JP6573393B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic system capable of forming an image on a recording material such as a multifunction peripheral, a copying machine, a printer, and a fax machine.

  In electrophotographic copying machines, the toner (developer) of a toner image (unfixed image) transferred to a recording material that is a recording medium to be conveyed is melted by heat and fused onto the recording material. A fixing device (image heating device) is provided.

  In order to increase the temperature at high speed, the fixing device has a fixing roller that is a heating medium with a small diameter, a resin film rotating body that is in pressure contact with the rotating body, and a thin metal rotating body that is induction heated. What is heated by heating is known. These are all intended to reduce the heat capacity of the rotating body, which is a heating medium, and to heat it with a heat source with good heating efficiency.

  According to Patent Document 1, in order to prevent the occurrence of envelope flaws, the pressing force per unit area of the first pressing roller and the second pressing roller on the heating roller is switched between the normal pressure mode and the envelope pressure mode. A pressure switching mechanism is provided in the fixing unit. In the envelope pressure mode, both the pressing force per unit area of the first pressing roller with respect to the heating roller and the pressing force per unit area of the second pressing roller with respect to the heating roller are both higher than in the normal pressure mode for fixing plain paper or the like. The size is reduced to prevent the generation of envelope flaws.

  According to Patent Document 2, in order to prevent the occurrence of envelope flaws, control is performed to switch the shape of the fixing nip portion N from a nip mode in which the flat portion and the curved portion are in contact to a nip mode in which only the flat portion is in contact. ing.

JP 2004-279702 A JP 2013-225039 A

  However, in the above configuration, in order to improve the envelope flaw, it is necessary to lower the pressing force per unit area more than necessary. At this time, the amount of heat is insufficient and fixing failure may occur.

  In the configuration of Patent Document 2, the pressurizing mechanism is complicated, and the separation accuracy may not be sufficiently secured due to the positional accuracy of the bending portion.

The present invention has been made in view of the above problems. An object of the present invention is to prevent the occurrence of envelope flaws and to prevent fixing failure, separation failure and belt slip.
To do.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes an image forming unit that forms a toner image on a recording material, a flexible endless belt, and an inner surface of the belt. A pressure applying member that is in contact with the rotating member that forms a nip portion together with the pressure applying member via the belt, and the belt rotates by the rotation of the rotating member and carries a toner image at the nip portion. And a fixing unit that fixes the toner image on the recording material by heating while nipping and conveying the recording material. A main pressure portion in the vicinity of the center of the recording medium, and an upstream protrusion and a downstream side projecting from the main pressure portion toward the belt on the upstream side and the downstream side in the recording material conveyance direction, respectively The pressure applying member and the rotating body are relatively disposed through the belt so that the upstream protrusion, the downstream protrusion, and the main pressure portion are in contact with the inner surface of the belt. The first pressure mode in a pressurized state, the pressure application so that the upstream protrusion and the downstream protrusion are in contact with the inner surface of the belt, and the main pressure portion is not in contact with the inner surface of the belt. A change mechanism capable of switching between a second pressurizing mode in which the member and the rotating body are relatively pressurized via the belt, and recording material information acquired regarding the recording material to be used. And an execution unit that controls the change mechanism to execute switching between the first pressurization mode and the second pressurization mode.

  According to the present invention, it is possible to prevent the occurrence of envelope flaws and prevent fixing failure, separation failure and belt slip.

Control flow chart of image forming apparatus of first embodiment Configuration model diagram of an example of an image forming apparatus Perspective view of fixing device (A) is a front view of the fixing device, (b) is a longitudinal front view of the device. (A) is a cross-sectional view of the main part of the fixing device, (b) is a partially enlarged view of (a), and (c) is a cross-sectional view of the pressure pad. (A) and (b) are a left side view of the fixing device and a left side view of a partly cutout. (A) and (b) are a right side view of the fixing device and a right side view of a partly cutout. Schematic diagram of fixing belt layer structure Eccentric cam shape illustration Explanatory drawing of belt unit position in pressurization configuration, pressure reduction configuration, and pressure release configuration The figure explaining the generation | occurrence | production mechanism of the envelope flaw in normal pressure mode (1st pressurization mode) The figure explaining the generation | occurrence | production mechanism of the envelope flaw in envelope pressure mode (2nd pressurization mode) Block diagram of control system Fixing device control flowchart Flow chart for explaining the control of the second embodiment. Flow chart for explaining the control of the third embodiment. Structural explanatory diagram of the fixing device in the fourth embodiment Structural explanatory diagram of the fixing device in the fifth embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, an example of an electrophotographic color copier having a plurality of drums will be described as an image forming apparatus. However, the present invention is not limited to this, and it is needless to say that the present invention can also be applied to various types of electrophotographic copying machines, printers, monocolor systems, and image forming apparatuses other than electrophotography.

  In the following description, an envelope-shaped recording material refers to a bag-shaped recording medium having a plurality of overlapping folds, such as an envelope, and is simply referred to as an envelope hereinafter. The recording material other than the envelope shape refers to a single sheet of normal paper including transparency paper, and hereinafter simply referred to as plain paper. These recording media are also collectively referred to as paper.

<< First Example >>
(1) Example of Image Forming Apparatus FIG. 2 is a schematic configuration diagram of a color copying machine in this embodiment. A is a reader unit, B is a printer unit, C is an operation unit, and D is an external device such as a PC (personal computer) or a print server. The reader unit A photoelectrically reads the image information of the original OR, and the printer unit B forms an image corresponding to the read image information on the paper P and outputs it as an image formed product.

  In the reader unit A, the document OR placed on the document table glass 50 is irradiated by the light source 52 of the reading optical system unit 51 and imaged on the CCD sensor 54 through the optical system 53. The reading optical system unit 51 moves in the direction of the arrow 55 (sub-scanning movement), photoelectrically reads the image information of the original OR, and converts it into an electric signal data string for each line. An image signal obtained by the CCD sensor 54 is sent to a printer control unit (execution unit: hereinafter referred to as a control unit) 57 of the printer unit B via the reader image processing unit 56, and is adjusted to the printer unit B by the control unit 57. Image processing is performed. The control unit 57 also receives an external input from the external device D as an image signal.

  Information (size, basis weight, type, etc.) of the paper type (recording material type) using the operation unit C or the external device D as an input unit can be set in the control unit 57. The control unit 57 can reflect information such as the paper type and basis weight set from these pieces of information (recording material setting information) in the operation control of the printer unit B.

  Next, the printer unit B will be described. The image signal from the reader image processing unit 56 is converted by the control unit 57 into a laser beam subjected to PWM (pulse width modulation). The polygon scanner 58 scans the laser beam and irradiates the photosensitive drum 61 of the image forming portions Pa to Pd. Pa is a yellow (Y) image forming unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit. Form an image.

  Since the mechanism configurations of the image forming units Pa to Pd are substantially the same, the Y image forming unit Pa will be representatively described below, and the addition and description of reference numerals for the constituent devices in the other image forming units Pb to Pd will be omitted. .

  In the Y image forming portion Pa, an electrostatic latent image is formed on the surface of the photosensitive drum 61 by the laser beam from the polygon scanner 58. Reference numeral 62 denotes a primary charger, which charges the surface of the photosensitive drum 61 to a predetermined potential and prepares for formation of an electrostatic latent image. A developing unit 63 develops the electrostatic latent image on the photosensitive drum 61 to form a toner image. A transfer roller (roll) 64 discharges from the back surface of the intermediate transfer belt 66 and applies a primary transfer bias having a polarity opposite to that of the toner. As a result, the toner image on the photosensitive drum 61 is transferred onto the intermediate transfer belt 66. The surface of the photosensitive drum 61 after the transfer is cleaned with a cleaner 65.

  The toner images on the intermediate transfer belt 66 are sequentially conveyed to the next image forming units Pb to Pd, and the toner images of the respective colors formed by the image forming units Pb, Pc, and Pd in the order of M, C, and Bk. Is transferred, and a four-color superimposed image is formed on the surface of the intermediate transfer belt. The toner image that has passed through the Bk image forming portion Pd is a toner image on the intermediate transfer belt 66 having a polarity opposite to that of the toner in a secondary transfer portion composed of a secondary transfer inner roller 67, a secondary transfer outer roller, and 68. Secondary transfer is performed on the paper P by the secondary transfer electric field.

  The sheet P is fed by one sheet from a plurality of sheet feeding cassettes 69 or 70 serving as recording material storage units in which sheets corresponding to a pre-selected specification are stored, and is transported by a transport path 71a, and has a predetermined control timing. Is introduced into the secondary transfer portion.

  The sheet P that has passed through the secondary transfer unit is conveyed by a conveyance path 71b and is introduced into a fixing device (fixing unit, fixing unit) F to be subjected to a toner image fixing process. When the sheet P exiting the fixing device F is in the single-sided printing mode, the sheet P is introduced into the conveyance path 71c and discharged onto the discharge tray 72 as a single-sided image formed product.

  In the double-sided printing mode, the sheet P on which the single-sided image is formed exiting the fixing device F is introduced into the double-sided conveyance path 71d, is switched back and is reintroduced into the conveyance path 71a. As a result, the paper P is reintroduced in a state where the paper P is turned upside down with respect to the secondary transfer portion, and thereafter, the paper P is transported through the same transport path as in the single-sided printing mode and is formed on the discharge tray 72 on the double-sided image formed product As discharged.

(2) Fixing Device FIG. 3 is a perspective view of the fixing device F, and FIGS. 4A and 4B are a front view and a longitudinal front view of the device F, respectively. 5A is an enlarged right side view taken along line (5)-(5) in FIG. 4A, FIG. 5B is a partial enlarged view of FIG. 5A, and FIG. 5C is a pressure applying member. It is a cross-sectional view of (pressure pad). 6A and 6B are a left side view of the apparatus F and a left side view with a part cut away. 7A and 7B are a right side view of the apparatus F and a right side view partially cut away.

  In the following description, the longitudinal direction of the fixing device F or a member constituting the fixing device F is a direction parallel to a direction orthogonal to the paper transport direction (recording material transport direction) a in the paper transport path surface. The short direction is a direction parallel to the paper conveyance direction a. Regarding the fixing device F, the front means the surface when the device is viewed from the paper entrance side, the back is the opposite surface (paper exit side), and the left and right are the left or right when the device is viewed from the front. The upstream side and the downstream side are the upstream side and the downstream side in the paper transport direction a.

  The fixing device F of the present embodiment is an image heating device of a belt heating method by induction heating, and roughly includes the following members and mechanisms.

a: Heating assembly (belt unit) 1 including a flexible endless belt (hereinafter referred to as a fixing belt or a belt) 6 as a first rotating body (fixing member) in contact with the toner image carrying surface of the paper P
b: Pressure roller 2 having elasticity as a second rotating body (pressure member) facing the belt 6
c: Coil unit (induction heating device, magnetic flux generating means) 3 as a heating source for heating the belt 6
d: Pressurizing mechanism 4 for forming a nip portion N that presses the belt 6 and the pressure roller 2 to heat (image heating processing; fixing) the toner image on the paper (on the recording material).
e: Changing mechanism for changing the pressure of the nip portion N by the pressurizing mechanism 4 The above-described members and mechanisms are disposed between the left and right side plates 5L and 5R of the apparatus chassis 5 of the fixing apparatus F.

(2-1) Heating assembly 1
The heating assembly 1 has a fixing belt 6 that is cylindrical and flexible. The belt 6 has a magnetic member (metal layer, conductive member) that generates heat by electromagnetic induction when passing through a region where a magnetic field (magnetic field, magnetic flux) generated from the coil unit 3 exists. In addition, a metal stay 7 inserted into the belt 6 is provided. A pressure pad (nip pad) 8 as a pressure applying member is attached to the lower surface of the stay 7 along the longitudinal direction.

  The pad 8 is a member that forms a nip portion (fixing portion, fixing nip portion) N by applying a predetermined pressing force between the belt 6 and the pressure roller 2, and is made of a heat resistant resin. As shown in FIGS. 5B and 5C, the pad 8 has a cross section in which a portion facing the inner surface of the belt 6 is composed of an upstream protrusion 8a, a main pressure portion 8b, and a downstream protrusion 8c. . That is, the pad 8 has a convex portion that is an upstream protruding portion 8a at the upstream portion of the nip portion N, and a convex portion that is a downstream protruding portion 8c at the downstream portion of the nip portion N, and between the convex portions 8a and 8b. The main pressure portion 8b is included. The main pressure portion 8b does not necessarily need to be flat, and may be farther from the inner surface of the belt 6 than a portion connecting the tip of the upstream projection 8a and the tip of the downstream projection 8c with a flat surface.

  More specifically, the pad 8 is a pressure applying member configured to form a nip portion N by relatively applying pressure toward the pressure roller 2 with the belt 6 interposed therebetween. In the cross section, the pad 8 has a main pressure portion 8b near the center of the nip portion N at a portion facing the inner surface of the belt 6, and an upstream side and a downstream side in the sheet conveying direction a with the main pressure portion 8b being inside. Are provided with convex portions 3a and 3c projecting from the main pressure portion 8b toward the belt 6. The pad 8 has a crown for correcting the bending when pressure is applied, and the crown amount used in this embodiment is 1. at the longitudinal center and the end (position of 200 mm from the center) of the pad 8. 6 mm.

  Since the stay 7 needs rigidity to apply pressure to the nip portion N, it is made of iron in this embodiment. Also, on the upper surface side (coil unit 3 side) of the stay 7, there is a magnetic core (inner magnetic core) 9 for concentrating the induction magnetic field on the belt 6 in order to efficiently heat the belt 6. It is arranged over the length.

  The left and right ends of the stay 7 protrude outward from the left and right ends of the belt 6, respectively. The left and right symmetrical flange members (fixing flanges) 10L and 10R are fitted to both ends. The flange members 10L and 10R are regulating members that regulate the movement of the belt 6 in the longitudinal direction (width direction: left-right direction) and the shape in the circumferential direction. The belt 6 is loosely fitted around the assembly of the stay 7, the pad 8 and the core 9. Movement of the belt 6 in the longitudinal direction is restricted by the inward surfaces of the flange members 10L and 10R.

  As will be described later, the base layer 6a (FIG. 8) of the belt 6 is made of a metal that generates heat by electromagnetic induction. Therefore, it is sufficient to provide flange members 10 </ b> L and 10 </ b> R having flange portions that simply receive the end portions of the belt 6 as means for restricting the shift of the belt 6 in the rotational direction in the longitudinal direction. Thereby, there is an advantage that the configuration of the fixing device F can be simplified.

  A temperature sensor TH such as a thermistor as temperature detecting means (temperature detecting element) for detecting the temperature of the belt 6 is disposed through a support member 11 having elasticity at the center of the longitudinal direction of the pad 8. The sensor TH is in elastic contact with the inner surface of the belt 6 by the member 11. As a result, even if a position variation such as the sensor contact surface of the rotating belt 6 undulates, the sensor TH follows this and maintains a good contact state with the inner surface of the belt 6.

  The heating assembly 1 is disposed by engaging the flange members 10L and 10R with the longitudinal guide slit portions 5a disposed on the side plates 5L and 5R, respectively. Accordingly, the heating assembly 1 as a whole has a degree of freedom to be movable in the vertical direction along the slit portion 5a between the side plates 5L and 5R.

  FIG. 8 is a model diagram showing the layer structure of the belt 6. In this embodiment, the belt 6 has a nickel base layer (magnetic member, metal layer) 6a having an inner diameter of 30 mm and manufactured by electroforming. The thickness of the base layer 6a is 40 μm. A heat-resistant silicone rubber layer is provided as an elastic layer 6b on the outer periphery of the base layer 6a. The thickness of the layer 6b is preferably set within a range of 100 to 1000 μm.

  In this embodiment, the thickness of the layer 6b is set to 300 μm in consideration of reducing the heat capacity of the belt 6 to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. Silicone rubber has a hardness of 20 degrees JIS-A and a thermal conductivity of 0.8 W / mK. Further, on the outer periphery of the layer 6b, a fluororesin layer (for example, PFA or PTFE) is provided as a surface release layer 6c with a thickness of 30 μm.

  In order to reduce the sliding friction between the inner surface of the belt and the sensor TH, a resin layer (sliding layer) 6d such as fluororesin or polyimide may be provided on the inner surface side of the base layer 6a with a thickness of 10 to 50 μm. In this example, a polyimide layer having a thickness of 20 μm was provided as the layer 6d.

  The belt 6 as a whole has a low heat capacity and flexibility (elasticity), and maintains a cylindrical shape in a free state. In addition to nickel, a metal such as an iron alloy, copper, or silver can be selected for the metal layer 6a. Moreover, the structure of laminating | stacking these metals on a resin base layer may be sufficient. The thickness of the metal layer 6a may be adjusted according to the frequency of a high-frequency current that flows in an exciting coil 15 (to be described later) of the unit 3 and the permeability / conductivity of the metal layer 6a, and may be set between about 5 and 200 μm.

(2-2) Pressure roller 2
The pressure roller 2 is disposed on the lower side of the heating assembly 1 so as to be rotatable between the side plates 5L and 5R via a bearing 12 with the axial direction being substantially parallel to the longitudinal direction of the assembly 1.

  In this embodiment, the roller 2 has a core rubber 2a made of iron alloy having a diameter of 20 mm in the longitudinal direction and a diameter of both ends of 19 mm, and a silicone rubber layer provided as an elastic layer 2b. The outer diameter is 30 mm. An elastic roller having a crown shape. On the surface, a fluororesin layer (for example, PFA or PTFE) is provided as a release layer 2c with a thickness of 30 μm. The hardness at the center in the longitudinal direction of the roller 2 is ASK-C70 °.

  A gear 13 is fixedly disposed at the right end of the cored bar 2a. The driving force of the driving motor M1 controlled by the control unit 57 is transmitted to the gear 13 via a transmitting means (not shown), and the roller 2 is driven in the counterclockwise direction indicated by the arrow in FIG. It is rotationally driven at a speed of

(2-3) Coil unit 3
The coil unit 3 is a heater for induction heating of the belt 6 (induction heating means), and is disposed on the upper surface side of the heating assembly 1, that is, on the side opposite to the roller 2 side of the heating assembly 1 approximately 180 °. The coil unit 3 includes an exciting coil (coil that generates magnetic flux) 15, a magnetic core 16, and the like in a long housing 14 along the longitudinal direction of the belt 6.

  The housing 14 is a horizontally long box-shaped molded product made of heat-resistant resin (an electrically insulating resin mold member) having a longitudinal direction in the left-right direction. The bottom plate 14 a side of the housing 14 is a surface facing the belt 6. The bottom plate 61a is curved inward of the housing 14 so as to follow a substantially half-circumferential range of the outer peripheral surface of the belt 6 in the cross section.

  In the coil unit 3, both end portions of the housing 14 are received by the left and right flange members 10 </ b> L and 10 </ b> R of the heating assembly 1 through brackets 17. Thus, the bottom plate 14a of the housing 14 faces the upper surface of the belt 6 with a predetermined gap (gap) α. In the coil unit 3, the left and right side plates of the housing 14 are tied to the flange members 10L and 10R on the respective sides by wire springs (not shown). That is, the coil unit 3 is integrated with the heating assembly 1.

  Accordingly, when the flange members 10L and 10R of the heating assembly 1 are pressurized and sink as described later, the coil unit 3 also sinks together while maintaining the gap α. Further, when the flange members 10L and 10R are floated by being depressurized or released, the coil unit 3 is also floated together while maintaining the gap α.

  The coil 15 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 a part of the peripheral surface and side surface of the belt 6. And it is applied to the inner surface of the bottom plate 14a that is curved to the inside of the housing and is housed inside the housing. A high frequency current is applied to the coil 15 from a power supply device (excitation circuit) 103 controlled by the control unit 57.

  The core 16 is an outer magnetic core (outer magnetic core) that covers the coil 15 so that the magnetic field generated by the coil 15 does not substantially leak outside the metal layer (conductive layer) of the belt 6. The core 16 is disposed along the longitudinal direction of the belt 6 and is divided into a plurality of lines in a direction orthogonal to the paper transport direction a, and is arranged around the winding center portion of the coil 15 and the surrounding area. It is comprised so that it may surround.

  The core 16 divided into a plurality is provided in a non-sheet passing portion in order to suppress a temperature rise in the non-sheet passing portion when a paper having a width smaller than that of the maximum width size usable in the apparatus is passed. The corresponding portion of the split core is moved in a direction to widen the gap with the coil 6 by a moving mechanism (not shown). As a result, the magnetic flux density passing through the belt 6 in the portion corresponding to the non-sheet passing portion is lowered, and the amount of heat generated in the belt portion is reduced. Since the movement control of the split core is out of the gist of the present invention, a detailed description is omitted.

(2-4) Pressurizing mechanism 4 and changing mechanism In this embodiment, the pressurizing mechanism 4 presses the pad 8 of the heating assembly 1 to the roller 2 with a predetermined pressing force (pressure) via the belt 6. The pressure means for forming a predetermined nip N between the belt 6 and the roller 2. In the present embodiment, the pressure of the pressurizing mechanism 4 can be changed by a changing mechanism.

  Hereinafter, a specific mechanism configuration will be described. A pair of left and right pressure levers 18L and 18R that are long in the front-rear direction (paper conveyance direction) as pressure members are disposed on the outer upper portions of the side plates 5L and 5R, respectively.

  The lever 18L is positioned above the pressurized portion 10a of the flange member 10L, and the rear end portion pivots so as to be rotatable in the vertical direction about the support shaft 18a with respect to the side plate 5L behind the flange member 10L. It is worn. That is, the lever 18L can operate in a direction in which the pressed portion 10a of the flange member 10L is pressed against the supporting shaft 18a or in a direction away from the pressed portion 10a. The front end of the lever 18L is located on the front side of the flange member 10L. The lever 18L is always urged to rotate downward about the shaft 18a by the spring force of a spring 19a of a spring-loaded screw 19L as an urging member disposed between the lever 18L and the side plate 5L.

  The lever 18R is positioned above the pressurized portion 10a of the flange member 10R, and the rear end portion pivots so as to be rotatable in the vertical direction around the support shaft 18a with respect to the side plate 5R behind the flange member 10R. It is worn. That is, the lever 18R can be operated in a direction in which the pressed portion 10a of the flange member 10R is pressed against the supporting shaft 18a or in a direction away from the pressed portion 10a. The front end portion of the lever 18R is located in front of the flange member 10R. The lever 18R is constantly urged to rotate downward about the shaft 18a by the spring force of a spring 19a of a spring-loaded screw 19R as an urging member disposed between the lever 18R and the side plate 5R.

  When the levers 18L and 18R are in a free state, the lower surfaces of the levers 18L and 18R are spring forces defined by springs 19a of spring-loaded screws against the upper surfaces of the pressurized portions 10a of the flange members 10RL and 10R, respectively. It's pushing enough. In this embodiment, this pressure is set to 550 N, for example. Thereby, in the heating assembly 1, the stay 7 and the pad 8 are pushed down together with the flange members 10RL and 10R, and the pad 8 presses against the roller 2 against the elasticity of the elastic layer 2b with the belt 6 interposed therebetween.

  As a result of this pressure contact, a nip N having a predetermined width is formed between the belt 6 and the roller 2 in the paper transport direction a. The pad 8 assists in forming a pressure profile in the nip N. The configuration at this time is hereinafter referred to as a pressurizing configuration.

  A cam shaft 21 is rotatably disposed between the side plates 5L and 5R via bearings 20 and 20. On the left and right ends of the shaft 21, eccentric cams (pressure release members) 22L and 22R that are symmetrical and have the same shape on the outside of the side plates 5L and 5R are fixed and arranged in the same phase. The cam 22L is located below the front end of the pressure lever 18L. The cam 22R is located below the front end of the lever 18R.

  A gear (pressure releasing gear) 23 is fixedly disposed at the left end of the shaft 21. A driving force of a pressure roller detaching motor (for example, a stepping motor) M2 controlled by the control unit 57 is transmitted to the gear 23 through a transmitting means (not shown), and the shaft 21, that is, the cams 22L and 22R is rotated. Is controlled. That is, the control unit 57 rotates the motor M2 according to a predetermined signal to rotate the gear 23 by a predetermined amount in a predetermined direction. The shaft 21 rotates according to the rotation of the gear 23, and the cams 22L and 22R rotate accordingly.

  By controlling the rotation of the cams 22L and 22R, the levers 18L and 18R are lifted and rotated against the spring force of the spring 19a of the spring-loaded screw 19L, whereby the pressure of the pad 8 on the roller 2 is changed.

  The bearings 20 and 20, the shaft 21, the cams 22 </ b> L and 22 </ b> R, the gear 236, and the motor M <b> 2 are changing mechanisms that change the pressure of the nip portion N by the pressurizing mechanism 4. Details of the pressure change of the pressurizing mechanism 4 will be described later.

(2-5) Fixing Operation In the standby state of the image forming apparatus, in the fixing apparatus F, the motor M1 is turned off and the rotation of the roller 2 is stopped. The pressurizing mechanism 4 is in a pressure release state, and the pressurization of the nip portion N is released. The power supply to the coil 15 of the coil unit 3 is turned off.

  The control unit 57 puts the pressurizing mechanism 4 into a pressurizing state at a predetermined control timing based on the input of the print job start signal (image forming job start signal). As a result, the nip portion N is in a pressurized state. Also, the motor M1 is turned on. Thereby, the roller 2 is rotationally driven at a predetermined speed in the counterclockwise direction of the arrow in FIG.

  Due to the rotation of the roller 2, the rotational force acts on the belt 6 by the frictional force between the surface of the roller 2 and the surface of the belt 6 at the nip portion N. While the inner surface of the belt 6 slides in close contact with the lower surface of the pad 8, the outer periphery of the stay 7, the pad 8 and the core 9 is driven to rotate in the clockwise direction indicated by the arrow in FIG. . A lubricant is applied to the pad 8 to reduce a sliding load with the belt 6. In this embodiment, fluorine grease was used in consideration of wraparound from the end when used near the fixing temperature adjustment temperature (180 ° C.).

  The movement in the thrust direction accompanying the rotation of the belt 6 is restricted by the flange portions of the left and right flange members 10L and 10R. The belt 6 is driven and rotated as described above by rotating the roller 2 by the motor M1 controlled by the control unit 57 at least during execution of image formation. This rotation is performed at substantially the same peripheral speed as the conveyance speed of the sheet P carrying the unfixed toner image t conveyed from the secondary transfer nip portion side. In the case of this embodiment, the surface rotation speed of the belt 6 is 300 mm / sec, and it is possible to fix 70 full-color images for A4 size and 49 for A4R size per minute.

  The controller 57 supplies an alternating current (high-frequency current) of 20 kHz to 50 kHz, for example, from the power supply device 103 to the coil 15. The coil 15 generates an alternating magnetic flux (magnetic field) by supplying an alternating current. The alternating magnetic flux is guided to the metal layer 6 a of the belt 6 on the upper surface side of the belt 6 rotating by the core 16. Then, an eddy current is generated in the metal layer 6a, and the metal layer 6a self-heats (electromagnetic induction heat) by Joule heat due to the eddy current, and the belt 6 is heated.

  That is, when the rotating belt 6 passes through the region where the magnetic field generated from the unit 3 is present, the metal layer 6a generates heat by electromagnetic induction and is heated all around. The temperature of the belt 6 is detected by the temperature sensor TH. The sensor TH detects the temperature of the portion of the belt 6 where the paper passes, and the detected temperature information is fed back to the controller 57. The control unit (temperature control function unit of the control unit) 57 maintains the detected temperature (information about the detected temperature) input from the sensor TH at a predetermined target temperature (fixing temperature: information corresponding to the predetermined temperature). Thus, the power supplied from the power supply device 103 to the coil 15 is controlled.

  That is, when the detected temperature of the belt 6 rises to a predetermined temperature, the power supply to the coil 15 is interrupted. In this embodiment, the temperature is adjusted by controlling the power input to the coil 15 by changing the frequency of the high-frequency current based on the detection value of the sensor TH so that the target temperature of the belt 6 is constant at 180 ° C. Is going. The target temperature may be configured to change the paper temperature (recording material temperature) by analogy with a temperature / humidity sensor E (FIG. 2) disposed in the image forming apparatus main body.

  In this embodiment, the belt 6 and the coil 15 of the coil unit 3 are kept electrically insulated by a 0.5 mm mold (the bottom plate 14a of the housing 14). The distance between the belt 6 and the coil 15 is 1.5 mm (the distance between the mold surface and the belt surface is 1.0 mm), and the belt 6 is uniformly heated.

  Since the coil unit 3 including the coil 15 is disposed not inside the belt 6 that becomes high temperature but outside, the temperature of the coil 15 does not easily become high temperature, electric resistance does not increase, and Joule heat is generated even when a high-frequency current flows. It is possible to reduce the loss due to Moreover, it can be said that it has contributed also to the diameter reduction (lower heat capacity) of the belt 6 by having arrange | positioned the coil 15 outside, and is excellent also in energy-saving property by extension.

  The warming-up time of the fixing device F of this embodiment has a very low heat capacity. Therefore, for example, when 1200 W is input to the coil 15, the target temperature of 180 ° C. can be reached in about 15 seconds, and the heating operation during standby is unnecessary, so that the power consumption can be kept very low.

  In the state where the roller 2 is driven and the belt 6 rises to a predetermined fixing temperature and is adjusted in temperature as described above, the paper P carrying the unfixed toner image t in the nip portion N is placed on the toner image carrying surface side of the belt P. It is guided and guided by the guide member 24 toward the 6 side. The sheet P is in close contact with the outer peripheral surface of the belt 6 at the nip portion N, and is nipped and conveyed along the nip portion N together with the belt 6.

  As a result, mainly the heat of the belt 6 is applied, and the unfixed toner image t is fixed to the surface of the paper P by heat and pressure under the pressure of the nip portion N. The sheet P that has passed through the nip portion N is conveyed from the outer peripheral surface of the belt 6 to the outside of the fixing device with the surface of the belt 6 being self-separated (curvature separation) by deformation of the exit portion of the nip portion N. In this embodiment, the paper P is introduced into the fixing device F by so-called central reference conveyance centered on the paper width. In FIG. 4A, O is the center reference line (virtual line).

(2-6) Pressure changing operation The cams 22L and 22R have two peak shapes as shown in FIG. The position of the belt 6 when the cams 22L and 22R rotate will be described with reference to FIG.

  FIG. 10A shows the normal pressure mode. In this mode, the planar portions of the cams 22L and 22R are in an upward rotation angle posture, and the cams 22L and 22R are not in contact with the levers 18L and 18R. Therefore, the spring force of the springs 19a of the spring-loaded screws 19L and 19R sufficiently acts on the levers 18L and 18R, and the pressure of the nip portion N is in a predetermined first pressure (normal pressure) (pressurization) Constitution).

  In the present embodiment, in the normal pressure mode (first pressurization mode), the force (total pressure at the nip) applied to the heating assembly (belt unit) 1 is 500N. Examples of the normal pressure include 100N to 900N.

  The cams 22L and 22R rotate clockwise in the normal pressure mode of FIG. 10 (a), and the levers 18L and 18R are resisted against the spring force of the spring 19a of the spring-loaded screw 19R. Push it up to the position 1) ((a) → (b)). Then, the pressure on the flange members 10L and 10R is reduced by half, and the position of the belt 61 is raised by ΔY1 ((a) → (b)). As a result, the pressure in the nip portion N is lower (weaker, lighter) than the first pressure in the normal pressure mode, and a predetermined envelope pressure mode (second pressurization mode) is set (pressure reduction configuration).

  In this embodiment, in this envelope pressure mode, the force applied to the heating assembly (belt unit) 40 (total pressure at the nip) is set to be 30N. Examples of the light pressure include 10N to 90N.

  When the cams 22L and 22R further rotate to push the levers 18L and 18R to the position of the second highest peak (peak 2), the belt 6 is further raised by ΔY2. Then, the pressure of the spring force of the spring 19a of the screw 19R with the spring against the flange members 10L and 10R is invalidated, and the belt 6 and the roller 2 enter the pressure release mode (pressure release state: pressure release configuration) ((b) → ( c)).

  The control unit 57 controls the fixing device F to the pressure release mode shown in FIG. 10C when the image forming apparatus is on standby or non-image forming. When the paper to be passed through the fixing device F is other than the envelope, the normal pressure mode shown in FIG. In the case of an envelope, the envelope pressure mode (pressure reduction configuration) shown in FIG. 10B is controlled.

(2-7) Pressurization Mode A pressurization mode at the nip portion N in the normal pressure mode and the envelope pressure mode of the fixing device F in this embodiment will be described with reference to FIGS. 11 (a) and 12 (a) are cross-sectional views when paper (plain paper) P other than the envelope passes through the nip portion N in each mode, and FIG. 11 (b) and FIG. b) shows cross-sectional views when the envelope passes through the nip portion N in each mode. Further, (c) in FIG. 11 and (c) in FIG. 12 show velocity distributions on the envelope cover when the envelope is passed in each mode.

  In the normal pressure mode, as shown in FIG. 11A, the upstream protrusion 8 a, the main pressure part 8 b, and the downstream protrusion 8 c of the pressure pad 8, which is a pressure applying member, are all in pressure contact with the belt 6. When the paper P other than the envelope is passed, the nip portion N has an upwardly convex shape due to the protrusions 8a and 8c on the upstream and downstream sides of the pad 8. Therefore, the paper discharged from the nip portion N is directed downward. It has become. Thereby, even when a sheet having a small basis weight and a low rigidity is passed, the separation property to the fixing belt 6 is sufficiently secured.

  On the other hand, when the envelope passes through the nip portion N in the normal pressure mode as shown in FIG. 11B, the portions not restrained by the front and back of the envelope are the protrusions 8a and 8b on the upstream and downstream sides of the pressure pad 8. Thus, the nip portion N has an upwardly convex shape. For this reason, due to the deformation of the envelope passing through the nip portion N, a difference in transport amount occurs between the upper surface and the lower surface of the envelope.

  FIG. 11C shows the transport amount (solid arrow) in the front and the transport amount of the reverse transport amount (dotted arrow) when the envelope is the long type No. 3. In the envelope, two sheets of front and back sheets are constrained on the front and back sides of at least one side in the belt width direction. In the case of long die No. 3, the position indicated by x is a restraint location. Since the front and back surfaces are continuous in the constrained portion, the nip portion N passes through an intermediate conveyance amount between the front and back conveyance amounts. Due to the difference in feed amount in the belt width direction between the constrained part and the non-constrained part of the envelope, a rotational moment as shown by the white arrow occurs, and the envelope 蓄積 w Will occur.

  In the present embodiment, since the purpose is to make the nip portion N convex in the normal pressure mode, the belt 6 does not have to be in contact with all the main pressure portions 8b of the pressure pad 8, and the main pressure portion It is only necessary that a part of 8b is in contact with the belt 6.

  In the envelope pressure mode, as shown in FIG. 12A, the upstream protrusion 8 a and the downstream protrusion 8 c of the pressure pad 8 are both in pressure contact with the belt 6, but the main pressure portion 8 b is separated from the belt 6. It becomes a state. When the paper P other than the envelope is passed, the nip portion is not an upward convex shape but a straight shape due to the rigidity of the protrusions 8 a and 8 c on the upstream and downstream sides of the pressure pad 8 and the belt 6. The sheet discharged from the nip portion N is discharged straight. In this case, there is no problem with the high-rigidity paper P that is two-layered like an envelope, but when the plain paper P with low basis weight and low rigidity is passed, the curvature of the belt 6 cannot be sufficiently secured. Separation may be insufficient.

  On the other hand, when the envelope passes through the nip portion N in the envelope pressure mode as shown in FIG. 12 (b), the nip portion N does not have an upward convex shape but a straight shape at the front and back of the envelope. It has become. Therefore, the deformation of the envelope passing through the nip portion N can be suppressed, and the difference in the feeding amount between the two sheets of the front and back of the envelope can be suppressed ((c) in FIG. 12). As a result, it is possible to suppress the occurrence of a speed deviation in the belt width direction between the constrained portion and the non-constrained portion of the envelope, thereby preventing the occurrence of envelope wrinkles.

In this embodiment, in the envelope pressure mode, the belt 6 is supported only by the upstream protrusion 8a and the downstream protrusion 8c of the pressure pad 8 as shown in FIG. The configuration in which the portion 8b does not contact the belt 6 has been described. In the envelope pressure mode, there is an exception that a part of the main pressure portion 8b is in contact. For example, there are cases where the upstream / downstream protrusions are not sufficiently high in the mechanical tolerance range, or where the upstream / downstream protrusions have become low due to durable wear. Further, in the envelope pressure mode, when an envelope having high rigidity passes through the nip portion N, the belt 6 may be deformed and the belt 6 may come into contact with the main pressure portion 3b of the pressure pad 8. There is no problem because the envelope is difficult to generate. As an envelope with high rigidity, for example, manufactured by Yamagata Co., Ltd., long 3 Sumi sticking AR Ultra White 130 pear frame, 120 mm × 235 mm, basis weight 130 g / m ^{2 and the} like can be mentioned.

(2-8) Control The control of the present embodiment will be described with reference to the control system block diagram shown in FIG. The control unit 57 exchanges various kinds of electrical information with the operation unit C and an external device (such as a PC or a print server) D, and comprehensively controls the printing operation (image forming operation) of the printer unit B. The operation unit C is a user interface that performs a print mode setting from a user (operator, user), inputs of various instructions and settings of printing conditions such as used paper and number of sheets, and notification of the apparatus status to the operator.

  Recording material type information (recording material information such as paper size, basis weight, and paper type) input by the user is sent to the recording material information processing unit 102 using the operation unit C or the external device D as an input unit, and the recording material information Information of the processing unit 102 is transferred to the CPU 100 of the printer control unit 57. The CPU 100 refers to the memory 101 and instructs the pressure control unit 104 to set the pressure of the fixing device F to a predetermined value based on information from the recording material information processing unit 102.

  That is, the CPU 100 of the printer control unit 57 controls the change mechanism based on the recording material information acquired regarding the recording material to be used, and executes switching between the first pressure mode and the second pressure mode.

  The pressure control unit 104 controls the pressure of the fixing device F to a predetermined pressure. That is, when the paper to be used is plain paper (setting information of the recording material other than the envelope), as described above, the motor is set so that the pressure of the fixing device F becomes the normal pressure (first pressure mode). The change mechanism is operated by controlling M2. In the case of an envelope (envelope setting information), the change mechanism is operated by controlling the motor M2 so that the envelope pressure (second pressurization mode) is obtained.

  Further, the CPU 100 controls the power supply device 103 that supplies power to the coil 15 based on the information of the temperature / humidity sensor E (FIG. 2) attached to the image forming apparatus main body and the detected temperature of the temperature sensor TH of the belt 6. The belt 6 can be controlled to a predetermined temperature. The CPU 100 can control the motor M1 that drives the pressure roller 2 to rotate or stop the pressure roller 2.

  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 (JOB). Thereafter, the CPU 100 determines whether or not the paper to be passed is an envelope job that is an envelope (S1000). If the paper to be passed is not an envelope, the CPU 100 sets the pressure of the fixing device F to the normal pressure mode (S1001), and performs an image forming operation and a fixing operation (S1003). In S1000, if the paper to be passed is an envelope, the envelope pressure mode is set (S1002), and the image forming operation & fixing operation (S1003) is performed.

  The fixing operation in the normal pressure mode and the envelope pressure mode will be described with reference to the flowchart shown in FIG. First, the CPU 100 drives the pressure roller detachment motor M2 to adjust the pressure of the fixing device F to a normal pressure (S1100). Next, the CPU 100 drives the pressure roller 2 by the drive motor M, rotationally drives the pressure roller 2 and the belt 6, applies a voltage to the coil 15, and heats the belt 6 (S1101). Heating and rotation are continued until the belt 6 reaches a predetermined temperature control temperature (S1102).

  When the mode determined in the flow of FIG. 1 is the envelope pressure mode, the pressure of the fixing device F is switched to the envelope pressure (S1103, S1104). The CPU 100 introduces the paper P on which the unfixed toner is placed into the nip portion N by the image forming operation of the image forming unit and fixes the unfixed toner on the paper P (S1105).

  The CPU 100 performs the operations of S1103 to S1105 until the print job is completed (S1106). When the print job is completed, the rotation of the drive motor M and the power supply to the coil 15 are stopped (S1107). Depending on the setting after the end of the print job, the pressure roller removal motor M2 is driven to change the pressure of the fixing device F to normal pressure or pressure release (S1108).

Table 1 shows the results of the experiment of this example. In the experiment, a long type No. 3 envelope (long 3 middle-ply book Kent CoC 80 made by Yamagata Co., Ltd., 120 mm × 235 mm, basis weight 80 g / m ² ), 10 in an environment of 30 ° C. and 80%. Pass the sheets continuously. If no envelopes were found out of the 10 sheets, it was marked as ◯. Further, in order to confirm the paper separation property, a full-color blue image of plain paper (CS520 A4 size manufactured by Canon, basis weight 52 g / m ² ) was fed in the same environment.

  In normal pressure mode, envelope flaws occur, but thin plain paper is not a problem. In the envelope pressure mode, envelope flaws did not occur, and paper wrapping around the fixing belt 6 due to poor separation occurred with thin plain paper. This is realized by the upstream protrusion 8a and the downstream protrusion 8c of the pressure pad 8 which is a pressure applying member, and pressure adjustment. That is, in the envelope pressure mode, a straight nip is formed and envelope flaws are prevented, and in the normal pressure mode, the separation property of thin paper can be ensured without problems by the convex shape of the nip.

  As described above, in the case of an envelope, the envelope pressure mode in which a straight nip is formed in which the fixing belt 6 is supported by the upstream and downstream protrusions 8a and 8c of the pressure applying member 8 is used. As a result, the generation of envelope flaws is prevented, and in the normal pressure mode, an upward convex nip is formed by pressurization by the upstream and downstream protrusions 8a and 8c of the pressure pad 8 and the main pressure portion 8b, thereby separating plain paper. It was possible to provide a fixing device that achieves compatibility.

<< Second Embodiment >>
In the second embodiment, in the configuration of the first embodiment, the flowchart of FIG. 1 is changed as shown in FIG. 15, and the rigidity of the envelope is determined based on at least one of the environmental temperature, the humidity, and the basis weight of the envelope. Whether to perform the envelope pressure mode is determined. In the same configuration as in the first embodiment, the same number is assigned and the description is omitted.

  The control of the second embodiment will be described with reference to the flowchart shown in FIG. The same operations as in FIG. 1 are omitted by giving the same numbers. In the configuration of the second embodiment, when the sheet to be passed in S1000 is an envelope, if it is determined that the rigidity of the envelope is higher than a predetermined value, the normal pressure mode is set. If it is determined that the envelope rigidity is equal to or less than the predetermined rigidity, the envelope pressure mode is set and the fixing operation is performed (S2000).

  That is, the CPU 100 as the control means has a determination unit that determines the rigidity of the recording material to be used. When the recording material information is an envelope, the CPU 100 determines that the rigidity of the envelope is higher than a predetermined value by the determination unit. In the case of a failure, the first pressurizing mode is executed.

  The rigidity of the envelope is determined by the CPU 100 from the basis weight information of the envelope set by the user from the external device D such as a PC or the input unit of the operation unit C and the temperature / humidity information from the environment sensor E. In the second embodiment, the CPU 100 of the printer control unit 57 determines the absolute moisture content in the air based on the temperature / humidity information from the temperature / humidity sensor E.

In the second embodiment, when the weight of water per kg of air is 8 g or more, it is determined that the envelope having a basis weight larger than 100 g / m ² has high rigidity and is set to the normal pressure mode, and 100 g / m ² For the following basis weights, the fixing operation is performed in the envelope pressure mode. When the weight of water per kg of air is less than 8 g, envelopes with a basis weight greater than 80 g / m ² are judged to have high rigidity and are set to the normal pressure mode. When the basis weight is 80 g / m ² or less Performs the fixing operation in the envelope pressure mode.

  Tables 2 and 3 show the results of experiments in the second embodiment. The experiment was performed when 10 sheets of envelopes 1) to 3) below were passed continuously in an environment of 30 ° C. and 80% (Table 2) and 15 ° C. and 10% (Table 3). is there. If there was no envelope flaw out of 10 sheets, it was rated as ○, and if even one sheet wrinkled, it was marked as x.

1) Long type No. 3 envelope (Long 3 middle sticking this Kent CoC 80 〒 frame pear, manufactured by Yamagata, 120 mm x 235 mm, basis weight 80 g / m ² )
2) Envelope with a basis weight of 100 g / m ² (long 3 middle-plyed Kent CoC 100 〒 frame, manufactured by Yamagata, 120 mm × 235 mm, basis weight 100 g / m ² )
3) Envelope with a basis weight of 130 g / m ² (long 3 Sumi affixed AR Ultra White 130 pear frame made by Yamagata, 120 mm x 235 mm, basis weight 130 g / m ² )
In the case of high temperature and high humidity such as 30 ° C and 80% environment (Table 2), the envelope stiffness is low, so in the normal pressure mode, envelope wrinkles occur at basis weights of 80 g / m ² and 100 g / m ^2. In the mode, an envelope flaw is not generated and a good image is obtained. In a thick envelope having a basis weight of 130 g / m ² , wrinkles are not generated due to the rigidity of the envelope, but in the envelope pressure mode, a sufficient nip width cannot be ensured, so that the amount of heat is insufficient and fixing failure occurs.

In the case of low temperature and low humidity such as 15 ° C. and 10% environment (Table 3), since the rigidity of the envelope is high, unlike Table ² , envelope flaws do not occur at a basis weight of 100 g / m ² in the normal pressure mode. However, in the envelope pressure mode, a sufficient nip width cannot be ensured, so that the amount of heat is insufficient and slight peeling (fixing failure) occurs.

  As described above, the configuration of the second embodiment is to determine the envelope rigidity based on at least one of the environmental temperature, humidity, and envelope basis weight, and to determine whether to perform the normal pressure mode. is there. Accordingly, by selecting the optimum mode for the basis weight of the envelope, it is possible to prevent the occurrence of envelope flaws and to prevent the occurrence of fixing failure due to the insufficient amount of heat supplied to the paper.

<< Third embodiment >>
In the third embodiment, in the configuration of the first embodiment, the flowchart of FIG. 14 is changed as shown in FIG. 16, and the apparatus is preheated and rotated at a normal pressure for a predetermined time. Thus, the slip is prevented from occurring even when endurance or high viscosity grease is used. In the same configuration as in the first embodiment, the same number is assigned and the description is omitted.

  The control of the third embodiment will be described with reference to the flowchart shown in FIG. The same operations as in FIG. 14 are omitted by giving the same numbers. In the configuration of the third embodiment, when the envelope pressure mode is selected in S1103, an operation of rotating (preheating) the apparatus for a predetermined time while maintaining the temperature control temperature is performed. (S3000).

Table 4 shows the results of experiments of the third embodiment. In the experiment, 600,000 sheets were fed by CS680 (A4 size manufactured by Canon, basis weight 68 g / m ² ) in the configuration of the first example. After that, the heating idle rotation time in the operation of S3000 in FIG. 16 was changed, and after changing to the envelope pressure, the case where the fixing belt 6 was rotated by being driven by the pressure roller 2 by the rotation of the driving motor M1 was marked as ◯.

  It can be seen that when the heating idling time is 5 seconds or less in the operation of S3000, the fixing belt 6 slips. This is because the grease in the fixing nip portion N is mixed with wear powder or the like due to durability and deteriorated to increase the viscosity. In the envelope pressure mode, since the fixing nip portion N is narrowed, transmission of driving force from the pressure roller 2 is weakened.

  Therefore, in the configuration of the third embodiment, heating idling is performed in a state where sufficient driving force is transmitted to the fixing belt 6 with normal pressure, and the deteriorated grease in the vicinity of the fixing nip portion N is sufficiently warmed to lower the viscosity. Thus, slipping of the fixing belt 6 was avoided. That is, when executing the second pressurizing mode, it is preferable to preheat and rotate the apparatus for a predetermined time in the first pressurizing mode and then shift to the second pressurizing mode.

  In this third embodiment, the heating idling time is always constant, but the durable sheet counter is necessary in consideration of the viscosity of the grease from the predetermined sheet number information, the temperature history of the temperature sensor TH of the fixing belt 6 and the like. Only the heating idle rotation may be used.

<< 4th Example >>
In the fourth embodiment, the coil unit (induction heating device) 3 for heating the belt 6 is eliminated and the belt 6 is heated by the halogen heater 15 'in the configuration of the first embodiment. In the same configuration as in the first embodiment, the same number is assigned and the description is omitted.

  As shown in FIG. 17, the halogen heater 15 ′ is disposed inside the stay 7 ′ and heats the belt 6 with radiant heat. The stay 7 'is made of heat-resistant glass that transmits the light from the halogen heater 15'. The halogen heater 15 ′ is connected to the power supply device 103 controlled by the CPU 100 of the control unit 57 as in the first embodiment, and based on the temperature information of the temperature sensor TH so that the temperature of the fixing belt 6 becomes a predetermined temperature. The CPU 100 controls ON / OFF.

  With the configuration described above, even when the halogen heater 15 ′ is used instead of the coil 15, the same effect as that of the first embodiment can be obtained.

<< 5th Example >>
The fifth embodiment also has a configuration in which the coil unit (induction heating device) 3 for heating the belt 6 is eliminated and the belt 6 is a belt 6 ′ having a resistance heating layer in the fixing device configuration of the first embodiment. In the same configuration as in the first embodiment, the same number is assigned and the description is omitted.

  The configuration of the fixing device of this embodiment is shown in FIG. A portion related to induction heating is eliminated from the fixing device configuration of the first embodiment, and the belt 6 is changed to a belt 6 'having a resistance heating layer.

  The configuration of the belt 6 'having a resistance heating layer in this embodiment will be described with reference to FIG. The belt 6 ′ in this embodiment has a five-layer composite structure including a slipping layer 6 d, a base layer 6 a ′, a heat generation layer 6 e, an elastic layer 6 b, and a release layer 6 c in order from the inner peripheral side to the outer peripheral side. Further, a feeding electrode portion (not shown) is provided at the end in the belt width direction.

  The belt 6 'has a base layer 6a' made of polyimide having an inner diameter of 4 mm. The thickness of this base layer 6a 'is 60 m. In the fifth embodiment, an insulating polyimide is used, but a resin belt such as polyimide amide, PEEK, PTFE, PFA, FEP, or a metal belt such as SUS or nickel can be used as the base layer 6a '. When a conductive material is used for the base layer 6a ', it is necessary to provide an insulating layer such as polyimide between the base layer 6a' and the heat generating layer 6e.

  A resin layer (sliding layer) 6d such as fluororesin or polyimide may be provided on the inner surface side of the base layer 6a 'in order to reduce sliding friction between the belt inner surface and the temperature sensor TH. In this example, 10 μm of fluororesin was provided.

  The heat generating layer 6e is formed between the base layer 6a 'and the elastic layer 6b. The heating layer 6e is a resistance heating element in which a polyimide resin containing carbon as conductive particles is applied on the base layer 6a 'with a uniform thickness. The total resistance value of the heat generating layer 6e is 10.0Ω. Therefore, the electric power generated when energizing an AC power supply with a voltage of 100 V is 1000 W. The resistance value may be determined as appropriate depending on the amount of heat generated as a fixing device, and can be adjusted as appropriate depending on the mixing ratio of carbon.

  Further, power supply electrode portions (not shown) are formed at both ends of the belt 6 ', and the power supply electrode portions (not shown) are electrically connected to both ends of the heat generating layer 6e. The power supply electrode portion is made of a material having conductive characteristics including silver and palladium.

  The power supply electrode portion of the belt 6 ′ is connected to the power supply device 103 controlled by the CPU 100 of the control portion 57 as in the first embodiment, and the temperature sensor TH is adjusted so that the temperature of the belt 6 ′ becomes a predetermined temperature. Based on the temperature information, ON / OFF control is performed by the CPU 100.

  With the configuration described above, even when the belt 6 ′ having a resistance heating layer is used instead of the coil 15, the same effect as that of the first embodiment can be obtained.

  As described above, when the fixing device of this embodiment is used, in the low heat capacity type fixing device, the generation of envelope flaws can be prevented and the generation of envelope flaws and the image quality can be adjusted according to the user's preference. Is possible.

《Other matters》
(1) In the fixing device F of the embodiment, the pressure pad 8 is pressed against the pressure roller 2 via the belt 6, but conversely, the pressure roller 2 is pressed via the belt 6. It is also possible to adopt a mechanism configuration that applies pressure to the pressure pad 8. Further, a mechanism configuration in which the pressure pad 8 and the pressure roller 2 are pressed against each other via the belt 6 may be employed. That is, a mechanism configuration in which the pressure pad 8 and the pressure roller 2 are relatively pressurized via the belt 6 can be provided.

  (2) The fixing device F that is a fixing unit is not limited to use as a device that heat-fixes an unfixed toner image formed on a recording material as a fixed image. It is also effective as a device for adjusting the surface properties of an image, such as improving the glossiness of an image by re-heating and pressurizing a toner image once fixed or presupposed on a recording material. Called device).

  (3) The image forming apparatus is not limited to the 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.

  61-68..Image forming part, P..Recording material, t..Toner image, F..Fixing part (fixing device), 6..Belt, 2-rotor, N..Nip part, 8..Pressure Applying member (pressure pad), 8a ... upstream protrusion, 8b ... main pressure part, 8c ... downstream protrusion, D ... operation part, 57 ... execution part (control part)

Claims (8)

An image forming unit for forming a toner image on a recording material;
A flexible endless belt, a pressure applying member in contact with the inner surface of the belt, and a rotating body that forms a nip portion with the pressure applying member via the belt, the belt being the rotating body An image forming apparatus comprising: a fixing unit that rotates by rotation of the recording medium and heats the recording material carrying the toner image at the nip portion while nipping and conveying the recording material.
In the cross section, the pressure applying member has a main pressure portion in the vicinity of the center of the nip portion at a portion facing the inner surface of the belt, and an upstream side and a downstream side in the recording material conveyance direction with the main pressure portion interposed therebetween, respectively. Having an upstream protrusion and a downstream protrusion protruding from the main pressure part toward the belt,
The pressure applying member and the rotating body are relatively pressed through the belt so that the upstream protruding portion, the downstream protruding portion, and the main pressure portion are in contact with the inner surface of the belt. The first pressure mode, the pressure applying member and the rotating body so that the upstream protrusion and the downstream protrusion are in contact with the inner surface of the belt and the main pressure portion is not in contact with the inner surface of the belt. A change mechanism capable of switching between a second pressurizing mode in which the pressure is relatively pressed through the belt;
An execution unit that controls the change mechanism based on the recording material information acquired with respect to the recording material to be used and executes switching between the first pressurization mode and the second pressurization mode. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the execution unit executes the second pressurizing mode when the recording material information is an envelope.   A determination unit configured to determine the rigidity of the recording material to be used, and when the recording material information is an envelope, the execution unit determines that the rigidity of the envelope is higher than a predetermined value by the determination unit; The image forming apparatus according to claim 2, wherein the first pressure mode is executed.   The image forming apparatus according to claim 3, wherein the determination unit determines the rigidity of the envelope based on at least one of temperature, humidity, and basis weight.   When executing the second pressurizing mode, the execution unit preheats and rotates the apparatus for a predetermined time in the first pressurizing mode and then shifts to the second pressurizing mode. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, further comprising a heating source that heats the belt, wherein the heating source is a coil that induction-heats the belt.   The image forming apparatus according to claim 1, further comprising a heating source that heats the belt, wherein the heating source is a halogen heater.   The image forming apparatus according to claim 1, wherein the belt includes a heat generating layer that generates heat when energized.