JP2013041191A - Fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that reliably reduces failure in which a recording medium is wound around a pressing rotation body without smearing a recording medium passing through a nip part with toner, and an image forming apparatus.SOLUTION: When temperature detected by temperature detection means 46 for detecting surface temperature of a pressing rotation body 30 reaches or exceeds a predetermined value, adjustment means 75, and 80 to 83 adjust the amount of heat transferred from a fixing member 20 to the pressing rotation member 30 to decrease the amount of heat in a state where at least the fixing member 20 of the fixing member 20 and the pressing rotation body is driven to rotate and a recording medium P is not conveyed to a nip part.

Description

  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.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing member and a pressure rotating body are pressed to form a nip portion, and a fixing process is performed while a recording medium is conveyed to the nip portion. Devices are widely used (see, for example, Patent Documents 1 and 2).

In such a fixing device, there is a problem that a recording medium to be separated from the fixing member and the pressure rotating body after the fixing step is wound around the pressure rotating body during double-sided printing. Such a problem occurs when the toner image already fixed on the front side of the recording medium is melted again by receiving heat directly from the pressure rotator during the fixing process to the back side of the recording medium (or This is because the adhesiveness of the recording medium to the pressure rotator increases.
In order to prevent the recording medium from being wound around the pressure rotator, a separation guide plate and a separation claw are installed on the outlet side of the nip portion so as to face the pressure rotator and pressurization is performed. A technique for forcibly separating a recording medium to be wound around a rotating body from a pressure rotating body is generally used (see, for example, Patent Documents 1 and 2).

  In the conventional fixing device described above, the toner gradually adheres and accumulates on the separation guide plate and the separation claws installed so as to face the pressure rotator over time, and the nip portion is caused by the adhered and accumulated toner. There is a problem that the recording medium passing through the recording medium is soiled.

In addition, when double-sided printing is performed by continuous paper passing, the surface temperature of the pressure rotator is further increased by heat transfer from the fixing member, and the toner image already fixed on the front surface of the recording medium is In some cases, the recording medium is remelted by receiving high heat from the pressure rotator, and the recording medium sticks to the pressure rotator with a considerably strong force. In such a case, even if a separation guide plate or separation claw is provided, the recording medium to be wound around the pressure rotator may not be sufficiently separated from the pressure rotator. It was.
Such a problem is that when a color image is printed on both sides by continuous paper passing, the image area ratio of the toner image formed on the recording medium is increased, and the adhesiveness when they are re-melted is also increased. Therefore, it was something that could not be ignored.
Further, in the fixing device of the type in which the fixing member is heated by electromagnetic induction, the temperature rise performance of the pressure rotator by heat transfer from the fixing member is enhanced by the high heating efficiency of the fixing member, Since the toner image is likely to be remelted, it is not particularly negligible.

  The present invention has been made to solve the above-described problems. The recording medium passing through the nip portion is not contaminated with toner, and the problem that the recording medium is wound around the pressure rotating body is reliably reduced. Another object of the present invention is to provide a fixing device and an image forming apparatus.

  According to a first aspect of the present invention, there is provided a fixing device that is heated by a heating unit and that rotates in a predetermined direction to heat and melt a toner image and fix the toner image on a recording medium, and the fixing member. A pressure rotator that forms a nip portion to which the recording medium is conveyed in pressure contact, a temperature detection means that detects a surface temperature of the pressure rotator, and a temperature detected by the temperature detection means is a predetermined value or more When at least the fixing member of the fixing member and the pressure rotator is rotationally driven and the recording medium is not conveyed to the nip portion, the addition from the fixing member is performed. Adjusting means for adjusting the amount of heat transferred toward the pressure rotating body to be low.

  In the present invention, when the surface temperature of the pressure rotator is a predetermined value or more, the pressure is applied from the fixing member at least when the fixing member is rotationally driven and the recording medium is not conveyed to the nip portion. The amount of heat transferred toward the rotating body is adjusted to be low. Accordingly, it is possible to provide a fixing device and an image forming apparatus in which the recording medium passing through the nip portion is not contaminated with toner, and the trouble that the recording medium is wound around the pressure rotating body is surely reduced. it can.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a fixing device. It is a schematic diagram which shows the state by which a nip width is varied by a moving mechanism. It is a graph which shows the change of the surface temperature of a pressure roller. It is a flowchart which shows another control at the time of color duplex printing mode. It is a flowchart which shows another control in the color double-sided printing mode.

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 onto which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 18 (image forming unit). 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 (timing roller) 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.

Note that the above-described transport procedure of the recording medium P is the case where an image is formed on one side of the recording medium P (during single-sided printing).
On the other hand, when double-sided printing is performed on one or a plurality of recording media P (when the double-sided printing mode is performed), the transport procedure from the paper supply unit 7 to the fixing device 19 is as follows. The recording medium P (after printing on the front side) after passing through the fixing device 19 is performed in the same manner as described above, and the double-sided conveyance path K2 is moved by the movement of the switching claw (not shown). And then conveyed to the reversing unit 100. Then, the recording medium P is reversely conveyed from the reversing unit 100 so that the front and rear ends thereof are reversed, and is guided again to the conveyance path K1 by the movement of a switching claw (not shown), and the secondary transfer nip (image forming unit). ) Again. Then, when printing is performed on the back surface of the recording medium P at the secondary transfer nip (image forming unit), it is discharged out of the apparatus main body by the discharge roller 9 through a fixing process at the position of the fixing device 19. Is done.

  In the present embodiment, double-sided printing is performed by the interleaf method. The interleaf system is a double-sided conveyance path such as a reversing unit between the front side image formation and the back side image formation of the recording medium P when performing double-sided printing by continuous paper passing. In this method, an image is formed on another recording medium P in a state of temporarily waiting.

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 generation unit) as a heating unit, a fixing roller 20 as a fixing member facing the induction heating unit 25, and a pressure rotation that presses against the fixing roller 20. A pressure roller 30 as a body, a first temperature sensor 45 for detecting the surface temperature of the fixing roller 20, a second temperature sensor 46 as a temperature detecting means for detecting the surface temperature of the pressure roller 30, and a nip width N at the nip portion. The moving mechanism 80 to 83, the inlet guide plate 41, the separation plate 43, the guide member 50, and the like are configured.

Here, the fixing roller 20 as a fixing member is formed 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 configured as described above, the heat generating layer of the sleeve layer 21 is electromagnetically heated by the magnetic flux generated from 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 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.
Further, a first temperature sensor 45 such as a thermopile (non-contact type temperature sensor) or a thermistor (contact type temperature sensor) is disposed at a position facing the fixing roller 20. The first temperature sensor 45 detects the temperature on the fixing roller 20 (fixing temperature). And based on the detection result by the 1st temperature sensor 45, the heating amount by the induction heating part 25 is adjusted.

Although not shown, the fixing roller 20 is provided with a gear that meshes with the drive gear of the drive motor 75 at the shaft portion at the end in the width direction. Then, the driving force is transmitted from the driving motor 75, and the fixing roller 20 is rotationally driven in the counterclockwise direction of FIG. As the fixing roller 20 rotates, the pressure roller 30 is rotated in the clockwise direction by the frictional resistance at the nip portion.
Here, the drive motor 75 functions as a rotation speed variable unit that varies the rotation speed of the fixing roller 20 and the pressure roller 30. Specifically, the drive motor 75 (rotational speed varying means) is a variable speed motor, and can vary the rotational speed of the fixing roller 20 to an arbitrary value. Then, by changing the rotation speed of the fixing roller 20, the rotation speed of the pressure roller 30 that is driven to rotate is also changed. In the present embodiment, during normal times, the rotation speeds of the fixing roller 20 and the pressure roller 30 are set so that the linear velocity at the nip portion is 200 mm / second.

  Referring to FIG. 2, a pressure roller 30 as a pressure rotator includes a core metal roller 33 made of aluminum, copper or the like, an elastic layer 32 made of silicone rubber or the like, and a release layer 31 made of PFA or the like. It is formed. The elastic layer 32 of the pressure roller 30 is formed to have a thickness of 1 to 5 mm. The release layer 31 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.

Here, 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.

  Further, a second temperature sensor 46 as a temperature detecting means such as a thermopile (non-contact type temperature sensor) or a thermistor (contact type temperature sensor) is disposed at a position facing the pressure roller 30 (pressure rotary member). Has been. Then, the surface temperature of the pressure roller 30 (pressure roller temperature) is detected by the second temperature sensor 46. Based on the detection result of the second temperature sensor 46, the amount of heat transferred from the fixing roller 20 toward the pressure roller 30 when not passing is adjusted by the adjusting means. explain in detail.

Here, referring to FIG. 2, in fixing device 19 in the present embodiment, nip width N (nip pressure) in the nip portion is increased or decreased by moving pressure roller 30 relative to fixing roller 20. Moving mechanisms 80 to 83 are installed.
Specifically, the moving mechanism includes a pressure lever 81, a cam 82, a tension spring 83, a stepping motor 80, and the like.
The pressure lever 81 is installed so as to be rotatable about a support shaft 81 a fixed to the side plate of the apparatus 19. Further, a shaft portion (ball bearing is installed) of the pressure roller 30 (core metal roller 33) is brought into contact with the central portion of the pressure lever 81, and one end side of the contact position is pulled toward the end. A spring 83 is connected. The other end of the tension spring 83 connected to the pressure lever 81 is connected to the frame of the device 19. Further, a cam 82 is in contact with one end side of the pressure lever 81.
The cam 82 has a rotating shaft 82a connected to the stepping motor 80 via a gear train. When the stepping motor 80 is driven, the cam 82 rotates about the rotation shaft 82a, so that the cam 82 is pushed against the urging force of the tension spring 83, and the pressure lever 81 is interlocked. It will turn. As a result, the nip width N between the fixing roller 20 and the pressure roller 30 (or the axial distance between the fixing roller 20 and the pressure roller 30) increases or decreases in conjunction with each other. The cam 82 is controlled in its rotational direction (angle) by pulse control of a stepping motor using an encoder connected to the rotary shaft 82a.

3A to 3C, in the present embodiment, outer peripheral surfaces of a plurality of cams 82 are formed so as to be variable to a plurality of nip widths N.
Specifically, FIG. 3A shows a state in which the posture in the rotational direction of the cam 82 is controlled so that the maximum nip width N1 is obtained when the normal fixing process is performed. Yes. FIG. 3B shows a case where the amount of heat transferred from the fixing roller 20 to the pressure roller 30 is reduced when the color duplex printing mode is performed, and the nip width N2 is smaller than the normal nip width N1. As shown, the posture of the cam 82 in the rotational direction is controlled. FIG. 3C shows a case where the amount of heat transfer from the fixing roller 20 to the pressure roller 30 is further reduced when the color double-sided printing mode is performed. The state in which the attitude of the cam 82 in the rotational direction is controlled so as to be completely separated (so that the nip width N becomes zero) is shown. When the rotation speed of the fixing roller 20 is varied by the drive motor 75 (rotational speed varying means) in the state shown in FIG. 3C (separated state), the pressure roller 30 is not driven to rotate, so the rotational speed is Even in such a case, it is assumed that the rotational speeds of the fixing roller 20 and the pressure roller 30 are varied by the drive motor 75 (rotational speed varying means).

  Referring to FIG. 2, the induction heating unit 25 includes a coil unit 26 (excitation coil), a core unit 27 (excitation coil core), a coil guide 28, and the like. The coil portion 26 is wound in the width direction (in the direction perpendicular to the paper surface of FIG. 2) by winding a litz wire bundled with thin wires on a coil guide 28 disposed so as to cover a part of the outer peripheral surface of the fixing roller 20. It is extended. The coil guide 28 is made of a resin material having high heat resistance and holds the coil portion 26 on the side facing the fixing roller 20. The core portion 27 is made of a ferromagnetic material such as ferrite (having a relative magnetic permeability of about 2500), and is used to form an efficient magnetic flux toward the heat generating layer of the fixing roller 20, and includes an arch core and a center core. It is composed of a side core and the like.

The fixing device 19 configured as described above operates as follows during normal operation.
The fixing roller 20 is driven to rotate counterclockwise in FIG. 2 by the drive motor 75, and the pressure roller 30 is rotated clockwise (driven rotation) 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 at a position facing the induction heating unit 25.

  Specifically, the oscillation circuit causes a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) to flow from the coil unit 26 to a coil unit 26 from a power supply unit (not shown) whose frequency is variable. 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 fed between the fixing roller 20 and the pressure roller 30 while being guided by the entrance guide plate 41 (arrow Y1). In the transport direction). 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.)
On the other hand, 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 which are characteristic in the present embodiment will be described in detail.
In the present embodiment, when the temperature (pressure roller temperature) detected by the second temperature sensor 46 (temperature detection means) is equal to or higher than a predetermined value, at least the fixing roller of the fixing roller 30 and the pressure roller 30. The amount of heat transferred from the fixing roller 20 to the pressure roller 30 in a state in which the recording medium P is not transported to the nip portion (when no paper is passed) in a state where the rotation of the roller 20 is driven ( The amount of heat transfer is adjusted by the adjusting means so as to be low. In the present embodiment, as an adjusting means for adjusting the amount of heat transfer from the fixing roller 20 to the pressure roller 30, a drive motor that functions as a rotation speed variable means for changing the rotation speed between the fixing roller 20 and the pressure roller 30. 75 and moving mechanisms 80 to 83 that vary the nip width N are used.

Specifically, the amount of heat transferred from the fixing roller 20 to the pressure roller 30 is reduced by reducing the rotation speed of the fixing roller 20 and the pressure roller 30 by the drive motor 75 (rotational speed variable means). It is adjusted to. This is because when the rotation speed of the fixing roller 20 decreases, the heat transfer amount per unit time transferred from the fixing roller 20 toward the pressure roller 30 decreases.
Further, by adjusting the nip width N by the moving mechanisms 80 to 83, the amount of heat transferred from the fixing roller 20 toward the pressure roller 30 is adjusted to be low. This is because as the nip width N decreases, the area of heat transferred from the fixing roller 20 to the pressure roller 30 (heat receiving area of the pressure roller 30) decreases.

FIG. 4 is a graph showing changes in the surface temperature of the pressure roller 30 when continuous paper feeding is performed.
In FIG. 4, a curve R1 shows a change in the pressure roller temperature when the nip width is set to N1 and the linear velocity of the fixing roller 20 is set to 200 mm / second (in the state of FIG. 3A). Curve R2 shows the change in pressure roller temperature when the nip width is set to N1 and the linear velocity of the fixing roller 20 is set to 100 mm / second, and the curve R3 is the fixing roller 20 with the nip width set to N1. 3 shows the change in pressure roller temperature when the linear velocity is set to 50 mm / second, and the curve R4 shows the nip width set to zero (in the separated state and in the state of FIG. 3C). A change in pressure roller temperature when the linear velocity of the fixing roller 20 is set to 50 mm / second is shown.
4 also shows that when the rotation speed of the fixing roller 20 (and the pressure roller 30) decreases, the amount of heat transfer from the fixing roller 20 toward the pressure roller 30 decreases, and the pressure roller 30 It can be seen that the temperature rise is reduced. Further, from comparison between the curve R3 and the curve R4, when the nip width N is reduced, the heat transfer amount from the fixing roller 20 toward the pressure roller 30 is reduced, and the temperature rise of the pressure roller 30 is reduced. Can also be estimated sufficiently.

In the present embodiment, as an adjustment unit that adjusts the amount of heat transfer from the fixing roller 20 to the pressure roller 30, a drive that functions as a rotation speed variable unit that varies the rotation speed of the fixing roller 20 and the pressure roller 30. Although both the motor 75 and the moving mechanisms 80 to 83 that vary the nip width N are used, only one of them can be used as the adjusting means.
Further, when the amount of heat transfer from the fixing roller 20 to the pressure roller 30 is reduced using the moving mechanisms 80 to 83, the pressure roller 30 in the pressure contact state may be changed to a separated state (FIG. 3 ( This is a change from the state of A) to the state of FIG. 3C.) The nip width N of the pressure roller 30 in the pressure contact state may be changed (from the state of FIG. 3A). This is a change to the state of FIG.

Here, in the present embodiment, when the color double-sided printing mode (a printing mode for forming a color image on both sides of the recording medium P) is performed, the fixing roller 20 to the pressure roller 30 at a predetermined timing. The drive motor 75 and the moving mechanisms 80 to 83 functioning as adjusting means are controlled so that the amount of heat transferred toward the head is reduced.
This is because, during color double-sided printing, toner images T for four colors are formed on the recording medium P, so the image area ratio on the recording medium P becomes particularly high and is already fixed on the front side of the recording medium P. When the toner image (a toner image facing the pressure roller 30) receives high heat from the pressure roller 30, the toner is remelted and the recording medium P is applied to the pressure roller 30 with a considerably strong force. It is because it becomes easy to adhere. In particular, when the color double-sided printing mode is performed by continuous paper feeding, the heat transfer amount by the fixing roller 20 is further increased, and thus the recording medium P is easily adhered to the pressure roller 30 with a stronger force.

On the other hand, in this embodiment, when color double-sided printing is performed, the control unit 70 controls the drive motor 75 so that the rotation speed of the fixing roller 20 is reduced, and the nip width N is reduced. Since the movement mechanisms 80 to 83 are controlled as described above (from the state of FIG. 3A to the state of FIG. 3B or FIG. 3C), the heat transfer from the fixing roller 20 is applied. The temperature rise of the pressure roller 30 can be reduced, and the recording medium P becomes difficult to adhere to the pressure roller 30. Therefore, the recording medium P on which color double-sided printing has been performed is separated cleanly from the pressure roller 30 even after the fixing process to the back surface, and a problem of winding around the pressure roller 30, and toner adhering and accumulating on the guide member 50. As a result, the problem of soiling the recording medium P is suppressed.
Note that such adjustment control by the adjusting means 75 and 80 to 83 is performed when the sheet is not passed (recording medium P) in order to avoid the influence on the fixed image due to the decrease in the rotation speed (linear speed) and the decrease in the nip width N. Is not passing through the nip portion). Further, the adjustment control is performed at least in a state where the fixing roller 20 is rotated in order to prevent a problem that the fixing roller 20 is locally heated by the induction heating unit 25 and overheated.

Here, in the present embodiment, when the color double-sided printing mode is performed by continuously feeding a plurality of recording media P (color double-sided printing mode by continuous paper feeding), the last one sheet before. The amount of heat transferred from the fixing roller 20 to the pressure roller 30 after the recording medium P to be passed passes through the nip portion and before the recording medium P to be passed last reaches the nip portion. It is also possible to control the drive motor 75 and the moving mechanisms 80 to 83 that function as adjusting means so as to be low.
This is because when the double-sided printing is performed by the interleaf method as in the image forming apparatus according to the present embodiment, the recording medium P that is passed one sheet before the last passes through the nip portion and is finally passed. The time until the recording medium P to be printed reaches the nip portion becomes longer, the amount of heat transfer from the fixing roller 20 toward the pressure roller 30 increases, and the temperature rise of the pressure roller 30 tends to increase. It is.

Specifically, as shown in FIG. 5, first, a signal for requesting the color duplex printing mode is received by the control unit 70 (steps S1 to S2), and a paper sensor (photosensor not shown) installed in the conveyance path is received. ), The recording medium P one sheet before the last (for example, when 50 continuous sheets are set, the recording medium P is passed through the 49th sheet) passes through the nip portion. Is detected (step S3), it is determined whether the pressure roller temperature detected by the second temperature sensor 46 is higher than a predetermined value (in this embodiment, set to 120 ° C.). (Step S4).
As a result, if it is determined that the pressure roller temperature is higher than the predetermined value, it is highly likely that the recording medium P is wound around the pressure roller 30, and the last recording medium P is passed through. In the meantime, the linear velocity of the fixing roller 20 is reduced from 200 mm / second to 40 mm / second, the pressure roller 30 is separated, and the fixing roller 20 is heated in that state, thereby applying pressure. The amount of heat transferred to the roller 30 is reduced (step S5). Then, with the temperature rise of the pressure roller 30 suppressed, the linear speed is returned to the normal time of 200 mm / second, the pressure roller 30 is returned to the pressure contact state, and the fixing roller 20 is heated in that state. The last recording medium P is guided to the nip portion, the fixing process is performed, and this flow is finished (steps S7 to S8).
On the other hand, if it is determined in step S4 that the pressure roller temperature is lower than the predetermined value, it is assumed that there is no problem that the recording medium P is wound around the pressure roller 30, and the linear velocity is set to normal. At the same time, the pressure roller 30 is maintained in pressure contact state, the last recording medium P is guided to the nip portion, the fixing process is performed, and this flow is finished (steps S6 to S8).

The control in the color double-sided printing mode is not limited to that shown in FIG. 5 and can be optimized according to the temperature rise of the pressure roller 30.
Specifically, the amount of heat transferred from the fixing roller 20 to the pressure roller 30 between the time when the request signal for performing the color duplex printing mode is received and the time when the color duplex printing mode is started is reduced. As described above, it is possible to control the drive motor 75 and the moving mechanisms 80 to 83 that function as the adjusting means.
Further, before the color double-sided printing mode is started, when the temperature of the pressure roller 30 is equal to or higher than a predetermined value, the drive motor 75 or the moving mechanism 80 to function as an adjusting unit until the temperature becomes lower than the predetermined value. 83 can also be controlled.
Further, when the adjustment means 75 and 80 to 83 are adjusted so that the amount of heat transferred from the fixing roller 20 to the pressure roller 30 is low, the target value of the surface temperature (fixing temperature) of the fixing roller 20 is reached. Can be controlled to be lower than the target value in the normal fixing process.

FIG. 6 is a flowchart summarizing these controls.
As shown in FIG. 6, when a signal (print signal) requesting printing is received by the control unit 70 (steps S11 to S12), it is determined whether the print signal is a color double-sided print mode signal. (Step S13).
As a result, when it is determined that the color double-sided printing mode is selected, it is further determined whether the pressure roller temperature detected by the second temperature sensor 46 is higher than a predetermined value (set to 120 ° C.). (Step S14).
As a result, when it is determined that the pressure roller temperature is higher than the predetermined value, it is highly possible that the recording medium P is wound around the pressure roller 30, and the linear velocity is changed from 200 mm / second to 40 mm. The pressure roller 30 is separated, and the fixing roller 20 is heated in a state where the target value of the fixing temperature is set to be 10 ° C. lower than the normal temperature. The amount of heat transfer is reduced (step S15). Thereafter, when it is determined in step S16 that the pressure roller temperature is lower than a predetermined value (set to 120 ° C.), the linear velocity is returned to the normal time of 200 mm / second and the pressure is increased. The roller 30 is returned to the pressure contact state, printing is started, and this flow is finished (steps S18 to S19).
On the other hand, if it is determined in step S13 that the color double-sided print mode is not selected, or if it is determined in step S14 that the pressure roller temperature is lower than a predetermined value, the recording medium is transferred to the pressure roller 30. Although it is difficult to cause the trouble of winding P, it is necessary to suppress the temperature increase of the pressure roller 30 to some extent, and the linear velocity is reduced from 200 mm / second to 80 mm / second and the pressure contact state of the pressure roller 30 is maintained. (Step S17). Then, the linear velocity is returned to the normal time of 200 mm / second, the pressure contact state of the pressure roller 30 is maintained, printing is started, and this flow is ended (steps S18 to S19).
Even when such control is performed, it is possible to prevent the recording medium P from being wound around the pressure roller 30 in the color duplex printing mode.

  As described above, in the present embodiment, when the surface temperature of the pressure roller 30 (pressure rotator) is equal to or higher than a predetermined value, at least the fixing roller 20 (fixing member) is in a rotationally driven state. Thus, the amount of heat transferred from the fixing roller 20 toward the pressure roller 30 is adjusted so that the recording medium P is not conveyed to the nip portion. Accordingly, the problem that the recording medium P is wound around the pressure roller 30 can be surely reduced without contaminating the recording medium P passing through the nip portion with toner.

In the present embodiment, the present invention is applied to the electromagnetic induction heating type fixing device 19 using the exciting coil 26 (induction heating unit 25) as a heating unit. However, a heater or a resistance heating element is used as the heating unit. The present invention can also be applied to the fixing device used.
In this 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 rotating body. However, a fixing belt or a fixing film is used as the fixing member. The present invention can also be applied to a fixing device used or a fixing device using a pressure belt as a pressure rotator.
In these cases, the same effect as in the present embodiment can be obtained.

In the present embodiment, the moving mechanism is configured to move the pressure roller 30, but the moving mechanism may be configured to move the fixing roller 20.
In the present embodiment, the present invention is applied to the fixing device 19 in which the fixing member 20 (heat generating layer) is directly electromagnetically heated by the induction heating unit 25. However, the fixing member is indirectly connected by the induction heating unit. The present invention is also applied to a fixing device that is heated by electromagnetic induction (for example, a device that heats a member abutting on the fixing member by electromagnetic induction heating using an induction heating unit and transfers heat from the member to the fixing member). Can be applied.
In these cases, the same effect as in the present embodiment can be obtained.

  In the present embodiment, in the color double-sided printing mode, the amount of heat transferred to the pressure roller 30 is controlled by the adjusting means 75 and 80 to 83. On the other hand, when the recording medium P is wound around the pressure roller 30 even during double-sided printing with a monochrome image, the adjusting means 75 and 80 are used not only in the color double-sided printing mode but also in the monochrome double-sided printing mode. ˜83 can control the amount of heat transfer to the pressure roller 30 to be reduced.

  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),
25 induction heating unit (heating means),
30 pressure roller (pressure rotator),
75 Drive motor (rotational speed variable means),
80 stepping motor (movement mechanism),
81 Pressurizing lever (moving mechanism),
82 cam (movement mechanism),
83 Tension spring (movement mechanism).

JP-A-9-114284 JP 2008-65042 A

Claims (10)

A fixing member that is heated by the heating means and rotates in a predetermined direction to heat and melt the toner image and fix it on the recording medium;
A pressure rotator that forms a nip portion in which a recording medium is conveyed in pressure contact with the fixing member;
Temperature detecting means for detecting the surface temperature of the pressure rotating body;
When the temperature detected by the temperature detecting means is equal to or higher than a predetermined value, at least the fixing member of the fixing member and the pressure rotator is rotationally driven, and the recording medium is in the nip portion. An adjusting means for adjusting the amount of heat transferred from the fixing member to the pressure rotator in a state where the fixing member is not conveyed; and
A fixing device comprising: A rotation speed varying means for varying the rotation speed of the fixing member and the pressure rotating body;
The adjustment means reduces the amount of heat transferred from the fixing member to the pressure rotator by lowering the rotation speed of the fixing member and the pressure rotator by the rotation speed variable means. The fixing device according to claim 1, wherein the fixing device is adjusted. A moving mechanism that varies the nip width in the nip portion by moving the pressure rotator relative to the fixing member;
2. The adjustment unit according to claim 1, wherein the amount of heat transferred from the fixing member toward the pressure rotating body is reduced by reducing the nip width by the moving mechanism. The fixing device described.   The adjustment unit is configured to reduce the amount of heat transferred from the fixing member to the pressure rotating body at a predetermined timing when a color double-sided print mode for forming color images on both sides of a recording medium is performed. The fixing device according to claim 1, wherein the fixing device is adjusted.   The adjustment unit is configured to perform the color double-sided printing mode by continuously passing a plurality of recording media, and finally after the recording medium to be passed one sheet before the last passes through the nip portion. 5. The adjustment according to claim 4, wherein the amount of heat transferred from the fixing member toward the pressure rotator is reduced before the recording medium to be passed through reaches the nip portion. The fixing device described.   The adjusting means transfers heat from the fixing member to the pressure rotator after receiving a request signal for performing the color duplex printing mode until the color duplex printing mode is started. The fixing device according to claim 4, wherein the amount of heat is adjusted to be low.   The adjusting means starts the pressure rotation from the fixing member until the temperature becomes a predetermined value or lower when the temperature of the pressure rotating body is a predetermined value or higher before the color duplex printing mode is started. The fixing device according to claim 4, wherein the amount of heat transferred toward the body is adjusted to be low.   When the adjustment means is adjusted so that the amount of heat transferred from the fixing member to the pressure rotator is low, the target value of the surface temperature of the fixing member is lower than the target value in the fixing step. The fixing device according to claim 1, wherein the fixing device is controlled to be low.   The fixing device according to claim 1, wherein the heating unit heats the fixing member directly or indirectly by electromagnetic induction heating.   An image forming apparatus comprising the fixing device according to claim 1.

Images