JP5846511B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein, and in particular, an electromagnetic induction heating type fixing device and an image provided with a demagnetizing coil. The present invention relates to a forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a technique is known in which a demagnetizing coil is installed in an electromagnetic induction heating type fixing device to suppress an excessive temperature rise in a non-sheet passing region of a heating member ( For example, see Patent Documents 1 to 3).

  In Patent Document 1, etc., in addition to the exciting coil, a plurality of pairs of degaussing coils are installed at both ends in the width direction in the induction heating unit of the fixing device at positions facing the exciting coil. The plural pairs of degaussing coils are arranged at positions corresponding to non-sheet passing regions of recording media of various sizes, and demagnetize the magnetic flux of the exciting coils generated at the opposed positions, thereby preventing the non-sheet passing of the heating member. The overheating of the area is suppressed.

On the other hand, in Patent Document 2 and the like, a temperature sensor (contact type thermistor) that detects the temperature of the end in the width direction of the fixing member corresponding to the position of the demagnetizing coil is installed, and the end in the width direction detected by the temperature sensor. A technique for driving the degaussing coil in accordance with the degree of temperature rise of the part is disclosed.
Further, in Patent Document 3 and the like, a temperature sensor (end temperature detector) that detects the temperature of the end in the width direction of the pressure member corresponding to the position of the demagnetizing coil is installed and detected by the temperature sensor. A technique for controlling the energization amount to the degaussing coil according to the temperature of the non-sheet passing region is disclosed.

In the conventional fixing device described above, the type and installation position of the temperature detection means for controlling the energization amount of the degaussing coil are greatly restricted.
Specifically, when a contact type thermistor is installed to detect the temperature of the end portion in the width direction of the fixing member as in Patent Document 2, a mark of contact of the contact type thermistor is formed on the surface of the fixing member. As a result, the trace also appears on the output image (fixed image). Therefore, it is necessary to use an expensive non-contact temperature sensor such as a thermopile as a temperature sensor for detecting the temperature at the end in the width direction of the fixing member.
In addition, since many members such as an excitation coil, a degaussing coil, and a separation plate are densely arranged around the fixing member, the temperature at the end in the width direction of the fixing member is set as in Patent Document 2, for example. It was difficult to secure a space for installing the temperature sensor for detection.

On the other hand, in Patent Document 3 or the like, a temperature sensor that detects the temperature of the end in the width direction of the pressure member corresponding to the position of the demagnetizing coil is installed, and the non-sheet passing region detected by the temperature sensor is installed. Since the energization amount to the degaussing coil is controlled according to the temperature, the effect of solving the above-described problem can be expected to some extent.
However, since the temperature difference between the temperature of the fixing member and the temperature of the pressure member is not always constant, the detection result of one temperature sensor installed at the end in the width direction of the pressure member as in Patent Document 3 or the like. Therefore, it is difficult to control the energization amount of the degaussing coil by judging the temperature rise in the non-sheet passing region. That is, in the above-described technique, a temperature rise in the non-sheet passing area is erroneously detected, and an excessive temperature rise occurs in the non-sheet passing area of the fixing member, or a temperature drop occurs at the end of the sheet passing area of the fixing member. May have occurred.

  The present invention has been made to solve the above-described problems, and has a high degree of freedom in the type and installation position of temperature detection means for controlling the energization amount of the degaussing coil. It is an object of the present invention to provide a fixing device and an image forming apparatus in which excessive temperature rise in a non-sheet-passing region is efficiently and reliably suppressed.

According to a first aspect of the present invention, there is provided a fixing device for fusing a toner image and fixing the toner image on a recording medium, and for detecting the temperature of the surface of the fixing member in a non-contact manner at a central position in the width direction. A contact temperature sensor, a pressure member that forms a nip portion that is pressed against the fixing member and transports a recording medium, and a plurality of temperature detection means that detects the temperature of the pressure member at a plurality of locations in the width direction; A heating member having a heating layer for heating the fixing member, an excitation coil that opposes the heating member, generates a magnetic flux and induction-heats the heating layer by the magnetic flux, and faces the excitation coil together they are arranged in the width direction of both ends, and a degaussing coil of one or more pairs to generate a magnetic flux in a direction to cancel the magnetic flux in the widthwise end portions generated by the exciting coil, the excited Coils, the heating amount of the heating layer based on a detection result of the non-contact temperature sensor is controlled so as to be adjusted, the plurality of temperature sensing means detects the temperature of the widthwise central portion of the pressure member One or a plurality of second temperatures for detecting the temperature at the end in the width direction of the pressure member corresponding to the position in the width direction of at least one demagnetizing coil of the pair or plural pairs of demagnetizing coils. A pair of or a plurality of pairs of degaussing coils, wherein the energization amount is controlled based on a detection result of the first temperature detection unit and the second temperature detection unit, and the first temperature detection unit When the temperature difference between the temperature detected by the second temperature detecting means and the temperature detected by the second temperature detecting means becomes a predetermined value or more, energization to the pair of demagnetizing coils corresponding to the second temperature detecting means is started. Is.

A fixing device according to a second aspect of the present invention is the fixing device according to the first aspect , wherein the temperature detected by the first temperature detecting means and the temperature detected by the second temperature detecting means. When the difference becomes less than a predetermined value, the pair of degaussing coils corresponding to the second temperature detection means are not energized.

A fixing device according to a third aspect of the present invention is the fixing device according to the first or second aspect , further comprising a switching circuit that turns on and off the energization of the pair or plural pairs of degaussing coils. The energizing amount of the pair or plural pairs of demagnetizing coils is controlled by changing the ratio of the time during which energization is turned on / off in a predetermined time period by the switching circuit.

According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the energization amount to the pair or plural pairs of degaussing coils is controlled by a predetermined number or more. In this case, continuous printing of the recording medium is performed and started after a predetermined time has elapsed since the continuous feeding of the recording medium was started, and stopped when the continuous feeding of the recording medium was completed. It is.

According to a fifth aspect of the present invention, there is provided the fixing device according to any one of the first to fourth aspects, wherein the pair or the plurality of pairs of degaussing coils are a plurality of types of recording media having different sizes. The heating range in the width direction of the heat generating layer can be varied corresponding to the sheet passing area.

An image forming apparatus according to a sixth aspect of the invention includes the fixing device according to any one of the first to fifth aspects.

  Since the present invention controls the energization amount of the degaussing coil based on the detection results of a plurality of temperature detection means that detect the temperature of the pressure member at a plurality of positions in the width direction, the type and installation position of the temperature detection means Therefore, it is possible to provide a fixing device and an image forming apparatus in which the excessive temperature rise in the non-sheet passing region in the fixing member is efficiently and surely suppressed by demagnetization by the demagnetizing coil.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. 2 is a configuration diagram illustrating a fixing device. FIG. It is a figure which shows the state of the magnetic flux generated by the induction heating part. It is the schematic which shows the positional relationship of an induction heating part and a temperature sensor. It is a flowchart which shows control of the degaussing coil based on the detection result of a temperature sensor. It is a graph which shows the temperature distribution of the width direction of a pressure roller.

Embodiment.
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is the main body of a tandem type color copier as an image forming apparatus, 2 is a writing unit that emits laser light based on input image information, 4 is a document reading unit that reads image information of a document D, and 7 is A paper supply unit for storing a recording medium P such as transfer paper, 11Y, 11M, 11C, and 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, and 12 is a photosensitive drum. 11Y, 11M, 11C, and 11BK are charged. 13 is a developing unit that develops an electrostatic latent image formed on each photoconductor drum 11Y, 11M, 11C, and 11BK, and 15 is each photoconductor drum 11Y. A cleaning unit that collects untransferred toner on 11M, 11C, and 11BK is shown.
Reference numeral 16 denotes an intermediate transfer belt cleaning unit that cleans the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred, and 18 a color image formed on the intermediate transfer belt 17 as a recording medium. A secondary transfer roller 19 for transferring the toner image onto P is an electromagnetic induction heating type fixing device for fixing a toner image (unfixed image) on the recording medium P.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, image information of the document D placed on the contact glass 5 is optically read by the document reading unit 4. Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.
Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .)
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the intermediate transfer belt 17, respectively. Here, a transfer bias roller (not shown) is installed at each facing portion so as to abut on the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photoconductive drums 11Y, 11M, 11C, and 11BK are sequentially transferred to the intermediate transfer belt 17 at the position of the transfer bias roller (primary transfer process). .)

Then, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the primary transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

Thereafter, the intermediate transfer belt 17 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 18. At this position, the secondary transfer backup roller sandwiches the intermediate transfer belt 17 between the secondary transfer roller 18 and forms a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 17 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip (secondary transfer process). At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 17.
Thereafter, the intermediate transfer belt 17 reaches the position of the intermediate transfer cleaning unit 16. At this position, the untransferred toner on the intermediate transfer belt 17 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 17 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip passes through a transport path K1 in which a paper feed roller 8, a registration roller, and the like are installed from a paper feed unit 7 disposed below the apparatus main body 1. It was transported via.
Specifically, a plurality of recording media P are stored in the paper supply unit 7 in a stacked manner. When the paper feed roller 8 is rotationally driven counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the transport path K1.

  The recording medium P transported to the transport path K1 temporarily stops at the position of the roller nip of the registration roller (not shown) that has stopped rotating. Then, the registration roller is driven to rotate in synchronization with the color image on the intermediate transfer belt 17, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 19. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing roller and the pressure roller.
The recording medium P after the fixing process is discharged as an output image by the paper discharge roller 9 to the outside of the apparatus main body 1 (moving in the direction indicated by the broken line arrow), and a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 19 installed in the image forming apparatus main body 1 will be described in detail.
As shown in FIG. 2, the fixing device 19 includes an induction heating unit 25 (magnetic flux generating unit), a fixing roller 20 (fixing member) as a heat generating member facing the induction heating unit 25, and a pressure member that presses the fixing roller 20. And thermistors 40A to 40D (temperature sensors) as temperature detecting means, an inlet guide plate 41, a spur 42, a separation plate 43, a guide member 50, and the like.

Here, the fixing roller 20 as a heat generating member is obtained by sequentially laminating a heat insulating elastic layer 22 made of foamed silicone rubber or the like and a sleeve layer 21 on a cored bar 23 made of iron or stainless steel. The outer diameter is about 40 mm.
The sleeve layer 21 of the fixing roller 20 is a multilayer structure in which a base material layer, a first antioxidant layer, a heat generating layer, a second antioxidant layer, an elastic layer, and a release layer are sequentially laminated from the inner peripheral surface side. Specifically, the base material layer is formed of stainless steel having a layer thickness of about 40 μm, and the first antioxidant layer and the second antioxidant layer are formed by strike plating treatment of nickel having a layer thickness of 1 μm or less. The heating layer is made of copper having a layer thickness of about 10 μm, the elastic layer is made of silicone rubber having a layer thickness of about 150 μm, and the release layer has a layer thickness of about 30 μm. It is formed of PFA (tetrafluoroethylene / barfluoroalkyl vinyl ether copolymer).
In the fixing roller 20 (heat generating member) configured as described above, the heat generating layer of the sleeve layer 21 is electromagnetically heated by the magnetic flux generated from the exciting coil 26 of the induction heating unit 25. The configuration of the fixing roller 20 is not limited to that of the present embodiment, and for example, the sleeve layer 21 can be separated without being bonded to the heat insulating elastic layer 22 (fixing auxiliary roller). However, when the sleeve layer 21 (fixing sleeve) is separated, it is preferable to install a member for preventing the sleeve layer 21 from moving in the width direction (thrust direction) during operation.

Here, a plurality of spurs 42 are juxtaposed in the width direction at a position facing the fixing roller 20 as a fixing member and upstream of the nip portion (upstream in the transport direction). The spur 42 guides the recording medium P fed into the nip portion to the nip portion. The spur 42 is formed in a saw-tooth shape so that even if it contacts an unfixed image on the recording medium P, the image does not rub.
In addition, a separation plate 43 is installed at a position facing the fixing roller 20 and downstream of the nip portion (downstream in the transport direction). The separation plate 43 is for preventing a problem that the recording medium P after the fixing process sent out from the nip portion is attracted to and wound around the fixing roller 20. That is, when the recording medium P after the fixing process is attracted to the fixing roller 20, the separation member 43 interferes with the leading end of the recording medium P to forcibly separate the recording medium P from the fixing roller 20.
Although not shown, a thermopile is disposed at a position facing the fixing roller 20 (the center in the width direction). The temperature on the fixing roller 20 (fixing temperature) is detected in a non-contact manner by the thermopile. And based on the detection result by a thermopile, the heating amount by the induction heating part 25 is adjusted.

Referring to FIG. 2, a pressure roller 30 as a pressure member is formed on a cylindrical member 32 made of aluminum, copper or the like, an elastic layer 31 made of silicone rubber or the like, a release layer made of PFA or the like (not shown). Is formed). The elastic layer 31 of the pressure roller 30 is formed to have a thickness of 1 to 5 mm. The release layer of the pressure roller 30 is formed so that the layer thickness is 20 to 50 μm. The pressure roller 30 is in pressure contact with the fixing roller 20. Then, the recording medium P is conveyed to a pressure contact portion (a nip portion) between the fixing roller 20 and the pressure roller 30.
In the present embodiment, a heater 33 such as a halogen heater is provided in the pressure roller 30 in order to increase the heating efficiency of the fixing roller 20. By supplying electric power to the heater 33, the pressure roller 30 is heated by the radiant heat of the heater 33, and the surface of the fixing roller 20 is heated via the pressure roller 30. The heating amount of the heater 33 is adjusted based on the detection result by the first thermistor 40 </ b> A that contacts the central portion in the width direction of the pressure roller 30.

Here, with reference to FIG. 2 and FIG. 4C, the thermistor as a plurality of temperature detecting means for detecting the temperature of the pressure roller 30 at a plurality of positions in the width direction is provided at a position where the pressure roller 30 abuts. 40A-40D (contact type thermistor) is provided. Specifically, the plurality of temperature detection means includes a first thermistor 40A as the first temperature detection means for detecting the temperature of the central portion in the width direction of the pressure roller 30, and one (a pair of demagnetization coils 27A to 27C). Thermistors (second thermistor 40B, third thermistor 40C, second thermistor 40C, second thermistor 40C, second thermistor 40C) that detect the temperature of the end in the width direction of the pressure roller 30 corresponding to the position in the width direction of one of the demagnetizing coils 4 thermistor 40D).
The energization amounts of the plurality of pairs of degaussing coils 27A to 27C are controlled based on the detection results of the plurality of thermistors 40A to 40D (temperature detection means). The control of the degaussing coil will be described in detail later.

Referring to FIG. 2, an inlet guide plate 41 is installed at a position facing the pressure roller 30 and upstream of the nip portion. The inlet guide plate 41 guides the recording medium P fed into the nip portion to the nip portion.
A guide member 50 is installed at a position facing the pressure roller 30 and downstream of the nip portion (a position facing the non-fixing surface of the recording medium P fed from the nip portion). Yes. The guide member 50 is for guiding the recording medium P sent from the nip portion after the fixing process toward the conveyance path after the fixing process.

The induction heating unit 25 includes an exciting coil 26, a plurality of pairs of demagnetizing coils 27A to 27C, a plurality of cores 28, 29, and 35, a coil guide 36 (holding member), and the like.
The induction heating unit 25 is configured to be separable from the main part of the fixing device 19. The main part of the fixing device 19 is separated from the induction heating unit 25 and taken out from the image forming apparatus main body 1 in a state where the door 100 is opened (the movement to the right in FIG. 1). .)

  The exciting coil 26 is formed by winding a litz wire bundled with fine wires on a coil guide 36 disposed so as to cover a part of the outer peripheral surface of the fixing roller 20 (heat generating member) having a heat generating layer (FIG. 2). (It can also refer to FIG. 4). The exciting coil 26 facing the fixing roller 20 generates a magnetic flux, and the heat generation layer of the fixing roller 20 is electromagnetically heated by the magnetic flux.

A plurality of pairs of degaussing coils 27A to 27C are arranged in parallel at both ends in the width direction so as to face the exciting coil 26 (see also FIG. 4). The degaussing coils 27 </ b> A to 27 </ b> C generate a magnetic flux in a direction that cancels the magnetic flux generated by the exciting coil 26 at both ends in the width direction.
Specifically, as shown in FIG. 3A, when the changeover switch of the switching circuit 60 is opened (when the degaussing coils 27A to 27C do not operate), the magnetic flux generated from the exciting coil 26 (indicated by the bold arrows in the figure). In other words, a magnetic circuit that passes through the heat generating layer 21 of the fixing roller 20 is formed. Therefore, an induced current flows through the heat generating layer, and the heat generating layer generates heat due to Joule heat.
On the other hand, as shown in FIG. 3B, when the changeover switch of the switching circuit 60 is closed (when some or all of the plural pairs of degaussing coils 27A to 27C operate), the exciting coil The magnetic flux generated by the magnetic flux 26 (shown by a thick arrow in the figure) is canceled out by the magnetic flux generated by the degaussing coils 27A to 27C (shown by the thick broken arrow in the figure) to become a very weak magnetic flux. In this way, the magnetic flux that heats the heat generating layer becomes very weak, and the heating amount of the fixing roller 20 can be reduced at positions facing the degaussing coils 27A to 27C (both ends in the width direction).
In addition, although illustration is abbreviate | omitted, the switching circuit 60 is each installed independently with respect to the 1st degaussing coil 27A, the 2nd degaussing coil 27B, and the 3rd degaussing coil 27C. In each of the three pairs of degaussing coils 27 </ b> A to 27 </ b> C, the energization amount is controlled by changing a ratio (duty [%]) of energization on / off in a predetermined time period by the switching circuit 60.

In the present embodiment, referring to FIG. 4, three pairs of degaussing coils 27A to 27C correspond to the B4 size, A4 size (or B5 size), and postcard size recording media P in the width direction (FIG. 4 in the horizontal direction). Then, the heating range in the width direction of the heat generating layer is varied by the three pairs of degaussing coils 27A to 27C in correspondence with the sheet passing areas of a plurality of types of recording media P having different sizes. Specifically, when an A3 size recording medium P (A3 length (hereinafter, “vertical” is simply referred to as “T”)) is passed in the vertical direction, all of the three pairs of degaussing coils 27A to 27C are used. When the changeover switch is opened and the B4 size recording medium P (B4T) is passed in the vertical direction, only the changeover switch of the first degaussing coil 27A is closed, and the A4 size recording medium P (A4T) is When the paper is passed in the direction, the changeover switch of the first degaussing coil 27A and the second degaussing coil 27B is closed, and when the postcard size recording medium P (H) is passed, three pairs of the degaussing coils 27A. All the changeover switches of ˜27C are closed.
Here, since the dimensional difference between the B5 size and the A4 size is relatively small, in the present embodiment, when the B5 size recording medium P (B5T) is passed in the vertical direction, the A4 size recording is performed. Similarly to the case where the medium P (A4T) is passed in the vertical direction, the changeover switches of the first degaussing coil 27A and the second degaussing coil 27B are closed. In the present embodiment, a demagnetizing coil used when a B5 size recording medium P (B5T) is passed in the vertical direction is used, and an A4 size recording medium P (A4T) is passed in the vertical direction. Although it is shared with the degaussing coil used in the case, a degaussing coil can be additionally provided for the B5 size.

In this way, the energization of the three pairs of degaussing coils 27A to 27C is changed depending on the paper size of the recording medium P to be passed. Here, in the present embodiment, as a method of detecting the paper size of the recording medium P, a method of detecting the temperature distribution in the width direction of the pressure roller 30 and indirectly determining the paper size is used.
Specifically, a plurality of thermistors 40A to 40D as temperature detecting means are arranged in the width direction so as to face (contact) the pressure roller 30 in accordance with the end positions of the paper sizes of various recording media P. Yes. More specifically, the first thermistor 40A (first temperature detecting means) is arranged in the center, and the second to fourth thermistors 40B are provided at positions corresponding to the first to third demagnetizing coils 27A to 27C, respectively. ˜40D (second temperature detecting means) is arranged. The temperature distribution in the width direction of the pressure roller 30 is detected by these four thermistors 40A to 40D (the temperature distribution in the width direction of the fixing roller 20 is indirectly detected). In the paper passing area, the heat of the pressure roller 30 is taken away by the recording medium P and the fixing roller 20, and in the non-paper passing area, the temperature of the pressure roller 30 is maintained higher than that in the paper passing area. Based on the temperature distribution in the width direction of the pressure roller 30, the paper size of the recording medium P being passed can be determined. Then, the degaussing coil to be energized and its energization amount are determined according to the detected temperature information (temperature distribution).

As described above, in the present embodiment, the contact thermistors 40A to 40D are not installed in the fixing roller 20 but the contact thermistors 40A to 40D are installed in the pressure roller 30 to control the demagnetizing coil and the energization amount. Therefore, the problem that the contact mark of the contact thermistor formed on the surface of the fixing roller 20 is generated on the output image (fixed image) is suppressed.
Further, many members such as the induction heating unit 25, the spur 42, and the separation plate 43 are densely arranged around the fixing roller 20, and it is difficult to secure a space for installing a plurality of temperature sensors. On the other hand, in the present embodiment, a plurality of thermistors 40A to 40D are installed on the pressure roller 30 with relatively few members disposed around without restriction of installation space.
Further, since the energization amount of the demagnetizing coil is controlled by determining the temperature rise in the non-sheet passing area using the plurality of thermistors 40A to 40D, the temperature rise in the non-sheet passing area is erroneously detected, and the fixing roller An excessive temperature rise occurs in the non-sheet passing area of 20 (or pressure roller 30), or a temperature drop occurs at the end of the sheet passing area of fixing roller 20 (or pressure roller 30). Can be suppressed.
In this embodiment, thermistors 40A to 40D (contact type temperature detection sensors) are used as the temperature detection sensors for detecting the temperature distribution, but non-contact type temperatures such as a thermopile are used as the temperature detection sensors for detecting the temperature distribution. A detection sensor can also be used.

Here, in the present embodiment, as shown in FIG. 4B, the three pairs of demagnetizing coils 27A to 27C are arranged at at least two height positions having different facing distances from the exciting coil 26. . Specifically, the three pairs of degaussing coils 27 </ b> A to 27 </ b> C are alternately arranged at two height positions so that the facing distance between adjacent degaussing coils (the facing distance to the excitation coil 26) is different. Specifically, the second demagnetizing coil 27B is disposed at a height position close to the exciting coil 26, and the first demagnetizing coil 27A and the third degaussing coil 27C (demagnetizing coils adjacent to the second degaussing coil 27B). Is disposed at a height position away from the exciting coil 26.
In the present embodiment, the opposing distance between the second degaussing coil 27B and the exciting coil 26 is set to about 2 mm, and the opposing distance between the first degaussing coil 27A (or the third degaussing coil 27C) and the exciting coil 26 is It is set to about 5 mm.

  Further, the three pairs of degaussing coils 27 </ b> A to 27 </ b> C are disposed so that adjacent degaussing coils partially overlap when viewed from above. That is, referring to FIG. 4A, the inner portion of the first degaussing coil 27A on the inner side (width direction center portion) is located above the outer portion of the second degaussing coil 27B on the outer side (width direction end portion side). It is arranged so as to overlap (upward in the direction perpendicular to the paper surface of FIG. 4A). Similarly, the portion of the third degaussing coil 27C on the loop outer side (width direction end portion side) is arranged to overlap the portion of the second degaussing coil 27B on the loop inner side (width side central portion side). .

  With such a configuration, the induction heating unit 25 becomes large in the height direction (the direction perpendicular to the paper surface in FIG. 4A), and the demagnetizing ability at the boundary portion between adjacent degaussing coils is insufficient. Defects that become are suppressed. Further, since the three pairs of degaussing coils 27A to 27C are arranged such that a part of the adjacent degaussing coils overlap when viewed from above, the center cores 28 installed in the loops of the adjacent degaussing coils , And the temperature distribution in the width direction of the fixing roller 20 is made uniform.

Referring to FIGS. 2 and 4A, the plurality of cores 28, 29, and 35 are made of a ferromagnetic material such as ferrite (relative permeability is about 2500), and the exciting coil 26 and the demagnetizing coil 27A. This is for controlling the magnetic path (which is a path in which magnetic flux is formed) by ˜27C to form an efficient magnetic flux toward the heat generating layer of the fixing roller 20. The plurality of cores includes a plurality of center cores 28, a plurality of arch cores 29, and two side cores 35.
The coil guide 36 is made of a heat resistant resin material or the like, and holds the exciting coil 26 and the degaussing coils 27 </ b> A to 27 </ b> C on the side facing the fixing roller 20.

Here, in the present embodiment, referring to FIG. 4A, the center core 28 disposed in the loop of the three pairs of degaussing coils 27A to 27C among the plurality of center cores 28 is arranged in the width direction. Adjacent portions of the three pairs of demagnetizing coils 27A to 27C with respect to the width direction are arranged so that a part of the adjacent center cores 28 overlap when viewed from the orthogonal direction (the short direction in FIG. 4A). It is formed so as to be inclined. Specifically, as shown in FIG. 4A, when viewed from above, the first demagnetizing coil 27A and the center core 28 installed in the loop are formed in a substantially triangular shape, and the second demagnetizing coil 27B and the third demagnetizing coil 27B The degaussing coil 27C and the center core 28 installed in those loops are formed in a substantially parallelogram.
As described above, even if there is a gap between the center cores 28 disposed in the adjacent demagnetizing coils, a part of the adjacent center cores 28 overlaps when viewed from the direction orthogonal to the width direction. Therefore, the effect of efficiently controlling the magnetic path by the center core 28 is uniformly exhibited over the width direction. Therefore, the demagnetization by the demagnetizing coils 27A to 27C is further uniformly performed in the width direction, and the temperature distribution in the width direction in the sheet passing area of the fixing roller 20 (heating member) is further uniformized.

The fixing device 19 configured in this way operates as follows during a normal image forming process.
The fixing roller 20 is driven to rotate counterclockwise in FIG. 2 by a drive motor (not shown), and the pressure roller 30 is rotated clockwise accordingly. The sleeve layer 21 (heat generation layer) of the fixing roller 20 is heated by the magnetic flux generated from the induction heating unit 25 (excitation coil 26) at a position facing the induction heating unit 25.

  Specifically, the oscillation circuit passes a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) whose frequency is variable to the excitation coil 26, so The magnetic field lines are formed so as to alternately switch in both directions toward the sleeve layer 21 of the fixing roller 20. By forming an alternating magnetic field in this manner, an eddy current is generated in the heat generating layer of the sleeve layer 21, and the heat generating layer generates Joule heat due to its electric resistance and is induction-heated. Thus, the sleeve layer 21 (fixing roller 20) is heated by induction heating of its own heat generation layer.

Thereafter, the surface of the fixing roller 20 heated by the induction heating unit 25 reaches a contact portion (nip portion) with the pressure roller 30. Then, the toner image T (toner) on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is sent between the fixing roller 20 and the pressure roller 30 while being guided by the entrance guide plate 41 (or the spur 42). (The movement in the transport direction of the arrow Y1.) The toner image T is fixed on the recording medium P by the heat received from the fixing roller 20 and the pressure received from the pressure roller 30, and the recording medium P is sent out between the fixing roller 20 and the pressure roller 30 ( This is the movement in the transport direction of the arrow Y2.)
The surface of the fixing roller 20 that has passed through the nip portion then reaches the position facing the induction heating unit 25 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

Hereinafter, the configuration and operation of the fixing device 19 that are characteristic of the present embodiment will be described in more detail.
As described above, in the present embodiment, based on the detection results of the plurality of thermistors 40A to 40D (temperature detection means) that detect the surface temperature of the pressure roller 30, a plurality of pairs of degaussing coils 27A to 27C are detected. The energization amount is controlled.

FIG. 5 is a flowchart showing control of the degaussing coils 27A to 27C based on the detection results of the thermistors 40A to 40D (temperature sensors).
As shown in FIG. 5, when the recording medium P is started to pass (steps S1 and S2), after a predetermined time has elapsed, the second thermistor 40B (the pressure roller corresponding to the position of the third demagnetizing coil 27C). 30 is a first temperature detecting means for detecting the temperature of the first thermistor 40 </ b> A (the center of the pressure roller 30 in the width direction). It is determined whether the temperature difference between the detected temperature and the detected temperature is equal to or greater than a predetermined value A (in this embodiment, it is set to 10 deg) (step S3).
As a result, if it is determined that the detected temperature of the second thermistor 40B (second temperature sensor) is greater than the detected temperature of the first thermistor 40A (first temperature sensor) by a predetermined value A or higher, Assuming that the temperature distribution in the width direction of the roller 30 is as shown by the solid line graph Q1 in FIG. 6, energization of all the three pairs of degaussing coils 27A to 27C is started (step S4). That is, it is assumed that small-size paper (in this embodiment, a postcard-size recording medium P) is continuously passed, and three pairs of demagnetizing coils 27A to 27C disposed in the non-sheet passing area. The demagnetization operation is performed for all of the above, preventing excessive temperature rise in the non-sheet passing region.
Thereafter, when it is confirmed that the continuous sheet feeding of the recording medium P is finished (step S5), this flow relating to the control of the degaussing coil is finished (step S6).

Here, in the energization control of the degaussing coils 27A to 27C in step S4, the temperature difference between the detected temperature of the second thermistor 40B and the detected temperature of the first thermistor 40A is determined, and the temperature difference is less than the predetermined value A. It is preferable to control so as not to energize the target pair of degaussing coils (the third degaussing coil 27C). That is, of the three pairs of degaussing coils 27A to 27C, the pair of third degaussing coils 27C closest to both ends in the width direction of the recording medium P that is continuously passed through are in contact with the central portion (paper passing area) in the width direction. On / off control is performed to reduce the temperature difference. In other words, the position in the width direction of the pressure roller 30 corresponding to the position of the third degaussing coil 27C is controlled so as to approach the target temperature together with the central portion (paper passing area) in the width direction. As a result, even when a part of the range in the width direction of the pressure roller 30 corresponding to the position of the third degaussing coil 27C is applied to the sheet passing area, the fixing temperature in that area is the target of the sheet passing area. Since the temperature is controlled to be close to the target temperature similarly to the central portion in the width direction without greatly lowering the temperature, a problem that fixing failure occurs at both ends of the output image (fixed image) is suppressed.
In order to solve the same problem, the on / off control of the third degaussing coil 27C is performed so that the detected temperature of the second thermistor 40B approaches a preset target temperature (for example, 180 ° C.). You can also do it. Specifically, when the detected temperature of the second thermistor 40B is equal to or higher than the target temperature B, the duty of the third degaussing coil 27C is set to 100%, and when the detected temperature of the second thermistor 40B is lower than the target temperature B, the third degaussing coil. It is possible to perform control such that the duty of 27C is set to 0%.

On the other hand, when it is determined in step S3 that the detected temperature of the second thermistor 40B (second temperature sensor) is not higher than the detected temperature of the first thermistor 40A (first temperature sensor) by a predetermined value A or more. Includes a detection temperature of the third thermistor 40C (second temperature detection means for detecting the temperature in the width direction position of the pressure roller 30 corresponding to the position of the second degaussing coil 27B) and the first thermistor 40A ( The temperature difference between the detected temperature of the pressure roller 30 and the detected temperature at the center in the width direction is set to a predetermined value A (in this embodiment, 10 deg). It is determined whether this is the case (step S7).
As a result, if it is determined that the detected temperature of the third thermistor 40C (third temperature sensor) is higher than the detected temperature of the first thermistor 40A (first temperature sensor) by a predetermined value A or higher, Assuming that the temperature distribution in the width direction of the roller 30 is as shown by a broken line graph Q2 in FIG. 6, energization of the first degaussing coil 27A and the second degaussing coil 27B among the three pairs of degaussing coils 27A to 27C is started. (Step S8). That is, it is assumed that medium-size paper (in this embodiment, the recording medium P is A4T size or B5T size) is continuously passed, and two pairs of papers arranged in the non-sheet-passing area are provided. The degaussing coils 27A and 27B are degaussed to prevent excessive temperature rise in the non-sheet passing area.
Thereafter, when it is confirmed that the continuous sheet feeding of the recording medium P is finished (step S5), this flow relating to the control of the degaussing coil is finished (step S6).

  Here, also in the energization control of the degaussing coils 27A and 27B in step S8, the temperature difference between the detected temperature of the third thermistor 40C and the detected temperature of the first thermistor 40A is determined, and the temperature difference is less than the predetermined value A. Then, it is preferable to control so as not to energize the pair of degaussing coils (the second degaussing coil 27B). That is, of the three pairs of degaussing coils 27A to 27C, the pair of second degaussing coils 27B closest to the both ends in the width direction of the recording medium P that is continuously passed through are in contact with the center in the width direction (paper passing area). On / off control is performed to reduce the temperature difference. Thus, even when a part of the width direction range of the pressure roller 30 corresponding to the position of the second degaussing coil 27B is applied to the sheet passing area, the fixing temperature in that area is the target of the sheet passing area. Since the temperature is controlled to be close to the target temperature similarly to the central portion in the width direction without greatly lowering the temperature, a problem that fixing failure occurs at both ends of the output image (fixed image) is suppressed.

On the other hand, when it is determined in step S7 that the detected temperature of the third thermistor 40C (third temperature sensor) is not higher than the detected temperature of the first thermistor 40A (first temperature sensor) by a predetermined value A or more. Includes a detection temperature of the fourth thermistor 40D (second temperature detection means for detecting the temperature of the position in the width direction of the pressure roller 30 corresponding to the position of the first degaussing coil 27A) and the first thermistor 40A ( The temperature difference between the detected temperature of the pressure roller 30 and the detected temperature at the center in the width direction is set to a predetermined value A (in this embodiment, 10 deg). It is determined whether this is the case (step S9).
As a result, if it is determined that the detected temperature of the fourth thermistor 40D (fourth temperature sensor) is higher than the detected temperature of the first thermistor 40A (first temperature sensor) by a predetermined value A or higher, Assuming that the temperature distribution in the width direction of the roller 30 is as indicated by a one-dot chain line graph Q3 in FIG. 6, energization of only the first degaussing coil 27A among the three pairs of degaussing coils 27A to 27C is started (step S10). . That is, it is assumed that a large size paper (in this embodiment, a B4T size recording medium P) is continuously passed, and the pair of degaussing coils 27A disposed in the non-sheet passing area is degaussed. An operation is performed to prevent overheating of the non-sheet passing area.
Thereafter, when it is confirmed that the continuous sheet feeding of the recording medium P is finished (step S5), this flow relating to the control of the degaussing coil is finished (step S6).

  Here, also in the energization control of the degaussing coil 27A in step S10, the temperature difference between the detected temperature of the fourth thermistor 40D and the detected temperature of the first thermistor 40A is determined, and the temperature difference becomes less than the predetermined value A. It is preferable to control so as not to energize the target pair of degaussing coils (the first degaussing coil 27A). That is, among the three pairs of degaussing coils 27A to 27C, the temperature of the pair of first degaussing coils 27A closest to the both ends in the width direction of the recording medium P that is continuously passed through is the temperature with respect to the center in the width direction (paper passing area) On / off control is performed to reduce the difference. As a result, even when a part of the width direction range of the pressure roller 30 corresponding to the position of the first degaussing coil 27A is applied to the sheet passing area, the fixing temperature in that area is the target of the sheet passing area. Since the temperature is controlled to be close to the target temperature similarly to the central portion in the width direction without greatly lowering the temperature, a problem that fixing failure occurs at both ends of the output image (fixed image) is suppressed.

On the other hand, when it is determined in step S9 that the detected temperature of the fourth thermistor 40D (fourth temperature sensor) is not higher than the detected temperature of the first thermistor 40A (first temperature sensor) by a predetermined value A or more. Assuming that the temperature distribution in the width direction of the pressure roller 30 is substantially uniform, all the energizations of the three pairs of degaussing coils 27A to 27C are turned off (step S11). That is, the maximum size paper (in this embodiment, the A3T size recording medium P) is continuously passed, and almost the entire area in the width direction of the pressure roller 30 is the paper passing area, and the both end portions. The demagnetization operation by the degaussing coils 27A to 27C is not performed on the assumption that no excessive temperature rise has occurred.
Thereafter, when it is confirmed that the continuous sheet feeding of the recording medium P is finished (step S5), this flow relating to the control of the degaussing coil is finished (step S6).

Here, in the control of the demagnetizing coils 27A to 27C described above, it is preferable to calculate and control the energization amount of the degaussing coil by proportional control, differential control, integral control, or control combining two or more thereof. As a result, the temperature ripple is reduced and the temperature of the non-sheet passing region is increased to the target temperature, compared with the case where the on / off control is performed to bring the temperature of the non-sheet passing region in the pressure roller 30 closer to the target temperature. It can be approached by responsiveness.
Specifically, when the third degaussing coil 27C is controlled by combining all of proportional control, differential control, and integral control in step S3 of FIG. 5, the current detected temperature of the second thermistor 40B is M0, and one control cycle If the detected temperature of the previous second thermistor 40B is M1, and the target temperature of the pressure roller 30 is N, the duty D of energization of the third degaussing coil 27C can be obtained by the following control equation.
D = Kp (M0−N) + Kd (M0−M1) + Ki · ∫ (M0−N) dt
In the above equation, Kp, Kd, and Ki are parameter values. In this embodiment, Kp is set to 100, Kd is set to 10, and Ki is set to 10. The target temperature N is set to 180 ° C.

The above-described control of the energization amount to the degaussing coils 27A to 27C is performed when a predetermined number or more of the recording media P are continuously fed, and for a predetermined time after the continuous feeding of the recording media P is started. It is preferable that the process is started after the elapse of time and stopped when the continuous sheet feeding of the recording medium P is completed.
Specifically, when a command for continuously passing a predetermined number of recording media P is input to the control unit of the apparatus main body 1, the degaussing coil after a predetermined time has elapsed since the continuous feeding of the recording media P was started. The control of the energization amount to 27A to 27C is started. Then, when a signal indicating the end of continuous paper feeding of the recording medium P is input, control of the energization amount to the degaussing coils 27A to 27C is stopped.
By performing such control, the energization amount to the degaussing coils 27A to 27C is controlled at times other than the time of passing paper, such as during warm-up and standby, and the rise of the fixing roller 20 and the pressure roller 30 is delayed. Or a problem in which the amount of power supplied to the degaussing coils 27A to 27C is controlled in a state in which an excessive temperature rise in the non-sheet passing region does not occur.

  As described above, in this embodiment, the demagnetization is based on the detection results of the plurality of thermistors 40A to 40D (temperature detection means) that detect the temperature of the pressure roller 30 (pressure member) at a plurality of positions in the width direction. Since the energization amount of the coils 27A to 27C is controlled, the types of thermistors 40A to 40 and the degree of freedom of installation positions are high, and the non-sheet passing region in the fixing roller 20 (fixing member) by demagnetization by the demagnetization coils 27A to 27C. It is possible to efficiently and reliably suppress the excessive temperature rise.

In the present embodiment, the present invention is applied to a fixing device using the fixing roller 20 as the fixing member and the pressure roller 30 as the pressure member. However, a fixing belt or a fixing film is used as the fixing member. The present invention can also be applied to an electromagnetic induction heating type fixing device or an electromagnetic induction heating type fixing device using a pressure belt or a pressure pad as a pressure member.
In the present embodiment, the present invention is applied to a fixing device using a fixing member (fixing roller 20) as a heat generating member that is induction-heated by the induction heating unit 25. However, the fixing member is heated as the heat generating member. The present invention can also be applied to a fixing device using a heating member. For example, a heating roller (heat generating member) that stretches a fixing belt as a fixing member is provided with a heat generating layer, and the fixing roller indirectly heats the fixing belt by induction heating the induction roller 25. The present invention can be applied even to an apparatus.
In these cases, the same effect as in the present embodiment can be obtained.

In the present embodiment, the present invention is applied to the fixing device 19 in which three pairs of demagnetizing coils 27A to 27C are installed. The present invention can be applied. Further, the present invention can naturally be applied to a fixing device in which two pairs or four or more pairs of degaussing coils are installed.
In these cases, the same effect as in the present embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 image forming apparatus body (apparatus body),
19 fixing device,
20 fixing roller (fixing member, heating member),
25 induction heating unit,
26 Excitation coil,
27A-27C degaussing coil,
30 pressure roller (pressure member),
40A-40D thermistor (temperature detection means, temperature sensor),
60 Switching circuit.

JP 2008-40176 A JP 2005-321642 A JP 2007-226126 A

Claims (6)

A fixing member that melts and fixes the toner image to the recording medium;
A non-contact temperature sensor for detecting the temperature of the surface of the fixing member in a non-contact manner at a center position in the width direction;
A pressure member that forms a nip portion to which the recording medium is conveyed in pressure contact with the fixing member;
A plurality of temperature detecting means for detecting the temperature of the pressure member at a plurality of locations in the width direction;
A heating member having a heating layer for heating the fixing member;
An exciting coil that opposes the heat generating member and generates a magnetic flux to inductively heat the heat generating layer with the magnetic flux;
A pair or a plurality of pairs of degaussing coils that are disposed at both ends in the width direction so as to face the excitation coil, and that generate magnetic fluxes at both ends in the width direction in a direction that cancels the magnetic flux generated by the excitation coil,
With
The excitation coil is controlled so that the heating amount of the heat generating layer is adjusted based on the detection result of the non-contact temperature sensor,
The plurality of temperature detection means correspond to the first temperature detection means for detecting the temperature of the central portion in the width direction of the pressure member and the position in the width direction of at least one of the pair or plural pairs of demagnetization coils. One or a plurality of second temperature detection means for detecting the temperature of the end portion in the width direction of the pressure member, and
The amount of energization of the pair or plural pairs of demagnetizing coils is controlled based on the detection results of the first temperature detection means and the second temperature detection means,
A pair of degaussing coils corresponding to the second temperature detecting means when the temperature difference between the temperature detected by the first temperature detecting means and the temperature detected by the second temperature detecting means becomes a predetermined value or more. A fixing device characterized by starting to energize the battery.   A pair of degaussing coils corresponding to the second temperature detection means when the temperature difference between the temperature detected by the first temperature detection means and the temperature detected by the second temperature detection means becomes less than a predetermined value. The fixing device according to claim 1, wherein power is not supplied to the fixing device. A switching circuit for turning on and off the energization of the pair or plural pairs of degaussing coils,
The energization amount of the pair or plural pairs of degaussing coils is controlled by varying a ratio of time for energization to be turned on and off in a predetermined time period by the switching circuit. The fixing device according to 1.   The control of the energization amount to the pair or plural pairs of degaussing coils is a case where a predetermined number or more of recording media are continuously fed, and a predetermined time has elapsed since the continuous feeding of the recording media was started. 4. The fixing device according to claim 1, wherein the fixing device is started later and stopped when the continuous sheet passing of the recording medium is finished.   The pair or the plurality of pairs of degaussing coils are arranged so that a heating range in a width direction of the heat generating layer can be changed corresponding to a sheet passing area of a plurality of types of recording media having different sizes. The fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1.

Images