JP6821413B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus having a fixing equipment for fixing the toner image on the recording material. Examples of the image forming apparatus include a copier, a printer, a fax machine, and a multifunction device having a plurality of these functions.

An electrophotographic copying machine or the like is provided with a fixing device for fixing a toner image transferred to a recording material by heat and pressure.

As the fixing device, in order to raise the temperature at high speed, the fixing roller is made thinner and smaller in diameter, the heated body is pressed against the rotating body of the resin film from the inside, and the rotating body of thin metal is heated by induction heating. Etc. are known. All of these are intended to reduce the heat capacity of the rotating body, which is a heating medium, and to heat with a heat source having good heating efficiency.

In the apparatus described in Patent Document 1, in order to prevent the occurrence of wrinkles on the envelope, the pressing force per unit area of the first pressing roller and the second pressing roller against the heating roller is set to the normal pressure mode and the envelope pressure mode. It is switched to. In the envelope pressure mode, both the pressing force per unit area of the first pressing roller against the heating roller and the pressing force per unit area of the second pressing roller against the heating roller are higher than in the normal pressure mode for fixing plain paper or the like. It is made smaller to prevent the occurrence of envelope wrinkles.

In the device described in Patent Document 2, in order to prevent the occurrence of envelope wrinkles, the shape of the fixing nip portion N portion is switched from the nip mode in which the flat portion and the curved portion abut to the nip mode in which only the flat portion abuts. There is.

Japanese Unexamined Patent Publication No. 2004-279702 Japanese Unexamined Patent Publication No. 2013-225039

However, in the above configuration, in order to improve the envelope wrinkles, it is necessary to reduce the pressing force per unit area more than necessary, and there is room for improvement.

A typical configuration of the image forming apparatus according to the present invention for solving the above problems is
An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image formed on the recording material at the nip, and
A drive rotating body that forms the nip portion with the endless belt and rotationally drives the endless belt.
A pad that presses the endless belt from its inner surface toward the drive rotating body, and is a first protrusion that protrudes from the base portion toward the drive rotating body at the base portion and the upstream end in the transport direction of the recording material. A pad having a portion and a second protruding portion protruding from the base portion toward the drive rotating body at the downstream end in the transport direction of the recording material.
The inner surface of the endless belt is located between the first protruding portion, the second protruding portion, and the first protruding portion and the second protruding portion in the transport direction of the recording material. The first mode in contact with the portion and the inner surface of the endless belt are in contact with both the first protruding portion and the second protruding portion, while the first protruding portion in the transport direction of the recording material. It is characterized by having a second mode located between the second projecting portion and a portion of the base portion separated from the base portion, and an execution unit that executes one of a plurality of modes including the second mode. To do.

According to the present invention, the above-mentioned problems are improved.

Control flowchart of the image forming apparatus of the first embodiment Structural model diagram of an example of an image forming device Perspective view of the fixing device (A) is a front view of the fixing device, and (b) is a vertical sectional front view of the device. (A) is a cross-sectional view of a main part of the fixing device, (b) is a partially enlarged view of (a), and (c) is a cross-sectional view of a pressure pad. (A) and (b) are the left side view of the fixing device and the left side view of a partial notch. (A) and (b) are a right side view of the fixing device and a right side view of a partial notch. Schematic diagram of the layer structure of the fixing belt Illustration of the shape of the eccentric cam Explanatory drawing of belt unit position in pressurization configuration, pressure reduction configuration, pressure release configuration The figure explaining the generation mechanism of the envelope wrinkle in the normal pressure mode (the first pressure mode). The figure explaining the occurrence mechanism of the envelope wrinkle in the envelope pressure mode (the second pressure mode). Control system block diagram Flow chart for fixing device Flow chart for explaining the control of the second embodiment Flow chart for explaining the control of the third embodiment Configuration explanatory view of the fixing device in the sixth embodiment Configuration explanatory view of the fixing device in the seventh embodiment Flow chart for explaining the control of the fourth embodiment The figure which shows the display state of the operation part

Hereinafter, examples 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 as an image forming apparatus will be described. However, it goes without saying that the present invention is not limited to this, and can be applied to various types of electrophotographic copying machines, printers, monocolor methods, and image forming devices other than electrophotographic.

Further, in the following description, the envelope-shaped recording material refers to a bag-shaped recording medium having a plurality of overlapping sheets and creases such as an envelope, and is hereinafter simply referred to as an envelope. The recording material other than the envelope-shaped recording material refers to a single sheet-shaped ordinary paper including transparency paper, and is hereinafter simply referred to as plain paper. In addition, these recording media are also collectively referred to as paper.

<< First Example >>
(1) Example of Image Forming Device FIG. 2 is a schematic configuration diagram of a color copier 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 document 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 forming product.

In the reader unit A, the document OR placed on the platen glass 50 is irradiated by the light source 52 of the scanning optical system unit 51, and is imaged on the CCD sensor 54 via the optical system 53. The reading optical system unit 51 moves in the direction of the arrow 55 (secondary scanning movement), photoelectrically reads the image information of the document OR, and converts it into an electric signal data string for each line. The image signal obtained by the CCD sensor 54 is sent to the printer control unit (execution unit: hereinafter referred to as the control unit) 57 of the printer unit B via the reader image processing unit 56, and is matched with 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) that uses the operation unit C or the external device D as the input unit can be set in the control unit 57. The control unit 57 can reflect information such as the paper type and the basis weight set from these 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 into a laser beam PWM (pulse width modulated) by the control unit 57. The laser beam is scanned by the polygon scanner 58, and the photosensitive drums 61 of the image forming units Pa to Pd are irradiated with the laser beam. Pa is a yellow (Y) image forming part, Pb is a magenta (M) image forming part, Pc is a cyan (C) image forming part, and Pd is a black (Bk) image forming part. Form an image.

Since the mechanical configurations of the image forming units Pa to Pd are substantially the same, the Y image forming units Pa will be described as a representative below, and the addition and description of the reference numerals to the constituent devices in the other image forming units Pb to Pd will be omitted. ..

In the Y image forming unit Pa, an electrostatic latent image is formed on the surface of the photosensitive drum 61 by a 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 to prepare for forming an electrostatic latent image. Reference numeral 63 denotes a developer, which develops an electrostatic latent image on the photosensitive drum 61 to form a toner image. Reference numeral 64 denotes a transfer roller (roll), which discharges from the back surface of the intermediate transfer belt 66 and applies a primary transfer bias having the opposite polarity to 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 transfer is cleaned with a cleaner 65.

Further, the toner image on the intermediate transfer belt 66 is sequentially conveyed to the next image forming portions Pb to Pd, and the toner images of each color formed by the image forming portions Pb, Pc, and Pd are formed 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. In the toner image that has passed through the Bk image forming unit Pd, the toner image on the intermediate transfer belt 66 has the opposite polarity to the toner in the secondary transfer unit composed of the secondary transfer inner roller 67, the secondary transfer outer roller, and 68. The secondary transfer is performed on the paper P by the secondary transfer electric field.

The paper P is fed from the paper feed cassette 69 or 70 as a plurality of recording material accommodating units in which the paper corresponding to the selection designation in advance is accommodated, and is conveyed by the conveying path 71a, and is conveyed at a predetermined control timing. Is introduced into the secondary transfer section at.

The paper P that has passed through the secondary transfer section is conveyed by the transport path 71b and introduced into the fixing device (fixing section, fixing device) F to undergo the toner image fixing process. When the single-sided printing mode is used, the paper P exiting the fixing device F is introduced into the transport path 71c and discharged onto the discharge tray 72 as a single-sided image forming product.

In the double-sided printing mode, the single-sided image-formed paper P leaving the fixing device F is introduced into the double-sided transport path 71d, switched back, and re-introduced into the transport 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 unit, and thereafter, the paper P is conveyed along the same transfer path as in the single-sided printing mode, and the double-sided image forming product is transferred onto the discharge tray 72. Is discharged as.

(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 fixing device F. 5 (a) is an enlarged right side view along the lines (5)-(5) in (a) of FIG. 4, (b) is a partially enlarged view of (a), and (c) is a pressure applying member. It is a cross-sectional view of (pressurizing pad). 6 (a) and 6 (b) are a left side view of the device F and a left side view of a partial notch. 7 (a) and 7 (b) are a right side view of the device F and a right side view of a partial notch.

In the following description, the longitudinal direction of the fixing device F or the members constituting the fixing device F is a direction parallel to the direction orthogonal to the paper transport direction (recording material transport direction) a in the paper transport path surface. The lateral direction is a direction parallel to the paper transport direction a. Regarding the fixing device F, the front is the surface of the device viewed from the paper inlet side, the back surface is the surface opposite to the back surface (paper outlet side), and the left and right are the left or right side of the device when viewed from the front. The upstream side and the downstream side are the upstream side and the downstream side with respect to the paper transport direction a.

The fixing device F of this embodiment is a belt heating type image heating device by induction heating, and is roughly classified into the following members and mechanisms.

a: A heating assembly (belt unit) 1 including an endless belt (hereinafter referred to as a fixing belt or belt) 6 having flexibility as a first rotating body (fixing member) in contact with the toner image carrying surface of the paper P.
b: Pressurized roller 2 having elasticity as a drive rotating body (pressurizing 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: A pressurizing mechanism 4 that forms a nip portion N by pressing the belt 6 and the pressurizing roller 2 to heat (image heat treatment; 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-mentioned members and mechanisms are arranged between the left and right side plates 5L and 5R of the device chassis 5 of the fixing device F.

(2-1) Heating assembly 1
The heating assembly 1 has a cylindrical and flexible fixing belt 6. The belt 6 has a magnetic member (metal layer, conductive member , conductive layer ) 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. It also has a metal stay 7 inserted inside the belt 6. 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. In the cross section of the pad 8, the 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 as shown in FIGS. 5B and 5C. ..

That is, the pad 8 has a convex portion as an upstream protrusion 8a in the upstream portion of the nip portion N and a convex portion as a downstream protrusion 8c in the downstream portion of the nip portion N, and is between the two convex portions 8a and 8b. It is configured to have a main pressure portion 8b.

The upstream-side protrusion 8a is a first protrusion that protrudes from the main pressure portion 8b, which is the base portion, toward the pressure roller 2 at the upstream end in the transport direction of the paper (recording material, envelope). The downstream side protrusion 8a is a second protrusion that protrudes from the main pressure portion 8b toward the pressure roller 2 at the downstream end in the paper transport direction. The main pressure portion 8b does not necessarily have to be flat, and may be farther from the inner surface of the belt 6 than the portion where the tip of the upstream protrusion 8a and the tip of the downstream protrusion 8c are connected by 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 sandwiched between them. Then, in the cross section, the pad 8 is located on the upstream side and the downstream side of the paper transport direction a with the main pressure portion 8b and the main pressure portion 8b in the vicinity of the center of the nip portion N facing the inner surface of the belt 6. It has convex portions 3a and 3c protruding from the main pressure portion 8b toward the belt 6. Further, the pad 8 is provided with a crown to correct the bending when pressure is applied, and the amount of crown used in this embodiment is 1. At the center and end of the pad 8 (position 200 mm from the center). It is 6 mm.

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

The left and right ends of the stay 7 project outward from the left and right ends of the belt 6, respectively. Symmetrically shaped flange members (fixing flanges) 10L and 10R are fitted to both ends thereof. The flange members 10L and 10R are regulatory 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 to the assembly of the stay 7, the pad 8, and the core 9. The movement of the belt 6 in the longitudinal direction is restricted by the inward surface of the flange members 10L / 10R.

As will be described later, the belt 6 is made of a metal whose base layer 6a (FIG. 8) generates electromagnetic induction heat. Therefore, as a means for restricting the longitudinal deviation of the belt 6 in the rotating state, it is sufficient to provide flange members 10L / 10R having a flange portion that simply receives the end portion of the belt 6. This has the advantage that the configuration of the fixing device F can be simplified.

A temperature sensor TH such as a thermistor as a temperature detecting means (temperature detecting element) for detecting the temperature of the belt 6 is arranged at the central portion of the length of the pad 8 via an elastic support member 11. The sensor TH is elastically in contact with the inner surface of the belt 6 by the member 11. As a result, even if the sensor contact surface of the rotated belt 6 is wavy or the like, the sensor TH follows this and maintains a good contact state with the inner surface of the belt 6.

The heating assembly 1 is arranged by engaging the flange members 10L and 10R with the vertical guide slit portions 5a arranged on the side plates 5L and 5R, respectively. Therefore, the heating assembly 1 has a degree of freedom that allows it to move in the vertical direction along the slit portion 5a between the side plates 5L and 5R as a whole.

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 an electroplating method. 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 the 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 fixed image suitable for fixing a color image. Silicone rubber has a hardness of JIS-A of 20 degrees 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.

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

The belt 6 has a low heat capacity as a whole, is flexible (elastic), and retains 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. Further, the structure may be such that the metals are laminated on the resin base layer. The thickness of the metal layer 6a may be adjusted according to the frequency of the high-frequency current flowing through the exciting coil 15 described later in the unit 3 and the magnetic permeability / conductivity of the metal layer 6a, and may be set between about 5 and 200 μm.

(2-2) Pressurized roller 2
The pressure roller 2 is rotatably arranged below the heating assembly 1 via a bearing 12 between the side plates 5L and 5R with the axial direction substantially parallel to the longitudinal direction of the assembly 1.

In this embodiment, the roller 2 has a core metal 2a made of an iron alloy having a diameter of 20 mm at the center in the longitudinal direction and a diameter of 19 mm at both ends, and a silicone rubber layer is provided as an elastic layer 2b, and has an outer diameter of 30 mm. An elastic roller having a crown shape. A fluororesin layer (for example, PFA or PTFE) is provided on the surface as a release layer 2c with a thickness of 30 μm. The hardness of the roller 2 at the center in the longitudinal direction is ASK-C 70 °.

A gear 13 is fixedly arranged at the right end of the core metal 2a. The driving force of the drive motor M1 controlled by the control unit 57 is transmitted to the gear 13 via a transmission means (not shown), and the roller 2 is determined as a drive rotating body in the counterclockwise direction of the arrow in FIG. It is driven to rotate at the speed of.

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

The housing 14 is a horizontally long box-shaped molded product (electrically insulating resin molding member) made of heat-resistant resin having a longitudinal direction in the left-right direction. The bottom plate 14a side of the housing 14 is the 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.

Both ends of the housing 14 of the coil unit 3 are received by the left and right flange members 10L and 10R of the heating assembly 1 via brackets 17. As a result, the bottom plate 14a of the housing 14 faces the upper surface of the belt 6 with a predetermined 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.

Therefore, 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 depressurized or depressurized and float, the coil unit 3 also floats together while maintaining the gap α.

The coil 15 is formed by using, for example, a litz wire as an electric wire, making it horizontally long and having a ship bottom shape, and winding the coil 15 so as to face a part of the peripheral surface and the side surface of the belt 6. Then, it is applied to the inner surface of the bottom plate 14a that is curved inside the housing and is housed inside the housing. A high-frequency current is applied to the coil 15 from the 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 to other than the metal layer (conductive layer) of the belt 6. The core 16 is arranged along the longitudinal direction of the belt 6 and is divided into a plurality of cores 16 in a direction orthogonal to the paper transport direction a and arranged side by side. It is configured to surround.

The core 16 divided into a plurality of cores 16 is formed in the non-passing portion in order to suppress the temperature rise of the non-passing portion when the paper having a width narrower than the maximum width size paper that can be used in the apparatus is passed. The split core of the corresponding portion is moved in a direction of widening the gap with the coil 6 by a moving mechanism (not shown). As a result, the magnetic flux density passing through the belt 6 of the portion corresponding to the non-paper-passing portion is lowered, and the amount of heat generated by the belt portion is reduced. Since the movement control of the split core is outside the main points of the present invention, detailed description thereof will be omitted.

(2-4) Pressurizing Mechanism 4 and Changing Mechanism In this embodiment, the pressurizing mechanism 4 pressurizes the pad 8 of the heating assembly 1 onto the roller 2 via the belt 6 with a predetermined pressing force (pressure). This is a pressurizing means for forming a predetermined nip portion N between the belt 6 and the roller 2. In this embodiment, the pressure of the pressurizing mechanism 4 can be changed by a changing mechanism.

Hereinafter, a specific mechanism configuration will be described. On the outer upper part of the side plates 5L and 5R, a pair of left and right pressurizing levers 18L and 18R as symmetrical pressurizing members are arranged in the front-rear direction (paper transport direction), respectively.

The lever 18L is located above the pressurized portion 10a of the flange member 10L, and the rear end portion is pivotally 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 the direction of pressing the pressurized portion 10a of the flange member 10L with the support shaft 18a as a fulcrum, or in the direction of separating from the pressurized portion 10a. The front end of the lever 18L is located on the front side of the flange member 10L. The lever 18L is constantly urged downward around the shaft 18a by the spring force of the spring 19a of the spring-loaded screw 19L as an urging member arranged between the lever 18L and the side plate 5L.

The lever 18R is located above the pressurized portion 10a of the flange member 10R, and the rear end portion is pivotally rotatable in the vertical direction about 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 operate in the direction of pressing the pressurized portion 10a of the flange member 10R with the support shaft 18a as a fulcrum, or in the direction of separating from the pressurized portion 10a. The front end of the lever 18R is located on the front side of the flange member 10R. The lever 18R is constantly urged downward about the shaft 18a by the spring force of the spring 19a of the spring-loaded screw 19R as an urging member arranged between the lever 18R and the side plate 5R.

When the levers 18L and 18R are in the free state, the lower surfaces of the levers 18L and 18R have a spring force defined by the spring 19a of the spring-loaded screw with respect to the upper surface of the pressurized portion 10a of the flange members 10RL and 10R, respectively. It's pushing enough. In this embodiment, this pressure is set to, for example, 550N. As a result, 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 sandwiches the belt 6 and presses against the roller 2 against the elasticity of the elastic layer 2b.

By this pressure welding, a nip portion 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 the pressure profile of the nip portion N. The configuration at this time is hereinafter referred to as a pressurized configuration.

A cam shaft 21 is rotatably arranged 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 / 22R having the same shape and symmetrically arranged on the outside of the side plates 5L / 5R are fixedly arranged in the same phase. The cam 22L is located below the front end of the pressurizing lever 18L. The cam 22R is located below the front end of the lever 18R.

A gear (pressure release gear) 23 is fixedly arranged at the left end of the shaft 21. The driving force of the pressurizing roller desorption motor (for example, stepping motor) M2 controlled by the control unit 57 is transmitted to the gear 23 via a transmission means (not shown) to rotate the shaft 21, that is, the cams 22L and 22R. Is controlled. That is, the control unit 57 rotates the motor M2 in response to a predetermined signal to rotate the gear 23 in a predetermined direction by a predetermined amount. 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 / 22R, the levers 18L / 18R are lifted and rotated against the spring force of the spring 19a of the spring-loaded screw 19L, so that the pressure of the pad 8 on the roller 2 is changed.

The bearings 20/20, the shaft 21, the cams 22L / 22R, the gear 236, and the motor M2 are changing mechanisms for changing 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 device F, the motor M1 is turned off and the rotation of the roller 2 is stopped. The pressurizing mechanism 4 is in the pressurization 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, which functions as an execution unit, puts the pressurizing mechanism 4 in a pressurized 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. As a result, 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, a rotational force acts on the belt 6 due to the frictional force between the surface of the roller 2 and the surface of the belt 6 at the nip portion N. The inner surface of the belt 6 slides in close contact with the lower surface of the pad 8, and the outer circumferences of the stay 7, the pad 8, and the core 9 are driven and rotated in the clockwise direction of the arrow in FIG. 5 at the same speed as the rotation speed of the roller 2. .. A lubricant is applied to the pad 8 to reduce the sliding load between the pad 8 and the belt 6. In this example, fluorine grease was used in consideration of wraparound from the end when used in the vicinity of the fixing temperature control temperature (180 degrees).

The movement of the belt 6 in the thrust direction due to rotation is regulated by the flange portions of the left and right flange members 10L and 10R. At least during image formation, the belt 6 is driven to rotate by the motor M1 controlled by the control unit 57, so that the belt 6 is driven to rotate as described above. This rotation is performed at a peripheral speed substantially equal to the transport speed of the paper P carrying the unfixed toner image t, which is 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 in A4 size and 49 in A4R size per minute.

The control unit 57 supplies, for example, an alternating current (high frequency current) of 20 kHz to 50 kHz from the power supply device 103 to the coil 15 that functions as a heating unit. 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 6a 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 Joule heat generated by the eddy current causes the metal layer 6a to self-heat (electromagnetic induction heat generation) and raise the temperature of the belt 6.

That is, when the rotating belt 6 passes through the region where the magnetic field generated from the unit 3 exists, the metal layer 6a generates electromagnetic induction heat and is heated all around to raise the temperature. 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 that is in the paper-passing area, and the detected temperature information is fed back to the control unit 57. The control unit (temperature control function unit of the control unit) 57 maintains the detection temperature (information about the detected temperature) input from the sensor TH at a predetermined target temperature (fixing temperature: information corresponding to the predetermined temperature). As described above, the power supply from the power supply device 103 to the coil 15 is controlled.

That is, when the detection temperature of the belt 6 rises to a predetermined temperature, the energization of the coil 15 is cut off. In this embodiment, the temperature is adjusted by changing the frequency of the high-frequency current based on the detection value of the sensor TH and controlling the power input to the coil 15 so that the temperature becomes constant at 180 degrees, which is the target temperature of the belt 6. Is going. The target temperature may be changed by analogizing the paper temperature (recording material temperature) by the temperature / humidity sensor E (FIG. 2) arranged 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 (bottom plate 14a of the housing 14). The distance between the belt 6 and the coil 15 is constant at 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 arranged outside the belt 6 which becomes hot, not inside the belt 6, the temperature of the coil 15 does not easily rise, the electrical resistance does not increase, and Joule heat is generated even when a high frequency current is passed. It is possible to reduce the loss due to. Further, by arranging the coil 15 on the outside, it contributes to reducing the diameter (reducing the heat capacity) of the belt 6, and it can be said that it is also excellent in energy saving.

The warm-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 degrees can be reached in about 15 seconds, and the heating operation during standby is unnecessary, so that the power consumption can be suppressed to a very low level.

In a state where the roller 2 is driven as described above and the belt 6 rises to a predetermined fixing temperature and is temperature-controlled, the paper P carrying the unfixed toner image t on the nip portion N belts the toner image supporting surface side. It is introduced by being guided by the guide member 24 toward the 6 side. The paper P comes into close contact with the outer peripheral surface of the belt 6 at the nip portion N, and is conveyed by sandwiching the nip portion N together with the belt 6.

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

(2-6) Pressure change 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 flat surface portion of the cams 22L / 22R is in an upward rotation angle posture, and the cams 22L / 22R are not in contact with the levers 18L / 18R. Therefore, the spring force of the spring 19a of the spring-loaded screws 19L / 19R sufficiently acts on the levers 18L / 18R, and the pressure of the nip portion N is in a predetermined first pressure (normal pressure) (pressurization). Constitution).

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

The cams 22L / 22R rotate clockwise in the normal pressure mode shown in FIG. 10A, and the levers 18L / 18R are moved to the first peak (peak) against the spring force of the spring 19a of the spring-loaded screw 19R. Push it up to the position of 1) ((a) → (b)). Then, the pressure on the flange members 10L and 10R is halved, and the position of the belt 61 rises by ΔY1 ((a) → (b)). As a result, the pressure of the nip portion N becomes a predetermined envelope pressure mode (second pressurization mode) lower (weak, light pressure) than the first pressure in the normal pressure mode (pressure reduction configuration).

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

When the cams 22L / 22R rotate further and push the lever 18L / 18R up to the position of the highest second peak (peak 2), the belt 6 is further raised by ΔY2. Then, the pressure of the spring force of the spring 19a of the spring-loaded screw 19R on 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 (execution unit) 57 controls the fixing device F to the pressure release mode shown in FIG. 10 (c) during standby or non-image formation of the image forming device. When the paper passed through the fixing device F is other than an envelope, the normal pressure mode shown in FIG. 10A is controlled. Further, in the case of an envelope, the envelope pressure mode (pressure reduction configuration) shown in FIG. 10B is controlled.

(2-7) Pressurization Mode The pressurization modes in the nip portion N of 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 and 12. 11 (a) and 12 (a) are cross-sectional views when a paper (plain paper) P other than an envelope passes through the nip portion N in each mode, FIG. 11 (b) and FIG. b) shows a cross-sectional view when the envelope passes through the nip portion N in each mode. Further, (c) of FIG. 11 and (c) of FIG. 12 show the velocity distribution applied to the envelope cover when the envelope is passed in each mode.

In the normal pressure mode, as shown in FIG. 11A, the upstream side protrusion 8a, the main pressure part 8b, and the downstream side protrusion 8c of the pressure pad 8 which is a pressure applying member are all in pressure contact with the belt 6. When paper P other than the envelope is passed through, the nip portion N has an upward convex shape due to the protrusions 8a and 8c on the upstream and downstream sides of the pad 8, so that the paper discharged from the nip portion N is in the downward direction. It has become. As a result, sufficient separability to the fixing belt 6 is ensured even when paper having a small basis weight and low rigidity is passed through.

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 on the front and back of the envelope are the protrusions 8a and 8b on the upstream and downstream sides of the pressure pad 8. As a result, the nip portion N has an upward convex shape. Therefore, the deformation of the envelope passing through the nip portion N causes a difference in the amount of transport between the upper surface and the lower surface of the envelope.

FIG. 11 (c) shows the feed amount of the front side (solid line arrow) and the back side of the envelope (dotted line arrow) when the envelope is the long type No. 3. The front and back of the envelope are two overlapping sheets of paper, and the front and back are restrained on at least one side in the belt width direction. In the case of long type No. 3, the position indicated by x is the restraint point. Since the front and back surfaces are continuous in the restrained portion, the nip portion N is passed through the nip portion N with an intermediate transport amount between the front and back transport amounts. Due to the difference in the feed amount in the belt width direction between the restrained part and the non-restrained part of the envelope, a rotational moment as shown by the white arrow is generated and stress accumulates, and the rigidity of the paper cannot be withstood. Occurs.

In this embodiment, since the purpose is to make the nip portion N have an upward convex shape in the normal pressure mode, it is not necessary for the belt 6 to be in contact with all of the main pressure portions 8b of the pressure pad 8, and the main pressure portion It suffices if a part of 8b is in contact with the belt 6.

In the envelope pressure mode, as shown in FIG. 12A, both the upstream protrusion (projection) 8a and the downstream protrusion (projection) 8c of the pressure pad 8 are in pressure contact with the belt 6, but the main pressure is increased. The portion (base portion) 8b is separated from the belt 6. Specifically, the main pressure portion 8b is in a state in which almost the entire area including the central portion in the recording material transport direction is separated from the inner surface of the belt 6.

When the paper P other than the cylinder is passed through, the nip portion does not have an upward convex shape but a substantially straight shape due to the rigidity of the protrusions 8a and 8c on the upstream and downstream sides of the pressure pad 8 and the belt 6. The paper discharged from the nip portion N is discharged straight. In this case, there is no problem with paper P having two sheets stacked like an envelope and having high rigidity, but when plain paper P having a small basis weight and low rigidity is passed through, the curvature of the belt 6 cannot be sufficiently secured. Separability may be inadequate.

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 in the portion not restrained on 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 feed amount between the front and back sheets of the envelope can be suppressed ((c) in FIG. 12). As a result, it is possible to suppress the occurrence of speed deviation in the belt width direction between the restrained portion and the non-restrained portion of the envelope, and prevent the occurrence of envelope wrinkles.

In this embodiment, in the envelope pressure mode, as shown in FIG. 12B, the belt 6 is supported only by the upstream protrusion 8a and the downstream protrusion 8c of the pressure pad 8, and the main pressure is increased. The configuration in which the portion 8b does not come into contact with the belt 6 has been described.

In the envelope pressure mode, exceptionally, a part of the main pressure portion 8b may suddenly come into contact with each other. For example, the height of the upstream / downstream protrusions is not sufficient within the mechanical tolerance range, or the upstream / downstream protrusions have become low due to durable wear. Further, when an envelope having high rigidity passes through the nip portion N in the envelope pressure mode, the belt 6 may be deformed and a part of the belt 6 may momentarily contact the main pressure portion 3b of the pressure pad 8. You can get it, but since it is an envelope that does not easily wrinkle, there is no problem.

Examples of highly rigid envelopes include Yamazakura's long 3 Sumi-pasted AR Ultra White 130 〒 frame pear, 120 mm x 235 mm, and basis weight 130 g / m ² .

The above-mentioned pressurization modes can be summarized as follows. There are a plurality of modes, a first mode, a second mode, and a third mode. Then, the control unit (execution unit) 57 can execute one of the plurality of modes including the above mode.

In the first mode, the inner surface of the belt 6 is between the upstream protrusion 8a and the downstream protrusion 8c of the pressure pad 8 and the upstream protrusion 8a and the downstream protrusion 8c in the paper transport direction. This mode is in contact with the located main pressure portion 8b. In the second mode, the inner surface of the belt 6 is in contact with both the upstream protrusion 8a and the downstream protrusion 8c of the pressure pad 8, while the upstream protrusion 8a and the downstream protrusion 8c are in contact with each other in the paper transport direction. This mode is separated from the portion of the main pressure portion 8b located between the two. The third mode is a mode in which the pressure applied between the belt 6 and the roller 2 is substantially released.

(2-8) Control The control of this embodiment will be described with reference to the block diagram of the control system shown in FIG. The control unit (execution unit) 57 exchanges various electrical information with the operation unit (selection unit) C and the external device (PC, print server, etc.) D, and print operation (image formation operation) of the printer unit B. ) Is controlled comprehensively. The operation unit C is a user interface for setting the print mode from the user (operator, user), inputting various instructions / settings of printing conditions such as used paper / number of sheets, and notifying the operator of the state of the device.

With the operation unit C and the external device D as input units, the 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, and the recording material information The 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 the information of the recording material information processing unit 102.

That is, the CPU 100 of the printer control unit 57 controls the changing 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.

The pressure control unit 104 controls the pressure of the fixing device F to a predetermined pressure. That is, as described above, when the paper used is plain paper (setting information for recording materials other than envelopes), the pressure of the fixing device F becomes the normal pressure (first pressurizing mode). The change mechanism is operated by controlling M2. Further, in the case of an envelope (envelope setting information), the motor M2 is controlled so that the envelope pressure (second pressurization mode) is set, and the changing mechanism is operated.

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 temperature detected by 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 pressurizing roller 2 to rotate or stop the pressurizing roller 2.

The control of this embodiment will be described with reference to the flowchart shown in FIG. First, the image forming apparatus accepts an image forming job (JOB). After that, the CPU 100 determines whether or not the paper to be passed is an envelope job, which is an envelope (S1000). If the paper to be passed through 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 and the fixing operation (S1003) are 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 pressurizing roller attachment / detachment motor M2 to adjust the pressure of the fixing device F to the normal pressure (S1100). Next, the CPU 100 drives the pressurizing roller 2 by the drive motor M, rotationally drives the pressurizing 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 by 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).

Then, the CPU 100 operates S1103 to S1105 until the print job is completed (S1106), and 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 print job is completed, the pressure roller attachment / detachment 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 experiments of this example. In the experiment, 10 long envelopes (long 3 medium-pasted Kent CoC 80 〒 frame pear, manufactured by Yamazakura Co., Ltd., 120 mm x 235 mm, basis weight 80 g / m ² ) were placed in an environment of 30 degrees and 80%. Pass paper continuously. Then, if there were no wrinkles in the envelopes out of 10 sheets, it was marked as ○, and if even one sheet had wrinkles, it was marked as ×. In addition, in order to confirm the paper separability, a plain paper (Canon CS520 A4 size, basis weight 52 g / m ² ) horizontal feed full-face blue image was passed in the same environment.

Envelope wrinkles occur in normal pressure mode, but thin plain paper is not a problem. In the envelope pressure mode, no envelope wrinkles occurred, and the thin plain paper was wrapped around the fixing belt 6 due to poor separation. This is realized by adjusting the pressure of the upstream protrusion 8a and the downstream protrusion 8c of the pressure pad 8 which is a pressure applying member. That is, it is shown that in the envelope pressure mode, a straight nip is formed to prevent envelope wrinkles, and in the normal pressure mode, the convex shape on the nip can ensure the separability of thin paper without any problem.

As described above, in the case of an envelope, an envelope pressure mode in which a straight nip 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 is used. This prevents the occurrence of envelope wrinkles, and in the normal pressure mode, the upper and downstream protrusions 8a and 8c of the pressure pad 8 and the main pressure portion 8b form an upward convex nip to separate the plain paper. We were able to provide a fixing device that achieves both properties.

<< Second Example >>
In the second embodiment, in the configuration of the first embodiment, the flowchart of FIG. 1 is modified as shown in FIG. 15, and the rigidity of the envelope is determined based on at least one of the environmental temperature, humidity, and the basis weight of the envelope. , It is for determining whether to perform the envelope pressure mode. 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 operation as in FIG. 1 is omitted by assigning the same number. In the configuration of the second embodiment, when the paper to be passed through S1000 is an envelope and it is determined that the rigidity of the envelope is higher than a predetermined value, the normal pressure mode is set. When it is determined that the rigidity of the envelope is equal to or less than a predetermined value, the envelope pressure mode is set and the fixing operation is performed (S2000).

That is, the CPU 100, which is a control means, has a determination unit for determining the rigidity of the recording material to be used, and the CPU 100 determines that the rigidity of the envelope is higher than a predetermined value by the determination unit when the recording material information is an envelope. If so, the first pressurization 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 input unit of the external device D such as a PC or the operation unit C, and the temperature / humidity information by the environmental 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 obtained by the temperature / humidity sensor E.

In the second embodiment, when the weight of water per 1 kg of air is 8 g or more, it is judged that the envelope having a basis weight larger than 100 g / m ² has high rigidity, and the normal pressure mode is set to 100 g / m ^2. In the case of the following basis weight, the fixing operation is performed in the envelope pressure mode. If the weight of water per 1 kg of air is less than 8 g, it is judged that the envelope with a basis weight larger than 80 g / m ² has high rigidity, and the normal pressure mode is set. When the basis weight is 80 g / m ² or less. Performs fixing operation in envelope pressure mode.

Tables 2 and 3 show the results of the experiments of the second embodiment. The experiment was based on the results when 10 sheets of envelopes 1) to 3) below were passed in succession under the environment of 30 degrees and 80% (Table 2) and 15 degrees and 10% (Table 3). is there. If there were no wrinkles on the envelope out of 10 sheets, it was marked as ○, and if even one sheet had wrinkles, it was marked as ×.

1) Long No. 3 envelope (long 3 medium-pasted book Kent CoC 80 〒 frame pear, manufactured by Yamazakura, 120 mm x 235 mm, basis weight 80 g / m ² )
2) Envelope with a basis weight of 100 g / m ² (long 3 medium-paste Kent CoC 100 〒 frame pear, manufactured by Yamazakura Co., Ltd., 120 mm x 235 mm, basis weight 100 g / m ² )
3) Envelope with a basis weight of 130 g / m ² (length 3 smeared AR Ultra White 130 〒 frame pear, manufactured by Yamazakura Co., Ltd., 120 mm x 235 mm, basis weight 130 g / m ² )
In the case of high temperature and humidity such as 30 degrees and 80% environment (Table 2), the rigidity of the envelope is low, so in the normal pressure mode, envelope wrinkles occur at a basis weight of 80 g / m ² and 100 g / m ² , but the envelope pressure. In the mode, there is no envelope wrinkle and a good image can be obtained. In a thick envelope with a basis weight of 130 g / m ² , wrinkles do not occur due to the rigidity of the envelope, but since the nip width cannot be sufficiently secured in the envelope pressure mode, the amount of heat is insufficient and fixing failure occurs.

In the case of low temperature and low humidity such as 15 degrees and 10% environment (Table 3), unlike Table ² , envelope wrinkles do not occur at a basis weight of 100 g / m ² in the normal pressure mode because the envelope has high rigidity. However, in the envelope pressure mode, the nip width cannot be sufficiently secured, so that the amount of heat is insufficient and slight peeling (improper fixing) occurs.

As described above, the configuration of the second embodiment determines the rigidity of the envelope based on at least one of the environmental temperature, humidity, and the basis weight of the envelope, and determines whether or not to perform the normal pressure mode. is there. As a result, by selecting the optimum mode for the basis weight of the envelope, it is possible to prevent the occurrence of wrinkles in the envelope and prevent the occurrence of improper fixing due to insufficient heat supply to the paper.

<< Third Example >>
In the third embodiment, in the configuration of the first embodiment, the flowchart of FIG. 14 is modified as shown in FIG. 16, and the apparatus is preheated and rotated at a normal pressure for a predetermined time. As a result, slippage does not occur even after durability or when highly viscous 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 operation as in FIG. 14 is omitted by assigning the same number. In the configuration of the third embodiment, when the envelope pressure mode is selected in S1103, the apparatus is heated and rotated (preheated and rotated) for a predetermined time while maintaining the temperature control temperature. (S3000).

Table 4 shows the results of the experiments of the third example. In the experiment, in the configuration of the first example, 600,000 sheets were passed in a horizontal feed of CS680 (Canon A4 size, basis weight 68 g / m ² ). 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 driven by the pressure roller 2 by the rotation of the drive motor M1 was marked with ◯.

It can be seen that the fixing belt 6 slips when the heating idle rotation time is 5 seconds or less in the operation of S3000. This is because the grease in the fixing nip portion N is mixed with abrasion powder and the like due to its durability and deteriorates, resulting in an increase in viscosity. In the envelope pressure mode, the fixing nip portion N becomes narrow, so that the transmission of the driving force from the pressurizing roller 2 becomes weak.

Therefore, in the configuration of the third embodiment, heating and idling are performed in a state where sufficient driving force is transmitted to the fixing belt 6 at normal pressure, and the durability-deteriorated grease near the fixing nip portion N is sufficiently warmed to reduce the viscosity. As a result, slippage of the fixing belt 6 was avoided. That is, when executing the second pressurization mode, it is preferable to preheat and rotate the device for a predetermined time in the first pressurization mode and then shift to the second pressurization mode.

In the third embodiment, the heating idle rotation time is always constant, but when the durable number counter is necessary in consideration of the viscosity of grease from the predetermined number information, the temperature history of the temperature sensor TH of the fixing belt 6, and the like. A configuration in which only heating and idling are performed may be used.

<< Fourth Example >>
Next, the fourth embodiment will be described. The description of the same configuration as that of the first embodiment will be omitted.

The control of this embodiment will be described with reference to the block diagram of the control system shown in FIG. The control unit 57 exchanges various types of electrical information with the operation unit C and the external device (PC, print server, etc.) D, and comprehensively controls the printing operation (image forming operation) of the printer unit B. The operation unit C is a user interface for setting the print mode from the user (operator, user), inputting various instructions / settings of printing conditions such as used paper / number of sheets, and notifying the operator of the state of the device.

Information on the recording material type (recording material setting information such as paper size, basis weight and paper type) input by the user is sent from the operation unit C or the external device D to the recording material information processing unit 102, and is sent to the recording material information processing unit 102. The information of 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 the information of the recording material information processing unit 102.

The pressure control unit 104 controls the pressure of the fixing device F to a predetermined pressure. That is, as described above, when the paper used is plain paper (setting information for recording materials other than envelopes), the pressure of the fixing device F becomes the normal pressure (first pressurizing mode). The change mechanism is operated by controlling M2. Further, in the case of an envelope (envelope setting information), the motor M2 is controlled so that the envelope pressure (second pressurization mode) is set, and the changing mechanism is operated.

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 temperature detected by 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 pressurizing roller 2 to rotate or stop the pressurizing roller 2.

As shown in FIG. 20A, the operation unit C functioning as a selection unit includes an operation panel 41 having a plurality of keys for performing key operations for giving instructions by the user, and a touch panel as a display unit such as a liquid crystal screen. It has a 403. The touch panel 403 is a manual input means capable of inputting various information by the user. The operation panel 41 has a start button (a button for instructing the start of image formation) 401 and a numerical input button (buttons of each number from 0 to 9) 402, which are hard keys (parts where the user performs key operations). , Sub power switch 404 is provided.

On the touch panel 403, instruction buttons related to image formation, which are soft keys (parts where the user performs key operations), are displayed. The instruction buttons are, for example, a button for setting the type of recording material (setting the basis weight of the paper), a button for instructing image formation on both sides of the recording material, and a button for instructing staple processing. And so on. Various instructions are given by the user touching these buttons (keys).

Since the touch panel 403 of the liquid crystal display unit of the operation panel 41 and the display screen displayed on the display of the PC (personal computer) as the external device D have a common interface, the same reference numerals 403 are given to both display screens below. I will explain.

When the user prints or copies, the paper type is selected from the display screen 403 shown in FIG. 20 (b). If the envelope key B101 is selected at this time, the display screen 403 switches to the screen shown in FIG. 20 (c), and the key B201 that prioritizes the improvement of envelope wrinkles or the key B202 that prioritizes image quality is selected. It is possible. The information designated by the user through the operation unit C or the external device D is transmitted to the CPU 100 through the recording material information processing unit 102.

The control of this embodiment will be described with reference to the flowchart shown in FIG. First, the image forming apparatus accepts an image forming job (JOB). The CPU 100 determines from the display screen 403 whether the envelope job has the envelope key B101 set by the user (S1000'). If the paper P to be passed is not an envelope, the CPU 100 sets the pressure of the fixing device F to the normal pressure mode (S1002'), and performs an image forming operation and a fixing operation (S1004).

In S1000', when the user is an envelope job in which the envelope key B101 is set from the display screen 403, the CPU 100 next determines whether or not the user has selected the wrinkle improvement mode in which the envelope wrinkle improvement key B201 is set. (S1001'). When the user has selected the wrinkle improvement mode, the pressure of the fixing device F is set to the envelope pressure mode (S1003'), and the image forming operation and the fixing operation are performed (S1004').

When the user has selected the image quality priority mode in which the image quality priority key B202 is set, the pressure of the fixing device F is set to the normal pressure mode (S1002'), and the image forming operation and the fixing operation are performed (S1004'). That is, the CPU 100 executes switching to the normal pressure mode (first pressurization mode) based on other image formation setting information even when the envelope setting information is used.

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 pressurizing roller attachment / detachment motor M2 to adjust the pressure of the fixing device F to the normal pressure (S1100). Next, the CPU 100 drives the pressurizing roller 2 by the drive motor M, rotationally drives the pressurizing 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 by the flow of FIG. 19 is the envelope 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).

Then, the CPU 100 operates S1103 to S1105 until the print job is completed (S1106), and 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 print job is completed, the pressure roller attachment / detachment motor M2 is driven to change the pressure of the fixing device F to normal pressure or pressure release (S1108).

Table 5 shows the results of the experiments of this example. In the experiment, under the environment of 30 degrees and 80%, in the image quality priority mode and the wrinkle improvement mode, in each mode, the Kent envelope of 1) and the envelope for the laser printer of 2) were 10 with a full blue image. I passed the paper continuously.

1) Kent Envelope Long No. 3 Envelope (Long 3 Medium Paste Book Kent CoC 100 〒 Frame None, Made by Yamazakura Co., Ltd., 120 mm x 235 mm, Basis Weight 100 g / m ² )
2) Long No. 3 envelope for laser printer (POD white 2.0 100 g / m2 frame pear, manufactured by Yamazakura Co., Ltd., 120 mm x 235 mm, basis weight 100 g / m ² )
At this time, the envelope wrinkles were marked as ◯ if no envelope wrinkles appeared out of 10 sheets, and × if even one envelope wrinkles appeared.

In the image quality priority mode, envelope wrinkles occur in Kent envelopes, but there is no problem with laser printer envelopes. This is because the laser printer envelope is treated with air holes and the like to suppress the occurrence of envelope wrinkles.

In the envelope pressure mode, envelope wrinkles did not occur in either envelope, but in both envelopes, uneven texture of the paper (s) and patterns (step unevenness) near the part where the envelopes were pasted occurred. This is because the envelope pressure of this embodiment reduces the pressure so that the surface layer of the fixing belt 6 cannot sufficiently follow the paper surface of the envelope.

As is clear from this experiment, even when fixing an envelope such as an envelope for a laser printer, which has a low risk of wrinkling, the image quality may be unnecessarily deteriorated if the fixing operation is performed with the envelope pressure. Therefore, such a problem can be avoided by configuring the user to freely select whether to prioritize the improvement of envelope wrinkles or the image quality as in the invention of the present embodiment.

<< Fifth Example >>
In this embodiment, in the fixing device configuration of the fourth embodiment, it is possible to register for each paper cassette whether to prioritize the improvement of envelope wrinkles or the image quality.

That is, the image forming apparatus has a paper feed cassette as a plurality of recording material accommodating portions. The CPU 60 controls the changing mechanism according to the paper information (recording material setting information) related to the paper cassette selected from the plurality of paper cassettes by the operation unit D, and sets the normal pressure mode (first pressurizing mode). Switching to the envelope pressure mode (second pressure mode) is performed.

Specifically, the envelope as the paper P housed in the upper paper cassette 69 in FIG. 2 is the Kent envelope of 1) in the sixth embodiment, and the paper P housed in the lower paper cassette 70. It is assumed that the envelope as is the envelope for the laser printer of 2). In this case, the upper paper cassette 69 can be set to the wrinkle improvement mode, and the lower paper cassette 70 can be set to the image quality priority mode. As a result, the user can print the envelope in the optimum mode without being aware of the mode at the time of printing.

As described above, when the fixing device of the present embodiment is used, it is possible to prevent the occurrence of envelope wrinkles in the fixing device of the low heat capacity system, and to adjust the occurrence of envelope wrinkles and the image quality according to the user's preference. Is possible.

<< 6th Example >>
In the sixth embodiment, in the configurations of the first to fifth embodiments, 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 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 arranged inside the stay 7'to heat the belt 6 with radiant heat. The stay 7'is made of heat-resistant glass that transmits the light of 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 is based on the temperature information of the temperature sensor TH so that the temperature of the fixing belt 6 becomes a predetermined temperature. It is ON / OFF controlled by the CPU 100.

With the above configuration, the same effect as in the first to fifth embodiments can be obtained even when the halogen heater 15'is used instead of the coil 15.

<< 7th Example >>
In the fixing device configuration of the first to fifth embodiments, the seventh 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 made into a belt 6'having a resistance heating layer. is there. In the same configuration as in the first embodiment, the same number is assigned and the description is omitted.

The fixing device configuration of this embodiment is shown in FIG. 18A. The part 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'with the resistance heating layer in this embodiment will be described with reference to FIG. 18 (b). The belt 6'in this embodiment has a five-layer composite structure of a slippery layer 6d, a base layer 6a', a heat generating layer 6e, an elastic layer 6b, and a release layer 6c in this order from the inner peripheral side to the outer peripheral side. Further, there is a feeding electrode portion (not shown) at the end portion 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 the base layer 6a'is 60 μm. Although insulating polyimide was used in the fifth embodiment, a resin belt such as polyimideamide, PEEK, PTFE, PFA or FEP, or a metal belt such as SUS or nickel can be used as the base layer 6a'. When a conductive material is used as 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.

On the inner surface side of the base layer 6a', a resin layer (slippery layer) 6d such as fluororesin or polyimide may be provided in an amount of 10 to 50 μm in order to reduce the sliding friction between the inner surface of the belt and the temperature sensor TH. In this example, a fluororesin of 10 μm 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 coated on the base layer 6a'with a uniform thickness. The total resistance value of the heating layer 6e is 10.0Ω. Therefore, the electric power generated when an AC power source having a voltage of 100 V is energized is 1000 W. The resistance value may be appropriately determined according to the amount of heat generated as the fixing device, and can be appropriately adjusted according to the carbon mixing ratio.

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

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

With the above configuration, the same effect as in the first to fifth embodiments can be obtained even when the belt 6'having the resistance heating layer is used instead of the coil 15.

As described above, when the fixing device of the present embodiment is used, it is possible to prevent the occurrence of envelope wrinkles in the fixing device of the low heat capacity system, and to adjust the occurrence of envelope wrinkles and the image quality 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 through the belt 6. The mechanism may be configured to pressurize the pressurizing pad 8. Further, the pressurizing pad 8 and the pressurizing roller 2 may be mechanically configured to pressurize each other via the belt 6. That is, the pressure pad 8 and the pressure roller 2 can be relatively pressurized via the belt 6.

(2) The fixing device F, which is a fixing portion, is not limited to use as a device for heating and fixing an unfixed toner image formed on a recording material as a fixed image. It is also effective as a device for adjusting the surface texture of an image, such as improving the glossiness of an image by heating and pressurizing the toner image once fixed or hypothesized on the recording material again (also fixed to such a device). Called a device).

(3) The image forming apparatus is not limited to the image forming apparatus for forming a full-color image as in the embodiment, and may be an image forming apparatus for forming a monochrome image. Further, the image forming apparatus can be implemented in various applications such as a copying machine, a fax machine, and a multifunction device having a plurality of these functions by adding necessary equipment, equipment, and a housing structure.

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

Claims (7)

An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image formed on the recording material at the nip, and
A drive rotating body that forms the nip portion with the endless belt and rotationally drives the endless belt.
A pad that presses the endless belt from its inner surface toward the drive rotating body, and is a first protrusion that protrudes from the base portion toward the drive rotating body at the base portion and the upstream end in the transport direction of the recording material. A pad having a portion and a second protruding portion protruding from the base portion toward the drive rotating body at the downstream end in the transport direction of the recording material.
The inner surface of the endless belt is located between the first protruding portion, the second protruding portion, and the first protruding portion and the second protruding portion in the transport direction of the recording material. The first mode in contact with the portion and the inner surface of the endless belt are in contact with both the first protruding portion and the second protruding portion, while the first protruding portion in the transport direction of the recording material. It is characterized by having a second mode located between the second protruding portion and a portion of the base portion separated from the base portion, and an executing portion that executes one of a plurality of modes including the second mode. Image forming device. When performing a fixing process on the envelope, the inner surface of the endless belt image forming apparatus according to claim 1, characterized in that apart from the portion of the base portion located in the midsection of the envelope. The execution unit executes the first mode when performing the fixing process on a predetermined recording material other than the predetermined envelope as the recording material, and the second mode when performing the fixing process on the predetermined envelope as the recording material. The image forming apparatus according to claim 1 or 2 , wherein the mode is executed. The image according to claim 1 or 2 , wherein when a predetermined envelope is subjected to a fixing process as a recording material, it has a selection unit for selecting one from the first mode and the second mode. Forming device. The execution unit according to any one of claims 1 to 4 , wherein the executing unit can execute a third mode in which the pressure applied between the endless belt and the driving rotating body is substantially released. Image forming device. The image forming apparatus according to any one of claims 1 to 5 , further comprising a heating portion for heating the endless belt. The image forming apparatus according to any one of claims 1 to 5, further comprising a coil that generates magnetic flux, and the endless belt having a conductive layer that induces heat generation due to the magnetic flux generated from the coil.