JP2017198824A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device which reduces slip of a heating rotating body.SOLUTION: An image heating device comprises: a heating rotating body and a pressurizing rotating body which form a nip part for heating an image on a recording material; a pressurization mechanism for pressurizing at least one of the heating rotating body and the pressurizing rotating body toward the other; a pressurization force changing mechanism which is capable of changing a pressurization force at the nip part by the pressurization mechanism to a first pressurization force or a second pressurization force which is lower than the first pressurization force; and a control part which controls the pressurization force changing mechanism and sets the pressurization force by the pressurization mechanism to the first pressurization force or the second pressurization force on the basis of a type of the recording material on which image heating processing is performed. The control part sets the pressurization force to the first pressurization force during execution of a preliminary rotating operation of the device for raising its temperature to a prescribed temperature by starting rotation of the heating rotating body and the pressurizing rotating body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image heating apparatus that heats a toner image on a recording material. This image heating apparatus can be used in an image forming apparatus such as an electrophotographic copying machine, a printer, a fax machine, or a multi-function machine thereof.

  In an electrophotographic image forming apparatus, a process of fixing a toner image on a recording material (recording medium, medium: hereinafter referred to as paper or paper) through charging, exposure, development, transfer, and fixing steps is generally used. It is.

  In an image forming apparatus, there are various fixing devices that are image heating devices that heat an unfixed toner image formed on a sheet. For example, as an on-demand method with high heat transfer efficiency and quick start-up of the device, a belt heating method fixing device that heats through a fixing belt (film) with a small heat capacity, that is, a belt fixing device has been proposed.

  The belt fixing device includes, for example, a ceramic heater (hereinafter referred to as a heater) as a fixed and supported heating body, and a heat-resistant resin belt (fixing belt: hereinafter abbreviated as a belt) as a heat transfer member that slides on the heater. Have). Further, an elastic pressure roller is provided as a pressure member that forms a fixing nip portion (hereinafter abbreviated as a nip portion) as a toner image heating and fixing region by being pressed against the heater via the belt. A sheet carrying an unfixed toner image is nipped and conveyed between the belt in the nip and the pressure roller, and the unfixed toner image is heated and melted and fixed on the sheet by heat from the heater via the belt. It is.

  In recent years, an IH (electromagnetic induction heating) type fixing device has been proposed in order to meet the needs of energy saving and speedup of an image forming apparatus. The IH type fixing device generates an eddy current in a thin heat generating layer provided in a heating rotating body by means of a magnetic field generated by an exciting coil as means for heating a heating rotating body (fixing rotating body) as a heated body, and generates Joule heat. This is a method of generating heat.

  In this method, the heat generation source is the fixing rotator itself, and there are few members interposed until reaching the nip portion. Therefore, as compared with a heat roller system using a halogen lamp, the time required for the temperature of the surface of the heating rotator to be an appropriate temperature for fixing can be shortened when the fixing device is started. Further, since the heat transfer path from the heat generation source to the toner melting point is short and simple, the heat efficiency is also high.

  The IH type fixing device includes a magnetic flux generating means including an exciting coil, a heating rotating body including a heat generating layer, and a magnetic core. There has also been proposed a fixing device in which the heating speed by IH is combined with an on-demand low heat capacity, and the startup time of the fixing device is shortened. On the other hand, in recent years, there has been an increasing need for a wide variety of paper such as envelopes and label paper.

  In these fixing devices, the heating rotator and the pressure rotator are pressed by the urging means, and the elastic layer provided on the heating rotator or the pressure rotator is elastically deformed to form the nip portion. . When the pressure applied by the urging means is low, the fixed image may not be glossy or the fixing property may be insufficient in the first place.

  However, when the pressure is high, the envelope may be wrinkled when the envelope is fed. This is because the applied pressure is high, and a large stress is applied to the paper, so that a plurality of papers overlap each other like an envelope. Therefore, in order to prevent such a problem, it is necessary to set the fixing pressure to be low.

  In order to achieve both the glossiness and fixability of plain paper and the like, as well as the wrinkling of the envelope and the peeling of the label paper, the pressure of the fixing device is made variable. A configuration is conceivable in which the heating rotator and the pressure rotator are brought into contact with each other with a high pressure when passing plain paper, and the pressure is set low when passing an envelope or label paper. As described above, there is a configuration example disclosed in Patent Document 1 as a configuration example that can change the pressing force of the fixing device.

JP 2007-101861 A

  According to the prior art, envelope wrinkles can be reduced by lowering the pressure of the fixing device when the envelope is fed. Further, in order to prevent generation of envelope wrinkles in a wide variety of envelopes, it is important to reduce the applied pressure as much as possible.

  However, if the applied pressure is too low, the driving force from the pressure rotator is not sufficiently transmitted to the heating rotator, and the heating rotator may slip.

  The present invention is a further development of this prior art. An object of the present invention is to provide an image heating apparatus that reduces the slip of the heating rotator.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a heating rotator and a pressure rotator that form a nip portion for heating an image on a recording material, and the heating rotation. A pressurizing mechanism for pressurizing at least one of the body and the pressurizing rotating body toward the other, and the pressurizing force of the nip portion by the pressurizing mechanism from the first pressurizing force and the first pressurizing force A pressurizing force change mechanism that can be changed to a lower second pressurizing force, and a control unit that controls the pressurizing force change mechanism, and is based on the type of recording material to be subjected to image heating processing, And a controller that sets the pressure to the first applied pressure or the second applied pressure, and the controller starts rotation of the heating rotator and the pressure rotator to a predetermined temperature. When the pre-rotation operation of the device for starting up is performed, the applied pressure is And setting the first pressure.

  ADVANTAGE OF THE INVENTION According to this invention, the image heating apparatus which reduces the slip of a heating rotary body can be provided.

Flowchart for explaining the control of the first embodiment. Configuration schematic diagram of an example of an image forming apparatus Front view of the fixing device of the embodiment Enlarged cross-sectional view of the main part of the device Side view of one end of the device Side view of the other end of the device The perspective view of the principal part of the apparatus which omitted the coil unit and cut off a part It is a top view of the principal part of the apparatus F which excluded the coil unit, and is the figure which shows the time of the state in which the paper S is introduced (A) is a schematic diagram of the layer structure of the fixing belt, (b) is a perspective view of the coil unit with the cover plate omitted, and viewed from the inside, (c) is a perspective view of the belt internal assembly in the belt unit. Block diagram of the control system (mainly showing relevant parts of the fixing device) Partially cutaway perspective view of one end of the fixing device Enlarged front view of one end of the fixing device 12 is an enlarged cross-sectional view taken along line (13)-(13) in the normal pressure mode. 12 is an enlarged cross-sectional view taken along line (14)-(14) in FIG. 12 (in normal pressure mode). Cam phase diagram Enlarged sectional view of the pressure mechanism on one end (in envelope pressure mode) Partially cutaway perspective view of one end of the fixing device (in pressure release mode) Timing chart in normal pressure mode Timing chart in low pressure mode Flowchart for explaining the control of the second embodiment. Timing chart in low pressure mode

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best mode of the present invention, the present invention is not limited to these examples.

Example 1
[Image forming apparatus]
FIG. 2 is a schematic sectional view of an example of the image forming apparatus. The image forming apparatus 1 is a tandem-intermediate transfer full-color electrophotographic copying machine equipped with an automatic document feeder 2.

  UY, UM, UC, and UK are four image forming units that form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Each image forming unit includes a photosensitive drum 3, a charger 4, a laser scanner 5, a developing device 6, a primary transfer charger 7, and a drum cleaner 8. In order to avoid complication of the drawing, the reference numerals for these devices in the image forming units UM, UC, UK other than the image forming unit UY are omitted. Further, since the electrophotographic process and image forming operation of these image forming units are known, the description thereof will be omitted.

  The toner images of the respective colors are primarily transferred onto the intermediate transfer belt 9 that is rotated from the drum 3 of each image forming unit in a predetermined manner. As a result, a four-color superimposed toner image is formed on the belt 9. On the other hand, a recording material (sheet: hereinafter referred to as paper or paper) S is fed from the cassette 10 or 11 or the manual feed tray 12 to one sheet. The sheet S passes through the conveyance path 13 and is introduced into the secondary transfer nip portion which is a pressure contact portion between the belt 9 and the secondary transfer roll 15 at a predetermined control timing by the resist roll pair 14. As a result, the four color superimposed toner images on the belt 9 are secondarily transferred onto the sheet S at once.

  In the image forming apparatus 1 according to the present exemplary embodiment, the mechanism unit is an image forming unit that forms an unfixed toner image on the sheet (recording material) S. The sheet S is introduced into a fixing device (fixing device) F, which is an image heating device, and heated and pressurized, whereby an unfixed toner image is melted and softened and fixed as a fixed image. In the single-sided image forming mode, the sheet S exiting the fixing device F is introduced to the conveyance path 16 side by the path control and is discharged onto the discharge tray 17.

  In the double-sided image forming mode, the sheet S on which the single-sided image has been formed exiting the fixing device F is introduced to the reverse conveyance path 18 side by route control, then switched back and introduced into the double-side conveyance path 19. Then, in a state where the front and back sides are reversed, the toner image is again formed through the conveyance path 13 and introduced into the secondary transfer nip portion to form a toner image on the back surface. Thereafter, it is introduced into the fixing device F as in the case of single-sided image formation, and is discharged as a double-sided image formed product onto the discharge tray 17. In the image forming apparatus 1 according to the first exemplary embodiment, the conveyance of the large and small width sheets S is performed based on a so-called central reference at the center of the sheet width. An apparatus configuration that performs sheet conveyance on a so-called one-side basis may also be used.

  Reference numeral 102 denotes an operation unit of the image forming apparatus 1. The operation unit 102 is a user interface (UI: User Interface, input unit, display unit) that exchanges electrical information with the control unit (printer control unit) 100 (FIG. 10). The operation unit 102 inputs an image forming mode setting and an instruction from the user (operator, user) to the control unit 100. In addition, the control unit 100 notifies the user of the state of the device to the operation unit 102. The control unit 100 comprehensively controls all the mechanism units of the image forming apparatus 1.

  As illustrated in FIG. 10, the operation unit 102 includes a main switch M-SW, an input unit (operation panel) 104, and a display unit (display: UI screen) 105. The input unit 104 is provided with various operation keys such as a ten key group for inputting the number of values, a print start button, a stop key, and a power saving button. The display unit 105 is a touch panel type liquid crystal screen, and displays various information such as a sheet display that allows selection of a sheet to be used, and various operation buttons. Various setting information of operation performed by the image forming apparatus, recording material information, and the like are also input to the control unit 100 by the displayed operation buttons.

  Various setting information of operation performed by the image forming apparatus, recording material information, and the like are also input to the control unit 100 from an external host device 200 such as a PC.

[Fixing device]
Regarding the fixing device F described below, the front side is the entrance side of the sheet S and the back side is the exit side of the sheet S. Left and right are left or right when the device F is viewed from the front side. In the present embodiment, the right side is one end side (drive side) and the left side is the other end side (non-drive side). Up and down are up or down in the direction of gravity. The upstream side and the downstream side are the upstream side and the downstream side in the conveyance direction (recording material conveyance direction) of the sheet S.

  3 is a front view of the fixing device F, FIG. 4 is an enlarged cross-sectional view of the main part of the device F, and FIGS. 5 and 6 are side views of one end side and the other end side of the device F, respectively. FIG. 7 is a perspective view of the main part of the apparatus F with the coil unit omitted and a part cut away, and FIG. 8 is a plan view of the main part of the apparatus F without the coil unit. It shows the state when FIG. 9A is a schematic diagram of the layer structure of the fixing belt, FIG. 9B is a perspective view of the coil unit viewed from the inside without the cover plate, and FIG. 9C is a perspective view of the belt internal assembly in the belt unit. FIG. 10 is a block diagram of the control system, and mainly shows the relevant part of the fixing device F.

  The fixing device F of this embodiment is an IH (induction heating) type-belt type image heating device, and roughly includes the following members and mechanisms.

a: Belt unit 20 including a flexible endless belt (hereinafter, referred to as a fixing belt or a belt) 21 as a first rotating body (heating rotating body: fixing member) that comes into contact with the toner image carrying surface of paper S
b: Pressure roller 30 having elasticity as a second rotating body (pressure rotating body: pressing member) facing the belt 21
c: Coil unit (induction heating device, magnetic flux generation means) 40 as a heater for heating the belt 21
d: Pressure mechanisms 500R and 500L that form a nip portion N that presses the belt 21 and the pressure roller 30 to heat an image on a sheet (on a recording material) (image heating processing: fixing).
e: Pressure changing mechanism capable of changing the pressure applied to the nip portion N by the pressurizing mechanisms 500R and 500L. f: A side plate on one end side and the other end side disposed on the bottom plate 61 and fixedly opposed to the bottom plate 61. An apparatus frame (chassis, housing) 60 having 62R and 62L and accommodating the above-described members and mechanisms.
(2-1) Belt unit 20
The belt unit 20 includes an endless belt 21 having a metal layer. The belt assembly includes a fixing pad 22, a pad member 23 that holds the fixing pad 22, a stay 24 that holds the pad member 23, and an inner core (inner magnetic core) 25 that covers the stay 24. . FIG. 9C is a perspective view of the belt inner assembly.

  The fixing pad 22, the pad member 23, and the stay 24 are all members that are long in the longitudinal direction (width direction) of the belt 21. One end portion and the other end portion of the stay 24 protrude outward from both end portions of the belt 21, and flange members 26R and 26L on one end side and the other end side are fitted to the protruding portions, respectively. The belt 21 is loosely fitted on the outside of the belt inner assemblies 22 to 25 between the opposing surfaces of the flange members 26R and 26L.

  A temperature sensor (temperature detection element) TH1 such as a thermistor is disposed in the longitudinally central portion of the stay 24 via an elastic support member 27. This sensor TH1 is elastically applied to the inner surface of the belt 21 in the widthwise central portion. It is in contact. As a result, even if a position variation such as the sensor contact surface of the rotating belt 21 undulates, the sensor TH1 follows this to maintain a good contact state with the inner surface of the belt 21.

  FIG. 9A is a layer configuration model diagram of the belt 21. The belt 21 has a metal base layer 21a having an inner diameter of about 20 to 40 mm. As the metal of the base layer 21a, an iron alloy, a nickel alloy, copper, silver, or the like can be appropriately selected.

  A heat resistant rubber layer is provided as an elastic layer 21b on the outer periphery of the base layer 21a. The thickness of the rubber layer is preferably set within a range of 100 to 800 μm. In the present embodiment, the thickness of the rubber layer is set to 200 μm in consideration of reducing the heat capacity of the belt 21 to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. Further, a fluororesin layer (for example, PFA or PTFE) is provided on the outer periphery of the elastic layer 21b as the surface release layer 21c.

  On the inner surface side of the base layer 1a, in order to reduce the sliding friction between the inner surface of the belt 21 and the temperature sensor TH, a slidable layer 21d having a high slidability may be provided at 10 to 50 μm. In this embodiment, a 30 μm polyimide layer is provided, and heat resistant grease as a lubricant is applied to the surface of the polyimide layer to maintain the lubricity of the inner surface of the belt 21.

  The pad member 23 holding the fixing pad 22 applies a pressing force between the belt 21 and the pressure roller 30 to form the nip portion N. The fixing pad 22 is made of a material having high hardness such as a metal such as stainless steel or ceramics, and has a shape extending in the longitudinal direction with a thickness of about 1 mm. The material of the pad member 23 is made of a heat resistant resin such as PPS or LCP.

  The stay 24 that holds the pad member 23 is a metal-made rigid member because it needs rigidity to apply pressure to the nip portion N. As a material of the stay 24, it is desirable that only the belt 21 generates heat by the coil unit 40 as a heater, and a non-magnetic material such as stainless steel which is not easily affected by induction heating is desirable.

  An inner core 25 is provided on the stay 24 on the coil unit 40 side in order to perform induction heating more effectively. As shown in FIG. 9C, the inner core 25 is divided into a plurality of parts in the longitudinal direction, and is arranged so as to gradually change the distance between the coil unit 40 and an exciting coil 41 described later. The inner core 25 is made of a material having high permeability such as ferrite that shields the magnetic flux so that the magnetic flux generated by applying a high-frequency current to the exciting coil 41 can be used more efficiently for heating the belt 21.

  The belt unit 20 engages flange members 26R and 26L on one end side and the other end side with vertical guide slit portions 62a formed on the side plates 62R and 62L on one end side and the other end side of the device frame 60, respectively. Are arranged. Therefore, the belt unit 20 as a whole has a degree of freedom to move vertically between the side plates 62R and 62L along the slit portion 62a.

(2-2) Pressure roller The pressure roller 30 is an elastic roller having an outer diameter of 30 mm, in which a metal cored bar 30a is provided with a rubber layer as an elastic layer 30b and a release layer 30c is provided on the surface. The pressure roller 30 is disposed on the lower side of the belt unit 20 so that its axial direction is substantially parallel to the longitudinal direction of the belt unit 20 and is rotatable between the side plates 62R and 62L via a bearing 63.

  A first drive gear G1 is disposed concentrically and integrally at an end portion on one end side of the core metal 30a. The driving force of the first motor (driving source) M1 controlled by the control unit 100 is transmitted to the gear G1 via a transmitting means (not shown), and the pressure roller 30 is used as a driving rotating body in FIG. At a predetermined speed in the counterclockwise direction of the arrow R30.

(2-3) Coil unit 40
The coil unit 40 is a heater for induction heating of the belt 21 and is disposed on the upper side of the belt unit 20. The coil unit 40 is configured by assembling an exciting coil (coil that generates magnetic flux) 41, an outer core (outer magnetic core) 42, and the like inside a long housing 43 along the longitudinal direction of the belt 21.

  The housing 43 is a horizontally long box-shaped molded product made of heat-resistant resin (a molded member having an electric insulating resin thickness of about 2 mm). The bottom plate 43 a side of the housing 43 is a surface facing the belt 21. The bottom plate 43a is curved inward of the housing 43 so as to follow a substantially half-circumferential range of the outer peripheral surface of the belt 21 in the cross section.

  In the coil unit 40, both end portions of the housing 43 are received by one end side and the other end side flange members 26 </ b> R and 26 </ b> L of the belt unit 20. As a result, the bottom plate 43a of the housing 43 faces the upper surface of the belt 21 with a predetermined gap (gap) α. In the coil unit 40, side plates on one end side and the other end side of the housing 43 are tied to flange members 26R and 26L on the respective sides by wire springs (not shown). That is, the coil unit 40 is integrated with the belt unit 20.

  Accordingly, when the flange members 26R and 26L of the belt unit 20 are pressed by the pressurizing mechanisms 50L and 50R and sink as described later, the coil unit 40 also sinks together with the belt unit 20 while maintaining the gap α. Further, when the flange members 26R and 26L are floated by being depressurized or released, the coil unit 40 is also floated together with the belt unit 20 while maintaining the gap α.

  The coil 41 is formed by using, for example, a litz wire as an electric wire, which is horizontally long and shaped like a ship bottom, and is opposed to the peripheral surface and part of the side surface of the belt 21. And it is applied to the inner surface of the bottom plate 43a that is curved to the inside of the housing and is housed inside the housing. A high frequency current of 20 to 60 kHz is applied to the coil 41 from a power supply device (excitation circuit) 101 controlled by the control unit 100. The metal layer (conductive layer) of the belt 21 is inductively heated by the magnetic field generated by the coil 41 due to this current application.

  The outer core 42 is an outer magnetic core that covers the coil 41 so that the magnetic field generated by the coil 41 does not substantially leak except for the metal layer (conductive layer) of the belt 21. And the outer core 42 is divided | segmented into 2 or more along the longitudinal direction, and is arrange | positioned along with the longitudinal direction like FIG.9 (b).

(2-4) Fixing Operation In the standby state (standby state) of the image forming apparatus 1, in the fixing device F, the pressure applied to the nip portion N by the pressure mechanisms 500R and 500L described later is substantially released by the pressure change mechanism. The pressure release mode (pressure release state) is maintained. The drive motor M1 is turned off, and the rotation of the pressure roller 30 is stopped. Power supply to the coil 41 of the coil unit 40 is turned off.

  Based on the input of the print job start signal (image forming job start signal), the control unit 100 starts the rotation of the pressure roller 30 and the belt 21 and raises the fixing device F to a predetermined temperature. A pre-rotation operation (preparation operation prior to the image forming operation) is executed.

  That is, the control unit 100 controls the pressurizing force changing mechanism at a predetermined control timing to place the pressurizing mechanisms 500R and 500L in a predetermined pressurizing mode (pressurized state). Thereby, the stay 24 of the belt unit 20 is pressurized to a predetermined pressure via the flange members 26R and 26L, and the in-belt assembly resists the elasticity of the elastic layer 30b against the pressure roll 30 via the belt 21. Pressurized. As a result, the fixing pad 22 is pressed against the pressure roller 30 via the belt 21, and a nip portion N having a predetermined width is formed between the belt 21 and the pressure roll 30 in the sheet conveyance direction a.

  Further, the control unit 100 turns on the drive motor M1. As a result, the pressure roller 30 is rotationally driven at a predetermined speed in the counterclockwise direction of the arrow R30 in FIG. Due to the rotation of the pressure roller 30, a rotational force acts on the belt 21 by a frictional force between the surface of the pressure roller 30 and the surface of the belt 21 in the nip portion N. While the inner surface of the belt 21 is in close contact with the fixing pad 22 and slides, the outer periphery of the belt inner assemblies 22 to 25 is driven to rotate in the clockwise direction indicated by an arrow R21 in FIG. . Movement in the thrust direction accompanying the rotation of the belt 21 is regulated by the flange portions of the flange members 26R and 26L.

  The control unit 100 applies a high-frequency current (alternating current) of 20 kHz to 60 kHz to the coil 41 from the power supply device (excitation circuit) 101. The coil 41 generates an alternating magnetic flux (magnetic field) by supplying a high frequency current. The alternating magnetic flux is guided to the metal layer 21 a of the belt 21 on the upper surface side of the belt 21 rotating by the core 42. Then, an eddy current is generated in the metal layer 21a, the metal layer 21a is self-heated (electromagnetic induction heat) by Joule heat due to the eddy current, and the belt 21 is heated.

  That is, when the rotating belt 21 passes through the region where the magnetic field generated from the coil unit 40 is present, the metal layer 21a generates heat by electromagnetic induction and is heated all around. The temperature of the belt 21 is detected by the temperature sensor TH1. The temperature sensor TH <b> 1 detects the temperature of the portion of the belt 21 that is the paper passing area, and the detected temperature information is fed back to the control unit 100. The control unit (temperature control function unit) 100 is a power source so that the detected temperature (information about the detected temperature) input from the sensor TH1 is maintained at a predetermined target temperature (fixing temperature: information corresponding to the predetermined temperature). The power supplied from the apparatus 101 to the coil 41 is controlled.

  In the present embodiment, the temperature is adjusted by changing the frequency of the high-frequency current based on the detection value of the temperature sensor TH so as to be constant at the target temperature of the belt 21 of 180 ° C., thereby controlling the power input to the coil 41. It is carried out.

  In the pre-rotation operation, the pressure roller 30 is driven, and the belt 21 rises to a predetermined fixing temperature and is in a temperature-controlled state. In this state, the sheet S carrying the unfixed toner image t in the nip N of the fixing device F is introduced from the image forming unit side while being guided by the guide member 64 with the toner image carrying surface side facing the belt 21 side. The The sheet S is in close contact with the outer peripheral surface of the belt 21 at the nip portion N, and is nipped and conveyed along with the belt 21 along the nip portion N.

  As a result, the heat of the belt 21 is mainly applied, and the unfixed toner image t is heat-pressure-fixed on the surface of the paper S under the pressure of the nip portion N. The sheet S that has passed through the nip portion N is self-separated (curvature separation) from the outer peripheral surface of the belt 21 due to deformation of the exit portion of the nip portion N, and further receives separation assistance by the separation guide 65, The paper is discharged and conveyed from the fixing device F by the guide member 66.

  The separation guide 65 has a certain gap (gap between the belt 21 and the belt 21 so that the paper S coming out from the exit portion of the nip portion N does not wind around the belt 21 and does not touch the belt 21 and damage the belt 21. ) Is arranged. The separation guide 65 is engaged with a part of the flange members 26R and 26L and is fixed by a biasing means such as a spring.

  When the print job (print job) ends, the control unit 100 stops the image forming apparatus after a predetermined post-rotation operation and shifts to the standby state. For the fixing device F, the pressure mechanisms 500R and 500L are returned to the pressure release mode. The drive motor M1 is turned off. The power supply to the coil 41 of the coil unit 40 is also turned off.

(2-5) Pressurization Mechanism In the first embodiment, the pressurization mechanisms 500R and 500L press (press) the flange members (pressing members) 26R and 26L of the belt unit 20 to press the belt 21 and the pressure roller 30. Is a mechanism for forming a nip portion N having a predetermined width in the sheet conveyance direction a. In the present embodiment, pressurizing mechanisms 500R and 500L that operate synchronously with the same configuration in the left-right symmetry are provided on the outer sides of the side plates 62R and 62L on one end side and the other end side of the apparatus frame 60, respectively. .

  The pressurizing mechanisms 500R and 500L are configured using a cam (pressure releasing cam) 501 in this embodiment, and include a cam 501, a pressurizing plate rotating shaft 502, a cam rotating shaft 504, a pressurizing plate 505, and pressurizing. The adjustment screw 506, a pressure support plate 507, and a pressure spring 508 are included. The pressure cam rotation shaft 504 is rotatably supported between the side plates 62R and 62L on one end side and the other end side. A cam 501 having the same shape is fixedly attached to one end and the other end of the shaft 504 in the same phase. A second drive gear G2 is attached concentrically to one end of the shaft 504.

  The pressure plate 505 and the pressure support plate 507 are supported by a pressure plate rotation shaft 502, and the pressure plate 505 can move freely with respect to the pressure support plate 507. Further, the pressure support plate 507 is supported by the pressure plate rotation shaft 502 penetrating the side plates 62R and 62L on the one end side and the other end side. It is fixed to the side plates 62R and 62L on the side by means 507b such as screws.

  A pressure adjustment screw 506 is fastened to the pressure support plate 507, and the spring load of the pressure spring 508 is shortened by the seating surface of the screw 506 by tightening the screw 506, and the spring load applied to the pressure plate 505. Can be increased. Since the pressure plate 505 is rotatably supported with respect to the pressure support plate 507 as described above, a moment is generated around the pressure plate rotation shaft 502 by the compression force of the pressure spring 508.

  The pressure plates 505 of the pressure mechanisms 500R and 500L on the one end side and the other end side are disposed so as to contact the upper surfaces of the pressure receiving portions 26a of the flange members 26R and 26L on the one end side and the other end side of the belt unit 20, respectively. ing. Therefore, when the pressure plate 505 is in a free state, the flange members 26R and 26L on the one end side and the other end side are pressed with a predetermined pressure (fixing pressure) in the direction of the pressure roller 30 by the moment generated in the corresponding pressure plate 505. .

  Therefore, the in-belt assemblies 22 to 25 are pressed against the pressure roll 30 against the elasticity of the elastic layer 30 b via the belt 21. As a result, the fixing pad 22 is pressed against the pressure roller 30 via the belt 21, and a nip portion N having a predetermined width is formed between the belt 21 and the pressure roll 30 in the paper conveyance direction a. Usually, the applied pressure is set to 550 N, for example.

  When releasing the applied pressure, the pressurizing cams 501 having predetermined eccentric amounts are simultaneously rotated in the same phase in the pressurizing mechanisms 500R and 500L on the one end side and the other end side, respectively. By the rotation of the pressure cam 501, the pressure plate 505 is pushed up about the shaft 502, and the pressure plate 505 is rotated until the contact between the pressure plate 505 and the flange members 26R and 26L is released, thereby releasing the applied pressure. The rotation of the pressure cam 501 is such that the driving force of the second drive motor M2 controlled by the control unit 100 is transmitted to the second drive gear G2 via the transmission means (not shown), and the shaft 504 is driven. In the pressurizing mechanisms 500R and 500L on the one end side and the other end side at the same time.

(2-6) Pressure Change Mechanism Next, the pressure change mechanism (pressure change mechanism: fixing pressure change mechanism) in this embodiment will be described with reference to FIGS. FIG. 11 is a perspective view of one end side (drive side) of the fixing device F, and a part of the pressure mechanism 500R is cut away. The pressure plate 505 has a first pressure plate (first pressure member) 505A and a second pressure plate (second pressure member) 505B. Both the first and second pressure plates 505A and 505B are rotatably engaged with the pressure support plate 507 about the pressure plate rotation shaft 502. That is, the first and second pressure plates 505A and 505B have the same swing center.

  The first pressure plate 505A is a first pressure spring (first elastic member) 508A, and the second pressure plate 505B is a second pressure spring (second elastic member) 508B. The flange member 26R is urged by a spring in a direction in which the flange member 26R is pressed against the pressure roller 30 side. In this case, the first pressure plate 505A pressurizes the flange member 26R via the second pressure plate 505B. In this embodiment, the first pressure spring 508A and the second pressure spring 508B are on the same straight line in the front-rear direction of the pressure mechanism 500R.

  Since the pressurizing mechanism 500L on the other end is the same mechanism as the pressurizing mechanism 500R on the one end side, the pressurizing mechanism 500R on the one end side will be representatively described below.

  FIG. 12 is an enlarged front view of one end side of the fixing device F. 13 is an enlarged sectional view taken along line (13)-(13) in FIG. 12, and FIG. 14 is an enlarged sectional view taken along line (14)-(14).

  The second pressing plate 505B has a protrusion 702a on a part of the surface that presses the flange member (pressing member) 26R. When the first pressure plate 505A pushes the protrusion 702a, the flange member 26R is simultaneously pressed by the first pressure plate 505A and the second pressure plate 505B.

  The first pressure spring 508A is set so as to generate a higher urging force than the second pressure spring 508B. For example, when a pressing force of 550 N is applied to the nip portion N, the first pressure spring 508A is set to bias 520 N, and the second pressure spring 508 B is set to bias the remaining 30 N. The nip force of 550 N is used for paper such as plain paper, glossy paper, and thick paper. Hereinafter, the state of the applied pressure (first applied pressure) is referred to as “normal pressurizing mode”. By appropriately controlling the pressure in the normal pressurization mode and the paper feeding speed and temperature control temperature, it becomes possible to satisfy not only plain paper but also fixing properties and glossiness of thick paper and glossy paper.

  A cam (pressure releasing cam) 505 as a pressure changing member is arranged on the side facing the pressure plate rotation shaft 502 with the flange member 26R interposed (inside). Similarly, a second drive gear (pressure release gear) G2 and a cam rotation shaft 504 are disposed outside the space containing the pressure plates 505A and 505B of the pressure support plate 507. The gear G2 and the cam 501 are arranged coaxially with the shaft 504, and are engaged so that the cam 501 is rotated by the rotation of the gear G2.

  The cam 501 has a shape in which two cams of a large cam portion (first cam) 501a and a small cam portion (second cam) 501b are arranged in parallel in the longitudinal direction, and has two cam profiles. Yes. Specifically, the small cam portion 501b can rotate the second pressure plate 505B around the shaft 502, and the large cam portion 501a can rotate the first pressure plate 505A around the shaft 502. That is, the large cam portion 501a and the small cam portion 501b are integrally formed, and the rotation center of the cam is the same.

  FIG. 15 shows the rotation amounts around the respective axes 502 of the second pressure plate 505B and the first pressure plate 505A by the small cam portion 501b and the large cam portion 501a when the rotation of the cam 501 is rotated. Show. In FIG. 15, the pressure state corresponds to 0 ° on the vertical axis, and the time when the pressure plates 505 </ b> A and 505 </ b> B rotate clockwise about the shaft 502 is positive (FIG. 11).

  The pressurizing force changing mechanism is a large cam portion (first cam) capable of changing the pressurizing force of the nip portion N by selectively swinging the first pressurizing spring 508A and the second pressurizing spring 508B. 501a and a small cam portion (second cam) 501b.

(2-7) Low Pressure Mode Next, a state where the nip pressure is low (hereinafter, low pressure mode) will be described with reference to FIG. When a print job (JOB) that passes the paper in the low pressure mode, for example, an envelope paper passing job, the fixing device F shifts to the low pressure mode.

  At that time, the control unit 100 drives the motor M2. Drive is transmitted from the motor M2 to the gear G2, and the gear G2 is rotated counterclockwise in FIG. 5, so that the cam rotating shaft 504 and the cam 501 engaged with the gear G2 by a parallel pin, D-cut, or the like. Rotate. FIG. 16 shows a state where the cam 501 has stopped in the low pressure mode and the fixing device F has shifted to the low pressure mode.

  In FIG. 16, the large cam portion 501a of the cam 501 pushes up the first pressure plate 505A, and the first pressure plate 505A is in a pressure release state. On the other hand, the small cam portion 501b does not touch the second pressure plate 505B, and the first pressure plate 505A and the second pressure plate 505B are not in contact with each other. Therefore, the pressing force of the first pressing spring 508A can be sufficiently received by the large cam portion 501a of the cam 501, and the pressing force of the first pressing spring 508A does not act on the flange member 26.

  Since the second pressure spring 508B is disposed on the second pressure plate 505B, only the second pressure spring 508B acts on the flange member 26 in the state of FIG. As described in the description of the normal pressure mode, the biasing force of the second pressure spring 508B is about 1/18 compared to the biasing force of the first pressure plate 505A. In comparison, the pressure applied in the low pressurization mode can be greatly reduced.

  Here, regarding the ratio of the pressures, the pressure F1 by the first and second pressure springs 508A and 508B in the normal pressure mode and the pressure F2 by the second pressure spring 508B in the envelope pressure state The ratio F1 / F2 is preferably 8 times or more.

(2-8) Pressure Release Mode When the image forming apparatus is not operating and the main switch M-SW (FIG. 10) is turned off or a paper jam occurs, the fixing device F enters the pressure release mode. Transition. In this case, the normal pressure mode or the low pressure mode is shifted to the pressure release mode shown in FIG.

  In the pressure release mode, unlike the low pressure mode, both the first pressure plate 505A and the second pressure plate 505B are lifted by the large cam portion 501a and the small cam portion 501b of the cam 501, respectively. Therefore, the cam 501 receives the urging forces of both the first pressure spring 508A and the second pressure spring 508B, thereby releasing the pressure applied to the nip portion N. By shifting to the pressure release mode, the plastic deformation distortion of the belt 21 and the pressure roller 30 and the paper removability at the time of paper jamming are improved.

(2-9) Pressure Friction Force As described in the fixing operation in (2-4), the pressure friction force generated at the nip portion N between the pressure roller 30 and the belt 21 caused by the rotational drive of the pressure roller 30 A rotational force acts on the belt 21. The belt 21 is in a driven rotation state while being in close contact with the downward surface of the fixing pad 22 and sliding.

The pressure friction force (driving force) at the nip N between the pressure roller 30 and the belt 21 is proportional to the applied pressure. That is, when the friction coefficient between the pressure roller 30 and the belt 21 is μ, in this embodiment, the pressure in the normal pressure mode is 550 N, and the pressure in the low pressure mode is 30 N.
・ Driving force in high pressure mode (F1): 550μ (N)
・ Driving force (F2) in low pressure mode: 30μ (N)
It becomes.

  Here, R is the sliding resistance due to the viscosity of the lubricant interposed between the fixing pad 22 and the inner surface of the belt 21. When the pressure frictional force at the nip portion N is less than the sliding resistance due to the viscosity of the lubricant, the belt 21 does not follow the pressure roller 30 and slips. Further, the fluorine-based heat-resistant grease as the lubricant has a property that the viscosity increases as the temperature decreases.

  In this embodiment, the relationship between the sliding resistance due to the viscosity of the lubricant at low temperature and the pressure friction force in the normal pressure mode and the low pressure mode is as follows.

・ Driving force in low pressure mode (F2) <Sliding resistance due to lubricant viscosity (R) <Driving force in high pressure mode (F1)
That is, when the driving force in the low pressure mode is lower than the sliding resistance of the lubricant, the belt 21 may not follow the rotation of the pressure roller 30 and slip in the low pressure mode. That is.

  On the other hand, when compared with the sliding resistance when the temperature of the lubricant is 180 ° C., the viscosity of the lubricant decreases, and the above relationship is as follows.

・ Sliding resistance due to lubricant viscosity (R) <Driving force in low pressure mode (F2) <Driving force in high pressure mode (F1)
That is, the driving force in the low pressure mode exceeds the sliding resistance of the lubricant, and the slip of the belt 21 can be suppressed even in the low pressure mode. That is, when the belt 21 is rotated in the low pressure mode, it is necessary to raise the lubricant in advance to the high temperature of the lubricant intervening on the fixing pad 22 and the inner surface of the belt 21 to reduce the viscosity.

(2-10) Pre-rotation operation The pre-rotation operation of the fixing device F in the present embodiment will be described based on the above-described fixing device configuration. The pre-rotation operation is generally a print preparation operation after receiving a print signal. The pre-rotation operation of the fixing device F is a temperature adjustment preparation operation in which the pressure roller 30 and the belt 21 are heated and idled until the belt 21 reaches a predetermined temperature. The control of this embodiment will be described with reference to the block diagram of the control system shown in FIG.

  Information such as the width and basis weight of the recording material type output by the user (paper size and paper type) is sent to the recording material information processing unit 114 from the operation unit 101 or the external host device 200 such as a PC to the control unit 100. It is done. Information of the recording material information processing unit 114 is transferred to the CPU 110. The CPU 110 refers to the memory 111 and instructs the pressure control unit 113 to set the pressure of the fixing device F to a predetermined value based on information from the recording material information processing unit 114. The pressing force control unit 113 controls the pressing force of the fixing device F to a predetermined pressure by a pressing force changing mechanism.

  The control of the present embodiment will be described using the flowchart shown in FIG. First, the image forming apparatus accepts an image forming job (print job) (S1). Thereafter, the CPU 110 determines whether or not the sheet to be passed is a low pressure mode job (S2). If the paper to be passed is not a low pressure mode job, the fixing device is started up in the normal pressure mode and a pre-rotation operation is performed (executed) until the belt temperature reaches 180 ° C. (S3). A forming operation and a fixing operation are performed (S6).

  If the job is a low pressure mode job in S2, the pre-rotation operation is performed until the belt temperature reaches 180 ° C., and then the pre-rotation is further performed for 30 seconds (S4). During this time, the viscosity of the lubricant present in the nip portion N is lowered so that the belt 21 does not slip even in the low pressure mode. Thereafter, the pressure is shifted to the low pressure mode (S5), and the image forming operation and the fixing operation (S6) are performed (S6).

  Next, the control of the present embodiment will be described with reference to the timing charts shown in FIGS. FIG. 18 is a timing chart when a normal pressure mode job comes. FIG. 19 is a timing chart when a low pressure mode job comes. Regarding the belt temperature, the temperature control temperature is made uniform for the sake of simplicity. The control unit 100 performs the following operation control.

  First, the operation in the normal pressure mode of FIG. 18 will be described. When the normal pressure mode job is received, the fixing device shifts to the normal pressure mode. Next, the pressure roller 30 is driven by the motor M1, and the pressure roller 30 and the receiving belt 21 are rotationally driven. Then, a voltage is applied to the exciting coil 41 to adjust the temperature of the belt 21 to 180 ° C. (normally pre-rotation operation). Thereafter, image forming is started and an image is output on a sheet. When the image formation is completed, the temperature control is stopped, the driving of the pressure roller 30 is stopped, and the pressure is released.

  Next, the operation in the low pressure mode of FIG. 19 will be described. When a job in the low pressure mode is received, the fixing device F shifts to the normal pressure mode. Next, the pressure roller 30 is driven by the motor M1, and the pressure roller 30 and the belt 21 are rotationally driven. Then, a voltage is applied to the excitation coil 41 to adjust the temperature of the belt 21 to 180 ° C. (normally pre-rotation operation).

  Thereafter, the pre-rotation is continued for 30 seconds while keeping the temperature of the belt 21 as it is. When the pre-rotation operation is completed, the temperature control and the pressure roller driving are once stopped, and the fixing device F shifts to the low pressure mode. Then, the pressure roller 30 is driven again to restart the temperature adjustment operation. Thereafter, image forming is started and an image is output on a sheet. When the image formation is completed, the temperature control is stopped, the driving of the pressure roller 30 is stopped, and the pressure is released.

  The control of the fixing device F of the above embodiment is summarized as follows. The controller 100 starts the rotation of the belt 21 and the pressure roller 30 and raises the pressure applied to the nip portion N to the first pressure (normal pressure) at the time of executing the pre-rotation operation of the apparatus for raising the temperature to a predetermined temperature. Pressure mode).

  When the paper on which the image heating process is performed is plain paper, the control unit 100 sets the pressure applied to the nip N to the first pressure (normal pressure mode). When the sheet on which the image heating process is performed is an envelope, the control unit 100 sets the pressure applied to the nip N to the second pressure (low pressure mode). The pressurizing force changing mechanism can substantially cancel the pressurizing force at the nip portion (pressure canceling mode).

  For paper of the same width and basis weight, when the image heating process is executed with the second pressure (low pressure mode), the pre-rotation operation time is heated with the first pressure (normal pressure mode). It is longer than the execution time of the pre-rotation operation when executing the process (FIG. 19).

Example 2
In Example 1, the pre-rotation time at the time of a job to be passed in the low pressure mode is managed by time, and is set so as to be uniformly longer for the job to be passed in the normal pressure mode (FIG. 19).

  In the second embodiment, a temperature sensor (temperature detection member) that detects the temperature of the pressure roller 30 is used to manage the execution time of the pre-rotation operation in the low pressure mode at the temperature of the pressure roller 30.

  In FIG. 4, TH <b> 2 is a temperature sensor that detects the temperature of the pressure roller 30. The temperature sensor TH2 is a non-contact thermistor and detects the surface temperature of the pressure roller 30 in a non-contact manner. The temperature sensor TH2 is disposed in correspondence with the longitudinal center position of the pressure roller 30.

  A flowchart of control in this embodiment is shown in FIG. In contrast to the flowchart of FIG. 1 of the first embodiment, the content of S4 is different. Steps S1, S2, S3, S5, and S6 other than this are the same, and thus the description thereof will be omitted.

  If the job is a low pressure mode job in S2, the pre-rotation operation is performed until the belt 21 reaches 180 ° C., and then the pre-rotation operation is extended until the surface temperature of the pressure roller 30 reaches 100 ° C. (S4). . When the surface temperature of the pressure roller 30 is 100 ° C. or higher, the viscosity of the lubricant present in the nip portion N is lowered to a point where the belt 21 does not slip even in the low pressure mode. Thereafter, the pressure is shifted to the low pressure mode (S5), and the image forming operation and the fixing operation are performed (S6).

  The control of this embodiment will be described using the timing chart shown in FIG. The control in the normal pressurizing mode is the same as that in FIG. Further, regarding the belt temperature, for the sake of simplification, the temperature control temperature is made uniform.

  When the low pressure mode job is received, the fixing device F shifts to the normal pressure mode. Next, the pressure roller 30 is driven by the motor M1, and the pressure roller 30 and the belt 21 are rotationally driven. Then, a voltage is applied to the exciting coil 41 to adjust the temperature of the belt 21 to 180 ° C. (normally pre-rotation operation).

  Thereafter, the pre-rotation operation is continued until the surface temperature of the pressure roller 30 reaches 100 ° C. When the pre-rotation operation is completed, the temperature control and the pressure roller driving are once stopped, and the fixing device F shifts to the low pressure mode. Then, the pressure roller 30 is driven again to restart the temperature adjustment operation. Thereafter, image forming is started and an image is output on the recording material. When the image formation is completed, the temperature control is stopped, the driving of the pressure roller 30 is stopped, and the pressure is released.

  The control of the second embodiment is summarized as follows. The controller 100 includes a temperature sensor TH2 that detects the temperature of the pressure roller 30, and the controller 100 performs a pre-rotation operation until the temperature of the pressure roller 30 detected by the temperature sensor TH2 reaches a predetermined temperature.

  As described above, it is possible to provide a fixing device corresponding to various paper types and sizes while suppressing slippage of the belt 21 and envelope wrinkles. The embodiment described here is only an example, and the setting values and the like are not limited thereto.

<< Other Examples >>
(1) In the embodiment, the image heating device has been described by taking a fixing device that heats and fixes an unfixed toner image formed on a sheet (on a recording material) as an example, but is not limited thereto. The present invention can also be applied to an apparatus (gloss enhancement apparatus) that increases the gloss (glossiness) of an image by reheating a toner image fixed or assumed on the paper P.

  (2) The image heating apparatus may have a device configuration in which the first rotating body and the second rotating body are both roller bodies, or may be an apparatus configuration in which both are endless belts. An apparatus configuration in which a roller body and the other is an endless belt may be employed.

  (3) The pressurizing mechanism of the image heating apparatus may be configured to pressurize at least one of the first rotating body and the second rotating body toward the other.

  (4) The image heating device may be any device configuration in which at least one of the first rotating body and the second rotating body is externally heated or internally heated by a heater, and the heater is not limited to the induction heating in the embodiment. . It may be a contact type heater or heat ray irradiation heating.

  (5) The image forming apparatus is not limited to an image forming apparatus that forms a full-color image as in the embodiment, and may be an image forming apparatus that forms a monochrome image. In addition, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multifunction machine having a plurality of these functions in addition to necessary equipment, equipment, and housing structure.

  F..Image heating device (fixing device), 21..Heating rotator (fixing belt), 30..Pressure rotator (pressure roller), N..Nip part, 500R.500L..Pressure mechanism, 100 .. Control part

Claims (13)

A heating rotator and a pressure rotator that form a nip for heating an image on the recording material;
A pressurizing mechanism for pressurizing at least one of the heating rotator and the pressurizing rotator toward the other;
A pressing force changing mechanism capable of changing the pressing force of the nip portion by the pressing mechanism into a first pressing force and a second pressing force lower than the first pressing force;
A control unit for controlling the pressurizing force changing mechanism, wherein the pressurizing force by the pressurizing mechanism is set to the first pressurizing force or the second pressurizing force based on the type of the recording material to be subjected to the image heating process. A control unit,
The controller sets the applied pressure to the first applied pressure when executing a pre-rotation operation of the apparatus for starting rotation of the heating rotating body and the pressurizing rotating body and raising the temperature to a predetermined temperature. An image heating apparatus.   2. The image heating apparatus according to claim 1, wherein when the recording material to be subjected to the image heating process is plain paper, the control unit sets the pressure to the first pressure. 3.   The image heating apparatus according to claim 1, wherein the control unit sets the pressurizing force to the second pressurizing force when the recording material to be subjected to the image heating process is an envelope.   The image heating apparatus according to claim 1, wherein the pressing force changing mechanism can substantially cancel the pressing force of the nip portion.   When the image heating process is executed with the second applied pressure with respect to the recording materials having the same width and basis weight, the execution time of the pre-rotation operation before the image heating process is executed with the first applied pressure. The image heating apparatus according to claim 1, wherein the image heating apparatus is longer than an execution time of the rotation operation.   A temperature detecting member that detects a temperature of the pressurizing rotating body; and the control unit performs the pre-rotation operation until a temperature of the pressurizing rotating body detected by the detecting member reaches a predetermined temperature. The image heating apparatus according to claim 1, wherein the image heating apparatus is characterized in that   The image heating apparatus according to any one of claims 1 to 6, wherein the heating rotator is an endless belt.   The image heating apparatus according to claim 7, wherein a lubricant is applied to an inner surface of the belt. The pressure mechanism includes a first pressure member pressed by a first elastic member and a second pressure member pressed by a second elastic member,
The pressurizing force change mechanism includes a first cam and a second cam that can change the pressurizing force of the nip portion by selectively swinging the first pressurizing member and the second pressurizing member. Have
The controller controls the pressure applied to the nip portion by the pressure mechanism based on the type of the recording material to be subjected to the image heating process, and applies pressure to both the first pressure member and the second pressure member. And a second pressure lower than the first pressure due to one of the first pressure member and the second pressure member. The image heating apparatus according to any one of claims 1 to 8.   The image heating apparatus according to claim 9, wherein the swinging centers of the first pressure member and the second pressure member are the same.   The image heating apparatus according to claim 9 or 10, wherein the first elastic member and the second elastic member are on the same straight line.   The image heating apparatus according to any one of claims 9 to 11, wherein the first cam and the second cam are integrally formed, and the rotation centers of the cams are the same.   The ratio F1 / F2 between the pressing force F1 by the elastic member at the first pressing force and the pressing force F2 by the elastic member at the second pressing force is 8 times or more. The image heating apparatus according to any one of 1 to 12.