JP5504150B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus including the same.

2. Description of the Related Art Conventionally, in image forming apparatuses such as printers and copiers, attention has been paid to a fixing device using a heated rotating belt capable of reducing the heat capacity in order to reduce the rise time and save energy.
Further, as a heating means for the heating rotating belt, an induction coil is disposed along the outer surface of the heating rotating belt, and the heat generating layer of the heating rotating belt is heated by the electromagnetic induction action caused by the magnetic flux generated by the induction coil. A fixing device that employs an induction heating (IH) method is drawing attention.

  In the electromagnetic induction heating type fixing device, the heat efficiency is higher and less than that of the type in which the heating rotating belt or the heating rotating roller is heated by a heating source such as a heater arranged inside the heating rotating belt or the heating rotating roller. It is possible to start up to a predetermined fixing temperature in a short time with power consumption. In particular, in a fixing device using a heating rotating belt, since the heat capacity of the heating rotating belt is small, the rise time until the temperature of the heating rotating belt reaches the fixing temperature is fast, and the power consumption can be further reduced.

In addition, in a fixing device that combines a heating rotating belt and an electromagnetic induction heating method, from the viewpoint of ensuring safety, the heating rotating belt has an abnormal temperature that exceeds a predetermined temperature so that the heating rotating belt is not excessively heated. When a certain temperature is reached, it is desirable to stop supplying power to the induction coil.
On the other hand, when the temperature of the heating rotating belt reaches an abnormal temperature equal to or higher than a predetermined temperature, the overheat prevention part such as a thermal cutoff or a thermal fuse that cuts off the power supply to the induction coil is heated. An arrangement has been proposed in which the rotating belt is disposed in a non-contact state with respect to the heating rotating belt (see, for example, Patent Document 1).

  In addition, there has been proposed an arrangement in which an excessive temperature rise prevention unit is disposed inside the heating rotary belt in contact with the inner peripheral surface of the heating rotary belt (for example, see Patent Document 2).

JP-A-2005-37858 JP 2005-190728 A

  However, in the fixing device described in Patent Document 1, since the excessive temperature rise prevention unit is disposed in a non-contact state inside the heating rotating belt, the excessive temperature rise prevention unit has an abnormal temperature higher than a predetermined temperature. The sensing timing is later than the timing at which the heating rotating belt reaches an abnormal temperature equal to or higher than a predetermined temperature. For this reason, the supply of power to the induction coil is interrupted after the heating rotary belt reaches an abnormal temperature equal to or higher than a predetermined temperature. As a result, the safety of the fixing device may not be ensured.

  Further, in the fixing device described in Patent Document 2, since the excessive temperature rise prevention unit is in contact with the inner peripheral surface of the heating rotary belt, the excessive temperature rise prevention unit is in contact with the rotation axis direction of the heating rotary belt. A difference in heat capacity is likely to occur between the portion and the portion that does not contact the portion. As a result, the temperature at the part where the excessive temperature rise prevention part is in contact is unlikely to rise, and temperature unevenness is likely to occur in the rotation axis direction of the fixing device. As a result, the quality of the image fixed by the fixing device becomes a factor of deterioration.

The present invention is provided with an excessive temperature rise prevention unit that cuts off the power supply to the induction coil when the temperature of the heating rotating belt is equal to or higher than a predetermined temperature, and prevents the excessive temperature rise while maintaining the quality of the image to be fixed. An object of the present invention is to provide a fixing device capable of improving the responsiveness of a part.
Another object of the present invention is to provide an image forming apparatus including the fixing device.

  The present invention includes an annular heating rotating belt having a first heat generating layer, a pressing member disposed inside the heating rotating belt and abutting against the inner surface of the heating rotating belt, and opposed to the heating rotating belt. A pressure rotating body that sandwiches the heating rotating belt with the pressing member to form a fixing nip with the heating rotating belt, and an outer surface of the heating rotating belt. An induction coil that is disposed along the outer surface at a predetermined distance from the outer surface and generates a magnetic flux for generating heat by heating the rotating rotating belt when power is supplied, and a magnetic path of the magnetic flux generated by the induction coil. The magnetic core portion to be formed and the inner surface side of the heating rotating belt are arranged to face the induction coil with the heating rotating belt interposed therebetween, and the heating rotating belt is positioned by contacting the inner surface. And a belt guide member that guides the rotation of the heating rotary belt, and is disposed in contact with the belt guide member, and when the temperature of the belt guide member is equal to or higher than a predetermined temperature, power is supplied to the induction coil. The present invention relates to a fixing device including an excessive temperature rise prevention unit that shuts off the heat.

  Moreover, it is preferable that the temperature sensing part of the excessive temperature rise prevention part is disposed in contact with the most downstream part of the belt guide member in the rotation direction of the heating rotating belt.

  In addition, the temperature sensing unit of the excessive temperature rise prevention unit is upstream of the central portion of the belt guide member in the rotation direction of the heating rotating belt when viewed in a direction orthogonal to the rotation direction of the heating rotating belt. On the side or the downstream side, it is preferable that the wire bundle portion formed by winding the wire constituting the induction coil is disposed in contact with a portion facing substantially the center in the rotation direction of the heating rotating belt.

  The first heat generating layer is formed to be thinner than a skin depth that is a depth at which a magnetic field penetrates, and the belt guide member includes a second heat generating layer that generates heat by magnetic flux that has passed through the heating rotating belt. Furthermore, it is preferable to have it.

  In addition, one or a plurality of image carriers on which electrostatic latent images are formed on the surface, a developing unit that develops the electrostatic latent images formed on the one or more image carriers as a toner image, and the image carriers The present invention relates to an image forming apparatus including a transfer unit that directly or indirectly transfers a toner image formed on a body onto a sheet-like transfer material, and the fixing device.

According to the present invention, there is provided an excessive temperature rise prevention unit that cuts off the supply of power to the induction coil when the temperature of the heating rotating belt is equal to or higher than a predetermined temperature, while maintaining the quality of the fixed image, A fixing device capable of improving the responsiveness of the temperature preventing unit can be provided.
In addition, the present invention can provide an image forming apparatus including the fixing device.

FIG. 3 is a diagram for explaining an arrangement of each component of the printer according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view for explaining each component of the fixing device 9 in the printer 1 of the first embodiment. FIG. 3 is a view of the fixing device 9 shown in FIG. It is sectional drawing for demonstrating each component of the fixing device 9 in the printer 1 of 2nd Embodiment of this invention. It is sectional drawing for demonstrating each component of the fixing device 9 in the printer 1 of 3rd Embodiment of this invention.

Hereinafter, a first embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.
The overall structure of a printer 1 as an image forming apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a front view for explaining the arrangement of components of the printer 1 according to the first embodiment.

As shown in FIG. 1, a printer 1 as an image forming apparatus according to the first embodiment includes an apparatus main body M and an image forming unit that forms a toner image on a sheet T as a sheet-like transfer material based on image information. GK and a paper supply / discharge unit KH that supplies the paper T to the image forming unit GK and discharges the paper T on which the toner image is formed.
The external shape of the apparatus main body M is comprised by case body BD as a housing | casing.

  As shown in FIG. 1, the image forming unit GK includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers (photosensitive members), charging units 10a, 10b, 10c, and 10d, and a laser as an exposure unit. Scanner units 4a, 4b, 4c, 4d, developing devices 16a, 16b, 16c, 16d, toner cartridges 5a, 5b, 5c, 5d, toner supply units 6a, 6b, 6c, 6d, drum cleaning unit 11a, 11b, 11c, 11d, static eliminators 12a, 12b, 12c, 12d, intermediate transfer belt 7, primary transfer rollers 37a, 37b, 37c, 37d, secondary transfer roller 8, counter roller 18, fixing And a device 9.

  As shown in FIG. 1, the paper supply / discharge unit KH includes a paper feed cassette 52, a conveyance path L for the paper T, a registration roller pair 80, a plurality of rollers or roller pairs, and a paper discharge unit 50. .

Hereinafter, each configuration of the image forming unit GK and the paper supply / discharge unit KH will be described in detail.
First, the image forming unit GK will be described.
In the image forming unit GK, charging by the charging units 10a, 10b, 10c, and 10d in order from the upstream side to the downstream side in order along the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, the laser scanner unit 4a, 4b, 4c, 4d exposure, development devices 16a, 16b, 16c, 16d development, intermediate transfer belt 7 and primary transfer rollers 37a, 37b, 37c, 37d primary transfer, static eliminators 12a, 12b, 12c, 12d Is eliminated, and cleaning is performed by the drum cleaning units 11a, 11b, 11c, and 11d.
In the image forming unit GK, secondary transfer by the intermediate transfer belt 7, the secondary transfer roller 8 and the opposing roller 18, and fixing by the fixing device 9 are performed.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is formed of a cylindrical member and functions as a photosensitive member or an image carrier. Each of the photosensitive drums 2a, 2b, 2c, and 2d is disposed so as to be rotatable in the direction of the arrow illustrated in FIG. 1 around a rotation axis that extends in a direction orthogonal to the traveling direction of the intermediate transfer belt 7. An electrostatic latent image can be formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d.

  Each of the charging units 10a, 10b, 10c, and 10d is disposed to face the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the charging units 10a, 10b, 10c, and 10d uniformly charges the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d negatively (minus polarity) or positively (plus polarity).

  The laser scanner units 4a, 4b, 4c, and 4d function as exposure units, and are spaced apart from the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d.

  Each of the laser scanner units 4a, 4b, 4c, and 4d scans and exposes the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d based on image information input from an external device such as a PC (personal computer). Thus, an electrostatic latent image can be formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d.

  The developing devices 16a, 16b, 16c, and 16d are provided corresponding to the photosensitive drums 2a, 2b, 2c, and 2d, respectively, and are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the developing devices 16a, 16b, 16c, and 16d attaches the toner of each color to the electrostatic latent image formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, and converts the color toner image into the photosensitive drum. 2a, 2b, 2c and 2d are formed on the respective surfaces. Each of the developing devices 16a, 16b, 16c, and 16d corresponds to four colors of yellow, cyan, magenta, and black. Each of the developing devices 16a, 16b, 16c, and 16d includes a developing roller disposed opposite to the surface of the photosensitive drums 2a, 2b, 2c, and 2d, a stirring roller for stirring the toner, and the like.

  Each of the toner cartridges 5a, 5b, 5c, and 5d is provided corresponding to each of the developing devices 16a, 16b, 16c, and 16d, and each color toner supplied to each of the developing devices 16a, 16b, 16c, and 16d. To accommodate. Each of the toner cartridges 5a, 5b, 5c, and 5d accommodates yellow toner, cyan toner, magenta toner, and black toner.

  The toner supply units 6a, 6b, 6c, and 6d are provided corresponding to the toner cartridges 5a, 5b, 5c, and 5d and the developing devices 16a, 16b, 16c, and 16d, respectively. The toners of the respective colors accommodated in 5d are supplied to the developing devices 16a, 16b, 16c, and 16d, respectively.

  To the intermediate transfer belt 7, the toner images of the respective colors formed on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred. The intermediate transfer belt 7 is stretched around a driven roller 35, a counter roller 18 including a driving roller, a tension roller 36, and the like. Since the tension roller 36 biases the intermediate transfer belt 7 from the inside to the outside, a predetermined tension is applied to the intermediate transfer belt 7.

  Primary transfer rollers 37a, 37b, 37c, and 37d are arranged to face each other on the side opposite to the photosensitive drums 2a, 2b, 2c, and 2d with the intermediate transfer belt 7 interposed therebetween.

  A predetermined portion of the intermediate transfer belt 7 is sandwiched between the primary transfer rollers 37a, 37b, 37c, and 37d and the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The predetermined portion thus sandwiched is pressed against the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Primary transfer nips N1a, N1b, N1c, and N1d are formed between the photosensitive drums 2a, 2b, 2c, and 2d and the primary transfer rollers 37a, 37b, 37c, and 37d, respectively. In the primary transfer nips N1a, N1b, N1c, and N1d, the toner images of the respective colors formed on the photoreceptor drums 2a, 2b, 2c, and 2d are sequentially primary-transferred onto the intermediate transfer belt 7, respectively. As a result, a full-color toner image is formed on the intermediate transfer belt 7.

  The static eliminators 12a, 12b, 12c, and 12d are arranged to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively.

  The drum cleaning units 11a, 11b, 11c, and 11d are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively.

  The secondary transfer roller 8 secondarily transfers the full-color toner image primarily transferred to the intermediate transfer belt 7 onto the paper T. A secondary transfer bias for transferring the full color toner image formed on the intermediate transfer belt 7 to the paper T is applied to the secondary transfer roller 8 by a secondary transfer bias applying unit (not shown).

  The secondary transfer roller 8 contacts or separates from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is configured to be movable between a contact position where the secondary transfer roller 8 is in contact with the intermediate transfer belt 7 and a spaced position where the secondary transfer roller 8 is separated from the intermediate transfer belt 7.

  A counter roller 18 is disposed on the opposite side of the intermediate transfer belt 7 from the secondary transfer roller 8. A predetermined portion of the intermediate transfer belt 7 is sandwiched between the secondary transfer roller 8 and the opposing roller 18. Then, the paper T is pressed against the outer surface of the intermediate transfer belt 7 (the surface on which the toner image is primarily transferred). A secondary transfer nip N <b> 2 is formed between the intermediate transfer belt 7 and the secondary transfer roller 8. In the secondary transfer nip N2, the full-color toner image primarily transferred to the intermediate transfer belt 7 is secondarily transferred to the paper T.

The fixing device 9 melts and presses the toner of each color constituting the toner image secondarily transferred onto the paper T and fixes the toner on the paper T.
Details of the fixing device 9 will be described later.

Next, the paper supply / discharge unit KH will be described.
As shown in FIG. 1, a paper feed cassette 52 that stores paper T is disposed below the apparatus main body M. In the paper feed cassette 52, a placement plate 60 on which the paper T is placed is disposed. The paper T placed on the placement plate 60 is sent out to the transport path L by the cassette paper feeding unit 51. The cassette paper feeding unit 51 includes a forward feed roller 61 for taking out the paper T on the placement plate 60 and a paper feed roller pair 81 for feeding the paper T one by one to the transport path L. Is provided.

  The conveyance path L for conveying the paper T includes a first conveyance path L1 from the cassette paper feeding unit 51 to the secondary transfer nip N2, a second conveyance path L2 from the secondary transfer nip N2 to the fixing device 9, and a fixing device. A third transport path L3 from 9 to the paper discharge unit 50, and a return transport path Lb for reversing the paper transporting the third transport path L3 from the upstream side to the downstream side and returning it to the first transport path L1. Prepare.

  Moreover, the 1st junction part P1 and the 2nd junction part P2 are provided in the middle of the 1st conveyance path L1. A first branch portion Q1 is provided in the middle of the third transport path L3.

  In the middle of the first conveyance path L1 (specifically, between the second joining portion P2 and the secondary transfer nip N2), a paper detection sensor (not shown) for detecting the paper T, A registration roller pair 80 for adjusting the skew (oblique feeding) correction and the toner image formation in the image forming unit GK and the conveyance timing of the paper T is disposed.

  An intermediate roller pair 82 is disposed between the first joining portion P1 and the second joining portion P2 in the first transport path L1. The intermediate roller pair 82 is disposed on the downstream side of the paper feed roller pair 81, sandwiches the paper T conveyed from the paper feed roller pair 81, and conveys it to the registration roller pair 80.

  A rectifying member 58 is provided in the first branch portion Q1. The rectifying member 58 rectifies the transport direction of the paper T that is unloaded from the fixing device 9 and transports the third transport path L3 from the upstream side toward the downstream side in a direction toward the paper discharge unit 50, and the paper discharge unit 50. The conveyance direction of the paper T that is conveyed from the downstream side toward the upstream side of the third conveyance path L3 is rectified in a direction toward the return conveyance path Lb.

  A paper discharge section 50 is formed at the end of the third transport path L3 on the paper transport direction side. The paper discharge unit 50 is disposed above the apparatus main body M. The paper discharge unit 50 discharges the paper T to the outside of the apparatus main body M.

  On the opening side of the paper discharge unit 50, a paper discharge stacking unit M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the apparatus main body M. A paper detection sensor is disposed at a predetermined position on each conveyance path.

  Next, a configuration related to the fixing device 9 which is a characteristic part of the printer 1 of the first embodiment will be described in detail. FIG. 2 is a cross-sectional view for explaining each component of the fixing device 9 of the printer 1 of the first embodiment. 3 is a view of the fixing device 9 shown in FIG.

As shown in FIG. 2, the fixing device 9 includes a heating rotating belt 9a, a pressure rotating body 9b pressed against (contacting with) the heating rotating belt 9a, a heating unit 70, a belt guide member 77, and a pressing member. 92 and a plurality of temperature sensors 95.

The heating rotating belt 9a is formed in an annular shape (endless belt shape). The heating rotary belt 9a is formed by a belt having a small heat capacity. The heating rotation belt 9a is configured to be rotatable in the first circumferential direction R1 around a second rotation axis J2 parallel to the paper width direction D2. In the present embodiment, the direction D2 orthogonal to the first circumferential direction R1 is also referred to as “paper width direction D2”. The heating rotating belt 9a generates heat by electromagnetic induction heating (IH; induction heating) using electromagnetic induction by using a heating unit 70 described later.
The heating rotating belt 9a is disposed in a region through which a magnetic flux generated by an induction coil 71 of the heating unit 70 described later passes.

  A pressing member 92, which will be described later, a belt guide member 77, which will be described later, and an excessive temperature rise prevention portion 79, which will be described later, are disposed inside the heating rotary belt 9a. The heating rotating belt 9a is stretched between the belt guide member 77 and the pressing member 92 in a state where a predetermined tension is applied.

  A pressing member 92 abuts on the inner peripheral surface (inner surface) of the heating rotating belt 9a on the pressure rotating body 9b side (the lower side in the vertical direction inside the heating rotating belt 9a), and a center core portion described later. The belt guide member 77 abuts on the 73 side (the upper side in the vertical direction inside the heating rotary belt 9a).

  The heating rotating belt 9a has a magnetic metal layer as a first heat generating layer. In the heating rotary belt 9a, an eddy current (induced current) is generated by electromagnetic induction by the magnetic flux passing through the heating rotary belt 9a without penetrating the heating rotary belt 9a. Joule heat is generated by the electric resistance of the heating rotating belt 9a due to an eddy current flowing through the heating rotating belt 9a. In this way, the heating rotating belt 9a generates heat by electromagnetic induction heating (IH) using electromagnetic induction by a heating unit 70 described later.

A surface release layer (not shown) as a low friction material is formed on the inner peripheral surface of the heating rotary belt 9a via an elastic layer (not shown). In the present embodiment, a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) tube having a low friction coefficient is used for the surface release layer, and silicon rubber is used for the elastic layer.
The pressing member 92, the belt guide member 77, and the excessive temperature rise prevention unit 79 will be described later.

  The heating rotating belt 9a forms a magnetic path of the magnetic flux generated by the induction coil 71 of the heating unit 70 by being arranged in a region through which the magnetic flux generated by the induction coil 71 of the heating unit 70 described later passes.

  The pressure roller as the pressure rotator 9b is formed in a cylindrical shape (annular shape). The pressure roller 9b is arranged on the lower side in the vertical direction of the heating rotary belt 9a so as to face the heating rotary belt 9a. The pressure roller 9b is configured to be rotatable in a second circumferential direction R2, which is the circumferential direction of the pressure roller 9b, around a first rotation axis J1 parallel to the paper width direction D2. The pressure roller 9b is formed to extend in the direction of the first rotation axis J1.

  The pressure roller 9b is disposed such that its outer peripheral surface comes into contact with the outer peripheral surface (outer surface) of the heating rotary belt 9a. The pressure roller 9b is disposed so as to press a pressing member 92 (described later) through the heating rotary belt 9a. The pressure roller 9b sandwiches a part of the heating rotating belt 9a between the pressing member 92 and forms a fixing nip F with the heating rotating belt 9a. The fixing nip F sandwiches the paper T and conveys the paper T.

  The pressure roller 9b includes a pressure roller body 941 and a shaft member 942 (see FIG. 2) coaxial with the first rotation shaft J1. The pressure roller body 941 includes a cylindrical cored bar member, an elastic layer formed on the outer peripheral surface of the cored bar member, and a release layer formed on the outer peripheral surface of the elastic layer. In this embodiment, iron is used for the core metal member, foamable silicon rubber is used for the elastic layer, and a PFA tube is used for the release layer.

  A rotation drive unit (not shown) for rotating the pressure roller 9b is connected to the shaft member 942 of the pressure roller 9b. The pressure driving roller 9b is driven to rotate at a predetermined speed by the rotation driving unit, and the heating rotating belt 9a contacting the outer peripheral surface of the pressure roller 9b is rotated by the rotation of the pressure roller 9b.

  The pressing member 92 is disposed inside the heating rotary belt 9a. The pressing member 92 abuts on the inner peripheral surface of the heating rotary belt 9a on the pressure roller 9b side inside the heating rotary belt 9a and presses the heating rotary belt 9a toward the pressure roller 9b. In this embodiment, the pressing member 92 is made of iron or SUS.

  The pressing member 92 is formed to extend long in the paper width direction D2. The pressing member 92 sandwiches the heating rotating belt 9a between the pressure roller 9b and forms a fixing nip F between the heating rotating belt 9a and the pressure roller 9b. The pressing member 92 contacts the inner peripheral surface of the heating rotary belt 9a while sliding.

  When the sheet T conveyed to the fixing nip F is conveyed after passing through the sheet passing area of the fixing device 9, the toner image is fixed. Here, the “sheet passing region” is a region through which the paper T conveyed to the fixing nip F passes between the heating rotating belt 9a and the pressure roller 9b. An area where the paper T, which is an area outside the paper passing area when the paper T is conveyed to the fixing nip F, does not pass is also referred to as a “non-paper passing area”.

  As shown in FIG. 3, a maximum sheet passing area 901 is set as a sheet passing area when the maximum length sheet T in the sheet width direction D2 is conveyed to the fixing nip F. The maximum sheet passing area 901 is set for each printer 1.

  Specifically, the heating-side maximum sheet passing area 901a is formed (set) as the maximum sheet passing area 901 in the heating rotating belt 9a on the outer peripheral surface of the heating rotating belt 9a. On the outer peripheral surface of the pressure roller 9b, a pressure side maximum sheet passing area 901b is formed as a maximum sheet passing area 901 in the pressure rotating body 9b corresponding to the heating side maximum sheet passing area 901a of the heating rotating belt 9a ( Set). The length in the direction parallel to the sheet width direction D2 in the heating-side maximum sheet passing area 901a is referred to as “maximum sheet passing width W1”.

Further, the minimum sheet passing area 903 is set as a sheet passing area through which the sheet T passes when the sheet T having the minimum length in the sheet width direction D2 is conveyed to the fixing nip F.
Specifically, the heating-side minimum sheet passing area 903a is formed (set) as the minimum sheet passing area 903 in the heating rotating belt 9a on the outer peripheral surface of the heating rotating belt 9a. On the outer peripheral surface of the pressure roller 9b, a pressure side minimum sheet passing area 903b is formed (set) corresponding to the heating side minimum sheet passing area 903a of the heating rotating belt 9a. The length in the direction parallel to the sheet width direction D2 in the heating-side minimum sheet passing area 903a is referred to as “minimum sheet passing width W3”.

In the fixing device 9 of the present embodiment, the sheet T having an intermediate length (intermediate width) whose length in the sheet width direction D2 is shorter than the maximum length and longer than the minimum length (minimum width). As the sheet passing area through which the sheet T passes when the sheet is conveyed to the fixing nip F, an intermediate sheet passing area 902 (a heating side intermediate sheet passing area 902a and a pressure side intermediate sheet passing area 902b) is set. The length in the direction parallel to the sheet width direction D2 in the heating-side intermediate sheet passing region 902a is referred to as “intermediate sheet passing width W2.”
Note that the paper passing area of the paper T is not limited to this, and can be set as appropriate for the paper T of each size.

The heating unit 70 will be described. As shown in FIGS. 2 and 3, the heating unit 70 includes an induction coil 71 and a magnetic core portion 72. The induction coil 71 is spaced apart from the outer peripheral surface of the heating rotary belt 9a by a predetermined distance and is disposed along the outer peripheral surface of the heating rotary belt 9a. The induction coil 71 is formed by winding a wire in a long shape in the paper width direction D2 in plan view (when viewed from above in FIGS. 2 and 3).
The induction coil 71 is formed longer than the length of the heating rotary belt 9a in the paper width direction D2.

The induction coil 71 is formed by winding a copper litz wire. The induction coil 71 is disposed so as to face a substantially half-circumferential outer peripheral surface on the upper side in the vertical direction of the heating rotary belt 9a.
As shown in FIGS. 2 and 3, the induction coil 71 is formed by winding a wire so as to surround a central region 718 formed so as to extend in the paper width direction D2.
In the present embodiment, the induction coil 71 is fixed by winding a wire on a support member (bobbin) 78 formed of a heat-resistant resin material.

  The induction coil 71 is connected to an induction heating circuit unit (not shown). An alternating current having a predetermined frequency is applied to the induction coil 71 from the circuit section for induction heating. The induction coil 71 generates magnetic flux for generating heat from the magnetic metal layer (first heat generation layer) of the heating rotating belt 9a when an alternating current (AC power) is applied from the induction heating circuit section. For example, an alternating current having a frequency of about 30 kHz is applied to the induction coil 71.

  The magnetic flux generated by the induction coil 71 is guided to a magnetic path which is a magnetic flux path formed by the heating rotary belt 9a and a magnetic core portion 72 (described later).

  The magnetic path is formed by the heating rotary belt 9a and a magnetic core 72 (described later) so that the magnetic flux generated by the induction coil 71 circulates in the circulation direction R3. The circumferential direction R3 is a direction that circulates so as to surround the wire portion of the induction coil 71 through the inner side of the inner peripheral edge 711A and the outer side of the outer peripheral edge 711B of the induction coil 71. The magnetic flux generated by the induction coil 71 passes through the magnetic path.

  The magnetic flux generated by the induction coil 71 is applied with an alternating current of a predetermined frequency from an induction heating circuit unit (not shown), and therefore, the magnitude and direction of the magnetic flux generated by periodic fluctuation of the alternating current to plus or minus. Changes. An induction current (eddy current) is generated in the heating rotating belt 9a due to the change of the magnetic flux.

  As shown in FIG. 2, the magnetic core portion 72 forms a magnetic path that circulates in the circumferential direction R <b> 3. The magnetic core portion 72 is disposed in a region through which the magnetic flux generated by the induction coil 71 passes and is formed mainly of a ferromagnetic material. Therefore, a magnetic path that is a path of the magnetic flux generated by the induction coil 71 is provided. Form.

  The magnetic core portion 72 includes an upper core portion 75 and a pair of side core portions 76 and 76. The upper core portion 75 is integrally formed by the center core portion 73 and the plurality of arch core portions 74. The center core portion 73 and the plurality of arch core portions 74 and 74 are formed integrally and continuously along the circumferential direction R3 of the magnetic path at a predetermined position in the paper width direction D2.

When viewed in the paper width direction D2, the center core portion 73 is located approximately at the center in the transport direction D1 of the paper T of the heating rotary belt 9a on the upper side in the vertical direction of the heating rotary belt 9a (near the center region 718). Be placed.
As shown in FIG. 2, the center core portion 73 forms a magnetic path between an arch core portion 74 (described later) and the heating rotary belt 9 a in the circulation direction R <b> 3 of the magnetic path. Center core portion 73 is disposed in the vicinity of central region 718 (in the vicinity of the wire disposed on inner peripheral edge 711A of induction coil 71).

  The center core portion 73 is separated from the outer peripheral surface of the heating rotary belt 9a by a predetermined distance and faces the outer peripheral surface of the heating rotary belt 9a. The center core portion 73 has a first facing surface 731 that faces the outer peripheral surface of the heating rotary belt 9a without sandwiching the wire portion of the induction coil 71.

  Further, as shown in FIG. 3, the center core portion 73 is formed in a substantially rectangular parallelepiped shape that is long in the paper width direction D2. The center core portion 73 is formed longer than the area corresponding to the maximum sheet passing area 901 in the sheet width direction D2.

  Each of the plurality of arch core portions 74 and 74 is disposed to face the outer peripheral surface of the heating rotating belt 9a with the wire portion of the induction coil 71 interposed therebetween. Each of the plurality of arch core portions 74, 74 is formed in a dome shape extending along the circumferential direction of the heating rotary belt 9a.

The plurality of arch core portions 74 are formed so as to extend from the upper side of the center core portion 73 to the upstream side and the downstream side in the transport direction D1.
As shown in FIG. 2, each of the plurality of arch core portions 74 and 74 has a magnetic path on the side opposite to the heating rotating belt 9 a (outside the induction coil 71) with respect to the induction coil 71 in the circulation direction R <b> 3 of the magnetic path. Form.

  Further, as shown in FIG. 3, each of the plurality of arch core portions 74 is disposed at a predetermined distance in the paper width direction D2. Each of the plurality of arch core portions 74 forms a plurality of magnetic paths that are spaced apart in the paper width direction D2 and circulate in the circumferential direction R3.

  As shown in FIG. 2, each of the pair of side core portions 76 and 76 forms a magnetic path between the heating rotary belt 9a and the arch core portion 74 in the circumferential direction R3 of the magnetic path. Each of the pair of side core portions 76 and 76 is arranged side by side with each of the plurality of arch core portions 74 and 74 in the circumferential direction R3 of the magnetic path.

Each of the pair of side core portions 76 and 76 is disposed in the vicinity of the outer peripheral edge 711 </ b> B of the induction coil 71. Each of the pair of side core portions 76, 76 is disposed to be opposed to the outer peripheral surface of the heating rotary belt 9a by being separated from the outer peripheral surface of the heating rotary belt 9a by a predetermined distance. Each of the pair of side core portions 76 and 76 has a second facing surface 761 that faces the outer peripheral surface of the heating rotating belt 9a without sandwiching the wire portion of the induction coil 71. Each of the pair of side core portions 76 and 76 is formed in a substantially rectangular parallelepiped shape that is long in the paper width direction D2.
As shown in FIG. 3, each of the pair of side core portions 76 and 76 is formed longer than an area corresponding to the maximum sheet passing area 901 in the sheet width direction D2.

The belt guide member 77 is disposed on the inner peripheral surface side of the heating rotary belt 9a. The belt guide member 77 is disposed to face the induction coil 71 with the heating rotating belt 9a interposed therebetween.
When viewed in the paper width direction D2, the belt guide member 77 has a circular cross section and is formed in a plate shape. The belt guide member 77 is in contact with the inner peripheral surface of the heating rotating belt 9a at approximately one third of the heating rotating belt 9a on the upper side in the vertical direction. The belt guide member 77 is formed long in the paper width direction D2. The belt guide member 77 is formed of a rigid material having a thickness of about 0.2 to 0.5 mm, for example, a nonmagnetic metal material such as SUS304.

  The belt guide member 77 positions the heating rotating belt 9a with respect to the induction coil 71 and guides the rotation of the heating rotating belt 9a that rotates about the second rotation axis J2. In addition, heat from the heating rotating belt 9a generated by electromagnetic induction heating is transmitted to the belt guide member 77. Therefore, the temperatures of the belt guide member 77 and the heating rotary belt 9a are substantially the same in the vicinity of the portion where they are in contact with each other.

  The excessive temperature rise prevention unit 79 is configured by, for example, a thermal cutoff. From the viewpoint of ensuring the safety of the fixing device 9, the excessive temperature rise prevention unit 79 causes the temperature of the heating rotating belt 9a to reach a predetermined temperature due to, for example, a runaway control unit or the like, failure or breakage of various switch units, or the like. When the temperature rises to the above abnormal temperature, the power supply to the induction coil 71 is cut off. In particular, when the heating rotary belt 9a stops rotating due to a runaway of the control unit or the like, the temperature of the portion of the heating rotary belt 9a facing the induction coil 71 may rise abnormally. There is a need to cut off the power supply to the urgent.

  The excessive temperature rise prevention unit 79 includes a temperature sensing unit 79 </ b> A that contacts the belt guide member 77 and senses the temperature of the belt guide member 77. For example, the temperature detection unit 79A uses a mechanical detection system such as a bimetal or a shape memory alloy that uses a property in which two metal plates having different thermal expansion coefficients are bonded to each other and the bending method changes according to a change in temperature. .

As shown in FIG. 2, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 has a rotation direction of the heating rotary belt 9a in the belt guide member 77 of the inner surface of the belt guide member 77 in a portion facing the induction coil 71. It arrange | positions in the state which contacted the most downstream part of (1st circumferential direction R1).
The portion of the belt guide member 77 on the most downstream side in the rotation direction (first circumferential direction R1) of the heating rotary belt 9a is heated by electromagnetic induction heating (IH) while the heating rotary belt 9a is rotating. This is the portion of the device 9 where the temperature rises the most.

  The excessive temperature rise prevention unit 79 cuts off the supply of power to the induction coil 71 when the temperature sensing unit 79A senses that the temperature of the belt guide member 77 is equal to or higher than a predetermined temperature.

Specifically, the excessive temperature rise prevention unit 79 has two terminals, and the two terminals of the excessive temperature rise prevention unit 79 are an induction heating circuit unit (not connected) that applies AC power to the induction coil 71. Are connected in series. When the temperature sensing unit 79A of the overheat prevention unit 79 senses that the temperature of the heating rotating belt 9a is equal to or higher than a predetermined temperature, the overheat prevention unit 79 is disconnected and the induction coil 71 is connected. The power supply is configured to be cut off.
That is, the excessive temperature rise prevention unit 79 is connected to the induction coil 71 by causing the same current as the current flowing through the induction coil 71 to flow, so that the over temperature rise prevention unit 79 is disconnected. Shut off the power supply to

  In the present embodiment, the fixing temperature of the fixing device 9 is set to be 230 to 240 ° C. And (operation) temperature which interrupts | blocks supply of the electric power to the induction coil 71 by the excessive temperature rise prevention part 79 is set to about 300 degreeC. In the present embodiment, from the viewpoint of ensuring the safety of the fixing device 9, the excessive temperature rise prevention unit 79 maintains the disconnection state when the supply of power to the induction coil 71 is interrupted (disconnection operation). To do.

  The temperature sensor 95 detects the temperature of the outer peripheral surface of the heating rotary belt 9a. The temperature sensor 95 is disposed in contact with the outer peripheral surface of the heating rotary belt 9a. Based on the temperature detected by the temperature sensor 95, a control signal is fed back to an induction heating circuit (not shown) to change the frequency of the alternating current, thereby keeping the temperature of the heating rotary belt 9a within a predetermined range. Such temperature adjustment is performed. The temperature sensor 95 is composed of, for example, an infrared temperature sensor.

Next, the operation of the printer 1 including the fixing device 9 of this embodiment will be described.
First, when the printer 1 is turned on, the charging units 10a, 10b, 10c, and 10d, the laser scanner units 4a, 4b, 4c, and 4d, the developing units 16a, 16b, 16c, and 16d are supplied from a power source unit (not shown). Electric power is supplied to each of the primary transfer rollers 37a, 37b, 37c, and 37d, the secondary transfer roller 8, a printer control unit (not shown), and the fixing device 9. Then, charging units 10a, 10b, 10c, and 10d, laser scanner units 4a, 4b, 4c, and 4d, developing devices 16a, 16b, 16c, and 16d, primary transfer rollers 37a and 37b, according to a control signal from the printer control unit, The operations of 37c, 37d, secondary transfer roller 8, intermediate transfer belt 7, and fixing device 9 are controlled.

  An accepting unit (not shown) of the printer 1 is an image forming instruction that is generated when an operation unit (not shown) arranged outside the printer 1 is operated, for example, while the printer 1 is turned on. Accept information.

Next, the printer 1 starts a printing operation.
Specifically, the paper T sent out from the registration roller pair 80 is transported to the transfer nip N2 between the intermediate transfer belt 7 and the transfer roller 8 through the first transport path L1. When the sheet T is conveyed to the transfer nip N2 in this way, first, the charging units 10a, 10b, 10c, and 10d are uniformly negative (negative polarity) on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. ) Or positive (positive polarity), and the laser scanner units 4a, 4b, 4c, and 4d irradiate the photosensitive drums 2a, 2b, 2c, and 2d with laser light from a laser light source (not shown), The surface of each of the photosensitive drums 2a, 2b, 2c, and 2d is scanned and exposed to remove charges. Thereby, electrostatic latent images are formed on the respective surfaces of the photosensitive drums 2a, 2b, 2c, and 2d.

  Subsequently, each of the developing devices 16a, 16b, 16c, and 16d attaches the toner of each color to the electrostatic latent image formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, and forms a color toner image. It is formed on the surface of each of the photoreceptor drums 2a, 2b, 2c, and 2d. Next, the toner images of the respective colors formed on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred onto the intermediate transfer belt 7. As a result, a full-color toner image is formed on the intermediate transfer belt 7.

  Subsequently, the toner image is secondarily transferred onto the paper T passing through the transfer nip N <b> 2 between the intermediate transfer belt 7 and the transfer roller 8. The sheet T on which the toner image is transferred is conveyed toward the fixing device 9 through the second conveyance path L2. Specifically, the paper T on which the toner image is formed is conveyed toward the fixing nip F formed by the heating rotating belt 9a and the pressure roller 9b of the fixing device 9.

  When the supply of power to the drive control unit of the fixing device 9 is started, the pressure roller 9b is rotationally driven by a rotation drive unit (not shown). As the pressure roller 9b is driven to rotate, the heating rotary belt 9a is driven to rotate.

Next, the fixing device 9 starts a heat generating operation.
Thereby, an alternating current is applied to the induction coil 71 from an induction heating circuit section (not shown). The induction coil 71 generates a magnetic flux for causing the heating rotary belt 9a to generate heat.

  The magnetic flux generated by the induction coil 71 is generated in the magnetic path formed by the heating rotary belt 9a, the center core portion 73, the plurality of arch core portions 74 and 74, and the pair of side core portions 76 and 76, and the inner peripheral edge 711A of the induction coil 71. Is passed (circulated) in the circumferential directions R3 and R3 so as to connect the inner side of the outer periphery and the outer side of the outer peripheral edge 711B.

  Then, by changing the magnitude and direction of the magnetic flux passing through the magnetic path, an eddy current (induced current) is generated by electromagnetic induction in the magnetic metal layer of the heating rotating belt 9a. When an eddy current flows through the heating rotating belt 9a, Joule heat is generated by the electric resistance of the heating rotating belt 9a, and the heating rotating belt 9a generates heat.

  Next, a portion (magnetic metal layer) that is heated by the electromagnetic induction heating (IH) of the heating rotating belt 9a by the rotation of the heating rotating belt 9a is formed by the heating rotating belt 9a and the pressure roller 9b of the fixing device 9. Are sequentially moved toward the fixing nip F. The printer 1 controls an induction heating circuit unit (not shown) so that a predetermined temperature is reached in the fixing nip F.

  Then, the paper T on which the toner image is formed is introduced into the fixing nip F of the fixing device 9, whereby the toner is melted and fixed on the paper T in the fixing nip F.

  Here, on the inner peripheral surface side of the heating rotary belt 9a, an arcuate belt guide member 77 that is in contact with the inner surface of the heating rotary belt 9a is disposed. Therefore, the belt guide member 77 positions the rotation path of the heating rotary belt 9a and guides the rotation of the heating rotary belt 9a. Thereby, the belt guide member 77 can stabilize the rotation of the heating rotary belt 9a.

  Further, the belt guide member 77 contacts the inner peripheral surface of the heating rotary belt 9a, thereby positioning the magnetic metal layer portion on the upper side in the vertical direction of the heating rotary belt 9a. Thereby, the magnetic flux passing through the heating rotary belt 9a is stabilized, and the heat generation efficiency of the magnetic metal layer portion of the heating rotary belt 9a can be stabilized.

  At the time of fixing as described above, the heat of the heating rotating belt 9 a generated by electromagnetic induction heating (IH) is transmitted to the belt guide member 77. The belt guide member 77 rises to a temperature that is equal to or substantially equal to the temperature of the heating rotary belt 9a in the vicinity of the portion that contacts the heating rotary belt 9a. Therefore, the temperatures of the belt guide member 77 and the heating rotary belt 9a are substantially the same.

  Then, when the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 senses that the temperature of the heating rotating belt 9a has reached a predetermined temperature or more, the induction heating circuit unit that applies AC power to the induction coil 71 ( The two terminals of the excessive temperature rise prevention unit 79 connected in series to the not-shown state are disconnected, and the supply of power to the induction coil 71 is interrupted. Then, the heating of the heating rotary belt 9a is stopped. This prevents the heating rotary belt 9a from being heated to an abnormal temperature that is equal to or higher than a predetermined temperature.

According to the printer 1 of the first embodiment, for example, the following effects are exhibited.
In the printer 1 of the first embodiment, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is disposed in contact with the belt guide member 77. Therefore, the response speed for detecting an abnormal temperature of the heating rotary belt 9a can be improved without delaying the timing when the heating rotary belt 9a is heated to a predetermined temperature or higher. Thereby, the responsiveness of interruption | blocking of the electric power supplied to the induction coil 71 can be improved. Therefore, it is possible to reduce the heating rotary belt 9a from being heated to an abnormal temperature. As a result, the safety of the fixing device 9 can be improved.

  Further, in the first embodiment, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is not brought into direct contact with the inner peripheral surface of the heating rotating belt 9a, but indirectly through the belt guide member 77. ing. Therefore, a difference in heat capacity is less likely to occur in the direction of the rotation axis J2 (paper width direction D2) of the heating rotary belt 9a. As a result, it is possible to suppress a decrease in the quality of the image fixed by the fixing device 9.

  Further, in the printer 1 of this embodiment, the belt guide member 77 positions the heating rotary belt 9a and guides the rotation of the heating rotary belt 9a. Therefore, the rotation of the heating rotary belt 9a can be stabilized. Thereby, the magnetic flux passing through the heating rotary belt 9a is stabilized, and the heat generation distribution of the heating rotary belt 9a can be stabilized.

  In the first embodiment, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is disposed in contact with the most downstream portion of the belt guide member 77 in the rotation direction of the heating rotating belt 9a. Therefore, it is possible to sense the temperature of the portion of the heating rotary belt 9a and the belt guide member 77 where the temperature rises the most. When the temperature of the heating rotating belt 9a exceeds a predetermined temperature, the power supply to the induction coil is cut off by detecting the temperature of the heating rotating belt 9a at the portion where the temperature rises most and improving the response speed. Responsiveness can be improved. Therefore, the safety of the fixing device 9 can be improved.

  Next, a second embodiment of the present invention will be described. The second embodiment will be described mainly with respect to differences from the first embodiment. The same components as those in the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted. For the points not specifically described in the second embodiment, the description of the first embodiment is appropriately applied or incorporated.

FIG. 4 is a cross-sectional view for explaining each component of the fixing device 9 in the printer 1 of the second embodiment.
In the second embodiment, the heating rotary belt 9a is mainly composed of a magnetic metal layer as a first heat generating layer. The magnetic metal layer of the heating rotating belt 9a is formed of a ferromagnetic material such as electroformed nickel. The magnetic metal layer (first heat generating layer) of the heating rotary belt 9a is configured to be thinner than the skin depth (magnetic field penetration depth), which is the depth at which the magnetic field penetrates.

  Further, the belt guide member 77 in the second embodiment includes a base material layer 771, a second heat generation layer 772 that generates heat on the heating rotary belt 9a side of the base material layer 771 by the magnetic flux that has passed through the heating rotary belt 9a, have. The base material layer 771 is formed of a nonmagnetic metal material such as SUS304 having a thickness of about 0.2 to 0.5 mm, and the second heat generation layer 772 is made of, for example, a magnetic metal such as nickel or SUS403 having a thickness of about 100 μm. It is formed.

Here, the skin depth (magnetic field penetration depth) of the magnetic metal layer (first heat generating layer) of the heating rotating belt 9a will be briefly described.
The skin depth is the depth from the surface of the magnetic metal layer of the heating rotary belt 9a where the value of the eddy current density is 1 / e (e: the base of natural logarithm) of the value of the surface of the magnetic metal layer of the heating rotary belt 9a. Say it. Eddy current hardly flows at a position where the depth from the surface of the magnetic metal layer is deeper than the skin depth. Thereby, the magnetic flux generated by the induction coil 71 does not reach a position deeper than the skin depth. Therefore, when the thickness of the magnetic metal layer is larger than the skin depth, the magnetic flux generated by the induction coil 71 is guided along the magnetic metal layer of the heating rotating belt 9a without penetrating the magnetic metal layer.

  On the other hand, when the thickness of the magnetic metal layer is thinner than the skin depth, the magnetic flux generated by the induction coil 71 penetrates the magnetic metal layer of the heating rotating belt 9a. The amount of magnetic flux penetrating the magnetic metal layer of the heating rotating belt 9a increases as the thickness of the magnetic metal layer is thinner than the skin depth. The thickness of the magnetic metal layer of the heating rotating belt 9a is appropriately set within a range thinner than the skin depth.

  In the present embodiment, the thickness of the magnetic metal layer (first heat generating layer) of the heating rotating belt 9a is 40 μm while the skin depth is 43.7 μm, and is generated in the induction coil 71. It is set so that about 50% of the magnetic flux penetrates the heating rotary belt 9a.

  In the fixing device 9 of the printer 1 of the second embodiment, a part of the magnetic flux generated by the induction coil 71 penetrates the magnetic metal layer (first heat generating layer) of the heating rotating belt 9a, and the belt guide is generated by the penetrated magnetic flux. The second heat generating layer 772 of the member 77 generates heat. Thereby, the magnetic metal layer of the heating rotating belt 9a and the second heat generating layer 772 of the belt guide member 77 can generate heat. Therefore, the heat generation efficiency of the fixing device 9 can be improved. Therefore, the rise time of the fixing device 9 can be further shortened.

Further, the belt guide member 77 generates heat up to a temperature close to the temperature of the heating rotary belt 9a because the second heat generation layer 772 of the belt guide member 77 generates heat. The temperature of the belt guide member 77 quickly follows the temperature of the heating rotary belt 9a by the heat transfer between the magnetic metal layer of the heating rotary belt 9a and the second heat generating layer 772 of the belt guide member 77. Go.
As a result, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 that is in contact with the belt guide member 77 can efficiently sense an abnormality in the temperature of the heating rotating belt 9a. Accordingly, it is possible to further improve the responsiveness of cutting off the power supplied to the induction coil 71.

According to the printer 1 of the second embodiment, the following effects can be obtained in addition to the effects shown in the first embodiment.
In the fixing device 9 of the printer 1 according to the second embodiment, the magnetic metal layer of the heating rotating belt 9a and the second heat generating layer 772 of the belt guide member 77 are heated by the magnetic flux generated by the induction coil 71, and the heat generation efficiency is increased. Can be improved. Therefore, the rise time can be further shortened compared to the fixing device 9 of the first embodiment. Therefore, power consumption can be further reduced.

  In addition, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 disposed in contact with the belt guide member 77 generates the heat of the second heat generation layer 772 of the belt guide member 77, and thus the temperature of the heating rotating belt 9a is efficiently increased. Can sense well. Accordingly, it is possible to further improve the responsiveness of cutting off the power supplied to the induction coil 71.

  Next, a third embodiment of the present invention will be described. About 3rd Embodiment, a different point from 1st Embodiment is mainly demonstrated, the same code | symbol is attached | subjected about the structure similar to 1st Embodiment, and detailed description is abbreviate | omitted. In the third embodiment, the description and illustration in the first embodiment are applied or used as appropriate for points that are not particularly described and illustrated.

  FIG. 5 is a cross-sectional view for explaining each component of the fixing device 9 in the printer 1 of the third embodiment. In the third embodiment, the position where the excessive temperature rise prevention unit 79 is arranged is different from that of the first embodiment.

  In the third embodiment, as shown in FIG. 5, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is viewed in a direction (paper width direction) D2 orthogonal to the rotation direction of the heating rotary belt 9a. On the downstream side of the belt guide member 77 with respect to the central portion in the rotation direction R1 of the heating rotary belt 9a, the heating guide belt 9a is formed by winding the wire constituting the induction coil 71. It arrange | positions in contact with the inner surface of the part which opposes a center.

  This is a portion facing the approximate center in the rotation direction R1 of the heating rotation belt 9a of the wire bundle constituting the induction coil 71 in the heating rotation belt 9a on the downstream side of the center portion in the rotation direction R1 of the heating rotation belt 9a. This is because when the heating rotary belt 9a is heated without rotating due to a failure of the fixing device 9 or the like, the heating rotary belt 9a has the highest temperature. The portion of the heating rotating belt 9 a that faces the approximate center in the rotation direction R 1 of the heating rotating belt 9 a of the wire bundle constituting the induction coil 71 is in contact with the belt guide member 77. As a result, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is disposed in contact with a portion of the belt guide member 77 facing the substantially center of the rotation direction R1 of the heating rotation belt 9a of the wire bundle of the induction coil 71. Thus, it is possible to sense the temperature of the highest temperature portion of the heating rotary belt 9a.

  In the present embodiment, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is a downstream portion of the belt guide member 77 in the rotational direction R1 of the heating rotating belt 9a, and the wire bundle portion of the induction coil 71 is downstream. Although it arrange | positions in contact with the part which opposes the approximate center of the rotation direction R1 of the heating rotation belt 9a in, it is not restrict | limited to this. The temperature detection unit 79A of the excessive temperature rise prevention unit 79 rotates the heating rotation belt 9a in the wire bundle portion of the induction coil 71 on the upstream side with respect to the central portion of the rotation direction R1 of the heating rotation belt 9a in the belt guide member 77. You may arrange | position in contact with the part which opposes the approximate center of direction R1.

According to the printer 1 of the third embodiment, the following effects can be obtained in addition to the effects shown in the first embodiment.
In the fixing device 9 of the third embodiment, the temperature sensing unit 79A of the excessive temperature rise prevention unit 79 is downstream of the central portion of the belt guide member 77 with respect to the rotation direction R1 of the heating rotating belt 9a. Are arranged in contact with a portion of the wire bundle facing the substantially center of the rotation direction R1 of the heating rotary belt 9a. Therefore, when the heating rotating belt 9a stops rotating due to a failure of the fixing device 9 or the like, the temperature of the highest temperature portion of the heating rotating belt 9a is sensed to the induction coil 71 by the excessive temperature rise prevention unit 79. It is possible to improve the responsiveness of cutting off the power supply. As a result, the safety of the fixing device 9 can be further improved.

  As mentioned above, although preferred embodiment was described, this invention can be implemented with a various form, without being limited to embodiment mentioned above.

The type of the image forming apparatus of the present invention is not particularly limited, and may be a copier, a facsimile, or a complex machine of these in addition to a printer.
The sheet-shaped transfer material is not limited to paper, and may be a film sheet, for example.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2a, 2b, 2c, 2d ... Photosensitive drum (image carrier), 8 ... Transfer roller (transfer part), 9 ... Fixing device, 9a ... Heating rotation belt , 9b... Pressure roller (pressure rotator), 16a, 16b, 16c, 16d... Developer, 71... Induction coil, 72. Overheating prevention part, 79A ... Temperature sensing part, 92 ... Pressing member, 771 ... Base layer, 772 ... Second heating layer, F ... Fixing nip, T ... Paper (material to be transferred)

Claims (3)

An annular heating rotating belt having a first heat generating layer;
A pressing member disposed inside the heating rotary belt and abutting against an inner surface of the heating rotary belt;
An annular pressure rotator disposed opposite to the heating rotating belt, wherein the heating rotating belt is sandwiched between the pressing member and a fixing nip is formed between the heating rotating belt and the pressing member. A rotating body,
It is composed of a wire bundle portion formed by winding a wire so as to surround a central region, and is arranged along the outer surface at a predetermined distance from the outer surface of the heating rotating belt, and the heating rotation is performed by supplying power. An induction coil that generates magnetic flux to heat the belt;
A magnetic core that forms a magnetic path of magnetic flux generated by the induction coil;
The heating rotating belt is made of a non-magnetic material, and is disposed on the inner surface side of the heating rotating belt so as to face the induction coil with the heating rotating belt sandwiched between the heating rotating belt. A belt guide member that guides the rotation of the heating coil, and the induction coil is configured from a portion facing the upstream portion of the heating rotating belt in the rotation direction with respect to the central region in the wire bundle portion that constitutes the induction coil. To the downstream end facing the portion closer to the downstream end than the center in the rotation direction of the heating rotating belt in the downstream portion in the rotation direction of the heating rotating belt from the central region of the wire bundle portion. An extended belt guide member;
An excessive temperature rise prevention unit that is disposed in contact with the belt guide member and shuts off the supply of power to the induction coil when the temperature of the belt guide member is equal to or higher than a predetermined temperature ;
The fixing device , wherein the temperature sensing unit of the overheat prevention unit is disposed in contact with the downstream end . The first heat generating layer is formed thinner than a skin depth, which is a depth at which a magnetic field penetrates,
The fixing device according to claim 1, wherein the belt guide member further includes a second heat generation layer that generates heat by a magnetic flux that has passed through the heating rotating belt. One or more image carriers on which electrostatic latent images are formed; and
A developing device for developing the electrostatic latent image formed on the one or more image carriers as a toner image;
A transfer unit that directly or indirectly transfers the toner image formed on the image carrier to a sheet-like transfer material;
Image forming apparatus and a fixing device according to claim 1 or 2.

Images