JP2017016052A - Fixation device and image formation apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device which has excellent responsibility and durability of a power cutoff element.SOLUTION: In a fixation device including: a cylindrical rotor 1 which has a conductive layer 1a and is rotatable; a magnetic core material 2 which is inserted to a hollow part of the rotor and is arranged along a generatrix direction of the rotor; an exciting coil 3 which is wound around the magnetic core material in a direction intersecting the axial direction L of the magnetic core material; and a pressure member 8 which forms a nip part N with the rotor. The fixation device generates an alternation magnetic field by flowing an AC current in the exciting coil, and fixes a toner image on a recording material while conveying the recording material P carrying the unfixed toner image T with the nip part by causing electromagnetic induction heating in the conductive layer. A conductive cylindrical member 21 through which the alternation magnetic field passes is installed separately from the rotor, and a power cutoff element 20 is arranged in a contact manner in the cylindrical member.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electromagnetic induction heating type fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and an image forming apparatus including the fixing device.

  An electrophotographic copying machine or printer is equipped with a fixing device that heats a recording material carrying an unfixed toner image while heating it and fixes the toner image to the recording material. As this fixing device, an electromagnetic induction heating type device capable of directly generating heat in a conductive layer of a rotating body such as a fixing sleeve for heating a recording material is known. This type of fixing device has the advantages that the temperature of the rotating body rises rapidly and power consumption is low.

  In Patent Document 1, an exciting coil and a magnetic core are arranged inside a rotatable cylindrical rotating body having a conductive layer, an alternating magnetic field is generated in the axial direction of the rotating body, and a circular current generated in the rotating body. An electromagnetic induction heating type fixing device is disclosed in which a rotating body is heated by Joule heat.

JP 2014-26267 A

  In the fixing device that directly generates heat from the conductive layer of the rotator as disclosed in Patent Document 1, the time for raising the rotator to the target temperature can be shortened by reducing the heat capacity of the rotator.

  However, the fact that the temperature raising time of the rotating body can be shortened means that the temperature of the rotating body rises quickly even when the control circuit of the fixing device changes and the rotating body overheats abnormally. For this reason, in such a fixing device configuration, it is necessary to quickly detect an abnormal temperature rise of the rotating body.

  Usually, in order to detect an abnormal temperature rise of the rotating body, a thermo switch is incorporated as an energization interruption element that urgently interrupts energization to the exciting coil in response to abnormal overheating of the rotating body.

  However, when the thermo switch is brought into contact with the rotating body in order to improve the responsiveness of the thermo switch, there is a problem that the bimetal, which is the heat sensitive part of the thermo switch, is scraped off due to the friction with the rotating body.

  An object of the present invention is to provide a fixing device excellent in responsiveness and durability of an energization interruption element, and an image forming apparatus including the fixing device.

In order to achieve the above object, the fixing device of the present invention includes:
A rotatable cylindrical rotating body having a conductive layer;
A magnetic core material inserted through the hollow portion of the rotating body and disposed along the generatrix direction of the rotating body;
An excitation coil wound around the magnetic core in a direction intersecting the axial direction of the magnetic core;
A pressure member that forms a nip portion together with the rotating body,
An alternating current is applied to the excitation coil to generate an alternating magnetic field, and the conductive layer is electromagnetically heated to fix the toner image on the recording material while transporting the recording material carrying the unfixed toner image at the nip portion. In the fixing device,
In addition to the rotating body, a conductive cylindrical member through which the alternating magnetic field passes is installed, and a current-carrying-off element is disposed in contact with the cylindrical member.

An image forming apparatus of the present invention includes an image forming unit that forms an unfixed toner image on a recording material,
An image forming apparatus having a fixing unit that fixes a toner image to a recording material.
The fixing unit includes the fixing device described above.

  According to the present invention, it is possible to provide a fixing device excellent in the response and durability of the energization interrupting element, and an image forming apparatus including the fixing device.

Cross section of image forming apparatus Sectional view of the fixing device of Example 1 Front view of the fixing device as viewed from the upstream side in the recording material conveyance direction Diagram for explaining electromagnetic induction heating of heat-generating layer by magnetic core and exciting coil Diagram for explaining the calculation method of the circumferential resistance value of the fixing sleeve FIG. 3 is a perspective view illustrating an arrangement mode of a fixing sleeve, a conductive ring, and a thermo switch in the fixing device according to the first exemplary embodiment. The figure which shows the temperature rise curve of the conductive ring and the fixing sleeve at the time of abnormal temperature rise of the fixing device of Embodiment 1. The perspective view which shows the arrangement | positioning aspect of the fixing sleeve in the fixing apparatus of Example 2, a conductive ring, and a thermo switch.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although the preferred embodiment of the present invention is an example of the best embodiment of the present invention, the present invention is not limited by the following examples, and various other configurations are possible within the scope of the idea of the present invention. It is possible to replace this with a known configuration.

[Example 1]
1. Image forming apparatus 100
An image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing a schematic configuration of an example of an image forming apparatus (monochrome printer in this embodiment) 100 using an electrophotographic recording technique.

  In the image forming apparatus 100, an image forming unit A that forms an unfixed toner image on the recording material P includes a photosensitive drum 101 as an image carrier, a charging member 102, a laser scanner 103, a developing device 104, Have Further, the image forming unit A includes a cleaner 109 that cleans the photosensitive drum, and a transfer member 108. Since the above-described operation of the image forming unit A is well known, detailed description thereof is omitted.

  The recording material P stored in the cassette 105 in the main body 100 </ b> A of the image forming apparatus 100 is fed out one by one as the roller 106 rotates. The recording material P is conveyed to a transfer nip formed by the photosensitive drum 101 and the transfer member 108 by the rotation of the roller 107. The recording material P on which the toner image has been transferred at the transfer nip portion is sent to a fixing portion (hereinafter referred to as a fixing device) B via a conveyance guide 110. The unfixed toner image T formed on the recording material P is heated and fixed on the recording material by the fixing device B. The recording material P exiting the fixing device B is discharged to the tray 113 by the rotation of the rollers 111 and 112.

2. Fixing device B
The fixing device B shown in this embodiment is an electromagnetic induction heating type device. FIG. 2 is a cross-sectional view showing a schematic configuration of the fixing device B according to the present embodiment. FIG. 3 is a front view of the fixing device B as viewed from the upstream side in the conveyance direction Y of the recording material P. FIG. 4 is a view for explaining electromagnetic induction heating of the heat generating layer 1a by the magnetic core 2 and the exciting coil 3. In FIG.

  The pressure roller 8 as a pressure member includes a cored bar 8a, an elastic layer 8b formed and coated in a roller shape on the outer peripheral surface of the cored bar 8a, and a release layer provided on the outer peripheral surface of the elastic layer 8b. 8c. The elastic layer 8b is preferably made of a material having good heat resistance such as silicone rubber, fluorine rubber, fluorosilicone rubber or the like. Both ends of the metal core 8a in the longitudinal direction perpendicular to the conveyance direction Y of the recording material P are rotatably held between the left and right side plates 13a, 13b of the fixing device B via bearings (not shown). is there.

  A stay 5 for reinforcing the sleeve guide 6 is disposed on a sleeve guide 6 inserted through a hollow portion of a fixing sleeve (hereinafter also referred to as a sleeve) 1 as a cylindrical rotating body. Both ends of the stay 5 and the sleeve guide 6 in the longitudinal direction perpendicular to the conveyance direction Y of the recording material P are held by the left and right side plates 13a and 13b. The sleeve guide 6 is made of a heat resistant resin PPS or the like. The pressure springs 17a and 17b are contracted between the longitudinal ends of the stay 5 and the spring receiving members 18a and 18b provided on the inner surfaces of the left and right side plates 13a and 13b of the top plate 14, respectively. Thus, a pushing force is applied to the stay 5.

  In the fixing device B of this embodiment, a pressing force of a total pressure of about 100 N to 250 N (about 10 kgf to about 25 kgf) is applied to the stay 5. With this pressing force, the lower surface of the sleeve guide 6 is pressed against the surface of the pressure roller 8 via the sleeve 1, whereby the pressure roller 8 forms a nip portion N having a predetermined width together with the sleeve 1.

  The pressure roller 8 is rotated (driven) in the direction of the arrow by driving a motor M as a driving means. The sleeve 1 follows the rotation of the pressure roller 8 and rotates in the direction of the arrow. At both ends in the longitudinal direction of the sleeve guide 6, flange members 12 a and 12 b that receive the end of the sleeve 1 when the sleeve 1 rotates and restrict the movement of the sleeve 1 are fitted. The material of the flange members 12a and 12b is preferably a heat resistant resin material.

  The sleeve 1 includes a cylindrical heat generating layer 1a as a conductive layer serving as a base layer, an elastic layer 1b stacked on the outer peripheral surface of the heat generating layer 1a, and a release layer 1c stacked on the outer peripheral surface of the elastic layer 1b. It is a cylindrical rotating body having a composite structure. The diameter of the sleeve 1 is 10 to 50 mm.

  An alternating magnetic field from an exciting coil 3 described later acts on the heat generating layer 1a formed of the conductive member, so that a circulating current I1 (see FIG. 4) is generated in the heat generating layer 1a and the heat generating layer 1a generates heat. This heat is transmitted to the elastic layer 1b and the release layer 1c, and the entire sleeve 1 is heated.

  The temperature detection of the fixing device B is performed by a non-contact type temperature detection element 9, 10, 11 disposed at the longitudinal center of the sleeve 1 perpendicular to the conveyance direction Y of the recording material P and at both longitudinal ends of the sleeve 1. Is done by. The temperature detecting element 9 detects the temperature of a region (passing region) Ap through which the recording material P passes on the surface of the sleeve 1, and the temperature detecting elements 10 and 11 detect the temperature of a region (non-passing region) Anp through which the recording material P does not pass. Detect.

  Here, the temperature control of the fixing device B is performed based on the temperature detected by the temperature detection element 9 at the center in the longitudinal direction of the sleeve 1, whereby the sleeve 1 is induction-heated and the temperature of the sleeve 1 surface is set to a predetermined temperature. The fixing temperature (target temperature) is maintained. Further, it is possible to detect the temperature rise when the recording material P is continuously printed by the temperature detecting elements 10 and 11 disposed at both ends in the longitudinal direction of the sleeve 1.

  The recording material P carrying the unfixed toner image T is heated while being nipped and conveyed by the nip portion N, whereby the toner image T is fixed on the recording material.

3. Magnetic core 2 and exciting coil 3
The magnetic core 2 is made of a cylindrical magnetic core material having a diameter of 10 mm, and is disposed through the hollow portion of the sleeve 1 by fixing means (not shown). That is, the magnetic core 2 is inserted through the hollow portion of the sleeve 1 and arranged along the generatrix direction of the sleeve 1. A magnetic path is formed by guiding the magnetic field lines generated by the exciting coil 3 to the inside of the sleeve 1.

  The exciting coil 3 is a coated copper wire and is wound around the magnetic core 2 in a spiral shape. That is, the exciting coil 3 is wound around the magnetic core 2 in a direction crossing the axial direction L of the magnetic core 2. When a high-frequency current as an alternating current is supplied from the high-frequency converter 16 to the exciting coil 3, an alternating magnetic field whose polarity is periodically reversed is generated in a direction parallel to the magnetic core 2. A circulating current I1 is generated in the heat generating layer 1a of the sleeve 1 so as to cancel this magnetic field, and the sleeve 1 is heated by Joule heat due to the circulating current, and the temperature rises.

4). Description of thermoswitch (energization interruption element) 20 and conductive ring (cylindrical member) 21 In the fixing device B of this embodiment, an energization interruption element that urgently interrupts energization of the exciting coil 3 in response to abnormal overheating of the sleeve 1. As a thermo switch. Here, when the thermo switch is arranged in a non-contact or indirect contact with the sleeve 1, the response time of the thermo switch is significantly slower than that in the contact arrangement, and the response time is the spatial distance between the thermo switch and the sleeve 1. It is greatly affected by variations.

  On the other hand, if the thermo switch is brought into contact with the inner surface of the sleeve 1 in order to improve the responsiveness of the thermo switch, there is a problem that the heat generation layer 1a which is the inner surface of the sleeve 1 is damaged and the heat generation distribution is affected. Further, the thermoswitch side has a problem that the bimetal which is the heat sensitive part is scraped by rubbing with the heat generating layer 1a and the responsiveness is affected.

  In the present embodiment, a thermo switch will be described as an example, but the same problem also occurs in other energization interrupting elements having a function of interrupting energization such as a thermal fuse or a thermostat.

  In view of the above, in this embodiment, a non-rotating conductive cylindrical member is installed separately from the sleeve 1, and the above-described problem is solved by arranging a thermo switch in contact with the cylindrical member.

  In FIG. 3, reference numeral 20 denotes a thermo switch as an energization interrupting element installed on the inner surface of the top plate 14 of the fixing device B via a base member 20b. And the bimetal part 20a which is a heat sensitive part of the thermoswitch 20 is made to contact the conductive ring 21 as a conductive cylindrical member.

  The conductive ring 21 is formed in a cylindrical shape by SUS304 having a diameter of 32 mm, a thickness of 50 μm, and a width of 5 mm, and is disposed in a region Anp on the surface of the sleeve 1 where the recording material P does not pass. The conductive ring 21 is held by members such as the flange member 12a, the side plate 13a, and the top plate 14 via a support member (not shown). That is, the conductive ring 21 is installed on the outside of the sleeve 1 so as not to rotate.

  Here, as a condition of the conductive ring 21, it is preferable that the heat capacity is smaller than that of the sleeve 1, and the circulation resistance (electric resistance when current flows in the circulation direction) is larger than that of the sleeve 1. Under such conditions, during normal temperature control, the thermo switch 20 can be turned off only during abnormal temperature rise without turning off the thermo switch 20. Further, the diameter of the conductive ring 21 is not limited to the diameter of the present embodiment, but the heat capacity increases as the diameter increases, and further, the temperature rise slows down due to the reduction of the circulating current, so that it is preferably 50 mm or less.

Here, the circular resistance of the heat generating layer 1a will be described. FIG. 5A shows the calculation method of the shape of the heat generating layer 1a and the circular resistance. When the cylindrical heat generating layer 1a has a length L [m], a diameter d [m], a thickness t [m], and a volume resistivity ρ [Ωm], the heat generating layer 1a is formed as shown in FIG. The electric resistance R _SLV when the current I is opened and flows in the arrow R direction is expressed by the following equation.

The circular resistance of the conductive ring 21 can be obtained using this equation.

  Next, a mechanism in which the thermoswitch 20 is turned off and the power supply is stopped when the sleeve 1 is abnormally heated will be described with reference to FIG. FIG. 6 is a perspective view showing the conductive ring 21 installed on the outside of the sleeve 1 and the thermoswitch 20 in contact with the conductive ring 21.

  As described above, when an alternating current flows through the exciting coil 3, an alternating magnetic field is generated in a direction parallel to the magnetic core 2. Inductive current (circular current) I1 (see FIG. 3) is generated in the heat generating layer 1a of the sleeve 1 so as to cancel this magnetic field, and the sleeve 1 is heated by Joule heat due to this circular current, and the temperature rises. Normally, the temperature of the sleeve 1 is controlled so as to be close to the fixing temperature of the toner based on the temperature detected by the temperature detecting element 9.

  On the other hand, an induced current (circular current) is also generated in the conductive ring 21 that forms a loop circuit with respect to the alternating magnetic field by the same mechanism. An induction current (circular current) I2 is generated in the conductive ring 21 so as to cancel out this magnetic field, and the conductive ring 21 is heated by Joule heat due to the circular current, and the temperature rises. The thermo switch 20 cuts off the circuit when the temperature of the conductive ring 21 exceeds a specified temperature. Here, in a state where the temperature of the sleeve 1 is controlled, that is, in a state where an alternating magnetic field of normal output is generated, the temperature of the conductive ring 21 does not reach the specified temperature of the thermo switch 20 and the thermo switch 20 operates. do not do.

  However, if an abnormality occurs in the temperature control circuit of the fixing device B and an alternating magnetic field that continuously increases the temperature of the sleeve 1 continues to be generated, the temperature of the conductive ring 21 continues to increase accordingly. When the temperature of the conductive ring 21 reaches the specified temperature by the thermo switch 20, the thermo switch 20 is turned off, the power supply to the exciting coil 3 is cut off, and the temperature of the sleeve 1 does not increase any more. Here, since the conductive ring 21 is not rotated and is disposed in contact with the bimetal portion 20a which is the heat sensitive portion of the thermo switch 20, the bimetal portion 20a is not scraped.

  In order to confirm the effect of the fixing device B of this embodiment, the operation of the thermoswitch 20 when the maximum power of 1500 W, which is the maximum input power of the fixing device B, is continuously applied was confirmed. Here, the thermoswitch 20 having a specified temperature of 300 ° C. was used. This is because the elastic layer 1b is damaged at 300 ° C. in the sleeve 1 of this embodiment. FIG. 7 shows a temperature rise curve of the temperature of the conductive ring 21 (the temperature detected by the thermocouple affixed for the experiment) and the temperature of the sleeve 1 (the temperature detected by the temperature detection element 9) when the maximum input power is continuously applied. Indicates.

  In the experiment, the thermoswitch 20 was turned off in 4.4 seconds after the power was turned on. At this time, the temperature of the sleeve 1 was 240 ° C., and it was confirmed that the power supply was cut off with a sufficient temperature margin. In FIG. 7, the broken lines indicate the temperatures of the conductive ring 21 and the sleeve 1 during normal temperature control, and the temperature of the conductive ring 21 reaches 300 ° C. as long as the sleeve 1 is temperature-controlled at the fixing temperature of 160 ° C. Since there is no, there is no possibility that the thermoswitch 20 is cut off.

  Such an effect appears because the sleeve 1 and the conductive ring 21 are arranged perpendicular to the alternating magnetic field generated by the exciting coil 3 so that the alternating magnetic field is canceled by the sleeve 1 and the conductive ring 21. This is due to the characteristic that a circular current is induced.

  As described above, in the fixing device B of the present embodiment, the conductive ring 21 through which the alternating magnetic field passes is installed outside the sleeve separately from the sleeve 1, and the thermo switch 20 is brought into contact with the conductive ring. , Durability can be ensured while improving the response of the thermo switch.

[Example 2]
Another example of the fixing device B will be described. In the first embodiment, the conductive ring 21 is installed outside the sleeve 1, whereas in this embodiment, the case where the conductive ring 22 is installed inside the sleeve 1 will be described. Note that the configuration of the fixing device B of the present embodiment is the same as that of the first embodiment except for the conductive ring 22 and the thermo switch 20, and thus the description thereof is omitted. FIG. 8 is a perspective view showing the conductive ring 22 installed inside the sleeve 1 and the thermoswitch 20 in contact with the conductive ring 22.

  The thermo switch 20 is installed inside the sleeve 1 via a base member (not shown). The pedestal member is held by a member such as the flange member 12a and the side plate 13a via a first support member (not shown). And the bimetal part 20a which is a heat sensitive part of the thermoswitch 20 is made to contact the conductive ring 22 as a conductive cylindrical member.

  The conductive ring 22 is formed in a cylindrical shape by SUS304 having a diameter of 20 mm, a thickness of 50 μm, and a width of 5 mm, and is installed inside the sleeve 1 in a region Anp on the surface of the sleeve 1 where the recording material P does not pass. The conductive ring 22 is held by members such as the flange member 12a and the side plate 13a via a second support member (not shown). That is, the conductive ring 22 is installed in the sleeve 1 so as not to rotate. As in the first embodiment, the conductive ring 22 preferably has a heat capacity smaller than that of the sleeve 1 and a circular resistance larger than that of the sleeve 1. As a result, the thermo switch 20 can be turned off only when the temperature rises abnormally.

  In order to confirm the effect of the fixing device B of the present embodiment, the operation of the thermoswitch 20 when the maximum applied power of 1500 W, which is the maximum input power of the fixing device B, is continuously applied as in the first embodiment was confirmed. In this embodiment, the thermoswitch 20 having a specified temperature of 300 ° C. was used. In the experiment, the thermoswitch 20 was cut off in 3.9 seconds after the power was turned on. At this time, the temperature of the sleeve 1 (detected temperature by the temperature detecting element 9) was 210 ° C., and the power supply was cut off with a sufficient temperature margin. Was confirmed.

  In the fixing device B of this embodiment, the conductive ring 21 is installed inside the sleeve 1 in the region Anp where the recording material P on the surface of the sleeve 1 does not pass, but in the region Ap where the recording material P on the surface of the sleeve 1 passes, You may install inside. In that case, since it is not necessary to consider interference with the flange members 12a and 12b, the sleeve 1 can be shortened.

  As described above, in the fixing device B of the present embodiment, the conductive ring 22 through which the alternating magnetic field passes is installed separately from the sleeve 1, and the thermoswitch 20 is brought into contact with the conductive ring. , Durability can be ensured while improving the response of the thermo switch.

1 fixing sleeve, 1a heating layer, 2 magnetic core, 3 excitation coil, 8 pressure roller,
20 thermo switch, 21, 22 conductive ring, 100 image forming device,
A image forming section, B fixing device, L axial direction of magnetic core, N nip section, P recording material

Claims (4)

A rotatable cylindrical rotating body having a conductive layer;
A magnetic core material inserted through the hollow portion of the rotating body and disposed along the generatrix direction of the rotating body;
An excitation coil wound around the magnetic core in a direction intersecting the axial direction of the magnetic core;
A pressure member that forms a nip portion together with the rotating body,
An alternating current is applied to the excitation coil to generate an alternating magnetic field, and the conductive layer is electromagnetically heated to fix the toner image on the recording material while transporting the recording material carrying the unfixed toner image at the nip portion. In the fixing device,
In addition to the rotating body, a conductive cylindrical member through which the alternating magnetic field passes is installed, and an energization interrupting element is disposed in contact with the cylindrical member.   The fixing device according to claim 1, wherein the cylindrical member is installed on the outside of the rotating body so as not to rotate.   The fixing device according to claim 1, wherein the cylindrical member is non-rotatably installed inside the rotating body. An image forming unit for forming an unfixed toner image on a recording material;
An image forming apparatus having a fixing unit that fixes a toner image to a recording material.
An image forming apparatus comprising the fixing device according to claim 1 as the fixing unit.