JP2018004674A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device that can reliably rotate a heating rotating body while reducing wrinkles on an envelope.SOLUTION: An image heating device comprises: a first rotating body 21 that applies heat to a toner image t formed on a recording material S at a nip part N; a second rotating body 30 that forms the nip part with the first rotating body; setting means that sets the pressure at the nip part to a first pressure when image heating processing is performed on a recording material of a first type, and sets the pressure at the nip part to a second pressure lower than the first pressure when the image heating processing is performed on a recording material of a second type; and a temperature sensor TH2 that detects the temperature of the second rotating body. When a temperature detected by the temperature sensor TH2 at the completion of the image heating processing on the recording material of the second type is equal to or lower than a predetermined temperature, the setting means switches the pressure at the nip part to a pressure higher than the second pressure.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 a copying machine such as an electronic Sash system, a printer, a fax machine, or a multi-function machine thereof.

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

  In an image forming apparatus, there are various fixing devices (fixing units) 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 type fixing device that heats through an endless 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. A fixing device that combines the speed of heating by IH and the low heat capacity of the on-demand system to further increase the startup time has been proposed. 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 pressure rotator or the heating 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 the paper is shifted when a plurality of paper is overlapped 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 pressurizing force when passing plain paper, and the pressurizing force 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 may not be sufficiently transmitted to the heating rotator, and the heating rotator may slip. It is a further development. An object of the invention is to provide an image heating apparatus that reliably rotates a heating rotator while suppressing envelope wrinkles.

In order to achieve the above object, a typical configuration of the image heating apparatus according to the present invention is as follows.
A first rotating body that heats the toner image formed on the recording material at the nip portion;
A second rotating body that forms the nip portion with the first rotating body;
When the image heating process is performed on the first type of recording material, the pressure of the nip portion is set to the first pressure, and when the image heating process is performed on the second type of recording material, the pressure of the nip portion is set to the first pressure. Setting means for setting a second pressure lower than the pressure of 1;
A temperature sensor for detecting the temperature of the second rotating body,
The setting means has a pressure higher than the second pressure when the temperature detected by the temperature sensor when the image heating process for the second type of recording material is completed is equal to or lower than a predetermined temperature. It is characterized by switching to.

  ADVANTAGE OF THE INVENTION According to this invention, the image heating apparatus which can rotate a 1st rotary body (heating rotary body) reliably can be provided, suppressing the wrinkle of a 2nd type recording material (envelope). .

Control flowchart in Embodiment 1 Configuration schematic diagram of an example of an image forming apparatus Block diagram of the control system (mainly showing relevant parts of the fixing device) 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 same apparatus which excluded the coil unit, and the figure which shows the time of the state in which the paper 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. Partially cutaway perspective view of one end of the fixing device Enlarged front view of one end of the fixing device 11A is an enlarged cross-sectional view taken along line (12)-(12) in the normal pressure mode. 11A is an enlarged cross-sectional view taken along line (13)-(13) (in normal pressure mode). Cam phase diagram Expanded cross-sectional view of the pressure mechanism on one end (in low pressure mode) Partially cutaway perspective view of one end of the fixing device (in pressure release mode) Control timing chart when the image forming job is a normal pressure mode job executed by setting the fixing device to the normal pressure mode Control timing chart for low pressure mode jobs The schematic diagram of the mode selection screen displayed on a display part in Example 2

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 of the present embodiment, the above-described mechanism unit is an image forming unit that forms an unfixed toner image on a sheet (recording material) S in order to execute an image forming job. 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 formation 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 and 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. FIG. 3 is a block diagram of a control system including the operation unit 102. The operation unit 102 is a user interface (UI: User Interface, input unit, display unit) that exchanges electrical information with the control unit 100. With this operation unit 102, various instructions such as image formation mode setting and selection of recording material to be used are input from the user (operator or 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.

  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 (recording material selection unit) that can select a sheet to be used, and various operation buttons. Various settings of operations performed by the image forming apparatus 1 are also input to the control unit 100 by the displayed operation buttons.

  The control unit 100 includes a CPU (Central Processing Unit) 110. In addition, the control unit 100 includes a pressure control unit 113, a memory 111, a recording material information processing unit 114, a timer 112, and the like for controlling the fixing device F and the like which will be described later. As will be described later, the timer 112 has a function of counting the time in the normal pressurization state (normal pressurization mode) after the end of the image forming job (JOB: print job).

  Reference numeral 200 denotes an external host device such as a personal computer, an image reader, or a facsimile. The host device 200 is connected to the control unit 100 via an interface, and various instruction information such as an image forming job and selection of paper to be used is also input from the host device 200 to the control unit 100. Conversely, various types of information are fed back from the control unit 100 to the host device 200.

[Fixing device]
Regarding the fixing device (fixing unit) 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.

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

  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: Endless belt having flexibility as a first rotating body (fixing member: heating rotating body) that heats the toner image formed on the paper S at the nip portion N (hereinafter, referred to as a fixing belt or a belt). Belt unit 20 including 21
b: a pressure roller 30 having elasticity as a second rotating body (pressure member: pressure rotating body) that forms a nip portion N with 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 for forming the nip portion N by relatively pressing the belt 21 and the pressure roller 30.
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 an assembly such as 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. 10C 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 first temperature sensor (temperature detection means: temperature detection element) TH <b> 1 such as a thermistor is disposed through an elastic support member 27 at the longitudinal center of the stay 24. The temperature sensor TH1 detects the temperature of the belt 21 and feeds it back to the control unit 100.

  The support member 27 protrudes to the outside of the inner core 25 through a through hole 24a provided at the longitudinal center of the upper surface of the stay 24 and a through hole 25a provided at an inner core position corresponding to the through hole 24a. Yes. The sensor TH1 supported at the tip of the support member 27 is in elastic contact with the inner surface of the central portion in the width direction of the belt 21. 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. 10A 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 TH1, a slippery layer 21d having 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. 10C, 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 of the coil unit 40 from an excitation 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 the other end of the core bar 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.

  Further, in order to detect the surface temperature of the pressure roller 30, a second temperature sensor (temperature detection means) TH <b> 2 is disposed in the vicinity of the central portion in the longitudinal direction of the pressure roller 30. As the temperature sensor TH2, a non-contact thermistor (NC sensor), a thermopile, or the like can be used. Although there is no problem even if it is a contact type, in this embodiment, a temperature sensor is provided in the paper passing area, and a non-contact type is adopted in order to avoid image defects such as streaks in the pressure roller 30. .

(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.

  Therefore, when the flange members 26R and 26L of the belt unit 20 are pressed by the pressurizing mechanisms 500L and 500R 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 plurality along the longitudinal direction, and is arrange | positioned along with the longitudinal direction like FIG.10 (b).

(2-4) Fixing Operation In the standby state of the image forming apparatus 1, the fixing device F is a pressurizing unit in which the pressure applied to the nip portion N by the pressurizing mechanisms 500 </ b> R and 500 </ b> L described later is substantially released by the pressurizing force changing mechanism. The release mode (pressure release state) is maintained. The first 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.

  The control unit 100 controls the pressurization changing mechanism at a predetermined control timing based on the input of the start signal of the image forming job (print job) to control the pressurization mechanisms 500R and 500L with normal pressurization (first pressurization). Pressure) in normal pressure mode (normal pressure 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.

  In addition, the control unit 100 turns on the first motor M1. As a result, the pressure roller 30 is rotationally driven at a predetermined speed in the counterclockwise direction indicated by 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 slides in close contact with the fixing pad 22, the outer periphery of the belt inner assemblies 22 to 25 is driven to rotate in the clockwise direction indicated by an arrow R 21 in FIG. 5 at the same speed as the rotation speed of the pressure roller 30. . 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 belt 21 is driven and rotated as described above by rotating the pressure roller 30 by the first motor M1 controlled by the control unit 100 at least during execution of image formation. This rotation is performed at substantially the same peripheral speed as the conveyance speed of the sheet S carrying the unfixed toner image t conveyed from the secondary transfer nip side.

  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 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 first 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 TH1 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 state in which the pressure roller 30 is driven and the belt 21 rises to a predetermined fixing temperature and is temperature-controlled as described above, the sheet S carrying the unfixed toner image t in the nip portion N is on the toner image carrying surface side. Is guided by the guide member 64 toward the belt 21 side and introduced. 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 image forming job is completed, as will be described later, the control unit 100 turns off the power supplied to the coil 41 of the fixing device F, turns off the first motor M1, and puts the fixing device F in the normal pressure mode. Wait.

  At this time, the timer 112 (FIG. 3) counts the standby time in the normal pressurizing mode (first pressurizing force). When the next image forming job is not submitted until the predetermined standby time counted by the timer 112 elapses, the control unit 100 normally sets the pressure state of the fixing device F by the pressure change mechanism when the predetermined standby time elapses. The pressure mode is changed to the pressure release mode. This will be described later.

(2-5) Pressurizing mechanism In the first embodiment, the pressurizing mechanisms 500R and 500L press (press) the flange members (pressed 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 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) Pressurizing force changing mechanism Next, the pressurizing force changing mechanism (pressurizing force switching mechanism: pressurizing force varying means) in the present 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 (first 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 the present embodiment, the first pressure spring 508A and the second pressure plate 505B 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. 11A is an enlarged front view of one end side of the fixing device F. FIG. 12 is an enlarged sectional view taken along line (12)-(12) in FIG. 11A, and FIG. 13 is an enlarged sectional view taken along line (13)-(13) in FIG. 11A.

  The second pressure plate 505B has a protrusion 702a (FIG. 13) on a part of the surface that presses the flange member (pressed 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 plain paper, glossy paper, thick paper and the like as the first type of recording material.

  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) 501 serving as a pressing force changing member is disposed on the side facing the pressure plate rotation shaft 502 with the flange member 26R interposed therebetween. 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 (first cam) 501b are arranged 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. 14 illustrates the amount of rotation about the shaft 502 of each of the second pressure plate 505B and the first pressure plate 505A by the small cam portion 501b and the large cam portion 501a as the cam 501 rotates. . In FIG. 14, 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).

(2-7) Low Pressurization Mode Next, a state where the nip pressure is lower than the normal pressurization mode (first pressurization pressure) (second pressurization pressure: hereinafter, low pressurization mode) will be described. When the image forming job is a job for passing the paper S with the fixing device F in the low pressure mode, for example, when the paper S to be used is an envelope as a second type of recording material (envelope paper passing job) The control unit 100 shifts the pressure state of the fixing device F to the low pressure mode.

  That is, when the user passes the envelope as the paper S, the envelope is set in a paper feeding unit such as a cassette or a multi-tray, and the operation unit 102 sets the print mode to envelope setting to perform copying or printing. The control unit 100 shifts the pressurization state of the fixing device F to the low pressurization mode when the envelope sheet passing job is performed.

  The transition to the low pressure mode is as follows. The control unit 100 drives the second motor M2. The drive is transmitted from the motor M2 to the second gear G2, and the gear G2 is rotated clockwise in FIG. 11, thereby allowing the shaft 504 and the cam 501 engaged with the gear G2 by a parallel pin, D-cut, or the like. Rotate. FIG. 15 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. 15, 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. For this reason, the pressing force of the first pressing spring 508A can be sufficiently received by the cam 501, and the pressing force of the first pressing spring 508A does not act on the flange member 26R.

  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 26R 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 spring 508A. Therefore, the pressurizing force (second pressurizing force) in the low pressurizing mode can be greatly reduced as compared with the normal pressurizing mode (first pressurizing force).

  Regarding the ratio of the pressing force, the ratio F1 between the pressing force F1 by the first and second pressing springs 508A and 508B in the normal pressing mode and the pressing force F2 by the second pressing spring 508B in the low pressing mode. / F2 is preferably 8 times or more.

  The above-described pressure change mechanism is summarized as follows. The pressurizing force changing mechanism selectively pressurizes the nip portion N by swinging the first pressurizing plate (first pressurizing member) 505A and the first pressurizing plate (second pressurizing member) 505B selectively. A large cam portion (first cam) 501a and a small cam portion (second cam) 501b.

  The control unit 100 that controls the pressurizing mechanism changes the pressurizing force of the nip portion N by the pressurizing mechanism based on the type of paper on which the image heating process is performed and the normal pressurizing mode (first pressurizing force) The low pressurization mode (second pressurization pressure) is set lower than the first pressurization pressure in the pressure mode.

  The normal pressure mode is a pressure applied by both the first pressure plate 505A and the second pressure plate 505B. The low pressurization mode is a pressurization force lower than that in the normal pressurization mode by the pressurization force of one of the first pressurization plate 505A and the second pressurization plate 505B (the second pressurization plate 505B in this embodiment).

(2-8) Pressure Release Mode When the image forming apparatus is not operating and the main switch M-SW (FIG. 3) is turned off or when a paper jam occurs, an image forming job is When the charging is not performed, the control unit 100 shifts the pressure state of the fixing device F to the pressure release mode.

  In that case, the normal pressure mode shown in FIGS. 11 to 13 and the low pressure mode shown in FIG. 15 are shifted to the pressure release mode shown in FIG. Unlike the low pressure mode in the pressure release 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. That is, the cam 501 receives the urging force of both the first pressure spring 508A and the second pressure spring 508B. As a result, the pressure applied to the nip portion is released. By shifting to the pressure release mode, the plastic deformation (strain) of the belt 21 and the pressure roller 30 and the removability of the paper at the time of paper jamming are improved.

(2-9) Fixing Driving Next, the driving force applied to the belt 21 by the pressure roller 30 will be described. The control unit 100 drives the first motor M1. Driving is transmitted from the motor M1 to the first gear G1, and the gear G2 is rotated clockwise in FIG. As a result, the pressure roller 30 is rotationally driven in the counterclockwise direction indicated by the arrow R30 in FIG. At this time, the rotational force acts on the belt 21 by the pressure frictional force generated in the nip portion N between the pressure roller 30 and the belt 21 caused by the rotational driving of the pressure roller 30. The belt 21 slides in close contact with the downward surface of the fixing pad 23 and is driven to rotate in the clockwise direction indicated by the arrow R21 in FIG.

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 normal pressure mode (F1): 550μ (N)
Driving force in low pressure mode (F2): 30μ (N)
It becomes.

  Here, R is a sliding resistance due to the viscosity of the lubricant interposed between the fixing pad 23 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 normal 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,
Sliding resistance due to lubricant viscosity (R) <Driving force in low pressure mode (F2) <Driving force in normal pressure mode (F1)
Thus, 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.

  In other words, when the belt 21 is rotated in the low pressure mode, it is necessary to raise the temperature of the lubricant existing on the fixing pad 23 and the inner surface of the belt 21 in advance 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. Here, 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 for heating and rotating the pressure roller 30 and the belt 21 until the belt 21 reaches a predetermined temperature. The control of this embodiment will be described with reference to the block diagram shown in FIG.

  Information (paper size and paper type) such as the width and basis weight of the recording material output by the user is sent to the recording material information processing unit 114 from the operation unit 102 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. The control unit 100 receives an image forming job (JOB) (S1), and performs a start-up operation (pre-rotation operation) of the image forming apparatus. The CPU 110 determines whether or not the job is a job for passing the paper S with the fixing device F in the low pressure mode (low pressure mode job).

  If the job is not in the low pressure mode, the fixing device F is started up in the normal pressure mode and the pre-rotation operation is performed until the belt temperature detected by the first temperature sensor TH1 reaches 180 ° C. A forming operation and a fixing operation are performed (S2 to S9).

  If the job is a low pressure mode job, 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. (S6, S15). .

  When the surface temperature of the pressure roller 30 detected by the second temperature sensor TH2 is equal to or higher than a predetermined threshold, that is, 100 ° C. or higher in this embodiment, the viscosity of the lubricant interposed in the nip portion N is low even in the low pressure mode. The belt 21 is lowered to a point where it does not slip. Thereafter, the pressure is shifted to the low pressure mode, and the image forming operation and the fixing operation are performed (S15 to S20).

  The control of the present embodiment will be described with reference to timing charts shown in FIGS. FIG. 17 is a control timing chart when the image forming job is a normal pressure mode job executed with the fixing device F in the normal pressure mode. FIG. 18 is a control timing chart in the case of a low pressure mode job. Regarding the fixing belt temperature, the temperature control temperature is made uniform for the sake of simplicity.

  When the control unit 100 receives the normal pressure mode job, the fixing device F shifts to the normal pressure mode (S2). Next, the pressure roller 30 is driven by the motor M1, and the pressure roller 30 and the belt 21 are rotationally driven (S3, S4). Then, a voltage is applied to the exciting coil 41 (S5), and the temperature of the belt 21 is adjusted to 180 ° C. (normally pre-rotation operation). Thereafter, image forming is started and an image is formed on the paper (S7). When the image formation is completed (S8), the temperature control is stopped (S9), the driving of the pressure roller 30 is stopped (S10), and the pressure release mode is entered if the next image forming job is not input within a predetermined time. Transition (S12 to S14).

  That is, when the image forming job is completed, the control unit 100 turns off the power supplied to the coil 41 of the fixing device F, turns off the first motor M1, and makes the fixing device F stand by in the normal pressure mode ( S8-S11). At this time, the timer 112 counts the standby time in the normal pressure mode. When the next image forming job is not submitted until the predetermined standby time counted by the timer 112 elapses, the control unit 100 changes the pressure state of the fixing device F from the normal pressure mode when the predetermined standby time elapses. The mode is shifted to the release mode (S12 to S14).

  Subsequently, the operation in the low pressure mode will be described. When receiving the low pressure mode job, the control unit 100 shifts the fixing device F to the normal pressure mode (S2). Next, the pressure roller 30 is driven by the motor M1, and the pressure roller 30 and the belt 21 are rotationally driven (S3, S4). Then, a voltage is applied to the exciting coil 41 (S5), and the temperature of the belt is adjusted 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. (predetermined temperature) (heat storage operation: S15, S21). 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 (S16). Then, the pressure roller 30 is driven again to restart the temperature adjustment operation. Thereafter, image formation is started (S17), and an image is formed on the paper. When the image formation is completed (S18), the temperature control is stopped (S19), and the driving of the pressure roller 30 is stopped (S20).

  At this time, if the temperature of the pressure roller 30 is 100 ° C. or higher, it is not necessary to perform the above-described heat storage operation (S21), and therefore the fixing device F stands by in the low pressure mode (S22, S23). When the temperature of the pressure roller 200 falls below 100 ° C., the process proceeds to the normal pressure mode (S22, S11), and the pressure release operation is performed after a predetermined time (S12 to S14).

  If the next image forming job is input in step S12, it is determined in step S24 whether the job is a low pressure mode job. If it is a low pressure mode job, the control proceeds to step S15. If it is not a low pressure mode job, the control proceeds to step S7.

  If the fixing device F waits in the low pressure mode in step S23 and the next image forming job is not input in step S25, the process proceeds to step S22. If the next image forming job is input, it is determined in step S26 whether the job is a low pressure mode job. If it is a low pressure mode job, the process proceeds to step S17. If the job is not a low pressure mode job, the fixing device F is shifted from the low pressure mode to the normal pressure mode in step S27, and the flow proceeds to step S7.

  The above control is summarized as follows. When the temperature detected by the temperature sensor TH2 after the end of the image forming job executed in the low pressurization mode in which the pressing force is the second pressing force is equal to or lower than the predetermined temperature, the control unit 100 The pressure change mechanism is controlled in a direction in which the pressure is changed from the second pressure to the first pressure. Here, in this embodiment, the second applied pressure is switched to the first applied pressure. However, the present invention is not limited to the first applied pressure, and includes switching to a pressure higher than the second applied pressure.

  When an image forming job using an envelope as a sheet (recording material) is executed, the control unit 100 controls the pressure change mechanism in a direction in which the pressure is set to the second pressure.

  When an image forming job using an envelope as a sheet is executed, the control unit 100 performs the following control when the temperature detected by the temperature sensor TH2 is equal to or lower than a predetermined temperature. That is, when the temperature detected by the temperature sensor TH2 becomes higher than the predetermined value, the pressure change mechanism is controlled in a direction in which the pressure is changed to the second pressure.

  The pressing force changing mechanism can substantially cancel the pressing force of the nip portion N, and the control unit 100 has passed a predetermined time after the end of the image forming job executed with the pressing force being the first pressing force. If the next image forming job has not been submitted until this time, control is performed as follows. That is, the pressing force changing mechanism is controlled in such a direction that the pressing force is substantially released from the first pressing force after the predetermined time has elapsed.

  The characteristic configuration of the fixing device F of the first embodiment is summarized as follows.

  a: A belt (first rotating body) 21 that heats the toner image t formed on the paper (recording material) S at the nip portion N is provided.

  b: A pressure roller (second rotating body) 30 that forms a nip portion N with the belt 21 is provided.

  c: When the pressurizing mechanisms 500L and 500R, the pressurizing force changing mechanism, and the control 100 are collectively referred to as setting means, the setting means is included. The setting means sets the pressure of the nip portion N to the first pressure when performing image heating processing on the first type of recording material such as plain paper, glossy paper, cardboard, and the like. When the image heating process is performed on the recording material, the pressure of the nip portion N is set to a second pressure lower than the first pressure.

  d: having a temperature sensor TH2 for detecting the temperature of the pressure roller 30;

  e: Then, when the temperature detected by the temperature sensor TH2 when the image heating process for the second type of recording material is completed is equal to or lower than a predetermined temperature, the setting means sets the pressure of the nip portion N to the first level. It is characterized by switching to a pressure higher than the pressure of 2.

  With the control 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. A user who frequently uses a low pressure mode such as an envelope does not cause an unnecessarily long waiting time each time an envelope is fed. The embodiment described here is only an example, and the setting values and the like are not limited thereto.

Example 2
In the first embodiment, the low pressure mode is maintained even after the low pressure mode job ends (S20 in FIG. 1) in accordance with the temperature of the pressure roller 30 detected by the second temperature sensor TH2. Examples (S22, S23).

  In the second embodiment, there is provided means for selecting whether or not to maintain the low pressure mode after completion of the low pressure mode job. That is, as shown in FIG. 19, a user who frequently passes a medium using a low pressure mode such as an envelope operates the operation unit 102 and selects the normal paper priority from the user setting items displayed on the display unit 105. Mode or envelope feeding priority mode can be selected. A is a key for selecting the envelope paper feeding priority mode, and B is a key for selecting the plain paper priority mode.

  In the envelope paper feeding priority mode, when the temperature detected by the temperature sensor TH2 is higher than a predetermined value after the end of the job executed with the applied pressure being the second applied pressure, the applied pressure is changed to the second applied pressure. This is a mode (first control mode) in which the apparatus is made to stand by while being held.

  In the plain paper priority mode, when the temperature detected by the temperature sensor TH2 is higher than a predetermined value after the job executed with the applied pressure set to the second applied pressure, the second applied pressure is set to the first applied pressure. This is a mode (second control mode) for controlling the pressurizing force changing mechanism in the direction of pressurizing.

  When the plain paper priority mode B in FIG. 19 is selected, the control flow is the same as in FIG. On the other hand, when the envelope paper feeding priority mode A is selected, since processing is performed at Y in S22 of the flowchart of FIG. 1, if the temperature of the pressure roller 30 detected by the temperature sensor TH2 is higher than 100 ° C., it is low. It will be in a standby state in pressurization mode. When the low pressurization mode JOB is executed again at this time, the heat storage operation is not performed, so that the envelope JOB can be ended earlier than before.

  On the other hand, when waiting in the low pressure mode, it is necessary to rotate the pressure release cam in order to switch back to the normal pressure mode, so the time required to output plain paper is slightly longer. Therefore, it is possible for the user to appropriately select which mode A or B has priority according to the use situation.

  In the second embodiment, an example is given in which the user selects from the user setting mode so that the user selects. However, a method in which the service person interviews the user about the usage status and selects from the service mode that is set exclusively by the service person. But it ’s okay.

  The configuration and control of the second embodiment are summarized as follows. The setting means described above includes the first control mode and the second control when the temperature detected by the temperature sensor TH2 after the image heating process for the second type of recording material is higher than a predetermined temperature. A selection unit that allows the operator to select one of the modes is provided. The first control mode is a control mode in which the apparatus stands by with the pressure at the nip portion kept at the second pressure. The second control mode is a control mode for switching to a pressure higher than the second pressure.

The selection unit includes a display unit, and the setting unit controls display contents on the display unit. The setting means displays a key for selecting the first control mode and a key for selecting the second control mode on the display unit. << Other Examples >>
(1) In the embodiment, the fixing unit (image heating device) is described as an example of a fixing device that heats and fixes an unfixed toner image formed on a sheet (on a recording material). Not limited. An apparatus (gloss improvement apparatus: also called a fixing apparatus in this case) that increases the gloss (glossiness) of the image by reheating the toner image fixed or assumed on the paper P is also included in the fixing unit.

  (2) In the fixing unit, the first rotating body and the second rotating body may both be a roller structure, or both may be an endless belt, or one of them may be a roller body. And the other may be an endless belt.

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

  (4) The heating configuration of the first rotating body may be an external heating configuration or an internal heating configuration, and is not limited to the induction heating of 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.

  1 .. Image forming apparatus, F .. Fixing part (image heating apparatus), 21.. First rotating body, 30.. Second rotating body, N .. Nip part, 500 (R, L). Pressurization mechanism, TH (1, 2) ... Temperature sensor, 100 ... Control unit

Claims (7)

A first rotating body that heats the toner image formed on the recording material at the nip portion;
A second rotating body that forms the nip portion with the first rotating body;
When the image heating process is performed on the first type of recording material, the pressure of the nip portion is set to the first pressure, and when the image heating process is performed on the second type of recording material, the pressure of the nip portion is set to the first pressure. Setting means for setting a second pressure lower than the pressure of 1;
A temperature sensor for detecting the temperature of the second rotating body,
The setting means has a pressure higher than the second pressure when the temperature detected by the temperature sensor when the image heating process for the second type of recording material is completed is equal to or lower than a predetermined temperature. An image heating apparatus characterized by switching to   In the case where the image heating process is performed on the second type of recording material, and the detection temperature of the temperature sensor is equal to or lower than the predetermined temperature, the setting unit detects that the detection temperature of the temperature sensor is the predetermined temperature. 2. The image heating apparatus according to claim 1, wherein when the temperature is higher than the temperature, the pressure of the nip portion is set to the second pressure.   The setting means is capable of substantially releasing the pressure of the nip portion, and the next image is displayed after a predetermined time elapses after the image heating process for the first type of recording material is completed. 3. The image heating apparatus according to claim 1, wherein when the formation job is not input, the pressure in the nip portion is substantially released after the predetermined time has elapsed.   The setting means controls the pressure of the nip portion when the temperature detected by the temperature sensor after the image heating process for the second type of recording material is higher than a predetermined temperature. It has a selection part which makes an operator choose one of the 1st control mode which makes an apparatus stand by with pressure, and the 2nd control mode which changes to a pressure higher than the 2nd pressure, The image heating apparatus according to any one of claims 1 to 3.   The image heating apparatus according to claim 4, wherein the selection unit includes a display unit, and the setting unit controls display contents on the display unit.   The image heating according to claim 5, wherein the setting unit causes the display unit to display a key for selecting the first control mode and a key for selecting the second control mode. apparatus.   The first rotating body is an endless belt, the second rotating body is a driving rotating body, and a lubricant is applied to the inner surface of the belt. An image heating apparatus according to claim 1.