temperature of the fixing belt 23 is substantially constant at 180 ° C. That is, the temperature detection element 28 detects the temperature of the fixing belt portion that is in the sheet passing area. The detected temperature information is fed back to the control circuit unit 100. The control circuit unit 100 controls the electric power input from the excitation circuit 101 to the coil 32 so that the detected temperature input from the temperature sensor 28 is maintained at a predetermined target temperature. When the detected temperature of the fixing belt 4 is raised to a predetermined temperature, the power supply to the coil 32 is cut off.

  The inner core 26 is located between the fixing belt 23 and the pressure stay 25 in order to prevent the magnetic flux of the coil unit 31 from acting on the metal pressure stay 25 and generating an induced current. It is arranged close to the inner surface of the fixing belt 23 so as to cover the surface. At this time, the gap between the inner surface of the fixing belt 23 and the inner core 26 is preferably about 0.5 to 3 mm. If it is 0.5 mm or less, the fixing belt 23 and the inner core 26 come into contact with each other, and an increase in torque or uneven gloss due to a partial temperature decrease of the fixing belt 23 occurs. If it is 3 mm or more, the magnetic coupling between the coil 32 and the inner core 26 is weakened, and the magnetic flux density penetrating the fixing belt 23 is weakened. As a result, the power supply capacity for generating heat from the fixing belt 23 becomes larger than necessary.

  As described above, the pressure roller 22 is driven, and the fixing belt 23 rises to a predetermined fixing temperature and is adjusted in temperature. In this state, the recording material P having the unfixed toner image T is introduced into the fixing nip portion N by being guided by the guide member 20 with the toner image carrying surface side facing the fixing belt 4 side. The recording material P is in close contact with the outer peripheral surface of the fixing belt 23 at the fixing nip portion N, and is nipped and conveyed along the fixing nip portion N together with the fixing belt 23. As a result, the heat of the fixing belt 23 is applied to the recording material P, and the unfixed toner image T is heat-pressure-fixed on the surface of the recording material P under the pressure of the fixing nip N. The recording material P that has passed through the fixing nip N is separated from the outer peripheral surface of the fixing belt 4 and conveyed outside the fixing device.

e: Temperature sensor 28
The temperature sensor 28 is desirably arranged so as to detect the temperature of the fixing belt portion corresponding to the image forming area in order to perform accurate temperature control. If the temperature sensor 28 is brought into contact with the outer surface of the fixing belt 23, the fixing belt 28 may be damaged. Although a method of providing a non-contact temperature sensor from the outside of the fixing belt 23 is also conceivable, a non-contact sensor having a high responsiveness such as a thermopile is disposed in the gap between the coil 32 and the fixing belt 23 where the heat generation amount of the fixing belt 23 is high. This is difficult in terms of heat resistance.

  Therefore, in this embodiment, the temperature detection unit of the temperature sensor 28 serving as a contact-type temperature detection element is provided in contact with the inner surface of the fixing belt 23 at the position in the longitudinal center of the fixing belt 23. Based on the detected temperature value of the temperature sensor 28, the temperature control function unit of the control circuit unit 100 controls the excitation circuit unit 101 to control the temperature of the fixing belt 23 to a target temperature of 180 ° C.

  When the temperature sensor 28 is disposed inside the fixing belt 23, noise due to the coil 32, heat resistance of the signal line 28 a, and friction with the inner surface of the fixing belt 23 must be prevented. The signal line 28 a is an electric wire that electrically connects the temperature sensor 28 and the control circuit unit 100. For this purpose, it is necessary to wire the signal line 28a of the temperature sensor 28 inside the pressure stay 25 and draw it out from the end of the pressure stay 25 in the fixing belt rotation axis direction (heating belt rotation axis direction). Therefore, it is necessary to provide openings 26 a and 25 a in a part of the inner core 26 and the pressure stay 25 that are close to the inner surface of the fixing belt 23, so that the signal line 28 a of the temperature sensor 28 is taken into the pressure stay 25. There is.

  In this embodiment, the temperature sensor 28 is in contact with the inner surface of the fixing belt 23. The signal line 28 a of the temperature sensor 28 is wired inside the pressure stay 25 through openings 26 a and 25 a provided in the inner core 26 and the pressure stay 25, and is drawn from the end of the pressure stay 25. Yes. The openings 26a and 25a are provided at positions facing a portion (a magnetic core at the center of the coil 32) 33a around which the coil 32 of the magnetic core 33 is wound. That is, the opening 25 a is provided on the upper surface of the central portion in the longitudinal direction of the pressure stay 25. An opening 26a is also provided on the upper surface of the central portion in the longitudinal direction of the inner core 26 so as to correspond to the opening 25a. The openings 26 a and 25 a are provided at positions facing the magnetic core 33 a at the center of the coil 32. On the inner surface of the pressure stay 25, an insulating seat portion 40 in which the base portion of the leaf spring 41 is molded is fixed. The leaf spring 41 extends outside the inner core 26 through the opening 25 a of the pressure stay 25 and the opening 26 a of the inner core 26. The leaf spring 41 is bent near the opening of the inner core 26 and downstream of the opening 26a in the fixing belt rotation direction, and a temperature sensor 28 is attached and supported at the tip. The temperature sensor 28 is elastically in contact with the inner surface of the fixing belt 23 by the elasticity of the leaf spring 41 at a substantially central position in the longitudinal direction of the fixing belt 23. The leaf spring 41 may or may not serve as the electrode of the temperature sensor 28. However, when a separate signal line is provided, a heat resistant tape is provided inside the leaf spring 41 in order to prevent sliding with the fixing belt 23. It is better to fix with etc. A signal line 28 a that electrically connects the temperature sensor 28 and the control circuit unit 100 circulates the inside of the pressure stay 25 from the insulating seat 40, and extends outward from one end (left end) of the fixing belt 23 in the rotation axis direction. Has been drawn to.

  The temperature sensor 28 is brought into contact with a region where the amount of heat generated by the coil 32 inside the fixing belt 23 is the highest, and detects the temperature of that portion. That is, the temperature sensor 28 is in contact with the portion of the inner surface of the fixing belt 23 that generates the highest amount of heat in the fixing belt circumferential direction (heating belt circumferential direction). In the present embodiment, the temperature sensor 28 is pressed by the leaf spring 41 so as to abut on the inner surface of the fixing belt at a position where the amount of heat generation is highest at the downstream side of the opening 26 a of the inner core 26 in the rotation direction of the fixing belt. Has been. If the temperature sensor 28 is brought into contact with the inner surface of the fixing belt with a leaf spring on the upstream side in the fixing belt rotation direction with respect to the opening 26a of the inner core 26, a stable contact pressure may not be maintained due to flapping of the fixing belt 23 or the like. Therefore, it is desirable to provide it on the downstream side.

  FIG. 8 shows the calorific value distribution of the fixing belt 23 at the portion facing the coil 32 (development view). There are portions H and H that generate a large amount of heat in two places. That is, the position where the heat generation amount of the fixing belt 23 is the highest is the central portion of the coil 32 in the fixing belt rotation direction shown in FIG. 3 and FIG. The temperature sensor 28 is disposed in contact with a position on the inner surface of the fixing belt 23 where the amount of heat generated by the coil 32 is the highest.

In the present embodiment, an insulating seat portion 42 in which the base portion of the second leaf spring 43 is molded is fixed to the inner surface of the pressure stay 25. The second leaf spring 42 also extends to the outside of the inner core 26 through the opening 25 a of the pressure stay 25 and the opening 26 a of the inner core 26. The leaf spring 42 is bent near the opening of the inner core 26 and upstream of the opening 26a in the fixing belt rotation direction, and a safety element (thermal fuse) 29 is attached to and supported at the tip. . The security element 29 is elastically in contact with the inner surface of the fixing belt 23 by the elasticity of the leaf spring 43 at a substantially central position in the longitudinal direction of the fixing belt 23. The leaf spring 43 may or may not serve as the electrode of the safety element 29. However, when the lead wire 29a is provided separately, the leaf spring 43 is provided with heat resistance inside the leaf spring 42 in order to prevent friction with the fixing belt 23. It is better to fix with tape. The safety element 29 is connected in series to the excitation circuit 101 via a lead wire 29a. The lead wire 29a traverses the inside of the pressure stay 25 from the insulating seat portion 42 and is drawn outward from one end portion (left end portion) of the fixing belt 23 in the rotation axis direction, like the signal wire 28a of the temperature sensor 28. Yes. The security element 29 is also brought into contact with a region where the amount of heat generated by the coil 32 inside the fixing belt 23 is the highest, and the temperature of that portion is detected. In this embodiment, as shown in FIGS. 3 and 8, the safety element 29 is in contact with the inner surface of the fixing belt at a position where the amount of heat generation is higher on the upstream side in the fixing belt rotation direction than the opening 26 a of the inner core 26. The plate spring 43 is pressed.

The safety element 29 is turned off when the fixing device 12 is caused to run out of heat for some reason and the temperature of the fixing belt 23 is overheated to an allowable temperature or more, and the power supply from the excitation circuit 101 to the coil 32 is quickly cut off. To do. If an image forming job is being executed, the job is also interrupted. As a result, the fixing device (fixing belt) can be prevented from being damaged. At this time, control is performed to display the fact that the image forming apparatus, particularly the fixing device is in an abnormal state, on the operation unit 102 (FIG. 7) including a liquid crystal display unit provided in the image forming apparatus to prompt the operator to repair the image forming apparatus. The circuit unit 100 outputs a signal.

  The size of the opening 26a provided in the inner core 26 and the size of the opening 25a provided in the pressure stay 25 are the same. Alternatively, the opening 26 a provided in the inner core 26 is smaller in size than the opening 25 a provided in the pressure stay 25. That is, the openings 25a and 26a of the pressure stay 25 and the inner core 26 have an opening width of the opening 25a so that an induction current is not generated in the metal pressure stay 25 by the coil 32. It is desirable to be configured narrower than the width. This is because when an induced current is generated in the metal pressure stay 25 in the fixing belt 23, a current flows in the direction of the magnetic field in the pressure stay 25, and the demagnetizing field reduces the heat generation amount of the fixing belt 23. Because it ends up. Further, if the opening width of the opening portion 25a of the pressure stay 25 is set to an opening width of 80 mm or more in the longitudinal direction among the length 360mm of the pressure stay 25, the bending strength of the pressure stay 25 is insufficient. . Therefore, the applied pressure in the fixing nip portion N is not uniform, and there is a possibility that image defects such as uneven glossiness may occur. From this point, it is desirable that the longitudinal opening width of the opening 25 a of the pressure stay 25 be suppressed to 20% or less of the length of the pressure stay 25 in the longitudinal direction. That is, the opening width of the opening 25 a provided in the pressure stay 25 in the pressure stay longitudinal direction (metal stay longitudinal direction) is 20% or less of the length of the pressure stay 25. The inner core 26 covers the outside of the pressure stay 25 so that a plurality of cores are bonded together as indicated by a dividing line a in FIG. The opening 26a of the inner core 26 is formed by partially increasing the interval between the plurality of cores.

  Next, the heat distribution of the cross section of the fixing belt when the openings 26a and 25a are provided in a part of the inner core 26 and the pressure stay 25 for the arrangement of the temperature sensor 28 and the wiring of the signal line 28a of the temperature sensor 28. Will be described in detail.

  FIG. 9 and FIG. 10 are developed schematic views of the coil 32, the fixing belt 23, the inner core 26, and the pressure stay 25, and a calorific value distribution diagram in the circumferential direction of the fixing belt 23 in the cross section of the fixing device. It is. The portion A is a portion corresponding to the inner width portion (the magnetic core 33a portion at the center of the coil) in the cross section of the wound coil 32. The portion B is a portion corresponding to the central portion in the width direction of each coil portion on the upstream side and the downstream side in the rotation direction of the fixing belt with respect to the inner width portion in the cross section of the wound coil 32.

  FIG. 9A shows a case where the inner core 26 and the pressure stay 25 are not provided with openings 26a and 25a. At this time, the heat generation amount distribution in the circumferential direction of the fixing belt 23 increases heat generation in the portions B and B and decreases heat generation in the portion A. This is because the magnetic field generated by the coil 32 in the direction of the surface of the fixing belt 23 increases the amount of heat generated by strengthening the magnetic field by the current flowing in the same direction in the portion B. In the portion A, the surface direction of the fixing belt 23 is caused by currents flowing in opposite directions between the coil portions on the upstream side and the downstream side in the fixing belt rotation direction relative to the inner width portion in the cross section of the wound coil 32. The amount of heat generated is reduced by weakening the magnetic field.

  Therefore, in order to accurately control the temperature of the fixing belt 23 based on the temperature detection of the temperature sensor 28, the temperature sensor 28 is not connected to the portion B where the heat generation amount of the fixing belt 23 is high but the portion B where the heat generation amount is high. It is necessary to provide a detector.

  Further, the heat generation efficiency of the fixing belt 23 in the case of FIG. 9A was 0.96. The belt heat generation efficiency is calculated from the resistance Rc (Ω) of the single coil measured by an impedance analyzer (Yokogawa Hewlett Packard 4194A) and the resistance Rc + b (Ω) in a state where the fixing belt is opposed to the belt. -(Rc / Rc + b). The meaning of this expression means the heat generation ratio of the fixing belt to the heat generation of the whole (coil + fixing belt). For example, when the distance between the coil and the fixing belt increases and the magnetic coupling becomes weak, the current flowing through the fixing belt decreases. As a result, the current circulating in the coil itself increases, and the ratio of heat generation in the coil increases. Thus, by comparing the heat generation efficiency, it can be determined whether or not the fixing belt can be efficiently heated.

  Next, with reference to FIG. 9B and FIG. 10, openings 26 a and 25 a are provided in a part of the inner core 26 and the pressure stay 25 in order to rotate the signal line 28 a of the temperature sensor 28. The case will be described.

Example 1: (b) of FIG.
As shown in FIG. 9B, the portion A is provided with the inner core 26 and the openings 26 a and 25 a of the pressure stay 25. The opening width in the circumferential direction of the fixing belt of the openings 26a and 25a is 5 mm, which is the same as the inner width D in the cross section of the coil 32, and the opening width in the longitudinal direction is also 5 mm.

  That is, according to the first embodiment, the openings 32a and 25a are provided in the portion of the inner core 26 and the portion of the pressure stay 25 corresponding to the portion A where the coil 32 weakens the magnetic field in the plane of the fixing belt 23. Is.

  The calorific value distribution in the circumferential direction of the fixing belt 23 according to the first exemplary embodiment is substantially the same as that in the case of FIG. 9A in which the inner core 26 and the pressure stay 25 are not provided with the openings 26a and 25a. Obtained. The heat generation efficiency was 0.96, the same as in the case of FIG.

Comparative Example 1: (a) of FIG.
As shown in FIG. 10A, the portion B is provided with the inner core 26 and the openings 26 a and 25 a of the pressure stay 25. The opening width in the circumferential direction of the fixing belt of the openings 26a and 25a is 5 mm, which is the same as the inner width D in the cross section of the coil 32, and the opening width in the longitudinal direction is also 5 mm.

  That is, in this comparative example 1, the openings 26a and 25a are provided in the portion of the inner core 26 and the portion of the pressure stay 25 corresponding to the portion B where the circumferential magnetic field due to the current of the coil 32 is the strongest. Is.

  In the heat generation amount distribution in the circumferential direction of the fixing belt 23 in the comparative example 1, the heat generation amount in the portions corresponding to the openings 26a and 25a is reduced. The heat generation efficiency at this time was 0.91.

Comparative Example 2: (b) of FIG.
As shown in FIG. 10B, the inner core 26 and the openings 26 a and 25 a of the pressure stay 25 are provided in the outer portion C of the opposed region of the coil 32. The opening width in the circumferential direction of the fixing belt of the openings 26a and 25a is 5 mm, which is the same as the inner width D in the cross section of the coil 32, and the opening width in the longitudinal direction is also 5 mm.

  In the heat generation amount distribution in the circumferential direction of the fixing belt 23 in the comparative example 2, the heat generation amount in the portions corresponding to the openings 26a and 25a is reduced. The heat generation efficiency at this time was 0.92.

Comparative Example 3: (c) of FIG.
In the first embodiment, the openings 26a and 25a of the inner core 26 and the pressure stay 25 are 7 mm wider than the inner width D (5 mm) of the coil 32 in the circumferential direction of the fixing belt (FIG. 10). (C)).

  If the opening width of the opening 26a of the inner core 26 in the fixing belt circumferential direction is made wider than the inner width D of the coil 32 as in the comparative example 3, the magnetic core 33a and the inner core 26 at the center of the coil. The interval between and becomes wider. As a result, the magnetic coupling becomes weak, and as a result, the heat generation amount of the fixing belt 23 is reduced. The heat generation efficiency at this time was 0.93. Therefore, it is desirable that the opening widths of the openings 26a and 25a are narrower than the inner width D of the coil 32 so that the magnetic coupling does not become too weak.

  As described above, in this embodiment, the temperature detection unit of the temperature sensor 28 is disposed at the location B where the heat generation amount of the fixing belt 23 is the highest. Further, in the region A where the coil 23 weakens the magnetic field of the fixing belt 23, the opening widths of the inner core 26 and the openings 26 a and 25 a of the pressure stay 25 are narrower than the inner width D of the coil 32 in the fixing belt circumferential direction. Configure. A signal line 28 a of the temperature sensor 28 is disposed inside the pressure stay 25.

  With this configuration, noise and damage of the signal line 28a of the temperature sensor 28 and a decrease in the heat generation amount of the fixing belt 23 can be prevented, and temperature control can be performed accurately and uniformly at the portion where the heat generation amount of the fixing belt 23 is the highest. Is possible.

  In the present embodiment, the opening 26 a is formed by opening a gap between the plurality of internal cores 26 bonded to the pressure stay 25, but the opening 26 a may be formed by making a hole in the internal core 26. .

  In this embodiment, the thermistor as the temperature detection element is described as an example. However, there is no problem even if it is applied to a thermo switch, a temperature fuse, or the like.

  In the embodiment described above, the belt member is used as the heat generating member. However, the same effect as the configuration using the belt member can be obtained even if a thin film member is used as the heat generating member.

  The image heating apparatus of the present invention is not only used as the image heating and fixing apparatus of the embodiment, but also, for example, an image heating apparatus that heats a recording material carrying an image and modifies surface properties such as glossiness, and an image to be worn. It can also be used as a heating device. Further, in an ink jet image forming apparatus, it can also be used as an image heating apparatus for drying a recording material on which an image is formed by an ink jet system.

It is a front model figure of the principal part of the fixing device (image heating device) of an example. It is also a longitudinal front model view. FIG. 3 is an enlarged cross-sectional model view taken along line (3)-(3) in FIG. 1. It is a disassembled perspective view of the structural member of a belt unit. FIG. 3 is a layer configuration model diagram of a fixing belt. It is a top view of a coil. It is a block diagram of a control system. It is a calorific value distribution diagram in a portion (development view) facing the coil unit of the fixing belt. It is explanatory drawing of the heat_generation | fever distribution of Example 1. FIG. It is explanatory drawing of the heat_generation | fever distribution of a comparative example. 1 is a schematic configuration model diagram of an example of an image forming apparatus.

Explanation of symbols

  12 .... Fixing device (image heating device), 21 .... belt unit, 22 .... pressure roller (pressure member), 31..coil unit, N..nip portion (fixing nip portion), 23..fixing Belt (heating belt), 23a ... conductive layer, 25 ... pressure stay (metal stay), 26 ... internal magnetic member, 25a, 26a ... opening, 28 ... temperature sensing element, 28a ... signal line 31 .. Heating means, 32 .. Coil, 33 .. Magnetic core, 33 a .. Magnetic core in the center of the coil, T .. Image, P .. Recording material

Claims (6)

A heating belt that has a conductive layer and is rotatable, a pressure member that is in pressure contact with the outer peripheral surface of the heating belt and is rotatable, and is located inside the heating belt so that the heating belt is directed toward the pressure member. A metal stay to be pressed, an inner magnetic member covering the inner peripheral surface of the heating belt of the metal stay, and disposed in the vicinity of the inner surface of the heating belt; and the heating belt disposed on the outer side of the heating belt. Heating means having a coil for generating an induced current in the conductive layer and a magnetic core, wherein the coil is configured to wind a part of the magnetic core, and the temperature of the heating belt. And a temperature control means for controlling the temperature of the heating belt based on the detection value of the temperature detection element, and carries an image at a nip portion between the heating belt and the pressure member. Shi An image heating apparatus for heating a recording material,
The temperature detection element is in contact with the inner surface of the heating belt, and the coil of the magnetic core is wound around the signal line of the temperature detection element around the internal magnetic member and the metal stay. An image heating apparatus, wherein the image heating apparatus is wired inside the metal stay through an opening provided at a position facing a part of the metal stay, and drawn from an end of the metal stay.   2. The image heating apparatus according to claim 1, wherein the temperature detection element is in contact with a portion of the inner surface of the heating belt that generates the highest amount of heat in the circumferential direction of the heating belt.   3. The image heating apparatus according to claim 1, wherein a width of the opening in a circumferential direction of the heating belt is narrower than an inner width in a cross section of the wound coil.   4. The image heating according to claim 1, wherein an opening width of the opening provided in the metal stay in a longitudinal direction of the metal stay is 20% or less of a length of the pressure stay. 5. apparatus.   The opening provided in the magnetic core and the opening provided in the metal stay have the same size, or the opening provided in the magnetic core is provided in the metal stay. The image heating apparatus according to claim 1, wherein the image heating apparatus is smaller in size than the opening.   The image heating apparatus according to claim 1, wherein the temperature detection element is in contact with an inner surface of the heating belt at a downstream side of the opening in the rotation direction of the heating belt.