JP2011022517A - Image forming apparatus, fixing device, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the lowering of a temperature of a fixing member provided in a fixing device. <P>SOLUTION: A control part 31 executes first control for controlling power supplied to an IH heater 80 heating a fixing belt 61 fixing a toner image on a recording material so that the fixing belt 61 may be set to a preset temperature and second control for supplying the power to the IH heater according to the timing of bringing a contact body coming into contact with the fixing belt 61 into contact with the fixing belt 61. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, a fixing device, and a program.

As a fixing device mounted on an image forming apparatus such as a copying machine or a printer using an electrophotographic system, an apparatus using an electromagnetic induction heating system is known.
For example, in Patent Document 1, an electromagnetic induction coil as a magnetic flux generating means is arranged inside a fixing roll made of a core metal cylinder made of magnetic metal, and an eddy current is induced in the fixing roll by an induced magnetic field generated by the electromagnetic induction coil. An electromagnetic induction heating type fixing device that directly heats the fixing roll is described.

JP 2003-186322 A

Here, in general, by configuring the fixing member that is directly heated by the electromagnetic induction method with a belt member having a small heat capacity, the time for raising the fixing member to the fixing set temperature (warm-up time) is shortened. For example, the temperature of the fixing member is likely to decrease due to heat flowing out to, for example, a sheet or member that contacts the fixing member.
An object of the present invention is to suppress a decrease in temperature of a fixing member provided in a fixing device.

  According to a first aspect of the present invention, there is provided a toner image forming unit that forms a toner image on a recording material, a fixing member that fixes the toner image formed by the toner image forming unit to the recording material, and the fixing member. A heating unit that heats, a first control that controls power supplied to the heating unit so as to set the fixing member at a predetermined temperature, and a contact body that contacts the fixing member contacts the fixing member. An image forming apparatus comprising: a control unit that performs second control for supplying power to the heating unit in accordance with timing.

The invention according to claim 2 further includes temperature detection means for detecting the temperature of the fixing member and outputting information related to the temperature to the control means, and the control means starts the first control. Before, the information regarding the temperature of the fixing member is acquired from the temperature detection unit, and the electric power supplied to the heating unit in one or both of the first control and the second control corresponding to the information 2. The image forming apparatus according to claim 1, wherein a value is determined.
According to a third aspect of the present invention, the operator is performed prior to the start of the toner image forming operation in order to cause the toner image forming means to execute a toner image forming operation for forming the toner image on the recording material. 2. The operation detecting means for detecting the operation of the control unit according to claim 1, wherein the control means performs the second control in response to the operation being detected by the operation detecting means. This is an image forming apparatus.
The invention according to claim 4 is configured to move between a position in contact with the fixing member and a position in contact with the fixing member, and pressurizes the fixing member by being set to a position in contact with the fixing member. And a pressing member that forms a region through which the recording material holding the toner image passes between the fixing member and the control unit is set to a position where the pressing member contacts the fixing member. The image forming apparatus according to claim 1, wherein the second control is performed in accordance with a timing to be performed.
The invention according to claim 5 is characterized in that the control means performs the second control in accordance with a timing at which the recording material is conveyed to a position in contact with the fixing member. An image forming apparatus.

  According to a sixth aspect of the present invention, there is provided a fixing member for fixing a toner image formed on a recording material to the recording material, and a power supplied to control the fixing member at a predetermined temperature. Heating means for heating the fixing member by being controlled by the control of No. 1 and the second control in which electric power is supplied in accordance with the timing when the contact body contacting the fixing member contacts the fixing member. A fixing device comprising:

The invention according to claim 7 further includes a temperature detecting means for detecting the temperature of the fixing member, and the heating means is used in one or both of the first control and the second control. The fixing device according to claim 6, wherein the electric power value is determined in accordance with a temperature of the fixing member detected by the temperature detecting unit before the first control is started.
According to an eighth aspect of the present invention, the heating unit is operated by an operator prior to the start of the toner image forming operation in order to cause the recording material to perform a toner image forming operation for forming the toner image. The fixing device according to claim 6, wherein the second control is performed in response to the control.
The invention according to claim 9 is configured to move between a position in contact with the fixing member and a position in contact with the fixing member, and pressurizes the fixing member by being set to a position in contact with the fixing member. And a pressing member that forms a region through which the recording material holding the toner image passes between the fixing member and the heating member is set at a position where the pressing member contacts the fixing member. The fixing device according to claim 6, wherein the second control is performed in accordance with the timing of the fixing.
According to a tenth aspect of the present invention, in the heating means, the second control is performed in accordance with a timing at which the recording material is conveyed to a position in contact with the fixing member. The fixing device.

  According to an eleventh aspect of the present invention, there is provided a function of controlling power supplied to heating means for heating the fixing member so that the fixing member for fixing the toner image to the recording material is set to a predetermined temperature. And a function of controlling to supply power to the heating unit in accordance with a timing at which a contact body that contacts the fixing member contacts the fixing member.

According to a twelfth aspect of the present invention, there is provided a function of acquiring information related to the temperature of the fixing member, and a function of determining a power value of power supplied to the heating unit in correspondence with information related to the temperature of the fixing member. The program according to claim 11, wherein the program is implemented.
According to a thirteenth aspect of the present invention, there is provided a function of recognizing an operator's operation performed prior to the start of the toner image forming operation in order to execute the toner image forming operation for forming the toner image on the recording material. The control for supplying electric power to the heating unit in accordance with a timing at which the contact body comes into contact with the fixing member is realized by further realizing and recognizing the operation of the operator. It is the program described.

According to the first aspect of the present invention, compared to the case where the present invention is not adopted, it is possible to suppress a decrease in the temperature of the fixing member provided in the fixing device mounted on the image forming apparatus.
According to the second aspect of the present invention, it is possible to reduce the waste of power consumed by the heating means as compared with the case where the present invention is not adopted.
According to the third aspect of the present invention, the time required for raising the fixing member to the fixing set temperature can be shortened as compared with the case where the present invention is not adopted.
According to the fourth aspect of the present invention, the amount of heat flowing out to the pressure member is compensated by contact of the pressure member with the fixing member, and the temperature of the fixing member is lowered from the fixing set temperature as compared with the case where the present invention is not adopted. This can be suppressed.
According to the invention of claim 5, the amount of heat flowing out to the recording material is compensated by the contact of the recording material on which the toner image is formed on the fixing member, and the temperature of the fixing member is set to the fixing setting compared with the case where the present invention is not adopted. It can suppress falling from temperature.

According to the sixth aspect of the present invention, it is possible to suppress a decrease in the temperature of the fixing member provided in the fixing device as compared with the case where the present invention is not adopted.
According to the seventh aspect of the present invention, it is possible to reduce the waste of power consumed by the heating means as compared with the case where the present invention is not adopted.
According to the eighth aspect of the present invention, the time required for raising the fixing member to the fixing set temperature can be shortened as compared with the case where the present invention is not adopted.
According to the ninth aspect of the present invention, the amount of heat flowing out to the pressure member is compensated by contact of the pressure member with the fixing member, and the temperature of the fixing member is lowered from the fixing set temperature as compared with the case where the present invention is not adopted. This can be suppressed.
According to the invention of claim 10, the amount of heat flowing out to the recording material is compensated by the contact of the recording material on which the toner image is formed on the fixing member. It can suppress that it falls from temperature.

According to the eleventh aspect of the present invention, a decrease in the temperature of the fixing member provided in the fixing device can be suppressed as compared with the case where the present invention is not adopted.
According to the twelfth aspect of the present invention, it is possible to reduce the waste of electric power consumed by the heating means as compared with the case where the present invention is not adopted.
According to the thirteenth aspect of the present invention, the time required for raising the fixing member to the fixing set temperature can be shortened as compared with the case where the present invention is not adopted.

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing device according to an exemplary embodiment is applied. FIG. 2 is a front view illustrating a configuration of a fixing unit of the present embodiment. FIG. 3 is a II-II sectional view of the fixing unit in FIG. 2. FIG. 3 is a cross-sectional layer configuration diagram of a fixing belt. (A) is a side view of an end cap member, (b) is a top view of the end cap member seen from the Z direction. It is sectional drawing explaining the structure of an IH heater. It is a figure explaining the state of a line of magnetic force in case the temperature of a fixing belt exists in the temperature range below the magnetic permeability change start temperature. FIG. 6 is a diagram illustrating an outline of a temperature distribution in a width direction of a fixing belt when small-size paper is continuously passed. FIG. 6 is a diagram for explaining a state of magnetic lines of force when the temperature of the fixing belt in a non-sheet passing region is in a temperature range exceeding the permeability change start temperature. It is the figure which showed the slit formed in a temperature sensitive magnetic member. It is a block diagram which shows an example of the circuit structure which controls the electric power supplied to an IH heater. It is a flowchart explaining an example of the content of the operation control regarding the image formation process which a control part performs. It is a figure explaining the timing which a control part performs forced heating control of a fixing belt. It is the flowchart which showed an example of the content of the determination process implemented when a control part performs post-processing. It is a block diagram which shows a part of internal structure of a control part. It is the figure which showed an example of the relationship between the detection temperature detected with the thermistor, and the designated electric power designated by the "power setting signal". 6 is a flowchart illustrating an example of the content of power setting processing performed by a control unit during warm-up processing for a fixing unit.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus to which the fixing device of the present embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem color printer, an image forming unit 10 that forms an image based on image data, an image reading unit 50 that reads an image from a document and generates read image data, and an image A control unit 31 that controls the operation of the entire forming apparatus 1 is provided. Further, for example, a communication unit 32 that receives an image formation command (hereinafter, “print job”) by communicating with a personal computer (PC) 3 or the like, and image data included in the print job received by the communication unit 32 And an image processing unit 33 that performs image processing on the read image data generated by the image reading unit 50, and a user interface (UI) unit 34 that receives operation input from the user and displays various information to the user. Yes.

The image forming unit 10 includes four image forming units 11Y, 11M, 11C, and 11K (also collectively referred to as “image forming unit 11”) arranged in parallel at a predetermined interval. Each image forming unit 11 forms an electrostatic latent image and a photosensitive drum 12 as an example of an image holding body that holds a toner image, and charging that uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. 13, an LED (Light Emitting Diode) print head 14 that exposes the photosensitive drum 12 charged by the charger 13 based on each color image data, and a developer that develops an electrostatic latent image formed on the photosensitive drum 12. 15. A drum cleaner 16 for cleaning the surface of the photosensitive drum 12 after transfer is provided.
Each of the image forming units 11 is configured in substantially the same manner except for the toner stored in the developing device 15, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do.

  The image forming unit 10 also receives the intermediate transfer belt 20 onto which the color toner images formed on the photosensitive drums 12 of the image forming units 11 are transferred, and the color toner images formed on the image forming units 11. A primary transfer roll 21 that sequentially transfers (primary transfer) to the intermediate transfer belt 20 is provided. Furthermore, a secondary transfer roll 22 that collectively transfers (secondary transfer) each color toner image transferred and superimposed on the intermediate transfer belt 20 onto a recording material (paper P), and each color toner image that has been secondarily transferred is a paper P. A fixing unit 60 is provided as an example of fixing means (fixing device) for fixing on the top. In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit.

On the other hand, the image reading unit 50 includes a first platen glass 51 on which a document is placed in a stationary state, and a platen cover 52 configured to cover the first platen glass 51. The platen cover 52 is configured to be opened and closed in accordance with a user operation, sets a state in which the document is placed on the first platen glass 51 in the open state, and is placed on the first platen glass 51 in the closed state. The original document is brought into close contact with the first platen glass 51. The platen cover 52 is provided with an open / close detection sensor (not shown) as an example of a detection unit that detects the open / close state of the platen cover 52, and transmits information related to the open / close state of the platen cover 52 to the control unit 31.
Further, the image reading unit 50 includes a second platen glass 55 that forms an optical opening for reading a document being conveyed, a document storage unit 53 that stores a plurality of documents, and a document stored in the document storage unit 53. A document conveying unit 54 that conveys one or both sides so as to pass through the second platen glass 55, and a document accumulating unit 56 that accumulates documents read by passing through the second platen glass 55 are provided. In addition, the document storage unit 53 is provided with a document detection sensor (not shown) as an example of a detection unit that detects that a document is stored in the document storage unit 53. Information on presence / absence is transmitted to the control unit 31.

When the image reading unit 50 reads a document placed on the first platen glass 51, the control unit 31 performs a first operation on the image reading unit 50 based on a user operation input from the user interface (UI) unit 34. An instruction to read the document placed on the platen glass 51 is given. Thereby, the image reading unit 50 reads one page of the document and transfers image data (read image data) obtained from the document to the image processing unit 33.
On the other hand, when the image reading unit 50 reads a document placed in the document storage unit 53, the control unit 31 moves the image reading unit 50 to the document storage unit 53 based on a user operation input from the UI unit 34. Instructs to read the placed document. As a result, the image reading unit 50 transports the document placed in the document storage unit 53 to the second platen glass 55 by the document transport unit 54. Then, the image reading unit 50 reads the original for one page by passing the entire original through the second platen glass 55, and transfers the read image data obtained from the original to the image processing unit 33.

<Description of Image Forming Process by Image Forming Apparatus>
Next, in the image forming apparatus 1 according to the present embodiment, the UI unit 34 issues a copy instruction from the user regarding a document placed on the first platen glass 51 of the image reading unit 50 or a document stored in the document storage unit 53. Is received, the control unit 31 of the image forming apparatus 1 recognizes it. In this case, the control unit 31 includes information on the open / closed state of the platen cover 52 from the open / close detection sensor disposed on the platen cover 52 and information on the presence / absence of a document from the document detection sensor disposed on the document storage unit 53. Based on either one or both, it can be configured to recognize whether the copy object is a document on the first platen glass 51 or a document stored in the document storage unit 53.
When the communication unit 32 receives a print job, the control unit 31 of the image forming apparatus 1 recognizes the print job.
Accordingly, the image forming apparatus 1 performs the following processing on the read image data generated by the image reading unit 50 and the print job received by the communication unit 32 under the operation control by the control unit 31. An image forming process is executed.

  First, image data from the PC 3 or the image reading unit 50 is subjected to predetermined image processing by the image processing unit 33. As a result, the image data for each color is decomposed and sent to each image forming unit 11. For example, in the image forming unit 11K that forms a black (K) toner image, the photosensitive drum 12 is uniformly charged at a predetermined potential by the charger 13 while rotating in the arrow A direction, and the image processing unit 33 is charged. The LED print head 14 scans and exposes the photosensitive drum 12 based on the K-color image data transmitted from. As a result, an electrostatic latent image relating to the K color image is formed on the photosensitive drum 12. The K-color electrostatic latent image formed on the photosensitive drum 12 is developed by the developing unit 15, and a K-color toner image is formed on the photosensitive drum 12. Similarly, yellow (Y), magenta (M), and cyan (C) color toner images are formed in the image forming units 11Y, 11M, and 11C, respectively.

Each color toner image formed on the photosensitive drum 12 of each image forming unit 11 is sequentially electrostatically transferred (primary transfer) onto the intermediate transfer belt 20 that moves in the direction of arrow B by the primary transfer roll 21, and each color toner is superimposed. A superimposed toner image is formed. The superimposed toner image on the intermediate transfer belt 20 is conveyed to a region (secondary transfer portion T) where the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper holding unit 40 to the secondary transfer unit T in accordance with the timing. The superimposed toner image is collectively electrostatically transferred (secondary transfer) onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 22 in the secondary transfer portion T.
As described above, each component unit arranged on the path from each image forming unit 11 to the secondary transfer roll 22 in the image forming unit 10 forms an operation (hereinafter referred to as a toner image) on the recording material (paper P). , “Toner image forming operation”).

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is conveyed to the fixing unit 60. The toner image on the paper P conveyed to the fixing unit 60 receives heat and pressure by the fixing unit 60 and is fixed on the paper P. Then, the paper P on which the fixed image is formed is conveyed to a paper stacking unit 45 provided in the discharge unit of the image forming apparatus 1.
On the other hand, the toner (primary transfer residual toner) adhering to the photosensitive drum 12 after the primary transfer and the toner (secondary transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer are respectively drum cleaner 16. , And the belt cleaner 25.
In this way, the image forming process in the image forming apparatus 1 is repeatedly executed for the number of printed sheets.

<Description of fixing unit configuration>
Next, the fixing unit 60 of this embodiment will be described.
2 and 3 are views showing the configuration of the fixing unit 60 of the present embodiment, FIG. 2 is a front view, and FIG. 3 is a sectional view taken along line II-II in FIG.
First, as shown in FIG. 3, which is a cross-sectional view, the fixing unit 60 is heated by electromagnetic induction by an IH (Induction Heating) heater 80 and an IH heater 80 as an example of a heating unit (magnetic field generation unit) that generates an alternating magnetic field. The fixing belt 61 as an example of a fixing member that fixes a toner image, the pressure roller 62 as an example of a pressure member disposed so as to face the fixing belt 61, and the pressure roller 62 through the fixing belt 61. A pressing pad 63 to be pressed is provided.
Further, the fixing unit 60 includes a holder 65 that supports constituent members such as the pressure pad 63, a temperature-sensitive magnetic member 64 that induces an alternating magnetic field generated by the IH heater 80 to form a magnetic path, and a temperature-sensitive magnetic member 64. A guide member 66 that guides the lines of magnetic force that have passed through the sheet and a peeling assisting member 173 that assists in peeling the paper P from the fixing belt 61 are provided.

<Description of fixing belt>
The fixing belt 61 is formed of an endless belt member having an original cylindrical shape, and has a diameter of 30 mm and a length in the width direction of 370 mm in the original shape (cylindrical shape), for example. Further, as shown in FIG. 4 (cross-sectional layer configuration diagram of the fixing belt 61), the fixing belt 61 includes a base material layer 611, a conductive heat generating layer 612 laminated on the base material layer 611, and a toner image fixability. The belt member has a multilayer structure including an elastic layer 613 for improving the surface and a surface release layer 614 coated on the uppermost layer.

The base material layer 611 is composed of a heat-resistant sheet-like member that supports the thin conductive heat generating layer 612 and forms the mechanical strength of the fixing belt 61 as a whole. In addition, the base material layer 611 is made of a material having a physical property (relative magnetic permeability, specific resistance) that allows the magnetic field to pass therethrough so that the AC magnetic field generated by the IH heater 80 acts to the temperature-sensitive magnetic member 64, and the thickness. Formed with. On the other hand, the base material layer 611 itself is configured not to generate heat or hardly generate heat due to the action of a magnetic field.
Specifically, as the base material layer 611, for example, a nonmagnetic metal such as nonmagnetic stainless steel having a thickness of 30 to 200 μm (preferably 50 to 150 μm), a resin material having a thickness of 60 to 200 μm, or the like is used.

The conductive heating layer 612 is an example of a conductive layer, and is an electromagnetic induction heating element layer that is electromagnetically heated by an alternating magnetic field generated by the IH heater 80. That is, the conductive heat generating layer 612 is a layer that generates an eddy current when the AC magnetic field from the IH heater 80 passes in the thickness direction.
In general, a general-purpose power source that can be manufactured at low cost is used as a power source for an excitation circuit that supplies an alternating current to the IH heater 80 (see also FIG. 6 below). Therefore, the frequency of the alternating magnetic field generated by the IH heater 80 is generally 20 k to 100 kHz by a general-purpose power source. Thereby, the conductive heat generating layer 612 is configured such that an alternating magnetic field having a frequency of 20 k to 100 kHz enters and passes therethrough.

The region where the alternating magnetic field can enter the conductive heat generating layer 612 is defined as “skin depth (δ)”, which is a region where the alternating magnetic field attenuates to 1 / e, and is derived from the following equation (1). (1) In the equation, f is the AC magnetic field frequency (e.g., 20 kHz), [rho is resistivity (Omega · m), the mu _r is the relative permeability.
Therefore, the thickness of the conductive heat generating layer 612 is determined by the skin depth (δ) of the conductive heat generating layer 612 defined by the equation (1) such that an alternating magnetic field having a frequency of 20 k to 100 kHz penetrates and passes through the conductive heat generating layer 612. It is configured in a thinner layer. Further, as a material constituting the conductive heat generating layer 612, for example, a metal such as Au, Ag, Al, Cu, Zn, Sn, Pb, Bi, Be, Sb, or a metal alloy thereof is used.

Specifically, a nonmagnetic metal such as Cu having a thickness of 2 to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ω · m or less (relative magnetic permeability is approximately 1) is used as the conductive heating layer 612.
In addition, the time required for the fixing belt 61 to be heated to a fixing set temperature (fixable temperature) set for melting and fixing the toner image on the paper P is shortened (hereinafter referred to as “warm-up time”). Also from the viewpoint, the conductive heat generating layer 612 is preferably formed in a thin layer.

Next, the elastic layer 613 is composed of a heat-resistant elastic body such as silicone rubber. The toner image held on the sheet P to be fixed is formed by laminating each color toner as powder. Therefore, in order to supply heat uniformly to the entire toner image at the nip portion N, it is preferable that the surface of the fixing belt 61 is deformed following the unevenness of the toner image on the paper P. Therefore, for example, silicone rubber having a thickness of 100 to 600 μm and a hardness of 10 ° to 30 ° (JIS-A) is suitable for the elastic layer 613.
Since the surface release layer 614 is in direct contact with the unfixed toner image held on the paper P, a material having a high release property is used. For example, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene), silicone copolymer, or a composite layer thereof is used. If the thickness of the surface release layer 614 is too thin, it is not sufficient in terms of wear resistance, and the life of the fixing belt 61 is shortened. On the other hand, if it is too thick, the heat capacity of the fixing belt 61 becomes too large and the warm-up time becomes long. Therefore, the thickness of the surface release layer 614 is preferably 1 to 50 μm in consideration of the balance between wear resistance and heat capacity.

<Description of pressing pad>
The pressing pad 63 is an example of a pressing member, and is constituted by an elastic body such as silicone rubber or fluorine rubber, and is supported by the holder 65 at a position facing the pressure roll 62. Then, it is arranged in a state of being pressed from the pressure roll 62 via the fixing belt 61, and a nip portion N is formed with the pressure roll 62.
The pressing pad 63 includes a pre-nip region 63a on the inlet side of the nip portion N (upstream side in the conveyance direction of the paper P) and a peeling nip region 63b on the outlet side of the nip portion N (downstream side in the conveyance direction of the paper P). Different nip pressures are set. That is, in the pre-nip region 63 a, the surface on the pressure roll 62 side is formed in an arc shape that substantially follows the outer peripheral surface of the pressure roll 62, thereby forming a uniform and wide nip portion N. Further, the peeling nip region 63b is formed so as to be locally pressed from the surface of the pressure roll 62 with a large nip pressure so that the radius of curvature of the fixing belt 61 passing through the peeling nip region 63b becomes small. As a result, a curl (down curl) in a direction away from the surface of the fixing belt 61 is formed on the paper P passing through the peeling nip region 63b to promote the peeling of the paper P from the surface of the fixing belt 61.

  In the present embodiment, a peeling assisting member 173 is arranged on the downstream side of the nip portion N as a peeling assisting means by the pressing pad 63. The peeling auxiliary member 173 is supported by the holder 172 in a state where the peeling baffle 171 is close to the fixing belt 61 in a direction opposite to the rotational movement direction of the fixing belt 61 (so-called counter direction). The curled portion formed on the paper P at the outlet of the pressing pad 63 is supported by the peeling baffle 171 to suppress the paper P from moving toward the fixing belt 61.

<Description of temperature-sensitive magnetic member>
Next, the temperature-sensitive magnetic member 64 is formed in an arc shape that follows the inner peripheral surface of the fixing belt 61, and a predetermined gap (for example, 0.5 to 2.5 mm) from the inner peripheral surface of the fixing belt 61. Although they are close to each other, they are arranged in a non-contact manner. The temperature-sensitive magnetic member 64 is disposed close to the fixing belt 61 because the temperature of the temperature-sensitive magnetic member 64 changes corresponding to the temperature of the fixing belt 61, that is, the temperature of the temperature-sensitive magnetic member 64 is changed. This is because the temperature is substantially the same as the temperature 61. Further, the temperature-sensitive magnetic member 64 is disposed in a non-contact manner with the fixing belt 61 because the heat of the fixing belt 61 is increased when the main switch of the image forming apparatus 1 is turned on and the fixing belt 61 is heated to the fixing set temperature. This is to prevent the heat from flowing into the temperature-sensitive magnetic member 64 and shorten the warm-up time.

Further, the temperature-sensitive magnetic member 64 has a “permeability change start temperature” (see below), which is a temperature at which the magnetic permeability of the magnetic characteristics changes suddenly, equal to or higher than a fixing set temperature at which each color toner image is melted. The elastic layer 613 and the surface release layer 614 are made of a material set in a temperature range lower than the heat resistant temperature. That is, the temperature-sensitive magnetic member 64 is made of a material having a characteristic (“temperature-sensitive magnetism”) that reversibly changes between ferromagnetic and non-magnetic (paramagnetic) in a temperature range including the fixing set temperature. . The temperature-sensitive magnetic member 64 induces magnetic lines of force generated by the IH heater 80 and transmitted through the fixing belt 61 in a temperature range equal to or lower than the magnetic permeability change starting temperature exhibiting ferromagnetism, so that the temperature-sensitive magnetic member 64 A magnetic path passing through the inside is formed. As a result, the temperature-sensitive magnetic member 64 forms a closed magnetic path that encloses the fixing belt 61 and the exciting coil 82 of the IH heater 80 (see FIG. 6 at a later stage). On the other hand, in the temperature range exceeding the permeability change start temperature, the temperature-sensitive magnetic member 64 crosses the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 in the thickness direction of the temperature-sensitive magnetic member 64. Make it transparent. Thereby, the magnetic lines of force generated by the IH heater 80 and transmitted through the fixing belt 61 form a magnetic path that passes through the temperature-sensitive magnetic member 64, passes through the inside of the guide member 66, and returns to the IH heater 80.
The “permeability change start temperature” here is a temperature at which the magnetic permeability (for example, the magnetic permeability measured by JIS C2531) starts to decrease continuously. For example, a member such as the temperature-sensitive magnetic member 64 This is the temperature point at which the amount of magnetic flux that passes through (the number of lines of magnetic force) starts to change. Therefore, the permeability change start temperature is a temperature close to the Curie point, which is the temperature at which magnetism disappears, but has a concept different from the Curie point.

As a material used for the temperature-sensitive magnetic member 64, a binary system temperature-sensitive magnetism such as an Fe-Ni alloy (permalloy) whose magnetic permeability change start temperature is set in a range of 140 (fixing set temperature) to 240 ° C., for example. A ternary temperature-sensitive magnetic alloy such as an alloy or Fe—Ni—Cr alloy is used. For example, in a Fe-Ni binary temperature-sensitive magnetic alloy, the magnetic permeability change start temperature can be set to around 225 ° C. by setting it to about Fe 64% and Ni 36% (atomic ratio). Such metal alloys such as permalloy and temperature-sensitive magnetic alloy are suitable for the temperature-sensitive magnetic member 64 because they are excellent in moldability and workability, have high thermal conductivity, and are inexpensive. As other materials, a metal alloy made of Fe, Ni, Si, B, Nb, Cu, Zr, Co, Cr, V, Mn, Mo or the like is used.
Further, the temperature-sensitive magnetic member 64 is formed with a thickness greater than the skin depth δ (see the above formula (1)) with respect to the AC magnetic field (lines of magnetic force) generated by the IH heater 80. Specifically, for example, when an Fe—Ni alloy is used, the thickness is set to about 50 to 300 μm. The configuration and function of the temperature-sensitive magnetic member 64 will be described in further detail later.

<Description of holder>
The holder 65 that supports the pressing pad 63 is made of a material having high rigidity so that the amount of bending in a state where the pressing pad 63 receives the pressing force from the pressing roll 62 becomes a certain amount or less. Thereby, the uniformity of the pressure in the longitudinal direction (nip pressure N) at the nip portion N is maintained. Furthermore, since the fixing unit 60 according to the present embodiment employs a configuration in which the fixing belt 61 is heated using electromagnetic induction, the holder 65 is made of a material that does not affect or hardly gives influence to the induced magnetic field. It is made of a material that is not affected or hardly affected by the induced magnetic field. For example, a heat-resistant resin such as glass-mixed PPS (polyphenylene sulfide) or a nonmagnetic metal material such as Al, Cu, or Ag is used.

<Description of induction member>
The induction member 66 is formed in an arc shape that follows the inner peripheral surface of the temperature-sensitive magnetic member 64, and has a predetermined gap (for example, 1.0 to 5.0 mm) from the inner peripheral surface of the temperature-sensitive magnetic member 64. Having a non-contact arrangement. The induction member 66 is made of a nonmagnetic metal having a relatively small specific resistance value, such as Ag, Cu, or Al. Then, when the temperature-sensitive magnetic member 64 rises to a temperature equal to or higher than the permeability change start temperature, an alternating magnetic field (line of magnetic force) generated by the IH heater 80 is induced, and the vortex is more vortexed than the conductive heating layer 612 of the fixing belt 61. A state in which the current I is easily generated is formed. Thereby, the thickness of the induction member 66 is a predetermined thickness (for example, 1.0 mm) sufficiently thicker than the skin depth δ (see the above formula (1)) so that the eddy current I can easily flow. It is formed.

<Description of Fixing Belt Drive Mechanism>
Next, a driving mechanism for the fixing belt 61 will be described.
As shown in FIG. 2 which is a front view, the fixing belt 61 is rotated in the circumferential direction while maintaining the cross-sectional shape of both ends of the fixing belt 61 in a circular shape at both axial ends of the holder 65 (see FIG. 3). An end cap member 67 to be driven is fixed. The fixing belt 61 directly receives the rotational driving force from both ends via the end cap member 67, and rotates and moves in the direction of arrow C in FIG. 3 at a process speed of 140 mm / s, for example.
5A is a side view of the end cap member 67, and FIG. 5B is a plan view of the end cap member 67 viewed from the Z direction. As shown in FIG. 5, the end cap member 67 is formed with a fixing portion 67 a fitted inside the both ends of the fixing belt 61 and has an outer diameter larger than that of the fixing portion 67 a, and when the end cap member 67 is attached to the fixing belt 61. Rotating through a flange portion 67d formed so as to project radially from the fixing belt 61, a gear portion 67b to which rotational driving force is transmitted, a support portion 65a formed at both ends of the holder 65, and a coupling member 167. A bearing bearing portion 67c that is freely coupled is provided. Then, as shown in FIG. 2, the support portions 65a at both ends of the holder 65 are fixed to both ends of the casing 69 of the fixing unit 60, whereby the end cap member 67 is coupled to the support portion 65a. It is rotatably supported via the bearing bearing portion 67c.
As a material constituting the end cap member 67, so-called engineering plastics having high mechanical strength and heat resistance are used. For example, phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, LCP resin and the like are suitable.

  As shown in FIG. 2, in the fixing unit 60, the rotational driving force from the drive motor 90 is transmitted to the shaft 93 via the transmission gears 91 and 92, and both are transmitted from the transmission gears 94 and 95 coupled to the shaft 93. It is transmitted to the gear portion 67b (see FIG. 5) of the end cap member 67. As a result, a rotational driving force is transmitted from the end cap member 67 to the fixing belt 61, and the end cap member 67 and the fixing belt 61 are integrally rotated.

On the other hand, a torque limiter (not shown) is disposed between the transmission gear 92 and the shaft 93, and when the fixing belt 61 is driven by the rotational driving force from the pressure roll 62, The transmission gear 92 rotates idly with respect to the rotational driving force, and the rotational driving force is not transmitted from the transmission gear 91 to the shaft 93.
That is, the pressure roll 62 disposed opposite to the fixing belt 61 is rotated from the drive motor 90 via a transmission gear 91 and a transmission gear (not shown) disposed on the rotation shaft 96 of the pressure roll 62. Driving force is transmitted. Further, the pressure roll 62 is configured to contact and separate from the fixing belt 61 according to the start / end of the fixing operation in the fixing unit 60 by a contact / separation mechanism (so-called “retraction mechanism”) (not shown). . As a result, when the pressure roll 62 is set in pressure contact with the fixing belt 61 in accordance with the start of the fixing operation, the pressure roll 62 receiving the rotational driving force from the drive motor 90 causes the fixing belt 61 to move. Rotate following. In that case, the rotational driving force from the drive motor 90 to the fixing belt 61 is blocked by the torque limiter.

As described above, in the fixing unit 60 of the present embodiment, before the fixing operation is started and in a state where the pressure roll 62 is not pressed against the fixing belt 61, the rotational driving force from the driving motor 90 The fixing belt 61 is directly driven to rotate.
On the other hand, in a state where the fixing operation is started and the pressure roll 62 is pressed against the fixing belt 61, the fixing belt 61 rotates following the pressure roll 62 that is rotated by the rotational driving force from the drive motor 90.

Returning to FIG. 3, such a pressure roll 62 is disposed at a position facing the fixing belt 61. Then, as described above, it is configured to contact and separate from the fixing belt 61 according to the start / end of the fixing operation in the fixing unit 60 by the contact / separation mechanism (not shown). Thereby, the pressure roll 62 is, for example, immediately before the fixing unit 60 starts the fixing operation and the first sheet is carried into the fixing unit 60 (for example, about 1-2 seconds before the sheet enters the nip portion N). ) Is set to a position in contact with the fixing belt 61. The pressure roll 62 rotates the fixing belt 61 in a direction of arrow D in FIG. 3 at a process speed of, for example, 140 mm / s while pressing the fixing belt 61. Accordingly, a nip portion N is formed in a state where the fixing belt 61 is sandwiched between the pressure roll 62 and the pressing pad 63, and the sheet P holding the unfixed toner image is passed through the nip portion N. Pressure is applied to fix the unfixed toner image on the paper P.
On the other hand, when the fixing operation in the fixing unit 60 is completed, the pressure roll 62 is set at a position separated from the fixing belt 61.

  The pressure roll 62 includes, for example, a solid aluminum core (cylindrical metal core) 621 having a diameter of 18 mm, and a heat-resistant elastic body layer 622 such as a silicone sponge having a thickness of 5 mm, which is coated on the outer peripheral surface of the core 621. Further, for example, a release layer 623 made of a heat-resistant resin coating such as PFA containing carbon having a thickness of 50 μm or a heat-resistant rubber coating is laminated. Then, in a state where the fixing belt 61 is in pressure contact with a contact / separation mechanism (not shown), the fixing belt 61 (pressing pad 63) is pressed by a pressing spring 68 (see FIG. 2) with a load of 25 kgf, for example.

<Description of IH heater>
Next, an IH heater 80 as an example of a magnetic field generation unit that performs electromagnetic induction heating by applying an alternating magnetic field to the conductive heat generating layer 612 of the fixing belt 61 will be described.
FIG. 6 is a cross-sectional view illustrating the configuration of the IH heater 80 of the present embodiment. As shown in FIG. 6, the IH heater 80 includes a support 81 made of a nonmagnetic material such as a heat resistant resin, and an exciting coil 82 that generates an alternating magnetic field. Also, a plurality of elastic support members 83 made of an elastic material such as silicone rubber for fixing the excitation coil 82 on the support body 81 are arranged along the width direction of the fixing belt 61, and are generated by the excitation coil 82. The magnetic core 84 which forms the magnetic path of an alternating magnetic field is provided. Further, a plurality of adjustment cores 89 arranged along the width direction of the fixing belt 61 and for adjusting the AC magnetic field generated by the exciting coil 82 in the longitudinal direction of the support 81 and the magnetic core 84 are covered from above. A magnetic core holding member 87 as an example of a holding member to be held, a pressure member 86 made of an elastic body such as silicone rubber that pressurizes the magnetic core 84 toward the support 81 through the magnetic core holding member 87, and shields the magnetic field. And an exciting circuit 88 for supplying an alternating current to the exciting coil 82.

The support 81 is formed in a shape whose cross section is curved along the surface shape of the fixing belt 61, and an upper surface (hereinafter referred to as “supporting surface”) 81 a that supports the exciting coil 82 has a predetermined gap from the surface of the fixing belt 61. (For example, 0.5 to 2 mm) is formed and set. Further, in the center of the support surface 81a, a pair of magnetic core support portions (convex portions) 81b1 and 81b2 that support the magnetic core 84 are along the longitudinal direction of the support body 81 (= direction perpendicular to the moving direction of the fixing belt 61). They are arranged in parallel. The magnetic core support portions 81 b 1 and 81 b 2 keep the gap between the magnetic core 84 and the support surface 81 a constant and support the magnetic core 84 so as to be movable along the rotation direction of the fixing belt 61.
Further, on both sides of the support surface 81a, the movement of the magnetic core 84 supported by the magnetic core support portions 81b1 and 81b2 in the moving direction (arc direction) of the fixing belt 61 is restricted within a predetermined range. A magnetic core restricting portion 81c that sets the position in the width direction of the fixing belt 61 (= direction orthogonal to the moving direction) is disposed.
Examples of the material constituting the support 81 include heat-resistant resins such as heat-resistant glass, polycarbonate, polyethersulfone, and PPS (polyphenylene sulfide), or heat-resistant resins obtained by mixing glass fibers with these materials. A non-magnetic material is used.

The exciting coil 82 is configured by winding, for example, 90 litz wires, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm and wound in a closed loop with a hollow shape such as an ellipse, an ellipse, or a rectangle. . Then, when an alternating current having a predetermined frequency is supplied to the exciting coil 82 from the exciting circuit 88, an alternating magnetic field centered around a litz wire wound in a closed loop is generated around the exciting coil 82. . Generally, the frequency of the alternating current supplied from the excitation circuit 88 to the excitation coil 82 is 20 k to 100 kHz generated by the general-purpose power source.
The elastic support member 83 is a sheet-like member made of an elastic body such as silicone rubber or fluorine rubber. The elastic support member 83 is set to press the excitation coil 82 against the support 81 so that the excitation coil 82 is fixed in close contact with the support surface 81a of the support 81.

For the magnetic core 84, for example, an arc-shaped ferromagnetic body made of a high-permeability oxide or alloy material such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, or temperature-sensitive magnetic alloy is used. And functions as a magnetic path forming member. The magnetic core 84 induces a magnetic force line (magnetic flux) generated by the alternating magnetic field generated by the exciting coil 82, and crosses the fixing belt 61 from the magnetic core 84 toward the temperature-sensitive magnetic member 64. A path of magnetic lines of force (magnetic path) is formed so as to pass through and return to the magnetic core 84. That is, the AC magnetic field generated by the excitation coil 82 is configured to pass through the inside of the magnetic core 84 and the inside of the temperature-sensitive magnetic member 64 so that the magnetic lines of force wrap the fixing belt 61 and the excitation coil 82 inside. A closed magnetic circuit is formed. As a result, the magnetic field lines of the alternating magnetic field generated by the exciting coil 82 are concentrated in a region facing the magnetic core 84 of the fixing belt 61.
Here, the magnetic core 84 is preferably made of a material having a small loss due to magnetic path formation. Specifically, the magnetic core 84 is desirably used in a form that reduces the eddy current loss (current path interruption or division by slits, thin plate bundling, etc.), and is preferably formed of a material having a small hysteresis loss.
Further, the length of the magnetic core 84 along the rotation direction of the fixing belt 61 is configured to be smaller than the length of the temperature-sensitive magnetic member 64 along the rotation direction of the fixing belt 61. Thereby, the leakage of magnetic lines of force to the periphery of the IH heater 80 is reduced, and the power factor is improved. Furthermore, electromagnetic induction to the metal member constituting the fixing unit 60 is suppressed, and the heat generation efficiency of the fixing belt 61 (conductive heat generation layer 612) is increased.

Each of the magnetic core holding members 87 is formed of a non-magnetic material such as SUS or resin, and part or all of the side surfaces (side surfaces on the direction orthogonal to the moving direction of the fixing belt 61) excluding the inner peripheral surface of the magnetic core 84. Each of the magnetic cores 84 is held so as to cover a part or all of the outer peripheral surface (the side surface opposite to the side where the fixing belt 61 is disposed). Thereby, the magnetic core holding member 87 restricts the movement of the magnetic core 84 within a predetermined region. Therefore, for example, even when some impact is applied to the magnetic core 84 to cause a crack, the fragments are prevented from moving (scattering) to other regions in the IH heater 80. As a result, the fragment of the magnetic core 84 concentrates the alternating magnetic field generated by the exciting coil 82, and functions to suppress the occurrence of abnormal temperature rise in the fixing belt 61 facing the fragment in the movement destination region.
The magnetic core holding member 87 has a function of transmitting the pressing force from the pressing member 86 to the magnetic core 84 and pressurizing the magnetic core 84 toward the magnetic core support portions (convex portions) 81b1 and 81b2 provided on the support body 81. Have.

  The adjustment magnetic core 89 has a rectangular parallelepiped shape (block shape) made of a high permeability oxide such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, magnetic shunt steel, or alloy material. A ferromagnetic material is used. Then, the adjustment magnetic core 89 has a longitudinal direction (= fixing) of a magnetic field induced by the fixing belt 61 with respect to an AC magnetic field formed by the magnetic core 84 and the temperature-sensitive magnetic member 64 arranged around the exciting coil 82. It functions as an adjusting magnetic member for leveling (reducing) the strength generated in the width direction of the belt 61. By averaging the strength of the magnetic field generated in the longitudinal direction of the support 81, temperature unevenness (temperature variation, temperature ripple) in the width direction of the fixing belt 61 is reduced. The adjustment magnetic core 89 is disposed in a space (region surrounded by the inner walls of the magnetic core support portions 81b1 and 81b2) formed in the inner region of the magnetic core support portions 81b1 and 81b2.

<Description of the state in which the fixing belt generates heat>
Subsequently, a state in which the fixing belt 61 generates heat by the alternating magnetic field generated by the IH heater 80 will be described.
First, as described above, the permeability change start temperature of the temperature-sensitive magnetic member 64 is within a temperature range that is not less than the set fixing temperature for fixing each color toner image and not more than the heat resistance temperature of the fixing belt 61 (for example, 140 to 240 ° C.). When the temperature of the fixing belt 61 is equal to or lower than the magnetic permeability change start temperature, the temperature of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 is also started corresponding to the temperature of the fixing belt 61. Below temperature. Therefore, since the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 pass through the fixing belt 61 and then pass through the inside of the temperature-sensitive magnetic member 64 along the spreading direction. To form a magnetic path. Here, the “spreading direction” means a direction orthogonal to the thickness direction of the temperature-sensitive magnetic member 64.

  FIG. 7 is a diagram for explaining the state of the lines of magnetic force (H) when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature. As shown in FIG. 7, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 are transmitted through the fixing belt 61. A magnetic path passing through the inside of the temperature-sensitive magnetic member 64 along the spreading direction (direction orthogonal to the thickness direction) is formed. Therefore, the number of magnetic field lines H (magnetic flux density) per unit area in the region crossing the conductive heat generating layer 612 of the fixing belt 61 increases.

  That is, after the magnetic field lines H are radiated from the magnetic core 84 of the IH heater 80 and pass through the regions R1 and R2 across the conductive heat generating layer 612 of the fixing belt 61, the magnetic field lines H enter the inside of the temperature-sensitive magnetic member 64 which is a ferromagnetic material. Be guided. Therefore, the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated so as to enter the inside of the temperature-sensitive magnetic member 64, and the magnetic flux density in the regions R1 and R2 increases. Further, even when the magnetic field lines H that have passed through the inside of the temperature-sensitive magnetic member 64 along the spreading direction return to the magnetic core 84 again, in the region R3 that crosses the conductive heating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 is increased. It is radiated toward the magnetic core 84 in a concentrated manner from the lower part. Therefore, the magnetic force lines H that cross the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated from the temperature-sensitive magnetic member 64 toward the magnetic core 84, and the magnetic flux density in the region R3 is also increased.

In the conductive heating layer 612 of the fixing belt 61 where the magnetic lines H cross in the thickness direction, an eddy current I proportional to the amount of change in the number of magnetic lines H per unit area (magnetic flux density) is generated. Thereby, as shown in FIG. 7, a large eddy current I is generated in the regions R1, R2 and R3 where the amount of change in magnetic flux density is large. The eddy current I generated in the conductive heat generation layer 612 generates Joule heat W (W = I ² R), which is the product of the specific resistance value R of the conductive heat generation layer 612 and the square of the eddy current I. Thereby, a large Joule heat W is generated in the conductive heat generating layer 612 where the large eddy current I is generated.
As described above, when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature, large heat is generated in the regions R1 and R2 and the region R3 where the lines of magnetic force H cross the conductive heat generating layer 612. Thereby, the fixing belt 61 is heated.

  By the way, in the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in the vicinity of the fixing belt 61 on the inner peripheral surface side of the fixing belt 61. As a result, the magnetic core 84 that guides the magnetic force lines H generated by the exciting coil 82 to the inside and the temperature-sensitive magnetic member 64 that guides the magnetic force lines H transmitted through the fixing belt 61 in the thickness direction are close to each other. The configuration is realized. For this reason, the AC magnetic field generated by the IH heater 80 (excitation coil 82) forms a loop with a short magnetic path, so that the magnetic flux density and the magnetic coupling degree in the magnetic path increase. Accordingly, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the magnetic permeability change start temperature, heat is more efficiently generated in the fixing belt 61.

<Description of function for suppressing temperature rise of non-sheet passing portion of fixing belt>
Next, the function of suppressing the temperature rise at the non-sheet passing portion of the fixing belt 61 will be described.
First, a case where small-size paper P (small-size paper P1) is continuously passed through the fixing unit 60 will be described. FIG. 8 is a diagram showing an outline of the temperature distribution in the width direction of the fixing belt 61 when the small size paper P1 is continuously fed. In FIG. 8, the maximum sheet passing area which is the maximum size width (for example, A3 width) of the sheet P used in the image forming apparatus 1 is Ff, and the small size sheet P1 (for example, smaller than the maximum size sheet P) (for example, , A4 (vertical feed) passes through the area (small size paper passing area) as Fs, and the non-sheet passing area through which the small size paper P1 does not pass is Fb. In the image forming apparatus 1, it is assumed that the sheet is passed based on the center position.

  As shown in FIG. 8, when the small size paper P1 is continuously passed, heat for fixing is consumed in the small size paper passing area Fs through which the small size paper P1 passes. Therefore, the temperature adjustment control at the fixing set temperature is performed by the control unit 31 (see FIG. 1), and the temperature of the fixing belt 61 in the small size paper passing area Fs is maintained within the range near the fixing set temperature. On the other hand, temperature adjustment control similar to that of the small-size paper passing area Fs is performed also in the non-paper passing area Fb. However, heat for fixing is not consumed in the non-sheet passing area Fb. For this reason, the temperature of the non-sheet passing area Fb is likely to rise to a temperature higher than the fixing set temperature. Then, when the continuous passage of the small size paper P1 is continued in this state, the temperature of the non-sheet passing region Fb rises, for example, higher than the heat resistance temperature of the elastic layer 613 and the surface release layer 614 of the fixing belt 61, and the fixing belt. 61 may be damaged.

  Therefore, as described above, in the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 is equal to or higher than the preset fixing temperature and is, for example, equal to or lower than the heat resistance temperature of the elastic layer 613 and the surface release layer 614 of the fixing belt 61. For example, an Fe—Ni alloy or the like having a magnetic permeability change start temperature set within the temperature range is used. That is, as shown in FIG. 8, the magnetic permeability change start temperature Tcu of the temperature-sensitive magnetic member 64 is equal to or higher than the fixing set temperature Tf, for example, a temperature equal to or lower than the heat resistance temperature Tlim of the elastic layer 613 and the surface release layer 614. It is set in the area.

Accordingly, when the small size paper P1 is continuously passed, the temperature in the non-sheet passing region Fb of the fixing belt 61 exceeds the magnetic permeability change start temperature of the temperature-sensitive magnetic member 64. Accordingly, the temperature in the non-sheet passing region Fb of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 also exceeds the permeability change start temperature in the same manner as the fixing belt 61 corresponding to the temperature of the fixing belt 61. For this reason, the temperature-sensitive magnetic member 64 in the non-sheet-passing region Fb has a relative magnetic permeability close to 1, and the properties as a ferromagnetic material disappear. The relative magnetic permeability of the temperature-sensitive magnetic member 64 decreases and approaches 1 so that the magnetic field lines H in the non-sheet-passing region Fb are not guided into the temperature-sensitive magnetic member 64 but pass through the temperature-sensitive magnetic member 64. become. Therefore, in the non-sheet passing region Fb of the fixing belt 61, the magnetic field lines H after passing through the conductive heat generating layer 612 are diffused, and the magnetic flux density of the magnetic field lines H crossing the conductive heat generating layer 612 is reduced. Thereby, the eddy current I generated in the conductive heat generation layer 612 is reduced, and the heat generation amount (Joule heat W) in the fixing belt 61 is reduced. As a result, an excessive temperature rise in the non-sheet passing area Fb is suppressed, and damage to the fixing belt 61 is suppressed.
As described above, the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 and suppresses an increase in temperature that suppresses an excessive temperature increase of the fixing belt 61 according to the detected temperature of the fixing belt 61. It also has a function as a department.

  The lines of magnetic force H after passing through the temperature-sensitive magnetic member 64 reach the guide member 66 (see FIG. 3) and are guided into this. When the magnetic flux reaches the induction member 66 and is induced therein, more eddy current I flows toward the induction member 66 where the eddy current I flows more easily than the conductive heat generation layer 612. Therefore, the amount of eddy current flowing in the conductive heat generating layer 612 is further suppressed, and the temperature rise in the non-sheet passing region Fb is suppressed.

  At this time, the thickness, material, and shape of the guiding member 66 are selected so that the guiding member 66 guides most of the magnetic force lines H from the exciting coil 82 and suppresses leakage of the magnetic force lines H from the fixing unit 60. . Specifically, the guide member 66 may be made of a material having a sufficiently thick skin depth δ. Thereby, even if the eddy current I flows through the induction member 66, the amount of heat generation is also minimized. In the present embodiment, the guide member 66 is made of Al (aluminum) having a substantially circular shape with a thickness of 1 mm along the temperature-sensitive magnetic member 64, and is not in contact with the temperature-sensitive magnetic member 64 (an average distance of, for example, 4 mm). ). As other materials, Ag and Cu are suitable.

  By the way, when the temperature in the non-sheet-passing region Fb of the fixing belt 61 becomes lower than the magnetic permeability change start temperature of the temperature-sensitive magnetic member 64, the temperature in the non-sheet-passing region Fb of the temperature-sensitive magnetic member 64 is also permeable. It becomes lower than the change start temperature. As a result, the temperature-sensitive magnetic member 64 changes to ferromagnetic again, and the magnetic field lines H are induced inside the temperature-sensitive magnetic member 64, so that a large amount of eddy current I flows through the conductive heating layer 612. Therefore, the fixing belt 61 is heated again.

  FIG. 9 is a diagram illustrating the state of the lines of magnetic force H when the temperature of the fixing belt 61 in the non-sheet passing region Fb is in the temperature range exceeding the permeability change start temperature. As shown in FIG. 9, when the temperature of the fixing belt 61 is in the temperature range exceeding the permeability change start temperature in the non-sheet passing area Fb, the temperature-sensitive magnetic member 64 in the non-sheet passing area Fb has a ratio. Magnetic permeability decreases. Therefore, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 change so as to easily pass through the temperature-sensitive magnetic member 64. Accordingly, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 (excitation coil 82) are radiated so as to diffuse from the magnetic core 84 toward the fixing belt 61 and reach the induction member 66.

That is, in the regions R1 and R2 where the magnetic force lines H are radiated from the magnetic core 84 of the IH heater 80 and cross the conductive heat generating layer 612 of the fixing belt 61, the magnetic force lines H are difficult to be guided to the temperature-sensitive magnetic member 64 and thus diffuse radially. As a result, the magnetic flux density (number of magnetic force lines H per unit area) of the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction decreases. Further, even in the region R3 that crosses the conductive heat generating layer 612 in the thickness direction when the magnetic force line H returns to the magnetic core 84 again, the magnetic force line H returns to the magnetic core 84 from the diffused wide region. The magnetic flux density of the magnetic field lines H crossing 612 in the thickness direction decreases.
Therefore, when the temperature of the fixing belt 61 is in a temperature range exceeding the permeability change start temperature, the magnetic flux density of the magnetic field lines H that cross the conductive heating layer 612 in the thickness direction decreases in the regions R1, R2, and R3. It becomes. As a result, the eddy current I generated in the conductive heating layer 612 where the magnetic field lines H cross in the thickness direction is reduced, and the Joule heat W generated in the fixing belt 61 is reduced. As a result, the temperature of the fixing belt 61 decreases.

As described above, when the temperature of the fixing belt 61 in the non-sheet-passing area Fb is in the temperature range equal to or higher than the magnetic permeability change start temperature, the magnetic field lines H are induced inside the temperature-sensitive magnetic member 64 in the non-sheet-passing area Fb. The magnetic field lines H of the alternating magnetic field generated by the exciting coil 82 cross the conductive heat generating layer 612 of the fixing belt 61 while diffusing in the thickness direction. Therefore, the magnetic path of the alternating magnetic field generated by the exciting coil 82 forms a long loop, and the magnetic flux density in the magnetic path passing through the conductive heating layer 612 of the fixing belt 61 decreases.
Thereby, for example, in the non-sheet passing region Fb where the small size paper P1 is continuously passed and the temperature rises, the eddy current I generated in the conductive heat generating layer 612 of the fixing belt 61 is reduced and the fixing belt 61 is not passed. The amount of heat generation (joule heat W) in the paper region Fb is reduced. As a result, an excessive temperature rise in the non-sheet passing area Fb can be suppressed.

<Description of the configuration for suppressing the temperature rise of the temperature-sensitive magnetic member>
In order for the temperature-sensitive magnetic member 64 to perform the function of suppressing the excessive temperature rise in the non-sheet passing region Fb described above, the temperature of each region in the longitudinal direction of the temperature-sensitive magnetic member 64 is the longitudinal direction of the fixing belt 61 facing it. It is necessary to fulfill a function as a detection unit that detects the temperature of the fixing belt 61 and changes according to the temperature of each region.
Therefore, regarding the temperature-sensitive magnetic member 64 itself, a configuration that is difficult to be induction-heated by the magnetic field lines H is adopted. That is, even if the temperature of the fixing belt 61 is equal to or lower than the permeability change start temperature and the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the temperature-sensitive magnetic member 64 is included in the magnetic force lines H from the IH heater 80. There is a magnetic field line H that crosses in the thickness direction. As a result, a weak eddy current I is generated inside the temperature-sensitive magnetic member 64, and a slight amount of heat is generated in the temperature-sensitive magnetic member 64 itself. For this reason, for example, when a large amount of image formation is continuously performed, the self-heat generated heat is accumulated in the temperature-sensitive magnetic member 64, and the temperature of the temperature-sensitive magnetic member 64 is also in the paper passing area (see FIG. 8). Shows an upward trend. Thus, when the self-heating due to eddy current loss is large, the temperature of the temperature-sensitive magnetic member 64 rises and unintentionally reaches the temperature at which the permeability change starts, and the magnetic characteristics of the paper passing area and the non-paper passing area are improved. The difference is almost eliminated and the temperature rise suppression effect may not be obtained sufficiently. Therefore, the correspondence between the temperature of the temperature-sensitive magnetic member 64 and the temperature of the fixing belt 61 is maintained, and the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 with high accuracy. It is necessary to suppress the Joule heat W generated in the member 64 itself.

Therefore, in order to reduce the eddy current loss and hysteresis loss in the temperature-sensitive magnetic member 64, first, the temperature-sensitive magnetic member 64 has physical properties (specific resistance value and magnetic permeability) that are difficult to be induction-heated by the lines of magnetic force H. Selected material is selected.
Second, the thickness of the temperature-sensitive magnetic member 64 exhibits ferromagnetism so that the magnetic field lines H are difficult to cross in the thickness direction of the temperature-sensitive magnetic member 64 at least in the temperature range below the permeability change start temperature. It is formed thicker than the skin depth δ in the state.

  Third, the temperature-sensitive magnetic member 64 is formed with a plurality of slits 64 s that divide the flow of the eddy current I generated by the lines of magnetic force H. Even if the material and thickness of the temperature-sensitive magnetic member 64 are selected so that induction heating is difficult, it is difficult to set the eddy current I generated in the temperature-sensitive magnetic member 64 to zero. Therefore, by dividing the flow of the eddy current I generated in the temperature-sensitive magnetic member 64 by the plurality of slits 64s, the eddy current I is reduced and the Joule heat W generated in the temperature-sensitive magnetic member 64 is kept low. .

  FIG. 10 is a view showing slits 64 s formed in the temperature-sensitive magnetic member 64. FIG. 10A is a side view showing a state in which the temperature-sensitive magnetic member 64 is installed on the holder 65, and FIG. 10B is a plan view seen from above (a direction). As shown in FIG. 10, in the temperature-sensitive magnetic member 64, a plurality of slits 64 s are formed orthogonal to the direction in which the eddy current I generated by the lines of magnetic force H flows. Therefore, when there is no slit 64s, the eddy current I (broken line in FIG. 10B) that flows as a large eddy over the entire longitudinal direction of the temperature-sensitive magnetic member 64 is divided by the slit 64s. Accordingly, when the slit 64s is formed, the eddy current I flowing through the temperature-sensitive magnetic member 64 (solid line in FIG. 10A) becomes a small eddy in the region between the slit 64s and the slit 64s, The amount of eddy current I as a whole is reduced. As a result, the amount of heat generated by the temperature-sensitive magnetic member 64 (Joule heat W) is reduced, and a configuration that hardly generates heat is realized. Therefore, the plurality of slits 64 s function as an eddy current dividing unit that divides the eddy current I.

In the temperature-sensitive magnetic member 64 illustrated in FIG. 10, the slit 64s is formed perpendicular to the direction in which the eddy current I flows. However, if the flow of the eddy current I is divided, for example, the eddy current I flows. You may form the slit inclined with respect to the direction. In addition to the configuration in which the slits 64 s as shown in FIG. 10 are formed over the entire region in the width direction of the temperature-sensitive magnetic member 64, the slit 64 s may be formed in a part in the width direction of the temperature-sensitive magnetic member 64. Further, the number, position, inclination angle, and the like of the slits may be set according to the amount of heat generated in the temperature-sensitive magnetic member 64.
Moreover, as a state where the inclination angle of the slit is maximized, the temperature-sensitive magnetic member 64 may be a small piece divided group in which the temperature-sensitive magnetic member 64 is divided into small pieces at the slit portion. The effect of is obtained similarly.

<Description of control of power supplied to IH heater>
Next, control of electric power supplied to the IH heater 80 will be described.
FIG. 11 is a block diagram illustrating an example of a circuit configuration for controlling the power supplied to the IH heater 80. As shown in FIG. 11, the electric power supplied to the IH heater 80 is generated by the electromagnetic induction heating control unit 100 provided in the control unit 31 (see FIG. 1) as an example of the control unit and the IH of the fixing unit 60. Control is performed by an excitation circuit 88 provided in the heater 80.
The electromagnetic induction heating control unit 100 in the control unit 31 controls the temperature change of the CPU 160 and the fixing belt 61 that operate in response to a control signal from a main CPU (Central Processing Unit) 110 that controls the operation of the entire image forming apparatus 1. An overtemperature detection circuit 162 for detecting, OR circuits 164 and 165 as logic elements, and an AND circuit 170 are provided.
The excitation circuit 88 of the IH heater 80 transmits and receives signals to / from the control circuit CPU 158, the relay 153 for inputting (connecting) / cutting off power from the external commercial power supply 180, and the electromagnetic induction heating control unit 100. A photocoupler 156 is provided. Further, the excitation circuit 88 includes an AND circuit 154 that is a logic element, a high-frequency switching circuit 152 that is a high-frequency generation circuit, an output port 150 that outputs power to the excitation coil 82, and an input port 151 that inputs power from the external commercial power supply 180. It has.

When the main switch (not shown) of the image forming apparatus 1 is turned on, the main CPU 110 of the control unit 31 first turns on the drive motor 90 (see FIG. 2), and the pressure roll 62 is connected to the fixing belt. The fixing belt 61 is directly rotated by the drive motor 90 in a state where it is not pressed against the belt 61. Then, the main CPU 110 sets the temperature of the fixing belt 61 to the CPU 160 of the electromagnetic induction heating control unit 100 in a state where the fixing belt 61 is rotated while the pressure roll 62 is not in contact with the fixing set temperature (for example, 140). Instruct to execute a temperature rise process (hereinafter referred to as “warming up process”) that rises to a predetermined “fixing preparation temperature” in the vicinity of (° C.) (for example, a temperature that is approximately 20 ° C. lower than the fixing set temperature). .
Here, by setting the pressure roll 62 in a non-contact manner from the fixing belt 61, the outflow of heat from the fixing belt 61 to the pressure roll 62 can be suppressed, and the temperature rise time to the fixing preparation temperature can be suppressed. Shortened.

Accordingly, the CPU 160 of the electromagnetic induction heating control unit 100 prepares for fixing the temperature of the fixing belt 61 based on the “temperature detection signal” from the thermistors 71 and 72 as an example of temperature detecting means for detecting the temperature of the fixing belt 61. Control for warming-up processing to set temperature.
Specifically, the CPU 160 turns on the relay 153 in the excitation circuit 88 and generates excitation from the high-frequency switching circuit 152 in response to the presence / absence of an “error signal” from the excitation circuit 88 and the temperature detection signal from the thermistors 71 and 72. The “permission signal” that permits the supply of the high-frequency current to the coil 82 is output to the AND circuit 170. Then, the AND circuit 170 responds to the control signal from the overheat detection circuit 162 and the “permission signal” from the CPU 160 to generate a signal (“IH_ON / OFF signal”) for controlling on / off of the IH heater 80. Output to excitation circuit 88.
Further, the CPU 160 outputs a “power setting signal” to the excitation circuit 88 based on a temperature detection signal from the thermistors 71 and 72 (mainly, the thermistor 71 disposed at the center of the fixing belt 61). Further, when the surface temperature of the fixing belt 61 rises above a specified value in light of the current operation state of the fixing unit 60, an “abnormal signal” indicating an abnormality is output to the OR circuit 164.
Further, the CPU 160 outputs a signal (“relay ON / OFF signal”) for controlling ON / OFF of the relay 153 provided in the excitation circuit 88 to the OR circuit 165.
Furthermore, the CPU 160 has completed the temperature raising process (warming up process) for raising the temperature of the fixing belt 61 to the fixing preparation temperature based on the “temperature detection signal” from the thermistors 71 and 72 (mainly, the thermistor 71). A notification signal (hereinafter referred to as “warming up completion signal”) for notifying this is output to the main CPU 110 of the control unit 31.

  The overheat detection circuit 162 of the electromagnetic induction heating control unit 100 detects a change in the surface temperature of the fixing belt 61 from the surface temperature of the fixing belt 61 detected by the thermistor 72 arranged on the end side of the fixing belt 61. . The overheat detection circuit 162 outputs a “normal signal” indicating that the surface temperature of the fixing belt 61 is in a normal state when the change amount of the surface temperature of the fixing belt 61 is within a predetermined range. To the AND circuit 170 and the OR circuit 164. On the other hand, when the amount of change in the surface temperature of the fixing belt 61 exceeds a predetermined range, an “abnormal signal” indicating that the surface temperature of the fixing belt 61 is in an abnormal state is sent to the CPU 160, the AND circuit 170, and the OR. Output to the circuit 164.

The AND circuit 170 is set to output an “IH_ON / OFF signal” to the excitation circuit 88 when the “permission signal” from the CPU 160 and the “normal signal” from the overheat detection circuit 162 are supplied. Yes.
The OR circuit 164 generates a drive signal for driving the relay 153 of the excitation circuit 88 based on the “abnormal signal” from the CPU 160 and the “abnormal signal” from the overheat detection circuit 162. The OR circuit 164 includes a semiconductor switch element 166 provided in the electromagnetic induction heating control unit 100 with a relay 153 connected to a DC power line 181 (for example, 5 V) and a thermo switch 70 including a thermostat, a thermal fuse, or the like. It is opened and closed by controlling. Specifically, the OR circuit 164 receives the semiconductor switch via the OR circuit 165 when at least one of the “abnormal signal” from the CPU 160 and the “abnormal signal” from the overheat detection circuit 162 is input. A signal for shutting off the element 166 is output. In that case, the current flowing from the DC power line 181 to the electromagnetic coil 153a arranged in the relay 153 is cut off, and the relay 153 is cut off. Thereby, the power supply from the external commercial power supply 180 to the excitation circuit 88 is stopped. At the same time, the CPU 160 of the electromagnetic induction heating control unit 100 controls the high frequency switching circuit 152 for the excitation circuit 88 without using the CPU 158 to directly supply the high frequency current to the excitation coil 82. Stop.
Further, even when the temperature of the fixing belt 61 rises abnormally and the thermo switch 70 which is an example of a blocking member is cut off, the current flowing from the DC power line 181 to the electromagnetic coil 153a arranged in the relay 153 is cut off, Relay 153 is cut off.

A photocoupler 156 provided in the excitation circuit 88 transmits and receives signals to and from the electromagnetic induction heating control unit 100. That is, the “power setting signal” from the CPU 160 of the electromagnetic induction heating control unit 100 is supplied to the photocoupler 156 via the signal line. Further, an “IH_ON / OFF signal” is supplied from the AND circuit 170 connected to the CPU 160.
On the other hand, the “error signal” from the CPU 158 of the excitation circuit 88 is output from the photocoupler 156 to the CPU 160 of the electromagnetic induction heating control unit 100 via the signal line.
Then, the photocoupler 156 outputs the supplied “power setting signal” to the CPU 158 of the excitation circuit 88. Further, the supplied “IH_ON / OFF signal” is output to the CPU 158 and the AND circuit 154.

A CPU 158 provided in the excitation circuit 88 controls driving of the high-frequency switching circuit 152. That is, the high frequency switching circuit 152 is driven and controlled based on the “power setting signal” supplied from the CPU 160 of the electromagnetic induction heating control unit 100. Further, the CPU 158 determines various errors in the IH heater 80, generates an “error signal”, and outputs an “error signal” to the CPU 160 of the electromagnetic induction heating control unit 100.
Further, the CPU 158 outputs an “IH_ON / OFF signal” to the AND circuit 154 based on the “IH_ON / OFF signal” supplied from the photocoupler 156 when no error or the like has occurred in the IH heater 80. . The AND circuit 154 outputs an “IH_ON / OFF signal” when the “IH_ON / OFF signal” from the CPU 158 of the excitation circuit 88 and the “IH_ON / OFF signal” from the photocoupler 156 are supplied simultaneously. Output to the high-frequency switching circuit 152.

The high frequency switching circuit 152 provided in the excitation circuit 88 applies power set by the CPU 158 to the excitation coil 82 via the output port 150 when the “IH_ON / OFF signal” from the AND circuit 154 is supplied. To do.
On the other hand, an AC voltage is supplied to the input port 151 to which power is input from the external commercial power supply 180 via a relay 153 and a noise filter (not shown). The AC voltage supplied via the input port 151 is supplied to each part of the excitation circuit 88.
Note that any one of the input ports 151 is provided with a fuse (not shown), and the power supply is cut off when an abnormality occurs. In addition, the excitation circuit 88 includes a rectifier circuit that rectifies the voltage of the external commercial power supply 180, a constant voltage circuit unit that adjusts the output voltage of the rectifier circuit to a certain level suitable for the operation of the CPU 158, and the like. Has been placed.

  As described above, the electromagnetic induction heating control unit 100 and the excitation circuit 88 perform the above-described control in accordance with an instruction from the main CPU 110 of the control unit 31, so that the temperature of the fixing belt 61 is set to a fixing set temperature (for example, 140 ° C. A temperature rise process (warming-up process) for raising the temperature to a fixing preparation temperature in the vicinity of) is executed. Here, the warm-up process when the main switch of the image forming apparatus 1 is turned on has been described. However, in such warming-up processing for setting the temperature of the fixing belt 61 to the fixing preparation temperature, the control unit 31 described later recognizes a predetermined operation input from the user (operator) by the UI unit 34, for example. The same process is performed in the warm-up process performed in such a case.

<Explanation for Stopping Power Supply to IH Heater After Warming Up Process>
Then, the main CPU 110 of the control unit 31 of the present embodiment continues the warm-up process when the main switch of the image forming apparatus 1 is turned on for about 30 seconds, and then the user about the document placed on the image reading unit 50 If neither the copy instruction from the printer nor the reception of the print job at the communication unit 32 is recognized, the CPU 160 of the electromagnetic induction heating control unit 100 is instructed to stop the power supplied to the IH heater 80. . Thereby, the supply of the high-frequency current to the exciting coil 82 is stopped.

As a result, wasteful power consumption in the fixing unit 60 is suppressed.
At this time, since the fixing belt 61 has a small heat capacity and further employs a configuration in which the fixing belt 61 is directly heated by the IH heater 80, the time required to raise the fixing preparation temperature (“warm-up time”) is short. For example, in the fixing unit 60 of the present embodiment, the warm-up time of the fixing belt 61 can be set to about 3 seconds. Therefore, it is possible to raise the fixing belt 61 to the fixing preparation temperature in a short time after the control unit 31 (main CPU 110) instructs to set the fixing belt 61 to the fixing preparation temperature. In particular, once the fixing belt 61 is raised to the fixing preparation temperature, the rise time to the fixing preparation temperature is further shortened. For this reason, even if the power supplied to the IH heater 80 is temporarily stopped, the warm-up process for the fixing belt 61 is completed in a short time after the user issues a new image formation instruction, so that the user's convenience is hardly impaired.

<Explanation of restarting power supply to IH heater>
Next, the control unit 31 (main CPU 110) executes a toner image forming operation prior to the toner image forming operation when the image forming unit 10 executes a toner image forming operation such as placing an original on the image reading unit 50. When the operation by the (operator) (hereinafter, “user operation”) is recognized, the CPU 160 of the electromagnetic induction heating control unit 100 sets the temperature of the fixing belt 61 as the fixing preparation temperature. Instructs execution of the raising process (warming up process). Accordingly, the CPU 160 sets the fixing belt 61 to the fixing preparation temperature, and prepares for the transition to the toner image forming operation in the image forming unit 10. However, even in that case, the toner image forming operation in the image forming unit 10 is performed within the warm-up time for the fixing belt 61 to reach the fixing preparation temperature, or within a predetermined time after the warm-up time has elapsed. There are cases where an instruction for confirmation (for example, a pressing operation of a copy start button (not shown) of the UI unit 34 by the user) is not recognized. In such a case, the main CPU 110 determines that more time is required until the toner image forming operation is executed, for example, depending on the user's circumstances or communication state. Then, the main CPU 110 instructs the CPU 160 to stop the power supplied to the IH heater 80. Thereby, the supply of the high-frequency current to the exciting coil 82 is stopped.

For example, the user places a document on the image reading unit 50, but the UI unit 34 is at a loss in setting the number of copies, setting the enlargement / reduction ratio, etc. The time until the toner image forming operation is actually started in the image forming unit 10 passes the warm-up time, and further, it may become long enough to pass a predetermined time after the warm-up process is completed. is there. In this case, by temporarily stopping the power supplied to the IH heater 80, the power consumption in the fixing unit 60 is reduced by the amount of consumption corresponding to the standby time after the warm-up time has elapsed.
Then, after the power supplied to the IH heater 80 is stopped, for example, various setting operations of the user in the UI unit 34 are finished, and a copy start button (not shown) is pressed from the UI unit 34 (in the image forming unit 10). The main CPU 110 again issues a warm-up process execution instruction. In this case, since the warm-up process has been executed before that, the fixing belt 61 reaches the fixing preparation temperature in a warm-up time shorter than 3 seconds. Therefore, the waiting time of the user is small and the inconvenience given to the user is small.

  As described above, in the fixing unit 60 of the present embodiment, the warm-up process is instructed to be executed, and the warm-up time or the warm-up time required for preparation of the toner image forming operation in the image forming unit 10 has elapsed. If an instruction (depression of the copy start button) for confirming execution of the toner image forming operation is not recognized within a predetermined time later, the power supplied to the IH heater 80 is temporarily stopped. Then, the warm-up process is executed again by pressing the copy start button thereafter. Assuming the above case, it is preferable to adopt such a procedure from the viewpoint of reducing power consumption and user convenience.

On the other hand, within the warm-up time when the fixing belt 61 that is performing the warm-up process reaches the fixing preparation temperature, or within a predetermined time after the warm-up time has elapsed, the copy start button is pressed in the UI unit 34, for example. When recognizing the operation (instruction to start the toner image forming operation), the main CPU 110 does not instruct the CPU 160 to stop the power supplied to the IH heater 80. Thereby, the supply of the high frequency current to the exciting coil 82 is continued as it is.
In this case, a toner image forming operation is subsequently executed in the image forming unit 10. That is, the toner image forming operation is started in the image forming unit 10, and the pressure roll 62 is, for example, immediately before the first sheet is carried into the fixing unit 60 (for example, 1 to 1 of the sheet entering the nip portion N). About 2 seconds before), the contact / separation mechanism sets the position in contact with the fixing belt 61.

<Explanation of warm-up process execution timing>
Here, the controller 31 (main CPU 110) instructs the execution of the temperature rise process (warming-up process), for example, a toner image forming operation in the image forming unit 10 such as placing an original on the image reading unit 50. This is a case where the main CPU 110 recognizes a user operation (“user operation”) that is performed prior to the toner image forming operation.
This “operation by the user” includes, for example, an operation by the user to open the platen cover 52 of the image reading unit 50. When the platen cover 52 is opened, the document is generally placed on the first platen glass 51 by the user in a stationary state. Therefore, it is assumed that a copy instruction for the original placed on the first platen glass 51 is subsequently issued. The operation by the user to open the platen cover 52 is obtained by acquiring information indicating that the platen cover 52 has been opened from an open / close detection sensor as an example of an operation detection unit in which the main CPU 110 detects the open / closed state of the platen cover 52. Is recognized by the main CPU 110.
Furthermore, the “user operation” includes, for example, an operation by the user that the document is stored in the document storage unit 53 of the image reading unit 50. When a document is stored in the document storage unit 53, it is generally assumed that a copy instruction for the document stored in the document storage unit 53 is issued subsequently. An operation by a user that stores a document in the document storage unit 53 is that the main CPU 110 stores the document in the document storage unit 53 from a document detection sensor as an example of an operation detection unit that detects that the document is stored in the document storage unit 53. The main CPU 110 recognizes the information indicating that it has been done.

The “user operation” includes, for example, a user input operation on a liquid crystal touch panel and a numeric keypad (not shown) configured in the UI unit 34. In general, in order to actually start a toner image forming operation in the image forming apparatus 1, as a previous step, setting of the number of copies in the UI unit 34, selection of the paper size and paper type to be used, setting of the enlargement / reduction ratio, etc. are performed by the user. Is done by. Therefore, when a user input operation is performed on the UI unit 34, it is assumed that a copy instruction is subsequently issued. The user's input operation is recognized by the main CPU 110 when the main CPU 110 acquires operation input information from the UI unit 34 that functions as an example of an operation detection unit.
In addition, the user's input operation to the UI unit 34 includes a pressing operation of a copy start button that is an instruction to start the toner image forming operation in the image forming unit 10 (an instruction to confirm execution of the toner image forming operation). It is.

  The “user operation” includes, for example, reception of an image forming command (print job) from the PC 3 or the like in the communication unit 32. That is, the reception of the print job transmitted to the communication unit 32 due to the user's operation of operating the PC 3 or the like to transmit the print job to the image forming apparatus 1 is also included in the “user operation” here. . When a print job is received by the communication unit 32, the toner image forming operation is executed by the image forming unit 10 unless a failure such as a communication error occurs before the toner image forming operation is started. Therefore, when a print job is received by the communication unit 32, it is assumed that a toner image forming operation is subsequently executed by the image forming unit 10. The reception of the print job is recognized by the main CPU 110 when the main CPU 110 acquires the print job from the communication unit 32 that functions as an example of the operation detection unit.

  As described above, in addition to the direct operation performed by the user on the image forming apparatus 1 such as opening the platen cover 52 of the image reading unit 50, the image forming apparatus 1 is connected via an external device such as the PC 3 connected to the image forming apparatus 1. Indirect operations performed by the user on the image forming apparatus 1 are also included in the “user operations”.

As described above, when the control unit 31 (main CPU 110) performs an operation by the user performed as a pre-stage of execution of the toner image forming operation in the image forming unit 10 or a pre-stage of execution of the toner image forming operation. An assumed user operation is set in advance as “user operation”. When the control unit 31 recognizes a predetermined “user operation” as described above, it is assumed that the toner image forming operation is continuously performed after the user operation, and the warm-up is performed. A process execution instruction is issued to prepare for the transition to the toner image forming operation.
Further, the control unit 31 instructs to start the toner image forming operation (copy start button) within the warm-up time for preparation of the toner image forming operation or within a predetermined time after the warm-up time has elapsed. Is not recognized, the power supplied to the IH heater 80 is temporarily stopped, and the warm-up process is executed again by pressing the copy start button thereafter. As a result, power consumption is reduced and user convenience is not easily lost.

  Note that when an instruction to perform warm-up processing is issued based on reception of a print job from the PC 3 or the like in the communication unit 32, the start instruction of the toner image forming operation is determined by reception of the print job. Unless a failure such as an error occurs, the process proceeds to a toner image forming operation in the image forming unit 10.

  In the present embodiment, the control unit 31 sets the temperature of the fixing belt 61 to the CPU 160 of the electromagnetic induction heating control unit 100 within a predetermined time after the warm-up time in the fixing unit 60 has elapsed. Control for maintaining the “fixing standby temperature” set between the fixing set temperature and the fixing preparation temperature is executed.

<Description of Operation Control for Image Forming Process>
Next, operation control related to image forming processing performed by the control unit 31 will be described.
FIG. 12 is a flowchart for explaining an example of the contents of the operation control related to the image forming process performed by the control unit 31.
As shown in FIG. 12, the control unit 31 monitors the predetermined “user operation” as described above based on signals from the image reading unit 50, the UI unit 34, and the communication unit 32 (see FIG. 12). Step 101). When a predetermined “operation by the user” is recognized (Yes in Step 101), the control unit 31 turns on the drive motor 90 (see FIG. 2 above) to the fixing unit 60 and adds it. An instruction is given to rotate the fixing belt 61 in a state where the pressure roll 62 is not pressed against the fixing belt 61 (step 102). Thereafter, the control unit 31 instructs execution of a temperature rise process (warming up process) (step 103).
On the other hand, when the predetermined “user operation” is not recognized (No in step 101), the control unit 31 continues to monitor the “user operation” (step 101).

And the control part 31 waits for transmission of the "warming-up completion signal" from the electromagnetic induction heating control part 100 (step 104). When the “warming up completion signal” is acquired from the electromagnetic induction heating control unit 100 (Yes in Step 104), the control unit 31 instructs execution of control for maintaining the fixing standby temperature (Step 105), and “operation by the user” is performed. It is determined whether or not the communication unit 32 has received a print job from the PC 3 or the like (step 106).
As a result, when the print job is received by the communication unit 32 (Yes in Step 106), the control unit 31 shifts to execution control of the toner image forming operation (see the subsequent stage) (Step 107).

When recognizing completion of a series of image forming processes (step 108), the control unit 31 determines whether or not post-processing (refer to the subsequent stage) of the image forming process is necessary (step 109), and post-processing is necessary. If there is (Yes in Step 109), post-processing of the image forming process is performed (Step 110). When the post-processing is completed, the process returns to step 101 again, and the control unit 31 monitors “operation by the user”.
On the other hand, when post-processing is not necessary (No in Step 109), when a series of image forming processes is completed, the process returns to Step 101 and the control unit 31 monitors “operation by the user”.

On the other hand, if the “operation by the user” is not reception of a print job from the PC 3 or the like in the communication unit 32, that is, if “operation by the user” in the image reading unit 50 or the UI unit 34 (step). 106), the control unit 31 acquires a signal indicating that the copy start button (not shown) has been pressed from the UI unit 34 within a predetermined time from the acquisition of the “warming up completion signal”. It is determined whether or not (step 111).
If a signal indicating that the copy start button has been pressed is not acquired from the UI unit 34 within a predetermined time from acquisition of the “warming up completion signal” (No in step 110), the control unit 31 instructs the fixing unit 60 to stop the power supplied to the IH heater 80 (step 112). Thereby, the supply of the high-frequency current to the exciting coil 82 is stopped. Further, thereafter, the fixing unit 60 is instructed to turn off the driving motor 90 and stop the rotation of the fixing belt 61 (step 113).
Thereafter, the control unit 31 returns to step 101 and monitors a predetermined “operation by the user”.

In addition, when a signal indicating that the copy start button has been pressed is acquired from the UI unit 34 within a predetermined time from the acquisition of the “warming up completion signal” (Yes in step 111), The control unit 31 shifts to execution control of the toner image forming operation in step 107.
When recognizing completion of a series of image forming processes (step 108), the control unit 31 determines whether or not post-processing of the image forming process is necessary (step 109). (Yes in step 109), post-processing of the image forming process is performed (step 110). When the post-processing is completed, the process returns to step 101 again, and the control unit 31 monitors “operation by the user”.
On the other hand, when post-processing is not necessary (No in Step 109), when a series of image forming processes is completed, the process returns to Step 101 and the control unit 31 monitors “operation by the user”.

<Description of Control of Electric Power Supplyed to IH Heater During Toner Image Forming Operation>
When the “operation by the user” is reception of a print job from the PC 3 or the like in the communication unit 32 (Yes in step 106 in FIG. 12), or the copy start button from the UI unit 34, for example, When (not shown) is pressed (Yes in step 111 in FIG. 12 above), it is determined that there is an instruction for finalizing the execution of the toner image forming operation in the image forming unit 10. The execution control of the toner image forming operation is performed (step 107 in FIG. 12).
The control unit 31 performs control (hereinafter, “forced heating control”) as an example of second control for forcibly heating the fixing belt 61 in the control of the power supplied to the IH heater 80 performed during the toner image forming operation. Do. In other words, the control unit 31 starts the toner image forming operation (when recognizing an instruction for confirming the execution of the toner image forming operation) and the timing of the specific operation in the fixing unit 60, and the exciting coil 82. Forced heating control is performed in which the high-frequency current is forcibly supplied to heat the fixing belt 61.

FIG. 13 is a diagram for explaining the timing at which the control unit 31 performs the forced heating control of the fixing belt 61.
When the control unit 31 recognizes reception of a print job from the PC 3 or the like at the communication unit 32, or when a copy start button (not shown) is pressed from the UI unit 34, for example, toner image formation is performed. By recognizing an instruction for confirming execution of the operation, the image forming unit 10 starts execution of the toner image forming operation. Therefore, as shown in FIGS. 13A and 13B, the fixing belt 61 is matched with the timing when the instruction for confirming the execution of the toner image forming operation is recognized and the execution of the toner image forming operation is started. The first forced heating control (FIG. 13 (i)) is performed for a predetermined time. As a result, the temperature of the fixing belt 61 is raised from the fixing standby temperature to the fixing set temperature.
Further, as shown in FIGS. 13A and 13C, the control unit 31 matches the timing at which the pressure roll 62 as an example of a contact body is brought into contact with the fixing belt 61 by a contact / separation mechanism (not shown). Then, the second forced heating control (FIG. 13 (ii)) for the fixing belt 61 is executed for a predetermined time. As a result, the amount of heat flowing out to the pressure roll 62 when the pressure roll 62 comes into contact with the fixing belt 61 is compensated, and the temperature of the fixing belt 61 is prevented from being lowered from the preset fixing temperature.

Further, as shown in FIGS. 13A and 13D, the control unit 31 detects the timing td seconds before the leading edge of the first sheet P as an example of the contact body enters the nip portion N of the fixing unit 60. At the same time, the third forced heating control (FIG. 13 (iii)) for the fixing belt 61 is executed for a predetermined time. As a result, the amount of heat flowing out of the paper P by the contact of the paper P on which the toner image is formed with the fixing belt 61 is compensated, and the temperature of the fixing belt 61 is prevented from decreasing from the fixing set temperature.
On the other hand, as shown in FIG. 13E, the period between the first forced heating control (i) and the second forced heating control (ii) (FIG. 13 (iv)), the second forced heating. A period between the control (ii) and the third forced heating control (iii) (FIG. 13 (v)) and a period after the third forced heating control (iii) is completed (FIG. 13 (vi)). Until the series of image forming processes is completed, the control unit 31 controls the CPU 160 of the electromagnetic induction heating control unit 100 as an example of the first control for maintaining the fixing belt 61 at the fixing set temperature. The control is executed.

  In this case, when the control unit 31 performs control to forcibly heat the fixing belt 61, the main CPU 110 of the control unit 31 shows the CPU 160 of the electromagnetic induction heating control unit 100 as shown in FIG. “Forced heating instruction signal” is output at the timing. The CPU 160 generates a “power setting signal” corresponding to the “forced heating instruction signal” from the control unit 31 and the temperature detection signals from the thermistors 71 and 72 (mainly thermistors 71). Is output to the excitation circuit 88. As a result, the CPU 158 provided in the excitation circuit 88 drives and controls the high-frequency switching circuit 152 based on the “power setting signal” supplied from the CPU 160 to forcibly heat the fixing belt 61.

  Here, for example, when the print job received by the communication unit 32 is a print job related to a color image, or when color image printing is designated as the print setting by the UI unit 34, for example, the main CPU 110 performs the first processing. The "forced heating instruction signal" output to the CPU 160 when instructing the forced heating control (FIG. 13 (i)) is output as the "color image forced heating instruction signal" for printing a color image. Also good. When the print job received by the communication unit 32 is a print job related to a black and white image, or when black and white image printing is designated as the print setting by the UI unit 34, for example, the black and white image is printed to the CPU 160. May be output as a “black and white image forced heating instruction signal”.

Thus, when the CPU 160 of the electromagnetic induction heating control unit 100 receives the “color image forced heating instruction signal” from the control unit 31, the “color image forced heating instruction signal” and the temperature detection signal from the thermistor 71. A “color image power setting signal” corresponding to the above is output to the excitation circuit 88. As a result, the CPU 158 provided in the excitation circuit 88 drives and controls the high-frequency switching circuit 152 based on the “color image power setting signal” acquired from the CPU 160, and from when the “monochrome image forced heating instruction signal” is acquired. The fixing belt 61 is forcibly heated by a large electric power.
In addition, when the CPU 160 of the electromagnetic induction heating control unit 100 receives the “monochrome image forced heating instruction signal” from the control unit 31, the “monochrome image forced heating instruction signal” and the temperature detection signal from the thermistor 71, A “monochrome image power setting signal” corresponding to the above is output to the excitation circuit 88. As a result, the CPU 158 provided in the excitation circuit 88 drives and controls the high-frequency switching circuit 152 based on the “monochrome image power setting signal” acquired from the CPU 160, and from when the “color image forced heating instruction signal” is acquired. The fixing belt 61 is forcibly heated with a small electric power.

<Description of post-processing of image formation processing>
Next, the implementation determination (step 109 in FIG. 12) regarding the post-processing of the image forming process performed by the control unit 31 after completion of the series of image forming processes and the contents of the post-processing (step 110 in FIG. 12) will be described.
In the fixing unit 60 of the present embodiment, as described with reference to FIG. 9 above, when the temperature of the temperature-sensitive magnetic member 64 exceeds the permeability change start temperature, the non-sheet passing region Fb (described above) of the fixing belt 61. The magnetic field lines H after passing through the conductive heat generating layer 612 in FIG. 8) are diffused to suppress an excessive temperature rise of the fixing belt 61 in the non-sheet passing region Fb. However, in the non-sheet passing area Fb where heat for fixing is not consumed, the temperature is higher than that in the small size sheet passing area Fs, and the amount of heat transferred from the fixing belt 61 to the pressure roll 62 is larger. Therefore, in the pressure roll 62 in the non-sheet-passing region Fb where the temperature has increased due to heat transfer from the fixing belt 61, the amount of expansion of air contained in, for example, the silicone sponge constituting the heat resistant elastic layer 622 is small. It becomes larger than the expansion amount in the paper passing area Fs. At that time, the air hole 624 (see FIG. 3) provided in the heat resistant elastic layer 622 forms a path for releasing air contained in the heat resistant elastic layer 622, for example, in silicone sponge to the outside. Thus, the expansion amount of the heat resistant elastic body layer 622 is reduced.

  However, even if air is released through the air holes 624 and the expansion amount of the pressure roll 62 is reduced as a whole, the outer diameter of the pressure roll 62 in the non-sheet passing area Fb is small. The tendency to become larger than the outer diameter of Fs remains. Therefore, the pressing force from the pressure roll 62 to the fixing belt 61 is higher in the non-sheet passing area Fb than the small size sheet passing area Fs, and the frictional force from the pressure roll 62 in the non-sheet passing area Fb is small. It becomes larger than the frictional force in the paper passing area Fs. As a result, different frictional forces act in the axial direction of the pressure roll 62 between the pressure roll 62 and the fixing belt 61, and the paper P may be wrinkled in the subsequent image forming process.

  Therefore, in the image forming apparatus 1 of the present embodiment, the series of image forming processes uses the paper P having a paper width smaller than the predetermined paper width, and more than a predetermined number of papers. In the case of P, after the series of image forming processes is completed, the pressure roll 62 and the fixing belt 61 are rotated without passing through the sheet for a predetermined time (so-called “idle rotation”). Perform “post-processing”. Accordingly, the temperature distribution in the axial direction of the pressure roll 62 is leveled, and the frictional force between the pressure roll 62 and the fixing belt 61 is averaged in the axial direction of the pressure roll 62 (the width direction of the paper P). Then, the occurrence of wrinkles on the paper P in the subsequent image forming process is suppressed.

Next, FIG. 14 is a flowchart illustrating an example of the content of the determination process performed when the control unit 31 performs post-processing.
As shown in FIG. 14, the control unit 31 uses the paper P used in the series of image forming processes to have a paper width larger than a predetermined paper width (for example, A4 size paper vertical feed: A4SEF). In the case of P (for example, vertical feed of B4 size paper: B4SEF) (No in S201), it is determined not to perform post-processing, and the pressure roll 62 is separated from the fixing belt 61 (S202). Thereafter, the determination process ends. The “paper width” in this specification refers to the paper length in the direction orthogonal to the conveyance direction of the paper P.
On the other hand, when the paper P used in the series of image forming processes is a paper P having a paper width equal to or smaller than a predetermined paper width (for example, A5 size paper vertical feed: A5SEF) ( In S201, the number of images formed (hereinafter referred to as “number of prints”) is determined (S203). If the number of prints is equal to or smaller than a predetermined first number of prints (Yes in S203), the control unit 31 determines not to perform post-processing, and separates the pressure roll 62 from the fixing belt 61 ( S202). Thereafter, the determination process ends.

  Further, if the number of prints is equal to or smaller than a predetermined second print number (> first print number) (No in S203, Yes in S204), the control unit 31 sets the pressure roll 62 to the fixing belt 61. In the contacted state, the fixing belt 61 and the pressure roll 62 are idled for a predetermined first time (S205). Thereafter, the pressure roll 62 is separated from the fixing belt 61 (S206), and the determination process is terminated.

Further, if the number of prints is equal to or smaller than a predetermined third print number (> second print number) (No in S204, Yes in S207), the control unit 31 moves the pressure roll 62 to the fixing belt 61. In the contacted state, the fixing belt 61 and the pressure roll 62 are idly rotated for a predetermined second time (> first time) (S208). Thereafter, the pressure roll 62 is separated from the fixing belt 61 (S209), and the determination process is ended.
Furthermore, if the number of prints is greater than the predetermined third number of prints (No in S204, No in S207), the control unit 31 will keep the pressure roll 62 in contact with the fixing belt 61 in advance. The fixing belt 61 and the pressure roll 62 are idled for a predetermined third time (> second time) (S210). Thereafter, the pressure roll 62 is separated from the fixing belt 61 (S211), and the determination process is ended.

In the case where a plurality of different image forming processes are continuously executed without stopping the operation of the fixing unit 60, for example, a print job is received by the communication unit 32 continuously after a series of image forming processes. If the paper width of the paper P used in the next image forming process is the same as or smaller than the paper width of the paper P used last time, the image forming process is not performed. Execute. In such a case, the non-sheet-passing area Fb of the pressure roll 62 in the previous image forming process is an area positioned on both ends of the non-sheet-passing area Fb of the pressure roll 62 in the next image forming process. It becomes. For this reason, the temperature distribution in the axial direction of the pressure roll 62 is almost uniform in the paper region passing through the fixing unit 60 in the next image forming process, and the pressure roll 62 has almost no difference in outer diameter. do not do. As a result, there is little possibility that the paper P will be wrinkled in the next image forming process. In such a case, no post-processing is performed.
On the other hand, when the paper width of the paper P used in the next image forming process is larger than the paper width of the paper P used last time, post-processing is executed, and after the post-processing is finished, the next image is processed. A forming process is performed.

<Description of internal configuration of control unit>
FIG. 15 is a block diagram illustrating a part of the internal configuration of the control unit 31. As shown in FIG. 15, the control unit 31 performs operation control related to image forming processing including power control (forced heating control) supplied to the IH heater and post-processing described above according to a predetermined processing program. Main CPU 110 for executing digital arithmetic processing, RAM 112 used as a working memory for the main CPU 110, ROM 113 for storing various setting values used for processing in the main CPU 110, rewritable and when power supply is interrupted Can also hold data, a non-volatile memory (NVM) 114 such as a flash memory backed up by a battery, and signals to each component connected to the control unit 31 (for example, the CPU 160 configuring the electromagnetic induction heating control unit 100) The interface (I / F) unit 115 for controlling the input / output of the device is provided.
Then, the main CPU 110 reads a processing program from an external storage device (not shown) into the main storage device (RAM 112), and realizes each function in the control unit 31.

  In addition, as another provision form regarding this processing program, there is a form that is provided in a state stored in the ROM 113 in advance and loaded into the RAM 112. Further, when a rewritable ROM 113 such as an EEPROM is provided, after the main CPU 110 is set, only a program is installed in the ROM 113 and loaded into the RAM 112. Further, there is a mode in which a program is transmitted to the control unit 31 via a network such as the Internet, installed in the ROM 113 of the control unit 31, and loaded into the RAM 112. Furthermore, there is a form in which the RAM 112 is loaded from an external recording medium such as a DVD-ROM or a flash memory.

[Embodiment 2]
In the first embodiment, when a predetermined “user operation” is recognized, the warm-up process is executed, and when the toner image forming operation is started by recognizing the confirmation of the execution of the toner image forming operation. Has described the configuration in which the forced heating control is performed on the fixing belt 61 in accordance with the operation of the fixing unit 60. In the present embodiment, a configuration will be described in which the power value for heating the fixing belt 61 by the warming-up process and the forced heating control is set according to the temperature of the fixing belt 61 before the warming-up process is started. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

<Description of power value setting according to fixing belt temperature before starting warm-up process>
When the control unit 31 (main CPU 110) of the present embodiment recognizes an “operation by the user” such as a main switch being turned on or a document being placed on the image reading unit 50, the electromagnetic induction heating control unit 100. CPU 160 (see FIG. 11) is instructed to execute a temperature rise process (warming up process) for setting the temperature of the fixing belt 61 to the fixing preparation temperature. Accordingly, the CPU 160 sets the fixing belt 61 to the fixing preparation temperature, and prepares for the transition to the toner image forming operation in the image forming unit 10. At that time, the CPU 160 acquires the temperature detection signal detected by the thermistors 71 and 72 (mainly, the thermistor 71 disposed at the center of the fixing belt 61). Then, the CPU 160 outputs, for example, a “power setting signal” in which a power value is specified in accordance with a temperature detection signal from the thermistor 71 to the excitation circuit 88. As a result, the CPU 158 provided in the excitation circuit 88 causes the high frequency switching circuit 152 so that the power of the power value specified in the “power setting signal” acquired from the CPU 160 is supplied from the high frequency switching circuit 152 to the excitation coil 82. Is controlled. As a result, the high frequency switching circuit 152 applies the power of the power value designated in the “power setting signal” to the exciting coil 82 via the output port 150 and heats the fixing belt 61.

The fixing belt 61 is in a different temperature state depending on the elapsed time from the previously executed image forming process, the number of prints in the previous image forming process, the current environmental temperature, and the like. For this reason, when performing the warm-up process or the forced heating control, if the power supplied from the high-frequency switching circuit 152 to the exciting coil 82 is uniformly set, the power may be wasted.
For example, when the elapsed time from the previous image forming process is short and a large number of sheets have been printed in the previous image forming process, the fixing belt 61 is maintained near the fixing preparation temperature or the fixing standby temperature. It is often done. Even in such a case, when the above-mentioned “operation by the user” is recognized, the warm-up process is necessary to make the temperature unevenness existing in the circumferential direction and the width direction of the fixing belt 61 uniform. However, if the fixing belt 61 is maintained in the vicinity of the fixing preparation temperature or the fixing standby temperature, the temperature unevenness can be made even with a small amount of power. For this reason, as in the case where the fixing belt 61 is at about room temperature, when the power to be used in the warm-up process is set, useless power is used.

Therefore, in the present embodiment, when the control unit 31 (main CPU 110) instructs execution of the warm-up process, the CPU 160 of the electromagnetic induction heating control unit 100 acquires, for example, a temperature detection signal detected by the thermistor 71. . Then, the CPU 160 outputs a “power setting signal” specifying the power value determined according to the temperature detection signal from the thermistor 71 to the excitation circuit 88.
Thereby, the power supplied from the high-frequency switching circuit 152 to the exciting coil 82 is set according to the temperature of the fixing belt 61 before the warm-up process is started, so that the power during the warm-up process is effectively used.

<Description of power value set corresponding to fixing belt temperature>
Here, FIG. 16 shows an example of the relationship between the temperature detected by the thermistor 71 (detected temperature Tm (° C.)) and the power value (specified power (W)) specified by the “power setting signal”. It is a figure.
In FIG. 16, when the print job received by the communication unit 32 is a print job related to a color image, for example, when color image printing is designated as print settings by the UI unit 34 (hereinafter, “color mode”). When the print job is a print job related to a monochrome image or when monochrome image printing is specified (hereinafter referred to as “monochrome mode”), the specified power is set to a different value even if the detected temperature is the same. An example may be shown.
In FIG. 16, when the detected temperature is within the same temperature range, the designated power in the color mode is set larger than or equal to the designated power in the monochrome mode. Furthermore, in the same mode, the specified power is set lower when the detected temperature is higher. However, a temperature region in which the specified power is set to the same value may be set even if the detected temperatures are in different temperature ranges. That is, in FIG. 16, the designated powers are W1 ≧ W3 ≧ W5 ≧ W7 ≧ W9, W2 ≧ W4 ≧ W6 ≧ W8 ≧ W10, W2 ≧ W1, W4 ≧ W3, W6 ≧ W5, W8 ≧ W7, W10 ≧ W9. , W1 ≠ W9, and W2 ≠ W10.
The relationship between the detected temperature and the specified power exemplified in FIG. 16 is stored as a table (hereinafter referred to as “relation table”) in the NVM 114 (see FIG. 15), for example.

FIG. 17 is a flowchart for explaining an example of the contents of the power setting process performed by the control unit 31 during the temperature rise process (warming up process) for the fixing unit 60.
As shown in FIG. 17, when the control unit 31 recognizes a predetermined “user operation” based on signals from the image reading unit 50, the UI unit 34, and the communication unit 32 (step 301), The control unit 31 instructs the fixing unit 60 to turn on the driving motor 90 (see FIG. 2 above) and rotate the fixing belt 61 in a state where the pressure roll 62 is not pressed against the fixing belt 61. (Step 302). Thereafter, the control unit 31 instructs the CPU 160 of the electromagnetic induction heating control unit 100 to execute a warm-up process (step 303).
Thereby, CPU160 of the electromagnetic induction heating control part 100 provided in the control part 31 acquires a temperature detection signal from the thermistor 71 (step 304). Then, the CPU 160 determines a power value to be supplied from the high-frequency switching circuit 152 to the exciting coil 82 based on the temperature detection signal from the thermistor 71 and the relationship table shown in FIG. 16, for example (step 305). CPU 160 outputs a “power setting signal” designating the determined power value to excitation circuit 88 (step 306). As a result, the high frequency switching circuit 152 of the excitation circuit 88 applies power of the power value designated by the “power setting signal” to the excitation coil 82 and heats the fixing belt 61.

  Note that the power value set when the fixing belt 61 is heated by the above-described forced heating control may be the same power value as the power value set in the warm-up process. Further, separately from the power value set during the warm-up process, a relationship table as shown in FIG. 16 above is created in advance as the power value set during the forced heating control, and from the thermistor 71 during the forced heating control. The power value may be determined based on the temperature detection signal and the relational table for forced heating control.

As described above, the fixing unit 60 provided in the image forming apparatus 1 according to the present embodiment recognizes a predetermined “user operation” and executes a temperature rise process (warming up process). Alternatively, when the toner image forming operation is started by recognizing the confirmation of the execution of the toner image forming operation thereafter, forced heating control for the fixing belt 61 is performed in accordance with the operation of the fixing unit 60.
As a result, a decrease in the temperature of the fixing belt 61 in the fixing unit 60 is suppressed, and the fixing belt 61 is maintained at the fixing set temperature.
Further, by setting the power value for heating the fixing belt 61 by the warm-up process or the forced heating control according to the temperature of the fixing belt 61 before the start of the warm-up process, wasteful power consumption is reduced. .

  In the present embodiment, the fixing unit 60 is described in which the temperature-sensitive magnetic member 64 is disposed in a non-contact manner with the fixing belt 61 and the temperature-sensitive magnetic member 64 itself does not easily generate heat. The IH heater 80 can be applied to the fixing unit 60 in which the temperature-sensitive magnetic member 64 is disposed in contact with the fixing belt 61 and the temperature-sensitive magnetic member 64 itself generates heat.

  The present invention also provides a fixing unit that heats the fixing belt with a heating element disposed in contact with the fixing belt, a fixing unit that heats a fixing member composed of a roll of metal or the like with a heating element such as a heater, and the like. It can also be applied to.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 32 ... Communication part, 34 ... User interface (UI) part, 60 ... Fixing unit, 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 70 ... Thermo switch, 71, 72 ... Thermistor, 80 ... IH heater, 82 ... Excitation coil, 84 ... Magnetic core, 88 ... Excitation circuit, 90 ... Drive motor, 100 ... Electromagnetic induction heating controller

Claims (13)

Toner image forming means for forming a toner image on a recording material;
A fixing member for fixing the toner image formed by the toner image forming unit to the recording material;
Heating means for heating the fixing member;
The first control for controlling the power supplied to the heating means so as to set the fixing member at a predetermined temperature, and the heating in accordance with the timing at which the contact body that contacts the fixing member contacts the fixing member. An image forming apparatus comprising: control means for performing second control for supplying power to the means. Temperature detecting means for detecting the temperature of the fixing member and outputting information on the temperature to the control means;
The control unit acquires information on the temperature of the fixing member from the temperature detection unit before starting the first control, and in accordance with the information, any of the first control and the second control is acquired. The image forming apparatus according to claim 1, wherein a power value supplied to the heating unit is determined by one or both of them. Operation detecting means for detecting an operation of an operator performed prior to the start of the toner image forming operation in order to cause the toner image forming means to execute a toner image forming operation for forming the toner image on the recording material. In addition,
The image forming apparatus according to claim 1, wherein the control unit performs the second control in response to the operation being detected by the operation detection unit. The fixing member is configured to move between a position in contact with the fixing member and a position in contact with the fixing member, and is set to a position in contact with the fixing member so as to pressurize the fixing member. A pressure member that forms a region through which the recording material holding the toner image passes;
The image forming apparatus according to claim 1, wherein the control unit performs the second control in accordance with a timing at which the pressure member is set to a position in contact with the fixing member.   The image forming apparatus according to claim 1, wherein the control unit performs the second control in accordance with a timing at which the recording material is conveyed to a position in contact with the fixing member. A fixing member for fixing the toner image formed on the recording material to the recording material;
Electric power is supplied in accordance with the first control in which the supplied electric power is controlled to set the fixing member at a predetermined temperature and the timing at which the contact body that contacts the fixing member contacts the fixing member. And a heating unit that heats the fixing member by being controlled by the second control. A temperature detecting means for detecting the temperature of the fixing member;
In the heating unit, the power value used in one or both of the first control and the second control is detected by the temperature detection unit before the first control is started. The fixing device according to claim 6, wherein the fixing device is determined according to a temperature of the fixing member.   The heating means performs the second control in response to an operation performed by an operator prior to the start of the toner image forming operation in order to execute a toner image forming operation for forming the toner image on the recording material. The fixing device according to claim 6, wherein: The fixing member is configured to move between a position in contact with the fixing member and a position in contact with the fixing member, and is set to a position in contact with the fixing member so as to pressurize the fixing member. A pressure member that forms a region through which the recording material holding the toner image passes;
The fixing device according to claim 6, wherein the second control is performed in accordance with a timing at which the heating unit is set to a position where the pressure member contacts the fixing member.   The fixing device according to claim 6, wherein the heating unit performs the second control in accordance with a timing at which the recording material is conveyed to a position in contact with the fixing member. On the computer,
A function of controlling the power supplied to the heating means for heating the fixing member so as to set the fixing member for fixing the toner image on the recording material to a predetermined temperature;
A program that realizes a function of controlling power to be supplied to the heating unit in accordance with a timing at which a contact body that contacts the fixing member contacts the fixing member. A function of acquiring information on the temperature of the fixing member;
The program according to claim 11, further realizing a function of determining a power value of power supplied to the heating unit in correspondence with information on the temperature of the fixing member. Further realizing a function of recognizing an operator's operation performed prior to the start of the toner image forming operation in order to cause the toner image forming operation to form the toner image on the recording material;
12. The program according to claim 11, wherein the control for supplying electric power to the heating unit is realized in accordance with the timing when the contact body contacts the fixing member by recognizing the operation of the operator.

Images